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

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.