Large drought‐induced aboveground live biomass losses in southernRockyMountain aspen forests

Abstract

AbstractWidespread drought‐induced forest mortality has been documented across multiple tree species inNorthAmerica in recent decades, but it is a poorly understood component in terrestrial carbon (C) budgets. Recent severe drought in concert with elevated temperature likely triggered widespread forest mortality of trembling aspen (Populus tremuloides), the most widely distributed tree species inNorthAmerica. The impact on the regional C budgets and spatial pattern of this drought‐induced tree mortality, which has been termed ‘sudden aspen decline (SAD)’, is not well known and could contribute to increased regional C emissions, an amplifying feedback to climate change. We conducted a regional assessment of drought‐induced live aboveground biomass (AGB) loss fromSADacross 915 km2of southwesternColorado,USA, and investigated the influence of topography on the severity of mortality by combining field measures, remotely sensed nonphotosynthetically active vegetation and a digital elevation model. Mean [± standard deviation (SD)] remote sensing estimate of liveAGBloss was 60.3 ± 37.3 Mg ha−1, which was 30.7% of field measuredAGB, totaling 2.7 Tg of potential C emissions from this dieback event. Aspen forest health could be generally categorized as healthy (0–30% field measured canopy dieback), intermediate (31–50%), andSAD(51–100%), with the remote sensing estimated mean (± SD) liveAGBlosses of 26.4 ± 15.1, 64.5 ± 9.2, and 108.5 ± 24.0 Mg ha−1, respectively. There was a pronounced clustering pattern ofSADon south‐facing slopes due to relatively drier and warmer conditions, but no apparent spatial gradient was found for elevation and slope. This study demonstrates the feasibility of utilizing remote sensing to assess the ramification of climate‐induced forest mortality on ecosystems and suggests promising opportunities for systematic large‐scale C dynamics monitoring of tree dieback, which would improve estimates of C budgets ofNorthAmerica with climate change.