Climate-induced tree mortality: earth system consequences for carbon, energy, and water exchanges
Citation
Patrick D Royer, Charlie Luce, Craig D Allen, Travis E Huxman, Alison Macalady, Henry D Adams, and David D Breshears, Climate-induced tree mortality: earth system consequences for carbon, energy, and water exchanges: .
Summary
One of the greatest uncertainties in global environmental change is predicting changes in feedbacks between the biosphere and atmosphere that could present hazards to current earth system function. Terrestrial ecosystems, and in particular forests, exert strong controls on the global carbon cycle and influence regional hydrology and climatology directly through water and surface energy budgets. Widespread, rapid, drought- and infestation-triggered tree mortality is now emerging as a phenomenon affecting forests globally and may be linked to increasing temperatures and drought frequency and severity. We demonstrate the link between climate-sensitive tree mortality and risks of altered earth system function though carbon, water, and [...]
Summary
One of the greatest uncertainties in global environmental change is predicting changes in feedbacks between the biosphere and atmosphere that could present hazards to current earth system function. Terrestrial ecosystems, and in particular forests, exert strong controls on the global carbon cycle and influence regional hydrology and climatology directly through water and surface energy budgets. Widespread, rapid, drought- and infestation-triggered tree mortality is now emerging as a phenomenon affecting forests globally and may be linked to increasing temperatures and drought frequency and severity. We demonstrate the link between climate-sensitive tree mortality and risks of altered earth system function though carbon, water, and energy exchange. Tree mortality causes a loss of carbon stocks from an ecosystem and a reduction sequestration capacity. Recent research has shown that the 2000s pinyon pine die-off in the southwest US caused the loss of 4.6 Tg of aboveground carbon stocks from the region in 5 years, far exceeding carbon loss from other disturbances. Widespread tree mortality in British Columbia resulted in the loss of 270 Tg of carbon, shifting affected forestland from a carbon sink to a source, and influenced Canadian forest policy on carbon stocks. Tree mortality, as an immediate loss of live tree cover, directly alters albedo, near-ground solar radiation, and the relative contributions of evaporation and transpiration to total evapotranspiration. Near-ground solar radiation, an important ecosystem trait affecting soil heating and water availability, increased regionally following the pinyon pine die-off. Conversely, forest canopy loss with tree mortality, is expected to increase regional albedo, especially for forests which experience winter snow cover, potentially offsetting the climate forcing of terrestrial carbon releases to the atmosphere. Initial hydrological response to die-off is likely a reduction in evapotranspiration, which can increase subsurface flow, runoff, groundwater recharge, and streamflow. Under some circumstances there may also be increased flood risks. We hypothesized thresholds of mean annual precipitation and canopy cover reduction identified from the forest harvesting literature as minima that must be exceeded for die-off to noticeably affect hydrologic processes. We note exceptions to these thresholds when snowmelt dominates the watershed hydrology and when mortality affects a single species with a unique hydrologic role. Management options for mitigating die-off effects on ecosystem and earth system processes and implementing post-die-off restoration will likely be limited and costly, requiring ecological and societal adaptation in many areas. As such, climate-induced tree mortality poses a significant risk to the current earth system function through altered exchanges of carbon, energy, and water between the land surface and atmosphere.
Published in AGU Fall Meeting Abstracts, on pages 1151 - 1151, in 2010.
