3288 Chapter 27 



A delay in bucking after the tree is felled with reduce tree moisture content, as 

 will a delay in getting wood to the weight scaling station (page 2356 and figs. 20- 

 15ABCD and 20-16). Also typically, wood moisture content is inversely core- 

 lated with wood specific gravity (fig. 8-1). 



To make a reasonable estimate of rough log weight based on cubic foot 

 content of wood, one must first pick the appropriate volume inside bark from the 

 tables, then multiply by an appropriate green density in pounds per cubic foot 

 based on knowledge of the log source; to this product add an appropriate 

 percentage (see sect. 13-3) to account for weight in the bark. 



Log weight to board feet log scale. — Weights of single logs or whole 

 truckloads can be accurately and quickly determined; less readily determined is 

 the weight per Mbf log scale. This is so because of species and regional variabil- 

 ity in wood moisture content and specific gravity, and also because cubic foot 

 content per Mbf, the primary determinant of weight, varies with diameter and 

 length of log, and with the various log scales. 



Data specific to southern hardwoods are scarce but some information is 

 available on northeastern hardwoods. 



Nyland et al. (1972) give the following rule-of-thumb for estimating Interna- 

 tional lA-inch log scale volume based on the weight of winter-cut tree-length 

 logs: volume in board feet is about 8 percent of weight in pounds for pieces 

 1 ,000-1 ,500 pounds, about 9 percent of weight for pieces 1 ,500-2,500 pounds, 

 and about 10 percent of weight for heavier logs. Their finding was based on a 

 sample of 278 tree-length pieces of mixed northern hardwood species cut in New 

 York. 



Trimble (1965) objected to weight scaling hardwood saw logs because it 

 would give equal value to all log grades. A realistic appraisal of value, he 

 contended, must take into account species, log diameter, log grade, and volume. 



Weight scaling. — Along with the shift to tree-length logging and hauling 

 came the need for a means of estimating volume without first bucking the pieces 

 into short logs for conventional scaling. Weight scaling proved fast and inexpen- 

 sive. The easiest method is to apply a constant conversion factor (board feet/ 

 pound, for example) to the net truckload weight. However, constant factors fail 

 to account for variation, among species, in average timber size among tracts, 

 seasonal variation caused by shifting harvesting operations between dry and wet 

 sites, or local utilization standards. Constant factors are even more inadequate if 

 two or more products are contained on the same load. 



Weight scaling is more reliable when the size of the pieces is taken into 

 account. Nyland (1973) measured 190 sample truckloads in which sugar maple, 

 red maple, beech, and yellow birch predominated. The difference between 

 estimated and actual volume averaged about 1 percent in groups of loads from 15 

 different woodlots. The regression equations he developed are as follows: 



Doyle volume, board feet = 0.08207(W) - 43.25815(N) + 465.711 (27-41) 



International V4-inch volume, board feet = 



0.09230(W) - 9.19587(N) + 420.158 (27-42) 



