Types of Succession

Succession is classified along several independent axes. By starting condition, primary succession develops in a genuinely barren area where no community existed before — its first colonisers are called pioneer species or the primary community, and because the site starts with no soil at all, this process generally takes a very long time (microbes, lichens and mosses are typical pioneers). Secondary succession, by contrast, develops on a site where an already-established community has been destroyed by some disturbance such as fire, flood or human activity — for example, herbs re-occupying a forest cleared by fire and excessive logging — and because soil cover is already present, it proceeds noticeably faster than primary succession. By which factors drive it, autogenic succession results from biotic factors: the existing vegetation itself modifies its own environment and thereby brings about its own replacement — as when larger forest trees cast shade that suppresses light-loving shrubs/herbs (heliophytes) while favouring shade-tolerant species (sciophytes). Allogenic succession, by contrast, results from abiotic/external factors such as soil erosion or leaching altering the nutrient status of the soil and thereby forcing a change in vegetation, rather than the existing plants driving the change themselves. By which organisms dominate the earliest stage, autotrophic succession occurs where green plants dominate early on, in habitats rich in inorganic substances, producing a steady increase in organic matter and energy flow over time; heterotrophic succession instead occurs where bacteria, fungi, actinomycetes and animals dominate early on, in organic-rich habitats, and shows a gradual decrease in energy c …