4.1.5 Changes in Ecosystems:Ecological Succession

of a Forest Biome

Assessment Statements

• 4.1.5 Explain the relationships among ecosystem stability, diversity, succession and habitat.

• 2.6.5 Describe the concept and processes of succession in a named habitat.

• 2.6.6 Explain the changes in energy flow, gross and net productivity, diversity and mineral cycling in different stages of succession.

• 2.6.7 Describe factors affecting the nature of climax communities.

Questions to think about:

– How does diversity change through succession?– How are habitat diversity and genetic diversity

related?– What provides stability in an ecosystem?– How does human activity modify succession?– What factors determine if an ecosystem can survive

change?

https://www.youtube.com/watch?v=jZKIHe2LDP8

There are two main types of Ecological Succession

• Primary Succession: The process of creating life in an area where no life previously existed.

• Secondary Succession: The process of re-stabilization that follows a disturbance in an area where life has formed an ecosystem.

Succession Defined:

• Natural, gradual changes in the types of species that live in an area;

• The gradual replacement of one plant community by another through natural processes over time

Primary Succession

• The development of an ecosystem in an area that has never had a community living within it

• Primary succession generally occurs after a natural disaster which lead to a major loss in diversity:– Volcanic eruption– Tsunami– Meteor impact– Glacial flow

Primary Succession

• Begins in a place without any soil – In the beginning there is only rock, sand,

volcanic ash. – Since there is no soil, there is no community.

Why is there no soil?

In order for there to be soil there must be nutrients like nitrogen. So … why is there no soil?

Primary Succession

. • Lichens, algae & bacteria begin growing on the rocks.

• Harsh conditions but limited competition.

• Over many years lichens break down rock into sand.

• Weathering and erosion break down rock into sand.

Primary Succession

• Lichens that do not need soil to survive

• Called PIONEER SPECIES (Why?)

Primary Succession

• Lichens grow larger.

• Some die.

• Decomposers arrive and break down the lichens. The dead lichens and waste materials of the decomposers enrich the sand.

• Nitrogen cycle begins. Eventually enough nutrients enter the sand and it becomes soil.

Primary Succession

• Seeds/spores are blown in by the wind or carried in by animals. Simple plants like mosses and ferns can grow in the new soil

• The plants grow and the soil gets enriched as plants die..

Primary Succession

• Herbs and weeds can grow in the thicker, enriched soil

• Roots start holding soil in place

Primary Succession

• The simple plants die, adding more organic material

• The soil layer thickens, and grasses, wildflowers, and other plants begin to take over

• More shade

Primary Succession

• Medium sized animals and birds make this their habitat.

• The vegetation grows closer together, reducing the amount of space available for growing.

• Competition between lichen and shrubs for the same space. Eventually one species (lichen) will die out (or move) and the

other species will survive (shrubs).

Primary Succession

• These plants die, and they add more nutrients to the soil

• Shrubs and tress can survive now

Primary Succession

• Insects, small birds, and mammals have begun to move in

• What was once bare rock now supports a variety of life

http://p2-raw.greenpeace.org

Primary Succession

• These plants die, and they add more nutrients to the soil

• Now larger trees can grow: Beech, Oak, Walnut, Maple…

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The Climax Community

• A climax community is a mature, stable community that is the final stage of ecological succession. In an ecosystem with a climax community, the conditions continue to be suitable for all the members of the community.

• Any particular region has its own set of climax species, which are the plants that are best adapted for the area and will persist after succession has finished, until another disturbance clears the area.

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These are Climax Communities

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• Two main physical factors determine the nature of the community that develops in an area. These are temperature and the amount of rainfall.

• If we place the amount of rainfall on a graph’s “x” axis, from 0-10, 10-20,and 20-30+ inches and the temperature along the “y” axis from hot, moderate, to cold, the various types of ecosystems will fit into the graph based on the conditions that they require.

Temperature

Cold Cold desert Tundra Taiga

Moderate Temperate forest Grassland Deciduous forest

Hot Hot desert Savanna Tropical forest

Rainfall (inches) 0-10 10-20 20-30+

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Primary Succession

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• Pioneer species colonize a bare or disturbed site. Soil building. • Changes in the physical environment occur (e.g., light,

moisture).

• New species of plants displace existing plants because their seedlings are better able to become established in the changed environment.

• Newly arriving species alter the physical conditions, often in

ways that enable other species to become established. • Animals come in with or after the plants they need to survive. • Eventually a climax community that is more or less stable will

become established and have the ability to reproduce itself. • Disturbances will start the process of succession again.

A summary of changes that occur during succession:

What if?

What if?

• Ecosystem Fragmentation?

What if?

• An avalanche?

What if?

• Deforestation?

Threats to Climax Communities

• Forest Fires• Humans building cities and roads (fragmenting

ecosystem)• Clearing a community for agricultural purposes• Deforestation

• Anything that destroys the existing community, but much of the soil remains. Sometimes, some of the organisms remain as well.

Secondary Succession

Secondary Seccession

Secondary Succession

• Organisms are destroyed but the soil is safe. • The soil already contains the seeds of weeds,

grasses, and trees as well as nutrients. More seeds are carried to the area by wind and birds.

• Succession begins again but the primary species are different.

• Because soil is present, this succession is faster.

Ecological Succession•N

Secondary Succession on an Abandoned Cornfield

Secondary Succession

• 1. Some seeds in the soil begin to grow.

Secondary Succession

• Larger shrubs move in.

Secondary Succession

• 3. Fast growing trees (such as pines) move in

• 4. These are followed by slower-growing hardwood trees

http://www.ux1.eiu.edu

More Succession Resources

• Mt St. Helens after 30 years https://www.youtube.com/watch?v=4RsMyVavT2Q

• Succession Song https://www.youtube.com/watch?v=rzE6BNNLew0