Upper-stem tree diameters are usually measured outside the bark with the only bark thickness measurements being made at breast height. The current study presents equations and coefficients for estimating the bark thickness in both the upper stem and at the stumps based upon the bark thickness at breast height, the size of the tree (DBH and total height), and the height to the measurement in question.

The upper-stem model presented is an extension of a previously published general hyperbolic ratio model. The model for bark ratio below breast height, a simple power function, is estimated as well. Both equations contain coefficients that account for the more rapid taper on trees with thicker bark.

The data used for fitting and testing the taper models consisted of measurements on over 3,000 conifer trees measured by members of the Northern California Forest Yield Cooperative and the USDA Forest Service. The data were split into two halves, one half for fitting and the other half for testing. The best upper-stem and below-DBH equations obtained from this analysis are discussed here; the remainder are listed in the Appendix.