NORTHERN SPRUCE TYPE 

 COMPOSITION OF SUBTYPES — SPRUCE TYPE 



The virgin subtype varies considerably in composition with the 

 altitude. At the upper edge of merchantable growth there is a 

 large admixture of balsam, while at the lower edge where it 

 merges into the hardwood type yellow birch and paper birch are 

 the important associate species. The composition percentages 

 given above are most representative of conditions in the middle 

 of the altitudinal range of the type. There spruce is the dom- 

 inant species, numerically and in volume, while balsam, paper 

 birch and yellow bir^h are merely unimportant associates. An 

 average stand is loM feet B. M. per acre although stands of 

 20 or 30M are not uncommon. In the virgin subtype little 

 damage is the rule, not because there are no serious enemies but 

 for the reason that fire, insects and wind may wipe the subtype 

 out, but they seldom affect it in a moderate degree. It is a case 

 of total immunity or complete destruction. When the subtype 

 is dry enough to burn the fire usually kills the young trees, 

 jumps to the crowns of the older timber, and also eats up the 

 shallow layer of soil. In the same way wind makes wide swaths 

 or throws over the timber on entire mountain slopes if it once 

 gets a leverage on a stand of spruce. Likewise, the great 

 insect enemy of this species, the spruce beetle {Dendroctonus 

 piceaperda) is a believer in no halfway measures. Working in 

 large colonies it systematically kills all the timber that comes 

 in its way. Fortunately little fungus damage occurs in this 

 subtype. 



The culled, cutover and burned subtypes are the result of 



