Site-Dependent Height-Age Models for Paper Birch in British Columbia

Abstract

In British Columbia, foresters use the height-age models for trembling aspen (Populus tremuloides Michx.) from the neighbouring province of Alberta to predict height and site index for paper birch (Betula papyrifera Marsh.) because height-age models for paper birch in British Columbia do not exist. The aspen model has not been extensively tested for local use on paper birch trees. Consequently, it is not known how well they predict the height growth of site trees. We rectified this situation by developing paper birch height-age models from locally collected stem analysis data for paper birch. Data from 61 plots in the Interior Douglas-Fir, Interior Cedar and Hemlock, and Sub-Boreal Spruce biogeoclimatic zones were fit to a model based on the log-logistic function. Differences in growth patterns between the zones were detected using indicator variables. This height-age model should be used for paper birch in the sampled biogeoclimatic zones in British Columbia because it is the best fitting model. An alternative model is available for sites not in the sampled zones. A comparison of the trembling aspen model and the paper birch model indicates that the difference between the models is small over most of the management age range of paper birch. The exception to this is at young ages and high site indexes, where paper birch is predicted to be taller than trembling aspen.