Interactive effects of drought and grazing on vegetation dynamics in the shortgrass steppe

Authors: BRADFIELD, SCOTT - Colorado State University; Augustine, David; OCHELTREE, TROY - Colorado State University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2026
Publication Date: 7/3/2026
Citation: Bradfield, S.J., Augustine, D.J., Ocheltree, T.W. 2026. Interactive effects of drought and grazing on vegetation dynamics in the shortgrass steppe. Rangeland Ecology and Management. 108:87-97. https://doi.org/10.1016/j.rama.2026.05.002.
DOI: https://doi.org/10.1016/j.rama.2026.05.002

Interpretive Summary: The rangelands of eastern Colorado are known to be highly resistant to degradation from grazing livestock, in large part because the dominant perennial shortgrasses (blue grama and buffalograss) are well-adapted to grazing. Even with intense grazing by prairie dogs, which clip the vegetation at a lower height than large grazers, these rangelands are capable of rapid regrowth when rains occur. Many studies have also shown that these rangelands are highly resistant to one or two years of drought, even when they are grazed by livestock. However, it remains unclear how the combination of multiple droughts and intensive grazing by prairie dogs may together affect the persistence of perennial grasses in these rangelands. We conducted a study in which we experimentally created a multi-year drought in rangelands both with and without prairie dog grazing, and monitored how the vegetation responded. After a multi-year drought, sites grazed by prairie dogs returned to less than half of their pre-drought grass production, while sites grazed by livestock returned to 80% of pre-drought grass production. These results suggest the combination of intense grazing and multi-year drought can lead to much slower plant recovery after the drought, compared to sites with less grazing pressure.

Technical Abstract: Grasslands comprise a large portion of the Earth’s terrestrial surface; they often occur in regions that have low precipitation and have evolved in the presence of grazing. The shortgrass steppe (SGS) of eastern Colorado has been shown to be highly resistant to grazing and droughts. Grazing promotes the dominance of C4 perennial grasses (mostly Bouteloua gracilis and Bouteloua dactyloides), which account for more than 70 percent of the vegetation cover. These species are also renowned for their drought tolerance and were one of the only species observed growing from existing crown tissue following the Dust Bowl. The dominance of the Bouteloua species is thought to be very stable in this ecosystem, taking one or more decades of changes in grazing or precipitation to result in changes in species composition. However, the interaction of grazing, and drought are rarely studied together and the research that has been done on this interaction has only focused on the intensity of cattle grazing with single year droughts. This research is focused on the interaction of droughts and grazing across varying grazing intensities (non-grazed, heavy cattle grazed, and moderate cattle grazed with prairie dogs) and two lengths of drought (single and multi-year). During a year of normal rainfall following a single-year drought, vegetation cover returned to >60% of pre-drought cover across all grazing intensities. In contrast, following a multi-year drought, cover returned to 50%, 40%, and 38% of predrought levels for ungrazed, cattle grazed and cattle + prairie dog grazed vegetation respectively. A particularly strong drought x grazing interaction was observed for aboveground net primary production (ANPP), where ungrazed and cattle grazed sites returned to >80% of their pre-drought ANPP regardless of prior drought intensity, but with intense grazing by both cattle and prairie dogs the vegetation only returned to 70% of predrought ANPP following a single-year drought and returned to <50% of predrought ANPP following the multi-year drought. Overall, our results suggest that the combination of high intensity grazing of cattle and prairie dogs combined with multi-year drought could lead to a tipping point which the SGS cannot quickly recover from.