The estimation of aboveground biomass density (organic dry mass per unit area) is required for balancing Canadian national forest carbon budgets. Tree biomass equations are the basic tool for converting inventory plot data into biomass density. New sets of national tree biomass equations have therefore been produced from archival biomass data collected at the beginning of the 1980s through the ENergy from the FORest research program (ENFOR) of the Canadian Forest Service. Since the sampling plan was not standardized among provinces and territories, data had to be harmonized before any biomass equation could be considered at the national level. Two features characterize the new equations: estimated biomass of the compartments (foliage, branch, wood, and bark) are constrained to equal the total biomass, and dependence among error terms for the considered compartments of the same tree is taken into account in the estimates of both the model parameters and the variance prediction. The estimation method known to economists as "seemingly unrelated regression" allowed the inclusion of dependencies among the error terms of the considered biomass compartments. Sets of equations based on diameter at breast height (dbh) and on dbh and height have been produced for 33 species, groups of hardwood and softwood, and for all species combined. Biomass predicted by the new equations was compared with that estimated from provincial equations to evaluate the loss of accuracy when scaling up from the regional to the national scale. Bias and error of prediction from the set of national equations based on dbh and height were generally more similar to those from provincial equations than to those of predictions from the set of equations based on dbh alone.Résumé : L'estimation de la densité de biomasse aérienne (matière organique sèche par unité de surface) est requise pour déterminer les bilans nationaux canadiens de carbone forestier. Les équations de biomasse d'arbre constituent l'outil de base pour convertir les données des placettes d'inventaire en densité de biomasse. C'est pour cette raison que les données de biomasse ont été récupérées d'archives nationales pour produire de nouvelles séries d'équations de biomasse d'arbre. Ces données ont été recueillies au début des années 80 par le Service canadien des forêts dans le cadre du programme de recherche appelé ÉNergie de la FORêt (ENFOR). Comme le plan d'échantillonnage n'était pas standardisé parmi les provinces et territoires, les données ont dû être uniformisées avant que les équations de biomasse puissent être considérées au niveau national. Deux propriétés caractérisent les nouvelles équations de biomasse : les estimés de composantes de biomasse (feuille, branche, bois et écorce) sont contraints à égaliser la biomasse totale et la dépen-dance parmi les termes d'erreurs pour les différentes composantes d'un même arbre est prise en considération dans les estimés des paramètres du modèle et dans la variance de la prédiction. La méthode d'estimation connue par les écono-mistes com...

1. Although the importance of plant community assemblages in structuring invertebrate assemblages is well known, the role that architectural complexity plays is less well understood. In particular, direct empirical data for a range of invertebrate taxa showing how functional groups respond to plant architecture is largely absent from the literature.2. The significance of sward architectural complexity in determining the species richness of predatory and phytophagous functional groups of spiders, beetles, and true bugs, sampled from 135 field margin plots over 2 years was tested. The present study compares the relative importance of sward architectural complexity to that of plant community assemblage.3. Sward architectural complexity was found to be a determinant of species richness for all phytophagous and predatory functional groups. When individual species responses were investigated, 62.5% of the spider and beetle species, and 50.0% of the true bugs responded to sward architectural complexity.4. Interactions between sward architectural complexity and plant community assemblage indicate that the number of invertebrate species supported by the plant community alone could be increased by modification of sward architecture. Management practices could therefore play a key role in diversifying the architectural structure of existing floral assemblages for the benefit of invertebrate assemblages.5. The contrasting effects of sward architecture on invertebrate functional groups characterised by either direct (phytophagous species) or indirect (predatory species) dependence on plant communities is discussed. It is suggested that for phytophagous taxa, plant community assemblage alone is likely to be insufficient to ensure successful species colonisation or persistence without appropriate development of sward architecture.

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