WOOD-LOTS ON FARMS 13 
pose of aiding and improving growth. These distinc- 
tions, however, are much more apparent than real. 
The fact that it often requires a century to produce a 
fine grade of timber does not imply that a forest, 
when planted, yields nothing until maturity. A 
spruce forest at first may consist of thousands of 
little trees per acre. At the end of ten years it should 
contain not more than 4,000 trees, at the end of 
twenty years 2,000, at the end of forty years 1,000, 
at the end of sixty years 500, at the end of eighty 
years 350, and at maturity (one hundred years) 250. 
Thus in ninety years fifteen-sixteenths of the number 
of trees and a large volume of wood have been re- 
moved from time to time by a careful system of thin- 
ning, yielding material of ever-increasing value as 
the forest grows older. In the case of irregular for- 
ests, which are forests consisting of trees of all ages 
mixed together, managed according to the selective 
system—that is, cutting here and there throughout 
the forest whenever trees are mature or whenever for 
the good of the forest their removal is prudent—an 
amount depending upon the size of the forest and the 
rate of growth may be cut every year, or every now 
and then. 
There may be, therefore, with forest as with agri- 
cultural crops a small but frequent yield. In the 
method of culture there is apparently a great differ- 
