Communities are not immortal - they will eventually be destroyed by some type of disaster. Massive earthquakes, devastating floods, hurricanes, volcanic eruptions, and major fires are all ways that communities are devastated. Ecological succession is the series of changes that occur as the area repopulates with new species. Succession occurs in two forms - primary and secondary.|
Primary succession occurs when a major disaster eliminates the soil. This is common after a volcanic eruption. Starting from bare rock, lichens and mosses are the pioneer producers (first) that begin colonizing the land. Pioneer animal species are commonly insects. It may take thousands of years for a climax community, a community that no longer changes, to regenerate. The rate of soil production determines the speed of ecological succession.
Secondary succession occurs when soil is still present after a major disturbance. Pioneer producers include weeds and rapid-growing grasses. Pioneer animals include many species of insects and rodents. A climax community is reached much more quickly than during primary succession.
In general, species diversity is lowest immediately after the disaster as the few pioneer species begin colonizing the new landscape. Species diversity rises as succession proceeds - more and more species colonize and grow in the new landscape. It reaches a maximum at the climax community stage.