DISCUSSION 



The results of this study, while based on a rather 

 restricted geographical sample, indicate that there is a 

 small but statistically significant difference between 

 diameter measurements taken at 1.37 m and those taken 

 at 1.3 m. The correction factors developed for Grand 

 County compare favorably with those presented by 

 Bruce (1979) and Berry (1980). For example, assuming a 

 10.0-inch measurement taken at 4.5 ft (1.37 m), the for- 

 mula developed by Bruce would yield a diameter of 

 10.05 at 1.3 m; Berry's correction would yield a diameter 

 of 10.05 at 1.3 m, and the correction presented here 

 would also yield 10.05. The implication is the equation 

 presented here developed from Rocky Mountain species 

 is functionally the same as those developed for naturally 

 grown West Coast species and plantation-grown white 

 spruce in Canada. 



Since most volume equations are a function of 

 diameter squared, it would follow that the next concern 

 would be the impact of these diameter differences on 

 volume. The relative difference (dash line in fig. 3) in 

 volume estimates using diameter measured at 4.5 ft as 

 opposed to 1.3 m is small. Generally, the largest relative 

 difference is in the 6-inch-diameter class and continues 

 to decUne as diameter increases. 



When this study was conducted, the trend in forest 

 measurements in the United States was very much 

 toward metric. Subsequent National poHcy, however, has 

 deemphasized the adoption of the metric standard. 

 Therefore, hard conversions to metric, in the near future 

 at least, will probably not be required. Soft conversions, 

 however, will still be required for comparative purposes 

 in the international arena. 



LU 



O 



< 



LlJ 



< 



LlJ 

 > 



0.6 I- 



0.5 



0.4 



0.3 



0.2 



0. 1 



6.0 



5.0 



4.0 



3.0 



2.0 



1.0 



6 8 10 12 14 16 18 20 

 AVERAGE RELATIVE DIFFERENCE (PCT) 



Figure 3.— Comparison of absolute (solid 

 line) vs. relative (dashed line) differences in 

 volume prediction using diameter measured 

 at 4.5 ft vs. 1.3 m for lodgepole pine in 

 Grand County, Colo. 



6 



