A NATIONAL PLAN FOR AMERICAN FORESTRY 



323 



Forsling 25 has pointed out that depletion of forage is accompanied 

 by severe soil losses without any material gain in the total water 

 obtainable from watersheds in this region. He studied conditions on 

 two subalpine watersheds of about 10 acres each at the head of Ephraim 

 Canyon, Utah. On watershed A, a 16 percent cover, mainly of 

 annuals, was maintained from 1915 to 1920, but was improved 

 gradually until in 1924 it reached 40 percent, made up chiefly of 

 perennial grasses and weeds. In this condition it was maintained 

 through the 6-year period 1924 to 1929. On watershed B, used as a 

 check, a 40 percent cover, largely of perennial grasses and weeds, 

 was maintained for the full period 1915 to 1929. Table 7 presents the 

 comparative data from these two watersheds. 



TABLE 7. Comparison of surface run-off and sediment removed from two water- 

 sheds under different densities of vegetative cover 



1 All storms coming as rain, or rain with snow and hail, and exclusive of storms that were snow only. 



It is significant that the difference in surface run-off in summer rains 

 between the two watersheds is 75 percent less after watershed A 

 reached a reasonably good vegetative condition. It is excessive 

 run-off from summer rainstorms that causes the destructive floods in 

 this locality. In both periods the records available indicate that 

 total surface run-off from summer rains amounted to less than one 

 twentieth of the total annual surface run-off from the watersheds. 

 Annual soil losses from watershed A in its depleted condition were 

 over 8 tons per acre, nearly 85 percent of which was the result of 

 summer rains. Approximately 133.8 cubic feet of soil per acre were 

 removed annually from watershed A in the 1915-20 period and 

 only 19.2 cubic feet per acre per year in the 1924-29 period. The 

 difference in sediment removed between the watersheds was strikingly 

 reduced following the improvement in vegetative cover 87 percent 

 between the first and last periods. 



Destructive floods have occurred in Utah in the last 10 years in 

 the thickly populated area near Salt Lake. Studies made by Prof. 

 Reed W. Bailey 26 of the Utah Agricultural College, in cooperation 

 with the Intermountain Forest and Range Experiment Station and 



25 Forsling, C. L. A Study of the Influence of Herbaceous Plant Cover on Surface Run-off and Soil 

 Erosion in Relation to Grazing on the Wasatch Plateau in Utah. U.S.Dept.Agr.Tech.Bul. 220. 1931. 



Bailey, Reed W. Statement in hearings before the House Committee on the Public Lands on H.R. 

 11816, 72d Cong., 1st sess. 1932. 



