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35 .. All forest areas have understory shrubs and grasses. The forest provides CAl.IFORNIA a stable biotic community usually resistant to 80il erosion. The Upper IIIDIInIIII Salt Desert Shrub ~ Desert Shrub _ GraBs Land r::::J National Forests ~ Wood Land ~ Mountain Brush ~ Defense. WL, Fisheries. Parks IlIII! National Parks & Monuments c:::J Outlines Indian Reservations Colorado River Basin has 28,710,000 acres of forest lands. Grazing and timber production extend over the areas of the upper basin forest. These lands have a large impact on the Colorado River ecosystem. One example is the allochthonous input of organic matter from the terrestrial ecosystem which frequently supports the higher organisms in the aquatic food chain. Generally, land use changes within terrestrial ecosystems will re- /if ~ j duce diversity of species and shift the structure of the ecosystem through elimination of sensitive species. In terrestrial plant communities, the shift is from trees toward shrubs and forbs, or mosses and lichens. How- NEVADA ever, more than simply structure and diversity are involved--simplification .. .. - ... .. of the plant community involves also a reduction of the total standing < crop of organic matter and a corresponding reduction in the total inven- ~ MEXICO tory of nutrient elements held within the system. The implications are .. .. ... the site to support life. Changes in the plant community (size, rate of ... .. ~ .. F , .. ~ that the changes may have important long-term effects on the potential of energy fixation, and species) will therefore affect the structure of the animal community as well. In particular, activities such as grazing, agri- culture, mining, and energy production have effected and will continue to effect such changes in the native plant and animal species of the basin. Basin Development and Environmental Change UlunD ST"TE' Dr.....T.E..' 0' TNt: "IT._'O" IUII["U O' f1t:CL"...,IOIll CO LORADO RIVER BASIN QUALITY OF WATER MAP Development Activities and Institutions .. .. n ._ .... ._ SCALf Of" MIL-II la- 400.70 Superimposed on the natural physical system is the use and manage- ",ULT If, tMI IIlEVIJE1Ilr:O.rltlUl,.,.. ment of the land and water within the basin. In order to satisfy the Figure 3. Terrestrial Ecosystems and Land Use in the Colorado River Basin.