Sensitivity of productivity to precipitation amount and pattern varies by topographic position in a semiarid grassland

Authors: Hoover, David; LAUENROTH, WILLIAM - Yale University; MILCHUNAS, DANIEL - Retired Non ARS Employee; Porensky, Lauren; Augustine, David; Derner, Justin

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2020
Publication Date: 2/9/2021
Publication URL: https://handle.nal.usda.gov/10113/7288692
Citation: Hoover, D.L., Lauenroth, W., Milchunas, D., Porensky, L.M., Augustine, D.J., Derner, J.D. 2021. Sensitivity of productivity to precipitation amount and pattern varies by topographic position in a semiarid grassland. Ecosphere. 12(2). Article e03376. https://doi.org/10.1002/ecs2.3376.
DOI: https://doi.org/10.1002/ecs2.3376

Interpretive Summary: Grassland productivity is an important part of terrestrial ecosystems, providing food for wild animals and livestock ,and driving global cycling of important elements such as carbon. Production is highly variable both in space and time due to a variety of environmental factors during periods of growth as well as legacies from past seasons. Understanding the patterns and drivers of variation in production at a local scale is important both to inform land manager decision-making and conserve natural resources. In this study, we examined how production varied by topographic positions over 36 years in a semi-arid grassland, as well as how precipitation and legacies influenced these dynamics. We had four main results 1. production was almost twice as high in the lowest part of the landscape than the highest, 2. production varied more in time than in space, 3. warm season grasses dominated all topographic positions and drove the total production patterns, 4. production was most sensitive to current year precipitation, but was also influence by legacies. These results suggest that the patterns of production variability in this semi-arid landscape are primarily driven by attributes of the current year precipitation, with the dominant warm season grasses key to the overall responses.

Technical Abstract: Aboveground net primary productivity (ANPP) in grasslands is an important integrator of terrestrial ecosystem function, a key driver of global biogeochemical cycles, and a critical source of food for wild and domesticated herbivores. ANPP exhibits high spatial and temporal variability, driven by a suite of factors including precipitation amount and pattern (e.g. spring total, number of events), biotic and abiotic legacies (e.g. prior years’ ANPP or growing season precipitation), and topographic heterogeneity. Global climate models forecast an altered hydrological cycle due to climate change, including higher precipitation variability and more extreme events, which may further increase spatiotemporal variability in ANPP. Therefore, it is essential to understand the sensitivity of this central ecosystem function to various precipitation metrics, legacies, and topographic positions to better inform sustainable grassland management. In this study, we analyzed long-term (36-year) ANPP data collected across a topographic sequence in the semiarid shortgrass steppe of North America to examine patterns and drivers of spatiotemporal variability in ANPP. We observed that 1) ANPP varied substantially by topographic position, with greater divergence during years with high production, 2) ANPP variability was higher temporally (16-fold maximum difference across years) than spatially (4-fold maximum difference across topographic positions), 3) warm season perennial grasses were the dominant plant functional type across all topographic positions and strongly influenced total ANPP dynamics, 4) ANPP had strong sensitivities to current-year precipitation amount and pattern that varied by plant functional type, as well as weaker sensitivities to precipitation and productivity legacies. Overall, the lowest topographic position had the highest sensitivity to precipitation, likely due to higher resource availability via the downhill movement of water and nutrients. These results suggest that temporal and spatial ANPP variability in shortgrass steppe is primarily driven by the combined effects of precipitation amount and pattern during the current year, with the dominant warm-season perennial grasses governing these responses.