Regeneration Dynamics of White Spruce, Trembling Aspen, and Balsam Poplar in Response to Disturbance, Climatic, and Edaphic Factors in the Cold, Dry Boreal Forests of the Southwest Yukon, Canada

The southwestern region of the Yukon Territory of Canada has experienced an unprecedented spruce bark beetle outbreak (Dendroctonus rufipennis) and an increase in the frequency of forest fires that extend beyond historical trends and that have caused significant impacts on forest structure and composition. A Strategic Forest Management Plan (SFMP) for the Champagne and Aishihik Traditional Territory located in the southwest Yukon was implemented in 2004 in response to the spruce bark beetle (D. rufipennis) infestation and increased fire risk. The plan has recommended salvage harvesting of beetle-killed stands as a strategy to facilitate the development of a timber industry in the region and reduce the fire risk around communities. One of the objectives of the SFMP is to maintain, restore, or enhance forest regeneration, which requires an understanding of regeneration dynamics in the region. In this study, we investigated the regeneration of white spruce (Picea glauca), trembling aspen (Populus tremuloides), and balsam poplar (Populus balsamifera) and the relationship with climatic, disturbance, and edaphic factors within the region. Multivariate canonical correlation analysis was used to assess the weighted relationship between regeneration presence/absence and environmental factors, and negative binomial regression analysis was used to model regeneration abundance of white spruce, trembling aspen, and balsam poplar. We found that although regeneration of all three species responded positively to disturbance, the broadleaved species occupied disturbed plots at higher ratios than white spruce. Regeneration of broadleaved species was higher in open sites with exposed aspects, indicating a preference for warmer sites with higher solar radiation inputs. These findings support the hypothesis that if fire increased in the region with the warmer climate predicted by the Intergovernmental Panel on Climate Change, then the region will probably experience an increase in broadleaved species, leading to a more heterogeneous landscape.