Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa
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Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.
KeywordsDisturbance Fire Grazing Plant community richness Species diversity
Thanks to H. Archibald, E. Amendola, M. Avolio, L. Calabrese, A. Chamberlain, C. Chang, K. Duffy, L. Ladwig, K. La Pierre, A. Lease, K. Murphy, T. Nelson, T. Schreck, A. Walters, J. Taylor, L. Zeglin, and A. Zinn for assisting in the field. Thanks to J. M. Blair, Konza Prairie LTER, Kruger National Park, L. Woolley, and SAEON for logistical support. Earlier drafts of this manuscript benefitted from comments by T. Young and two anonymous reviewers. The experiments comply with the current laws of South Africa where the research was performed. This research was supported by grants to M. Smith from the NSF Ecosystem Studies and Geography and Regional Science Program (DEB-0841917) and the Andrew W. Mellon Foundation.
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