Disturbances

Disturbances are discrete events or processes that disrupt normal environmental conditions, causing changes in resource availability, habitat structure, and the organisms present. They can be natural or human-caused, occurring suddenly or over extended periods, and they vary in intensity, spatial scale, and recurrence. Disturbances differ from chronic stress in that they are episodic and often lead to abrupt ecological change.

Natural disturbances include wildfires, storms, floods, droughts, insect outbreaks, and volcanic eruptions. Anthropogenic disturbances arise from activities such as deforestation, urbanization, mining, agriculture, and dam operations. The study of disturbances focuses on disturbance regimes—the typical pattern of disturbance over time, including frequency, size, severity, and predictability—and their effects on species composition, diversity, and ecosystem processes such as nutrient cycling and regeneration. Disturbances can create gaps and spatial heterogeneity, influencing successional trajectories and enabling pioneer species to establish. Outcomes depend on pre-disturbance conditions, the event's severity and scale, and post-disturbance environmental factors. In many systems, moderate disturbances enhance resilience by maintaining diversity, while extreme disturbances can trigger long-term regime shifts.

Disturbances interact with climate change, which can alter disturbance regimes by increasing the frequency and intensity of events such as fires and storms, thereby reshaping landscapes. The term is also used in other fields, where disturbances denote external inputs or noise that affect systems, such as engineering signals or social disruptions.