Assessing the Risk of Hydraulic Function Failure for Tropical Forests Under Future Climate Changes

Authors

Zachary Robbins¹* (zjrobbins@lanl.gov), Chonggang Xu¹, Bradley Christoffersen², Ryan Knox³, Rosie A. Fisher⁴, Rutuja Chitra-Tarak¹, Martijn Slot⁵, Kurt Solander¹, Lara Kueppers^3,6, Charles Koven³, Nate McDowell⁷, Jeffrey Chambers³

Institutions

¹Los Alamos National Laboratory, Los Alamos NM; ²University of Texas–Rio Grande Valley, Edinburg, TX; ³Lawrence Berkeley National Laboratory, Berkeley, CA; ⁴CICERO Center for International Climate Research, Oslo, Norway; ⁵Smithsonian Tropical Research Institute, Panama City, Panama; ⁶University of California–Berkeley, CA; ⁷Pacific Northwest National Laboratory, Richland, WA

URLs

• https://ngee-tropics.lbl.gov

Abstract

Tropical forests play a critical role in regulating regional and global climates. However, recent drought-induced mortality in tropical forests suggests possible thresholds beyond which communities face the risk of widespread mortality. Modeling plant physiological response to drought is crucial to accurately forecast tropical forests and their carbon storage.

Hydraulic function failure in xylem due to embolism and dehydration, resulting from both water stress in the soil and high vapor pressure deficit in the air due to warming, is a crucial avenue for future mortality. A diverse set of plant hydraulic traits determine a plant’s water use strategies. Future droughts may disproportionately impact functional strategies that avoid drought through investments in greater water access or storage or tolerate it through investments in increased water stress resistance. Using 1,000 ensembles of hydraulic and growth traits, researchers parameterized a plant hydrodynamic model within FATES coupled to the land surface model within E3SM for the forests of Barro Colorado Island, Panama. This model was calibrated against observational data from Barro Colorado Island to constrain plant hydrodynamic, carbon, and water fluxes. These ensemble parameterizations were then used under multiple climate scenarios to assess the risk of hydraulic failure and resulting mortality. Drastic increases were observed in the mean number of months in which plant species faced risk of hydraulic failure (>60% loss of stem hydraulic conductivity). However, the likelihood of potential hydraulic failure was highly trait dependent, with some functional types experiencing no increase in mortality. Researchers further analyzed the traits that make plant functional types more vulnerable to hydraulic failure. The results suggest the critical importance of considering hydraulic failure risk in simulating regional carbon cycles in tropical forests.