Timber Cutting and Water Yields 



599 



tect the soil. Other similar sets of plots 

 were left with reserve stands of 2,000, 

 and 4,000, and 6,000 board feet of 

 merchantable timber an acre, so that 

 a considerable variety in remaining 

 canopy densities was provided. It 

 should be emphasized that even the 

 heaviest cutting by no means cleared 

 off the plots. On the average, each 

 acre still contained 147 trees in the 

 diameter range between S 1 /? and 9/j 

 inches, as well as a number of still 

 smaller trees and a little underbrush. 



After the plots were cut over, fur- 

 ther records were obtained on all of 

 the water-yield factors until 1944, 

 when the study was temporarily dis- 

 continued. In addition to these quan- 

 titative data, observations have been 

 made each year since 1940 to deter- 

 mine whether the different cuttings 

 had damaged the plots appreciably, 

 whether erosion was beginning, and 

 how rapidly the plots were becoming 

 covered again with conifer reproduc- 

 tion and other vegetation. 



The results of all this detailed rec- 

 ord-taking showed a decided increase 

 in the amount of the water available 

 for stream flow as a result of the timber 

 cutting. Out of a total precipitation 

 of about 24/ 2 inches a year, about 32 

 percent was absorbed by canopy inter- 

 ception in the uncut stand, as com- 

 pared to only 11 percent in the most 

 heavily cut-over plots. This smaller 

 amount of interception was, of course, 

 caused by trees smaller than 9/j inches 

 in diameter. 



Additional losses due to other forms 

 of evaporation and to transpiration 

 averaged about 26 percent of the total 

 precipitation on the uncut plots and 

 about 34 percent on the heavily cut- 

 over areas. When all forms of water 

 consumption were combined, the re- 

 mainder was only about 10/j inches 

 of water available for stream flow 

 under virgin-forest conditions as com- 

 pared to about 13/2 inches as a result 

 of the heavy cutting. Thus the severe 

 opening of the forest increased the 

 amount of available water a full 30 

 percent as compared to uncut condi- 



tions. To back up those results, the 

 other timber-cutting treatments fell in 

 line between the two extremes : For the 

 light, moderate, and the dense reserve 

 stands the amounts of water available 

 for stream flow were 11/s, 12/3, and 

 about 12^2 inches. 



Such gains are definitely worth 

 while. In round terms, they mean that 

 removing merchantable timber on each 

 4 to 5 acres of high-altitude watershed 

 land should make it possible to irri- 

 gate another acre of valuable land in 

 the valleys below. Not only that, but it 

 will increase the capital value of the 

 watershed land itself through a treat- 

 ment which ordinarily pays for itself 

 and almost always gives a profit to the 

 landowner and the timber operator; 

 and it will supply wood products to 

 western people. 



That is true, of course, only if the 

 treatment does not do damage to the 

 land by starting an accelerating cycle 

 of erosion and land depletion. Under 

 the climatic conditions of the high 

 mountain areas this is not likely to oc- 

 cur and is certainly not indicated by 

 observations made since the plots were 

 cut over. As in the Wagon Wheel Gap 

 study, the only traces of erosion up to 

 1947 were small gullies cut in skid roads 

 and trails that contribute insignificant 

 quantities of sediment to the streams. 

 Except in those places, almost no bare 

 soil is exposed, and a new stand of 

 conifer reproduction is slowly begin- 

 ning to occupy areas opened on the 

 plots; in some places aspen is beginning 

 to come in. 



SIMILAR INCREASES in the available 

 water have shown up in other experi- 

 ments, in which snow storage and rain- 

 fall were studied in stands of young 

 lodgepole pine, aspen, and open areas. 

 The last of these, several acres in extent 

 and somewhat exposed to wind, stored 

 a little less snow than was found in 

 leafless aspen stands, but the smallest 

 amounts were found under the dense 

 cover of pine. Snow storage and rain 

 penetration in the young pine forest 

 have been substantially increased by 



