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Forest Ecology

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2.2 Types of Ecosystem

Ecosystem are categorized into natural and artificial ecosystem.

Natural Ecosystem: Terrestrial and Aquatic

• Terrestrial (28.20 %): Forest, Grass/range, Desert (Tundra)

• Aquatic (71.80 %) : Fresh water and Marine or Ocean

Lentic ( pools, ponds, lakes stagnated or slow moving water , sizes

range up to thousand Km2, season or perinnial, limited biodiversity

because of isolated from other water sources)

Lotic ( streams/rivers or rapidly moving water )

Wetland ( inundated water or soil saturated )

Based on distance from the land surface and depth of light penetration into water Lentic

ecosystem is further divided into 3 zones:

• Littoral Zone

•Limnetic Zone

•Profundal Zone

Littoral Zone: also called euphotic zone

• shallow water zone, close to land surface, light penetrate ( up to 10 m), rich in O2 circulation,

absorb more of the Sun‘s heat and is warmest,

• sustains a fairly diverse community, include several species of algae (like diatoms),

chlorophyll bearing long rooted and floating aquatic plants.

• plants make their own food, photosynthesis and respiration take place,

• transfer of energy and food waves take place from one trophic level to another

• vegetation and animals living in the littoral zone are food for other creatures such as turtles,

snakes, ducks and aquatic birds

• Primary Producers : plants rooted to the bottom and algae attached to the plants and to any

other solid substrate ( Monochoria, cyprus, rumex, water lily, water hysinth, hydrilla, algae

(diatoms)

• Primary Consumers : tiny crustaceans, flat worm, insect larvae, grazing snails, turtles,

• Secondary consumers and top carnivores : clams, insects (the egg and larvae stages of some

insects are also found), fishes, turtles, snakes, ducks, aquatic birds and some other amphibians

• Decomposers : insects and algae, fungus etc

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Limnetic Zone : also called diaphotic zone

• Zone below Littoral zone

• Dipper than Littoral zone

• Far from land surface and up to effective light penetration zone called ( up to 100 m depending

upon turbidity)

• absorb less heat than littoral zone, photosynthesis takes place

• Primary producers ( Autotrophs) : phytoplankton

• Primary consumers (Heterotrophs) : Zooplankton

• Secondary consumers : insects

• Higher consumers : fishes

( Phytoplankton : single celled microscopic plants covered with two shells, photosynthesing

microscopic organisms, needs sunlight, H2O, CO2 and nutrients, use water, CO2 and the

presence of chlorophyll within their cell photosynthesize and prepare foods and acts like primary

producers. This is autotrophic. Ex: seaweed and algae.)

( Zooplankton : are carnivores or herbivores plankton, heterotrophic plankton, feed on

phytoplankton. Ex : jellyfish, Krill, some fishes )

Profundal Zone : also called aphotic zone

• Zone below Limnetic zone

• Dipper than Limnetic zone

• No enough light to support primary producers

• Aphotic zone

• dissolved O2 and CO2


Forest Ecology


• decomposers (bacteria and fungi are the community of organisms and they feed on detritus )

and release inorganic nutrient . Detritus are the dead organic matter ( dead bodies of plankton,

OM drifted down from Littoral and Limnetic zones

• Primary consumers : Benthos ( bottom dwelling bacteria or fungi that are attached to or crawl

along the sediments at the bottom of the lake)

• The sediments underlying the profundal zone also support a large population of bacteria and

fungi. These decomposers break down the organic matter reaching them, releasing inorganic

nutrients for recycling.

• The profundal zone is chiefly inhabited by primary consumers that are either attached to or

crawl along the sediments at the bottom of the lake.

• Organisms associated with this zone are only Heterotrophs ( detritus feeder) and carnivores (

snails, crabs, fishes etc)

• Decomposers Primary consumers ( Benthos) Carnivores

Lotic ( streams/rivers or rapidly moving water )

• Differs from lentic ecosystem

• because of water current, the water is usually oxygenated

• photosynthesis play minor role in food chain

• Large portion of energy and food available for the consumers is from land or terrestrial

ecosystem

In conclusion, aquatic ecosystem ( Ponds and lake ecosystem) :

Producers : green plants or algae either flooting or suspended or rooted at the bottom

Consumers : Primary consumers ( Tadpole larvae of frog, fishes, and other aquatic animals that

consume producers). Secondary producers : Big fishes, water snakes, crabs etc. Tertiary

consumers : water birds, dulfin, turtles, crocodile etc


Forest Ecology



Forest Ecology


Terrestrial Ecosystem :

Forest : A forest ecosystem is a natural woodland unit consisting of all plants, animals and

micro-organisms (Biotic components) functioning together with all of the non-living physical

(Abiotic) factors of the environment.

• Complex assemblage of biotic and abiotic components

• Most productive ecosystem than grass land and desert ecosystem

• Forest ecosystem is made up of soil, water, plants, animals, insects, fungi, and bacteria. All of

these things must interact with each other to form the ecosystem.

• Forest ecosystem represent the largest and most ecologically complex systems. They contain a

wide assortment of trees, plants, mammals, reptiles.

• Forest ecosystem represent the largest and most ecologically complex systems.

• Forest ecosystem function as habitats for organisms, hydrological flow modulators, and soil

conservers, constituting one of the most important aspects of the biosphere.

• Physical and chemical processes such as energy flow and nutrient cycling takes place.

• Forested ecosystems have great effect on the cycling of carbon, water, and nutrients, and

these effects are important in understanding long-term productivity. Cycling of carbon,

oxygen, and hydrogen are dominated by photosynthesis, respiration, and decomposition

• Energy flow from producers to carnivores and food web at atrophic levels controls the

productivity of forest ecosystem

• In the energy flow, only 10% of energy passed from one trophic level to next trophic level or

there is diminishing energy or biomass as we move from lowest trophic level to top trophic

level.

• Forest ecosystem provides ecological services and play important role in carbon

sequestration

• Forests are central to all human life because they provide a diverse range of resources, they

store carbon, aid in regulating climate, purify water and mitigate natural hazards such as

floods

• Forests ecosystems sustain human societies and allow them to prosper, due to the nutritional,

environmental, cultural, recreational and aesthetic resources they provide. We all depend

directly or indirectly on the products and services of ecosystems, including crops, livestock,

fish, wood, clean water, oxygen, and wildlife.

World forests biome :

• Borel or taiga forests ( 24%)

• Temperate forests ( 13%)

• Subtropical forests (8%)


Forest Ecology


•Tropical forest (49%)

• Plantation (6%)

Life Zone ( Ecological Zone of Nepal)

• By altitude

• Nival Zone > 5000 m : zone of permanent snow, some life such as moss and lichen present on

exposed rock

• Alpine Zone ( 4000-5000m) : alpine grassland/range land with junipers thickets,

rhododendron bushes and cushion plants

• Sub-alpine Zone ( 3000-4000m) : fir, birch and rhododendron species

• Temperate Zone ( 2000-3000m) : evergreen oak and rhododendron, conifers and broadleaf

species

• Sub-tropical Zone (1000-2000m) : blue pine, chirpine, oaks, chilaune,

• Tropical Zone (< 1000m) : Mostly sal and khair

Vegetation Types and Eco-region of Nepal

Vegetation Types Eco-region Altitude

Montane grasslands and

shrublands

Trans-Himalayan alpine

shrub/ meadow 4400-5000

West Himalayan alpine


East Himalayan alpine


North-west Himalayan

alpine shrub/ meadow >4000

Sub-alpine conifer forests Trans-Himalayan subalpine

conifer 3000-4000

West –Himalayan subalpine

conifer 3000-

4000

East –Himalayan subalpine

conifer

3000-4000

Temperate broadleaved

forests

West Himalayan

broadleaved

1500-3000

East Himalayan broadleaved 1500-3000

Tropical forests/sub-

tropical conifer forests

Himalayan sub-tropical pine 1000-2000


Forest Ecology


Sub-tropical broadleaved

forests

Himalayan sub-tropical

broad leaved

500-1000

Grassland, savannahs and

shrubl ands

Terai-Duar savannahs and

grassland

< 500

Desert Ecosystem :

Classified on the basis of temperature and rainfall

• Deserts ecosystem are defined as regions wherein the average annual precipitation seldom

exceeds more than 10 inches per year, and the amount of water lost to evapo-transpiration is

much more than the amount of water gained by precipitation.

• A desert ecosystem relies on an area that receives little to no precipitation and the temperature

is very cold to very hot

• In the desert ecosystem, climate is a deciding factor for the existence of life forms. In deserts,

temperatures can reach up to 115° F during the day, and come down to 32° F at night.

• Desert environment is very harsh in terms of climate, soil and plants. Life does exist in this

harsh environment. Numerous plants and animal species have adapted to these unsuitable

conditions

• Such extreme temperature makes it difficult for life forms to survive in the deserts, unless they

adapt to this harsh climate. Many plants and animals have adapted themselves over the years,

and have become an important part of the desert ecosystem

• Deserts are home to a number of species of animal and plant kingdom. Biodiversity of the

deserts ecosystem is as unique as other ecosystem. Each of these species play a crucial role

in the desert ecosystem food chain

• Like in most of the other ecosystems, plants are the primary producers, while rodents, insects

and reptiles which feed on these plants are the primary consumers. Then come the secondary

consumers, who mainly comprise larger reptiles and insects which feed on primary consumers

• Decomposers = Bacteria and fungi

• Two components Abiotic and biotic interacts

• At the top of the desert food chain are the apex predators in the form of birds and mammals.

• Most prominent members of the desert animals include desert tortoise, rattlesnakes, hawks,

owl, ostrich, bobcat, jackals, fox, kangaroo rats, mountain lions, etc.

• Most of these desert animals are nocturnal, i.e. active during the night, and spend the persist

during the day.


Forest Ecology


• Water being scarce in deserts, these animals have also modified themselves to make the most

of the available water. Some animals absorb water from plants, while others store it in their

fatty tissues.

• Desert vegetation mostly are cacti sps and sucullent plants.. These plants have modified

themselves to sustain in the desert environment.

• Some plants store water in the specialized tissues, while others have small leaves with hair

like structures which reduce the evaporation of moisture.

• Desert are classified into hot and cold deserts

• Prominent difference between the two is the form of precipitation, which is snowfall in cold

deserts and rainfall in hot deserts. Irrespective of whether it is a hot or a cold desert, the

characteristic traits of both almost remain the same

Hot deserts

• These areas exist under a moisture deficit, which means they can frequently lose more

moisture through evaporation than they receive from annual precipitation.

• The largest hot desert in the world, northern Africa's Sahara, reaches temperatures of up to

122 degrees Fahrenheit (50 degrees Celsius) during the day.

• Desert plants may have to go without fresh water for years at a time. Some plants have

adapted to the arid climate by growing long roots that tap water from deep underground.

• Deserts are part of a wider classification of regions called "drylands."

Cold deserts :

• Cold desert ecosystem : higher elevation, low temperature and rainfall scanty, frost and

snow are common, very poor soil, deficient in organic matter and nutrient but rich in

minerals, cold desert occurs in Himalayan region.

• Cold deserts are also known as polar deserts. Antarctica is the earth's largest cold desert, and

the Arctic is the second largest. Gobi desert in Asia is another example of cold desert

• Low soil productivity, growth of xerophytes, cold desert in Ladhakh and tibet of Himalayas,

• Vegetation sparse, drought resistance, water storing sucullant like cactus,

• They are environments that receive less than 10 inches of rain or snow per year and that have

extremely cold temperatures year-round

• Cold desert never rises above 50 degrees Fahrenheit in the summertime.The type of

environment represented by cold deserts is called tundra.

• This makes for a very harsh environment for plants and animals to survive in

• Plants that grow in the cold desert regions are very hardy and adapted to the extreme winter

cold.

• As with many annual plants, cold desert plants have a summer time and short growing season,


Forest Ecology


• Several types of mosses, grasses, herbs and lichens also live cold desert.

Food Web in Desert Ecosystem :

1st Trophic Level: Primary Producers = Trees, shrubs, cactus, wildflowers, grasses

2nd

Trophic Level:

Primary Consumers

Herbivores = camel, mule, deer, rabbits, ants, squirrel, rats and mice, some insects , some

reptiles the largest of which are the tortoise

3rd Trophic Level: Secondary Consumers ( small predators)

Small Carnivores = snakes, lizards,

4th Trophic Level:

Tertiary Consumers ( Large predators)

Carnivores = Eagle, vulture, Fox, wolf, wild cat, panther etc

Grassland Ecosystem :

• About one quarter of the earth is covered by grasslands ecosystem


Forest Ecology


• Grasslands are areas where the vegetation is dominated by grasses (Poaceae) and other

herbaceous and non-woody plants.

• Grasslands are defined as lands prevailed by grasses instead than big trees and shrubs

• Grassland ecosystem are influenced over time by : Local climate, plant communities,

variation of local Landscape, disturbances such as fire and floods, organisms that live in them

• Natural grasslands primarily occur in regions that receive between 250 and 900 mm annual

rainfall as compared with deserts , which receive less than 250 mm and forests, which receive

more than 2,000 mm.

•. Grassland ecosystem is in a transition between the desert and the forest.

• Average daily temperatures range between -20 and 30 °C.

•. There are two major classifications of grasslands:

• Tropical grasslands or Savanna are those grasslands that are nearest to the equator or . in the

southern hemisphere They are very hot or warm throughout the year. Tend to get more

precipitation than those in the. Some grasses grow more than 7 feet (2 meters), and have

roots extending several feet into the soil.

• Temperate grasslands are those far away from the equator or in the northern hemisphere with

warm summers and cold winters with rain or some snow

• Grasslands are also classified into : Mixed grasslands grasses that grow up around 50-80 cm

high and about 300-500 mm of rain per year.

• Short grasslands : get very little rainfall per year, less than 200mm rain per year

• Grassland ecosystem consists of grasses, flowers, shrubs, herbs in which shrubs and trees are

hardly can find.

• Each grassland type has its specific herbivores and carnivores

• Grassland herbivores are fleet footed animals that live in herds as protective mechanism

• Characteristics of grassland animals : Run type (blackbuck, wolf, leopard etc) and burrowing

type (rabbit, porcupine, hedgehog etc) as protective and adapting mechanisms

• Grasslands also have an enormous number of insects. These insects attract a large number of

predatory animals like the lizards and birds.

• Various types of grasses that mainly grow up in the grassland ecosystem such as ryegrass,

foxtail, wild oats, buffalo grass and purple needle grass.


Forest Ecology


• Tropical and sub-tropical grasslands are home to many large herbivores such as bison,

zebras, rhinoceros , elephant, wild horses etc and carnivores like lions , tiger, wolves ,

leopards etc. Other animals of this region include deer, wild dogs, jackal , mice, jack rabbits ,

snakes fox, owls, etc

• Temperate grasslands herbivores are antelopes, wild boar etc and carnivores are leopards,

wolf, wild cat, fox, jackal etc.

• Several wild sheep and goat such as the Goral are found in Himalayan pastures.

• The largest herbivore of the Terai grassland is the elephant. It requires an enormous amount

of tall grass to feed on. The Terai grasslands form the habitat of the Swamp deer, Wild

buffalo and the Rhinoceros.

• Tropical grasslands are warm year round, but usually have a dry and a rainy season.

• Temperate grasslands have shorter grasses and have two seasons: a growing season and a

dormant season. During the dormant season, no grass can grow because it is too cold.

International Terminology for Grassland Ecosystem :

• The South America‘s grasslands are called ―Pampas‖,

• The North American grassland are called ―Praire‖

• European grassland are called ―Steppes‖

• The African grassland is called the ―Serengeti‖ or ―Savanna‖ . Savanna is also available in

Australia, South America and India

• There is a huge area of grassland that stretches out from Siberia to Ukraine which is known as

the ―Russian steppes‖.

• In Himalayan region, the grassland are normally called pastures which extends up to the

snowline. These grasslands at the lower level are found along with coniferous or broad-leaved

forests.

• The Terai grasslands at the foothills of the Himalayas consist of tall elephant grass along with

Sal forest is usually referred as Terai-Duar savannah and grassland

Grassland Ecosystem of Nepal :

It is an ecosystem in which the plants and animal communities along with the abioitic factors

like soil, air, water, temperature, topography and solar energy interact.

The grassland ecosystem of Nepal can be classified as :

Tropical grassland (upto 1000m) : dominated by the grasses like Saccharum spontaneum and

Imperata cylindrica. Some also contain 2 m tall Cymbopogon jwarancusa and Bothriochloa

intermedia. Eupatorium is gradually replacing many of the palatable species.


Forest Ecology


Sub-tropical grassland (1000 -2000m) : mostly associated with Pinus roxburghii forests. They

are heavily grazed and are infested with Eupatorium sps(Banmara), Pteridium aquilinum

(bracken fern), Urtica parviflora and Artemisia vulgaris.

Temperate Grassland (2000-3000m) : are associated with oak or mixed broad-leafed species

such as Quercus or bluepine forests. These grassland very important, but degrading due to heavy

grazing for many years

Sub-alpine Grassland (3000-4000 m) : are associated with a variety of shrubs. The common

genera are Berberis, Caragana, Hippophae, Juniperus, Lonicera, Potentilla, Rosa, and Spiraea

and Rhododendron.

Alpine Grassland (4000-5000m): are associated with Rhododendron shrubs. The main types of

vegetation, based on the specification of areas, are Kobresia, Cortia depressa, and Carex /

Agrostis / Poa associations. Common plant species are Kobresia spp. and Agrostis sps.

Steppe: It is situated in Trans Himalayan area of Dolpa and Mustang. Productivity of these range

is very low due to overgrazing by animals


Forest Ecology


Desert food web


Forest Ecology



Forest Ecology


Analysis of Ecosystem :

Structural system, functional system and regulation of an ecosystem

In analysis of ecosystem, we generally undertake study on following elements of an ecosystem :

• Biotic and abiotic components and their properties,

• Quantity of materials needed for organisms

• Rate of organic matter produced and used up in respiratory process

• Quantity of energy passed from one trophic level to another

• Driving forces of light, temperature, rainfall,

• Soil structure and nutrient, litter fall, death of organisms,

• Mineralization, recycling of nutrients,

This is a study or analysis of structural, functional and regulation systems of an ecosystem

with space and time .

• The structural system includes biotic ( autotrophs, heterotrophs, decomposers ) and abiotic

components (Inorganic substance, organic substance, climate, topography and edaphic

factors).

• Functional analysis (Metabolic process of the living plants and animals or organisms.

