15 



slope of the Cascades, Douglas fir grows largest and densest, though 

 it is often outnumbered in tlie forest by western hemlock, arborvita?, 

 and Sitka spruce. Here the annual rainfall is from GO to more than 

 100 inches, three-fourths of which falls in the "wet season," from 

 November to April, inclusive. 



In western Oregon Douglas fir forms nearl}^ 80 per cent of the 

 forest, and its principal associates are usually Sitka spruce close to 

 the coast and giant arborvita? and western hemlock farther inland. 

 On the coast of southern Oregon and northern California Douglas 

 fir is mixed with Port Orford cedar and redwood. 



An average stand of Douglas fir in this region is from 35,000 to 

 60,000 feet per acre, and stands have been found occasionally which 

 would run from 150,000 to 250,000 feet per acre. South of Crater 

 Lake, in Oregon, the forest form of this region gradually passes over 

 into that of the Sierra region. 



SIERRA REGION. 



The Sierra region includes the range of Douglas fir in the Sierra 

 Nevada, the southern extremity of the Cascades, and parts of the 

 cross ranges of southern Oregon. It is characterized by, the preva- 

 lence of sugar and yellow pines, incense cedar, and white fir mixed 

 in varying proportions with Douglas fir. Large pure Douglas fir 

 stands are rare in this region, and the drier conditions in which the 

 tree grows, as compared with its range farther north, make the 

 forest more open than in the north coast type. In these forests 

 Douglas fir is secondary in commercial importance to the i^ines. 

 In the northern and western portions of this region the forest grades 

 into that of the north coast region. Near the southern extremity 

 bigtree forms an important part of the forest. South of the range of 

 Douglas fir in California it is represented by another species of the 

 same genus, bigcone spruce, which closely resembles it in form but 

 not in silvical characteristics. 



In this region Douglas fir finds a mild, humid climate w^ith moder- 

 ate daily and seasonal ranges of temperature. The growing season 

 is long. There is usuall}^ a rainy and a dry season, the latter of about 

 three months' duration, from July to September. The annual rain- 

 fall varies between 20 and GO inches. In this climate Douglas fir 

 grows rapidly in protected situations, and attains a size nearly equal 

 to that of the north Coast fir. 



NORTHERX ROCKY MOUXTAIX REGIOX. 



The northern Rocky Mountain region includes part of southern 

 British Columbia, northeastern Washington, northern Idaho, and 

 northwestern Montana. In its relatively humid climate, as compared 



[Cir. 150] 



