448 A NATIONAL PLAN FOR AMERICAN FORESTRY 



1896, 1901, and 1902. Beginning in 1904 livestock were excluded 

 from the canyon except for drift (the national forest was established 

 in 1903). By 1909 the vegetation had materially improved. A heavy 

 storm in August 1909 that resulted in floods from the still depleted 

 Ephraim and Six Mile Canyons, on either side of Manti Canyon, 

 caused little injury in Manti Canyon. On September 18 and 19, 

 1910, a 1.59-inch rainfall following one of 1.16-inch on September 16 

 in the grazed Ephraim Canyon resulted in a heavy flood. A 1 .18-inch 

 rainfall on September 18 and 19 following a 1.51-inch rainfall on 

 September 16 in the protected Manti Canyon produced no flood. 

 Since then destructive floods have been unknown in Manti Canyon. 

 In recent years there has been a considerable improvement in the 

 vegetative cover in Ephraim Canyon, and no floods of consequence 

 have occurred. 



That the restoration of herbaceous cover in large openings in the 

 subalpine timber type contributes to the control of surface run-off and 

 erosion from summer storms is shown by studies of the Intermountain 

 Forest and Kange Experiment Station 76 on two watershed areas of 

 about 10 acres each in the head of Ephraim Canyon, Utah. Alpine 

 fir, spruce, and brush occupy completely a few square rods of each 

 area; otherwise, the cover consists of herbaceous vegetation only. 

 In 1915, when the studies began, one area (B) was in reasonably good 

 condition, about 40 percent of its soil surface being covered largely 

 with perennial grasses and weeds. This cover was maintained during 

 the study period, through careful grazing management. The thin 

 vegetative stand, mainly of annuals, that was present on the other 

 area (A) in 1915 occupied only about 16 percent of the soil surface. 

 After being maintained in about that condition for 6 years the cover 

 on this area was improved, through protection from grazing and 

 through artificial reseeding, until about 40 per cent of the soil surface 

 was covered, chiefly with perennial grasses and weeds. 



By comparing the quantities of surface run-off and of sediment 

 removed from the two areas during the 6-year periods 1915-20 and 

 1924-29, as a ratio of results on A divided by those on B, it was found 

 that the increase in vegetative cover on area A had caused a reduction 

 of 64 percent in surface run-off from summer rains and a reduction of 

 54 percent in soil material removed in erosion by summer storms. 

 An even greater percentage reduction occurred in the difference be- 

 tween areas A and B in the two periods in respect to the surface run- 

 off and sediment removed per inch of summer rainfall. The actual 

 quantity of soil removed from area A was 133.8 cubic feet per year in 

 the 1915-20 period and only 19.2 cubic feet per year for the 1924-29 

 period. This decrease is not precisely representative of the results 

 of the increase in vegetative cover since the rainfall was lower in the 

 latter period than in the former. Since, in the three years of record, 

 summer storms carried off 85 percent of all the soil washed from 

 area A annually during the period when the cover was depleted, and 

 since summer storms are largely responsible for the destructive floods 

 in this locality, these reductions in summer run-off and quantity of 

 sediment carried by summer run-off indicate a definite influence of 

 plant cover in reducing danger of destructive floods from rains on such 

 mountain watersheds. 



76 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. Bui. 220, 1931. 



