[Chap. LIU THE VEGETATION OF NORTH AMERICA 



793 



only a little more than a century has passed since the lands away from 

 the larger rivers and lakes were occupied and brought under agricultural 

 and industrial control. During this short period most of the original vege- 

 tation has been destroyed. The accumulated fertility of the upper soil 

 horizons has been exploited by wasteful methods of cultivation and 

 destructive grazing, often accompanied by excessive drainage, erosion, 

 and the floating of the top soil to the river bottoms and the ocean. 



Conservation (Figs. 421-424, 25-26, and 180-181). Only recently has 

 there been official recognition of and real concern about our decadent 



Fig. 422. Ungrazed and overgrazed grama grassland in New Mexico. Photo from 

 U. S. Soil Conservation Service. 



