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 is 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 cuttings are possible. 



The first cutting is made about 20 years before the end of the rota- 

 tion, removing about half of the original number of trees. After 

 reproduction is secured and is well started, the remainder of the 

 original stand is removed in a final cutting. 



