Variable effects of long-term livestock grazing across the western United States suggest diverse approaches are needed to meet global change challenges

Authors: Copeland, Stella; Hoover, David; Augustine, David; Bates, Jonathan - Jon; Boyd, Chad; Davies, Kirk; Derner, Justin; DUNIWAY, MICHAEL - Us Geological Survey (USGS); Porensky, Lauren; Vermeire, Lance

Submitted to: Applied Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/7/2023
Publication Date: 3/14/2023
Citation: Copeland, S.M., Hoover, D.L., Augustine, D.J., Bates, J.D., Boyd, C.S., Davies, K.W., Derner, J.D., Duniway, M.C., Porensky, L.M., Vermeire, L.T. 2023. Variable effects of long-term livestock grazing across the western United States suggest diverse approaches are needed to meet global change challenges. Applied Vegetation Science. 26(1). Article e12719. https://doi.org/10.1111/avsc.12719.
DOI: https://doi.org/10.1111/avsc.12719

Interpretive Summary: Livestock grazing is widespread across diverse regions in the western US, yet variability in the long-term effects of grazing is poorly characterized. We compiled several decades of in-depth research at rangeland research sites in different ecoregions and ecosystems to describe differences and similarities with respect to long-term grazing outcomes. We describe how the characteristics of dominant grass species, climate, and livestock grazing intensity can drive variability across ecosystems and regions. We highlight how relationships between climate and vegetation can lead to predictable and reversible in response to livestock grazing in more productive regions with grazing-tolerant warm-season grasses. In contrast, more water-limited ecosystems with composition dominated by cool-season grasses may be less dynamic, yet with the potential to shift to lower productivity states if higher grazing intensity leads to soil erosion. We also discuss how variability in livestock grazing can affect how rangeland vegetation responds to invasive species and climate change. Overall, research from these long-term rangeland sites suggests that the effects of livestock grazing on plant community resistance and resilience vary strongly based on ecosystem context, and variation should be considered explicitly in managing these systems.

Technical Abstract: Aims: Livestock production is the most widespread land use globally and occurs across a diverse set of ecosystems. Variability in long-term livestock grazing impacts across ecosystems is poorly characterized, particularly at larger spatial scales, despite strong relationships with various ecosystem services related to soil fertility and stabilization and vegetation productivity. Here we examine the effects of grazing on vegetation and the implications for resistance and resilience to global change. Methods: We use six long-term research stations in the western United States, spanning two ecoregions, multiple ecosystems, and 311 total site-years of research. Across these sites we evaluate convergence and divergence of vegetation response to grazing vs grazing removal, focusing on interactions with drivers of global change. Results: We found that at long time scales (multiple decades), grazing has numerous convergent and divergent effects across ecoregions and ecosystems. Similarity among precipitation patterns and plant traits linked to grazing and production timing were key elements explaining convergence or divergence in long-term patterns of livestock grazing response. Ecosystem differences across western US rangelands are also associated with variable effects of grazing on resistance and resilience to invasive species and climate change. Conclusions: These results suggest that unique ecosystem or ecoregion responses to future global change may result from complex interactions between grazing and environmental factors, such as precipitation timing and plant traits. Adapting livestock and grazing management to specific ecosystem vegetation and climate variability is needed to manage for the myriad global changes affecting rangeland production and diversity.