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Custom Soil Resource Report <br />soil development process; a characteristic hydrology, particularly infiltration and runoff <br />that has developed over time; and a characteristic plant community (kind and amount <br />of vegetation). The hydrology of the site is influenced by development of the soil and <br />plant community. The vegetation, soils, and hydrology are all interrelated. Each is <br />influenced by the others and influences the development of the others. The plant <br />community on an ecological site is typified by an association of species that differs <br />from that of other ecological sites in the kind and/or proportion of species or in total <br />production. Descriptions of ecological sites are provided in the Field Office Technical <br />Guide, which is available in local offices of the Natural Resources Conservation <br />Service (NRCS). <br />Total dry-weight production is the amount of vegetation that can be expected to grow <br />annually in a well managed area that is supporting the potential natural plant <br />community. It includes all vegetation, whether or not it is palatable to grazing animals. <br />It includes the current year's growth of leaves, twigs, and fruits of woody plants. It does <br />not include the increase in stem diameter of trees and shrubs. It is expressed in pounds <br />per acre of air-dry vegetation for favorable, normal, and unfavorable years. In a <br />favorable year, the amount and distribution of precipitation and the temperatures make <br />growing conditions substantially better than average. In a normal year, growing <br />conditions are about average. In an unfavorable year, growing conditions are well <br />below average, generally because of low available soil moisture. Yields are adjusted <br />to a common percent of air-dry moisture content. <br />Characteristic vegetation (the grasses, forbs, and shrubs that make up most of the <br />potential natural plant community on each soil) is listed by common name. Under <br />rangeland composition, the expected percentage of the total annual production is <br />given for each species making up the characteristic vegetation. The amount that can <br />be used as forage depends on the kinds of grazing animals and on the grazing season. <br />Range management requires knowledge of the kinds of soil and of the potential natural <br />plant community. It also requires an evaluation of the present range similarity index <br />and rangeland trend. Range similarity index is determined by comparing the present <br />plant community with the potential natural plant community on a particular rangeland <br />ecological site. The more closely the existing community resembles the potential <br />community, the higher the range similarity index. Rangeland trend is defined as the <br />direction of change in an existing plant community relative to the potential natural plant <br />community. Further information about the range similarity index and rangeland trend <br />is available in the "National Range and Pasture Handbook," which is available in local <br />offices of NRCS or on the Internet. <br />The objective in range management is to control grazing so that the plants growing <br />on a site are about the same in kind and amount as the potential natural plant <br />community for that site. Such management generally results in the optimum <br />production of vegetation, control of undesirable brush species, conservation of water, <br />and control of erosion. Sometimes, however, an area with a range similarity index <br />somewhat below the potential meets grazing needs, provides wildlife habitat, and <br />protects soil and water resources. <br />Reference: <br />United States Department of Agriculture, Natural Resources Conservation Service, <br />National range and past.;rr ~an??bo^ <.