Ecological succession describes the process by which the species composition of an ecological community changes over time. These changes are often set in motion by specific events or conditions that disrupt an existing ecosystem.
Distinguishing Secondary Succession
Secondary succession occurs in areas where a pre-existing biological community has been disturbed or removed, yet the underlying soil, seed bank, and some forms of life remain intact. This distinguishes it from primary succession, which begins on newly formed land where no soil or life previously existed. The presence of existing soil and dormant life provides a foundation for faster recovery.
The intact soil contains essential nutrients and organic matter, allowing for quicker plant establishment. The soil seed bank, a natural storage of viable seeds, can rapidly germinate after a disturbance. This allows pioneer species, often fast-growing grasses, to quickly colonize the disturbed area.
Natural Events that Trigger Succession
Natural disturbances play a significant role in initiating secondary succession by clearing existing vegetation while largely preserving the soil and its biological components. Wildfires, for instance, burn most vegetation but return nutrients to the soil as ash, stimulating new growth from surviving seeds or roots. Some plant species have adaptations, such as cones that open with heat, benefiting from fire for seed dispersal.
Floods and hurricanes also trigger secondary succession by removing vegetation and altering landscapes. Flooding can deposit new sediments or scour existing topsoil, while intense winds can fell trees. These events typically leave soil structure and dormant biological material intact, allowing new plant communities to emerge. Landslides similarly clear vegetation, exposing underlying soil and initiating a new successional sequence. Disease outbreaks affecting specific plant populations can also create openings in a forest canopy, allowing other species to colonize available light and space.
Human Activities that Initiate Succession
Human activities frequently create conditions that lead to secondary succession by disturbing existing ecosystems. Deforestation, often for agriculture or urban development, involves the removal of trees and other vegetation. This process exposes the soil, and if the land is subsequently abandoned, secondary succession begins as native plants reclaim the area.
Agricultural abandonment, where cultivated fields are no longer farmed, is a common cause of secondary succession. The previously tilled soil, rich in nutrients and containing a seed bank, facilitates the rapid establishment of pioneer species, such as weeds and grasses, followed by shrubs and trees.
Urbanization and other development projects, including road and building construction, clear land of existing ecosystems. Once construction is complete or areas are left undeveloped, secondary succession can commence on the disturbed ground.
Mining operations also cause significant land disturbance by removing large volumes of earth and vegetation. Following the cessation of mining and subsequent reclamation efforts, these areas undergo secondary succession as plants begin to recolonize the re-contoured and often revegetated land. Large-scale pollution events, particularly those that eliminate plant life over an area, can also initiate secondary succession by creating barren patches where new communities must establish. These human-induced changes reshape landscapes globally, demonstrating the broad impact of human actions on ecological processes.