14 PRINCIPLES OF AMERICAN FORESTRY. 



It is known that some trees will do very well in the shade 

 of other trees. This gives a chance to grow trees in a sort 

 of two-storied fashion, having the land nearly covered with 

 the foliage of one set of trees which require the full exposure 

 to sunlight, and underneath, the land covered with the 

 foliage of trees which will endure the shade of those above 

 them, just as pumpkins can be grown under corn. On 

 account of this peculiarity of trees, foresters have divided 

 them into two classes, one of which is called light-demand- 

 ing and the other shade-enduring. The words tolerant and 

 intolerant are also used as distinguishing the peculiarity of 

 trees in this respect, and they are perhaps better terms. 

 Trees that are known as tolerant generally have a thicker 

 mass of foliage than those that are intolerant of shade. 

 This simply means that their lower leaves can withstand 

 the shade of their upper leaves. While it is not an absolute 

 rule that tolerant species have a thick mass of foliage and 

 intolerant trees open foliage, yet it is so generally true that 

 where this characteristic of a tree is known it serves as a 

 very reliable indication. Most trees are much more tolerant 

 of shade when young than when old. Among our tolerant 

 trees may be mentioned the Spruce, Oak, Balsam, White 

 Cedar, Red Cedar, Hornbeam, and Hard Maple. Among 

 our intolerant species are Poplars, Cottonwood, Willows, 

 Soft Maple, and Birch. Of our native pines, the White Pine 

 is much more tolerant than either the Jack or the Norway 

 Pine, which are quite intolerant of shade and soon succumb 

 if they are protected from the full sunlight. 



Trees Protect One Another and are Mutually Helpful, 

 and many trees that are quite hardy on the limits of their 

 growth when grown in groups, will fail if grown singly, as 

 for instance the Hard Maple in exposed parts of Minnesota. 

 Trees also interfere with one another and struggle for light 

 and soil conditions, and the weaker trees are destroyed. So 

 true is this that where the land is thickly seeded with even- 