• Energy flow at various trophic levels, Bio-geochemical cycling i.e pathways of circulation of

organic and inorganic elements within an ecosystem


Forest Ecology


• Regulation ie form of adoption or change behavior of an organism of an ecosystem with

change of ecosystem structure.

Ecosystem Analysis : Cause – Effect Relationship

Ecosystem Analysis

Structural System : It includes study of biotic and abiotic components. In biotic

component, we study :

• the composition of biological community ( spp, properties, structure, density,

frequency/number, life history, growth, survival , death of organisms, organisms response to

change in abiotic components and nutrients etc)

• biomass produced by organisms , trophic level (producers, consumers, decomposers),

• quantity of materials needed for the growth and survival of the organisms

• the rate at which the organic matter is built up and disappeared and used up for in the

respiratory process

In abiotic components, we study :

• The driving force of light, temperature, rainfall, range of condition of existence, geology, soil

structure, soil texture, soil nutrient, thickness of soil profile, chemical and physical properties of

soil, mineralization, recycling of nutrients, slope, altitude/topography, aspects , quantity and

distribution of abiotic materials etc


Forest Ecology


Functional System : This includes the study of :

• rate of nutrient cycling within an ecosystem,

• range of energy flow or move through an ecosystem via the trophic level/food-web

• photosynthesis and respiration process

• energy loss, energy use by organisms

• decomposition of organic matter, release of inorganic or chemical energy, nutrient pool

• assessment of gross and net primary productivity etc

Ecosystem Regulation : This includes the study of :

• form of adoption or behavior change of organisms of ecosystem with change of ecosystem

structure

• ways in which the ecosystem regulate itself ( Intra and inter specific interactions)

• interactions between biotic and abiotic components

• bottom-up and top-down regulations etc.

Energy in an Ecosystem

• Living organism can use energy in two forms

• Radiant and Fixed energy

• Radiant energy = electromagnetic wave such as sun light

• Fixed energy = chemical energy in organic substances, which is broken down and release for

energy need for plants

• Only a small fraction of incident radiant energy ( about 3 %) can be utilized by plants

• This radiant energy is converted into chemical energy by photosynthetic process of

autotrophs

• 6 CO2 (from atmosphere)+ 6H2O (from soil) + light = 6C6H12O6 ( sugar in plant cell ) +

6O2 ( release in atmosphere)

• Sugar converted into inert energy rich organic substances such as starch, which plants stored

them

• Starch combined with other sugar molecule and form carbohydrates such as cellulose

• Cellulose combined with nitrogen, phosphorus and sulfur produce proteins, nucleic acid and

hormones

• All the above reactions are necessary for plants growth, maintenance of the body tissues and

functions of the plants


Forest Ecology


• Sugar produced during photosynthesis will be oxidized and produce CO2 and H2O and usable

chemical energy

• 6C6H12O6 + 6O2 = 6 CO2 + 6H2O + usable energy

• Oxidation of sugar or any organic molecule to get usable energy by organism is called

respiration

• Energy released by respiration is lost permanently to the ecosystem

• In each transformation from one trophic to another some energy is lost as heat energy

Pattern of Flow of Energy Through the Ecosystem

Solar Energy

Producers

( autotrophic plants Primary consumers Primary carnivores

/phytoplankton)

Dead remains Secondary carnivores

Raw materials Decomposers ( bacteria/fungi)

(organic/inorganic salts)

Sun

• Only a small fraction of the light energy reaching the earth is tapped

• Autotrophs or green plants utilize only about 3% of incident energy in photosynthesis

6 CO2 (from atmosphere)+ 6H2O (from soil) + light = 6C6H12O6 ( sugar in plant cell ) + 6O2

( release in

energy

atmosphere)

• Respiration : ( Oxidation of sugar to get usable energy by organism )

6C6H12O6 + 6O2 == 6 CO2 + 6H2O + usable energy ( permanently lost to the ecosystem)


Forest Ecology


Inputs and losses of energy at each trophic level : R1 R2 R3 R4 A2 A3 A4 F1 C1 F2 C2 F3 C3 F4 C4 A = assimilation of food by the organisms at each trophic level F = energy loss in the forms of faeces and other excretory /dead products C = energy lost through decay R = energy lost to respiration

Solar radiation

1. Autotrophs

2. Herbivore

3. Primary

carnivore

4. Secondary carnivore

DECOMPOSITION

Ecosystem Productivity :

• All the energy that the plant fixes results formulation of sugar in the plants leaves

• Sugar produced in the leaves of green plants is derived from CO2 and H2O combined with

solar energy

• Thus the energy incorporated into living tissue of plants is either in terms of the light energy

utilized or in terms of the sugar produced

• All the energy used by plants is converted into chemical energy. So the entire energy uptake

of plants can be measured by measuring the total amount of sugar produced.

• This amount of entire energy uptake by plants or sugar produced is known as gross primary

production. This is the total amount of organic matter that plant produces through

photosynthesis. It is a total weight in all the parts of root, steam, leaves, fruits etc

• It is not easy to measure gross primary productivity (organic matter) because some of the

sugar produced by photosynthesis will be lost immediately through plant respiration

• one can measure the total organic matter actually present in the plant (biomass) by deducting

the sugar or energy lost through respiration from the gross primary production, which is called

Net primary production .

• NPP ( energy stored in plant biomass with time or biomass) = GPP – energy loss during

respiration.

GPP = NPP + Energy loss during respiration


Forest Ecology


If GPP = respiration, no change in stored energy

GPP < respiration, biomass decreases

GPP > respiration, accumulation of biomass takes place

GPP depends upon climate conditions ( temp, rainfall, solar radiation etc ) availability of

nutrient

( N, P, S ). Productivity is expressed in terms of grams or kilo-calories per sq meter/day or per

year

Ecosystem Productivity : The movement of energy within an ecosystem via producers,

consumers and decomposers is ecosystem productivity (bio-mass or the total living matter in a

given place during a given time).

Primary Productivity (Producers level) : The rate of energy trapping by green plants governs

the rate of production of organic material from simple inorganic substances in a given area over a

given period of time. Therefore, the primary productivity is the rate of energy conversion or

increase in organic biomass produced by green plants

Gross Primary Productivity ( GPP): The rate at which photosynthesis captures energy. In other

word, an ecosystem's GPP is the total amount of organic matter that it produces through

photosynthesis. It is a total increase in weight in all the parts of root, steam, leaves, fruits etc

NPP : The energy that remains (as biomass) after plants and other producers carry out

cellular respiration. Net primary productivity (NPP) describes the amount of energy that

remains available for plant growth after subtracting the fraction that plants use for respiration.

6 CO 2 + 6 H2O + light energy = C6 H12O6 + 6 O2 ( During photosynthesis )

C6 H12O6 + 6 O2 = 6 CO2 + 6 H2O + Heat energy ( During respiration)

Secondary productivity ( Consumers level) : It refers to the production of living maters or

organic matters by consumers and decomposers in a given time and space

Secondary Production :

• Energy required for other trophic levels in an ecosystem will be furnished from the energy

derived from primary production

• Some energy (in the form of food) is consumed by herbivores. Carnivores eat herbivores to

meet the energy required by them

• Much of the eaten (ingested) food will not be absorbed (assimilated) , herbivores assimilate

only 10 % of ingested food.

• Assimilation rate (coefficient) of carnivores will be higher than the herbivores, example fish

assimilate 86 – 96 % of ingested food

• Assimilation of ingested food varies with food substances such as in the form of protein, fat,

carbohydrates etc.


Forest Ecology


• Unassimilated food materials leaves the animal‘s body as waste materials which serves as

energy source for other organisms like detritus ( dead organic matters) feeders like saprophage (

many bacteria and fungi)

• Assimilated food or energy use by consumers for metabolic processes, such as respiration,

excretion and secretion.

• The resultant amount of energy stored in the tissues of heterotrops ( herbivores or carnivores)

is called Net secondary production

• Gross secondary production = total food material (energy) ingested by the heterotrophs -

materials lost as waste or faeces or material defaecated

• Gross secondary production can be measured directly by measuring the amount of food

ingested minus material defaecated

Measurement of Productivity :

• O2 Meaurement method ( Light and Dark Bottle Method)

• CO2 Measurement Method (CO2 Assimilation Method)

• Chlorophyll Method

• Harvest Method

• PH Method

• Radioactive Tracers method

1. O2 Meaurement method ( Light and Dark Bottle Method)

• Used for aquatic ecosystem

• Take two bottles one light and another dark of same material and same weight and

volume

• Take samples of concentration of phytoplankton from lake or river or sea suspended at

the bottom of the bottles

• The light bottle ensure light inside the bottle and photosynthesis takes place while dark

bottle excludes light and no photosynthesis takes place and only respiration from the

phytoplankton population takes place

• In light bottle photosynthesis and respiration takes place while in dark bottle only the

respiration takes place but no photosynthesis

• In light bottle some of the CO2 is used by the phytoplankton for photosynthesis and at the

same time some of the O2 is produce due to respiration ( refer the equations for photosynthesis

and respiration)

• In dark bottle O2 is used due to respiration by phytoplankton and release Co2


Forest Ecology


•Imagine a base bottle of the same dimension and constituents as of dark bottle and light

bottle.

Expose on

sunlight

Initial bottle Dark bottle

Light bottle

Wt. of Light bottle - wt. of initial bottle = NPP = GPP – respiration ( amount of O2 left )

Wt. of Initial bottle – wt. of Dark bottle = Respiration

Wt. of Light bottle – wt. of Dark bottle = GPP

Example : Assume, weight of O2 in Initial bottle = 8 mg O2 /L ; Wt. of light bottle would be

increased due to added O2 by photosynthesis = 10mg O2/L ; Wt of dark bottle would be

decreased due to use of O2 by respiration = 5 mg O2 / L

Light – Initial bottle = 10-8 = 2 = NPP ; Initial – dark bottle = 8 – 5 = 3 = Respiration

And Light – Dark bottle = 10 – 5 = 5 = GPP

• CO2 Measurement Method (CO2 Assimilation Method)

• Used for terrestrial ecosystem

• Take two plastic tents or plastic cover one light and another dark of same material and

same size

• Take two sample sites at ground assuming that plant materials, soil , moisture

conditions etc. of these sites are identical.

• Cover one site by light plastic cover or tent and another by dark plastic cover or tent

• In the site having light plastic cover or tent, plant photosynthesis inside the cover takes

place while in the site having dark plastic cover or tent only the plant respiration takes

place but no photosynthesis

• In the white plastic cover site, inject air from one side and draw air from other side

Draw air Incoming air

site with white plastic tent or cover site with dark plastic tent or cover

• Measure the CO2 concentration in incoming and out going air by infrared gas analyzer

• In the white cover site, the CO2 concentration in the drawn air will be less than the CO2

concentration in the incoming air ( because some CO2 of the incoming air is used by the

plants in the photosynthesis

•CO2 concentration in incoming air - CO2 concentration in drawn air = CO2 use by plants for

photosynthesis = NPP (OM)

• In the site of dark plastic cover there is no photosynthesis and only respiration of plants

take place I, e CO2 release by plants


Forest Ecology


• The CO2 use by plants for photosynthesis in the white cover site + CO2 release by plants in

dark cover site = GPP

( Refer the formula that GPP = NPP + respiration )

3. Chlorophyll method :

• Used for aquatic ecosystem

• Estimation of production can be done by using chlorophyll and light data

• Calculate the chlorophyll content of plants by using Colorimeter

• Involves the determination of chlorophyll content of a plant per gram or per square meter

•The quantity of chlorophyll content tends to increase or decrease with the amount of

photosynthesis , which varies at different light intensities

•The chlorophyll per square meter indicates the food manufacturing potential of plants which is

proportional to the NPP.

4. Harvest method

• Widely used in terrestrial ecosystem

• Most useful for estimating production on ecosystem of cultivated land and range where

production starts from zero at seeding or planting time and becomes maximum at harvest

• It involves clipping or removal of vegetation at periodic intervals and drying , which gives the

biomass in grams per square meter

• The caloric value of the material can also be determined by bomb calorimeter and the biomass

is converted into kilocalories per square meter

• To be more accurate, plant material must be sampled and clipped through out the growing

season and the production can be measured for each individual species determined

Modified Dimension Analysis Method :

• Measurement of height and diameter (DBH) of sample trees in sample plots

• A set of sample trees of sample plots are cut , measured and weighed at the end of growing

season ( green and dry weight of wood, leaves, barks, twigs, roots, flower are taken )

• By calculations, annual production of barks, leaves, twigs, roots, flowers, roots etc can be

estimated ). This gives NPP of trees of sample plot and estimate for whole area of forest

5. PH Method

• This method is used for aquatic ecosystem

• This method is based on the principle that the water PH is a function of dissolve CO2 content

in water ( which is decreased by photosynthesis and increased by respiration by aquatic

animals)

• This method is useful for laboratory analysis of micro-organisms ecosystem


Forest Ecology


• At laboratory, sample water is bring and by the use of pH electrode and recorder the day time

photosynthesis and night time respiration of micro-organisms is determined and the primary

and gross production is calculated for the samle water and then to the whole ecosystem

Plant variability and diversity

Phenotypic and genotypic variation :

Phenotype :

• Observable characters or traits (height ,leaf number, leaf size etc ) of an organism such as

morphology, development, physiological properties , behavior etc. is called phenotype. Or it is

observable properties of an individual organisms. Phenotype is an organism's actual observed

properties, such as development of morphologic parts or behavior of plants

• The phenotype is the descriptor of the physical properties of the organism, its physiology,

morphology and behavior.

• Phenotype physical properties are controlled and are the results from an organism‘s genes and

the influences of the environment and the interactions between them.

• In other words, phenotype (the physical expression of a traits or observable properties) is a

product of the interaction between a set of genes and an environment.

Genotype :

• The genetic constituent of an individual is termed as genotype. Genotype characteristics or

traits are never observable or visible.

• Genotype is the genetic makeup of a cell, an organism, or an individual usually with reference

to a specific character under consideration. ― Genotype " gives full hereditary information of an

organism. The genotype represents its exact genetic makeup — the particular set of genes it

possesses.

• Genotype is influenced by : internal environment of cells, tissue, and biochemical reaction and

external environment like temperature, moisture and light.

• Genotype of an organism is the inherited characteristics it carries within its genetic code. Not

all organisms with the same genotype look or act the same way because appearance and behavior

are modified by environmental and developmental conditions.

Variability or variation : To what extent an individual can be changed

Sources of plant variability : Genetic sources (major sources) and Environmental sources

Genetic sources : mutation, recombination, gene flow and hybridization

Environmental sources : internal environment of an organism ( cells , tissues etc) and external

physical environment ( biotic and abiotic )

Phenotypic and Genotypic variation :

• Phenotypic variation represents to what extent an individual can be changed or enable to adapt

to change over time,


Forest Ecology


• Phenotypic variation is due to interaction of underlying heritable genetic variation and the

environment

• Genotypic variation represents adaptation by the population enabling it to change over time

• Genotypic variation originates in mutation and recombination, which is affected by natural

selection, migration and genetic drift (random change in gene frequency)

• Genotype variation are Continuous or Regular (quantitative or polygenic traits such as body

size and skin pigmentation ) and Discontinuous or Sharp ( qualitative traits such as form,

structure etc) .

•

• Phenotype is a result of the effect of environment on genotype

• The relationship or interaction between phenotypic, genotypic variation and the environment is

as follows :

Phenotype variation = Genotype variation + External environment

Vp = Vg + Ve, where

Vp = Phenotypic variation; Vg = genetic variation ; Ve = external environmental variation

Vp = Vg + Ve + V ge (genetic environment)

• The degree of genetic control over phenotypic organisms is a heritability, which is expressed

by the ratio of Vg/Vp

• If this ratio is more than 75 %, which means the high heritability ( indicates strong genetic

control over trait characteristics like branchiness , bole form, bark structure, stem wood density,

diameter, height, susceptibility to insects and diseases are genetically controlled)

• If the ratio is less than 75 %, which indicates low heritability or weak genetic control and

indicates a strong environment control (like soil, moisture, temperature etc) over the trait

characteristics


Forest Ecology


Sources of Phenotype differences ( variations) or what causes phenotype variation or differences : Interrelationship of genotype, environment and phenotype variation

Genotype : Gene

Plant Process Plant processes Phenotype variation

+ External Factors

DNA and RNA

Time, space, light, heat, water, soil, nutrients,

chemicals, other organisms

Photosynthesis, respiration, water and chemical uptake, transpiration, cell division , chemical reactions etc,

Age, growth rate, habit, complexity,

resistance to : Pests, moisture

stress, light extremes, heat

stress, symbiosis

Summary : Genotype is genetic make up or genetic constituents of individuals which

represent the sum total of heredity and is not visible, where as Phenotype of an individual

is visible traits, characteristics, properties, functions which are produced by the interaction

between genotype and environment such as tallness and dwarfness etc

DNA : Deoxyribonucleic acid, a self-replicating material present in nearly all living organisms

as the main constituent of chromosomes.

A nucleic acid that carries the genetic information in the cell and is capable of self-replication

and synthesis of RNA

RNA : Ribonucleic acid, a nucleic acid present in all living cells. Its principal role is to act as a

messenger carrying instructions from DNA


Forest Ecology


Genetics and the Evolutionary Sequence

Genetics : Came from Greek word ― gene‖ which means ― become or to grow. Genetics is

―Biological science‖, which deals with the mechanism of hereditary, causes of variations in

genes ( hereditary unit) , evolution (change in gene pool) and development in living organisms.

Genetics cause evolutions and development in living organisms.

(Gene : a particular segment of DNA molecules, which determines the heredity of a particular

trait or characteristic of an organism)

Evolutionary Sequence : The word evolution has a variety of meanings. The fact that all

organisms are linked via descent to a common ancestor is often called evolution.

• The cumulative change in genotype or genetic make up of population of species overtime or

during the course of successive generations is evolution or simply this is a change in gene

frequencies.

• In biology, evolution is the process by which populations of organisms acquire and pass on

traits ( phenotypic) from one generation to generation through the change in genotype or gene

frequency.

• Biological evolution is genetic change in a population from one generation to another

• Therefore, evolution is a change in the gene pool of a population over time. A gene is a

hereditary unit that can be passed on unaltered for many generations. The gene pool is the set of

all genes in a species or population.

• For example, all living organisms alive today have descended from a common ancestor (or

ancestral gene pool).

• For evolution to take place there should be : population ( collection of individuals, each

harboring a different set of traits.) , mutation of genes of different individual species ,

individuals are selected,

• Individual organism do not evolve, they retain the same genes throughout their life. But

population evolve.

