INTERIOR FORESTS 141 



At the southwestern end of Alaska the following diameters were 

 attained in 100 years' growth: 



Inches 



Sitka spruce 18 



Red cedar 18 



Farther north the growth would, of course, be slower because 

 of the shorter growing season so that the average for the t)^e 

 would be comparable to growth conditions in the spruce type of 

 the northeastern United States where the yield per acre in 100 

 years is 15M board feet. 



Interior Forests. — The- composition of the forests in the Yukon 

 and Kuskokwim River valley basins has already been referred 

 to above. All the species are specially adapted to cold, dry 

 climates. White spruce, Picea canadensis, is the most abundant 

 and the most important commercially. It is the only species 

 that is suitable for even small saw timber and also shares with 

 the other species the burden of supplying the firewood needs. 

 Birch and cottonwood are, however, considered better for this 

 latter purpose. 



With the variation in soil conditions there is a corresponding 

 variation in the composition of the stands. In the deep soiled 

 bottomlands along the streams pure stands of white spruce some- 

 times occur but a mixture of this species with cottonwood and 

 birch is more common. On the slopes immediately above the 

 stream bottoms the same mixture prevails but the indi\ddual 

 trees are distinctly smaller and less vigorous. On the ridges tree 

 growth is scattered and stunted and generally confined to the 

 depressions. On such poorly drained sites black spruce is the 

 common species. 



Growth is slow even in the bottoms. The following data are 

 taken from Kellogg 's " The Forests of Alaska ": * 



Forest Service Bull. 81, " The Forests of Alaska," R. S, Kellogg, 1910. 



