How Ecosystems Rebuild After Disaster

By the end of this lesson, you will be able to describe how primary and secondary ecological succession change the populations and variety of species in an ecosystem after it is disturbed.

Ecosystems do not stay the same forever. Floods, wildfires, hurricanes, volcanic eruptions, and human activities like construction or farming can wipe out living things in an area. What happens next is called ecological succession, which is the gradual, step-by-step change in the types of species living in an area over time.

Primary succession is the rebuilding that happens where there is no soil at all, such as on bare rock left by a landslide or on cooled lava. The first living things to arrive, like lichens and mosses, are tough and few in number. As they grow and die, they slowly break rock into soil, which can take hundreds or even thousands of years. Only after soil forms can grasses, shrubs, and finally trees move in, so populations and species diversity, the number of different kinds of species in an area, increase very slowly.

Secondary succession happens where a disturbance damages a community but leaves the soil behind. Think about the pine forests near Bastrop, Texas, after a large wildfire. The trees burned, but the soil, roots, and seeds survived underground. Within a single growing season, grasses and wildflowers sprout, insects return, and rabbits and birds follow. Shrubs and young pines come next, and over many decades the forest may look much like it did before.

The big difference is speed and starting point. Primary succession starts from bare rock with almost no life, while secondary succession starts with soil already full of seeds, so populations recover and diversity climbs much faster.

Try it: If a Texas farm field is abandoned and left alone, which type of succession will happen there, and why?