Chapter 3: How ecosystems work Section 3.3: How ecosystems change

What is succession? §Succession is a regular pattern of changes over time in the types of species in a community. §The process of succession may take hundreds or thousands of years.

The community that eventually forms if the land is left undisturbed is called the climax community.

How does succession begin? §Pioneer species are the first organisms to colonize any newly available area and start the process of succession. §Some pioneer species include grasses, weeds and lichen.

There are two types of succession: §Secondary succession §Primary succession

Secondary succession is a pattern of change that occurs on a surface where an ecosystem has previously existed. Ex. Mt. St. Helens and old field succession.

In succession, each new community that arises makes it more difficult for the previous one to survive.

Old Field Succession

Natural fires caused by lightning are a necessary part of secondary succession in some communities. §Some species of trees depend on fire for survival. §Some species of animals depend on fire because they feed on new plant life that sprouts after land is cleared.

Primary succession is succession that occurs on surfaces where no ecosystems previously existed. Ex. new land after volcanic eruptions and glaciers.

Primary succession is slower than secondary succession because it occurs where there is no soil.

How is soil formed? §Algae and fungus (lichen) break down rocks. §Water may also break down rocks. §Soil accumulates as dust particles in the air are trapped in cracks in rocks and lichen remains accumulate. §Fertile soil is formed from the broken rocks, decayed organisms, water and air.