Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

Aims: Our study aimed to: (1) document the preindustrial (1925) forest composition prior to extensive logging; (2) document the magnitude of changes from 1925 to 2005; and (3) identify the relative influence of logging and natural disturbances as drivers of the present-day forest composition.

Location: Boreal forest in central Quebec, eastern Canada.

Methods: We used a dense network of georeferenced historical (~1925) forest plots (n = 30 033) to document preindustrial forest composition. We evaluated the magnitude of changes with the present-day using modern plots (1980s to 2000s). We reconstructed a long-term, spatially explicit history of logging, spruce budworm outbreaks (Choristoneura fumiferana [Clem.], SBO), and fire using historical maps and field surveys.

Results: In the preindustrial period, late successional coniferous taxa (Abies balsamea and Picea spp.) dominated the landscape, whereas early successional deciduous taxa (Betula spp. and Populus spp.) were confined to recently burned areas. In the present-day landscape, large areas dominated by late successional coniferous taxa have been replaced by early successional deciduous taxa. Forest communities dominated by early successional deciduous taxa increased sharply throughout the study area. Logging has been a minor driver of these changes compared to fire and SBOs.

Conclusions: This study demonstrates the importance of documenting the long-term history of both anthropogenic and natural disturbances in order to assess their relative contributions to the development of the present-day forest ecosystems. Natural disturbances have remained the main drivers of forest composition during the 20th century, whereas logging played a less important role. In the current context of global change, long-term experimental research is required to help forecast impacts of natural disturbances and forest management on boreal forest composition.