Sensitivity of Shrub–Grass Dynamics to Plant Hydraulics Under Drought in FATES and BiomeE
Authors
Kevin Wilcox1,2* (k_wilcox@uncg.edu), Anping Chen3, Ensheng Weng4, Kate McCulloh5, Kimberly O’Keefe6, Lydia Zeglin7, Jesse Nippert7
Institutions
1Department of Biology, University of North Carolina–Greensboro, NC; 2Department of Ecosystem Science and Management, University of Wyoming, Laramie, WY; 3Department of Biology, Colorado State University, Fort Collins, CO; 4Center for Climate Systems Research, Columbia University, New York, NY; 5Department of Botany, University of Wisconsin–Madison, WI; 6Department of Biological Sciences, St. Edwards University, Austin, TX; 7Department of Biology, Kansas State University–Manhattan, KS
Abstract
Shrubs are encroaching upon and eradicating many grasslands across Earth. Researchers currently have limited understanding about why this is occurring and the resulting consequences for critical ecosystem services, such as carbon sequestration. This project is designed to address both of these knowledge gaps through a combination of observational, experimental, and process-based modeling approaches in tallgrass prairie of eastern Kansas. The team measured a wide range of above- and belowground morphological and physiological characteristics of shrubs and grasses, as well as soil carbon turnover rates within the grass–shrub ecotone. Researchers imposed a multiyear drought experiment to understand responses of grasses, shrubs, and carbon cycling to water stress. The team is incorporating this empirical understanding into process-based models to test hypotheses about why shrub encroachment is occurring and to project impacts of encroachment on ecosystem carbon storage. Some major findings from the project to date include: (1) shrub encroachment will likely increase under increased drought frequency global change scenarios. Researchers think this is because shrub species in this system have smaller yet more numerous conduits in roots, leading to more stable photosynthesis of shrubs during drought compared with herbaceous species; (2) increased atmospheric carbon dioxide (CO2) may decrease the ability of fire to knock back shrubs because of rapid colonization rates of shrubs under increased CO2; and (3) Instead of the expected increases in carbon storage by shrubs in deeper soils, less carbon storage was found across all depths under shrubs due to lower root growth.
Here, the team focuses on the impact of droughts on shrub encroachment rates and will show results from benchmarking activities with long-term shrub/grass abundance data from Konza Prairie Biological Station and sensitivity analysis of shrub and grass plant functional types to various hydraulic parameters in two vegetation demographic models, FATES and BiomeE. These results provide mechanistic understanding of how shrub–grass boundaries may shift under various global change scenarios and identify areas where additional empirical understanding is needed.