Calibration of volume and component biomass equations for Douglas-fir and lodgepole pine in Western Oregon forests

Abstract

Using data from destructively sampled Douglas-fir and lodgepole pine trees, we evaluated the performance of regional volume and component biomass equations in terms of bias and RMSE. The volume and component biomass equations were calibrated using three different adjustment methods that used: (a) a correction factor based on ordinary least square regression through origin (OLS-RTO method); (b) a correction factor based on OLS with intercept (OLS-WI method); and, (c) an inverse approach. The regional volume equations performed fairly well and produced similar results as the locally fitted volume equations of the same form but the regional predicted component biomass estimates were highly biased. All adjustment methods improved the performance of regional equations for the calibration dataset. Based on leave-one-out cross validation, the calibration based on OLS-RTO and OLS-WI methods reduced the RMSE for all species-component combinations. The inverse approach improved the performance of the regional equations for Douglas-fir but it did not improve lodgepole pine regional biomass equations. The decreasing trend of RMSE in component biomass estimation by using randomly selected trees to calibrate regional equations slowed down considerably after five trees.

Citation

Poudel, Krishna P.; Hailemariam, Temesgen. 2016. Calibration of volume and component biomass equations for Douglas-fir and lodgepole pine in Western Oregon forests. The Forestry Chronicle. 92(2): 172-182.