• When a population is evolving, the ratio of different genetic types is changing

• Evolution can be divided into microevolution and macroevolution. The kind of evolution at

phenotype or genotype level is microevolution. Larger changes, such as when a new species is

formed, are called macroevolution.


Forest Ecology


• Different individuals have different capabilities to survive and reproduce in a given set of

environmental conditions

• This different survival and reproduction capabilities are the results of having genotype

variation in individuals

• The genotype having best survival and reproduction capabilities are the best adapted to their

environment and will make the largest contribution to the next generation by producing much

more off-spring than those of others.

• Evolution takes place for that genotype that are fittest and the best adapted in the existing

environmental condition and provide much more off-springs than those of others

The speed and direction of evolution are variable with different species lines and at different

times.

• Continuous evolution over many generations can result in the development of new varieties

and species ( we can now see the diversity of millions of species).

• Likewise, failure to evolve in response to environmental changes can, and often does, lead to

extinction.

• Evolution results from natural selection and adaptation

Natural selection

• The process of evolution by which forms of life having traits that better enable them to adapt

to specific environmental pressures, such as predators, changes in climate, or competition for

food or mates, will tend to survive and reproduce in greater numbers than others of their kind

• Some types of organisms within a population leave more offspring than others. Over time, the

frequency of the more productive type will increase. The difference in reproductive capability is

called natural selection.

• Natural selection is the only mechanism of adaptive evolution; it is defined as degree of

difference of reproductive success of pre- existing classes of genetic variants in the gene pool.

• The most common action of natural selection is to remove unfit variants as they arise via

mutation. In other words, natural selection usually prevents new alleles from increasing in

frequency.

Adaptation : Genotype changes in an individual or population so that any living organism

survives or grows better to the existing environment.

Organisms can respond to environmental stress in such a way that their tolerance zones may

change. The genetic changes that occur during the evolution of the species because of mutation

and natural selection are called adaptation.

Gynecology : Concept of ecotype, ecophene and types of ecotype


Forest Ecology


• first used by Swedish scientist : Turession (1923)

• Study of variability of plant species population, hereditary, habitat types , variations of

gene frequency, adaptive property of population of species, mutation, local inter breeding

in relation to change in the environment etc

Ecotype : A species that is specially adapted to a particular set of environment. It is also

defined as the product arising as a result of the genotypic response of a population to a

particular habitat.

( species show different levels of tolerance to a given limiting factor over its geographical

distribution, these locally adapted populations are called ecotypes and is the result of

genetic change resulting in different physiological responses to different environment)

• Species with wide geographical distribution almost always develop locally adopted

populations, which is called ecotype. These populations have optimum and limits of

tolerances adjusted to local conditions.

Ecotype: A locally adapted population of a widespread species. Such populations show minor

changes of morphology and/or physiology, which are related to habitat and are genetically

induced. Nevertheless they can still reproduce with other ecotypes of the same species.

Typically, ecotypes exhibit phenotypic differences (such as in morphology or physiology)

stemming from environmental heterogeneity and are capable of inter-breeding with other

geographically adjacent ecotypes without loss of fertility or vigor.

Examples :

• Reindeer species (population ) : found in tundra and forest ecosystem. So ,there are two

ecotypes of reindeer. They migrates between two ecosystems ( habitats , environments)

•Arabis fecunda, a herb, is divided into two ecotypes : One low elevation group live near the

arid, warm environment and are tolerance to drought and another group is found in high

elevation .

• Dolphin has two ecotypes : Riverine and oceanic ecotypes

• Scot pines ( Pinus sylvestris) : has 20 ecotypes ( Scotland to Siberia) all capable of inter

breeding

Important characteristics of Ecotype :

• variations are phenotypic : morphological, physiological or phenology

• phenotypic difference is due to population response on phenotypic variance and

environmental heterogeneity

• ecotypes are isolated and disconnected entities

• genetically and environment based

• adapted to specific environment condition

• capable of inter-breeding with other geographically adjacent ecotype without loss of fertility

or vigor


Forest Ecology


• variations are associated with habitat types

Types of Ecotypes : Climatic ecotype , Edaphic ecotype, Biotic ecotype

Climatic ecotypes: are species that are found adaptive in different climatic zones

Edaphic ecotypes : occurs especially in saline soils and in soil having moisture stress or in

harsh edaphic conditions

Biotic ecotypes : occurs in areas subject to heavy grazing pressure. Example : around a drinking

hole in a game reserve. Plants are usually upright height, prostrate and less liable to have their

vegetation and reproductive portions removed.

Four different ecotypes of Physcomitrella patens,

Ecophene or Ecades : Individual plants of same species within a population differ in visible

appearance such as height, erectness, thickness of leaves etc in differing environmental

conditions are known as Ecophene or Ecades

Story of moths : distinct

1. Moth ( Biston betularia) : two types : light and dark colored

Prior to 1848 , the population of dark colored = < 2 % and light colored more

In 1898, frequency of dark colored moth increased to 95 % and light color less

This change in increase in population of dark colored from light color moth = change in gene

pool ( set of all genes in a population) = This change in gene pool is Evolution

Moth color is single gene = hereditary unit

2. At the time of industrial revolution in England, dirt from industries darken the trees around .

Two types of moths, light and dark colored used to landed on the trees.

Birds could see only the light colored moths at the dirt environment, and mostly eat light colored

moth.

As a result dark colored moth survived, produce more offspring against predator( birds). This

increase in frequency of dark colored moth is Natural Selection.

Ecological considerations at the species level :

• As population of a species change over time, and if the segment of the population migrate

into new areas or new environment , then the migrated population of that species become

diverse in terms of their genetic characteristics

• Due to geographic separation and diverse environment factors of the new site, the migrated

population become less able to exchange genes with other population and becomes

reproductively isolated

• These geographic isolation and reproductive isolation are the main cause among others for

speciation

This phenomena can be shown as follows :


Forest Ecology


1st. Stage : a single population of species in a homogenous environment

2nd. Stage : Migration to the new environment produces separation of race and species

environment separation

3rd. Stage : Further separation and migration produces geographic isolation of some species

geographic isolation

4th. Stage : Some of these isolated species separate with respect to genic and chromosomal changes which controls reproductive isolating mechanism

reproductive isolation

5th. Stage : If these geographically isolated population re-exit together in the same region , then they remain diverse because of the reproductive isolation barriers which separate them. No inter breeding with the original species takes place

This says that geographic isolation leads to reproductive isolation which in turn leads to speciation

Geographic isolation can lead to reproductive isolation, divergence and speciation.


Forest Ecology


Four steps leading to speciation.

different habitats, the divided populations become differentiated through

the accumulation of differences.

and they overlap again. Interbreeding does not occur.

New species typically evolve by two steps:

•geographic isolation–separation into distinct populations with different evolutionary pressures;

•reproductive isolation–evolutionary changes in each population that prevent interbreeding when

populations come into contact.

The Process of Species Formation Four Steps:

•Single population or reproductive community.

•Development of a reproductive barrier (formation of allopatric populations).

•Differentiation of the separated populations.

•New species can no longer interbreed if barrier disappears and become sympatric.

22


Forest Ecology



Forest Ecology


Unit 4 : Autecology

• Autecology deals with the ecological study of one species of organism. It includes the study of

life history, population dynamics, behavior, habitat of a single species and so on. Such as Bengal

tiger, sal tree, sal borer,

• Synecology : deals with the ecological studies of communities or entire ecosystem. For

example the study of whole deserts, caves or temperate or tropical forests or grassland as a whole

• Autecology and synecology are interelate.

• Synecoliogist makes a outline of the whole pictures where as autecology describes the minute

and finer details of organism s of an ecosystem

Introduction to concept of site productivity and Law of Minimum :

• Tree crown is surrounded by heat, light, O2,CO2, precipitation, wind, lightning etc and affects

the tree life. These are climatic factors related to atmosphere in which the areal portion of the

tree grows

• Tree roots are surrounded by soil nutrients and water , soil is also a medium for anchorage of

soil or soil is the storehouse of minerals and water.

• Soil factors also comprise of all physiographic components ( altitude, aspect and slope),

physical, chemical and biological components of soil

• These factors (soil and climatic factors) which a particular site must supply to the plants.

Productivity of the site directly depend upon these factors.

• The individual of climatic and soil factors is not acting in an isolated way but are acting

interdependently and interrelated

• Among these factors only few factors exert more influence and needs more in quantity for

plant growth such as air temperature, sunlight, water and macro nutrients ( C,H,O, S,N, P, K, Ca,

Mg) while other factors needs in small quantity ie micro nutrients ( B, Cu, Cl, Fe, Mn, Mo,

and Zn) and are also essential.

Forest site productivity : is the production that can be taken at a certain site with a given

genotype and a specified management regime.

•The term site productivity is often use to refer to that part of the site potential pick up by the

trees for wood production

• Forest site productivity may be defined as the potential of a particular forest stand to produce

aboveground wood volume, which is calculated on stem wood volume for conifers, but may

include branch volume for broadleaved tree species.


Forest Ecology


• Forest Site productivity is a quantitative estimate of the potential of a site to produce plant

biomass, which is based on two concepts : site potential and how that site potential is taken up

by a given forests stand

• site potential is the capability of the site to produce plant biomass (net primary production),

irrespective of how much of this potential is utilized by the vegetation

• Site productivity depends both on natural factors inherent to the site and on management-

related factors

•The natural or environmental factors which influence the life and development of organisms

and in turn the site productivity are grouped into four main factors. They are climate, soil,

topography and biotic influences

• The greatest impact on tree growth or site productivity decrease or increase is made by climate,

soil, topography and biotic . The distribution of species and community, physiological and

reproductive process are greatly influenced by these factors

• For many purposes, the maximum mean annual volume increment is considered a suitable

measure of site productivity.

• Within this narrower context, site productivity is often quantified as an index, typically site

class or site index . Such indices are defined in different ways and are widely used for

management purposes.

• Site Index - A relative measure of forest site quality based on the height (in feet) of the

dominant trees at a specific age (usually 25 or 50 years, depending on rotation length). Or, this

is a height of a tree at a specified index or base age and are used as an indicator of site quality .

Site index information helps estimate future returns and land productivity for timber and wildlife.

• Site quality : A classification of sample tree according to how well the tree reflects the

productive potential of the site.

Liebig's law of the minimum


Forest Ecology


• The concept first stated by J. von Liebig in 1840, Liebig's Law of the Minimum, often simply

called Liebig's Law or the Law of the Minimum, is a principle developed in agricultural science

• It states that growth, size etc. of a plant and composition of a population of species is

controlled not by the total of resources available, but by the scarcest resource.

•This concept was originally applied to plant or crop growth, where it was found that increasing

the amount of plentiful nutrients did not increase plant growth but the growth of plant was

improved with increasing amount of the limiting nutrient (the one most scarce in relation to

"need")

• Justus von Liebig's Law of the Minimum states that yield is proportional to the amount of the

most limiting nutrient, whichever nutrient it may be. From this, it may be inferred that if the

deficient nutrient is supplied, yields may be improved to the point that some other nutrient is

needed in greater quantity than the soil can provide, and the Law of the Minimum would apply in

turn to that nutrient.

•The examine the relative role of these factors for plant growth is known as ― Law of

minimum‖ proposed by Liebig . Which is also called Liebig ― Law of Minimum‖

Example :

• Liebig used the image of a barrel-now called Liebig's barrel-to

explain his law. Just as the capacity of a barrel with staves of

unequal length is limited by the shortest stave

• This is same in case of plant . So a plant's growth is limited by the nutrient in shortest supply.


Forest Ecology


Example :

• Imagine you are building a dog house using nails and boards. As long as you have both, you

can continue building. When you run out of nails, you have to stop building. Nails (or rather lack

of nails) are ―limiting‖ your building process. So you buy a 5 kg of nails and return to work.

Inevitably, you will run out of boards next. Even though you still have plenty of nails, you need

more boards to continue building. Now boards are ―limiting‖. You could have truckload of nails

brought to your house, but it won‘t help the doghouse get built, because you need boards.

•This is an example of Liebig‘s Law of the Minimum, which states that plant growth will

continue as long as all required factors are present (e.g. light, water, nitrogen, phosphorus,

potassium etc.). When one of those factors is depleted, growth stops. Increasing the amount of

the ―limiting‖ component will allow growth to continue until that component (or another) is

depleted.

• Liebig's Law has been extended to biological populations. For example,

the growth of a biological population may not be limited by the total

amount of resources available throughout the year, but by the minimum

amount of resources of the greatest scarcity available to that population at the time of year.

•The nutrient most typically ―limiting‖ algae growth in lakes is phosphorus. If phosphorus

concentrations can be controlled, then algae can be controlled…usually. Sometimes, other

nutrients or conditions can limit algae. In some lake , for example, light is the factor that most

often limits algae growth.

•That is, the growth of a population of animals might depend not on how much food is available

in summer, but on how much

food is available in winter.

• Law of Minimum apply not only to nutrients but also to climatic and edaphic factors

The size and composition of a population may control by either available minimum quantity of

mineral nutrients or climatic and edaphic factors

• The law that those essential elements for which the ratio of supply to demand (S/D) reaches a

minimum will be the first to be removed from the environment by life processes

• J. von Liebig, recognized phosphorus, nitrogen, and potassium as minimum in the soil

• In the ocean the limiting elements are phosphorus, nitrogen, and silicon.


Forest Ecology


Minimum limit Optimum Maximum limit

limit

Growth

Low Environmental factor High

( i.e temperature)

Factors affecting ecosystem :

• Light :

• Only sunlight has greatest ecological significance, most vital and essential abiotic

element of ecosystem, photosynthesis or syntheses of food by green plants depends , in

turn support all animals and most microbial life of earth

• Daily and season activities of plant and animal and microbial life

• From ecological point of view, light controls plant‘s structure, form, shape, tissue

differentiation, chlorophyll production, leaf structure, stomata , transpiration, growth and

development flowers, seeds, fruits, locomotion, local distribution etc.

• Light is extremely variable, variance in quality ( wave length or color), intensity ( gram

calories) and duration ( length and duration of day) influence on different ecosystem

• Regulating of amount and quality of light in particular ecosystem depends on

transparency of air and water and strata of vegetation, angle of incidence, latitude,

altitude, aspects, season, time of day, amount absorbed and dispersed by atmosphere,

fog, clouds, suspended dust and water particles etc,

• In forests, major portion of light absorbed by trees vegetation and light receiving in the

exposed area will be reduced by approx 90-98 %.

• About 10% of the total light reaching on the water surface reflects back to the atmosphere

and only 90% pass in the downward of water surface., which will be selectively

absorbed at different depth of water.


Forest Ecology


• Non-lethal limiting factors both at maximum and minimum level, however the efficiency

of photosynthesis process declines steadily with increasing light intensity

Effects of light on plants :

• Formation of Chlorophyll : formation of chlorophyll pigments, ( full sun light in the upper

most surface has larger number, while leaves under shade has few in number )

• Quality of photo synthesis : increases with intensity and saturates at certain level and the

process declines afterwards , this point called compensation intensity. Low intensity low rate of

photosynthesis. At full sunlight it best utilizes only 5% of light energy for photosynthesis.

• Plants are grouped based on the level of photosynthesis : Shade loving ( maintain high rate of

photosynthesis at low intensity of light) ; Photophobic or Sciophytes ( grow better in sun but can

also grow fairly well in shade) and photophilous or heliophytes ( needs high intensity of light

and adversely affects by shade)

• Sunlight prefering plants are P. roxburghii, D. sisso, A. catechu, T. grandis, A. cardifolia,

Terminalia spp and Sal ( heliophytes)

• Shade prefering plants are . A. pindrow, C. deodara, D. latifolia etc (Sciophytes)

• At high intensity, reduces the rate of synthesis of carbohydrates and protins. ( (because the

photo-oxidation of chlorophylls takes place)

• Light effects the movement of plants which is called heliotropism or phototropism ( stem

elongation towards light ( positive phototropism) and roots are negative phototropism. Leaves

grow transversely to light.

• Light inhibits the production of auxins or growth harmones so influences on the shape and

size of plants

• Development of flowers, fruits and seeds is affected by light intensity. Diffused light or

reduced light promotes the development of vegetative structures and causes delicacy. Intense

light favors the development of flowers, fruits and seeds

• Light intensity affects the growth of bacteria and fungi, their spore and germination are

regulated by light factors

• Light effects opening and closing of stomata and has heating effects which in turn affect

transpiration and affects absorption of water

• In most of the plants, respiration rate increases with increase in light intensity. Some plants

respiration rate decreases with increases in intensity of light

• Seeds of many plants are light sensitive ie either their germination requires light or is inhibited

by light


Forest Ecology


• Photoperiodism in plants : Actual duration or length of the day is a significant factor in the

growth and flowering of wide variety of plants. Based on this, plants are classified into Short-

day plants, long day plants and day neutral plants

•The stomata remain opened in the light and closed in the dark, the opening of stomata during

daytime increases CO2 and O2 exchange between plants and atmosphere.

• Transpiration and respiration of plants increases during daytime

• Light is an important factor in the distribution of plants.

The Temperature :

• Temperature is a measure of heat energy content in an object

• Solar radiation is the main source of heat that controls the temperature regime on the earth

• Soil surface temperature depends upon the rate of absorption of solar energy and the rate at

which it is dissipated

• Dissipation of heat or temperature depends upon the amount of vegetation and litter cover and

also on the color, moisture content and other physical properties of soil

• Solar radiation warms up atmosphere and soil and thereby raising their temperature

• The temperature of the atmosphere affects the activities of shoots while the soil temperature

affects that of their roots

• Temperature helps warming of plants/animal bodies and initiate continuation of various

physiological activities such as transpiration, respiration and photosynthesis.

• High temperature increases transpiration and respiration while low temperature decreases them

.

• In general the rate of respiration increases as temperature rises from O to 4o degree C while

it decreases at temperature < o and > 40 degree C, however it varies with the type of vegetation

• Air temperature regulates the activities of enzymes and controls all chemical reactions in the

plant body.

• Increases cambial activity in the shoot portion and essential for germination of seeds

• Affects physiological and cambial activities and thereby growth of the plants

• Soil temperature influence on absorption of soil moisture which increases with increase in

temperature up to a certain limit.


Forest Ecology


• The intensity of Soil moisture absorption by plants depends on soil temperature gradient .

Higher the soil temperature decreases the absorption and lower the temperature also decreases

the absorption capacity, depending upon plant types and their response to soil temperature.

