18 PRACTICAL FORESTRY IN THE ADIRONDACKS. 
could be obtained again in 36 years.' If the principle of a sustained 
annual yield were carried out it would be necessary to cut about one 
thirty-sixth of the total crop each year. There would be at the end of 
that period 36 years’ increment on one thirty-sixth of the tract, 35 
years’ increment on one thirty-sixth, 34 years’ increment on one thirty- 
sixth, ete., or, to strike a general average, 18 years’ growth on the whole 
tract. If the whole area were cut in one year there would be 36 years’ 
growth on the entire tract at the end of 36 years. If the annual growth 
were 0,5 standards per acre on, say, 9,000 acres, 36 years’ growth would 
amount to 90,000 standards, as against 45,000 standards under the sys- 
tem of a sustained annual yield. In this example the principle that in 
virgin forest the growth is equalized by the loss through decay and 
destructive natural agencies, which is entirely true over a large tract, 
is applied to small areas. In individual sections it is probable that on 
account of windfall the loss will very much exceed the growth. There 
will be other instances, however, where the trees are inostly young and 
thrifty, and the growth will so far exceed the decay as to counterbalance 
the loss elsewhere. (PI. III). 
A further consideration in favor of cutting over the whole area in a 
short time is the question of taxes. In the Adirondacks they are reduced 
about one-half after lumbering. By the same reasoning as in the fore- 
going discussion, under the system of a sustained annual yield, full 
taxes would have been paid on one-half the area at the end of 36 years. 
Under the other system the taxes would be lowered on the whole tract 
at the end of the first year. Moreover, the cost of logging would be 
much less if the timber were taken out in one or a few years and much 
better contract prices could be made. The cost of superintendence, 
marking, ete., would likewise be proportionately smaller under the 
iitermittent system. 
REMOVAL OF DEAD AND UNSOUND TREES. 
The class of thinnings known as cleanings, by which the dead, 
dying, and unsound trees are removed, is considered very important in 
Europe. Often the entire tract is cleaned every year or within short 
periods. The purpose is twofold: First, to utilize the wood before it 
decays, and second, to prevent the breeding of insects. Inasmuch as 
the dead trees can not be utilized in the present instance, their removal 
would be very expensive and the object attained would not justify the 
outlay. The cutting of unsound timber is also impracticable, because 
such trees in most places can not be utilized. If left standing, on the 
other hand, they help to shade the ground and distribute a certain 
amount of seed. 
THINNINGS AND IMPROVEMENT CUTTINGS. 
It frequently happens in the Adirondacks that young Spruces of 
even age grow in very dense masses, and if some of the trees were 
1 See page 65. 
