Updated generalized biomass equations for North American tree species

Historically, tree biomass at large scales has been estimated byapplying dimensional analysis techniques and field measurements such as diameter at breast height (dbh) in allometric regression equations. Equations often have been developed using differing methods and applied only to certain species or isolated areas. We previously had compiled and combined (inmeta-analysis) available diameter-based allometric regression equations for estimat-ing total aboveground and component dry-weight biomass for US trees. This had resulted in a set of 10 consistent, national-scale aboveground biomass regression equations for US species, as well as equations for predicting biomassof tree components asproportions of total abovegroundbiomass. In this updateof ourpublishedequation databaseandrefinementofourmodel,wedevelopedequationsbasedonallometric scaling theory,using taxonomic groupings andwood specific gravity as surrogates for scaling parameters thatwe could not estimate. The newap-proach resulted in35 theoretically basedgeneralized equations (13 conifer, 18hardwood, 4woodland), compared with the previous empirically grouped 10. For trees from USDA Forest Inventory and Analysis Program (FIA) plots, with forest types grouped into conifers andhardwoods, previous andupdatedequations producednearly identical estimatesthatpredicted20percenthigherbiomassthanFIAestimates.Differenceswereobservedbetweenpre-vious and updated equation estimates when comparisons were made using individual FIA forest types.