Résumé - CAFD

Ecological factors explaining the location of the boundary between the mixedwood and coniferous bioclimatic zones in the boreal biome of eastern North America.

Yassine Messaoud, Yves Bergeron, Alain Leduc.

Aim Climate is often regarded as the primary control determining the location of an ecotone between two vegetation zones. However, other ecological factors may also be important, especially when the northern limit of the dominant species of a vegetation zone extends further than the limit of the zone itself. This study aimed to identify the ecological variables explaining the transition between two zones within the boreal biome in Quebec (eastern Canada): the southern mixedwood forests dominated by balsam fir ( Abies balsamea ) and white birch ( Betula papyrifera ), and the northern coniferous forests dominated by black spruce ( Picea mariana ).

Location Quebec (eastern Canada).

Methods Data from 5023 sampling plots from the ecological inventory of the Québec Ministry of Natural Resources distributed throughout the two bioclimatic zones were used in logistic regressions to determine the relationships between the presence or absence of balsam fir stands and different abiotic and biotic variables, at both stand and landscape scales.

Results The presence of balsam fir stands was negatively related to the thick organic horizons, coarse xeric deposits and low positions on the slope, whereas stands were favoured by high elevations, steep slopes and moderate drainage. These results defined the suitable conditions for the development of balsam fir stands. In the coniferous zone these suitable conditions were less abundant. Furthermore, the saturation level of suitable sites was lower, as well as the incidence of balsam fir stands in unsuitable sites (overflow). Balsam fir stands were mostly located near lakes and rivers. All significant variables at both the stand and landscape scales explained between 34 and 42% of the location of the potential northern distribution limit of the mixedwood zone.

Main conclusions Our results suggest the important role of historical factors related to post-glacial vegetation and past disturbances in determining the relative abundance of balsam fir in both zones of the boreal biome.