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

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.

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

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