150 UNITS OF MEASUREMENT FOR STANDING TIMBER 



For most species, the point 4^ feet above ground has been accepted 

 by foresters for measurement of diameter as it falls above the swell- 

 ing and at a convenient height for use of calipers. This height is also 

 used in England and India. In Continental Europe, 1.3 meters, or 

 4.3 feet, is the standard height. 



This measurement at 4| feet is termed diameter breast high, and 

 is abbreviated both in speech and record to D.B.H. Measurement 

 outside bark is always indicated by the abbreviation. 



In the Philippines and other tropical countries it will be impossible 

 to use a similar height for many species owing to the development 

 of buttresses on the trunks. Such species will probably have to be 

 measured either above the flare, or at a height of 16 to 20 feet, by 

 eye, using the 4| foot standard point only for species and types which 

 permit it. 



Where D.B.H. is adhered to for species like Western larch, red 

 cedar or Douglas fir on the Pacific Coast, butt swelling greatly inter- 

 feres with the uniformity of the volumes for these specias for trees of 

 given diameters when compared with other species like western yellow 

 pine whose swelling seldom reaches this height. This apparent dif- 

 ference in volume may be from 20 to 40 per cent in favor of the pine. 



126. Bark as Afifecting Diameter in Volume Tables. For species 

 whose bark is of uniform thickness for trees of the same D.B.H., the 

 diameter taken outside the bark is preferable as a standard of classi- 

 fication to diameter inside the bark. The cruiser has no time to measure 

 bark thickness except on occasional test trees. The width of bark, 

 however, is seldom uniform. For trees of the same diameter, it is thick- 

 est on exposed and on rapidly growing trees, and thinnest on sheltered, 

 crowded and slow-growing or suppressed trees (§ 113). The larger 

 the trees, the greater the actual thickness of bark, and the wider the 

 possible variation in thickness. This thickness may range from 2 

 to 5 inches and over, on West Coast species. Volume tables based 

 on diameter inside bark, therefore, are more consistent and accurate 

 as tables, than those based on outside bark measurement. 



But this would require the tallyman to throw ofT the double width 

 of bark from every tree tallied. The experienced cruiser, who deals 

 with single average trees only, can from his experience throw off the 

 proper average width of bark for the selected tree, increasing the deduc- 

 tion for open and exposed situations and vice versa. There is no 

 such choice in the tally of every tree. The mistakes made in mental 

 arithmetic and the errors in guessing the proper width of bark to allow 

 would be more serious than discrepancies in the table. In practice, 

 then, D.B.H. would have to be recorded and average bark thickness 

 afterwards deducted previous to computing the volume. 



