Climatic and management determinants of large herbivore production in semiarid grassland

Authors: Derner, Justin; Raynor, Edward; REEVES, JUSTIN - Colorado State University; Augustine, David; MILCHUNAS, DANIEL - Colorado State University

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2019
Publication Date: 12/5/2019
Publication URL: https://handle.nal.usda.gov/10113/6766646
Citation: Derner, J.D., Raynor, E.J., Reeves, J., Augustine, D.J., Milchunas, D. 2019. Climatic and management determinants of large herbivore production in semiarid grassland. Agriculture, Ecosystems and Environment. 290:106761. https://doi.org/10.1016/j.agee.2019.106761.
DOI: https://doi.org/10.1016/j.agee.2019.106761

Interpretive Summary: We used 80 years of long-term large herbivore production data with consistent grazing treatments to evaluate both climatic and management determinants on large herbivore production in semiarid grassland. Cattle were stocked and managed in short-grass steppe pastures at heavy, moderate, and light stocking densities for the duration of the study. The magnitude of seasonal precipitation effects on production was greatest under heavy grazing intensity with the effect of spring, winter, and the prior growing season’s precipitation being 47, 88, and 96% greater, respectively, than moderate grazing intensity. Production instability increased under heavy grazing intensity, and winter and spring precipitation, but not summer precipitation, mediated livestock production with increasing sensitivity as grazing intensity increased.

Technical Abstract: Knowledge of climatic and management influences on large herbivore production (LHP, kg/ha) is needed for low productivity, semiarid grasslands to address potential consequences of both increasing climate variability and the need to increase animal protein 70% for human consumption by 2050. Here, we evaluate the influence of climatic variability and herbivore density on LHP in semiarid grassland using a unique long-term (80 years: 1939-2018) grazing study with three grazing intensities based on forage utilization (light, moderate and heavy). Seasonal variation in precipitation, but not temperature, was the primary influence on LHP. Winter (October-March) and spring (April-June), but not summer (July-September), precipitation during the current year positively influenced LHP across the 3 grazing intensities, whereas prior growing season (prior April-September) precipitation was consistently a negative influence. Although spring precipitation was the most influential seasonal weather variable for LHP, the effect of winter precipitation closely followed under all three grazing intensities, suggesting that non-growing season precipitation is essential for soil water storage to initiate production of sufficient high-quality forage in the subsequent grazing season, resulting in a positive feedback on LHP. A key finding from our analysis was that the effect of summer precipitation is smaller than the combined effects of winter and spring precipitation. As such, much of the variation in LHP can be predicted by seasonal weather parameters that are known early in the growing season. The magnitude of seasonal precipitation effects on LHP was greatest for heavy grazing; consequently LHP with heavy grazing is more reliant on primary production produced in the current year to increase LHP as forage quantity is more limiting than forage quality. Moreover, stability of LHP across years (range: 7.5 to 34.6 kg/ha) was less with heavy grazing, which results in “boom-bust” economics that threaten sustainability of operations. Management adaptations to mitigate climatic variability, therefore, will be most necessary and advantageous when land managers employ heavy grazing intensities. Despite the substantial interannual variability in precipitation that characterizes semiarid grasslands, our results show that proactive flexibility by land managers in adjusting grazing management decisions to seasonal precipitation amounts would reduce enterprise risk and improve confidence in decision-making, profitability, production efficiency and environmental sustainability from semiarid grasslands.