Large-scale and local climatic controls on large herbivore productivity: Implications for adaptive rangeland management

Authors: Raynor, Edward; Derner, Justin; Hoover, David; PARTON, WILLIAM - Colorado State University; Augustine, David

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2019
Publication Date: 1/10/2020
Citation: Raynor, E.J., Derner, J.D., Hoover, D.L., Parton, W., Augustine, D.J. 2020. Large-scale and local climatic controls on large herbivore productivity: Implications for adaptive rangeland management. Ecological Applications. 30(3). Article e02053. https://doi.org/10.1002/eap.2053.
DOI: https://doi.org/10.1002/eap.2053

Interpretive Summary: This article evaluates the role of sea surface temperature anomalies, the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) in concert with local precipitation and density of livestock in livestock production. Livestock production peaked with heavy stocking rates. However, the variability of livestock production under heavy stocking was as much as 91% greater than lower stocking rates when PDO phase was cold relative to variability under warm phase PDO. Furthermore, the degree to which increased density of livestock improved livestock production was related to PDO phase, ENSO magnitude, prior growing season precipitation, and non-growing season precipitation. Key findings emphasize two points: (1) relationships between prevailing climate modes and livestock production are sensitive to non-growing season precipitation; and (2) the magnitude of larger-scale ENSO and PDO phase effects on local precipitation-livestock production relationships is contingent on density of livestock. Thus, knowledge of the PDO phase, ENSO magnitude, and recent precipitation could be used by livestock producers to better match numbers of livestock with forage availability and provide a buffer against the negative impacts of dry years.

Technical Abstract: Rangeland ecosystems worldwide are characterized by a high degree of uncertainty in precipitation, both within and across years. This uncertainty creates challenges for livestock managers seeking to match herbivore numbers with forage availability to prevent vegetation degradation and optimize livestock production. Here, we assess variation in annual large herbivore production (LHP, kg/ha-1) across multiple herbivore densities over a 78-year period (1940-2018) in a semi-arid rangeland ecosystem (shortgrass steppe of eastern Colorado, USA) that has experienced several phase changes in global level sea surface temperature (SST) anomalies Pacific Decadal Oscillation (PDO) and the El Niño–Southern Oscillation (ENSO). We examined the influence of prevailing PDO phase, magnitude of late winter (February-April) ENSO, prior growing season precipitation (prior April-prior September) and precipitation during the six months (prior October-current April) preceding the growing season on LHP. All of these are known prior to the start of the growing season in the shortgrass steppe, and could potentially be used by livestock managers to adjust herbivore densities. Annual LHP was greater during warm PDO irrespective of herbivore density, while variance in LHP increased by 69% (moderate density) and 91% (high density) under cold-phase compared to warm-phase PDO. No differences in LHP attributed to PDO phase were observed with low herbivore density. ENSO effects on LHP, specifically La Nina, were more pronounced during cold-phase PDO years. High herbivore density increased LHP at a greater rate than at moderate and low densities with increasing fall and winter precipitation. Differential gain, a weighted measure of LHP under higher relative to lower herbivore densities, was sensitive to prevailing PDO phase, ENSO magnitude, and precipitation amounts from the prior growing season and current fall-winter season. Temporal hierarchical approaches using PDO, ENSO, and local-scale precipitation can enhance decision-making for flexible herbivore densities. Herbivore densities could be increased above recommended levels with lowered risk for managers during warm-phase PDO to result in greater LHP and less variability. Conversely, during cold-phase PDO, managers need be cognizant of the additional influences of ENSO and prior fall-winter precipitation as herbivore densities will likely need to be lowered to accommodate increased risk of forage shortages.