Ecological Succession

Succession happens because early arrivals change the place enough to let later species move in and outcompete them. On bare rock, this is primary succession: there is no soil, so lichens and mosses have to show up first. They break down rock chemically and physically, and when they die their remains mix with mineral grit to make the first thin soil. That soil holds a little water and nutrients, enough for grasses and small herbs. More plant death adds more organic matter, soil deepens, shrubs root in, then fast-growing trees, and eventually a mature, shade-tolerant forest that can reproduce itself in its own shade: the climax community.

Secondary succession starts after a disturbance that leaves soil behind, like a fire, a flood, or an abandoned farm field, so it skips straight past the slow soil-building stage. Seeds, roots, and soil organisms already survive in the ground, so grasses and weeds appear within a season and woody plants follow in a few years rather than centuries. This is why a logged forest recovers far faster than a lava flow starting from zero.

A climax community is not frozen. It is stable only relative to the fast turnover of earlier stages: species composition still shifts slowly with climate, and a single fire, storm, disease outbreak, or clearing can knock it back to an earlier stage and restart the whole sequence. An abandoned farm field shows the full timeline in human terms, moving from annual weeds to perennials and grasses within a few years, shrubs and pioneer trees like pines within a few decades, and a hardwood forest resembling the original climax by roughly 100 to 150 years later.