FOREST PLANTING IN THE LAKE STATES 43 
THINNING, PRUNING, AND INTERMEDIATE CUTTINGS 
More trees are planted in forest plantations than will live to 
be harvested in the final crop, and it is therefore desirable to thin 
out some of them, unless losses have been so heavy or the spacing 
is so wide that less than 400 or 500 trees to the acre remain. As- 
suming that there have not been heavy losses, a certain proportion 
of the trees should ordinarily be cut before the competition between 
them becomes so severe that considerable numbers are dying nat- 
urally. 
If the trees are spaced 6 by 6 feet, a first thinning should be made 
when they are about 25 years old. At this age, the trees will be 
from 1 to 7 inches in diameter, and only a few of those which are 
cut will be large enough to be otherwise marketable, but they prob- 
ably will have sufficient value locally for fuel to pay for the cost 
of cutting them, The benefit of. the operation will then come in the 
increased growth and improved quality of the remaining stand. 
With 8 by 8 foot spacing, thinning does not become necessary 
until the trees are 40 or 50 years old, but at that time the product 
of the thinning will undoubtedly be merchantable for pulpwood 
or fuel and will bring a small profit over the cost of the operation. 
Plantations spaced 5 by 5 feet or closer should be thinned when 
they are about 15 years old and before they will yield marketable 
wood material. (PI. 4.) Thinnings in spruce of this age can 
usually be marketed at a good profit in December for Christmas 
trees. 
As there are several methods of making thinnings, the advice of 
a forester 7 should be obtained to assist in marking the trees to 
be cut. As a general principle, thinnings should be made lightly 
and frequently, even though the procedure is often not feasible 
economically. In Germany thinnings are made every 10 years 
and give 25 per cent of the net profit from the whole forest crop. 
Always in a thinning operation, trees which show evidence of 
disease or insect work or are crooked or broken should be removed. 
Pruning the trees in forest plantations by cutting off the dead 
and lower green limbs with a saw or ax is sometimes practiced. If 
an ax is used, the branches should be cut from beneath by upward 
strokes to avoid splitting. The branches should be trimmed close 
to the trunks so that the new wood that will form over the branch 
scars will be without knots, making the lumber of higher value. 
Since logs for sawing are usually cut in 16-foot lengths, pruning for 
the production of high-quality logs should be to a height of IT feet 
from the ground. This can be done for the higher branches by at- 
taching a saw to a pole. Only the 200 or 300 trees to the acre which 
are most vigorous and will make up the final timber crop need be 
pruned. 
The effect of the pruning on the quality of the timber was demon- 
strated in a northern white pine stand in New Hampshire (11, 1$). 
The best trees, which were to be kept for the final crop, were pruned 
when they were 3 or 4 inches in diameter. After 20 years they had 
added sufficient clear wood to make cutting profitable. The owner 
of this area found that the pruning increased the value of his lum- 
7 Lists of names and addresses of consulting foresters are sent out by the Forest Service, 
United States Department of Agriculture, Washington, D. C, upon request. 
