COS 172-1 - Grazing impacts on plant communities and soil carbon in high elevation meadows

Abstract: Rangelands encompass nearly half of the Earth’s ice-free land mass, and the associated introduction of nonnative herbivores as livestock (e.g. cattle) can have significant impacts on ecosystem structure and function, including plant communities and associated carbon storage. However, our ability to predict the magnitude and direction of these impacts has been deeply hindered by 1) the context-dependent nature of ecosystem responses to herbivores and 2) a paucity of data at appropriate spatial and temporal scales to measure carbon impacts. To address this challenge, we leveraged a twenty-year rooted frequency vegetation dataset consisting of 36 permanent plots from meadows across the Golden Trout Wilderness, Kern Co., CA, where grazing was removed in 2000 from two of four grazing allotments. In 2021-2022, we resurveyed vegetation across all plots, and measured soil organic carbon using 45 cm deep cores. Both grazed and ungrazed allotments span a range of elevations and hydrogeomorphic meadow types, which enabled us to examine plant and soil carbon responses to two decades of grazing cessation across a range of environmental contexts.



We found that overall, grazed meadows had significantly lower vegetation cover, rooting depth, and depth to ground water than ungrazed meadows. Bare ground was 15% greater in grazed meadows vs. ungrazed. Mean rooting depth was over twice as deep (43 vs 16 cm) in ungrazed vs. grazed meadows, and depth to groundwater was an average of 8 cm deeper in grazed vs. ungrazed meadows. Effects of grazing on species richness varied across grazing allotment, meadow type, and elevation, with little to no effect in riparian low or high gradient meadows, and stronger effects on discharge slopes, subsurface low gradient meadows and at higher elevations. Across all meadow types, grazing had a weak negative effect on soil organic carbon. However, we found a strong positive relationship between both rooting depth and sedge cover (Carex vesicaria, C. nebrascensis, C. utriculata), between sedge cover and soil organic carbon, and a negative relationship between grazing and sedge cover. These results demonstrate that vegetation responses to livestock grazing mediate grazing impacts on soil carbon storage. Consideration of this response mechanism can help to guide sustainable livestock management strategies, including recent interest in nature-based carbon capture on rangelands in California and globally.