216 



WOOD AND FOREST. 



In general, cold affects the forest just as poor soil and drought do, 

 simplifying its composition and stunting its growth. In Canada there 

 are only a few kinds of trees, of which the hardwoods are stunted ; 

 south of the Great Lakes, there is a great variety of large trees; 

 farther south in the southern Appalachian region, there is a still 

 greater variety, and the trees are just as large ; and still farther south 



in tropical Florida, there is 

 the greatest variety of all. 

 The slopes of a high moun- 

 tain furnish an illustration 

 of the effect of temperature. 

 In ascending it, one may 

 pass from a tropical forest 

 at the base, thru a belt 

 of evergreen, broad-leaved 

 trees, then thru a belt of de- 

 ciduous broad-leaved trees, 

 then thru a belt of conifers 

 and up to the timber line 

 where tree life ceases. Figs. 

 61, and 62. 



LIGHT. 



More than by any other 

 factor, the growth of trees 

 in a forest is determined by 

 the effect of light. All 

 trees need light sooner or 

 later, but some trees have 

 much more ability than 



others to grow in the shade when young. Such trees, of which maple 

 and spruce are examples, are called tolerant, while others, for in- 

 stance, larch, which will endure only a comparatively thin cover or 

 none at all, are called intolerant. The leaves of to^rant trees endure 

 shade well, so that their inner and lower leaves flourish under the 

 shadow of their upper and outer leaves, with the result that the whole 

 tree, as beech and maple, makes a dense shadow; whereas the leaves 

 of intolerant trees are either sparse, as in the larch, or are so hung 

 that the light sifts thru them, as in poplar and oak. The spruces and 



Fig-. 60. Northern Forest, Young- Spruce 



Growing- Under Yellow Birch. Santa Clara, 



New York. U. S. Forest Service. 



