A large number of regional-scale, drought-induced forest mortality events have been documented in the past 50 years, raising questions of forest resilience to drought under future climates. These questions have led to a large and rapidly-expanding body of experimental and modeling work to characterize the causes of tree mortality and forest response to drought. However, due to limited understanding of the hydrological and eco-physiological conditions leading from severe heat and drought to tree mortality, it has still proven difficult to ascertain whether forests will be more or less vulnerable to drought in the future. In this talk, we will discuss several model applications across a range of complexity used to link hydro-climatic variability with tree water and carbon balances toward quantification of tree drought stress and mortality thresholds. We develop a fully coupled soil-plant-atmosphere continuum and atmospheric boundary layer model to explore interaction of multiple climate change factors – temperature, humidity, rainfall amount and seasonality, and CO2.
Results/Conclusions
The model studies described above lead to two results. First, the statistics of climatic water deficit, specifically the frequency, duration, and intensity of soil moisture deficits predict observations of canopy cover loss. Canopy cover loss was predicted across a regional rainfall gradient and across watershed-scale variation in soil moisture. Secondly, simulations for 13 biomes across the globe show that the predicted impacts of future changes in humidity and CO2 offset those of heat and drought consistently across ecosystems.