• In general, temperature plays vital role in the growth, distribution, germination etc of the plant

communities. Increase in temperature creates conditions to grow vegetation well . while

decrease in temperature limits the vegetation growth

Temperature and Plant growth :

• Temperature ia an important factor in the life process of plants

• Water, which is a major constituent of of protein of plants is highly sensitive to temperature

range

• Difference in temperature also affects the availability of moisture in the soil and atmosphere

• Plants activities normally takes at temperature range from 0 to 50 degree centigrade, but it

depends on types of plants

• Plants normally die if the temperature exceeds 50 degree C

• Rise in temperature beyond the optimum range results decrease in plants activities and plants

die with excess of the optimal level

Plant

activity

0 10 20 30 40 50

------ Optimum ------ Temperature ( C)

range


Forest Ecology


Plant types according to heat requirement :

• Megathoms : high degree of heat required throughout the year ( desert plants)

• Mesothoms : neither very hot nor very cold conditions required ( tropical/subtropical)

• Microthoms : required cold (temperate plants)

• Hekistothoms : very cold condition, severe winter ( alpine plants)

Plants types according to dormant condition :

• Phanerophytes : seeds bearing plants, dormant buds in the plant body

• Chamaephytes : buds are situated close to the ground

• Hemicryptophytes : buds pass the unfavorable season in the soil surface, protected by soil

itself or by litters

• Cryptophytes : buds survive completely in the ground

• Therophytes : complete their life cycle within a single favorable season and remain dormant

in the form of seed throughout the unfavorable season

Water :

• Water is Important factor influencing vegetation.

• The growth, reproduction and distribution of animals are also affected by water factors. The

germination of seeds and establishment of seedlings are directly affected by water.

•water is essential for respiration , transpiration, germination and viability of seeds

• Water is a raw material for photosynthesis, translocation of manufactured food inside the plant

body. For all chemical activities inside the plant body require water

• Water is essential for physiological activities and soil formation process.

• Water acts as universal solvent and dissolves all mineral nutrients as solutes enters to the plant

and move through the tissues

• Water is required for physical and chemical weathering of soil and translocation of the

weathered materials from one place to another

• Water forms 90 to 95 % constituent part of cell wall and 80% part of protoplasm which is the

physical basis of life form of plants.

• The areas having high water tables invites shallow rooted plants and are sensitive to draught

and frost. The areas having low water table invites long rooted plants to tap much water from

down surface. Too much and too little water are both detrimental to plants and animals

•Water determines the nature of vegetation that survive in a particular area and used as a basis

of classifying vegetation in broad temperature zones. Water is also responsible for the

distribution of important plant species and forests. The mosture and temperature acting together

determine the distribution of plants and animal lfe


Forest Ecology


Total amount of rainfall Name of zone Nature of vegetation

2500 mm or more Wet zone Wet evergreen

< 2500 to > 900mm Intermediate or moist 1. Wet semi-evergreen

2. Moist deciduous

< 900 mm Dry zone 1. Dry deciduous

2. Desert and semi desert

thorn forests and scrub

•The main sources of water available to the plants are precipitation ( rain, snow, ice, clouds , hail

etc - contributing major part ) where as dew and frost, atmospheric moisture or humidity

contributes negligible portion

• Plants use water in two ways, firstly in the process of photosynthesis and secondly in

transpiration.

• Water loss in photosynthesis is negligible almost 1 % of the water absorbed by the roots, where

as loss through transpiration accounts for more than 90% of the water taken from soil.

• The mechanism of water absorption and rate of water flow from soil to plants are primarily

controlled by water evaporating from the leaves, which in turn depend on air temperature and the

velocity of wind.

• For survival and growth, plants must maintain water balance i.e they must gain as much water

as they lose.

• In plants, the rate and magnitude of photosynthesis, respiration, absorption of nutrients, growth

and metabolic process are influenced by amount of water availability.

Movement of water inside the plant body :

Root epidermis root cortex root xylem stem xylem leaf veins

leaf mesophyll stomata atmosphere

7 epidermis

6 cortex

5 Bast fibre


Forest Ecology


4 phloem

• Xylem

2 protoxylem

• Availability of water in the soil : It has three categories :

• Gravitational water = water retain in soil for short period, plants use. This may not be

available for long period since the gravitational force drained them beyond the root zone

• Hygroscopic water = water retain in the soil particles near the root level after the

gravitational water has been drained away and may not be available to the plant because the

gravitational force drained them out

• Capillary water = available to the plant from the gravitational water through the capillary

action

Exchange of water vapor between plant and atmosphere :

Transpiration

• Transfer of water vapor from plants to atmosphere

• Water vapor will move out from the leaves into the surrounding air unless the vapor pressure

between the air and plant body is in equilibrium or unless the outside air is saturated ( moisture

equilibrium )

Evaporation

• Transfer of water vapor from land, water surface and from the canopy of tree (intercepted

water) to the atmosphere

Evapo-transpiration

• Transfer of water vapor by both evaporation and transpiration

•The actual rate of water movement is proportional to the vapor pressure gradient between the

plant/soil or surface and the atmosphere

• Lower the RH, the greater the evaporation from the soil and higher the transpiration from the

plants

• Absolute Humidity : amount of water vapors present in atmosphere

• Relative humidity : ratio of the actual amount of water vapors in the atmosphere to the

amount of water vapor that can be held in the air at a particular air temperature and pressure.

• As the air warms, The RH drops as long as the moisture content of the air is constant.

• RH is lower by day and higher by night. The daily range of RH is greater in the valley and less

at high elevation

• Low relative humidity increases water loss through transpiration and affects plant growth

where as high relative humidity reduce transpiration loss of water.


Forest Ecology


• In lower plants, water is essential for fertilization where as in higher plants the pollination and

seed dispersal are affected through the agency of water in many ways

• Prolonged flooding and drought are both detrimental to plants and in both the cases plants die

in the absence of oxygen in the root zone.

• Soil drought reduce plant growth causing dieback of plants. Drought injured plants are very

susceptible to out break of insects and fire.

Ecological groups of plants in relation to soil and water : Plants and animals exhibits

considerable variations in the requirements of water and has been classified on the basis of soil

and water requirements .

1. Hydrophilous : hydrophytes ( in water) and Helophytes ( in marsh)

2. Xerophilous plants : on the basis of soil - Oxylophytes ( on acid soil) and Psychrophytes ( on

saline soil) and Psammophytes ( on sand and gravel), Chersophytes ( on waste lands),

Eremophytes ( deserts and steppe), Psilophytes ( on savannah) Sclerophyllous foramation ( bush

and forests) Coniferous frmations ( forests)

3. Mesophilous Plants : On the basis of water requirement : Hydrophytes ( plants living in

water and require large quantities of water) , Xerophytes ( tolerate extremely dry condition and

survive long period without water ), Mesophytes ( requires moderate amounts of water)

Climate :

• Sum total of all climatic factors such as temperature, air pressure, humidity,

precipitation, sunshine, cloudiness, winds throug out the year or averaged over a series of

month, season, years, decade or even longer.

• climate differs from weather, which is short lasting meteorological events and the time

scale is for few days

• Weather refers to the unpredictable changes in air that take place over a short period of

time. Climate is the usual, predictable pattern of weather in an area over a long period of

time.

• Climate is affected by the sun, the wind, the oceans and other bodies of water, landforms,

and even people.

• Climate, statistics of weather averaged over a time period that contains many weather

events, usually at least a month or Long term weather over a period of 30 to 40 years

or more constitutes climate

• Climate is a major dominant of the distribution of vegetation on a broad or regional scale

• Microclimate : the more variable climate between the ground surface and few meters above

the ground surface ( short distance) over a long period.

• Microclimate directly imposes on most organism being the zone of greatest disturbances and

showing the greatest differences within short distance


Forest Ecology


• Microclimate may significantly determine the local distribution of species and communities

viewed over thousands of year .

Major components of climate system :

• Atmosphere : circulation, absorption and transmission of solar radiation

• Oceans : Regulator of atmospheric temperature, gas concentrations, storage and transport of

heat and gases

• Cryosphere : ( ice caps and floating sea ice) - influences the surface

energy balance by albedo and contributes to energy exchange between the surface and

atmosphere.

• Land/biosphere : size and position of land, characteristics of lakes, rivers, soil moisture, and

vegetation ( a vital climate control concerning the carbon up take) etc

The climate system involves interaction in many ways :

• Living organisms, particularly forests and plants, play a key role

in atmospheric heat, moisture and energy budgets close to the surface.

• the interaction of the air, sea, ice, land/biota with solar

radiation

• Variations of gaseous and particulate constituents of the Atmosphere and changes in the Earth

position relative to the sun vary the amount and distribution of sunlight received.

• The temperature of the oceans has a marked influence on the heating and moisture content of

the atmosphere.

• The sun radiant energy drives the atmospheric circulation by wind and heat transfer and it

drives the circulation of the oceans.

• The atmosphere and oceans are both influenced by the extent and thickness of ice, as well as

by the shape and composition of the land surface.

World classification of climate :

Classification Criteria

1. Precipitation

2. Temperature

3. Soil Water Balance

4. Air Masses

5. Geographic Distribution

The Koeppen’s System of Climate Classification The Köppen Climate Classification System is the most widely used for classifying the world's

climates. The Köppen system recognizes five major climate types based on the annual and

monthly averages of temperature and precipitation.

A - Moist Tropical Climates : high temperatures year round and large amount of year round rain.

Moist with adequate precipitation in all months and no dry season. Rainforest climate in spite of

short, dry season in monsoon type cycle


Forest Ecology


B - Dry Climates: little rain and high daily temperature range. Two subgroups : semiarid or

steppe, and arid or desert Dry-hot with a mean annual temperature over 18°C (64°F). Dry-cold

with a mean annual temperature under 18°C (64°F)

C – Humid Climates : land/water differences play a large part. warm,dry summers and cool, wet

winters. Moist with adequate precipitation in all months and no dry season. Hot summers where

the warmest month is over 22°C (72°F). Warm summer with the warmest month below 22°C

(72°F). Cool, short summers with less than four months over 10°C (50°F)

D - Continental Climates : can be found in the interior regions of large land masses. Total

precipitation is not very high and seasonal temperatures vary widely. Moist with adequate

precipitation in all months and no dry season. Hot summers where the warmest month is over

22°C (72°F). Warm summer with the warmest month below 22°C (72°F). Cool, short summers

with less than four months over 10°C (50°F) . Very cold winters with the coldest month below -

38°C (-36°F)

E - Cold Climates : These climates are part of areas where permanent ice and tundra are always

present. Only about four months of the year have above freezing temperatures.

Water Balance ET=evaporation from surface + transpiration from plants

Ocean water balance => P + R = E

Land water balance => P = ET + R

Global => P = E

Soil Water Budget Potential ET-how much water a plant could use if it had unlimited supply-depends on temp

Actual ET-how much water plants actually used

P=PET medium climate ex:Ontario

P<PET dry climate ex:Sudan

P>PET wet climate ex:tropical rainforest

general water balance equation is:

P = Q + E + ΔS where

P is precipitation Q is runoff E is evapotranspiration ΔS is the change in storage (in soil or the

bedrock)

Elements affecting climate :

I. The Sun and Climate

• The original source of climate is the sun. Wind and water carry the sun‘s heat around the

globe.

• climate is also affected by latitude. The sun‘s rays hit the earth more directly at low latitudes.

Places at higher latitudes receive only angled rays of the sun.


Forest Ecology


• The areas near the Equator are known as the Tropics. They lie between the Tropic of Cancer

(23 ½˚ N latitude) and the Tropic of Capricorn (23 ½˚ S). The Tropics experience a hot climate

year-round.

II. The Wind’s Effect on Climate

•. Movements of air are called winds. Winds follow typical patterns, affecting climate.

• Monsoons are powerful seasonal winds that blow over continents for months at a time. They

are found mainly in Asia and some areas in Africa.

• Thunderstorms sometimes produce tornadoes, or funnel-shaped windstorms.

• Violent tropical storms called hurricanes form over the warm waters of the Atlantic Ocean in

the late summer and early fall. When the same type of storm hits Asia, it is called a typhoon.

• A long period of extended dryness is called a drought.

III. Ocean Currents and climate

• Moving streams of water called currents carry warm or cool water through the oceans.

These currents affect the climate of land areas. Winds that blow over warm currents, for

example, carry warm air to land areas.

IV. Landforms and Climate

• The shape of land and the location of landforms in relation to one another and to water also

affect climate.

• Local winds are patterns of wind caused by landforms in a particular area. Some local winds

occur because land warms and cools more quickly than water. AS a result, cool sea breezes keep

coastal areas cool during the day. After the sun sets, the land cools down, and cool breezes blow

out to sea.

• The higher the elevation a place has, the cooler it will be.

• As air moves up the windward side of mountain peaks, it becomes cool and loses its moisture.

The air that crosses over the peaks is dry, creating a rain shadow. A rain shadow is a dry area on

the leeward side of the mountains. The dry air of a rain shadow warms up again as it moves

down mountainsides, giving the region a dry or desert climate.

Climate role on vegetation development :

• Areas with tropical rain climate have year-round rains that produce lush vegetation and thick

rain forests. Tall hardwood trees such as mahogany, teak and ebony form a canopy, or top layer

of the forest.

• Tropical savanna areas have a definite wet season, while the remainder of the year is hot and

dry. Savannas, or broad grasslands with few trees, are found in these areas.

• Humid subtropical climate where rain falls throughout the year. Oak, magnolia and palm trees

grow here


Forest Ecology


• The marine climate occurs along coastal areas that receive winds from the ocean. Winters are

rainy and summers are cool in these areas. Deciduous and coniferous trees grow in this climate.

• The coastal Mediterranean climate also has rainy, mild winters. It differs from the marine

climate in that the Mediterranean climate experiences hot, dry summers. Shrubs and short trees

grow in this climate.

• The humid continental climate has long cold and snowy. Summers are short and may be very

hot. Deciduous trees and vast grasslands grow here.

• In the subarctic climate, winters are severely cold and bitter. Huge evergreen forests called

taiga grow here.

• Tundra climate : Closer to the Poles than the subarctic zone lie areas of vast rolling plains

without trees. This region is known as the tundra and is harsh and dry. In these parts, much of the

lower layers of soil stay permanently frozen and are known as permafrost. Only sturdy grasses

and low berry bushes grown here.

• The ice cap climate is found at the Poles and on the ice sheets of Antarctica and Greenland. No

vegetation grows here. Only lichens can live on the rocks.

• Highland Climate : A highland, or mountain, climate has cool or cold temperatures throughout

the year. No trees grow above the timberline.

• Desert climates—the driest climates—have less than 10 inches of rainfall a year. Only

scattered plants like cacti can live here. Many deserts are surrounded by partly dry grasslands

known as steppes. The Great Plains of the United States has a steppe climate, which averages 10

to 20 inches of rain a year.

Nepalese context :

Climate types Vegetation development

1. Tropical Mostly broadleaf and hardwood type of vegetation and grassland

2. Sub-tropical Chir pine and broad leaf type of vegetation

3. Temperate Blue pine, Spruce, Oak Juniper, Rhododendron, Maple, Cedar and

Cypress etc.

4. Alpine Alpine medows, Alpine scrubs, Fir-blue pine, Larch, Oak etc.

5. Arctic or Tundra Lichens and mosses, exposed rock and mostly covered by snow


Forest Ecology


type

The Impact of People on Climate :

• People‘s actions affect climate. For example, cities are warmer than rural areas because

streets and buildings absorb more heat than plants and trees do. In addition, people burn

fuels, which raises temperatures.

• People are burning coal, oil and natural gas as sources of energy. The buildup of the gases

from the burning of these substances has prevented warm air from rising and escaping into

the atmosphere. This is known as the greenhouse effect, in which the earth‘s temperature

will increase.

• Dense forests that receive high amounts of rain each year are known as rain forests. People

burn trees to clear rain forests, which leads to the greenhouse effect. Also, less water

evaporates if there are fewer trees, decreasing rainfall.

Soil and its importance on vegetation

• outermost layer of earth crust where plats grow

• composed of organic and mineral nutrients

• factors responsible for soil formation are climate, biological agencies, parent rock, topography

and time

• weathering (physical and chemical) and climate ( temperature and precipitation) acts together

to disintegrate the parent rocks or earth crust in a process of soil formation

Physical properties of soil includes : soil texture, structure and porosity

• Soil texture : size groups of soil particles

clay = particles < 0. 002 mm ; silt = 0.002 – 0. 02; fine sand = 0.02 – 0.2 mm ; coarse sand = 0.2

– 2.0 mm; gravel = > 2.0 mm

Soil class or textural group such as : clayey soil = < 50% sand particles, < 50 % silt particles

and 30% or more clay particles

Loamy soil = 30-50% sand particles, 30-50% silt particles and < 20% clay particles

• Soil Structure : combination of the individual soil particles of different sizes into aggregates.

Such as : Single grained ( sand dunes); Crumby ( aggregates 3mm or less in diameter); Granular

(aggregates up to 6 mm in diameter); Cloddy ( irregular shaped aggregates > 25 mm in diameter)

• Porosity : the extent to which the gross volume of the soil is unoccupied by solid particles or

the space unoccupied by solid particles

Forest soil profile :


Forest Ecology


O1 : surface litter

O2 : humus layer

A : the upper most horizon or surface layer of mineral soil (eluviation)

B : zone of accumulation (illuviation) enriched with materials washed

from A horizon

C : upper most layer of parent material, which is in the process of

forming true soil under the influence of weathering

D : The unaffected parent rock or other material

Soil formation, transportation and deposition by agents

Rocks/minerals deposited in lake Lacustrine

streams Alluvial

Ocean marine

water transported ice till/moraine

wind transported

Gravity transported

Formed in place wind Dunes(sand

Loess(silt)

gravity colluvial

residual

parent

materials


Forest Ecology


Soil Texture and Tree growth relationship :

Poor medium good medium poor

Sandy loam clay loam heavy clay

Soil and vegetation :

• Soil is an important for the growth of vegetation. The soil is important to tree growth in

numerous ways

• Soil provides water and nutrient for the vegetation to grow. vegetation acts as a media to

anchorage the soil.

•Vegetation can improve the physical and chemical properties of soil.

• Besides rainfall intensity, the physical and chemical properties of soil are also responsible

to degree of soil erosion in which the plant grow

•It provides trees with essential nutrients and is a store house for water and oxygen, all of

which are necessary for the physiological processes associated with tree growth.

•The soil also provides space for root growth and the entire plant with mechanical support.

