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

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 biomass for all plots was 2.2 t.ha(-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 following 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-bring 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 support previous studies showing that aspen forests are moisture limited in this region, which poses concerns for the future under a changing climate.