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:=_-.. y <br />..F . 1. . <br />~~~, <br />r' <br />C. <br />:~ <br />' For the purpose here, an extended discussion of climate and the in- <br />,_ -- f),uence on weathering and soil formations is not necessary; rather the <br />effects of climate on vegetation and hydrology (variables 5, 7, ZO) are the <br />cost important for understanding the geomorphology and hydrology of Zone 1. <br />Vegetation (Variable 5) <br />_ -. There can be no question of the highly significant effect of vegeta- <br />y[ion on landforms and erosion rates. In the IInited States veQetationa3 --~~r` <br />hezk-or-we~ht increases as about the cube of mean annual precipitation <br />Q,angbein and Schur, 1958) and a significant reduction in erosion and <br />imo t y{eld can be anticipated as precipitation increases or as vegeta- <br />ion increases in a eiven climtic situation. Figure 2-3 shoos such'a re- <br />r:ticn from an experi~:.ertal area in Utah. T_he relationship is ex-poaential <br />aad an extrapolation of [he curve indicates a maximum of 50,000 pounds per <br />acre of erosion with zero ground cover. However, there is no reason to <br />believe that such value will be achieved. Although on Figure 2 ~ an asymp- <br />" '^ ovroach to the v axis {s indicated by th= avid inc~ease of erosion <br />'~ Here t es of rou cow there Tub` Y c a maximum rice of <br />g--~- ~ --~ -- t <br />oe for a given soil or rock type which will be reached before rtround <br />My°' is zero. The curve 'could. plateau at that value, as the dashed line <br />=u3dests: If this is t-ue they Figure 2~ leads to the conclusion that with <br />=ass t`~an about8 Coe cent cover, v_e~etation is probably relatively iaeffec- <br />=~° `~ cone oll'n erosion On the other hand, above about i0 percent <br />~=~~tional vegetation will not significaet~v reduce erosion. These <br />- ~= ~is to v<o rarannat Pr"err+vQness for erosion con'rol should be g+ven <br />• 2-9 <br /> <br /> <br />