SUCCESSION

HOW DO ECOSYSTEMS RESPOND TO CHANGE?

• A change in structure ensures a change in function and species composition.

• Ecological succession is the gradual and fairly predictable change in species composition of an area over time.

• During succession, some species colonize and their populations become more numerous, whereas other species populations decline and even disappear.

Succession in Volcanic Areas

• Krakatau – August 27, 1883 (Sundra Strait between Sumatra and Java)

KRAKATAU

• 10:02 am explosion (100-150 megatons of TNT)• The sound of the explosion traveled at the speed of

sound around the world 7 times.• Blackened sky with showers of ash and heavy,

suffocating sulfur filled the sky and rained down on the previous tropical rainforest ecosystem.

• Island collapsed causing a 40 meter high tsunami along the shores of Java and Sumatra killing 40,000 people.

• Krakaktau had been replaced by an undersea crater 7 km long and 270 m deep.

• All traces of life were extinguished!

KRAKATAU

SUCCESSION OF KRAKATAU• Rakata the southern

remnant of of Krakatau survived as a sterile obsidian-laced pumice island.

• Life quickly re-established.

• Spiders “ballooned” making their way to the island “aeolian plankton”

SUCCESSION OF KRAKATAU• Other organisms that undergo long-distance dispersal as hitchikers

include: springtails, crickets, earwigs, barklice, bacteria, fungal spores, nematode worms, and mites.

• Organisms that fly on their own include moths, butterflies, dragonflies, true flies, beetles, birds, bats, and wasps.

• The monitor lizard and reticulated python swim.• Rafting on logs and branches occurred by insects, snakes, frogs,

and small mammals.• Waterspouts can pick up fish and transport them to lakes and

streams.• Seeds pass through the guts of birds and mammals. Pioneer plants

(morning glory) and grasses moved in first, then Casuarina pine, and now it is covered entirely by Asian rain forest, but NOT the climax community that existed prior to the eruption.

• As the biodiversity of primary producers, so did the biodiversity of the food web.

Primary Succession on a Newly Established Volcanic Island

Primary Succession – involves the gradual establishment of biologic communities in an area that has not been occupied by life before.

SUCCESSION OF KRAKATAU

Secondary Succession on Krakatau

Secondary Succession – involves the re-establishment of a biotic community in an area where a biotic community was previously present.

Population Dynamics

• Population numbers are becoming more stable a Century after the eruption.

• The composition of the populations are less stable.

• E.O. Wilson

“The thick green forests offers testimony to the ingenuity and resilience of life”

Primary Succession

• Lifeless area.• Pioneer species (lichens and mosses) create

soil (chemical and physical weathering).• Young soils support bacteria, fungi, insects, and

small worms (adds organic material to soil as they die).

• Perennial grasses and herbs.• All early successional plants grow low to the

ground, can establish large populations quickly under harsh conditions.

Primary Succession

• After hundreds of years the soil matures (deep and fertile) and midsuccessional species grow.

• These species include: herbs, grasses, and low shrubs and later include trees that require lots of sunlight.

Primary Succession

• As midsuccessional stage species grow and create shade areas they are replaced by late successional species.

• Primary succession occurs fastest in humid tropical areas and slowest in dry polar areas.

Terrestrial Primary Succession

Exposed rocks become colonized by lichens and mosses to create a soil. May take hundreds to thousands of years to establish a fertile soil

Small herbs and shrubs

Heath mat

Pine, spruce and aspen

Climax Community

Balsam fir, paper birch, white spruce

Boreal Forest Biome

Secondary Succession

• Occurs where soil or bottom sediment remains where an area has been disturbed or destroyed.

• Abandoned farmlands, burned or cut forests, heavily polluted areas, land that has been dammed or flooded.

