A disturbance is an event that changes environmental conditions, removes organisms or alters resource availability in a community. Examples include fire, storms, floods, grazing, volcanic eruptions and human land use.

After disturbance, community composition often changes through ecological succession.

Primary succession begins where a biological community and developed soil are largely absent, such as newly exposed rock. Colonization starts with organisms capable of establishing under those conditions, and later organisms modify the environment in ways that can facilitate or inhibit other species.

Secondary succession begins after a disturbance removes much of a community but leaves important biological legacies such as soil, seeds, roots or surviving organisms. Recovery can therefore proceed much faster than in primary succession.

Succession is not necessarily a fixed march toward one inevitable 'climax community.' The trajectory depends on dispersal, surviving organisms, disturbance severity, climate, species interactions and chance. Repeated disturbances can maintain mosaics of patches at different stages.

Species can influence succession in several ways:

• facilitation: early colonists make conditions more suitable for later species;
• inhibition: established species suppress later colonists;
• tolerance: later species can establish despite earlier occupants when conditions permit.

Succession therefore describes directional community change after environmental disruption, while recognizing that multiple trajectories and persistent disturbance regimes are possible.