Classification of Plant Succession

Succession is classified by the moisture level of its starting habitat into three broad classes: hydrosere (starting where water is plentiful, such as ponds, lakes, streams and swamps), mesosere (starting where moisture is adequate), and xerosere (starting where moisture is minimal) — with xerosere further split by substrate into lithosere (starting on bare rock), halosere (starting in saline water) and psammosere (starting on sand). The chapter details two of these in full. Hydrosere is succession in a freshwater ecosystem, beginning with pioneer phytoplankton and culminating, over seven named stages, in a forest climax: the phytoplankton stage (pioneer blue-green algae, green algae, diatoms and bacteria enrich the pond's organic matter and nutrients through their life activity and death); the submerged plant stage (silt and decomposed plankton build a loose mud bottom, allowing rooted submerged hydrophytes such as Hydrilla to appear); the submerged free-floating stage (as the pond reaches roughly 2–5 feet deep, rooted floating plants such as Nelumbo and Nymphaea plus free-floating species such as Azolla colonise it, gradually making it shallower still); the reed-swamp (amphibious) stage (rooted-floating plants are replaced by plants able to live both in water and air, such as Typha and Phragmites, as water level falls further); the marsh meadow stage (mat-forming sedges and grasses such as Carex and Cyperus colonise the now-shallow, marshy ground, absorbing large amounts of water and drying the soil out); the shrub stage (as marsh vegetation disappears and the soil dries further, terrestrial shrubs such as Salix and trees such as Populus invade and accumulate humus); and finally the forest stage, the hydrosere's climax community, which may develop into temperate mixed forest, tropical rain forest or tropical deciduous forest depending on the region. Lithosere is a type of xerosere that starts on bare, water- and nutrient-free rock, and progresses through six named stages to the same kind of forest climax: the crustose lichen stage (pioneer crustose lichens secrete acids that weather the rock into small particles, building the first thin soil layer, though very slowly); the foliose lichen stage (foliose lichens replace crustose ones, secreting further acids that loosen more rock and improve the habitat's water-holding capacity); the moss stage (xerophytic mosses replace the foliose lichens as conditions change, adding more humus and moisture through their own death and decay); the …