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Data from: The role of browsers in maintaining the openness of savanna grazing lawns

Citation

Voysey, Michael et al. (2020), Data from: The role of browsers in maintaining the openness of savanna grazing lawns, Dryad, Dataset, https://doi.org/10.5061/dryad.76hdr7st3

Abstract

1. In savannas, ruminant herbivores can have divergent impacts on tree recruitment and resulting woody cover. Heavy grazing by cattle results in woody thickening, whereas intensive grazing by wildlife instead tends to be associated with lower woody cover.

2. To disentangle why woody cover is low in areas heavily grazed by wildlife, we tested (I) whether short-grass environments attract indigenous mammalian browsers; (II) whether preference for short grass decreases with browser body mass because of differences in predator susceptibility; and (III) whether these translate into suppression of seedlings and saplings on grazing lawns, thus maintaining their openness.

 3. This work was conducted in Kruger National Park (KNP) and Hluhluwe iMfolozi Park (HiP), South Africa. In KNP, the effect of grass height on browser abundance (estimated using dung counts), and on the utilisation of woody plants by browsers (using a bite-score approach) was tested. An exclosure experiment tested the effect of grass height and browser removal on seedling survival and sapling growth of a dominant woody plant species in a short- and tall-grass mosaic. Finally, in HiP, the effect of grass height and browser removal were tested on the growth rates of a range of woody species, monitored over ten years, across ten sites.

4. Steenbok and impala selected short- over tall-grass as preferred browsing sites, while elephant preferred tall grass. Browser abundance on short grass decreased with browser body mass, indicating that predator avoidance might be a key factor driving small-bodied browsers to utilize grazing lawns. Grass height did not explain variation in the utilisation of woody plants by browsers.

5. Seedling survival was lowest in short grass and when browsers were present, with mortality occurring in two out of every three seedlings. Also, sapling growth was lowest in short grass, although browser removal had no effect. Evidence for increased browser impact on grazing lawns was clearest from our long-term exclosure experiment in HiP, which demonstrated that the effect of browsers on sapling growth rates was strongly modified by the presence of short grass.

6. Synthesis. These results provide support for the hypothesis that browsers, particularly small-bodied browsers and mixed feeders, are attracted to short-grass habitats, and that, they help maintain grazing lawn openness by suppressing woody seedling survival and sapling growth where grass is kept short by grazers.