37 



Above the yellow pine zone, fires, except in the drier portions of 

 this region, are usually followed by dense, pure stands of aspen, 

 which often cover whole watersheds with an even- aged forest of light- 

 foliaged trees. In the shade of aspen thickets Douglas fir, together 

 with Avhite fir and, at high altitudes, alpine fir and Engelmann spruce, 

 finds excellent conditions for reproduction. In the lower part of the 

 spruce belt a thrifty but slow-growing reproduction of Engelmann 

 spruce, alpine fir, and Douglas fir may often be found under aspen 

 cover on old burns. On account of its rapid growth, aspen only a 

 year or two older than the coniferous reproduction may be ten times 

 as high, and the more tardy spruce and firs may receive the benefit of 

 its shade until they are 50 feet tall and as many years old. From 

 that time on the aspen ceases to be a factor in the forest. As a rule, 

 therefore, aspen is not to be considered a forest weed, and its value 

 as a nurse crop for the future stand should not be underestimated. 

 Owing to the optimum conditions which aspen stands, when not too 

 dense, offer for the development of Douglas fir, they are to be rec- 

 ommended as planting sites for this species, especially on southerly 

 slopes and in regions characterized by extremes of temperature. 



CONCLUSIONS. 



A careful study of Douglas fir leaves no doubt that, at least from 

 a silvicultural point of view, there are two forms of Douglas fir, one 

 of which inhabits the region between the Cascades and Sierra Nevada 

 and the coast, while the other grows throughout the Rocky Mountain 

 region. Proof of this variation is to be found in the results of exten- 

 sive cultural experiments in Germany, France, and England, in 

 morphological differences in the fir throughout its range, and 

 especially in the varying silvical requirements of the species and the 

 immensely different conditions of environment to which it is subjected 

 in different regions. The actual relationship between the two forms 

 is probably that of climatic varieties, although some authorities con- 

 sider them distinct species and others botanical varieties. 



As a general rule, subject to local modification, Douglas fir is best 

 managed in w^estern Washing-ton and Oregon by clean cutting and 

 surface burning, and in the norHiern and central Eocky Moun- 

 tains by selection cutting with brush piling and burning. In Cali- 

 fornia and in the southern Rocky Mountains it is neither the most 

 nor the least valuable tree, and should be discriminated against in 

 the yellow pine zone and favored in competition with other species. 

 Its hardiness and the high value of its timber render it especially 

 fitted for planting, particularly in mining regions. Excellent condi- 

 tions for planting are to be found under the light shade of aspen 

 stands, particularly in the southern Rockies. 



[Cir. 150] 



