Effects of large mammalian herbivore exclusion on the physiognomy, species composition and boundary dynamics of woody vegetation, across a vlei/upland boundary

The ‘Nwashitsumbe vlei in the Kruger National Park is separated from a mopane matrix by the vlei/upland boundary. The boundary has been delineated in terms of grass species and soil characteristics, but not woody vegetation, which is an integral component of savanna ecosystems. A large exclosure provided the opportunity to study the effects of large mammalian browser exclusion on boundary dynamics and woody vegetation characteristics. The vlei/upland boundary differs from the surrounding patch types in species composition, slope, electrical conductivity and pH characteristics. Each characteristic has a slightly different spatial distribution pattern across the boundary, probably resulting from differential responses to different or the same vectors and disturbance agents. These characters should be viewed holistically as they overlap to form a complex three-dimensional boundary. Woody species distribution is more patchy than that of the grasses. Life-history strategy responses are suggested as possible causes for differences in distribution pattern. Browsing disturbance has altered the structure, composition and possibly the function of the woody vegetation boundary. This study suggests that the vlei/upland boundary is more sensitive to large mammalian herbivore impact than the surrounding patch types. Such changes and differences are of concern to managers who aim to maintain biodiversity. Current monitoring, in the Kruger National park, of woody vegetation responses to herbivore impact occurs at too coarse a scale to detect change in either the boundary or the species guild-specific responses identified in this study. It is recommended that they be used as indicators of herbivore mediated change in the landscape.