Ecological succession describes the natural process by which the mix of species and their habitats in an area changes over time. This gradual transformation leads to predictable shifts in the biological community’s composition, allowing ecosystems to evolve and adapt.
What is Secondary Succession?
Secondary succession is a type of ecological change occurring in areas where a biological community previously existed but was disturbed or removed. These disturbed areas retain existing soil and often some remnant life, such as seeds, spores, or underground root systems. It is the process of re-establishing a complete ecological community using this remaining foundation after an ecological disturbance.
How Secondary Succession Differs from Primary Succession
The primary distinction between secondary and primary succession lies in their starting conditions. Primary succession begins in areas devoid of life and soil, such as newly formed volcanic rock or bare sand dunes. In contrast, secondary succession occurs where soil is already present.
Because soil and some life forms remain, secondary succession proceeds much faster than primary succession. The existing soil provides essential nutrients and a medium for new plant growth, accelerating the recovery process and allowing for quicker re-colonization.
A Detailed Example: Forest Recovery After Disturbance
An example of secondary succession is the recovery of a forest after a wildfire. A fire often leaves the soil largely intact, enriched by ash that provides nutrients. Within days or weeks, pioneer species emerge. These are typically fast-growing annual plants, weeds, and grasses like fireweed, horseweed, or asters, which sprout from seeds in the soil or dispersed by wind. Ferns and moss can also begin growing weeks to months post-fire.
Within a few years, these herbaceous plants are joined by small shrubs and fast-growing, sun-loving trees such as aspens, birches, poplars, pines, or red cedars. These intermediate species begin to shade out the initial pioneer plants, altering the environment. As these trees mature, they create a denser canopy, impacting light availability on the forest floor. This stage also sees the return of various animal species, with insects often being among the first, followed by birds and small mammals seeking food and shelter in the regenerating habitat.
Over several decades, typically between 50 and 150 years, slower-growing, shade-tolerant trees like oaks and hickories begin to establish themselves in the understory. These species gradually outcompete and replace the earlier, faster-growing trees. Eventually, if left undisturbed, the forest reaches a relatively stable and mature state known as a climax community, characterized by a dominant presence of these long-lived, shade-tolerant trees.
Significance in Ecosystems
Secondary succession plays a significant role in maintaining the health and resilience of ecosystems. It allows landscapes to recover and restore biodiversity following natural disturbances or human activities. This process contributes to ecosystem stability, ensuring that environments can adapt and bounce back from changes.
Through the sequential colonization of different species, secondary succession facilitates nutrient cycling and the development of complex food webs. It highlights the dynamic nature of ecosystems, demonstrating their capacity for renewal and self-organization over time. Understanding this process is important for conservation efforts and managing landscapes that have experienced disturbances.