Secondary SuccessionTemperate Deciduous Forest Biome

Annual Weeds

Perennial weeds and grasses

ShrubsYoung Pine Forest

Mature Oak-Hickory Forest

Species Found at Various Stages of Succession

Early Successional Species

Rabbit

Quail

Ringneck Pheasant

Dove

Bobolink

Pocket Gopher

Midsuccessional Species

Elk

Moose

Deer

Ruffed grouse

Snowshoe hare

Bluebird

Late Successional Species

Turkey

Martin

Hammond’s flycatcher

Gray squirrel

Wilderness Species

Grizzly bear

Wolf

Caribou

Bighorn Sheep

California condor

Great horned owl

Table 8-1Page 158

Table 8-1 Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession

Characteristic

Ecosystem Structure

Plant size

Species diversity

Trophic structure

Ecological niches

Community organization(number of interconnecting links)

Ecosystem Function

Biomass

Net primary productivity

Food chains and webs

Efficiency of nutrient recycling

Efficiency of energy use

Immature Ecosystem(Early Successional Stage)

Small

Low

Mostly producers, few decomposers

Few, mostly generalized

Low

Low

High

Simple, mostly plant herbivorewith few decomposers

Low

Low

Immature Ecosystem(Late Successional Stage)

Large

High

Mixture of producers, consumers, and decomposers

Many, mostly specialized

High

High

Low

Complex, dominated by decomposers

High

High

How Do Species Replace One Another?

• 1. Facilitation – promotion of growth due natural enrichment of soil.

• 2. Inhibition – early successional species can hinder the establishment and growth of other species. Removal of the inhibitors by fire, bulldozer or other disturbance is the only way to allow other species to establish.

• 3. Tolerance – late successional plants are unaffected by plants at earlier stages.

What is the Role of Disturbance in Succession?

• A disturbance is a discrete event in time that disrupts an ecosystem or community.

• Natural disturbances = fires, hurricanes, tornadoes, droughts, and floods.

• Anthropogenic disturbances = deforestation, overgrazing, and plowing.

• Disturbances create openings for opportunistic species to colonize areas and change the community structure of an area.

Opportunistic Phragmites australis

What is the Role of Fire in Succession?

• Fires start by lightening in the following biomes: savanna, temperate grasslands, chaparral, temperate rain forest, and northern coniferous forest.

• Fire burns older trees by burning biomass and releasing seeds as cones open in intense heat = ensures regeneration.

Fire Suppression

• Fire suppression can be very dangerous. It allows for the build up of large quantities of flammable underbrush and undergrowth.

• It allows conifers to grow very large and store energy as biomass.

• BOTH contribute to fuel for the fire, making a moderate forest fire catastrophic!

Forest Fires

After the Fire…

Long Island’s Pine Barrens

Protected by Long Island’s Pine Barrens Copmmission

Richard Amper

The Healthy Forest Restoration Act

• On December 3, 2003, President Bush signed into law the Healthy Forests Restoration Act of 2003 to reduce the threat of destructive wildfires while upholding environmental standards and encouraging early public input during review and planning processes.

The Healthy Forests Restoration Act: • Strengthens public participation in developing high priority forest

health projects; • Reduces the complexity of environmental analysis allowing federal

land agencies to use the best science available to actively manage land under their protection;

• Provides a more effective appeals process encouraging early public participation in project planning; and

• Issues clear guidance for court action against forest health projects

The Healthy Forest Restoration Act

• Controversy – Is Bush just allowing additional opportunity for logging companies to come into forests and thin them out to make money?

Is Succession Predictable?

• General patterns of succession are predictable.• Research indicated that there is no ecological plan

leading to ecological balance or equilibrium. • Succession can be highly variable, chaotic, and

unpredictable.• We do know there will be changes to structure, function,

and species composition that will continue to change over time due to facilitation, inhibition, and tolerance.

• The Earth’s ecosystems are dynamic and resilient. Research shows that ecosystems with high diversity in primary producers are the most resilient ecosystems.

Climax Community in Temperate Deciduous Forest