Secondary succession is a natural process where an ecosystem recovers or changes after a disturbance. It occurs in areas where a biological community previously existed and the soil, or substrate, remains largely intact. This process involves the sequential progression of species and communities re-establishing in the disturbed environment.
Starting Conditions for Secondary Succession
Secondary succession begins following events that disrupt an existing ecosystem without completely removing its soil and some life forms. Common triggers include natural disasters such as wildfires, floods, and hurricanes, which can clear vegetation but leave the ground fertile. Human activities like logging, deforestation, or the abandonment of agricultural fields also initiate this process.
Unlike primary succession, where life colonizes barren land, secondary succession benefits from the pre-existing soil, which contains nutrients and organic material. This remaining soil often harbors a seed bank, along with surviving roots or underground plant organs, allowing for quicker re-establishment of plant life. The presence of these remnants significantly accelerates recovery compared to primary succession.
Stages of Community Change
The process of secondary succession unfolds in distinct stages, beginning with the colonization of disturbed areas by opportunistic species. The initial phase, known as the pioneer stage, sees the rapid growth of grasses, weeds, and other herbaceous plants. These fast-growing species are often well-adapted to disturbed conditions and play a role in stabilizing the soil and adding organic matter.
As the pioneer species establish, they gradually create conditions that favor the growth of other plants, leading to the intermediate stage. During this phase, shrubs and faster-growing, shade-intolerant trees, such as pines, poplars, or birches, begin to replace the initial herbaceous plants. Biodiversity increases as more species arrive and compete for resources like sunlight and nutrients. The changing vegetation structure also provides new habitats for various animal species.
The progression continues towards a more stable and diverse ecosystem, eventually reaching a climax community. This theoretical endpoint is characterized by a relatively stable balance of species that can self-perpetuate, like a mature deciduous forest. In a climax community, the environment can sustain larger, more complex organisms, and significant changes in species composition are less frequent unless another disturbance occurs. However, ecosystems are dynamic, and even climax communities experience small-scale disturbances and ongoing subtle shifts.
Factors Shaping the Succession Process
Several environmental and biological variables influence the rate and specific trajectory of secondary succession. Climate, including temperature and rainfall patterns, significantly affects plant growth and species survival, thus dictating which species can thrive and how quickly the community develops. For instance, warm, wet climates support faster successional rates than cold or arid ones.
The characteristics of the remaining soil, such as its type, depth, and nutrient content, also play a substantial role. Soil with a richer nutrient base and better water retention can support a wider variety of plant life and accelerate recovery.
Proximity to other established ecosystems is another factor, as nearby mature communities can serve as sources of colonizing species through seed dispersal by wind, water, or animals. The severity and intensity of the initial disturbance also determine the starting point and pace of succession. A less severe disturbance, which leaves more remnants of the previous community, leads to a faster recovery.