Wood specific gravity (SG) has long been used by foresters as an index for wood properties. More recently, SG has been widely used by ecologists as a plant functional trait and as a key variable in estimates of biomass. However, sampling wood to determine SG can be problematic; at present, the most common method is sampling with an increment borer to extract a bark-to-pith core-a difflcult task requiring considerable physical eflort and sometimes repeated borings to hit the pith, with potential to damagc the trunk of small trees. Here, we test a novel sampling method that reduces the effort to obtain an adequate increment core and results in less wood extracted from the tree. The Wiemann approximation predicts the point along a radius at which the wood SG equals the disk cross-sectional SG. When SG changes linearly across the radius, the point of approximation is at two-thirds of the radial distance. As a test, we compare SG at various points along the radius with the true SG of the disk. At all points except the point of approximation (i.e., at two-thirds of the radial distance), wood SG differed significantly fiom the true cross-sectional mean SG, whereas at two-thirds of the radial distance. the wood SC did not differ significantly from the tree mean SG for a group of 128 tropical trees and 25 temperate trees that had been sampled bark to pith. Overall. the method shows promise in that wood SG of a tree may be estimated accurately and without bias by boring the tree only to the point of approximation, that is, one-sixth of the trunk diameter. However, boring to one-sixth of the diameter provides an unbiased estimate of SG only if radial variation in SG is a linear function of radial distance. A limitation of the method is that an initial subsarnple of trces must be bored to determine the pattem of radial variation in a species befbre the approximation can be applied to other individuals.
Wiemann, Michael C.; Williamson, G. Bruce. 2012. Testing a Novel Method to Approximate Wood Specific Gravity of Trees. Forest Science, 2012; pubiished online February 16.2012 ttp:/idx.doi.org/10.58219/forsci.10-049.