28 BULLETIN 139, U. S. DEPARTMENT OF AGRICULTURE. 
the stand. After that, they should be repeated every 7 or 10 years. 
In practice, however, this can rarely be carried out, because of the 
present lack of market for small saplings and the prohibitive cost of 
logging scattered trees. Thinnings in young pine stands should not 
be heavy or the height growth will be impaired. The trees will not 
prune so well, and the soil will not be sufficiently shaded toward the 
end of the rotation to prevent weeds from getting a foothold and 
endangering reproduction. Heavy thinnings, moreover, are likely 
to result in windf all, as was well illustrated in the case of the thinned 
stand of Norway and white pine on the Grand Marais Lighthouse 
Reservation a few years ago. The winds off Lake Superior are very 
heavy at times. Many of the trees left standing on the lighthouse 
reservation lean badly and appear to have their roots loosened. In 
this case the thinning was probably deferred too long and then made 
too heavy. 
IMPROVEMENT CUTTINGS. 
In mature and overmature stands where, as in the case of parks, 
the aim is not so much to secure young growth as to maintain the 
present stand, loss would be avoided if systematic improvement 
cuttings are made at intervals of from 15 to 25 years. The Norway 
pine trees removed should be those with straggling and light-green 
foliage, stag-headed, or clearly so overmature that they will not 
survive until the next cutting. It would be better even to cut a 
few healthy trees in clumps, in order to increase the amount to be 
logged per acre, than not to cut at all. When an overmature forest 
is cut systematically, it is possible to clear up the occasional wind- 
falls, which are bound to occur in old age. 
MANNER OF CUTTING. 
In any partial cut of the stand the trees to be removed should 
be marked beforehand, in order to insure that the thinning will be 
carried out as planned. The method usually followed is to blaze or 
stamp the roots and bole of the trees to be cut. Close utilization 
of the material marked is even more important. The owner should 
see to it that stumps are cut low (from 12 to 16 inches, depending 
on the size of the timber), the tops utilized to the full merchantable 
limit (in the Lake States usually 6 inches), and that logs partially 
defective are removed, even if they contain only from 20 to 25 per 
cent of merchantable material. It is, of course, necessary to use 
great care not to damage reproduction which is to form the second 
crop. Roads, skidding trails, skidways, and the cutting of seed 
trees should be designed with this in view. 
