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Xerosere is aplant succession that is limited by water availability. It includes the different stages in axerarch succession. Xerarch succession of ecological communities originated in extremely dry situation such as sanddeserts, sand dunes, salt deserts, rock deserts etc. A xerosere may includelithoseres (on rock) andpsammoseres (on sand).[1]
Bare rocks are produced whenglaciers recede orvolcanoes erupt. The erosion of these rocks is caused by rainwater and wind, which are loaded with soil particles. The rainwater combines with atmospheric carbon dioxide thatcorrodes the surface of the rocks and produces crevices. Water enters these crevices, freezes, and expands to separate boulders. These boulders move down by gravity and wear particles from the rocks. Also, when the wind loaded with soil particles strikes against the rocks, it removes soil particles. All these processes lead to the formation of a bit of soil at the surface of these bare rocks. Animals such asspiders which can hide between boulders or stonesinvade these rocks. These animals live by feeding on insects that have been blown in or flown in.Algal andfungal spores reach these rocks by air from the surrounding areas. These spores grow and form symbiotic associations,lichen, which act aspioneer species of bare rocks. The succession process starts whenautotrophic organisms start living in the rocks.
Foliose lichens have leaf-like thalli, while thefruticose lichens are like small bushes. They are attached to the substratum at one point only, therefore, do not cover the soil completely. They can absorb and retain more water and are able to accumulate more dust particles. Their dead remains are decomposed to humus which mixes with soil particles and help building substratum and improving soil moisture contents further. The shallow depressions in the rocks and crevices become filled with soil andtopsoil layer increases further. These autogenic changes favor growth and establishment of mosses.
Thespores of xerophytic mosses, such asPolytrichum,Tortula, andGrimmia, are brought to the rock where they succeed lichens. Theirrhizoids penetrate soil among the crevices, secrete acids and corrode the rocks. The bodies of mosses are rich in organic and inorganic compounds. When these die they add these compounds to the soil, increasing the fertility of the soil. As mosses develop in patches they catch soil particles from the air and help increase the amount of substratum. The changing environment leads to migration of lichens and helps invasion of herbaceous vegetation that can out-compete mosses.
Herbaceous weeds, mostly annuals such asasters,evening primroses, andmilk weeds, invade the rock. Their roots penetrate deep down, secrete acids and enhance the process of weathering. Leaf litter and death of herbs addhumus to the soil. Shading of soil results in decrease inevaporation and there is a slight increase in temperature. As a result, the xeric conditions begin to change andbiennial andperennial herbs and xeric grasses such asAristida,Festuca, andPoa, begin to inhabit. These climatic conditions favor growth of bacterial and fungal populations, resulting in increase in decomposition activities.
The herb and grass mixture is invaded by shrub species, such asRhus andPhysocarpus. Early invasion of shrub is slow, but once a few bushes have become established, birds invade the area and help disperse scrub seeds. This results in dense scrub growth shading the soil and making conditions unfavorable for the growth of herbs, which then begin to migrate. Thesoil formation continues and its moisture content increases.
Change in environment favors colonization of tree species. The tree saplings begin to grow among the scrubs and establish themselves. The kind of tree species inhabiting the area depends upon the nature of the soil. In poorly drained soilsoaks establish themselves. The trees form canopy and shade the area. Shade-loving scrubs continue to grow as secondary vegetation. Leaf litter and decaying roots weather the soil further and add humus to it making the habitat more favorable for growth to trees. Mosses and ferns make their appearance and fungi population grows abundantly.
The succession culminates in a climax community, the forest. Many intermediate tree stages develop prior to establishment of a climax community. The forest type depends upon climatic conditions. The climax forest may be:
![[1]](/mt/?noimg=&dark=on&url=https%3a%2f%2fwww.google.com%2fimgres%3fimgurl%3dhttps%253A%252F%252Fupload.wikimedia.org%252Fwikipedia%252Fcommons%252F8%252F8c%252FFlavoparmelia_caperata_-_lichen_-_Caperatflechte.jpg%26amp%3btbnid%3dm8UKZoL1AlQQAM%26amp%3bvet%3d1%26amp%3bimgrefurl%3dhttps%253A%252F%252Fen.wikipedia.org%252Fwiki%252FFoliose_lichen%26amp%3bdocid%3dCga9lMnQ_oiByM%26amp%3bw%3d4928%26amp%3bh%3d3264%26amp%3bhl%3den-IN%26amp%3bsource%3dsh%252Fx%252Fim){kind=link}