A NATIONAL PLAN FOR AMERICAN FORESTRY 



451 



FOREST TYPES AND THEIR WATERSHED-PROTECTION VALUES 



Of the 204,873 square miles in the basin 92,226 square miles 

 (approximately 59,025,000 acres), or 45 percent, is forest land, located 

 principally in the rougher mountain country. This forest land sup- 

 ports some of the most valuable timber in the West. 



Near the point where the Columbia River passes through the 

 Cascade Range the Pacific Coast Douglas fir type occurs, forming a 

 dense stand of large trees with heavy undergrowth and litter. Where 

 uncut and unburned it serves unusually well in controlling run-off 

 of the heavy precipitation which occurs in that part of the drainage, 

 often totaling 80 inches a year. Chinook winds in winter sometimes 



FIGURE 14. Columbia River Basin and Pacific Cascade drainages. 



cause such rapid melting of snow as to bring about floods of short 

 duration. After fires the land is likely to reclothe quickly with a new 

 growth of timber reproduction or of shrubs and herbaceous vegetation 

 that is effective in preventing erosion and, at least moderately, in 

 slowing down run-off. The Douglas fir areas have been classified 

 as of major watershed-protection influence. 



On areas of lower precipitation throughout the basin, at the lower 

 fringe of the timber, the main tree cover is scattered ponderosa pine 

 or juniper. The trees ordinarily do not form a closed canopy. Litter 

 is scant. Here precipitation usually averages about 15 to 25 inches a 

 year, with a dry summer period. Run-off from these forests is not 

 particularly large or rapid except in occasional instances when snows 

 melt rapidly or semitorrential rains fall. In these open forest stands 

 the principal erosion-control influence is the undergrowth of herbs 

 and shrubs. On large areas the perennial herbaceous vegetation has 



