Relative influence of precipitation and grazing on a salt desert shrub plant community

Authors: Stonecipher, Clinton - Clint; THACKER, ERIC - Utah State University; RALPHS, MICHAEL - Retired ARS Employee

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2021
Publication Date: 6/9/2022
Citation: Stonecipher, C.A., Thacker, E., Ralphs, M.H. 2022. Relative influence of precipitation and grazing on a salt desert shrub plant community. Western North American Naturalist. 88(2):245-253.

Interpretive Summary: Long-term vegetation monitoring is essential to understand plant responses to both climate and grazing. The objective of this study was to monitor the long-term effects of precipitation on vegetation changes within a salt desert shrub plant community and determine if grazing by livestock altered the vegetation during this time. The study was located in southern Utah within the Colorado Plateau. Two sites were selected. One exclosure was constructed at each site and vegetation cover was measured inside and outside the exclosure to separate the effect of grazing from precipitation on vegetation change. Shrubs were the dominant vegetative cover at the start of the study with snakeweed being the dominant shrub accounting for 53% of total plant cover. As snakeweed died out due to drought, other shrubs such as Castlevalley saltbrush, bud sagebrush, and winterfat increased in cover. Each of these shrubs displayed positive correlations with current winter or cool season precipitation. Cover of galleta grass increased over the study and became the dominant species by the end of the study. Our study showed that winter and spring grazing at moderate stocking rates was not detrimental to these desert plant communities and that climatic conditions had the dominant influence on vegetation.

Technical Abstract: Long-term vegetation monitoring is essential to understand plant responses to both climate and grazing. The objective of this study was to monitor the long-term effects of precipitation on vegetation changes within a salt desert shrub plant community and determine if grazing by livestock altered the vegetation during this time. The study was located in southern Utah within the Colorado Plateau. Two sites were selected. One exclosure was constructed at each site and foliar cover was measured inside and outside the exclosure to separate the effect of grazing from precipitation on vegetation change. Shrubs were the dominant vegetative cover at the start of the study with Guiterrezia sarothrae being the dominant shrub accounting for 53% of total plant cover. As G. sarothrae died out due to drought, other shrubs such as Atriplex cuneata, Picrothamnus desertorum, and Krascheninnikovia lanata increased in cover. Each of these shrubs displayed positive correlations with current winter or cool season precipitation. Cover of Pleuraphis jamesii increased over the study and became the dominant species by the end of the study. Our study showed that winter and spring grazing at moderate stocking rates was not detrimental to these desert plant communities and that climatic conditions had the dominant influence on vegetation.