Ecological Succession

Ecological Succession

• Series of changes that occur during the development of an ecosystem

• the gradual replacement of one community by another until a stable long-lasting stage is reached

Changes in the Community

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What determines what the final Community will be????

• 1. Climate (temperature & moisture) and Soil Quality

• 2. In the U.P., the climate is pretty much the same, so differences in soil type influence the community type.

Four Basic Communities

• A. Pine

• B. Boreal Forest

• C. Northern Hardwoods

• D. Bog/Swamp

Why does Succession Happen?

• Each community alters the physical features of a site making it less favorable for its members and more favorable for competitors.

• In other words, each community brings about its own demise.

How long does Succession Take?

• Succession depends on the size of the ecosystem but generally takes hundreds to thousands of years.

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Types of Succession• Primary Succession – soil building occurs

on previously uninhabited site

• Examples:– Bare rock lichen moss herbs trees– Sand dune grass blueberry

cherry/poplar trees

Pioneer Species

• The first species to occupy a bare site

• Characteristics: - tough (can endure extremes of temperature - lack of moisture - lack of nutrients

Secondary Succession• Occurs on a site on which the established

community has been removed (soil already present)

• Disturbances include: – Fire (commonly used to control undergrowth)– Farming– Logging– Over-grazing– Urbanization

Climax Community

• The eventual community that occupies the site after the disturbance – it will remain that way unless it is disturbed.

• If a forest is removed, secondary succession begins with perennial weeds, poplar and cherry trees, and sometimes pine. Often fireweed is an indicator species of the stage.

• If the disturbance is severe enough, it may set it back to primary succession – may take a tremendously long time for climax community to be reached.

• In general, as succession proceeds, food chains are replaced by food webs, there is more biomass and species diversity, and the ecosystem is more stable – what might destroy an early stage does not cause as great an effect at later stages

Make Up of a Community

• Depends on tolerances of the species involved

• Tolerance– 1. Shade tolerant species – can photosynthesize

adequately at very low levels of light ex. Maple, oak seedlings, certain species of fern

– 2. Shade intolerant species – require bright light to photosynthesize enough to survive ex. Cherry, poplar, grass

How Does Succession Happen?

• Cherry/poplar seedlings colonize a disturbed site. As they grow, they shade the ground. Young cherry and poplar seedlings cannot grow in the shade but oak/maple seedlings thrive there. Eventually, oaks/maples shade the cherry and poplar trees, reducing the light to below the compensation intensity, and those trees die.

Indicator Species

• Species that live only in certain stages of succession or under very specific conditions

• Examples:– Yew – an evergreen shrub found

only in mature hardwood forests– Sphagnum moss – found only in

bogs and swamps

Disclimax Community

• Artificial communities that are maintained only by constant intervention by man ------ they are never allowed to reach the climax stage of succession

• Examples: park, farmer’s field, lawn

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are needed to see this picture.

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are needed to see this picture.

Ecotone• The transition zone

between two adjacent communities

• Example: Where a field blends into a forest -often there is a greater diversity of life in an ecotone, because the more tolerant species from each community can be found there

The End