A NATIONAL PLAN FOB AMERICAN FORESTRY 535 



RELATION OF GRAZING TO OTHER FOREST RESOURCES 



Soil is the basic forest-land resource. The retention of the fertile 

 humus layer of top soil is essential to continued productivity. This 

 depends on satisfactory maintenance of the protecting plant cover. 

 In their original condition the forested slopes and valleys, except 

 on a tew areas of very unproductive soil, were well covered with dense 

 forests or open tree stands and an under story of herbaceous and 

 shrubby plants. This cover, together with its litter of decaying 

 vegetable matter, had built up the surface soil into a friable condi- 

 tion, added to it a large quantity of rich organic matter, protected it 

 from beating rains, and maintained it in a condition for maximum 

 penetration of precipitation. The result was that the forest cover 

 prevented excessive run-off or abnormal erosion. Through conserva- 

 tion of precipitation the productive soil yielded abundantly. 



Overgrazing as well as fires set in an effort to improve forage have 

 seriously depleted the herbaceous and shrubby vegetation and the 

 litter on extensive areas of practically all forest types. Heavy rains 

 falling on such exposed soils have started erosion which has stripped 

 away much of the fertile surface layer. On an important portion of 

 the Boise Kiver watershed in Idaho, for example, depleted by past 

 overgrazing, a survey by the Forest Service disclosed that only 35 

 percent of the grazed forest and brush types had escaped erosion. 

 On the eroded portion a large part of the upper soil layer has been lost 

 by widespread sheet and gully erosion. Six inches or more of the rich 

 topsoil has also been lost from large areas of such important water- 

 sheds as the foothills of the upper San Joaquin Valley and the moun- 

 tains of central Utah. The raw subsoil remaining is incapable of pro- 

 ducing the plant cover the land once supported. Years of careful 

 management will be required to restore the soil and vegetation, yet 

 this must be done if the accelerated erosion is to be controlled. 



It should be clearly understood that this loss of soil productivity 

 by erosion following improper range practices affects not the stock- 

 man alone but the general public quite as deeply. Loss of productivity 

 of the range resource, if allowed to proceed unchecked, removes 

 taxable wealth and possibilities for current income, thus directly 

 affecting community welfare. Furthermore, rapid run-off from de- 

 pleted slopes, especially that from rainstorms, and the erosion debris 

 which it carries increase the destructiveness of floods, and add greatly 

 to the silting problem of reservoirs and of other irrigation works in 

 the West. For example, an official of the Indian Service reported 4 to 

 Congress that the Zuni Reservoir in New Mexico had in 22 years 

 filled with erosion debris to over 70 percent of its capacity, practically 

 destroying its usefulness. The heavy investment in irrigated farm 

 lands, in irrigation and power properties, and the urban values built 

 up by these developments far outweigh the values represented in the 

 livestock enterprise ^ dependent upon the watersheds. Farm land 

 values in the Boise irrigation project alone of over $53,000,000 are 

 equal to $31 for every acre of the watershed. The public therefore, 

 is vitally concerned in the condition of the watersheds. 



< Hearings before Subcommittee of House Committee on Appropriations on Interior Department Appro- 

 priation BUI for 1931, 71st Cong.-, 2d sess., pp. 304-305. 



168342 33 vol. 1 35 



