An ecological disturbance is a temporary event that changes an ecosystem’s structure, resource availability, or physical environment. These events act as powerful forces that reshape the patterns of life by altering the organization of its components. This disruption sets the stage for change, influencing the structure of populations and the overall character of the environment.
Causes of Ecological Disturbances
The origins of these events are separated into two categories: natural and human-caused. Natural disturbances include events like wildfires ignited by lightning, floods from heavy rainfall, volcanic eruptions, and diseases that spread through plant or animal populations. The scale of these events can range from a single tree falling in a forest to a massive hurricane impacting an entire coastline.
Human activities, also known as anthropogenic disturbances, alter ecosystems. Deforestation for agriculture or lumber removes foundational species and changes the physical environment. Pollution can contaminate soil and water, while urban development replaces natural habitats with impervious surfaces like concrete and asphalt.
Ecosystem Response to Disturbances
Following a disturbance, an ecosystem begins a recovery process known as ecological succession, where species gradually replace one another as the community rebuilds. The path of this recovery depends on the environment’s state immediately after the event.
There are two main types of succession. Primary succession occurs on surfaces devoid of life and soil, such as the bare rock left behind by a retreating glacier or a new lava flow. This is a slow process, requiring pioneer species like lichens to create soil. Secondary succession happens in disturbed areas that retain soil and some life, like a forest regrowing after a fire. Because soil is already present, recovery through secondary succession is much faster.
The Role of Disturbances in Ecosystems
While the immediate effects can appear destructive, disturbances are a natural part of many ecosystems. They are not inherently negative, instead playing a part in maintaining environmental health and biodiversity. By clearing out dominant species, disturbances create openings and release resources like sunlight and nutrients.
This reset allows new or less common species a chance to establish themselves, preventing any single species from dominating a habitat. This cycle of disruption and recovery increases species richness and creates a mosaic of habitats. A landscape that experiences periodic disturbances, like the fire-dependent veld in South Africa, is often more resilient and diverse than one that remains unchanged.