598 



Yearbook^ of Agriculture 1949 



silvicultural method, it is not so com- 

 monly usable in watershed manage- 

 ment as some other methods, such as 

 selection cutting. In this way, though, 

 the Wagon Wheel Gap studies were 

 similar to the other watershed research 

 that has been conducted. 



Until quite recently there has been 

 a singular dearth of studies employing 

 practical silvicultural methods; only 

 two seem to need mention here. 



In California, Dr. Joseph Kittredge 

 made a number of experiments to find 

 out various aspects of forest influences. 

 Using those experiments as a back- 

 ground, as early as 1936 he set up 

 what may be considered a first-class 

 objective of watershed management in 

 areas where water shortages exist : "To 

 select species of minimum foliage vol- 

 ume and transpiration and to main- 

 tain them by forest management at 

 minimum sizes and densities compati- 

 ble with protection of the soil." 



In Idaho, Charles A. Connaughton 

 examined the accumulation and melt- 

 ing of snow as they were affected by 

 mature ponderosa pine, with and with- 

 out an understory of young trees or 

 reproduction; by reproduction stands 

 alone; and by open land, with and 

 without a cover of sagebrush. Taking 

 the open areas without sagebrush as 

 100 percent, he found the following 

 relative amounts of snow stored in the 

 other cover types at the time of greatest 

 snow accumulation in the spring: 

 Sagebrush, 100.9 percent; pine repro- 

 duction, 94.6 percent; virgin pine 

 without reproduction, 75.5 percent; 

 and virgin pine with reproduction, 

 70.2 percent. The last snow disap- 

 peared almost simultaneously on open 

 and brush-covered areas, about 3/> 

 days later in the virgin forest without 

 reproduction, and about 8 days later 

 in the stand of reproduction alone and 

 where it occurred under virgin timber. 



Although this did not give quanti- 

 tative data on factors other than snow, 

 it did demonstrate how forest and 

 other vegetation with different kinds 

 of crown and densities of canopy af- 

 fected interception and shading and 



therefore the storage and melting of 

 snow. 



It was not until Mr. Connaughton 

 moved to Colorado in 1936 that ex- 

 periments were finally started to show 

 how selective timber cutting of high- 

 altitude conifers would influence all of 

 the more important factors associated 

 with water yields. In conjunction with 

 the Division of Timber Management 

 Research, the Division of Forest In- 

 fluences in the Rocky Mountain For- 

 est and Range Experiment Station 

 began a series of studies with this ob- 

 jective in 1938. They consisted of 20 

 harvest-cutting plots located in a for- 

 est of mature lodgepole pine, covering 

 a small, rugged drainage basin in the 

 headwaters of the Colorado River near 

 Fraser, Colo. The timber on the plots 

 ranged in merchantable volume (in- 

 cluding only trees larger than 9/2 

 inches in diameter) from 7,600 board 

 feet an acre to about 17,000 board 

 feet, and averaged 11,900 board feet. 



One of the primary objects of those 

 plot experiments was to learn how 

 timber cutting by selection methods 

 affects the growth and reproduction 

 of this type of forest. Along with the 

 studies, however, detailed records were 

 collected on a series of important fac- 

 tors involved in water production: 

 The storage and melting of snow, the 

 amounts of net precipitation reaching 

 the snow or ground under the forest 

 canopy, and the relative dryness of the 

 soil under the forest at the end of each 

 summer's growing period, when tran- 

 spiration and evaporation had finished 

 drawing out soil moisture. 



The records were first collected in 

 1938 and 1939, before any timber cut- 

 ting was done on the plots, to show 

 how the various factors behaved under 

 a virgin forest. Then 16 of the plots 

 were cut over in 1940 by selection 

 methods, so as to leave stands of sev- 

 eral different densities, and 4 of them 

 were left uncut as a check. On another 

 set of 4, all of the merchantable timber 

 was removed so that only trees smaller 

 than 10 inches in diameter remained 

 to provide a partial cover and help pro- 



