Xerosere
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Xerosere is a
Stages
Bare rocks
Bare rocks are produced when
Foliose and fruticose lichen stage
Foliose lichens have leaf-like thalli, while the fruticose 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 and topsoil layer increases further. These autogenic changes favor growth and establishment of mosses.
Moss stage
The spores of xerophytic mosses, such as Polytrichum, Tortula, and Grimmia, are brought to the rock where they succeed lichens. Their rhizoids 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.
Herb stage
Herbaceous weeds, mostly annuals such as
, begin to inhabit. These climatic conditions favor growth of bacterial and fungal populations, resulting in increase in decomposition activities.Shrub stage
The herb and grass mixture is invaded by shrub species, such as
Tree stage
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 soils oaks 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.
Climax stage
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:
- Oak-hickory climax forest
- In dry habitat oaks and hickories are climax vegetation. There is only one tree stage and forests are characterized by presence of scrubs, herbs, ferns, and mosses.
- Beech-hemlock climax forest
- These climax forests develop in mesic climates. The dominant vegetation is beech and hemlock. There are many intermediate tree stages. The other vegetation types include herbs, ferns, and mosses.
- Beech-maple climax forest
- These climax forests develop in mesic climates in the Northeastern United States. The dominant vegetation is sugar maple.
- Spruce-alpine fir climax forest
- At high altitudes in Rocky Mountains the climax forest is dominated by spruces and alpine firs.
See also
References
- ^ Cooper, W.S. (January 1, 1913). The climax forest of Isle Royale, Lake Superior, and its development. Bot. gazette.