Water and carbon fluxes along an elevational gradient in a sagebrush ecosystem

Authors: Flerchinger, Gerald; Fellows, Aaron; Seyfried, Mark; Clark, Pat; LOHSE, KATHLEEN - Idaho State University

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2019
Publication Date: 5/29/2019
Citation: Flerchinger, G.N., Fellows, A.W., Seyfried, M.S., Clark, P.E., Lohse, K.A. 2019. Water and carbon fluxes along an elevational gradient in a sagebrush ecosystem. Ecosystems. https://doi.org/10.1007/s10021-019-00400-x.
DOI: https://doi.org/10.1007/s10021-019-00400-x

Interpretive Summary: The Great Basin region in the western US is changing rapidly due to a variety of stresses including woody encroachment, cheat grass invasion, land use intensification, and climate change. Observations of ecosystem processes across landscapes where elevation and climate change within a short distance provide invaluable information on the effects of changes in climate on vegetation ecosystems. As part of the Reynolds Creek Critical Zone Observatory, a network of research sites was established across such a gradient in elevation and climate within a sagebrush ecosystem located in Reynolds Creek Experimental Watershed. The sites span an elevation of 1425 to 2111 m, transitioning from sites with precipitation dominated by rainfall to those dominated by snow. This paper reports findings from the first two years of observation from the network. Results suggest that the sensitivity of the sites to climate change will play out differently depending on whether vegetation productivity is water-limited or temperature-limited. Long-term monitoring across this gradient capturing a range of weather patterns will provide the opportunity to assess how these ecosystems respond to different stress conditions and the resultant changes in vegetation composition and productivity.

Technical Abstract: Observations of ecosystem processes across gradients provide invaluable information on the effects of potential changes. Results from the first two years of observation from a network of four eddy covariance systems are presented to quantify differences in water and carbon fluxes along a climate gradient within a sagebrush ecosystem and to make inferences about the potential impacts of climate warming. The network is part of the Reynolds Creek Critical Zone Observatory and contributes to ongoing long-term environmental research and monitoring by the USDA Agricultural Research Service at the Reynolds Creek Experimental Watershed. Data from the network is being made publically available through t'1e AmeriFlux Network. The sites include a Wyoming big sagebrush site, a low sagebrush site, a post-fire mountain big sagebrush site, and a mountain big sagebrush site located at elevations of 1425, 1680, 1808 and 2111 m. Climate variation follows the montane elevation gradient; mean annual precipitation at the sites is 290, 337, 425, and 795 mm, respectively, and mean annual temperature is 8.9, 8.4, 6.1, 5.4°C. Annual Gross Ecosystem Production (GEP) for the sites averaged 349, 555, 712, and 814 gC/m2, respectively for the two years. Annual Net Ecosystem Production (NEP) indicated that the low elevation Wyoming big sagebrush site was nearly carbon-neutral for 2015, while the other sites with higher precipitation input had a net flux of 110 to 150 gC/m2 to the ecosystem. All sites had a net carbon flux of about 100 to 190 gC/m2 to the ecosystem during 2016. Carbon flux and evapotranspiration (ET) peaked about a month earlier at the lower elevation sites, but with limited precipitation the vegetation also encountered water stress much earlier. Data from these sites were supplemented with data from previous studies to further substantiate a linear relation between GEP and ET reported in the literature. Sensitivity of the sites to climate warming was investigated using model simulations. Results suggest that climate warming will play out differently depending on whether ET and GEP are temperature or water limited. Climate warming will likely have a negligible impact on annual ET at lower elevations, but rather shift ET earlier in the season and prolong the period of water stress. Conversely, results suggest that climate warming may significantly increase ET at higher elevations where it and GEP are energy limited; thus ET and GEP may increase with climate warming at higher elevations.