Site-Specific Douglas-Fir Biomass Equations from the Siskiyou Mountains, Oregon, Compared with Others from the Pacific Northwest
Douglas-fir equations for aboveground biomass components were developed for the Long-Term Ecosystem Productivity Study in the Siskiyou Mountains of southwestern Oregon. The equations were based on data from 32 Douglas-fir trees randomly selected via probability proportional to size from a single stand. Our equations were then compared with nationally generalized equations, other published and widely used Pacific Northwest equations, recent site-specific equations from southwestern Washington, and the USDA Forest Service Forest Inventory and Analysis (FIA) Program regional equations and the component-ratio method. FIA predictions for stemwood were similar to the Siskiyou estimates, predicting on average 97% of our Siskiyou equation. The FIA component ratio method compared the best to our total aboveground biomass for a 70-cm dbh tree, predicting 103% of the Siskiyou estimate. The frequently used Pacific Northwest equations predicted higher and the Washington equation lower total aboveground biomass than ours. Crown component predictions varied much more widely by as much as 3-fold. Our protocols were most similar to those used in the Washington study, offering opportunities for analysis of site-specific metadata as covariants in future biomass investigations.