372 



GENERAL BOTANY 



Rockies, and the North Pacific coast. The red, white, and black 

 spruces are found mainly in the northeastern and Appalachian 

 forests ; the Engelmann spruce has its home in the Rocky Moun- 

 tains; while the Sitka spruce, so important in the construction 

 of aeroplanes in the World War, is found exclusively on the 



Pacific coast. The hab- 

 itat of the spruces is 

 thus confined largely 

 to well-drained up- 

 lands or to mountain 

 slopes. Like many 

 other plants, spruces 

 are often found to be 

 occupying situations 

 to which they are not 

 perfectly adapted, in- 

 cluding marshes and 

 swamps, on account 

 of the lack of compe- 

 tition in these habitats 

 with the more highly 

 organized hard woods, 

 such as the oak and 

 maple. 



Tolerance. An im- 

 portant factor in the 

 distribution and suc- 

 cess of the spruces 

 is due to the light 



requirement of the different species, especially in the younger 

 stages of growth. They belong to the so-called tolerant trees, 

 which have the power to grow, while young, in the shade of 

 other trees (Fig. 225). " Having once gained a foothold in a 

 selection forest, the young spruce grips life tenaciously, strug- 

 gles along for many years under the shade of the forest, and 

 gradually forces its way upward as natural thinning reduces the 

 number of its overtopping competitors." Balsam is often found 



FIG. 225. Virgin stand of red spruce with repro- 

 duction of tolerant spruce and fir in the White 



Mountains, New Hampshire 

 Photograph by the United States Forest Service 



