COS 222-1 - Does grazing affect the ability of the Shortgrass steppe to withstand multiple droughts?

Abstract: The shortgrass steppe of Eastern Colorado is a semi-arid region that experiences significant temporal and spatial variation in precipitation. It is also a region prone to drought conditions given the limited amount of precipitation that it receives, it is habitually on the verge of being in a drought which can be initiated by missing 1-2 rain events in a season. It is also anticipated that precipitation in this region will experience droughts at higher frequencies and intensities due to global climate change. In this research We monitored plant cover, density and production across three long-term grazing treatments that consisted of non-grazed, heavy cattle grazed, and moderate cattle grazed with prairie dogs. To estimate cover and density, we used a point frame over 1 m2 plots with two 1 m transects that were centered on the sides of the plots and crossed in the center. There were 41 pins spaced at 5 cm intervals. Ground cover was estimated by dividing the number of pins with hits by the total number of pins. Production was estimated by clipping a 0.0626 m2 area withing the plot. We recorded ground cover and production across a 4-year period in which the shortgrass steppe experienced two years of average precipitation (2019 and 2021) and two years that had growing season droughts (2020 and 2022). From 2019-2021, the percent cover in July fluctuated between years but the grazing treatments were not significantly different from each other, however in the drought of 2022, there is a significant difference between the grazing treatments (p< 0.0001). In this year, the heavy grazed treatment had the greatest amount of cover (40.7%), followed by the non-grazed treatment (25.2%) and the prairie dog treatment had almost no vegetation cover (5.6%). This suggests that the grazing intensity has somewhat of a hormetic effect on the ability of the system to withstand repeated droughts in that increasing grazing intensity is beneficial to an extent, but there is a tipping point where it starts to become detrimental.