•The type of soil dictates how best it can be managed to obtain the highest yield as well as

the type of tree to grow and silvicultural management to adopt.

• From stand point of tree growth is recognized as productive only, if the soil has adequate

water intake and water holding capacity, good aeration, adequate depth, and adequate

supply of essential nutrients in available accounts.

• distribution and rate of growth of forest stands are influenced mainly by those

physical, chemical and biological characteristics of the soil which favour the availability of

water, nutrients and air to the trees.


Forest Ecology


• The physical properties such as texture, structure , porosity of a soil largely determine

the ways in which the plants grow. Once the physical properties of soil deteriorate it will be

difficult to recover its properties.

• physical properties are harder to alter than chemical ones

• must chemical shortcomings can be made good simply by adding the necessary fertilizer

while.

• The effects of soil texture are frequently reflected in the composition and rate of growth

of forest vegetation.

• Generally loam and day soils appear suitable for trees with high moisture and high

nutrient requirements.

• Soil aggregate can greatly modify the effect of texture as a factor affecting some

important

phenomenon related to the growth depending on the size, shape and management.

• Soil structures largely determine the porosity and pore size distribution of soil; and the

movement air and water within the soil.

• Aggregate soils, readily infiltrated by rain water, are well aerated and facilitated

penetration of root systems.

• Soils of single aggregate or puddle structure hinder the growth of trees through being

impermeable to rain water or being easily waterlogged and poorly aerated.

• Air in the soil is also very important to tree life.

• The supply of oxygen available in the soil influences seed germination, while all the parts of

the tree below ground, require oxygen for respiration.

• Soil reaction influences both the distribution and growth of forest vegetation.

• Soils with low oxygen content cannot be tolerated for a long period by tree which respire

aerobically except they posses special adaptive devices such as stilt roots, breathing roots

• shallowness of soil limits its utility restricting the supply of moisture, air,

and utility by restricting the supply of moisture, air, and nutrients available to the forest stand

and through reduction of stand stability.

• Generally, deep permeable soils through which tree

roots can develop extensively If moisture is limited for instance.

•Deeper rooted plants may be able to find enough water to keep alive. This is usually the case

with deep-rooted savannah trees which survive the dry season even through the associated

grasses dieback.

• The importance of soil chemical properties in tree growth are the

mineral content, soil reaction or degree of acidity or alkalinity (pH) and the cation exchange

capacity of the soil.


Forest Ecology


Silvicultural techniques can be employed to improve soil conditions. E.g. drastic opening of

canopy is done with the aim of stimulating decay of organic matters by increased rate of

decomposition.

• In some cases drainage schemes may improve the growth of non-mature spp which can do well

in water logged condition.

Nutrient cycle :

• Ecologists may refer to ecological recycling, organic recycling, biocycling, cycling,

biogeochemical recycling, natural recycling, or just recycling in reference to the work of nature

• A nutrient cycle (or ecological recycling) is the movement and exchange of organic and

inorganic matter back into the production of living matter.

• The process is regulated by food web pathways that decompose matter into mineral nutrients.

Nutrient cycles occur within ecosystems. Ecosystems are interconnected systems where matter

and energy flows and is exchanged as organisms feed, digest, and migrate about.

• Minerals and nutrients accumulate in varied densities and uneven configurations across the

ecosystem.

• Ecosystems recycle locally, converting mineral nutrients into the production of biomass, and on

a larger scale they participate in a global system of inputs and outputs where matter is exchanged

and transported through a larger system of biogeochemical cycles.

• global biogeochemical cycles describe the natural movement and exchange of every kind of

particulate matter through the living and non-living components of the Earth, nutrient cycling

refers to the biodiversity within community food web systems that loop organic nutrients or

water supplies back into production.

• Solar energy flows through ecosystems along unidirectional and non-cyclic pathways, whereas

the movement of mineral nutrients is cyclic.

• Nutrient cycle include carbon cycle, sulfur cycle, nitrogen cycle, water cycle, phosphorus

cycle, oxygen cycle, among others that continually recycle along with other mineral nutrients

into productive ecological nutrition.

• Global biogeochemical cycles are the sum product of localized ecological recycling regulated

by the action of food webs moving particulate matter from one living generation onto the next.

Earths ecosystems have recycled mineral nutrients sustainably for billions of years.


Forest Ecology


Nutrient inputs, accumulation and return :

• Minerals that are taken up into forest trees are eventually returned to the forest soil except for

the amount carried out of the forest in logs and other forest products

• Minerals are returned to the surface of the soil by litter fall and through the washing and

leaching effects of rain on tree foliage and stems

• Mammals, insects, earthworms, fungi and bacteria on the forest floor and in the soil attack the

accumulating organic matter, decompose it and makes it re-available for plants nutrition

• Sources : ----- litter

---- -rainfall and stem fall, through fall

----- Acid precipitation

----- Soil biota (soil organism)

• Litter fall : leaves, small twigs, bark, flower, fruits etc add 1500-5000kg of oven dry organic

materials to the surface by a fully stocked forest/ha/year. Leaf litter roughly accounts 70% of the

total. Total litter production of evergreen forests exceeds than deciduous forests by 13 % ( global

scale)


Forest Ecology


• Understory vegetation plays important role in the circulation of nutrient. It often contribute up

to 28% of total litter ( this part is often neglected)

• Large woody debris such as decaying tree trunk and stumps constitute a major component of

the organic matter of the forest floor

• Below ground litter such as root materials that dies each year and decay in the soil and release

nutrient in the soil

Mineral Cycling : Carbon cycle

Carbon is an essential part of life on Earth. It plays an important role in the structure,

biochemistry, and nutrition of all living cells

• Carbon cycle is the biogeochemical cycle by which carbon is exchanged among the

Lithosphere ( Earth crust) , Hydrosphere( ocean and water bodies) , Biosphere (vegetation) of the

earth and and Atmosphere.

• Soils/geology, oceans / water bodies, forests/vegetation and the atmosphere store carbon.

These stores can act as sources or sinks at different times. Sources release more carbon than they

absorb, while sinks soak up more than they emit. A carbon sink can store carbon for a long period

of time. Carbon on Earth is stored in the following major sinks:

• Lithosphere (Earth‘s crust). The lithosphere consists of fossil fuels and sedimentary rock

deposits such as limestone, dolomite and chalk. It is by far the largest carbon sink on earth. It

contains around 4000 gigatonnes of carbon.

• Biosphere. Biosphere carbon is also known as green carbon. Around 42,000 gigatonnes of

carbon are present in the biosphere. Biosphere carbon is divided into three carbon pools: living

biomass, dead biomass and soil.

• Hydrosphere ( ocean/water bodies) . The oceans contain around 36,000 gigatonnes of carbon,

mostly in the form of bicarbonate ion (over 90%, with most of the remainder being carbonate).

Ocean waters contain dissolved carbon dioxide and calcium carbonate in the form of shells and

marine organisms.

• Atmosphere. Carbon exists in the atmosphere in the form of carbon dioxide. Around 750

gigatonnes of carbon are present in atmosphere. Although it is a small percentage of the

atmosphere (approximately 0.04% ), it plays a vital role in supporting life. Other gases

containing carbon in the atmosphere are methane and chlorofluorocarbons.

The movement of carbon, in its many forms, between the four major sinks mentioned above is

described as the carbon cycle.

•


Forest Ecology


Mineral Cycling :Carbon cycle :

• The movement of carbon, in its many forms, between the four major sinks mentioned above is described as the carbon cycle.

The basic carbon cycle is:

1. Plants convert atmospheric carbon dioxide to carbohydrates by photosynthesis;

2. Animals and microorganisms consume and oxidize these carbohydrates to produce carbon dioxide and other products; and

3. Carbon dioxide returns to the atmosphere. On a global level, the total carbon cycle is more complex and involves carbon stored in fossil fuels, soils, oceans and rocks.

Animal assimilation

(dead, decay, decomposition

and respiration)

Animal Fats

CHO and protein in

plant

Photosynthesis CO2 Atmosphere

Fossilization

Industries vehicle

fire / fuel

•Carbon (C) is the building block of life. It is the fourth most abundant element in the universe,

after hydrogen (H), helium (He) and oxygen (O).

• All life is made up of carbon.

• Fifty percent of the dry weight in the human body is made up of it.

• It also exists in the environment as an element in carbonate rocks, petroleum, natural gas, steel,

organic matter, and the air we breathe.

• In the form of carbon dioxide, carbon is a greenhouse gas.

• Massing of greenhouse gases in the atmosphere threatens to raise the temperature of the earth,

acid rain, raising sea levels and disrupting the climates that agricultural systems depend on. T

• The concentration of CO2 in the atmosphere has increased by 30 percent since the beginning

of the industrial revolution.

Minral Cycling : Nitrogen cycle :

Cyclic movement of nitrogen in different chemical forms from the environment to organism and

then back to environment is a nitrogen cycle..

•Nitrogen is a macro nutrient used by plants.

•Nitrogen cycles have an atmospheric component linked to the soil by nitrogen fixation, and de-

nitrification; so falls more or less under edaphic nutrient cycles type.

•Plants obtain most of their nitrogen from soil as nitrate or ammonium ions, former being more

important.


Forest Ecology


•Worldwide, atmospheric fixation accounts for around 10 KG/Ha/Yr of the biosphere nitrogen

flow.

•On land, more than 60% fixation is due to agro-ecosystems, and most of the remainder is fixed

in forests.

•Other ecosystem accounts for about 7% of total nitrogen fixation

•Overall, atmospheric fixation represents abut 2% of global nitrogen assimilation, rest being

cycled in nongaseous forms.

Some Symbols used in N2 Cycle : Nitrogen N2

Nitrite NO2-

Nitrate NO3-

Ammonia NH3

Ammonium NH4+

Stages of Nitrogen Cycle :

• Fixing atmospheric N2 : Through the precipitation /lightning some atmospheric N2

mixed with water falls on the ground.

• Nitrogen Uptake ( Ammonification) : A few kinds of bacteria on soil convert gaseous

nitrogen to ammonia (NH3). The decomposers also decompose the dead plant parts and

animal body and the dropping of animals add NH3 . This NH3 (ammonia ) quickly

dissolves into cytoplasm to form ammonium (NH4), which can be taken by plants

(organism bacteria from genus rhizobium; occurs generally in legume), which is called

ammonification. N2 NH3 ( ammonia) NH4 ( ammonium)

• Nitrogen Mineralization : The animals eat these plants and add organic N2 to soil by

dropping and decomposition of dead body. This organic nitrogen again converts into

inorganic nitrogen compound (NH4) . This process is called nitrogen mineralization. It is

the process of converting the organic nitrogen into inorganic nitrogen . Organic N

NH4

4. Nitrification Nitrification is a two steps process by which ammonium (NH4

+) in the soil is converted first to

nitrite ions (NO2-), then to nitrate ions (NO3

-) by nitrifying bacteria in the soil. Nitrate ions are

easily taken up by plants as a nutrient and also are readily leached from most soils.

NH4+

NO3- (Nitrate)

Step 1

NH4+ + O2 NO2

- + 2H

+ + H2O + 275 KJ energy

Step 2

NO2- + 1/2O2 NO3

- + 76 KJ energy

5.Denitrification


Forest Ecology


Certain bacteria convert nitrite (NO2-) or nitrate (NO3

-) to gaseous nitrogen. This returns

nitrogen to atmosphere. It is an anaerobic process that is carried out by denitrifying bacteria,

which convert nitrate to dinitrogen in the following sequence:

NO3- NO2

- NO N2O N2.

Nitrogen Cycle :

Nitrogen Cycle :

Atmospheric Nitrogen

herbivores, carnivores

(1. Fixing N2)

N2 Dead bodies and OM PPT / Lightning

innert N2

ground

decomposers N fixing plants

(Dinitrification) add N2 Action of ( 3.Mineralization bacteria

denitrifying bacteria Ammonia (NH3 (2. Ammonification) Nitrate Nitrite Ammonium (NH4)

4.Nitrification ( by Nitrifying bacteria)

(Nitrification)

Mineral cycling : Phosphorus cycle :

• Phosphorus is the key to energy in living organisms,

• phosphorus gives energy to animals, driving an enzymatic reaction, or cellular transport.

• Phosphorus is also the glue that holds DNA together, binding deoxyribose sugars together,

forming the backbone of the DNA molecule. Phosphorus does the same job in RNA.

• Keystone of getting phosphorus into trophic systems are plants. Plants absorb phosphorous

from water and soil into their tissues, tying them to organic molecules. Once taken up by plants,

phosphorus is available for animals when they consume the plants.

• When plants and animals die, bacteria decomposes their bodies, releasing some of the

phosphorus back into the soil.


Forest Ecology


• Once in the soil, phosphorous can be moved 100s to 1,000s of miles from were they were

released by riding through streams and rivers. So the water cycle plays a key role of moving

phosphorus from ecosystem to ecosystem.

• In some cases, phosphorous will travel to a lake, and settle on the bottom. There, it may turn

into sedimentary rocks, limestone, to be released millions of years later.

• Unlike other cycles of matter compounds, phosphorus cannot usually be found in air as a gas.

This is because at normal temperature and circumstances, it is a solid/liquid in the form of red

and white phosphorus. . .

• It usually cycles through water, soil and sediments.

• Phosphorus is typically the limiting nutrient found in streams, lakes and fresh water

environments

•As rocks and sediments gradually wear down, phosphate is released.

• In the atmosphere phosphorus is mainly small dust particles.

• Initially, phosphate weathers from rocks. The small losses in a terrestrial system caused by

leaching through the action of rain are balanced in the gains from weathering rocks.

• In soil, phosphate is absorbed on clay surfaces and organic matter particles and becomes

incorporated (immobilized).

• Herbivores obtain phosphorus by eating plants, and carnivores by eating herbivores.

• Herbivores and carnivores excrete phosphorus as a waste product in urine and feces.

•Phosphorus is released back to the soil when plants or animal matter decomposes and the cycle

repeats.

• Phosphates move quickly through plants and animals; however, the processes that move them

through the soil or ocean are very slow, making the phosphorus cycle overall one of the slowest

biogeochemical cycles.

Phosphorus cycle .


Forest Ecology


Rock cliff

Weathering of rock

Phosphorus in soil

Plants assimilate

phosphorus from soil

Herbivores and

carnivores

Decomposition by fungi and

bacteria

Phosphorus in river and

Ocean

Feces and

urines

Phosphate from

fertilizer

Mineral Cycling : Potassium Cycle :


Forest Ecology


Potassium exists in the soil as dissolved K+ ions (solution K), exchangeable K, nonexchangable

K, and mineral K .

Plants take up potassium as K+ ions.. Plants can only directly absorb solution K, and

exchangeable K.

K is not bound in organic forms, but is quickly released back into the soil from crop residues and

roots.

Mineral K is contained largely in un-weathered primary minerals such as feldspars and micas.

K exists in finite quantity in the soil and can limit plant use of other nutrients

K in the soil is primarily controlled by inorganic processes

. Plants require K for photosynthesis, translocation of sugars, starch

production in grains, nitrogen fixation in legumes, and protein synthesis.

•In corn and other crops, K strengthens stalks and stems, thus helping with disease and

lodging.

Fire and adaptation to fire :

Kinds of Fire :

• Ground fire : Takes place where there is a heavy accumulation of litter. In a dry litter, fire is

rapid and extinguishes quickly, but in moist litter the fire is slow and the heat of the fire makes

the inner surface of soil get dry. Fire persists for a longer period. All herbaceous plant die and

some woody shrubs and trees survive because of thick protective bark and deep roots


Forest Ecology


• Surface fire : Fire burns the surface litter and herbaceous species and are less destructive and

sweeps faster. Fire burns the tree, shrubs and soils. After the fire, lots of new seedlings and new

shoots emerge in the ground

• Crown fire : Affects the crown of the trees. Spreads in the top layer from the canopy of one

tree to another tree. It kills the trees, shrubs and herbs most devastatingly. The nest of birds, the

baby birds and the insects hibernating on the tree crown are killed. The underground plant parts

and buried seeds escape the death.

Influences of Fire :

Chemical and Physical properties of soil:

• Increases the soil pH ( because of acid combustion and chemical reaction at high

temperatures)

• Decreases cation exchange capacity of soil

• Alters OM, reduces soil organisms and nutrient loss through oxidation and volatization (result

is nitrogen loss), loss of N, S,K, Na, Z, Fe, Cu.

• Affects on the dry matter accumulation, which in turn, decreases the carbon and nutrient pools

of soil.

• Destroy texture, structure and porosity of soils by affecting the clay content

• Removing overhead vegetation, fire can lead to increased solar radiation on the soil surface by

day, resulting in greater warming at day, and to greater cooling at night.

• Disappearance of leaves reduce plant transpiration and leaf interception of rain,

• Creates an impermeable crust at the soil surface, which may lead to increased soil erosion

through surface run-off and reduce water holding capacity,

• Exposure to sunlight, wind and high evaporation will make soil more dry.

• Reduce fungi but increases bacteria.

• While in prescribed burning, fire is a management tool that releases soil nutrient

available to the plants. Reduces the devastating fire havocs. Releases complex organic

compound

Genetic adaptation of plant species

• Fire is a dominant factor for genetically adopted plant community. Grassland and pine forest

are genetically adapted community which foster frequent fire.

• There is a symbiosis relationship between pine forest community and grassland with fire.

• Grassland and Savanna communities might not have existed without fire.

• Fire is one of the basic natural forces that has influenced plant community over evolutionary

periods of time.


Forest Ecology


• Certain community require fire to maintain their position in the ecosystem and fire is a driving

force for their management such as chirpine, teak, eucalyptus

• Fire encourages species establishment, development, composition and diversity in certain

plant communities. The composition of the plant community and diversity are some

consequences of fire impact on ecosystem.

• After fire, succession takes place and over a period of time some species reached to its climax.

• Repeated fire invites regeneration and establishment of fire resistant and fire adapted species

in the community

• Area devastated by fire will be colonized by the hardy and most promising species able to

adopted in deteriorated soil and other environment condition created by fire.

• Fire create wildlife habitat. For instance, the repeated fire on the shrub land of Africa and north

America have developed grass communities where the condition were suitable to develop

wildlife habitats and attracting wildlife population

• After fire the site will have abundance of insects , parasites and fungi

Fire : Adaptation to it :

• Plant species adaptation to fire .

