Monitor And Constrain Tropical Ecosystem Sensitivity to Moisture: Progress in Characterizing Ecohydrology of a Tropical Moist Forest Under Experimental Throughfall Exclusion

Authors

Xiangtao Xu¹* (xx286@cornell.edu), Coral del Mar Valle-Rodríguez¹, Xavier Comas², Xi Yang³, Tana Wood⁴, Charlie Koven⁵, Maria Uriarte⁶, Vincent Humphrey⁷, Chris Smith-Martin⁸

Institutions

¹Cornell University, Ithaca, NY; ²Florida Atlantic University–Boca Raton, FL; ³University of Virginia, Charlottesville, VA; ⁴International Institute of Tropical Forestry, Luquillo, Puerto Rico; ⁵Lawrence Berkeley National Laboratory, Berkeley, CA; ⁶Columbia University, New York City, NY; ⁷ETH Zurich, Zurich, Switzerland; ⁸University of Minnesota–Twin Cities, Minneapolis/St. Paul, MN

Abstract

How tropical vegetation responds to moisture changes and how these responses in turn regulate ecosystem water dynamics constitutes a major uncertainty in ecohydrological predictions in Earth System Models (ESMs). In this project, the team aims to improve mechanistic understanding of plant-mediated ecohydrology by monitoring and modeling ecosystem dynamics at a new manipulative throughfall exclusion (TFE) experiment at Luquillo LTER station, Puerto Rico. Researchers focus on investigating (1) the coupling between soil moisture and vegetation water content; (2) the relatively unconstrained plant ecohydrological processes such as leaf angle responses to water stress and root hydraulic redistribution; and (3) the implications of site-level manipulative experiment results on modeling long-term vegetation dynamics in the tropics.

Field campaigns in 2023 have installed in situ sensors and collected critical pre-treatment data. Researchers now have several months of continuous data from GNSS sensor pairs that can provide one of the first ground-based vegetation optical depth measurements for tropical forests. Researchers have also installed soil moisture and soil water potential sensors that can sample horizontal and vertical heterogeneity in soil water conditions. These point soil moisture measurements agree qualitatively with soil moisture estimates with ground-penetration radar (GPR) from the campaigns, implying the potential of using GPR in monitoring 2D and 3D moisture patterns and dynamics in the system. Additionally, researchers have preliminary stem and root sapflow data from representative species to infer plant hydrodynamics and root hydraulic redistribution, and preliminary terrestrial laser scanning (TLS) suggests it is possible to monitor canopy leaf angle changes under water stress (Yang et al. 2023). These field data and other tropical data such as tree rings provided by additional collaborators (Xu et al. 2024) will be assimilated into ED2.2-hydro and E3SM Land Model-FATES to explore the implications of tropical ecosystem sensitivity to moisture constrained by the TFE experiment.

References

Yang, X., et al. “Leaf Angle as a Leaf and Canopy Trait: Rejuvenating its Role in Ecology with New Technology,” Ecology Letters