A NATIONAL PLAN FOR AMERICAN FORESTRY 675 



been made, and for the development of improved strains, and per- 

 haps hybrids, etc., on which nothing has been done. 



FOREST AND RANGE INFLUENCES 



The limited number of attacks on the erosion-stream-flow problem 

 on forest and range lands in the United States, initiated prior to the 

 last decade, dealt with watersheds or duplicate watersheds as a 

 whole, whether forested or range covered. Valuable information 

 was obtained, but much that was necessary to a real understanding 

 of the role of vegetative cover, forest and otherwise, in erosion con- 

 trol and stream-flow regulation remained very obscure because of 

 offsetting factors. 



The present attack is in a few regions breaking this complex prob- 

 lem down into its constituent factors, such as the influence of the 

 kind of cover (i.e., whether forest, chaparral, brush, or grass, or 

 combinations of them), of the density of cover, of litter, of the char- 

 acter and rate of precipitation, of the degree of slope, or the kind of 

 soil, or the requirements of transpiration, and is investigating each 

 factor separately. Despite the fact that the latter phase of the work 

 is only 2 or 3 years old, it is already giving extremely significant 

 results, some of which go far beyond what foresters have ever dared 

 to claim. The work on individual factors ought soon to lead to far 

 more productive attacks on small and later on large watersheds than 

 have heretofore been possible. Incidentally there is already specific 

 reason to believe that detailed, exact measurements giving concrete 

 results of the kind which the engineer is trained in and regularly 

 deals with, such as are now coming out of the erosion-stream-flow 

 work, may help materially to bridge the gap which has existed 

 between the points of view of engineers and foresters on the forest- 

 erosion-stream-flow relationship. 



The Forest Service has done nothing on wind erosion and dune 

 movement; relatively little on the relationships between forests and 

 snow; has made some progress on purely local influences of shelter- 

 belts in the plains region; and is only beginning to study the pos- 

 sibility of a general amelioration of climatic conditions over large 

 areas. 



Possibly one of the most valuable results of our erosion-stream-flow 

 research is that while details are obscure or unknown, it has helped 

 to give to us and to the profession a new and far better appreciation 

 of the probable role of forest and brush and grass, or of the natural 

 vegetative cover, on the whole erosion-stream-flow relationship. It 

 has given a better appreciation of what forest and range deteriora- 

 tion or destruction probably mean in destructive floods, silted stream- 

 beds and reservoirs, buried agricultural lands, water in the least 

 usable forms for irrigation, and in reduced productivity of forest and 

 range lands. It has helped to bring out the fact that water may in 

 many instances already, and in many more instances in the future 

 probably will be, the most valuable product of forest and range lands 

 and that every other form of use must be regulated to this end. It 

 has made us realize that this aspect of the forest and range problems 

 in the United States is one of the most important with which we 

 shall have to deal in future managment, and that it is even more 

 important in the formulation of land policies in the broadest sense 

 of the word. 



