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ENVIRONMENTAL EFFECTS in the fall or lasts longer in the spring, these animals will be forced to remain longer on winter ranges at lower elevations. Winter ranges are generally much smaller than summer ranges (Figure 11), and there is keen competition among game ani- mals and between big game and livestock. As aresult, the length of time which elk and deer are forced to spend on winter ranges affects the numbers that survive from year to year. Livestock can be shipped to better pasture during the winter, or given supplemental feed to carry them through. The whole ecological system will eventually become in- volved if the basic food input, vegetation, is disturbed. The species of mammals, birds, and insects that depend upon a food source will reflect changes in the abundance of that food source. In turn, the predators for these vegetarian species will also be affected. Eventually, nature's scavengers, those life forms that feed upon carrion or are responsible for the decomposition of organic matter, will also respond to the changes. Even the char- acter and formations of the soil will in time be altered by a change in the kind of vegetation growing on it. SNOWPACK, .CLOUD-SEEDlNG, AND THE COLORADO RIVER . . . . . . .. . . . .. . . .. . .. . . w..29o~~ _ _ _____.. .. WINTER . . PARKLANOS. FOREST ::. . MEADOWS .. . . . MOUNTAIN GOAT I ' '" ~\J . "~EE: .. J I"""' .. o,~.~.,'l. ~ 1 SHEEP w. ... JIJUne 10 September) ... .. 0 .. .. . __ _ IQ.O~ SUMMER .~ ~ Effects on Streams and Lakes A layer of snow on the ice cover of mountain lakes prevents the sunlight from penetrating to the plants in the water. Plants need light in order to carryon the growth process, photosynthesis, in which they transform carbon dioxide into oxygen. At the same time, decaying organic matter is consuming what little oxygen is dissolved in the water. If plants can't get enough light to make oxygen, the dissolved oxygen may become so depleted that the fish, insects, and other aquatic animals perish. Increasing the snow cover on lakes would tend to increase the number of mountain lakes that have such a winter kill and also the fre- quency with which it occurs. The same kind of winter kill can happen in streams that freeze over, but often a snow blanket on a stream acts as insulation that prevents it from freezing solid. Snowbanks sometimes collapse into streams that do not 39 ~ t for grazIng above the timberline need windswept areas where enough of the snow is blown off to allow them to forage for food. More snow at high elevations may mean fewer good foraging areas. The forest ranges from timberline down to about 7000 feet. By increasing the moisture available, WOSA will prolong the growing season for forage plants upon which big game (deer and elk) as well as livestock (sheep and cattle) depend for spring, summer, and fall food. If deep snow accumulates earlier 38 It regimes and animals that depend upon I Fig. 11. Vegetation and browsing lli i' ,,: I I, l. i J I I: II II ~ I;: ~ H ~ ;,'