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Regionally fitted allometric equations for individual trees and root-to-shoot ratio values are normally used to estimate local aboveground and belowground forest biomass, respectively. However, uncertainties arising from such applications are poorly understood. We developed equations for both aboveground and belowground biomass using destructive sampling for three dominant upland boreal tree species in northwestern Alberta, Canada. Compared with our equations, the diameter-based national equations derived for use across Canada underestimated aboveground biomass for Picea glauca (Moench) Voss but gave reasonable estimates for Populus balsamifera L. and Populus tremuloides Michx. The national equations based on both tree diameter and height overestimated aboveground biomass for the Populus species but underestimated it for Picea glauca in our study area. The approach of root-to-shoot ratio proposed by the Intergovernmental Panel on Climate Change (IPCC) overestimated belowground biomass by 16%-41%, depending on forest cover type, in comparison with our values estimated directly on site, with the greatest bias in deciduous-dominated stands. When the general allometric equations for aboveground biomass and the root-toshoot ratio for belowground biomass were combined to estimate stand biomass, overestimation could be as high as 18% in our study area. The results of our study support the development of improved regional allometric equations for more accurate local-scale estimations. Incorporating intraspecific variation of important traits such as tree taper may be especially helpful. Key words: EMEND (Ecosystem Management Emulating Natural Disturbance), intraspecific trait variation, root-to-shoot ratio, tree taper, wood density. On utilise generalement des equations allometriques ajustees a l'echelle regionale pour les arbres individuels et des valeurs du rapport racines-tiges pour estimer respectivement la biomasse forestiere locale, aerienne et souterraine. Cependant, les incertitudes decoulant de telles applications sont mal comprises. Nous avons developpe des equations de biomasse aerienne et souterraine en utilisant un echantillonnage destructif pour trois especes d'arbres boreales dominantes dans les hautes terres du nord-ouest de l'Alberta, au Canada. Comparativement a nos equations, les equations nationales basees sur le diametre developpees pour etre utilisees partout au Canada sous-estimaient la biomasse aerienne de Picea glauca (Moench) Voss, mais donnaient des estimations raisonnables pour Populus balsamifera L. et Populus tremuloides Michx. Les equations nationales basees sur le diametre et la hauteur des arbres surestimaient la biomasse aerienne des especes de Populus L., mais la sous-estimaient pour Picea glauca dans notre zone d'etude. L'approche du rapport racines-tiges, proposee parle Groupe d'experts intergouvernemental sur l'evolution du climat (GIEC), a surestime la biomasse souterraine de 16 a 41% selon le type de couvert forestier par rapport a nos valeurs estimees directement sur le site, le biais le plus important etant observe dans les peuplements domines par les feuillus. En combinant les equations allometriques generales pour la biomasse aerienne et le rapport racines-tiges pour la biomasse souterraine pour estimer la biomasse du peuplement, la surestimation pouvait atteindre 18% dans notre zone d'etude. Les resultats de notre etude justifient le developpement d'equations allometriques regionales ameliorees pour des estimations plus precises a l'echelle locale. L'incorporation des variations intraspecifiques des attributs importants, tels que le defilement de la tige des arbres, peut etre particulierement utile. [Traduit par la Redaction] Mots-cles : amenagement ecosystemique, variations intraspecifiques des attributs, rapport racines-tiges, defilement de la tige, densite du bois., Introduction Increasing pressure to reduce net carbon dioxide (CO2) emissions in light of climate change is spurring development of global strategies such as carbon markets that encourage carbon offsets through [...]

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