CHAPTER Xm 

 SILVER PINE TYPE 



General Conditions. — This is a well developed but restricted 

 type confined to northwestern Montana, northern Idaho and 

 northeastern Washington. Even within this area it is not found 

 thruout but merely on the lower slopes of the mountains. It does 

 not reach the upper slopes nor descend into the vaUeys but occurs 

 abundantly only between elevations of 3000 and 6000 feet above 

 sea level. This does not, of course, mean that the dominant 

 species, silver pine (Pinus monticola,) is not found above or 

 below these elevations. As a matter of fact it descends to sea 

 level at the Straits of Fuca and attains an elevation of 10,000 feet 

 in the Sierras. But the type is not of commercial importance 

 except in the region referred to above. 



Climate seems to be the controlling factor in the distribution 

 of this type. In general it is moderately cool and moist. To be 

 specific, the total annual precipitation does not exceed 40 inches, 

 the mean annual temperature is about 45° F., and only five 

 months have average temperatures above 32° F. The type is 

 probably restricted from extending to lower elevations because 

 the precipitation is less in the semi-arid vaUeys while its upper 

 limit seems to be determined by the length of the growing 

 season. 



The topography of the lower slopes upon which the type is 

 foimd is characteristically gentle. The type does not reach up 

 on to the upper slopes. Hence the soil is deep and alluvial in 

 character being derived mainly from the wash of the slopes above. 



While silver pine is the most abundant species and the most 

 important commercially, red cedar (Thuya occidentalis) and hem- 

 lock (Tsuga occidentalis) are also found in the type. They 

 always occupy a subordinate position, however. Both are tol- 

 erant enough to grow well under the silver pine and mixed stands 



