Fire and Grazing Change Herbaceous Species Composition and Reduce Beta Diversity in the Kalahari Sand System
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Abstract
After rainfall and soils, fire and herbivory are two of the main determinants of savanna ecosystems. Although the interactive effects of fire and herbivores on soil and vegetation are widely acknowledged few studies have addressed these two factors in concert, and none of the studies has focused on the Kalahari sand system. We experimentally studied how annual late dry season fires and grazing affect herbaceous plant species composition, above- and belowground biomass, and soil and grass nutrient concentrations in the nutrient-poor semi-arid Kalahari system in northern Botswana. Four treatments (fire, grazing, fire + grazing, and no-fire–no-grazing) were applied for two consecutive years in the late dry season. Plant species composition was affected by treatment and year. The no-fire–no-grazing treatment was distinctly different from all the other treatments in terms of species composition. Beta diversity was lower on the fire treatment and grazing treatment, but not where fire and grazing were combined. Fire and grazing alone or in combination did not have a substantial effect on biomass, soil and plant nutrients or plant species alpha diversity. Plant nitrogen was the only element that differed between treatments, with high concentrations on all the grazed treatments in the first year and low levels on the fire-alone treatment during the second year. The results show that fire and grazing mainly affect species composition and large-scale biodiversity patterns as indicated by the no-fire–no-grazing treatment being distinctly different from other treatments, suggesting the evolutionary adaptation of this dystrophic Kalahari sand system to herbivory and fire.
Keywords
beta diversity fire herbivory Kalahari plant species composition semi-arid savanna soil nutrientsNotes
Acknowledgments
The study was part of the Botswana-Norway Institutional Cooperation and Capacity building Project (BONIC) jointly funded by the Department of Wildlife and National Parks (DWNP) of Botswana and Norwegian Agency for Development (NORAD). We thank the Department of Agricultural Research in Sebele for providing a laboratory for chemical analysis and a number of DWNP officers for helping in the field. We also appreciate comments from RJ. Naiman and three anonymous reviewers which improved the quality of the manuscript.
Supplementary material
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