Ecological SuccessionEcological Succession

•Succession refers to the normal, Succession refers to the normal, gradual changes that occur in the gradual changes that occur in the

types of species that live in an area.types of species that live in an area.•Succession is a process by which one Succession is a process by which one

biotic community is replaced by biotic community is replaced by another until a climax community another until a climax community

develops.develops.

Succession from Rock to Succession from Rock to ForestForestSome 240 years ago a glacier began retreating in Some 240 years ago a glacier began retreating in

Glacier Bay, AlaskaGlacier Bay, Alaska

The glacier left behind a rocky terrain completely The glacier left behind a rocky terrain completely devoid of organic matterdevoid of organic matter

The process that begins in a place without any soil The process that begins in a place without any soil is called is called Primary SuccessionPrimary Succession

An Example of Primary Succession: Glacier Bay, AlaskaAn Example of Primary Succession: Glacier Bay, Alaska

Primary SuccessionPrimary Succession

Pioneer organismsPioneer organisms such as such as microbesmicrobes, , lichenslichens, and , and mossesmosses are the first are the first

to inhabit a rock promoting soil to inhabit a rock promoting soil formation.formation.

Primary SuccessionPrimary Succession

Eventually, enough soil is built up Eventually, enough soil is built up so that grasses can succeed the so that grasses can succeed the

pioneer organisms.pioneer organisms.

Primary SuccessionPrimary Succession

Grasses are replaced by shrubs, which Grasses are replaced by shrubs, which are replaced by fast-growing trees.are replaced by fast-growing trees.

Primary SuccessionPrimary Succession

Coastal Sitka Spruce Coastal Sitka Spruce Forest, Southeast AlaskaForest, Southeast Alaska

Succession occurs differently Succession occurs differently in different places around in different places around

the world.the world.

The types of grasses, fast-The types of grasses, fast-growing trees, and climax-growing trees, and climax-community plants vary with community plants vary with the location and climate of the location and climate of

an area.an area.

A Climax Community Is Not A Climax Community Is Not Truly FinalTruly Final

Humans or nature can destroy it.Humans or nature can destroy it.

A Climax Community Is Not A Climax Community Is Not Truly FinalTruly Final

In this case, succession starts over with In this case, succession starts over with grasses as Secondary Succession.grasses as Secondary Succession.

Secondary SuccessionSecondary Succession

After a forest fire, not much is left except After a forest fire, not much is left except dead trees and ash-covered soil.dead trees and ash-covered soil.

However, these places do not remain However, these places do not remain lifeless for long.lifeless for long.

Secondary SuccessionSecondary Succession

• The topsoil, which may The topsoil, which may have taken 1000’s of have taken 1000’s of years to form, is not years to form, is not destroyed.destroyed.

• Spores and seeds which Spores and seeds which lie dormant are then lie dormant are then allowed to develop.allowed to develop.

• Sequence may be Sequence may be crabgrass, tall grass crabgrass, tall grass and horseweed, and horseweed, softwood then softwood then hardwood.hardwood.

Secondary SuccessionSecondary Succession

• The soil already contains the seeds of The soil already contains the seeds of weeds, grasses, and trees.weeds, grasses, and trees.

• More seeds are carried to the area by More seeds are carried to the area by wind and birds.wind and birds.

• Other wildlife may move in.Other wildlife may move in.• Succession that begins in a place that Succession that begins in a place that

already has soil and was once the already has soil and was once the home of living organisms is called home of living organisms is called

secondary successionsecondary succession..

Secondary SuccessionSecondary Succession

Secondary succession occurs faster and has Secondary succession occurs faster and has different pioneer species than primary different pioneer species than primary

succession because soil is already present.succession because soil is already present.

The cause may be a natural disturbance such The cause may be a natural disturbance such as a forest fire or farming. as a forest fire or farming.

In 1850, Connecticut was almost entirely open In 1850, Connecticut was almost entirely open land cleared for farming or timber. land cleared for farming or timber.

Today, Connecticut has been mostly Today, Connecticut has been mostly reforested through the process of reforested through the process of

secondary succession as farming has left secondary succession as farming has left the state since the 1800's.the state since the 1800's.

Climax CommunitiesClimax Communities

• A community that has reached a stable stage of A community that has reached a stable stage of ecological succession is called a climax community.ecological succession is called a climax community.

• It is a combination of plants and animals that use the It is a combination of plants and animals that use the available resources most efficiently.available resources most efficiently.

• Diversity and balance are maintained in a climax Diversity and balance are maintained in a climax community because as trees die, they provide community because as trees die, they provide nutrients for new communities of organisms.nutrients for new communities of organisms.

How do ecosystems change How do ecosystems change over time?over time?

•Ecosystems change over time by a process know as succession in which one biotic community is replaced by another until a climax community develops.

•Succession is often caused by changes in the environment brought about by the current community.

•Succession can also occur because of changes in climate and natural catastrophes such as fire, hurricanes, floods, and volcanic eruptions.

•Humans cause succession by cutting down forests, polluting the environment and overdeveloping an area.

How do new communities How do new communities begin in areas without life?begin in areas without life?

•By a process known as primary succession. Pioneer organisms such as microbes, lichens, and mosses are the first to inhabit a rock promoting soil formation.

•They survive drought, extreme heat and cold, and other harsh conditions and start the soil-building process.

•Soil begins to form as lichens and the forces of weather and erosion help break down rocks into smaller pieces.

•When lichens die, they decay, adding small amounts of organic matter to the rock.

•Plants such as mosses and ferns can grow in this new soil.

•Thus begins the process for higher order plants.

How do pioneer species How do pioneer species compare to climax compare to climax

communities?communities?

Pioneer species are the first organisms to occupy an area and do not need soil to survive.

Examples of pioneer species would be organisms such as microbes, lichens, and mosses.

Climax communities are the last communities to occupy an area.

Climax communities are a combination of plants and animals. They tend to be stable and self-perpetuating.