02102nas a2200361 4500008004100000245011900041210006900160300001400229490000700243520104200250653004101292653000901333653001401342653001201356653002001368100001601388700002001404700002401424700002001448700001801468700001801486700001901504700002001523700001601543700001201559700002001571700001701591700001701608700001601625700001701641700001701658856006501675 2016 eng d00aShared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands0 aShared drivers but divergent ecological responses Insights from  a666 - 6820 v663 a

Fire and grazing, key determinants of structure and function of savanna grasslands worldwide, have been extensively altered by humans. We used existing long-term manipulations of fire and grazing in North American and South African mesic savanna grasslands, as well as new experiments, to determine whether the impacts of fire and grazing by large herbivores differed between these systems. We found that despite a body of literature suggesting that these savanna grasslands respond uniquely to fire and grazing, their ecosystem responses (aboveground productivity) were generally similar. In contrast, plant-community responses to fire and herbivores diverged strongly between systems. The differences in plant-community responses, as well as convergence in ecosystem function, were underpinned by a common mechanism: the response of grass dominance to changing fire and grazing regimes. As a result, divergent responses of plant communities to altered fire and grazing regimes did not preclude convergence in ecosystem function.

10aAboveground net primary productivity10afire10agrassland10aGrazing10aplant community1 aSmith, M.D.1 aKnapp, Alan, K.1 aCollins, Scott., L.1 aBurkepile, D.E.1 aKirkman, K.P.1 aKoerner, S.E.1 aThompson, D.I.1 aBlair, John, M.1 aBurns, C.E.1 aEby, S.1 aForrestel, E.J.1 aFynn, R.W.S.1 aGovender, N.1 aHagenah, N.1 aHoover, D.L.1 aWilcox, K.R. uhttps://academic.oup.com/bioscience/article/66/8/666/246414102932nas a2200157 4500008004100000245016400041210006900205300001300274490000800287520232900295653001402624100002002638700001902658700001602677856008102693 2015 eng d00aFunctional differences between dominant grasses drive divergent responses to large herbivore loss in mesic savanna grasslands of North America and South Africa0 aFunctional differences between dominant grasses drive divergent  a714 -7240 v1033 a

Grazing and fire are disturbances integral to the evolution and maintenance of savanna grasslands. Humans are altering or completely eliminating these disturbance regimes at a global scale, with important consequences for savanna ecosystem structure and function. It is unknown whether the alteration of these disturbance regimes will have similar effects on grass communities of savanna grasslands in different geographic regions that vary in their biogeographic and evolutionary histories, as well as in the diversity of extant grazers. Here, we examined the effects of large herbivore loss on different aspects of grass community structure – taxonomic, phylogenetic and functional – across a range of fire frequencies in C4-dominated mesic savanna grassland sites of North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). The goal of the study was to determine whether the loss of large herbivores exerted a consistent effect on the grass communities of two physiognomically similar grasslands with different biogeographic and grazing histories. The removal of large herbivores resulted in divergent responses in the grass communities at Konza and Kruger that was consistent across fire treatments. At Konza, there was a rapid and significant response to grazing exclusion while the response was muted and transient at Kruger. Functional syndromes associated with grazing resistance were generally conserved across sites, and it was the functional strategies of the dominant species at each site that drove the divergent responses. Further, our study supports the hypothesis that grazing and aridity may be selective forces that act in parallel as those species that were grazing resistant also occupied drier niches. Synthesis. Our study demonstrates that savanna grassland communities with different biogeographic and grazing histories respond differently to the removal of large herbivores and that climate, fire and grazing are interactive forces in maintaining savanna grassland diversity and function. We show that the functional attributes of the dominant grasses, which are in part driven by the biogeographic and grazing history experienced, are the most relevant in predicting the response of savanna ecosystems to the loss of large herbivores.

10aphylogeny1 aForrestel, E.J.1 aDonoghue, M.J.1 aSmith, M.D. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1237602006nas a2200145 4500008004100000245013900041210006900180300001500249490000800264520146600272100002001738700001901758700001601777856006701793 2014 eng d00aConvergent phylogenetic and functional responses to altered fire regimes in mesic savanna grasslands of North America and South Africa0 aConvergent phylogenetic and functional responses to altered fire a1000 -10110 v2033 a

The importance of fire in the creation and maintenance of mesic grassland communities is well recognized. Improved understanding of how grasses – the dominant clade in these important ecosystems – will respond to alterations in fire regimes is needed in the face of anthropogenically driven climate and land-use change. Here, we examined how grass communities shift in response to experimentally manipulated fire regimes at multiple levels of community diversity – taxonomic, phylogenetic and functional – in C4-dominanted mesic savanna grassland sites with similar structure and physiognomy, yet disparate biogeographic histories. We found that the grass communities were similar in their phylogenetic response and aspects of their functional response to high fire frequency. Both sites exhibited phylogenetic clustering of highly abundant species in annually burned plots, driven by species of the Andropogoneae, and a narrow range of functional strategies associated with rapid post-fire regeneration in a high-light, nitrogen-limited environment. By examining multiple facets of diversity in a comparative context, we identified convergent phylogenetic and functional responses to altered fire regimes in two mesic savanna grasslands. Our results highlight the importance of a common filtering process associated with fire that is consistent across grasslands of disparate biogeographic histories and taxonomic representation.

1 aForrestel, E.J.1 aDonoghue, M.J.1 aSmith, M.D. uhttps://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.12846