thinned and 16,264 feet in the unthinned plot. 

 More striking is the growth at different periods. 

 The average growth per acre for the first 35 

 years was 410 board feet per acre. During the 

 first five years of the experiment the unthinned 

 plot grew more than the thinned plot, 996 board 

 feet per year as against 857 board feet. But in 

 the last five years the growth of the thinned plot 

 was 1241 board feet and of the unthinned plot 

 1086 board feet. Evidently the effects of thin- 

 ning are cumulative. Height growth as volume 

 growth was stimulated. 



Another factor in thinning is that the capital 

 invested in wood is smaller in the thinned forest 

 and the interest earned greater even if the rate of 

 growth were no more. Thus in the thinned plot 

 described above the growth during the past five 

 years was at the rate of 39% on the invested 

 capital or at the average rate of 7.8% per year. 

 In the unthinned forest it was 22 % for five years 

 or 4.5% per year. The early returns from thin- 

 nings, where they can be sold at a profit, reduce 

 the cost of raising a crop of timber. 



REPRODUCTION CUTTINGS 



As pointed out elsewhere, planting is of rela- 

 tively little importance in this forest. By proper 

 cutting the forest will reproduce itself. The for- 

 ester's skill is required to so regulate this repro- 

 duction that the percentage of valuable species 

 will be greater in the next generation. Following 

 clear cutting the reverse is often the case. In the 

 Yale study it was found that the number of trees 

 and shrubs on an acre cut clear five years 



37 



