THE IXFLUEXCE OF TIIIXXIXG 



25 



the logging operations, a slight increase is again noted, indicating a 

 recovery from the low vigor period. From 1903 to 1908 a very rapid 

 growth is indicated, followed by depression points in 19 10 and 1913. 

 The measurements for 191 5 do not represent the entire year's growth, 

 since the records were taken during the latter part of that summer. 

 The curve shows plainly the effect of the thinning as influencing the 

 annual growth in hemlock, and records the reaction to the shock of 

 exposure as well as the response to environment following the cutting. 

 In comparing the two curves and the data from which they were 



Fig. I. — Curies for -western hemlock and grand fir, showing the increase in width of annual 



rings due to thinning 



platted, it is found that the hemlock responded more vigorously to the 

 thinning than did the grand fir. In hemlock the increase in periodic 

 annual growth for the period 1903 to 191 5, inclusive, over the period 

 from 1896 to 1902, inclusive, is 242 per cent. A like figure for grand 

 fir is 216 per cent — a balance in favor of hemlock of 26 per cent. 



A comparison of the average crown of the hemlocks upon the thinned 

 area and those upon the unthinned area (Table i) shows a striking 

 contrast. The average crown size of the hemlocks on the cut-over area 

 is 1,065 square feet and on the uncut area 374 square feet. The differ- 



