SOIL COVERS 



155 



come serious throughout more than lialf of the United States, due 

 largely to the remo\al of the natural plant cover, in some cases by 

 unwise forestry practices or by fires and in many cases by over- 

 grazing. One large branch of the Federal Government, the Soil 

 Conservation Service, now spends a great deal of its time and energy 

 in devising practical ways to combat these destructive forces. The 

 restoration of the natural plant cover plays a large part in the pro- 

 gram of the Soil Conservation Service. 



100. Soil Covers.— The presence, or absence, of a soil cover is a 

 factor of considerable importance. Soil covers may be living or 

 non-living. The more important effects of a non-living cover are 



> / i iM 





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Fig. 68.— "Bad Lands," Sioux County, Nebraska. Produced by water erosion. 



(Photograph by Raymond J. Pool.) 



protection against loss of water and against rapid changes of tem- 

 perature. If the soil repeatedly freezes and thaws during the winter 

 many plants are "heaved" upward, their roots are more or less 

 broken, and they may suffer death from loss of water through 

 exposure to the air. An efficient soil cover largely prevents this. 

 A covering of snow is perhaps the most effective of all soil covers 

 in protecting low plants from wind and from rapid temperature 

 changes. The effect of a snow cover is well seen in some Arctic 

 regions where many woody plants are entirely unable to endure the 

 cold dry winds of winter if unprotected. Such plants grow upward 

 each summer as far as is possible in the limited time but each winter 



