22 
SPECIAL CONSIDERATIONS IN THINNING, 
The three questions in thinning which always confront the forest 
manager are: When to begin and how often to repeat the thinnings; 
how severely to thin at one time or how many trees to permit to grow; 
which trees to take out. 
These questions of course can only be answered according to the 
special conditions of each case. As a rule it will be best to begin this 
series of thinnings when the signs of the struggle for light begin to 
show themselves unmistakably; that is to say, when a decided differ- 
ence in individual development can be seen and the dominant growth 
be discerned from the laggards. 
On strong soils and with light-needing species this occurs sooner, and 
the time for interference is more easily determined ; but in these cases 
assistance is also less urgent than on poorer soils, where more individ- 
uals are struggling in an even fight, and usually the separation into 
dominant growth and suppressed or laggards does not take place easily 
and early, and here, therefore, it is more needful to give timely assist- 
ance. 
In practice a consideration for beginning these thinnings is also the 
possibility of using or marketing the material cut out. But this is a 
proper consideration only because we do not know yet when it is prolit- 
able to spend time or money for thinning merely for the benefit of the 
remaining growth. 
As arule the thinnings are begun in light-foliaged, rapid-growing 
trees with the fifteenth to twenty-fifth year, while with shade-enduring 
species one may wait until the twenty-fifth to thirtieth year; that is, 
the time when the greatest annual height growth is attained and diam- 
eter development is desirable. 
The questions how much to cut out and how soon to repeat the opera- 
tion are somewhat interdependent. 
In small wood lots, where the owner uses perhaps the thinned out 
material himself, a continuous gradual thinning is best, while on large 
areas if may not be practicable to do otherwise than to subject a larger 
area to the operation at once and repeat it in a few years. In such a 
case enough must be taken out to avoid crowding until a second thin- 
ning, and yet not to cut so severely as to interrupt the crown cover too 
long and lay bare the soil. 
The oftener the thinnings are repeated the better for the remaining 
growth. The repetition may be made every 2 or 3 years in pines and 
rapid-growing soft woods, while in shade-enduring and slow growers 
every 5 years may be sufficient. Condition of the growth and judg- 
ment alone can determine this. The same is true as regards the amount 
to be thinned out. 
I repeat that there are always three considerations to be kept in view 
and their requirements balanced, namely, conservation or improvement 
