Table 4.— Effect of grouping several visual volume estimates for a tree, pinyon and juniper are combined 



Mean of Mean of Median of Range of percent 



Diameter FS1 and FS1, FS2, FS1, FS2, errors for 



class FS2^ and BLM and BLM single estimates^ 



3- 6.9 



-0.003 [ 



-1%] 76 



0.006 [ 1%]35 



-0.008 



-1%]35 



- 8 to 



7 



7-10.9 



-.141 [ 



-5%]111 



- .070 [ - 2%]50 



-.223 



- 7o/o]50 



- 10 to 







11 - 14.9 



- .894 [ 



-11%] 66 



- .455 [ - 6%]38 



-.688 



- 9%]38 



-11 to 



-5 



15-18.9 



.068 [ 



1%] 35 



.521 [ 4%]18 



.484 



: 3%]18 



-11 to 



2 



>19 



-1.422 [ 



-5%] 14 



.417 [ 2%] 8 



-.350 



-1%] 8 



- 8 to 



-1 



^f^ean visual volume difference, followed in brackets by mean difference expressed as a mean percent of destructive 

 volume, followed by sample size. 



^Thiis is the range of errors corresponding to the value in brackets for 

 FS1. FS2, and BLM kept separately. 



For example, our volume equation using destructive 

 segmentation had rather large confidence intervals. The 

 confidence bands in figures 2 and 3 correspond to 

 roughly ±40 and ±50 percent of the predicted cubic 

 foot volume for a single pinyon and juniper, respectively. 

 This implies much variation in the data. As a result, our 

 volume equation coefficients are the best "least squares" 

 coefficients for the mix of diverse tree forms in our sam- 

 ple data. A slightly different mix of tree forms could re- 

 sult in much different regression coefficients. In other 

 words, we suggest that volume equations based on vis- 

 ual segmentation only be used in the local areas where 

 the segmentation data were collected. This practice will 

 reduce the probability of extrapolation errors from use 

 of an inappropriate volume equation. The ease and sim- 

 plicity of the visual segmentation procedure allows the 

 option to develop new volume equations or at least 

 check existing equations for use in any woodland inven- 

 tory or cruise. 



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8 



