The purpose of the thinnings is not only to se- 

 cure a mixture of valuable and healthy specimens 

 but to secure increased growth through the added 

 soil moisture available to their roots and sunlight 

 available to their crowns. After the first thin- 

 ning all subsequent thinnings would yield a profit 

 because there will be other products besides cord- 

 wood. In the most highly developed forestry 

 practice a considerable proportion of the total 

 growth of a forest is removed from time to time 

 in the form of thinnings. This is in marked con- 

 trast to prevailing practice in this country where 

 all material is removed in one final cutting. Care 

 must be taken not to open up the forest by such 

 thinnings to such an extent as to produce an ad- 

 vanced growth of young trees and shrubbery. 



Experiments 1 in thinning white pine stands 

 over a period of 20 years, beginning when the 

 forest was 35 years old, have brought out some 

 very interesting facts. In a plot which was 

 rather heavily thinned four times, 81% of the 

 original trees were removed during the period, 

 while in an unthinned check plot 32% of the 

 trees died from natural causes. At the beginning 

 of the experiment in 1905 the stand per acre in 

 each case was about 14,500 board feet. In all 

 15,294 board feet per acre were removed from 

 the thinned plot and the stand at the end of the 

 period was 17,562 board feet so that the yield at 

 age 55 yrs. was 32,856 board feet. In the un- 

 thinned plot the stand at age 55 yrs. was 30,520 

 board feet. The growth during the 20 year 

 period was therefore 18,192 board feet in the 



1 The Results Secured in Treating Pure White Pine Stands 

 by R. C. Hawley Yale Univ. School of Forestry Bui. No. 20. 



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