Ecological Succession

Succession:

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

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 soil already is present

Primary Succession

• The development of an ecosystem in an area that doesn’t have a community living within it and no soil.

• An area in which a community has never lived before, would be a new lava or rock from a volcano that makes a new island.

Primary Succession

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

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

Why is there no soil? What is soil?

So … why isn’t there any soil?

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Primary Succession

Primary Succession

• Lichens are a mutualistic symbiotic relationship between a fungus and a photosynthetic bacteria (cyanobacteria)

• Lichens begin growing on the rocks (Pioneer Species – First species to populate the area after the disturbance). Over many years lichens break down rock into sand.

Primary Succession

• Lichens grow larger. Some die.

• Decomposers (detritivores) arrive and break down the lichens.

• The dead lichens and waste materials of the decomposers enrich the sand to create “soil.”

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Primary Succession

Primary Succession

• Seeds are blown in by the wind or carried in by animals. Simple plants like mosses 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

Primary Succession

• The simple plants die, adding more organic material

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

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Primary Succession

• Insects, small birds, and mammals wait on plants to move in (need plants to survive)

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Primary Succession

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

• Shrubs and tress can survive now

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Primary Succession

• Pioneer species colonize a bare or disturbed site. Soil building. • 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:

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.

Climax Community

• A stable group of plants and animals that is the end result of the succession process

• Does not always mean big trees– Grasses in prairies– Cacti in deserts

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These are Climax Communities

Threats to Climax Communities

• Forest Fires• Flooding, Volcanic eruptions• Human “Development”

What if?

Secondary Seccession

Secondary Succession

• Organisms are destroyed but the soil is safe.

• The soil already contains the seeds of weeds, grasses, and trees. More seeds are carried to the area by wind and birds.

• Because soil is present, this succession is faster.

Secondary Succession•N

Secondary Succession

• Some seeds in the soil begin to grow.

Secondary Succession

• Larger shrubs move in.

Secondary Succession

• Fast growing trees (such as pines) move in

• These are followed by slower-growing hardwood trees