6oo 



YearbooJ^ of Agriculture 1949 



thinning the stands, though enough 

 trees were left to provide a future for- 

 est and to give partial shade and soil 

 protection. 



Still further studies have been started 

 more recently in the spruce-fir forest 

 type, which occupies watershed lands 

 even higher in altitude than lodgepole 

 pine, reaching on up to timber line. 

 While these experiments are only well 

 under way, the preliminary results are 

 similar in trend to those obtained in 

 lodgepole pine. 



These influences, you may say, have 

 been observed only on plots up to this 

 time; perhaps things are different on 

 a watershed. In order to test this possi- 

 bility, small watersheds have been 

 placed under experimental control at 

 the Fraser Experimental Forest and 

 elsewhere in the Colorado Rockies, 

 with plans for treating one watershed 

 at each place by desirable silvicultural 

 methods. The results of these tests will 

 not be available for several years. 



In the meantime, however, the plot 

 findings are fairly well supported by 

 the Wagon Wheel Gap results and by 

 detailed observations of soil conditions 

 and erosion after timber cutting at a 

 number of places in the high Rockies 

 of Colorado and southern Wyoming. 

 At every cut-over area visited, whether 

 recent or old, cutting in lodgepole pine 

 and in the spruce-fir type has not 

 caused any serious degree of erosion or 

 site deterioration. 



Finally, although their application 

 may be quite different, the same gen- 

 eral influences of timber cutting on 

 water yields seem to apply to regions 

 other than the western mountains. In 

 watershed studies in the southern Ap- 

 palachian Mountains, C. R. Hursh 

 and M. D. Hoover found substantial 

 increases in total water yields follow- 

 ing the removal of a hardwood forest. 

 When all of the woody vegetation was 

 cut and laid on the ground to protect 

 the soil and reduce evaporation, an- 

 nual yields were increased about 17 

 inches. Worth while increases in sum- 

 mer flow were also found to result from 

 cutting only the vegetation on narrow 



strips close to the stream channels, 

 leaving the other watershed vegetation 

 intact. 



WlTH THE RESEARCH INFORMATION 



gained up to now, we cannot supply 

 all of the necessary answers to ques- 

 tions that the watershed forester must 

 ask as he plans the management of 

 water-producing land. Detailed studies 

 still have to be made under a variety 

 of conditions to show how the prin- 

 ciples now at hand need to be altered 

 to meet local problems. But we do have 

 a set of basic principles on which sound 

 but preliminary watershed-manage- 

 ment plans can be established : 



1. Forest vegetation, like all other 

 plants, consumes water in considerable 

 quantities through interception, tran- 

 spiration, and evaporation. 



2. Removing a part or all of the 

 forest cover by timber cutting should 

 reduce this water consumption, thus 

 making more water available for total 

 yields. 



3. Such thinning or opening of the 

 forest is likely to result in some site 

 deterioration, though it may be minor 

 in degree. But this point calls for cau- 

 tion and careful observation by the 

 manager as he works with his forest. 



4. If site and soil deterioration are 

 sufficient to cause rainfall excesses (in- 

 cluding excesses in water from melting 

 snow) in any substantial amount, the 

 resulting overland flow, passing over 

 inadequately protected soil, will almost 

 always cause soil erosion and flashy, 

 silt-laden floods. This will cause fur- 

 ther site deterioration and the reduc- 

 tion of soil storage and infiltration 

 capacities. With more water running 

 off over the watershed surface, less will 

 get into underground storage and the 

 ground-water table, and, as a result, 

 summer flow of streams will likely be 

 lowered and springs will dry up. To- 

 gether with flashy spring freshets and 

 summer floods, this will mean a com- 

 plete change of stream habits entirely 

 for the worse. 



5. If, on the other hand, no dam- 

 aging rainfall excess results from tim- 



