PERIODICAL LITERATURE 379 



The mean annual growth of this plot was 156 feet at 25 years, 

 and had in three years increased to 178 cubic feet per acre, and the 

 current annual growth to 372.9 cubic feet per acre. Thus the culmina- 

 tion of the growth has not as yet been attained. The thinning made 

 when the plot was 25 years old removed 33.9 per cent of the total 

 number of trees, but only 21.2 per cent of the volume ; the average 

 diameter was increased .4 of an inch and the average height .3 of a 

 foot. The thinning made three years later removed 24.8 per cent of 

 the number of trees and 15.5 per cent of the volume; the average 

 diameter was increased .2 of an inch and the height .3 of a foot through 

 the thinning. The volume had in the three years increased by 36 

 per cent. • 



The three plots, being on about the same quality of site are there- 

 fore quite comparable in several respects. The effect of early and 

 frequent thinning on volume growth is clearly shown by the figures 

 tor Plot No. 1 when compared with Nos. 2 and 3. The figures show 

 that, with early and frequent thinnings, the amount to be removed 

 becomes more nearly a constant per cent of the number of trees and 

 of the volume. The stand, too, becomes more regular, as is shown 

 by the slight increase in the average size of the trees in Plot No. 1 

 after the thinning. Plot No. 1 has a mean annual growth nearly twice 

 that of Nos. 2 and 3. Neither site nor degree of stocking would 

 account for such a difference. Originally, Plot No. 1 must have con- 

 tained 2,100 trees per acre at least. 



Mr. T. S. Hansen, to whom we are indebted for this brief, add's a 

 comparison with figures on the growth of Douglas fir in this country. 

 The best comparison can probably be made with that given in a yield 

 table by T. T. Hunger, in U. S. Forest Service Circular 175, for a 

 30-year-old stand on quality I soil. 



Comparison of Plots and Yield Table 



* Without inclusion of thinnings. 