There are four mechanisms (pillars or strategies ) for species adaptation on fire:

a) Preventing from fire damage (before the fire occurs)

b) Recovering from fire damage (after the fire occurred)

c) Colonizing sites after fire (after the fire occurred)

d) Promoting fire occurrence

a) Thick insulated bark ( many pines and oak species) , deep rooting tap root in young plants

(oaks), rapid juvenile growth ( many pine species), branching habit and self pruning

ability ( upper branching and high self pruning)

• Quick sprouting from various portions of the plants, recovering from root collar or

stump, Dormant buds near the soil surface initiate new shoots after the crown is killed,

dying back ability

• Early seed production, light wind-borne seeds, heat induced germination

• Leaves coated in flammable oils that encourage an intense fire and cones of some pines

shed seeds only in high temperature induce by fire or smoke

Some more points on plant adaptation to fire :

• Various species of plants, have adaptations to ensure their species‘ survival after a fire.

• To survive a fire, a plant must be able to insulate itself from the heat of the flames. Bark

thickness is one of the most important factors determining fire resistance of trees. Ponderosa


Forest Ecology


pine, Douglas Fir, longleaf pine, slash pine, oaks are examples of trees with thick bark that acts

as insulation.

• Small woody plants and shrubs, which normally have thin bark, tend to use the soil as an

insulating layer to protect them. Individual plants resist being killed in fires by producing new

growth (shoots) from underground roots or tubers.

• Some plants protect their buds as an adaptive strategy to survive a fire. Buds can be protected

by layers of succulent foliage. The buds of the longleaf pine are protected by a thick cluster of

needles. Some plants even protect their buds by locating them within the main stem and roots. A

few species of poplar trees in several parts of the world possess this characteristics.

• Retention of seeds by plants until a fire does occur and seed dispersal takes place by fire are

other examples of fire adaptation. A number of pine species around the world, have cones open

only as the result of heat from a fire. Their cones are held closed by a resin that is sensitive to

and opens in high temperatures generated by wild land fires

• There are some plant species called ―Obligate seeders‖ . These plants have large, fire-activated

seed banks that germinate, grow, and mature rapidly following a fire, in order to reproduce and

renew the seed bank before the next fire.

• Some plant species are called ― Resprouters.‖ that is fire-tolerant species, which are able to

withstand a degree of burning and continue growing despite damage from fire. These species

store extra energy in their roots to recover and re-growth following a fire. For example, the

Mountain Grey Gum tree (Eucalyptus cypellocarpa) starts producing a mass of shoots of leaves

from the base of the tree

• Some plants are Fire-resistant plants, which suffer little damage from fire . These include

large trees whose flammable parts are high above surface fires. Ponderosa Pine (Pinus

ponderosa) is an example of a tree species that suffers virtually no crown damage under a

naturally mild fire, because it sheds its lower, vulnerable branches as it matures

• Some plants have leaves coated in flammable oils that encourage an intense fire. Heat causes

their fire-activated seeds to germinate and the young plants can then establish in a burnt site .

• Some trees like Pinus, Larix, Quercus etc. have deep rooting taproot and fire resistant thick

bark which insulating effect against heat. They have tall trunk and pruning ability so avoid from

ground and surface fire.

• Some tree species have fire resistant foliage with lots of water on leaves and very little resin or

oil content can also escape from fire damage

• Litter of some hardwood species like maple tree species decompose very quickly so reduces

the opportunity for fire ignition and spread

• Many Eucalyptus species of Australia have dormant buds located in the lower part of the

trunk and under the soil surface stem and root parts, escape from fire killing and get activated to

produce new branches after fire is over.


Forest Ecology


• Some tree species like oaks and hickories develop deep root system and store food reserves

for rapid regeneration of new shoots after the fire is over

• Some tree species produce hard coated seeds and protect embryo of seeds from the heat of sub-

surface soil by fire. Germination takes place in a favorable season when the seed coat is cracked

by fire.

• Certain tree species like Pinus, Rhus species have no true seed dormancy period, so germinate

at any favorable season following post fire rain

• Re-sprouting ability and bark thickness , stimulation of seed dispersal are adaption against

fire.

• Desert shrubs of different parts of world have deep roots, small leaves, and high tolerance to

hot, dry conditions.

2. Animals adaptation to fire :

• Fire has less effect on mammals and birds than that of plants

• Like plants, animals display a range of abilities to cope with fire, but they differ from plants in

that they must avoid the actual fire to survive.

• Although birds are vulnerable when nesting, they are generally able to escape a fire; indeed

they often profit from being able to take prey fleeing from a fire and to re-colonize burned areas

quickly afterwards.

• Birds have ability to fly and run quickly over along distance

• Mammals are often capable of fleeing a fire, or seeking cover if they can burrow.

• Amphibians and Reptiles may avoid flames by burrowing into the ground or using the

burrows of other animals. • Amphibians in particular are able to take refuge in water or very wet mud.

• Some arthropods also take shelter during a fire, although the heat and smoke may actually

attract some of them.

• Microbial organisms in the soil vary in their heat tolerance but are more likely to be able to

survive a fire the deeper they are in the soil.

• Soil fauna like earthworm, snails, spiders, ants and nematodes are reduced quickly and

increases there after

• Death of mammals and birds are largely due to smoke suffocation than by burning

• Wildlife species have developed different methods or strategies to escape fires.

• Animals such as deer, bear and kangaroo, which are accomplished runners and jumpers, use

their skills to escape the flames.


Forest Ecology


• Other animals such as mice, shrews, snakes, lizards, and tortoises use burrows to escape fire.

• Mature birds can fly to a safer area until the flames have passed.

• However, since nestlings and chicks may be unable to fly, they cannot escape the fire‘s path.

Their remains attract scavengers and predators, such as wild dogs, foxes, and vultures, to

recently burned areas.

• Sawflies, red pine cone beetles, and maple leaf cutters are examples of nuisance pests whose

numbers are reduced by wildland fires.

• Although some insect populations decline as a result of fire, ants seem to increase. Ant

populations have been recorded as more numerous in burned areas than in unburned areas.

• Many microbial organisms (decomposers) also increase in numbers following fire.

• Plants and animals that have structural and behavioral adaptations to survive in habitats

frequented by fire are said to live in a fire dependent community. Plants that are highly adapted

to fire are called Pyrophytes.

The Atmosphere :

• Protective blanket over the Earth, able to nurture life on earth

• Atmosphere constitutes sources of many gas out of which CO2, O2, N2 and transport water

from the land and ocean and back to the land.

• Absorbs most of the cosmic rays from the outer space and electromagnetic radiation from sun

and protects living things from their effects.

• Atmosphere maintain the heat balance of the earth

Composition of atmosphere near the ground surface (% by volume) :

Major components : Minor components Trace components Nitrogen (78.09) Argon ( 9.34 × 10 -1) Neon(1.82 × 10 -3

Oxygen (20.94) Carbon dioxide ( 3.25 × 10 -2) Helium ( 5.24 × 10 -4)

Water vapor ( 0.1-5) Methane ( 2 × 10 -4)

Krypton ( 1.14 ×

10 -4 )

Nitrous oxide (

2.5 × 10 -5)

Hydrogen ( 5 ×

10 -5)

Ozone (trace) and

others

Different Layer of Atmosphere

Thermosphere:

• Altitude range : 85 to 500 km

• Temperature range : - 92 to1200 C

• Important chemicals : O2 +, O+, NO+


Forest Ecology


Mesosphere :


• Temperature range : - 2 to -92 C

• Important chemicals : O2 +, NO+

Stratosphere :



• Important chemicals : O3

Ozone in this region absorbs ultraviolet radiation

Troposphere :



• Important chemicals : N2, O2 , CO2, H20

Role of Animals in Ecosystem :

• Contribute in food chains, energy flow and nutrient cycling

• Breakdown OM and release nutrient

• Allows natural regeneration and succession ( by dispersing seeds and pollen) and

germination of seeds

• Regulate forest composition and development

• Influence forest pattern and process

• Provide ecosystem services such as recreation, hunting, meat, milk and medicine

• Rich biodiversity creates ecological integrity in changing climate

• Carnivores predation can keep herbivores population balance , which minimize over

utilization of plants and over grazing

• Herbivores grazing enhance uniform utilization of the plant community and maintain

population balance in the ecosystem

• Decrease the epidemic of pest and injurious insects population

Plant Defense Adaptation

(Plants and its parts are subject to attack at all stages in their life cycle by organisms. Plants

develop defense mechanism to survive or adapt against the attack )


Forest Ecology


Plant Adaptation : a heritable or genetically characteristics or trait that enables plants to

better survive and reproduce within a given set of environmental conditions.

An alteration in structure or function of a plant or animal that helps it change over the course of

successive generations in order to be better suited to live in its environment.

These alterations in structure and function in a plant can be visualized through :

• Texture and composition of plant surface

• Presence of specialized organs of tissues ( thorns)

• Absence of nutrients required for the pests or animals ( unpalatable)

• Presence of hormones like structure that repel the insects

• Accumulation of secondary compounds ( alkaloids, tarpenes )

The kinds of defenses use by plants are : Thorns, resin ducts, accumulation of alkaloids,

terpenes, phenolics, cacogenic glycosides

• Trees like orange, junipers, pine, roses etc have prickles, spines, thorns or sharp needle

leaves that deter browsing.

• Oil or resin come out of resin ducts in needle and shoots and bark in conifers deter foliage

feeders and bark beetles.

• A high concentration of tannins in oak leaves deter insect feeding.

• Presence of toxic vines and parasites also deter animals from feeding on associated tree species

( symbiosis relation ) .

• Produce distasteful chemicals that deter further feeding.

• Produce chemicals that affect herbivores‘ physiology

Damage in Forest Stands :

• Animals do damage in forest stand.

• From seeds and seedlings to mature tree, no forest tree is free from animal damage.

• Seedlings of all woody species bark removed by hares, stem and root girdling by mice as well

as trampling and browsing by deer.

•Mature trees are subject to attack by insect feeders.

• Bark eaters rodents ( hares, mice, monkey, bear etc. ) may kill a large number of trees.

• Juice sucking insects ( wood pickers), bud eating birds ( sparrow), squirrel and other animals

cause great harm to the forest stand.

• Elephant detach the branches of the tree and sometime uproot the trees.


Forest Ecology


• The insects, birds, squirrels, mice and rodents eat seeds.

• Some animals eat and destroy seeds at sowing time.

• Squirrels cut conifer cones.

• Deer browsing is probably the most common injury in the forest.

• High deer population limits the seed germination, forests regeneration and stand development.

Unit 5 : Synecology

Synecology is a study of groups of organisms ( or species) which are associated together in an

ecosystem .

• A group of individuals of the same species is population. Population of different species in a

given set of environment is community, which is the biotic component of an ecosystem.

• Biotic community as ― assemblage of plants, animals, bacteria and fungi that live in an

environment and interact with one another forming a distinctive living system with its own

composition, structure, environmental relations, development and function

• Therefore the study of the community properties and the interaction among organism s of the

community is termed as Synecology.‖

Site or habitat : The whole environmental set up which is occupied by organisms is site or

habitat

Forest site Quality : Sum total of all the factors ( climatic, edaphic, and biological) affecting

the capacity of the site to produce forest biomass.

• Site quality refers to the combination of physical and biological factors of a particular

geographic location or site. Site quality are generally inherent to the site, but may be influenced

by management.

Production vs site productivity : Production is the quantitative measurement of forest

biomass in terms of cu. m / year/unit area ( yield table or volume table) , where as

Site productivity : quantitative estimate of the potential of a site (capability of the site to produce

plant biomass ) to produce plant biomass.

• Forest site productivity may be defined as the potential of a particular forest stand to produce

aboveground wood volume.

• Site productivity is often quantified as an index, site class or site index, which are widely used

for management purposes.

• Most commonly, site indices are based on estimates of stand height at a given age.


Forest Ecology


• Site productivity reflects potential of site on the production of forest biomass,

• Site productivity depends on site quality, which in turn , depends on natural factors inherent

to the site ( soil and climate) and the management regime such as silvicultural practices like

site preparation , choice of species, thinning, spacing, regeneration etc.

Measurement of Forest Productivity ( or site quality or site productivity ) :

1. Direct Measurement

• Generally measured in terms of the gross volume of bole wood per unit area per year over the

normal rotation.

• Gross volume : the total amount of wood in all trees within a given unit of time without

deduction for natural mortality, removal by human or decrease in wood volume by diseases or

pests

• It is measured in the form of mean annual increment ( MAI)

• MAI : Average annual rate of growth ( total increment/age)

2. Indirect Measurement of Forest Productivity ( or site quality or site productivity of a

given species)

-- Site index Method

-- Plant Indicator of site

-- Environment factors as a measure of site

-- Multiple factor methods of site classification

• Mean annual increment (MAI) or mean annual growth

• It refers to the average growth per year a tree or stand of trees has exhibited/experienced to a

specified age.

• For example, a 20-year old tree that has a dbh of 10.0 inches has an MAI of 0.5 inches/year.

• MAI is calculated as MAI = Y(t) / t where Y(t) = yield at time t. Mean Annual Increment

m3/ha/yr (MAI) = Volume of stand (m3/ha)/Age of stand (yrs)

• The Mean Annual Increment is simply the average volume production per year for a forest of

known age:

•MAI starts out small, increases to a maximum value as the tree matures, then declines slowly

over the remainder of the tree's life. Throughout this, the MAI always remains positive.

• Periodic or Current Annual Increment (CAI) is the increase in volume at a particular age and is

determined by annual measurements of standing volume.

Example:

Periodic or Current Annual Increment (CAI) at age 2 (m3/ha/yr) = (Volume at age 3) - (Volume

at age 2)


Forest Ecology


• MAI differs from Periodic or current Annual increment (PAI or CAI) because the PAI or CAI

is simply the growth for one specific year

• The point where the MAI and PAI or CAI meet is typically referred to as the Biological

rotation age . This is the age at which the tree or stand would be harvested if the management

objective is to maximize long-term yield.

• the PAI or CAI will increase rapidly in the early years, up until competition for light, moisture

or nutrients causes CAI to reach its peak. The decline in CAI can be more rapid than the early

rise.

•Direct methods are not based on site factors, which are not pragmatic because the

productivity is based on site factor but also are based on genetic factors

Indirect Method of Measuring Forest Productivity

a. Site Index Method :

• The relationship between tree height and age

• The height of the dominant portion of forest stand at a specified standard age ( rotation) is

commonly termed as site index

• The height of trees of a given species in a given forest stand and of a given standard age

is more closely related to the capacity of a given site to produce wood of that species

• Site index curves : Site index curves are drawn for different sites for a particular given

species with height-over-age


Forest Ecology


• Tree height measure at specified age is best related to the site productivity of a given species

• Marked differences in the height growth of dominant trees occur on site of different quality

• The height of the dominant trees on the richest site may be 3 to 4 times more than on the

poorest site

In Nepal, the Sal tree has attain a height of more than 35 meter at the age of 120 years at the

richest site while less than 15 meters on the poorest site . The richest site is termed as quality I

and the poorest site quality IV

The normal correlation of height with different quality class is as follows :

Quality Class Height of dominant trees in a stand

I 35 m and above

II 25 m to < 35 m

III 15 m to < 25 m

IV < 15 m

• Plant Indicator of site :

• Plants of the site themselves are measures of the site ( called photometers)

• Both the trees and understory plant species ( herbs, shrubs) can be used as indicator

species.

---- ‖ Steno ― species are indicator of good site quality such as Black

walnut, white ash, yellow poplar

---- ― Eury ― species are indicator of bad site quality such as black

oak, white oak

---- Ground vegetation or understory species are useful indicators

because they are long lived, relatively unaffected by stand density and

easily identified in all season

----- Species groupings along the environment gradient can also be

used as site indicators

---- Occurrence of Vitex negundo or indigofera pulchella in Sal forest

indicates a very poor site

• Environment factors as a Measure of Site

• Environment factors are used to measure the forest site productivity

• This is primarily used for the growth of forest in abandoned agricultural land; area subjected

to fire; logged in areas; heavy grazed areas ; and areas having other disturbances, area to be

converted from one forest type to another type

• In such areas a small supply of in the environment or physical factors will result in measurable

changes in the growth of forests ( based on law of minimum)


Forest Ecology


• Site productivity can be measured from the analysis of the physical environment rather than

from the vegetation

Climatic factors : Site with high rainfall deficits produce less forest growth than sites with

small rainfall deficits, high and low temperature both reduce forest growth

• With increasing elevation, normally precipitation will be high and temperature will be low. Site

quality may be increased or decreased with the combined effects of precipitation and

temperature

• Therefore, precipitation and temperature are related to forest tree growth as a measure of site

quality

Topographic and Soil factors :

• Topography and soil should also be considered in determining the site quality of forest and are

the indicators of forest productivity.

• Soil physical and chemical properties as well as elevation, slope, aspects, longitude and

latitude of the site are variables to determine the site index to measure the productivity of forest

D. Multiple Factor Method of Site Classification :

• Multiple factor method is also used to determine the site quality

• This is based on the fact that the site quality is the sum of the total factors affecting the

capacity of land to produce forest

• The more factors are taken better is the estimate of site productivity

• Multiple factor system, also called ―The Baden-Wurttemberg System ― has integrated

geography, geology, climate, soil, and sociology in determining the site quality

• In this method, Regional classification of growth were determined and the areas were sub

divided into growth districts

• Districts were sub divided into local and local classification of site quality were done

• Site quality mapping at local level were done

• Evaluation of growth and productivity were done at local level site quality

• Silvicultural and management recommendations were made for each species and species

mixture foe each site

• Comprehensive summary for each growth areas and comparison between different growth

areas were done


Forest Ecology


Regional classification of growth were determined and the areas were sub divided into growth districts

Districts were sub divided into local and local classification of site quality were done

Site quality mapping at local level were done

Evaluation of growth and productivity were done at local level site quality

Silvicultural and management recommendations were made for each species and species mixture foe each site

Comprehensive summary for each growth areas and comparison between different growth areas were done

Concepts of competition and survival :

• As the number of individuals of a sps. increase at the limited space, plants compete each

other for space, nutrient , moisture and light.

• Since the competition is within the individual of the same sps . of a population, the

competition is called intra-specific competition.

• They may also compete with individuals of other sps that enter into that area, which is called

inter-specific competition.

• Due to intra and inter specific competitions and interaction s with biotic and abiotic

components of that area , the environment of the site will be modified and slowly it becomes

unsuitable for the existing community, and the site will slowly be replaced by new invaders

or community

• Finding the modified environment more suitable for other sps, more sps will enter into the

area and compete with the previous occupants.

