Define primary and secondary succession
http://en.wikipedia.org/wiki/Primary_succession
Primary succession and secondary succession are two types of ecological succession, which refer to the process by which communities of plants and animals change over time in a given area.
1. Primary Succession:
Primary succession occurs in areas where no biotic community previously existed, such as on bare rock surfaces, newly formed volcanic islands, or retreating glaciers. It is a slow and gradual process that involves the following steps:
Step 1: Colonization of Pioneer Species: The process begins with the colonization of pioneer species, such as lichens and mosses. These organisms are able to tolerate extreme conditions and can survive in minimal soil or organic matter.
Step 2: Soil Formation: The pioneer species help in breaking down rocks and create small crevices where debris accumulates, gradually forming soil. As more organic matter, like dead plant material, accumulates, the soil becomes richer and more suitable for other plant species.
Step 3: Succession of Plant Communities: With time, larger plants such as grasses, shrubs, and small trees start to grow in the newly formed soil. As these plants die and decompose, they enrich the soil further, paving the way for larger, more complex plant communities.
2. Secondary Succession:
Secondary succession occurs in areas where a biotic community has been disturbed or removed due to natural disasters (like forest fires or hurricanes) or human activities (such as clear-cutting or agriculture abandonment). Unlike primary succession, secondary succession begins with soil already present, facilitating a faster process. The key steps involved in secondary succession are as follows:
Step 1: Pioneer Species Colonization: Following disturbance, pioneer species, such as weeds, grasses, and fast-growing plants, quickly occupy the area. These species are able to grow in harsh conditions and rapidly cover the exposed soil.
Step 2: Succession of Plant Communities: As the pioneer species grow and die, they gradually build up organic matter and improve soil conditions. This allows other plant species, including shrubs and trees, to establish and develop more complex plant communities. Over time, the composition and structure of the plant communities return to a state similar to the pre-disturbance stage, reaching a climax community.
In summary, primary succession occurs in areas without any pre-existing biotic community, starting from rock or barren surfaces, while secondary succession occurs in areas where a previous biotic community has been disrupted or removed.