Xerosere

Xerosere is a pattern of plant succession that occurs on very dry, xeric substrates and represents the early stages of primary succession in arid environments.

Initiating organisms typically include cyanobacteria, crustose lichens, and mosses that can tolerate extreme dryness. These pioneers form a thin organic layer, weather the substrate, and help stabilize the surface, while some cyanobacteria fix atmospheric nitrogen to enrich the developing soil.

As moisture is retained and microhabitats develop, drought-tolerant annuals and perennials establish, followed by grasses, then shrubs, and finally, in some climates, small trees. Soil depth and organic matter increase as litter accumulates, soil crusts form, and nutrients become more available.

The final stage varies with climate and substrate; in deserts the climax can be a xerophytic shrubland or open woodland. The pace of a xerosere is generally slow on very dry rock or calcareous pavement and can be accelerated by seed introduction.

Xerosere is distinguished from other seral sequences by its starting point on permanently dry habitats. It is contrasted with lithosere, psammosere, and hydrosere, which begin on rock, sand, and water-rich environments, respectively. The concept informs ecological restoration and soil stabilization efforts.