Improving Models of Stand and Watershed Carbon and Water Fluxes with More Accurate Representations of Soil-Plant-Water Dynamics in Southern Pine Ecosystems
Authors
Tom O’Halloran1,2,* (tohallo@clemson.edu), Jean-Christophe Domec3,4, Jamie Duberstein1, Cheng-Wei Huang5, A. Chris Oishi6, Brian Viner7, Tom Williams1
Institutions
1Baruch Institute of Coastal Ecology and Forest Science, Georgetown, SC; 2Department of Forestry and Environmental Conservation, Clemson University, Clemson, SC; 3Nicholas School of the Environment, Duke University, Durham, NC; 4Bordeaux Sciences Agro, France; 5Portland State University, Portland, OR; 6U.S. Forest Service, Coweeta Hydrologic Laboratory, Southern Research Station, Coweeta, NC; 7Savannah River National Laboratory, Aiken, SC
Abstract
Despite strong fundamental knowledge about the key processes through which plant hydraulics affect water uptake and productivity, researchers currently lack several key components necessary for a predictive understanding of ecosystem response to future climate conditions. These components include mechanistic understanding of plant-mediated hydraulic processes in under-studied systems and representations of biophysical factors affecting coupled water-carbon cycles in models. This project focuses on longleaf pine ecosystems, once a dominant forest type in the southeast U.S. that is undergoing large-scale efforts to be restored through much of its native range. During project year two, the team accomplished several goals with a focus on field measurements. Researchers installed an extensive array of tree root and trunk sap flow sensors, including some capable of detecting bidirectional root flow at night. The team also installed moisture probes in tree trunks and soil profiles to quantify tree and soil water storage. A soil respiration and evaporation experiment was initiated to collect pretreatment data; next year the roots will be severed to eliminate root flow in the treatment plot. These measurements will determine whether hydraulic redistribution (HR) affects shallow soil moisture and subsequently respiration or evaporation. Researchers also successfully quantified tree canopy leaf photosynthetic parameters by harvesting canopy branches and measured predawn and midday leaf water potentials, which are needed for modeling HR. Root mass and area profiles were measured in three replicates up to one meter. Soils were sent to the University of Indiana to measure hydraulic parameters. Data collection at AmeriFlux towers US-HB2 (mature longleaf) and US- HB3 (young longleaf) continued uninterrupted. The team installed a new understory eddy covariance system at US-HB2 with a new PhenoCam to track phenology of the longleaf understory.
Measurements resumed at AmeriFlux tower US-Akn at Savannah River National Laboratory, and a soil moisture profiler was installed. Advances in model development include an ecosystem respiration module accounting for both autotrophic and heterotrophic respiration, as well as a stochastic precipitation module described by the Marked Poisson process that will translate the precipitation results from Energy Exascale Earth System Model (E3SM) climate simulations to evaluate the impacts of future climate scenarios on the ecosystem water and carbon fluxes.