THE ROLE OF ASPEN IN REFORESTATION 251 



aspen covered ar6as are the most favorable for artificial reforesta- 

 tion and that such areas will therefore yield the best returns from 

 a limited expenditure of funds. On the other hand, the fact that 

 these conifers sometimes reproduce themselves on burns not 

 covered by aspen, while in other instances they have failed to 

 reproduce on aspen covered areas, has given rise to the opinion 

 that the occurrence of conifers under aspen is merely a coincidence, 

 due to a similarity of soil requirements. The idea has even been 

 advanced that aspen through its shade, root competition and leaf 

 litter hinders coniferous reproduction. 



The effect of an aspen cover upon the establishment of Douglas 

 fir has been under investigation at the Fort Valley Experiment 

 Station since 1911. Both planting and direct seeding have been 

 attempted in typical aspen thickets and adjoining openings. Due 

 mainly to the activity of rodents in destroying the seed, the sowings 

 have yielded negative results and, therefore, this article will deal 

 only with the results of planting. 



The area selected for this experiment occupies a level bench on 

 the south slope of the San Francisco Mountains at an altitude of 

 8700 feet. No bed rock occurs near the surface but huge granite 

 boulders lying on the surface or partially imbedded in the soil are 

 much in evidence. The soil is a sandy to gravelly loam of gi-anitie 

 origin. Unlike the soil found in the lower altitudes of this region, 

 it is fairly rich in humus. 



A summary of meteorological records for the growing season, 

 May 1-September 30, of the past three years follows: mean air 

 temperature 11.5°C. (52.7° F.); mean soil temperature at a depth 

 of 60 cm., 9.5°C. (49.1° F.); total precipitation 27.7 cm. (10.9 

 inches); total evaporation 39.9 cm. (15.7 inches); mean daily 

 wind movement 58.4 kilom. (36.2 miles). The total annual pre- 

 cipitation is about 75 cm. (30 inches), of which approximately 

 one-half comes in the form of snow. The early-summer dry sea- 

 son, while less prolonged than in the lower altitudes, is the crit- 

 ical period for the establishment of young plants. Practically no 

 rain falls from April 15 to July 15. Moisture is undoubtedly 

 the most important factor in determining the presence or absence 

 of ditTerent types of vegetation. 



