REFERENCES 203 



removes two or three whorls of branches at intervals of 

 three to four years. The live crown is maintained at one- 

 half to one-third the total height of the tree. At the age of 

 20 years the tree is 26 feet high, 4 inches in D. B. H. with a 

 top three inches outside the bark at 17 feet above ground 

 and live crown eight feet in diameter. From this point on 

 all branches are kept alive by thinnings and a diameter 

 growth maintained, at top of the first log, of 0.4 or 0.5 inch 

 per year. The cost of this pruning amounts to 10 cents per 

 tree at 20 years or $4 to $5 per thousand feet board measure 

 at end of a 50 year rotation. The value of one-half the lum- 

 ber is raised from $20 to $40 per thousand, which indicates 

 a handsome return from the pruning. 



As intensive silviculture develops, pruning is an operation 

 which will be employed as a regular part of the management, 

 particularly in plantations. Where pruning is to be em- 

 ployed, it may be possible to lower planting costs by use of a 

 wider spacing in the plantations than could be employed if 

 dependence had to be placed upon natural pruning for the 

 production of clear stems. 2 



REFERENCES 



1. KNAPP, FREDERICK B. Silviculture of White Pine (Pinus strobus). 

 Bulletin 106, Massachusetts Forestry Association. 



2. FROTHINGHAM, E. H. White Pine under Forest Management. Bulletin 

 13, United States Department of Agriculture, 1914, pp. 38-39. 



FISHER, R. T. The Yield of Volunteer Growth as affected by Improvement 



Cutting and Early Weeding. Journal of Forestry, Vol. 16, 1918, pp. 



493-506. 

 ILLICK, J. S. Sandy Ridge Improvement Cutting. Journal of Forestry, Vol. 



15, 1917, pp. 104-105. 



NISBET, J. Studies in Forestry. Oxford, 1894. Pp. 203-209. 

 RETAN, G. A. Note on an Improvement Cutting. Forestry Quarterly, Vol. 



14, 1916, pp. 777-778. 

 SCHLICH, W. ' Manual of Forestry. 4th edition. London, 1910. Pp. 298-303. 



