Height-diameter equations for ten tree species in the inland Northwest

Abstract

Individual tree height-diameter equations were developed for ten major species in the inland Northwest. The Wykofffunction in the Stand Prognosis Model and the Lundqvist function were fit to data which included many large-sized trees. The two models fit the data equally well for all species. Prediction results using the existing Prognosis equation, the refitted Wykofffunction, and the Lundqvist function showed that the three models predicted similar heights for trees of small diameter. However, both the refitted Wykofffunction and the Lundqvist function predicted larger tree heights for trees with dbh greater than 20 in. for most species. The estimated heights for tree diameters of 70 or 80 in. from the Lundqvist function were closer to the observed "asymptotic" tree heights than the other two. The Lundqvist function showed lower prediction errors for the validation data for the majority of the tree species, especially for large-sized trees.