Packer (1963) prescribed ground cover densities of at least 70 percent and soil 

 bulk densities no greater than 1.04 g./cc. as necessary to maintain soil stability on 

 the Gallatin elk winter range in south-central Montana. 



Using a rainfall simulator on a subalpine cattle range in central Utah, Meeuv-zig 

 (1965) found that soil erosion was more closely correlated with the proportion of soil 

 surface protected from direct raindrop impact by plants, litter, and stone than any 

 other measured variable. However, this relation between protective cover and soil ero- 

 sion is strongly influenced by soil bulk density; the influence of cover is greatest at 

 high bulk density and is least at low bulk density. If protective cover exceeds 85 per- 

 cent, the amount of soil eroded is small, irrespective of bulk density. 



The results of a study on the sheet erosional behavior of seven diverse summer 

 range sites in Idaho, Montana, and Utah are presented in the following sections of this 

 paper. This study was designed to augment the previously reported studies and to pro- 

 vide means for predicting sheet erosion potential under a variety of slope, soil, and 

 cover conditions. Soil eroded from small plots (20 by 30.5 inches, or about 0.1 milacre 

 in size) under simulated high-intensity rain was measured and related to slope gradient, 

 weight and areal cover of vegetation and litter, and several soil properties. 



STUDY AREAS 



The study areas are located on middle-to-high-elevation herbaceous rangelands 

 (fig. 1). All such areas are grazed by livestock during the summer except Area 2 on 

 the Davis County Experimental Watershed from which grazing has been excluded for more 

 than 30 years. Following are details of each area: 



1. Great Basin Experimental Area (GBEA) , Manti-LaSal National Forest, central 

 Utah. This is sheep range with a wide variety of grass and forb species. Soils are 

 mostly silty clay loams and clay loams derived from sedimentary rock, predominantly 

 limestone but containing some shale and sandstone. Elevations of study plots ranged 

 from 7,000 to 10,000 feet; most were about 9,000 feet. 



2. Davis County Experimental Watershed (DCEW) , Wasatch National Forest, northern 

 Utah. This area was the source of serious floods during the period 1923 to 1933. Much 

 of this watershed was contour trenched and seeded to grass during the period 1933 

 through 1936. Grazing has been excluded since 1933. Soils are mostly silt loam and 

 loam. Parent materials vary from metamorphic gneisses and schists to conglomerates, 

 sandstone, and shales. Elevations of study plots were between 8,000 and 9,000 feet. 



3. Vigilante Experimental Range and Monument Ridge in the Gravelly Range, Beaver- 

 head National Forest, southwestern Montana. This is cattle and sheep range dominated 



by Idaho fescue (Festuca idahoensis) in many parts and by native forbs or seeded grasses 

 such as crested wheatgrass (Agropyron desertorum) in others. Soils are mostly silt loam 

 and silty clay loam derived from red shales, siltstone-shales , and glacial till. Eleva- 

 tions of study plots were between 7,000 and 9,500 feet. 



4. Diamond Mountain Cattle Allotment near Flaming Gorge, Ashley National Forest, 

 eastern Utah. This is an experimental grazing area where much of the native sagebrush- 

 grass vegetation has been replaced with introduced grass species. Soils are loams and 

 sandy loams derived from sedimentary rocks. Plots were at about 8,000 feet. 



5. Basalt range north of Seven-Devils, Nezperce National Forest, central Idaho. 

 Study plots in this area were located in grassy openings in open ponderosa pine stands. 

 Soils are loams and silt loams derived from basalt. Most plots were near 5,000 feet. 



2 



