litter, humus, sprouting bushes, and small trees have not 

 been removed by the cutting and will be destroyed by a fire. 

 And as the fires spread to uncut areas vast damage is done by 

 destruction of standing timber, underlying shrubs, and espe- 

 cially the litter and the humus under timber, in the soil, and 

 in dried-out peat bogs. 



In the third place, in forest, wood-lot, and grass areas, and 

 in cut-over areas that would otherwise have begun to renew 

 themselves, overgrazing has entered as a destructive force. 

 Overgrazing destroys the young sprouts and the grass, exposes 

 the soil to disturbance by hoofs and rain, and thereby to the 

 invasion of erosion. 



As soon as the litter and humus are removed by any of 

 these influences, the soils which they have protected and 

 kept open are exposed to the mechanical influence of falling 

 and running water; the surface is sealed by the puddling 

 rains and the action of sheet erosion; absorption and percola- 

 tion diminish; and the force of the increased run-off washes 

 the soils into the ponds and streams. This sheet erosion 

 is eventually followed by gully erosion, the slopes are 

 stripped in places to the underlying subsoil or rock, the 

 area affected becomes barren waste, and most of the pre- 

 cipitation passes directly to the rivers and the seas. Soils 

 and waters which might have served men are lost. 



[c] REMOVAL OF SOD COVER. 



As important as the removal of natural forest cover, 

 although not as extensive, is the destruction of sod cover. At 

 the beginning of settlement of the United States the areas 

 not occupied by forests forest openings, valley bottoms, 

 the prairies and the great plains were covered by grasses 

 and herbs. These grasses and herbs contributed to the 

 humus, kept the soil open and absorbent, served as a re- 

 tarding influence on run-off and in general promoted in- 

 filtration. As population has increased, more and more of 

 these native grasslands have been turned under for cultiva- 

 tion of cash crops; and in many sections of the West they 

 have been subjected to excessive grazing, particularly of sheep, 

 which graze closely and often destroy even the roots of the 



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