A NATIONAL PLAN FOR AMERICAN FORESTRY 449 



EROSION 



As these flood situations indicate, in the Great Basin erosion of 

 mountain and foothill slopes is intimately related to flood destructive- 

 ness. Some floods are so heavily charged with erosion debris that 

 they become mud-rock flows. Doubtless the most serious phase of 

 this erosion, however, is soil wastage from slopes. Close observation 

 of soil conditions on the Wasatch Plateau in central Utah indicates 

 that in large areas of open grassland in the forest, 6 inches or more of 

 the fertile topsoil has been lost through sheet erosion. Observations 

 by the Forest Service show that in the juniper-sagebrush type along 

 the edges of the Toyabe National Forest, Nev., on private land, on 

 the public domain, and to some extent on national-forest land, con- 

 siderable areas are cut with shoestring or larger gullies, accompanied 

 by sheet erosion. In Keese River Valley, also, there are gullies 2 or 3 

 feet to 8 or 10 feet deep in this type. Another area a few miles north 

 of Elko shows considerable surface erosion and some gully erosion. 

 On most of the forest area in the Great Basin erosion has not gone so 

 far but that it can undoubtedly be checked by restoring the vegetative 

 cover. 



While abnormal erosion has been severe in all forest types in the 

 Great Basin, preliminary surveys by the Forest Service show that it 

 is most serious in the pinon-juniper type, which occupies two thirds 

 or more of the basin. This type is largely characterized by orchard- 

 like stands of pinon and juniper, scattered oak and other brush, and 

 herbaceous growth. The pinon-juniper type occupies the lower, drier 

 foothills and mountains, where the annual rainfall ordinarily totals 

 only 12 to 16 inches, part of which may come in occasional semitor- 

 rential rains. At best the vegetation is scant and little litter accu- 

 mulates. On large parts of the area, particularly in the public domain, 

 even this scant stand has been reduced one half or more. Sheet and 

 gully erosion occurs almost throughout the pinon-juniper type, 

 although within the national forests the vegetative cover in this type 

 has shown on the whole a slow but steady improvement and the 

 excessive loss of soil is being checked. 



The loss of soil productivity through erosion is shown by studies of 

 the Intermountain Forest and Range Experiment Station of soils from 

 openings of the subalpine timber type in Ephraim Canyon. The 

 growth of many-flowered bromegrass and of wheatgrass was more 

 than twice as great and that of peas more than eight times as great 

 on noneroded as on eroded soils. Furthermore, eroded soils used 38, 

 23, and 80 percent more water for each pound of growth in brome- 

 grass, wheatgrass, and peas, respectively, than did the noneroded soils. 



WATERSHED-PROTECTION REQUIREMENTS 



The 19^ million acres of forested land within the Great Basin has 

 been classified according to watershed-protection influence as approxi- 

 mately 5/ million acres of major influence, 12 million acres of moderate 

 influence, and 2 million acres of slight influence. ^ (See fig. 13.) 

 Those lands classified as of major influence are chiefly mountain 

 forested areas, the water from which is in great demand or on which, 

 if their cover becomes depleted, destructive floods may originate, and 

 foothill or low mountain areas, chiefly woodland, having readily 

 erosible soils, the erosion of which might seriously endanger irrigation 



