University of Phoenix
Science 256: People, Science, and the Environment
Ecosystem Succession Paper
Succession is a phenomenon of transition in community structure and function which is time related and often occurs in a somewhat predictable manner. Primary succession, (fig 5-4, pg 87) occurs following formation of a new, yet barren habitat for colonization. Such a habitat may be formed by volcanic activity, glacial activity, or strip-mining; it initially lacks soil. A study of Glacier Bay, AL, showed that following retreat of the glacier, the ground was first colonized by mosses and lichens, then dwarf willows, then alders, then Sitka spruce. After about 200 years, a stable spruce-hemlock forest resulted.
Secondary succession, (fig 5-5, pg 88) occurs where an existing community is destroyed (i.e. by fire), but since the soil remains, recolonization is much more rapid than colonization during primary succession. Old field succession is a good example of secondary succession (this is what happens to agricultural land after farming stops).
Once it was thought that succession normally resulted in a stable, diverse community in the "climax" state (this state is often described as the condition whereby the web in species interactions becomes so intricate that no additional species can fit into the community unless niches become available by localized extinction), but now this assumption is not so widely held among ecologists.
Succession is related to a number of factors including the following:
Initial colonizers are often characterized by good dispersal mechanisms. Frequently, they are "fugitive species", unable to compete well in established communities but successful
in communities without competitors. Naturally, they must be tolerant of the abiotic factors existing in the area. Growth rate and size at maturity may also affect success. Activities of the biota themselves may affect the process of succession. Inhibition...