IIO ECONOMIC MAMMALOGY 



denudation of the hillsides, the transported debris covering and injur- 

 ing or destroying fields and pastures in the valleys. The storm waters, 

 no longer held in check by the loose soil and vegetation, rush down the 

 slopes and produce disastrous floods where they were formerly un- 

 known. The partial restoration of original range conditions by the re- 

 moval of sheep has resulted soon in lessening the violence of floods. 

 Erosion and floods due to overgrazing in the Manti Forest before it 

 was made a national forest, caused damage to the extent of $225,000, 

 while on Sevier River, Utah, sediments derived from erosion due to 

 overgrazing covered and were estimated in 1916 to have damaged farm 

 lands to the extent of $i5o,ooo. 6 These are but illustrative examples 

 out of many such instances now known. 



Botanists observe that when the virgin prairie surface is disturbed 

 by plowing, or in the construction of roads and the like, weeds at once 

 spring up in the loosened soil, where only grass grew when it was com- 

 pact. Thus on western plains the graded roadsides are often soon lined 

 with a thick growth of sunflowers, "snow-on-the-mountain" and other 

 plants that do not ordinarily invade the undisturbed soil except here 

 and there as single plants or small clusters. Where prairie sod has been 

 plowed and the fields then abandoned they are soon covered with a 

 dense growth of sunflowers and other weeds. A similar result has been 

 observed to follow the destruction of the original vegetative cover by 

 overgrazing and excessive trampling of the soil by large flocks of 

 sheep or herds of cattle, even on slopes not steep enough for serious 

 erosion to occur, "useless weeds" being substituted for the original 

 vegetation. 7 The inevitable result of excessive overgrazing on the plains 

 of the Rocky Mountain states is so to reduce the forage that the range 

 will not support even sheep. In the national forests of the mountains, 

 where precipitation is much greater and consequently the effects of 

 overgrazing not so extreme, it has been found necessary to provide, in 



6 Reynolds, Grazing and floods : A study of conditions in the Manti National 

 Forest, U. S. Forest Service Bull. No. 9, 1911. Dana, Farms, floods and erosion, 

 Yearbook U. S. Dept. Agric. for 1916, pp. 107-134. Cottam, Man as a biotic factor il- 

 lustrated by recent floristic and physiographic changes at the Mountain Meadows, 

 Washington County, Utah, Ecology, x, 361-363, 1929. Forsling, A study of the influ- 

 ence of herbaceous plant cover on surface run-off and soil erosion in relation to 

 grazing on the Wasatch Plateau in Utah, U. S. Dept. Agric. Technical Bull. No. 220, 

 I93i. 



7 Colville, Forest growth and sheep grazing in the Cascade Mountains of Ore- 

 gon, U. S. Div. Forestry Bull. No. 15, 1898. Shreve, Changes in desert vegetation, 

 Ecology, x, 364-373, 1929. Campbell, Vegetative succession in the Prosopis sand 

 dunes of southern New Mexico, Ecology, x, 393-398, 1929. Jardine and Forsling, 

 Range and cattle management during drought, U. S. Dept. Agric. Bull. No. 1031, 

 1922. 



