10 A MANUAL OK FORESTRY 



may start, but in the course of their various struggles and under 

 innumerable external influences their ranks are so thinned that 

 only a few hundred grow into fair-sized trees. A stand of 

 1000 trees per acre 20 feet high by the time it is 80 feet high 

 and correspondingly large will seldom contain over 400 trees to 

 the acre. The trees that are killed in this constant strife fall 

 t> the ground after a few years, decay, and add to the humus of 

 <i!. As the forest grows old gaps are caused by these 

 deaths and reproduction again takes place. Whether the same 

 kind of trees will come in depends upon the conditions at that 

 time. 



In every region certain combinations of forest trees and under- 

 brush are characteristic of different sites. As already explained, 

 this community of tree life is called a "type," and is influenced 

 by soil, exposure, elevation, moisture, and other factors. As 

 examples of types, we may mention the " spruce slope type," 

 characteristic of the steep mountain slopes of northern New 

 England, and " chestnut oak type," of the trap ridges of Connect- 

 icut. Under natural conditions such a forest type maintains 

 itself century after century on the site to which it has become 

 adapted. Accordingly it is known as the permanent type of 

 that particular site. Circumstances not in the regular course 

 of nature may entirely change the conditions and cause the 

 appearance of a different forest type. Such influences are wind- 

 fall, extensive damage by heavy snows, by insects or fungi, by 

 fires, and by lumbering or clearing for farming. The type 

 following any change of this sort is a temporary type, as, for 

 example, the "poplar type" on burns, or the "old-field type" 

 on abandoned cleared lands. Gradually this temporary type, 

 if It it to itself, will change into the permanent type and after 

 perhaps fifty or one hundred years the forest will have the form 

 and composition that it had before the change. Such is nature's 

 way of asserting her rights. 



Every forest type will be found under a considerable variety 

 of condition of soil, moisture, etc., and, of course, will make its 

 best development where the sum total of conditions is most 



