TY - JOUR
T1 - Drought exacerbates negative consequences of high-intensity cattle grazing in a semiarid grassland
AU - Souther, Sara
AU - Loeser, Matthew
AU - Crews, Timothy E.
AU - Sisk, Thomas
N1 - Funding Information:
We are grateful to the Diablo Trust, the Flying M ranch, and the U.S. Forest Service for their support and collaboration on this long-term effort. We thank the dozens of undergraduate students from Northern Arizona University, Prescott College, and Yakima Valley College that contributed to the fieldwork, as well as many graduate students at NAU. This study has been supported through funding from U.S. Department of Energy, the Environmental Protection Agency, U.S. Department of Education, Arizona Game and Fish Department, the Ecological Restoration Institute, the Merriam-Powell Center for Environmental Research, and the Olajos-Goslow Endowment for?Environmental Science and Policy at Northern Arizona University.
Publisher Copyright:
© 2019 by the Ecological Society of America
PY - 2020/4/1
Y1 - 2020/4/1
N2 - Grasslands managed for grazing are the largest land-use category globally, with a significant proportion of these grasslands occurring in semiarid and arid regions. In such dryland systems, the effect of grazing on native plant diversity has been equivocal, some studies suggesting that grazing reduces native plant diversity, others that grazing increases or has little impact on diversity. One impediment toward generalizing grazing effects on diversity in this region is that high levels of interannual variation in precipitation may obfuscate vegetative response patterns. By analyzing a long-term data set collected over a 20-yr period in a semiarid grassland, we explicitly evaluated the role of climate in regulating the effect of cattle grazing on plant communities, finding that climate interacted with grazing intensity to shape grassland communities. Community composition of plots that were intensively grazed varied considerably in response to climatic variation and native species richness was low relative to ungrazed and moderately grazed plots. Following a severe drought in 2002, exotic species richness rapidly increased in the high-intensity grazing plots. While this pattern was mirrored in the other treatments, exotic species richness increased to a greater extent and was slower to return to pre-drought levels in the high-intensity grazing plots. Overall, moderate grazing, even compared to grazing cessation, stabilized grassland communities through time, increased resilience to drought, and maintained the highest levels of native plant diversity and lowest levels of exotic diversity. These findings suggest that grazing, at moderate levels, may support grassland resilience to climate change in semiarid regions. However, grazing that exceeds tolerances, particularly in combination with extreme climatic events, like drought, can alter plant composition over relatively long timescales and possibly increase invasibility by nonnative species.
AB - Grasslands managed for grazing are the largest land-use category globally, with a significant proportion of these grasslands occurring in semiarid and arid regions. In such dryland systems, the effect of grazing on native plant diversity has been equivocal, some studies suggesting that grazing reduces native plant diversity, others that grazing increases or has little impact on diversity. One impediment toward generalizing grazing effects on diversity in this region is that high levels of interannual variation in precipitation may obfuscate vegetative response patterns. By analyzing a long-term data set collected over a 20-yr period in a semiarid grassland, we explicitly evaluated the role of climate in regulating the effect of cattle grazing on plant communities, finding that climate interacted with grazing intensity to shape grassland communities. Community composition of plots that were intensively grazed varied considerably in response to climatic variation and native species richness was low relative to ungrazed and moderately grazed plots. Following a severe drought in 2002, exotic species richness rapidly increased in the high-intensity grazing plots. While this pattern was mirrored in the other treatments, exotic species richness increased to a greater extent and was slower to return to pre-drought levels in the high-intensity grazing plots. Overall, moderate grazing, even compared to grazing cessation, stabilized grassland communities through time, increased resilience to drought, and maintained the highest levels of native plant diversity and lowest levels of exotic diversity. These findings suggest that grazing, at moderate levels, may support grassland resilience to climate change in semiarid regions. However, grazing that exceeds tolerances, particularly in combination with extreme climatic events, like drought, can alter plant composition over relatively long timescales and possibly increase invasibility by nonnative species.
KW - cattle grazing
KW - climate change
KW - drought
KW - exotic species
KW - plant diversity
KW - resilience
KW - southwestern United States
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U2 - 10.1002/eap.2048
DO - 10.1002/eap.2048
M3 - Article
C2 - 31758870
AN - SCOPUS:85072232136
SN - 1051-0761
VL - 30
JO - Ecological Appplications
JF - Ecological Appplications
IS - 3
M1 - e02048
ER -