. RANGE PRESERVATION AND EROSION CONTROL. 17 



The above summations show clearly thai the maximum velocity of 

 wind in the spruce-fir type exceeds by about 200 per cenl thai in the 

 aspen type at certain periods. These gales on the elevated plateaus, 

 especially where the ground cover is sparse, have a marked effect on 

 the movement of the soil and without doubt are an important factor 

 in causing erosion when the surface soil is dry and exposed (PI. II). 

 It is especialty important, therefore, that the vegetable cover on 

 these elevated lands be maintained in a maximum state of density in 

 order to bind the soil firmly. 



VEGETATIVE COVER. 



While the foregoing data indicate that the extent of surface run- 

 off and erosion are determined by the combined action of a number 

 of factors, the vegetative cover is the most important single control- 

 lable factor under the conditions in question. Man has little control 

 over climate and topography, and improvement in soil conditions 

 most favorable to the control of erosion on the range lands under 

 discussion must be accomplished chiefly through the improvement 

 in the vegetative cover. Even this possibility of control is limited 

 primarily to what can be accomplished by management of the lands 

 so as to favor the development of the native vegetation to the great- 

 est possible extent because western range conditions in general are 

 not favorable to the planting of cultivated species. This importance 

 of the native vegetative cover in maintaining conditions unfavorable 

 to erosion may be considered both a drawback and an advantage, for, 

 on the one hand, certain precautions must be taken in harvesting the 

 forage crop in order to preserve and maintain the vegetation ; but on 

 the other hand, there are relatively few lands which, under proper 

 management, can not be revegetated enough so that serious erosion 

 and destructive floods may be prevented. 



Anybody on a virgin or completely Vegetated range during a 

 heavy rainstorm can not fail to notice to what a great extent the 

 vegetation, whether grass, weed, browse, or timber, protects the soil 

 and increases its power of soaking up the water. Instead of the 

 entire force of the rain falling on an unprotected and exposed soil 

 surface, as in the absence of vegetation, the rain is intercepted more 

 or less by the vegetation, so that by the time the water reaches the 

 soil surface its original force is broken. There are several reasons 

 why a well vegetated surface offers the best condition for absorp- 

 tion and underground storage of water. The foliage and stems of 

 the vegetation form a storage place from which water drips slowly 

 to the ground for considerable time after each rain; and the leaves 

 and stems, in a more or less advanced stage of decay, absorb mois- 



46360°— IS— Bull. 675 3 



