A pioneer organism, also known as a disaster taxon, is an organism that moves into an area with no life, or that returns to an area that has become empty after a natural disaster, mass extinction, or another major event that destroys most life in the previous ecosystem. A group of these organisms that can reproduce among themselves is called a pioneer species.

Natural disaster

After a natural disaster, lichens and algae are common pioneer organisms. Mosses often grow after lichens but are not considered pioneer organisms. These pioneer organisms may prefer certain temperatures. Lichens usually grow in areas with more rainfall, while algae and mosses tend to grow in areas with more humidity.

Pioneer organisms change their environment and create conditions that allow other organisms to live. Sometimes, other organisms can also be pioneer organisms. Birds are often the first animals to live on newly formed islands, and seeds, like those from coconuts, may be the first to grow on soil that has no plants.

Extinction event

Because the fossil record isn't very detailed, scientists often identify pioneer organisms as those that lived hundreds, thousands, or even a million years before or after an extinction event. For example, after the Permian–Triassic extinction event 252 million years ago, Lystrosaurus, a tusked therapsid, was considered a disaster taxon.