In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. A disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem.
Major ecological disturbances may include fires, flooding, storms, insect outbreaks and trampling. Earthquakes, various types of volcanic eruptions, tsunami, firestorms, impact events, climate change, and the devastating effects of human impact on the environment (anthropogenic disturbances) such as clearcutting, forest clearing and the introduction of invasive species can be considered major disturbances.
Not only invasive species can have a profound effect on an ecosystem, but also naturally occurring species can cause disturbance by their behavior. Disturbance forces can have profound immediate effects on ecosystems and can, accordingly, greatly alter the natural community’s population size or species richness. Because of these and the impacts on populations, disturbance determines the future shifts in dominance, various species successively becoming dominant as their life history characteristics, and associated life-forms, are exhibited over time.
The scale of disturbance ranges from events as small as a single tree falling, to as large as a mass extinction. Many natural ecosystems experience periodic disturbance that may broadly fall into a cyclical pattern. Ecosystems that form under these conditions are often maintained by regular disturbance. Wetland ecosystems, for example, can be maintained by the movement of water through them and by periodic fires. Different types of disturbance events occur in different habitats and climates with different weather conditions. Natural fire disturbances for example occur more often in areas with a higher incidence of lightning and flammable biomass, such as longleaf pine ecosystems in the southeastern United States.