Ecological Succession
Ecological succession is the process of change in the species composition of an ecological community over time, following a disturbance or the formation of a new habitat. Primary succession occurs on bare, previously uncolonised substrate (e.g., newly formed volcanic rock), beginning with pioneer species such as lichens and mosses that gradually modify the environment for subsequent species. Secondary succession occurs in areas where a community has been disturbed but soil remains (e.g., after a forest fire), proceeding more rapidly to a stable climax community because soil and seed banks persist.
Stages of Primary Succession in a Terrestrial Ecosystem
| Stage | Community Type | Dominant Species | Approximate Timescale |
|---|---|---|---|
| 1. Bare Rock | No community | None (abiotic substrate) | Year 0 |
| 2. Pioneer Stage | Lichens, mosses | Crustose lichens, Cyanobacteria | Years 1–50 |
| 3. Herbaceous Stage | Grasses, ferns | Annual grasses, sedges | Years 50–100 |
| 4. Shrub Stage | Shrubland | Shrubs, small woody plants | Years 100–200 |
| 5. Early Forest Stage | Open woodland | Pioneer trees (Birch, Alder) | Years 200–500 |
| 6. Climax Community | Mature forest | Oak, Beech, Climax conifers | 500+ years |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Biodiversity
Biodiversity refers to the variety of life on Earth at all its levels — from genes and species to ecosystems — and the ecological processes that support this variety. It is typically measured at three levels: genetic diversity (variation within species), species diversity (number and abundance of species in an area), and ecosystem diversity (variety of habitats, communities, and ecological processes). High biodiversity generally confers ecosystem stability, resilience to disturbance, and a wider range of ecosystem services such as food, medicine, and clean water for human societies.
Keystone Species
A keystone species is an organism that has a disproportionately large effect on its ecosystem relative to its abundance or biomass; if removed, the ecosystem would change dramatically or collapse entirely. The concept was introduced by ecologist Robert T. Paine in 1969 following his experiments showing that removing sea stars (Pisaster ochraceus) from intertidal communities caused mussels to dominate and biodiversity to plummet. Keystone species can be predators, ecosystem engineers, or mutualists, and their identification is critical for conservation and wildlife management.
Carrying Capacity
Carrying capacity (K) is the maximum population size of a species that a given environment can sustain indefinitely, given the available food, water, habitat, and other essential resources. When a population reaches K, growth rate slows to zero because limiting factors such as resource competition, predation, and disease increase death rates and decrease birth rates. The concept is central to the logistic growth model, which describes how populations grow rapidly when small and stabilize as they approach K.
From Latin successio, meaning "a following after, a coming into the place of another", from succedere ("to follow after"). The concept of ecological succession was formally developed by Frederic Clements around 1916, who introduced the idea of the climax community.