Which Dependent Variable in Site Index-Height-Age Regressions?

Abstract

Abstract Two regressions relating height and site index can be calculated from stem analysis data. Site index estimation curves obtained by regressing site index on height and age differ from height growth curves obtained by regressing height on site index and age. The first provide estimates of site index for stands of known present age and height, while the second provide estimates of expected heights at different ages for stands of specified site index. The traditional type of height over age "site index curve" does not provide optimum estimates of site index. Magnitude and practical importance of differences depend on the amount of unexplained variation present. Appropriate uses of the two systems of curves and some sources of bias are discussed. Forest Sci. 20:74-87.