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the predominant species in a plant community (phytocoenosis).
Species are considered dominant for a given stratum, or story, of the plant community; any story may have one or more dominants. There are three dominants, for example, in a moss-whortleberry-fir forest: green moss, whortleberry, and spruce. The so-called absolute dominance of a species is determined by the area occupied by its members in proportion to that of the sample. This measure is sometimes replaced by that of relative dominance, the ratio of the area covered by the members of a species to the area covered by all plants in a story. Dominance is also sometimes expressed by the volume of organic material represented by the species, or by the number of that species in the area. The units in plant communities—associations, formations, and so forth—are labeled according to the names of their dominant species. In the USSR about 1,500 species are found as dominant; they make up the bulk of the plant products used by man. As indicators of soil and microclimatic conditions, dominants serve as a basis of agricultural zoning.