CONTROL OF GIPSY MOTH BY FOREST MANAGEMENT. 47 
It should be remembered that equal numbers in all size classes 
would not be a sufficient representation to make a many-aged stand 
a selection forest, in the sense that that term is used here, and that 
where suppressed trees have been removed equal sizes may be roughly 
accepted as an indication of equal ages, although a wide variation 
actually exists in these respects. To insure the perpetuation of a 
selection forest managed on the selection system there must be a much 
greater representation of the smaller than of the larger trees. ‘Theo- 
retically, if a rotation of 100 years is adopted and cuttings are 
planned to be made every 10 years, the trees should be divided into 10 
classes, each of which should occupy one-tenth of the available ground 
area and crown space. 
In stands other than that. now under consideration, it might well 
happen that the stand remaining after the cuttings and thinning had 
been made could be described better as an even-aged than as a selec- 
tion forest. The representation of trees in the smaller size classes 
might be much more even aged than that of the trees in the larger 
size classes which were removed and which gave it originally the 
characteristics of a selection forest. This is likely to be the case in 
stands which have been heavily pastured for a long period of years. 
In such cases the form of management should be changed from the 
“selection” system described above to the “shelter-wood” system. 
Even-aged stands.—In even-aged stands, whether occurring nat- 
urally or produced by the management of uneven-aged stands as sug- 
gested above, the shelter-wood system may be used with a rotation of 
70 to 100 years. The shelter-wood system somewhat resembles the 
system of successive cuttings, already described for other plots, ex- 
cept that the interval between cuttings is longer, natural reproduction 
instead of planting is depended upon to secure a new stand, and care 
is taken to maintain as nearly as possible a crown cover of uniform 
density over the whole area. This system is not likely to be practi- 
cable for stands of this kind in the immediate future. The essential 
principles of its application are to open the stand gradually in order . 
to prevent too sudden exposure of existing young growth and to 
secure additional reproduction under the shelter of the old stand 
before it 1s wholly removed. The possibility of using it depends 
chiefly upon market conditions and logging costs. When these are 
most favorable several cuttings are made, but under present Amer- 
ican conditions not more than two onttings are possible. 
The first cutting 1 is made about 20 years before the end of the rota- 
tion, removing about half of the original number of trees. After 
Perr ocucion is secured and is well started, the remainder of the 
original stand is removed in a final cutting. 
