B53D-0586
Linking Tropical Forest Function to Hydraulic Traits in a Size-Structured and Trait-Based Model
Friday, 18 December 2015
Poster Hall (Moscone South)
Bradley O Christoffersen1, Manuel Gloor2, Sophie Fauset2, Nikolaos Fyllas3, David Galbraith2, Tim R. Baker2, Lucy Rowland4, Rosie Fisher5, Oliver Binks4, Maurizio Mencuccini6, Patrick Meir7, Nathan G McDowell1, Chonggang Xu1 and Sanna Sevanto1, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)University of Leeds, School of Geography, Leeds, United Kingdom, (3)University of Athens, Ecology and Systematics, Athens, Greece, (4)University of Edinburgh, School of GeoSciences, Edinburgh, United Kingdom, (5)National Center for Atmospheric Research, Boulder, CO, United States, (6)ICREA at CREAF, Barcelona, Spain, (7)University of Edinburgh, Edinburgh, EH9, United Kingdom
Abstract:
A major weakness of forest ecosystem models is their inability to capture the diversity of responses to changes in water availability, severely hampering efforts to predict the fate of tropical forests under climate change. Such models often prescribe moisture sensitivity using heuristic response functions that are uniform across all individuals and lack important knowledge about trade-offs in hydraulic traits. We address this weakness by implementing a process representation of plant hydraulics into an individual- and trait-based model (Trait Forest Simulator; TFS) intended for application at discrete sites where community-level distributions of stem and leaf trait spectra (wood density, leaf mass per area, leaf nitrogen and phosphorus content) are known. The model represents a trade-off in the safety and efficiency of water conduction in xylem tissue through hydraulic traits, while accounting for the counteracting effects of increasing hydraulic path length and xylem conduit taper on whole-plant hydraulic resistance with increasing tree size. Using existing trait databases and additional meta-analyses from the rich literature on tropical tree ecophysiology, we obtained all necessary hydraulic parameters associated with xylem conductivity, vulnerability curves, pressure-volume curves, and hydraulic architecture (e.g., leaf-to-sapwood area ratios) as a function of the aforementioned traits and tree size. Incorporating these relationships in the model greatly improved the diversity of tree response to seasonal changes in water availability as well as in response to drought, as determined by comparison with field observations and experiments. Importantly, this individual- and trait-based framework provides a testbed for identifying both critical processes and functional traits needed for inclusion in coarse-scale Dynamic Global Vegetation Models, which will lead to reduced uncertainty in the future state of tropical forests.
