The ability of national and multipurpose ecological classification systems to provide an optimal zonation for a fire regime is questionable. Using wildfire (.1 ha) point data for the 1980-99 period, we defined zones with a homogeneous fire regime (HFR) across Canada and we assessed how these differ from the National Ecological Framework for Canada (NEFC) units of corresponding scale, i.e. ecoprovinces. Two HFR zonations were produced through spatially constrained clustering of (i) 1600-km 2 cells and (ii) the smallest units of the NEFC system, i.e. ecodistricts, using attributes for natural and anthropogenic fires. Thirty-three HFR zones were identified. HFR zonations showed smaller differences among each other than with NEFC ecoprovinces. Comparisons with ecoprovinces suggested general agreement of generalised fire regime values with HFR zones but with poor zone boundary correspondence. Ecoprovince zonation led to an overgeneralisation of fire regime estimates with less variation captured than by the HFR zonations, especially that using gridded fixed-area cells. Estimates of fire-return interval strongly differed between a priori and HFR zonations. The use of large-scale NEFC units or a zonation using its smallest units may constrain our ability to accurately quantify and portray fire regime variability across the country. The alternative empirical HFR zonation using gridded cells refines the location and nature of fire risk.

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Large secondary-nesting birds such as ducks rely on appropriate cavities for breeding. The main objective of this study was to assess the availability of large cavities and the potential of a managed boreal coniferous landscape to provide nesting trees within the breeding area of the eastern population of Barrow's Goldeneye (Bucephala islandica), a cavity-nesting species at risk in Canada. Woodpecker surveys were conducted in both conifer and mixed-wood landscapes, and cavities were sought in line transects distributed in unharvested and linear remnant stands of balsam fir (Abies balsamea) and black spruce (Picea mariana) as well as in cutblocks. No Pileated Woodpeckers (Dryocopus pileatus) were detected in the breeding area of Barrow's Goldeneye, but the species was present in the nearby lowland area in which trembling aspen (Populus tremuloides) is abundant. Only 10 trees (0.2% of those sampled) supported cavities considered suitable for Barrow's Goldeneye in terms of dimensions and canopy openness. Most of the suitable cavities found during this study were nonexcavated apical (chimney) cavities in relatively short snags that showed advanced states of decay. A diameter-at-breast-height threshold was determined for each tree species, after which the probability of cavity occurrence was enhanced in terms of potential cavity trees for Barrow's Goldeneye. Remnant linear forest sites had lower potential tree densities than did their unharvested equivalents. Large cavities were thus a rare component in this boreal landscape, suggesting that they may be a limiting factor for this population at risk. Current even-aged forest management that mainly relies on clear-cut practices is likely to further reduce the potential of this landscape to provide trees with suitable cavities. RÉSUMÉ. Les oiseaux de grande taille qui sont des utilisateurs secondaires de cavités, comme les canards, dépendent de cavités adéquates pour nicher. L'objectif principal de cette recherche était d'évaluer la disponibilité de grandes cavités et le potentiel d'un paysage de forêt boréale coniférienne aménagée à fournir des arbres dans lesquels le Garrot d'Islande (Bucephala islandica) de la population de l'Est, une espèce cavicole en péril au Canada, peut nicher. Des relevés de pics ont été effectués dans des paysages conifériens et mixtes, et des recherches de cavités ont été faites dans des transects situés en forêts non récoltées et en forêts résiduelles linéaires de Sapin baumier (Abies balsamea) et d'Épinette noire (Picea mariana), ainsi que dans des parterres de coupe. Aucun Grand Pic (Dryocopus pileatus) n'a été observé dans l'aire de nidification du Garrot d'Islande, mais cet excavateur primaire était présent dans les basses terres avoisinantes, où le Peuplier faux-tremble (Populus tremuloides) est abondant. Seulement 10 arbres, soit 0,2 % des arbres échantillonnés, avaient des cavités jugées adéquates (bonnes dimensions et ouverture du couvert forestier suffisante) pour le Garrot d'Islande. La plupart des cavités trouvées au cours de cette...

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