Ecological Succession:

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.

Ground fire in the Richland Creek Wilderness, Buffalo River Arkansas
By skuensting

The Yellowstone National Park fire at Grant Village, July 23, 1988

By Jeff Henry [Public Domain] via Wikimedia Commons.

The rapid growth of fireweed after the 1988 Yellowstone Fires.

By Mongo - See page for author [Public domain], via Wikimedia Commons

Yellowstone National Park, about 15 years after the major fire.
By skuensting

The grasses that grew in place of the thick forest fostered the growth of herbivores.
By skuensting

Primary succession on volcanic rock

Nevilley at the English language Wikipedia [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

Secondary succession in an abandoned field

By Tomasz Kuran aka Meteor2017 [Creative Commons Attribution-Share Alike 3.0 Unported].