• This results the former species subdominant or eliminated completely


Forest Ecology


• Addition of OM, nutrient and moisture by the plant communities makes increase availability

of food and home for animals to join the community

• The interactions between the plants , animals and the environment further takes place and

modify the environment , consequently fresh invasion of other species and animals takes place

which leads to the process of succession.

• Finally a stage is reached when the final community becomes stabilized and can maintain

itself in the equilibrium or study state with the climate of that area.

• This last stage is mature, self maintaining and reproducing community and relatively

permanent

• The vegetation is tolerant of the environmental condition, contains wide diversity of species,

well developed structure, complex food chain, equilibrium in nutrient uptake and return and its

living biomass is in steady state

Forest and grass communities, structure and diversity

• Forest community, structure and diversity

Community ( individual plant, population, community). The vertical profile of a plant

communities is known as its structure. Diversity is (sps. richness and abundance)

• Well developed forest ecosystem has several layers of vegetation from top to bottom : Top

story or canopy and under story . Within under story : shrub layer, seedling or herb layer;

mosses and lichens layer and finally forest floor or ground layer ( where decomposition of

litter takes place and nutrient are released to the nutrient cycle) and lower than this is root

layer or soil strata

• The canopy is a major site for energy fixation and has major influence on the forests

• With fairly open canopy, the sunlight reach to the understory strata and the understory

vegetation richly developed, while in the closed canopy the vegetation of the understory will

poorly developed

• At the canopy level, the tree must spend some of its energy of the photosynthesis for the

development of woody tissue of stem and branches.

• At closed canopy, the under story strata will receive less light for photosynthesis and to

survive but the advantage is that the understory need not share much of its energy for the

development of woody tissue of stem and branches. The herbs does not need to spend more

of its modest energy for the development of woody tissues and branches.

• Therefore, the Forest Structure involves a gradient of growth forms . That is upper and

lower trees ; upper and lower shrubs; upper and lower herbs and soil surface mosses for the

adaptation in the gradient of light intensity

• Along the gradient of the growth forms, two extremes that is ranging from upper canopy level

to herbs or mosses/ lichens level exists.


Forest Ecology


• The upper extreme i.e upper canopy level : photosynthesis at full level of light intensity ,

massive investment of energy to stem and branch structure and formation, accumulation of

food reserve in a root system or root mass is smaller than the above ground structure.

• The lower extreme i.e lower herbs level : photosynthesis at low level of light intensity, small

investment of energy to above ground supporting structure, accumulation of food reserve in a

root system more massive than the above ground structure.

• Therefore, variety of life in the forest is directly related to the number and development of

layers of the forest. For example : the rain forest has greater species diversity and so the layer or

stratification of forest is more.

• If certain layer is destroyed or absent , the animals they shelter and support are also missing.

• Thus a well developed forest supports a rich diversity of life

Grassland communities :

• In grassland communities, only three strata such as : herbaceous layer ; ground or mulch layer

; and the root layer are recognized.

• The root layer is more pronounced in grassland ecosystem than any other ecosystem.

• The root layer provides permanent residence to soil bacteria, fungi, protozoans, nematodes,

earthworms, spiders, insects and other invertebrates

Species diversity in communities :

• Species diversity is a measure of the diversity of plant sps. within an ecological community

• It includes both species richness (the number of species in a community) and the ―evenness of

species‗ or ―abundances‖.

• Species diversity is influenced by species richness. All else being equal, communities with

more species are considered to be more diverse. For example, a community containing 10

species would be more diverse than a community with 5 species.

• Species diversity is also influenced by the ―evenness of species‖, which is a relative

abundance of individuals in the species found in a community. Evenness measures the variation

in the abundance of individuals per species within a community. Communities with less variation

in the relative abundance of species are considered to be more ―even‖ than a community with

more variation in relative abundance. Consider the following two communities.

Species richness in a community = No. of species in a community (, communities with more

species are considered to be more diverse. For example, a community containing 10 species

would be more diverse than a community with 5 species. )

Evenness or abundance = relative abundance of individuals in the species


Forest Ecology


• In A and B species richness is same ( 5 in both the cases)

• In A, all five species have the same abundance, no variance and more even

• In B, there is great variation in abundance , and not even

• Communities with greater evenness are considered to have greater species diversity, even

though species richness of the two communities is equal

• Community A is more species diversity than Community B

Relationship of species richness and abundance :

Species richness = ( S – 1 )/ log N, where S = Number of species and N = Number of

individual in each species ( abundance)

Diversity Index

H = - ∑ Pi log Pi, where, H is diversity index ( Shannon-weaver Function), Pi is proportion of

the total number of plants( individuals) consisting in i th species and i = 1 to S

• Species diversity tends to be low in physically controlled ecosystem and high in biologically

controlled ecosystem

Forest communities and changes in the ecosystem :

Forest communities is the complex of biotic and abiotic factors

Biotic factors includes : trees, shrubs, herbs, bacteria, fungi, protozoa, arthopods, vertebrates and

many others

Abiotic factors include : gases, minerals, soil, geology, waters and other site factors.

Changes in forest ecosystem : occurs due to changes in weather and climate

• Diurnal change :

During night – temperature low, moisture and humidity relatively high, plant active on

respiration ( consume O2 and release CO2 ). Some animals are in dormant stage and some are

active. During daytime- the conditions will be reverse .

• Seasonal change : Forest ecosystem changes seasonally around the year, Biotic community

and their activities will be changed as season changed ( such as growth, leaf fall, sprouting ,

pollination, reproduction, pollination etc )

• Long term climatic change : Forest ecosystem changes over the change in climatic condition

• Ecosystem biota change : Biota changes over time, colonization, immigration, migration,

dispersal , mutation, natural selection etc


Forest Ecology


Competition :

• In an ecosystem, there exists various kinds of relationship among species inhibiting the

ecosystem

• One of the relationship is competition among species, plants compete with each other for

space, nutrient, light, moisture, air, warmth etc. They compete for these elements for the growth,

reproduction and survival

• Limited supply of at least one resource (such as space, nutrient, food, light, warmth,

moisture) used by both usually facilitates competition

• When two or more organisms in the same community seek the same resource (e.g., nutrient,

food, water, light, warmth, air, space etc ), which is in limiting supply to the individuals seeking

it, they compete with one another.

• Birds, rodents and ants may compete for seeds in desert environment

• Competition in animals is often for food, water and mates, space, nesting sites, wintering sites,

safer sites from predators

• Competition in plants is for light, water, nutrients and space, pollinators

• Competition is an important process affecting the distribution and abundance of plants and

animals

• Species competition may have a negative effect upon one another. But they also have

neutral and beneficial effect.

• If the competition is among members of the same species, it is called intraspecific.

• Competition among individuals of different species it is referred to as interspecific

competition.

• Individuals in populations experience both types of competition to a greater or lesser degree.

• Interspecific competition is normally not as fierce as intraspecific competition, unless in case

of a sudden drastic change. Intraspecific competition is the most conspicuous competition in

grasslands, where, for example, cheetahs and hyenas are often killed by lion .

• Intraspecific competition does not effect the composition of the forest type and therefore has

no effect on forest succession

• Interspecific competition results in a natural succession from one forest composition to another

• In the case of forests, competition takes place in even and uneven aged stands and in the

main canopy or over storey of the forest and in the under storey

• Competition between species at the same trophic level of an ecosystem, who have common

predators, increases drastically if the frequency of the common prey in the community is

decreased.


Forest Ecology


There are two different process of competition :

1. Exploitation or Resource competition ( Scramble competition)

• competition occurs when a number of organisms of same or different species utilize common

resources that are in short supply

• competition occurs between individuals when the species or individuals reduce the supply of

the limiting resource or resources needed for survival.

• By such competition , the exclusion of one organism by another can occur when the dominant

organism requires minimum amount of the limiting resource to survive ( Law of minimum).

• The dominant species reduce the quantity of the resource to some critical level with respect to

the other organism.

2. Interference or Interface competition : ( contest competition) :

• Competition occurs when the organisms seeking a resource harm one another in the process

even if the resources is not In short supply

• Competition occurs when an individual directly prevents the physical establishment of another

individual in a portion of a habitat.

Example : established plants can preempt ( prevent) the invasion and colonization of other

individuals by way of dense root mats, peat and litter accumulation etc.

Interaction :

• Limited supply of at least one resource (such as space, nutrient, food, light, warmth, moisture)

used by both usually facilitates this type of interaction,

• competition may also exist over other services and 'amenities', such as females for

reproduction (in case of male organisms of the same species).

Types of interaction

The neutral effect is called neutralism and the beneficial effect is called mutualism or proto-

cooperation , if one species is benefited and other is harmed is called predation and one benefit

but does not harm the other is called commensalism and one species is harmed by any other

species and derives no benefits is called amensalism

Types of

Interaction

Species

A

Species

B

Nature of competition Example

Competition (

interference and

resource use type)

- - Both A and B are affected competition of Sal

and Khair trees

Neutralism O O Both A and B are not affected Rabbits/deer and frogs

live together in a

grassland no

interaction between

them.


Forest Ecology


Mutualism + + Favorable to both A and B and is

obligatory

Insect pollination of

flowers

Predation or

parasitism

+

(predator)

- (prey) A benefited B affected (

predation/prey relationship)

Wolf and rabbit

Commensalism + O A benefited but B not affected Insects decomposing

Caracas

Amensalism O - B affected but A not affected The walnut tree

secretes a chemical

from its roots that

harms neighboring

plants

Mutualism interaction

Symbiotic Non-symbiotic

Symbiotic : In this interaction , individuals live together and interact physically and their

relationship is biologically essential for survival. At least one member of the pair cannot live

without close contact with the other. For example, the fungal-algal symbiosis that occurs in

lichens. Lichen is a mass of fungal hyphae that forms around a algae cells. In this mutualism, the

algae produces carbohydrates and other food by products through photosynthesis and

metabolism, while the fungus absorbs the required minerals and water to allow for these

processes to occur.

Non- symbiotic : In this interaction, the two organisms live independently, but cannot survive

without each other. The most obvious example of an interaction of this type is the relationship

between flowering plants and their insect pollinators.

Tolerance :

• Tolerance is the capacity of a plant to maintain its fitness through growth and reproduction

after sustaining damage.

• In a broad sense, tolerance deals with the general capacity of a plant to be genetically adopted

and physiologically compatible with unfavorable conditions

• Tolerance often may Influence the evolution of plant defense and the composition of plant

communities.

• Forest tree that can survive and prosper under a forest canopy is said to be tolerant. It also

refers to the relative capacity of a forest plant to survive and prosper in the under storey


http://en.wikipedia.org/wiki/Black_walnut

Forest Ecology


Recognition of tolerance

• Occurrence in the under storey

• Response to release rapid growth following removal of over storey

• Crown and bole development ( lower branches will be foliated longer and the boles tend to be

more tapered)

• Stand structure ( tolerant trees persists over long periods of time in natural mixed stands )

• Growth and reproductive characteristics ( height grow of tolerant Sps. is faster than the non-

tolerant species, tolerant tree mature later, flower later and more irregularly and live longer than

intolerant trees

Law of Tolerance ( Shelford’s Law ) :

“ Each ecological factor to which an organism responds has maximum and minimum limiting

effects between which lies a range or gradient that is known as the limits of tolerance‖

Example : CO2 is necessary for the plant growth, small increase in CO2 in atmosphere will

increase rate of plant growth. If the increase in CO2 is too much then results toxic effect to

plant. So there is gradient of minimum and maximum requirement of CO2 for the plant growth.

Similarly, a small amount of additions of arsenic to human diet will have a tonic effect, but the

increase in the arsenic dose more than the requirement may cause fatal death.


Forest Ecology


( Lower limit of tolerance)

Zone of intolerance Zone of physiological Zone of physical (upper limit of toleran

stress stress Zone of intolerance

Minimum limit Optimum Maximum limit

limit

Growth

Organism organism organism organism

Absent infrequent infrequent absent

Low Environmental factor High

( i.e temperature)

Forest stand structure :

• Dominant :

--- trees with crowns extending above the general level of the canopy

--- receiving full light from above and partly from side

--- crown well developed

• Co-dominant :

--- trees with crowns forming the general level of the canopy or somewhat below

--- receiving full light from above but only moderate amounts from the side

--- usually with medium sized crowns and more or less crowded in the sides

• Intermediate :

--- trees shorter than the co-dominant class but with crowns extending into the canopy formed

by the dominants and co-dominants

--- receiving some direct light from above but little from sides

--- usually with small crowns considerably crowded on the sides

• Suppressed :

--- trees with their crowns entirely below the general canopy level

--- receiving no direct light from above or from the sides


Forest Ecology


Succession : Progressive replacement of one community by another until a relatively stable

community occupies the area is called ecological succession. It is the ―birth‖ of an ecosystem

and subsequently ―aging‖ process of its abiotic and biotic features

• The development of the community by the action of vegetation and the geological factors on

the environment leading to the establishment of new species is termed as succession .

• The occurrence of relatively definite sequence of communities over a long period of time in the

same area resulting in establishment of stable or climax community, is known as ecological or

biotic succession.

• Succession is a continuing and directional process marked by large number of changes in the

vegetation, the fauna, the soil, and the microclimate of the area with the passage of time

• These changes occur together mutually affecting one another with simple cause and effect

relationships

• Ecological succession is a complex dynamic interaction between the species composition of

the community inhibiting the ecosystem

• Due to the close interactions between site factors and the plant communities, a continuous

changes take place in the biota of a particular area

• In succession, involvement of both flora and fauna takes place. Changes in fauna is led by

changes in flora

• It is the universal process of directional change in vegetation during the course of time

.

•The first community which is inhabiting the area will be referred as 'pioneer community' and

the last and stable community formed in the area will be referred as 'climax community'.

• The intermediate communities are called 'transitional or seral communities'. The whole series

of changes in community characteristics from pioneer stage to climax stage constitute a 'sere' and

the intermediate stages are the 'seral stages'.

• Usually the initial stages of succession are comprised of lower forms.

Causes of succession :

1. Biotic factors : Interactions among the organisms in a community, as called biotic factors, influence the

structure, composition and function of a community. In succession, during period of time a

community makes the area less favourable for itself and more favourable for the next serial

community.

2. Physiographic factors : Includes physical and chemical factors of the environment such as landslides, erosion,

catastrophic factors, etc.

3. Ecesis or continuing factors : These are the processes such as migration, aggregation,

competition and reaction etc, which causes succession of population as a result of changes,

chiefly in the soil features of the area


Forest Ecology


Process of Succession (F.E. Clement , 1916)

1. Nudation: Succession begins with the development of a bare site or area , called Nudation by

several reason s such as vocanic eruption, landslide, flooding, erosion, deposition, fire, disease

or other catastrophic agency.

2. Migration: It refers to arrival of propagules of various organisms and their settlement in the

nude or bare areas. The seeds , pores or other propagules of the species reach the bare area

through the action of air, water or animals

3. Ecesis: It involves successful establishment of immigrant plant species or initial growth of

vegetation in the new area. It includes germination of seeds or propagules, growth of seedlings

and starting of reproduction by plants.

Aggregation : the successful invasive or immigrants individual s of species increase their

number by reproduction and aggregate in a large population

4. Competition: As the numbers of individuals of species increase due to reproduction and

multiplication, species began to compete for space, light and nutrients. ( inter-specific and intra-

specific competition takes place, biotic and aboitic interactions takes place, ),

5. Reaction: During this phase autogenic changes affect the habitat resulting in replacement of

one plant community by another.

--- Environment is modified and progressively becomes unsuitable for the existing community,

which sooner or later is replaced by new invaders or another community ( serial community).

---- Finding the modified area more suitable, more species enter the area and compete with the

previous occupants. This results in a balance among the species in which the former species is

brought down to a sub-dominant status or is completely eliminated.

---- The addition of OM, nutrients, and more moisture in the substratum by small plants makes it

suitable for larger ones.

---- Increase availability of foods allows various kinds of animals to join the community and the

resulting interactions further modified the environment and paves the way for fresh invasion by

other species and animals .

---- This process coninues until a stabilized community exists. . Reaction phase leads to

development of a stabilization or climax community.

6. Stabilization or climax : Eventually a stage is reached when the final terminal community

becomes more or less stabilized for a longer period of time and it can maintain itself in the

equilibrium or steady state with the climate of that area

--- This last serial stage is mature, self-maintaining, self reproductive and are relatively

permanent and is tolerant of the environmental condition it has imposed itself


Forest Ecology


Stages of succession :

• Pioneer stage

--- Initial stage of succession

-- Species grow in this stage are termed as ― Pioneer ‖

--- Species that invades a bare area such as newly exposed soil or environment

• Serial stage

--- Intermediate stage

--- Species grow in this stage are termed as ―Sere‖


http://en.wikipedia.org/wiki/File:Forest_succession_depicted_over_time.png

Forest Ecology


• Climax stage

--- Final stage

--- no further primary succession exists

Stage of succession ( continued) : The primary and secondary successions may be of the

following types depending on the moisture contents :

• Hydrach or hydrosere : The succession when starts in the aquatic environment such as

ponds, lakes, streams, swamps, bogs etc

• Mesarch : the succession when begins in an area where adequate moisture is present

• Xerach or xerosere : the succession when starts in xeric or dry habitat having minimum

amounts of moisture such as dry deserts, rocks etc. It has 3 types

a) Lithosere – succession initiating on rocks. b) Psammosere – succession initiating on sand

and c ) Halosere - succession starting on saline soil

• Sometimes, succession is classified as Autotrophic and Heterotrophic succession

• Autotrophic succession : characterized by early and continued dominance of

autotrophic organisms like green plants. It begins in a predominant inorganic

environment and the energy flow is maintained indefinitely

• Heterotrophic succession : characterized by early dominance of heterotrophs such as

bacteria, fungi and animals

Stages Xerach Mesarch Hydrach

1 Dry rock /soil Moist but aerated Water

2 Lichens - Submerged water

3 Lichens and mosses - Semi Floating plants

4 Mosses and forbs Mostly annuals Floating plants/ emergents

5 Perennial forbs and grasses Perennial forbs/grasses Sedges and mat plants

6 Mixed herbaceous Mixed herbaceous Mixed herbaceous

7 Shrubs Shrubs Shrubs

8 Intolerant sps Intolerant sps Intolerant sps

9 Semi-tolerant trees Semi-tolerant trees Semi-tolerant trees

10 Tolerant trees Tolerant trees Tolerant trees

Primary Succession :

• The development of the biota in unoccupied sites without any catastrophic disturbances

• It is also termed as autogenic succession

• The displacement of one group of species by another results from the development within the

ecosystem itself by the development of the vegetation, soil and micro-climate of the site etc

• This process terminates after a long period or series of intermediate stage


Forest Ecology


• It is the process of species colonization and replacement in which the environment is initially

or virtually free of life. That is the process starts with base rock or sand dunes or river delta or

glacier debris and it ends when the climax is reached. The sere involved in primary succession is

called pre-sere.

