Long-term monitoring of summer ranges provides evidence for inter-annual variability but not directional change in forage resources at the US Sheep Experiment Station

Authors: Wilmer, Hailey; Spiess, Jonathan; Moffet, Corey; KLEMENT, KEITH - University Of Wyoming; WALKER, JOHN - West Texas A & M University; BURNS, AMIRA - Orise Fellow; Taylor, Joshua; LAYCOCK, WILLIAM - University Of Wyoming

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Monitoring data can help managers make science-informed decisions on rangelands. There is relatively little rangeland science published about summer grazing areas in the mountains of the US Intermountain West. This study analyzes a long-term dataset from a study established at the US Sheep Experiment Station Summer Range in 1959. Using modern statistical tools, we find little change in plant communities between 1959-1978. However, we do find distinctions between four vegetation types in the study area, with the most difference between sagebrush dominated and high elevation grasslands. This information can help managers adapt their grazing and habitat management to continue to sustain resilient rangeland ecosystems and livelihoods.

Technical Abstract: Vegetation monitoring data can help managers better understand plant community dynamics and herbivore ecology and therefore support the resilience of rangelands. Monitoring data can be useful for managers of high elevation grazing areas used by livestock during summer months across the US Intermountain West, where relatively little grazing ecology research has been conducted and where social acceptance of livestock grazing is declining. In this study, we examine plant community composition data collected across tall forb, open conifer, high elevation grassland, and sagebrush dominated locations (n=59) in 1959, 1978, and 1994 at the US Sheep Experiment Station (USSES) Summer Range in Beaverhead County, Montana. Historical archives at the USSES show how social controversy over sheep grazing drove the collection and implementation of monitoring data for multiple generations of researchers and land managers, though the dataset was never published. To bring the dataset to light, we ask 1) to what extent do plant communities in four vegetation types in 1959 differ from one another?; 2) what environmental gradients are correlated with these differences?; and 3) to what extent do plant community composition, biomass, and rangeland cover characteristics in the four vegetation types differ over the 35 year study period (1959-1994)? After processing the data with modern quality assurance methods, physically verifying plots, and cleaning the species database, we used a combination of parametric and non-parametric statistical analyses. We detected 122 species or species groups. We found separation in the composition of between sagebrush and grassland vegetation types, with notable overlap between open conifer, tall forb, and sagebrush plant communities. Dissimilarity among the four vegetation types correlated with slope, aspect, and weather variables. We detected little directional change in plant communities over the study period. Herbaceous biomass measurements tracked precipitation, remaining similar in 1959 and 1994 but peaking in 1978 for all vegetation life forms (except shrubs). We discuss the ecological drivers of high elevation grazing land vegetation communities, including the role of climate and snow and grazing. We also discuss the implications of the findings relative to rangeland livestock production resilience.