Gross Bark Volume 



Gross bark volume is defined as the bark volume for the entire stem without allow- 

 ance for fissure or void volume. The value was obtained for each tree by subtracting 

 the volume inside bark from the volume outside bark. The volume in each case was cal- 

 culated in the manner previously described for the calculation of stem volume. Because 

 d.o.b. at stump height was not obtained during the field measurements, that particular 

 value was estimated from the bark-thickness equations developed for each species. 



Stump Diameter » D.B.H. Relationship 



The relationship between diameter at stump height, i.b., and diameter at breast 

 height, o.b., was obtained for each tree using the information obtained from field 

 measurements. 



METHODS OF REGRESSION MODEL 

 CONSTRUCTION 



The development of the models for table construction proceeded in four steps: 

 (1) selection of the independent variables, (2) graphic analysis, (3) regression anal- 

 ysis, and (4) final selection of the model. 



Development of Tables 



The regressions and resulting tables were prepared specifically to make use of 

 measurements that are commonly obtained under field conditions. With this in mind, 

 diameter breast height, outside bark (d.b.h., o.b.), and total height were used as 

 fundamental independent variables for all stem, top, and bark volume estimates. Diam- 

 eter outside bark was used to predict bark thickness, again because of the relative 

 simplicity of field measurements. Stump diameter, i.b., one of the measurements taken 

 during the data collection, was used as the independent variable in developing the 

 d.b.h. -stump diameter equations. 



Random samples, varying from 10 to 20 percent of the total number of observations 

 in each data set, were drawn for graphic analysis. These analyses provided insights 

 for the selection of the form of the variables, from which one or more models were 

 postulated. Stepwise, least squares multiple regression techniques, using the improve- 

 ment in the "F" statistic as a delimiter, were used to develop the models. When more 

 than one model seemed statistically appropriate, an examination of the residuals was 

 helpful in selecting the final model. 



With the exception of the stand volume equations, all volume predictions incorporate 

 logarithmic models. Logarithmic expressions for the estimation of tree stem volume 

 have been widely used since 1933, when the method was proposed by Schumacher and Hall 

 (1933) . Investigators in other fields have likewise found the procedure useful 

 (Baskerville 1972; Zar 1968). 



4 



