COMPARATIVE INCREMENT. 

 COMPARATIVE INCREMENT. 



19 



Table 8 gives the increment growth of western yellow pine, Douglas 

 fir, and blue spruce. The mean annual growth, the periodic annual 

 growth, and the periodic annual growth per cent are shown at each 

 decade. 



Table 8. — Increment of western yellow pine, Douglas fir, and blue spruce. 1 



Age. 



Mean annual growth. 



Periodic annual growth. 2 























Pine. 



Fir. 



Spruce. 



Pine. 



Fir. 



Spruce. 



Pine. 



Fir. 



Spruce. 



Years. 



Cu.ft. 



Cu.ft. 



Cu.ft. 



Cu.ft. 



Cu.ft. 



Cu.ft. 



Per ct. 



Per ct. 



Per ct. 



10 



0. 0003 

 .0011 



0. 0002 

 .0011 



0002 



0. 0003 



0. 0002 



0. 0002 









20 



.0009 



.0019 



.0021 



.0015 



15.20 



16.80 



15.89 



30 



.0033 



.0036 



.0034 



.0077 



.0085 



.0085 



12.72 



12.97 



14.28 



40 



.0086 



.0092 



.0115 



.0247 



.0261 



.0358 



11.10 



10.96 



12.71 



50 



.0167 



.0192 



.0347 



.0490 



.0589 



.1276 



8.29 



8.88 



11.61 



60 



.0309 



.0353 



.0986 



.1019 



.1159 



.4180 



7.57 



7.53 



10.92 



70 



.0518 



.0568 



.1935 



.1777 



.1860 



.7527 



6.47 



6.10 



7.73 



80 



.0856 



.0841 



.2641 



.3221 



.2756 



.7687 



6.14 



5.14 



4.42 



90 



.1173 



.1161 



.3355 



.3710 



.3719 



.8972 



4.26 



4.32 



3.48 



100 



.1532 



.1549 



.3924 



.4459 



.5039 



.9036 



3.39 



3.88 



2.60 



110 



.1960 



.2025 



.4560 



.6242 



.6790 



1. 0921 



3.38 



3.59 



2.44 * 



120 



.2436 



.2509 



.5113 



.7668 



.7932 



1.1203 



3.02 



3.03 



2.01 



130 



.2966 



.3002 



.5625 



.9274 



.8920 



1. 1764 



2.73 



2.58 



1.74 



140 



.3483 



.3518 



.6078 



1.0264 



1.0220 



1.1975 



2.35 



2.31 



1.51 



150 



.3959 



.3964 



.6484 



1.1028 



1.1217 



1. 2166 



2.04 



2.06 



1.33 



160 



.4486 



.4476 





1. 1987 



1. 2159 





1.80 



1.85 





170 



.4991 



.4971 





1.3074 



1.2883 





1.66 



1.65 





180 



..5455 



.5443 





1.3347 



1.3472 





1.46 



1.47 





190 



.5920 



.5897 





1.4263 



1. 4059 





1.35 



1.33 





200 



.6379 



.6332 





1.5112 



1. 4603 





1.26 



1.22 





210 



.6801 



.6751 





1.5250 



1.5123 





1.12 



1.12 





220 



.7185 



.7156 





1.5337 



1.5603 





1.01 



1.04 





230 



.7550 



.7536 





1.5499 



1.5972 





.93 



.96 





240 



.7888 



.7900 





1. 5654 



1. 6272 





.86 



.89 





250 



.8162 



.8245 





1.5730 



1.6514 





.79 



.83 





260 



.8459 



.8571 





1. 5893 



1.6721 





.74 



.78 





270 



.8728 



.8861 





1.5730 



1.6415 





.69 



.71 





280 



.8963 



.9117 





1.5315 



1.6013 





.62 



.65 





290 



.9165 



.9338 





1. 4821 



1.5536 





.57 



.59 





300 



.9334 



.9527 





1. 4226 



1.5009 





.52 



.53 





310 



.9466 



.9681 





1.3422 



1. 4304 





.46 



.48 





320 



.9579 



.9803 





1. 3087 



1.3591 





.43 



.44 





330 



.9675 







1.2650 







.40 







340 

 350 



.9741 

 .9790 







1. 2017 

 1. 1465 







.37 

 .34 



















360 



.9820 







1.0870 







.31 

















1 Based on the measurements of 180 western yellow pines, 185 Douglas fir, and 135 blue spruce. 



V— v 200 



2 The periodic annual growth per cent was computed by the formula p= X — ,in which "p" is the 



rate per cent, "V" the present volume, " v " that "n" years ago, and "n" the number of years in the period 

 which in this case is 10. 



From this table it is seen that up to the age of 280 years there is 

 very little difference in the mean annual growth of western yellow 

 pine and Douglas fir. But after this the fir takes the lead, and at 

 the age of 320 years its mean annual growth is almost as great as that 

 of pine when the latter species is 40 years older. At the age of 40 

 years the mean annual growth of spruce increases over that of pine 

 and fir, until at 1 50 years it is more than one- third greater. 



Since there is a difference in the three species in respect to mean 

 annual growth, there is a corresponding difference in respect to 

 periodic annual growth. However, this difference is not great in 

 the case of spruce at the age of 150 years; this is because the growth 



