A NATIONAL PLAN FOR AMERICAN FORESTRY 



431 



The mountain brushland type, prevailing mainly on slopes at eleva- 

 tions below those supporting good stands of ponderosa pine, covers 

 more than one fifth of the forest area. In this type oak brush is the 

 most common species. 



Practically throughout the basin, the coniferous, aspen-brush, and 

 mountain brushland types have been classed as of major watershed 

 protective influence. By retarding snow melt, and by facilitating 

 the absorption of snow and rain water into the soil, they reduce the 



RELATIVE INFLUENCE OF FORESTS 

 ON WATERSHEDS 



MAJOR INFLUENCE: 

 MODERATE: INFLUENCE 

 '''/''//\ SLIGHT INFLUENCE 



ARKANSAS -RED RIVE* 

 DRAINAGES 



FIGURE 12. Colorado River Basin and portion of upper Rio Grande Basin. 



crests of floods resulting from snow run-off, aid in maintaining a 

 sustained flow of water in springs and streams, and protect the soil 

 against abnormal erosion. These functions are especially important 

 on steep, rugged mountain slopes having a normally scant soil layer 

 or soils of sedimentary origin and having an average annual pre- 

 cipitation of about 20 inches to 35 inches or more, much of which 

 comes as winter snow and tends to run off rapidly in the spring unless 

 the slopes are well protected with vegetation. Where these forest 

 types occur on undulating or level plateau areas from which run-off 

 normally is not rapid and on soils derived from lava or basalt that 



