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Custom Soil Resource Report <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, shrubs, and understory trees that make <br />up most of the potential natural plant community on each soil) is listed by common <br />name. Under rangeland composition and forest understory, the expected percentage <br />of the total annual production is given for each species making up the characteristic <br />vegetation. The percentages are by dry weight for rangeland. Percentages for forest <br />understory are by either dry weight or canopy cover. The amount that can be used as <br />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 pasture handbook. <br />71 <br />