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Custom Soil Resource Report <br />An ecological site, plant association, or habitat type is the product of all the <br />environmental factors responsible for its development. It has characteristic soils that <br />have developed over time throughout the soil development process; a characteristic <br />hydrology, particularly infiltration and runoff that has developed over time; and a <br />characteristic plant community(kind and amount of vegetation).The hydrology of the <br />site is influenced by development of the soil and plant community. The vegetation, <br />soils, and hydrology are all interrelated. Each is influenced by the others and <br />influences the development of the others. The plant community on an ecological site, <br />plant association, or habitat type is typified by an association of species that differs <br />from that of other ecological sites, plant associations,or habitat types in the kind and/ <br />or proportion of species or in total production. Descriptions of ecological sites are <br />provided in the Field Office Technical Guide, which is available in local offices of the <br />Natural Resources Conservation Service (NRCS). Descriptions of plant associations <br />or habitat types are available from local U.S. Forest Service offices. <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,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 />14