What Is Secondary Succession?
Secondary succession describes a type of ecological change where a biological community re-establishes itself in an area that previously supported life. This process occurs after a significant disturbance has altered the existing ecosystem, but the soil or underlying substrate largely remains intact. Organisms recolonize the disturbed habitat, gradually leading to the development of a new, complex community of plants and animals.
The Process of Secondary Succession
Secondary succession begins when a disturbance disrupts an established ecosystem, clearing much of the existing vegetation. Initial colonizers are fast-growing pioneer species, such as grasses and weeds. These species quickly establish themselves in the disturbed soil, benefiting from available sunlight and nutrients.
Over time, these pioneer plants modify the environment, adding organic matter to the soil and providing shade. This creates conditions more suitable for other plant species, like shrubs and small, fast-growing trees, to take root. These intermediate species outcompete the initial pioneers, shifting the plant community.
As larger trees grow, they create more shade, further influencing which species can thrive. Slower-growing, shade-tolerant trees eventually dominate, moving the ecosystem toward a more stable, mature community. The presence of existing soil, along with dormant seeds and root systems, accelerates this recovery process.
Common Scenarios and Examples
Various events can trigger secondary succession. Forest fires are a common natural cause, clearing vast areas of vegetation but leaving nutrient-rich ash and soil behind. Floods or landslides also cause secondary succession, destroying plant life but deposit nutrient-rich sediments.
Human activities also initiate this ecological process. Abandoned agricultural fields, for instance, are examples where cultivated land is left to revert to its natural state. Logging operations, particularly clear-cutting, remove trees but leave the soil and some plant remnants. Natural disasters like hurricanes uproot trees and damage vegetation, creating opportunities for secondary succession. In each scenario, the underlying soil structure and its stored seed bank play a role in the ecosystem’s recovery.
Secondary vs. Primary Succession
Secondary succession differs from primary succession in its starting conditions. Primary succession begins in environments devoid of soil, such as newly formed volcanic rock or land exposed after a glacier retreats. Organisms must first colonize the exposed rock and begin the slow process of soil formation.
Secondary succession occurs where soil is already present, often with remnants like seeds or root systems. Primary succession can take hundreds or even thousands of years to reach a stable state, as soil development is slow. Secondary succession progresses much faster, often completing its stages within decades to a few centuries, due to the immediate availability of soil and residual nutrients.