38 THE ADIRONDACK SPRUCE 
ble food material; and, Second, by the increased 
spread and efficiency of the roots and crowns. 
In the Adirondacks, where the forest is dense and the 
climate cool, a deep layer of humus accumulates. 
When the forest is thinned the humus disintegrates 
more rapidly on account of the admission of the sun’s 
rays and the freer circulation of air, and an increased 
amount of food material is made available for the 
growth of the trees. The immediate increase in 
growth is probably due to this cause. How long it will 
last depends upon the length of time before the humus 
disappears. Professor Hartig, of Munich, estimates 
this period, under favorable conditions, at about ten 
years. 
The effec of openings in the forest on vigorous and 
suppressed trees alike is to give them more room for 
development, a larger and better apparatus of roots 
and leaves for gathering and digesting food, and so to 
increase their rate of growth in diameter and height. 
The practice of thinning is based on this capacity 
for increased growth on the part of trees which have 
been more or less vigorously set free, or, in other 
words, on the part of the members of a piece of forest 
which has been thinned. The removal of a certain 
number of trees from overcrowded woods increases the 
final product, instead of decreasing it, and an additional 
product is obtained from the wood cut in the thinning. 
In this way the total output of a piece of forest in final 
cuttings and thinnings together is greater than it would 
be without silvicultural attention. 
