Q.Define plant succession. Distinguish between primary and secondary succession.

Plant (ecological) succession is the gradual, directional, sequential process by which one plant community in an area is progressively replaced by another over time, eventually leading to a stable, self-perpetuating climax community. It proceeds through a recognisable series of seral stages, each of which alters the local environment — chiefly by building up soil, organic matter, and shelter — in ways that allow the next, usually more complex, community to establish itself.

Primary versus secondary succession

Primary succession begins on a bare, essentially lifeless substratum that has never before supported vegetation and that has no soil to begin with — bare exposed rock, for instance, or a newly formed pond. With no soil, no seed bank, and no organic matter already present, primary succession must build everything from scratch, which makes it a slow process.

Secondary succession occurs on a site that previously carried vegetation and still retains soil, but whose existing plant cover has been removed or disturbed by an event such as fire, deforestation, or the abandonment of farmland. Because soil, some organic matter, and often a bank of dormant seeds or root fragments already exist at the outset, secondary succession skips the slow soil-building early stages that primary succession must go through — which is exactly why the climax stage is reached much faster in secondary succession than in primary succession.

Xerarch succession …