Forest mortality risk to future climate and hydrology in a riparian woodland ecosystem

Xiaonan Tai, Biology, New Jersey Institute of Technology, NJ, Martin D. Venturas, School of Biological Sciences, University of Utah, Salt Lake City, UT, D. Scott Mackay, Geography, SUNY-Buffalo, Paul D. Brooks, Geology & Geophysics, University of Utah, Salt Lake City, UT and Lawrence B. Flanagan, Biological Sciences, University of Lethbridge, Lethbridge, AB, Canada

Background/Question/Methods
The future risk of forest mortality is poorly understood, despite the widespread observations of mortality events across the globe. While the direct effects of future climate and elevated CO2 have been studies when evaluating future forest mortality risk, the role of lateral hydrological flow has rarely been considered, especially in riparian ecosystems that are influenced by both climate and stream flow. Here we quantified the fingerprint of lateral flow on future forest mortality risk using a coupled plant hydraulics-hydrology model, ParFlow-TREES. We forced ParFlow-TREES with multiple ESM projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5) experiments and evaluated forest function and mortality risks at whole ecosystem and across the landscape.

Results/Conclusions
We find the joint consideration of lateral and climatic factor could generate different predictions of mortality risk compared to climate alone. Further, the water-saving and drought ameliorating effects of anticipated future CO2 concentrations are small when non-local hydrological processes are introduced. These findings challenge the prevailing expectation of elevated CO2 to reduce mortality risk and call for re-evaluation of vegetation persistence in altered climatic and hydrological conditions. The effect of the lateral hydrological flow is often overlooked in future projections of forest mortality risk, but this work highlights the need to assess these effects more explicitly moving forward.