Forests and Forestry 137 



increased accumulation of wood in the trunk. 

 Naturally, in making these thinnings, individuals 

 that are of particularly vigorous development are 

 favored, and their weaker fellows selected for the 

 axe. Such thinnings are repeated from time to 

 time. They require the exercise of much skill and 

 discretion on the part of the forester, for besides 

 the growth of the saplings several other things 

 must be considered. For instance, care must be 

 taken that the fertility of the soil is not injured by 

 too much light being admitted to the forest floor. 

 In such cases, what is known as raw humus is apt 

 to be formed, — a kind of peat generated on dry 

 land, which, like its kin in the bog, is inimical to 

 most forms of plant life. Too much thinning may 

 also cause the invasion of an excessive growth 

 of weeds, either of grasses, herbs, or underbrush, 

 which may hinder the reproduction of the desired 

 species. Various other objects are attained by 

 light or severe thinnings, as occasion may require. 

 A discussion of these would lead us too far into 

 silvicultural details of purely technical interest. 



Nor can we give a detailed description of the 

 various systems of silviculture known to foresters, 

 each of which has its peculiar advantages and 

 drawbacks, making sometimes the one, then the 

 other, most adapted to existing circumstances. 

 A few of the most important of these systems we 

 may mention in passing. A forest may be com- 

 posed of trees all of the same species and the same 

 age ; consequently, the time when it will be most 