• Primary succession takes a very long time (more than thousands of years in case of climax

forest on bare rock).

Secondary succession :

• It is the process of change in primary succession that occurs after an ecosystem is disturbed but

not totally demolished.

• Succession following severe disturbance or removal of a pre-existing community are called

secondary succession

• In this situation, organic matter and some organisms from the original community will remain,

thus the successional process does not start from scratch.

• Consequently, secondary succession is more rapid than primary. It is seen in areas burned by

fire or cut by farmers for cultivation. The sere involved in secondary succession is called sub-

sere

Sere = The transitional series of community which develop during the process of

succession

The concept of climax :

• If the succession allowed to progress without any disturbances a stage is reached when no

more changes in vegetation structure and soil are seen. This is climax

• Climax is a stage when the final terminal community becomes more or less stabilized for a

longer period of time and it can maintain itself in the equilibrium or steady state with the climate

of that area

• At this stage the vegetation is in equilibrium with the environment and stays unchanged.

• Climax stage is mature, self maintaining, self re-producung and relatively permanent

•. The vegetation in the climax stage is tolerant to environment conditions imposed upon it.

The climax community is characterized by an equilibrium. It has wide diversity of species, a well

developed spatial structure, complex food chain and its living organisms is in steady state.

Climax : a final, mature, stable, self maintaining and self reproducing state of vegetational

development that culminates ( ends) plant succession on any given site.

In climax, the equilibrium exists between :

• Gross primary production and total respiration

• Energy captured from sunlight and energy released by decomposition

• Uptake of nutrients and the return of nutrients by litter fall

Characteristics of Climax


Forest Ecology


•The vegetation is tolerant of environmental conditions.

•It has a wide diversity of species, a well-drained spatial structure, and complex food chains.

• The climax ecosystem is balanced. There is equilibrium between gross primary production and

total respiration, between energy used from sunlight and energy released by decomposition,

between uptake of nutrients from the soil and the return of nutrient by litterfall to the soil.

• Individuals in the climax stage are replaced by others of the same kind. Thus the species

composition maintains equilibrium.

• It is an index of the climate of the area. The life or growth forms indicate the climatic type.

Climax Theories : In the concept of climax, there are three different kinds of theoretical

approaches :

• Mono-climax theory : Developed by Frederick Clements. This theory says there is only

one climax solely determined by the climate, no matter how great the variety of

environmental conditions is at the start. In other word , vegetational climax is

determined by climate only , irrespective of other factors

• All seral communities in a given region if allowed sufficient time, would ultimately

converge to a single climax

• The whole landscape would be clothed with a uniform plant and animal community

• All other communities than the climax one are recognized as sub-climax, dis-climax, pre-

climax and post climax

Mono –climax theory : There is only one climax i.e climatic climax which is controlled or

determined by regional climate. This theory is not popular/possible as there are other

environment factors such as soil and topography, fire, animals etc that control the climax .

Ecologists have lots of criticisms in this theory

2. Poly-climax theory : Developed by Tansley. This theory says the climax vegetation of a

region consists of not just one type i.e climatic type but a mosaic of vegetational climaxes

controlled by soil moisture, soil nutrients, topography, slope exposures, fire and animal activities

• Each stable community at the climax stage is prefex as edaphic climax, topographic climax,

biotic climax and fire climax etc

For instances : grassland communities are often influenced by fire , grazing and other biotic

factors so are considered as biotic climax

3. Climax Pattern Theory : Developed by : Whittaker, Mac Intosh and Sellack.

This theory says , the composition, species structure and balance of climax community are

determined by the total environment of the ecosystem not only by climatic factor alone. The

pattern of climax vegetation will change as the physical environment factor change


Forest Ecology


Types of Climax :

• Climatic climax: It is the climax which is developed or controlled by climatic factors or

climatic influences. Climate as the dominant community – forming factor. It is also recognized

the importance of soil, topography, relief and biotic factors as being additional dimensions to the

climatic factor which delayed the progress of vegetation to a climatic climax.

• Edaphic climax: A climax community ( differing from the climatic climax) of the area which

is formed due to the influence of soil factors such as chemical, physical and water content of soil.

Succession ends in an edaphic climax.

• Pre-climax : The plant community with more xerophytic vegetation than the general climax (

climatic climax) on drier condition or low moisture containing sites. Pre-climax vegetation is

found under conditions drier than the usual climate of the region.

• Post climax: A plant community with more mesophytic vegetation ( plants that grow in

neither too dry or too wet condition) on wetted condition or high moisture containing sites than

the general climax (climatic climax). It actually occurs on sites very much moister than the

normal sites in that climatic region.

• Biotic climax or sub-climax: A climax owing to the action of biotic factors which differs from

the general climax (climatic climax) of the area.

• Catastrophic Climax: Emergence of climax vegetation due to the effect of repeated

catastrophic event such as a wildfire.

• Dis-climax: When a stable community, which is not the climatic climax or edaphic climax for

the given site, is maintained by man or his domestic animals is designated as Dis-climax

(disturbance climax) or anthropogenic sub-climax (man-generated). For example, overgrazing by

stock may produce a desert community of bushes and cacti where the local climate actually

would allow grassland to maintain itself.

Retrogression : It means a return to simpler and less dense or even impoverished form of

community from an advanced or climax community.

• In most cases, the causes of retrogression are allogenic ( forces from outside the ecosystem

become severe and demanding. For example : most of our natural forest stands are degrading

into shrubs, savanna or desert like stands by the severity of grazing animals, excessive removal

of woods, leaf , biomass etc lead to retrogression

• Retrogressive succession occurs where a disturbance causes the climatic climax vegetation to

revert to a previous phase

• It results therefore in the replacement of a community of plants of higher ecological order with

a community of lower ecological order.

•This means that the community becomes increasingly simplistic with a lower biomass and a

fewer species


Forest Ecology


•This may occur e.g. due to a change in climate. For example; increased frequency of drought

will cause a decrease in plant productivity and diversity – this would be likely to result in the

replacement of perennial species by annuals

• Overgrazing and a change in soil stability may also cause retrogression following vegetation

deterioration

• A retrogression may be temporary or permanent, depending on the extent of the disturbance.

Adaptations to a change in the environment may be short-term or long term.

–Short-term

•Physiological–ex. increased respiration at high altitudes.

•Morphological–ex. increased insulation (fur) in winter.

•Behavioral–ex. Hibernation

Adaptations cont‘d

–Long term adaptation involves evolution and natural selection. Ex. animals in cold

environments have decreased surface area compared with relatives in warm environments.

Herbivores have developed adaptations to deal with fluctuations in available food supplies:

–Put on extensive layers of fat during seasons of abundance.

–Some will migrate to where food is available.

–Others hibernate during seasons of hardship.

–Respond to seasons of scarcity by making do with foods of relatively low nutritional value.

Regulating (climate, floods, nutrient balance, water filtration)

Provisioning (food, medicine, fur, minerals)

Cultural (science, spiritual, ceremonial, recreation, aesthetic)

Supporting (nutrient cycling, photosynthesis, soil forma

tion)

Generally, aboveground volume production is calculated on stem wood volume for conifers, but

may include branch volume for broadleaved tree species. For many purposes, mean annual

increment (volume) is considered a suitable measure of site productivity.

Natural selection : the process by which forms of life having traits or characters that better

enable them to adapt to specific environmental pressures, as predators, changes in climate, or

competition for food or mates, will tend to survive and reproduce in greater numbers than others

of their kind, thus ensuring the perpetuation of those favorable traits or characters in succeeding

generations.


Forest Ecology


Contents

1.Definition, Concept, Scope and Importance of Carbon

Sequestration

2. Methods of measurement of Carbon Sequestration

3.Basic concept of Kyoto Protocol (Carbon trade)


Forest Ecology


Background

• How do we keep CO2 out of the atmosphere? - sequester it

What is Carbon Sequestration ?

The removal and storage of carbon from the atmosphere (that would otherwise be released

into the atmosphere) in carbon sinks (such as oceans, forests or soils) through physical or

biological processes, such as photosynthesis. (Source: Green Facts)

CS is a way of managing the amount of carbon dioxide (Co2) that is released into the

atmosphere by burning carbon-based fuels—predominantly carbon-rich petroleum fuels.

A relatively new idea brought about by the concern that high concentrations of atmospheric

C02 contribute to global warming.

CS is the general term used for the capture and long-term storage of carbon dioxide. Capture

can occur at the point of emission (e.g. from power plants) or through natural processes (such

as photosynthesis).

Understanding differently, CS is the process of increasing the carbon content of a reservoir

other than the atmosphere.

Climate Change

Adaptation Mitigation


Forest Ecology


The process through which agricultural and forestry practices remove carbon dioxide (CO2) from

the atmosphere.

The term “sinks” is also used to describe agricultural and forestry lands that absorb CO2.

Ecosystems are important source and sinks of carbon

It is critical to define whether a system releases or absorb CO2 from atmosphere.

Through the photosynthesis green vegetation absorb CO2 from the atmosphere and store some

of this carbon in plant above and below ground biomass.

Decomposition of organic matter, respiration, disturbance such as fire release CO2 to

atmosphere as a source.

Why CS ?

• Reduce the level of atmospheric Co2 to the optimum level.


Forest Ecology


• Prevent global climate change by enhancing carbon storage in trees and soils, preserving

existing tree and soil carbon, and by reducing emissions of green house gases.

• Environmental and social benefits for sustained livelihoods.

Type and methods of CS

There are three main methods in various states of discovery and development:

Near term storage in the terrestrial biosphere where vegetation would soak up the C02 and

store it in biomass and soil.

Long term storage in the earth’s soil by pumping CO2 into existing or drilled/excavated sub-

surface reservoirs.

Long term storage in the earth’s oceans where CO2 would be injected thousands of feet deep

and trapped by the water.

Sequestration methods include:

Enhancing the storage of carbon in soil (soil sequestration);

Enhancing the storage of carbon in forests and other vegetation (plant or Bio-sequestration);

Storing carbon in underground geological formations (geo-sequestration);

Storing carbon in the ocean (oceansequestration); and

Subjecting carbon to chemical reactions to form inorganic carbonates (mineral carbonation).

Nature of sequestration in terrestrial ecosystems

Various TEs such as forests, grasslands, agricultural systems and degraded land, have different

potential of carbon storage. For instance, forest ecosystems contain more carbon per unit area

than any other land types (accounting for 60% of total C in TEs) and their soils are of major

importance for CS (FAO 2001).


http://www.aph.gov.au/library/pubs/climatechange/responses/mitigation/carbon.htm





Forest Ecology


However, CS rates vary depending on plant species, soil type, region, climate, topography and

management practices that can affect plant productivity (Lal 1999).

At a local scale, CS in TE is largely influenced by light conditions, water availability, soil water

holding capacity and its nutrient content.

Local conditions could modify the frequency and severity of natural risks such as forest fires,

strong winds etc., increasing the probability of CO2 emissions and hence carbon loss from these

systems (Heimann and Reichstein 2008).

TEs sequestered about 2.6 x109 g C per year of all atmospheric emissions during the period

2000-2007 representing net reductions of about 30% (according to 2006 levels) (GCP 2008).

They have the potential of eventually sequestrating about 2 Gt C/year under intensive

management and/or manipulation scenarios of a significant fraction of these systems (DOE

1999). Table 1 shows the different present stocks and net primary production (NPP) of various

terrestrial biomes.


Forest Ecology


Rh (respiration by

microorganisms

Components of the terrestrial carbon cycle


Forest Ecology


Terrestrial sequestration

Bio sequestration

– Global forest resource assessment report indicate that the total carbon content in the world forest

ecosystem

• biomass account 44%

• Soil carbon upto 30 cm depth include 46%

• Dead wood 6%

• Litter 4%

– Average estimated carbon stock in the nepalese forest is 203 ton/ha (including shrub land)

– Worlds’ average 161.1 ton/ha (FAO 2006)


Forest Ecology


Scope of CS in various forms

Bio Sequestration

Terrestrial sequestration consists of storing CO2 in soils and vegetation near the earth’s surface.

Tree-plantings, no-till farming, wetlands restoration, land management on grasslands and

grazing lands, fire management efforts, and forest preservation.

More advanced research includes the development of fast-growing trees and grasses and

working out in the genomes of carbon-storing soil microbes.

The uptake of CO2 by vegetation will decrease with time as plants grow to their full capacity and

become limited by other resources such as nutrients, and regrowth potential in previously

cleared or sparsely vegetated areas is fulfilled.

Biological storage could be enhanced through agricultural and forestry practices and

revegetation, but the capacity is limited and longevity of storage depends on the final fate of the

timber or plant material. However, carbon sequestration from revegetation and plantation

programs could provide a significant shorter-term contribution to climate change mitigation.

Soil sequestration


Forest Ecology


It is estimated that soils contain between 700 giga tonnes (Gt,109 tonnes) and 3000 Gt of

carbon, or more than three times the amount of carbon stored in the atmosphere as carbon

dioxide.

However, most agricultural soils have lost 50–70 per cent of the original soil organic carbon pool

that was present in the natural ecosystem prior to clearing and cultivation. When forests are

converted to agricultural land, the soil carbon content decreases.

Given the enormous carbon storage capacity of soils, it has been suggested that with

appropriate changes in management practices, they could represent a significant sink for

atmospheric CO2. Managing agricultural soils to increase their organic carbon content can also

improve soil health and productivity by adding essential nutrients and increasing their water-

holding capacity.

Oceanic Sequestration

Pumping CO2 into the deep ocean basins (350-3000 meters), where it is anticipated it may form

lakes of liquid, supercritical, or solid hydrates.

The thinking on this disposal scenario is that it would stabilize in the ocean depths, or slowly

dissolve into the ocean waters.

This option has been under study for several years, but there are many potential environmental

downsides to its implementation, and it is not a high priority research focus till this time.

Geo-sequestration

Geo-sequestration is the injection and storage of greenhouse gases underground, out of

contact with the atmosphere. The most suitable sites are deep geological formations, such as

depleted oil and natural gas fields, or deep natural reservoirs filled with saline water (saline

aquifers).

Geo-sequestration is part of the three-component scheme of carbon capture and storage (CCS),

which involves:


Forest Ecology


capture of CO2 either before or after combustion of the fuel

transport of the captured CO2 to the site of storage, and

injection and storage of the CO2.

Research is continued. Not commonly practiced

Mineral sequestration

Mineral sequestration (otherwise known as mineral carbonation) involves reaction of CO2 with

metal oxides that are present in common, naturally occurring silicate rocks.

The process mimics natural weathering phenomena, and results in natural carbonate products

that are stable on a geological time scale.

There are sufficient reserves of magnesium and calcium silicate deposits to fix the CO2 that

could be produced from all fossil fuel resources.


Forest Ecology


Though the weathering of CO2 into carbonates does not require energy, the natural reaction is

slow; hence as a storage option the process must be greatly accelerated through energy-

intensive preparation of the reactants.

The technology is still in the development stage and is not yet ready for implementation

Methods for carbon measurement and assessment

Measurement of carbon biomass

Different methods are used for measuring carbon in soil, water or atmosphere.

Conventional methods such as dry combustion


Forest Ecology


Sophisticated methods such as laser-induced breakdown spectroscopy (LIBS) for rapid carbon

analysis

Methods used for measuring carbon in biomass include:

Non-destructive sampling for biomass (application of algometric or cylinder equations or

estimation tree root biomass from proximal root and algometric relations)

Destructive sampling of soil and vegetation (harvesting vegetation, taking samples of litter and

soil); and

Remote Sensing methods that assess carbon in vegetation but less useful to measure soil C

directly (unless bare)

Measurement of the Forest Carbon in Nepal (ANSAB, ICIMOD, FECOFUN)

1 Delineation of project boundaries

2 Stratification and boundary mapping of stratum

3 Pilot inventory for variance estimation

4 Capacity building and orientation of the locals

5 Field measurements in the permanent plots (AGB, BGB, soil, dead wood, herbs & litter)

6 Data analysis (calculation of carbon stock density)

7 Leakage analysis belt and monitoring

8 Report preparation

Source: Guidelines for measuring carbon stocks in community-managed forests

Carbon sequestration


Forest Ecology


Kyoto Protocol

– It is an intergovernmental agreement to stabilize greenhouse gases in the atmosphere,

at a level that would prevent adverse changes to the climate.

– A protocol was outlined in Kyoto in 1997 which is popularly known as the Kyoto

Protocol.

– The developed countries with emission reduction targets are called the Annex 1

countries,

– whereas those without targets are known as non-Annex 1 countries.

– The Annex 1 countries can invest in JI (Joint Implementation)/CDM projects as well as

host JI projects, and non-Annex 1 countries can host CDM projects.

– The Kyoto Protocol negotiations were completed in late 1997.

– The protocol establishes legally binding, mandatory emissions reductions

for the six major greenhouse gases.


Forest Ecology


– Carbon dioxide (C02)

– Methane (CH4)

– Nitrous oxide (N20)

– Hydrofluorocarbons (HFCs)

– Perfluorocarbons (PFCs)

– Sulphur hexafluoride (SF6)

– It requires that Annex I countries (listed again in Annex B of theProtocol)

reduce their aggregate greenhouse gas emissions by 5% below 1990 levels

Key Existing Kyoto Protocol Provisions

– Obligations of All Parties

– Emissions Reductions

• emissions of such gases by at least 5% below 1990 levels in the commitment period 2008 to

2012.”

• two of the most difficult issues unresolved in 1997 at Kyoto and still under discussion are

related to counting emissions of a nation,

• (1) emissions trading — specifically, how much of a country’s obligation to reduce emissions

can be met through purchasing credits from outside, vs. taking domestic action; and

• (2) the extent to which carbon sequestration by forests, soils and agricultural practices can

be counted toward a country’s emission reductions.


Forest Ecology


Carbon or Emissions Trading

Carbon / Emissions Trade

A market proposed by the Kyoto Protocol in which each country participating receives a limit on

the carbon emissions.

Countries (and/or companies) may buy and sell the emissions limits assigned to them.

Carbon trade is intended to be an attempt to reduce overall carbon emissions while still allowing

companies that may have difficulty doing so to have an outlet for transition. It is also called

emissions trading.

Carbon sequestration


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