Sagebrush Steppe Productivity, Environmental Complexity, and Grazing: Insights From Remote Sensing and Mixed-effect Modeling

Domestic livestock grazing is the primary land use across the planet, but the relationship between grazing and rangeland productivity is difficult to determine because it is influenced by a variety of ecological and management factors. Fine-scale environmental data available through remote sensing are increasingly used to understand land use changes, such as grazing. In this study, we assessed the relationship between a variety of grazing and rangeland productivity metrics while accounting for environmental complexity within the sagebrush steppe ecosystem of Montana. We created mixed-effect generalized linear models using remotely sensed productivity as response variables. Explanatory variables included management and field-based grazing data combined with remotely sensed abiotic and biotic environmental factors. We found point-level field measures of grazing (e.g., cow patties, percentage of dung in Daubenmire plots, and number of plants grazed) showed positive effects, especially on perennial forbs and grasses. Grazing measures at the pasture-level showed a small negative effect on annual forbs and grasses. Grazing metrics tended to have smaller covariate effects on rangeland productivity compared to environmental factors, and interaction effects between grazing and environmental factors were common. This study provides insight into the relationship between grazing and plant productivity in the sagebrush steppe rangeland of Montana and highlights the importance of assessing the effects of grazing using multiple scales while accounting for environmental complexity.