Ecological Succession
The directional change in species composition of a community over time after disturbance or on newly exposed substrate.
Ecological succession is the directional change in the species composition of a community over time. Primary succession begins where no soil exists — on bare rock, lava flows, or glacial till. Secondary succession follows disturbances that remove existing vegetation but leave soil and seed banks intact, such as fire, farmland abandonment, or storm damage.
In primary succession, pioneer species such as lichens and mosses colonize bare surfaces, accelerate weathering, and build the first thin soils; grasses and herbs follow, then shrubs, then trees. Secondary succession proceeds through similar stages much faster because the soil and its seed bank are already present. The traditional endpoint, the climax community, was once seen as a stable final state; modern ecology emphasizes that disturbances such as fire regimes maintain mosaics of different successional stages rather than a single equilibrium.
The mechanisms driving succession are facilitation — early species modify the environment in ways that benefit later ones — plus inhibition and tolerance, formalized in the classic model of Connell and Slatyer (1977). Rates depend on climate, the available species pool, and disturbance frequency: succession is slow in deserts and tundra, faster in temperate and tropical climates.
Understanding succession matters for restoration ecology, for predicting vegetation recovery after fires, and for conservation planning in landscapes shaped by human disturbance. The concept was formalized by Clements (1916), who saw communities as superorganisms, and revised by Gleason, who emphasized individualistic species behavior — a debate that still shapes how ecologists model community change. The photosynthesis of plants and algae supplies the energy that flows through every successional stage.
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biology disturbance ecology ecosystems
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