Populus tremuloides stands continue to deteriorate after drought-incited sudden aspen decline

Abstract

Reports of forest damage have increased with the frequency of climatic extremes, but longer term impacts of such events on population dynamics of forest trees are generally unknown. Incited by the turn-of-the-century drought, sudden aspen decline (SAD) damaged 535 000 ha of Populus tremuloides Michx. in the Southern Rockies ecoregion of western North America. Although spread of the disease stopped in about 2009, most of the affected stands continued to deteriorate. Remeasurement of plots in southwestern Colorado showed that, since the peak of the epidemic, live basal area in sick plots decreased by an additional 28% to only 38% of that in healthy plots. Sick plots had much more recent damage than healthy plots, with almost three times as much recently dead basal area, over twice the density of recently dead trees, and almost four times as much recent crown loss. The important contributing agents in SAD were still active in sick stands in 2013. Density of small regeneration showed opposite trends, increasing in healthy plots and decreasing in sick plots. Timely regeneration treatments may be needed in some such stands to facilitate recovery. In addition to acute damage from climatic extremes, long-term decline diseases like SAD will likely be a common signature of forest damage from climate change.