Impacts of a regional drought on the productivity, dieback, and biomass of western Canadian aspen forests

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Abstract
We examined the impacts of a severe, regional drought (2001-2002) on trembling aspen (Populus tremuloides Michx.) forests in the western Canadian interior. A total of 150 plots were established in 25 study areas as part of a regional-scale study (CIPHA). Aspen health and mortality were assessed annually during 2000-2005, and changes in stem biomass were estimated using tree-ring analysis and plot-based measurements. Net mean increment in living bio- mass for all plots was 2.2 tha -1 � year -1 during 2000-2002 but subsequently decreased to near zero. This collapse was driven by a more than two-fold increase in stem mortality and a 30% decrease in regional stem growth during and fol- lowing the drought. The analysis showed that spatial variation in aspen productivity and biomass across the region was positively related to multiyear mean values of a climate moisture index and mineral soil silt content but was negatively related to levels of insect defoliation and wood-boring insects. In contrast, mortality and dieback was best correlated with minimum annual climate moisture index, which provided a measure of short-term drought severity. The results sup- port previous studies showing that aspen forests are moisture limited in this region, which poses concerns for the future under a changing climate.