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Rangeland Productivity and Plant Composition-Archuleta County Area, Tom Smith South Pit <br />Colorado; and Piedra Area, Colorado, Parts of Archuleta, Hinsdale, La Plata, <br />Mineral, and Rio Grande Counties <br />Rangeland Productivity and Plant Composition <br />In areas that have similar climate and topography, differences in the kind and <br />amount of rangeland or forest understory vegetation are closely related to the kind <br />of soil. Effective management is based on the relationship between the soils and <br />vegetation and water. <br />This table shows, for each soil that supports vegetation suitable for grazing, the <br />ecological site; the total annual production of vegetation in favorable, normal, and <br />unfavorable years; the characteristic vegetation; and the average percentage of <br />each species. An explanation of the column headings in the table follows. <br />An ecological site is the product of all the environmental factors responsible for its <br />development. It has characteristic soils that have developed over time throughout <br />the soil development process; a characteristic hydrology, particularly infiltration and <br />runoff that has developed overtime; and a characteristic plant community (kind and <br />amount of vegetation). The hydrology of the site is influenced by development of <br />the soil and plant community. The vegetation, soils, and hydrology are all <br />interrelated. Each is influenced by the others and influences the development of <br />the others. The plant community on an ecological site is typified by an association <br />of species that differs from that of other ecological sites in the kind and/or proportion <br />of species or in total production. Descriptions of ecological sites are provided in the <br />Field Office Technical Guide, which is available in local offices of the Natural <br />-Resources Conservation Service (NRCS). <br />Total dry-weight production is the amount of vegetation that can be expected to <br />grow 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 <br />animals. It includes the current year's growth of leaves, twigs, and fruits of woody <br />plants. It does not include the increase in stem diameter of trees and shrubs. It is <br />expressed in pounds per acre of air-dry vegetation for favorable, normal, and <br />unfavorable years. In a favorable year, the amount and distribution of precipitation <br />and the temperatures make growing conditions substantially better than average. <br />In a normal year, growing conditions are about average. In an unfavorable year, <br />growing conditions are well below average, generally because of low available soil <br />moisture. Yields are adjusted 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 <br />can be used as forage depends on the kinds of grazing animals and on the grazing <br />season. <br />Range management requires knowledge of the kinds of soil and of the potential <br />natural plant community. It also requires an evaluation of the present range <br />similarity index and rangeland trend. Range similarity index is determined by <br />comparing the present plant community with the potential natural plant community <br />on a particular rangeland ecological site. The more closely the existing community <br />resembles the potential community, the higher the range similarity index. <br />Rangeland trend is defined as the direction of change in an existing plant <br />community relative to the potential natural plant community. Further information <br />about the range similarity index and rangeland trend is available in the "National <br />Range and Pasture Handbook," which is available in local offices of NRCS or on <br />the Internet. <br />USDA Natural Resources Web Soil Survey 2.0 11/6/2007 <br />am- Conservation Service National Cooperative Soil Survey Page 1 of 6 <br />Page 21