356 JOURNAL OF FORESTRY 



on stem. The thickness of the bark is, no doubt, dependent upon the 

 absolute dimensions of the tree, upon age, locality and situation, and 

 perhaps also on the density of the stand. 



In this variation of the thickness of bark lies one of the difficulties 

 with respect to the preparation of universal form class volume tables. 



We believe that local or regional differences in volume tables arise to 

 a large extent from differences in bark thickness. A comparatively 

 thin-barked species, like spruce, for instance, would not offer so many 

 difficulties in the preparation of a general form class table as, for in- 

 stance, Douglas fir, with its very variable bark-thickness. Butt swelling 

 is, however, large in spruce. 



Of the two writers of this article, the one who has carried on the in- 

 vestigations in the East is better satisfied with the results than his 

 western co-worker; that is, with the possibilities of the application of 

 Jonson's theories for practical purposes in Canada. Root swelling and 

 bark of very varying thickness are against us in the virgin forests of 

 the West. A study of root swelling and thickness of bark in various 

 localities and situations would of course largely reduce the difficulties 

 connected with the preparation of general tables, as apparently the form 

 of the stem inside bark agrees almost exactly with that of an eastern 

 relative of the same form class. 



We believe, however, that at any rate Jonson's theory is of great 

 value, even in our big timber, in reducing the number of field measure- 

 ments required to prepare an ordinary volume table. Working on this 

 basis, a volume table for western white pine form measurements of 

 only 16 trees has been prepared. 



The first step was to plat the taper inside the bark of all the trees on 

 cross section paper and to draw one taper curve representing the aver- 

 age of 16. Next a curve was drawn showing the percentage of the 

 d.b.h. inside bark of the diameters at dififerent per cents of the length 

 above breast height. Then, from this curve the value in per cent of 

 d.b.h. of the top diameter of each 16-foot log above a 2-foot stump was 

 determined for five 30-foot height classes (80 to 160 feet.) 



Average bark thickness at d.b.h. was determined for each diameter 

 class from the field measurements and subtracted from each 2-inch 

 diameter class, thus giving the inside bark diameter class. From this 

 last the diameters at the top of each log were determined, the logs were 

 scaled, and the b.f . contents of each tree computed. 



