Patch and species specific responses of savanna woody vegetation to browser exclusion

Abstract

The impact of browsers on the structure of woody vegetation has been well documented in savanna landscapes but the spatial distribution of these impacts is poorly understood. Savannas are structurally heterogeneous and the effects of browsers are unlikely to be evenly distributed across them. A mammalian exclosure in northern Kruger Park, South Africa, was used to explore the impacts of 15 years of browser exclusion on woody vegetation across a wetland/upland boundary. Woody patches inside the exclosure were taller than those outside of the exclosure and differential patch and species specific responses were observed within and without the exclosure. A boundary between upland and wetland patch types showed the greatest response to browser exclusion in terms of woody species composition, height and stem diameter. Browser impacts are not distributed evenly across the landscape, but are focused on certain patch and species types. Browsers have the potential to markedly alter system heterogeneity. Landscape heterogeneity is an integral component of biodiversity, but is often not explicitly dealt with in protected area management. Typically monitoring of vegetation change in conservation areas occurs at broad scales and would not detect the change in either the patch type or species specific responses identified in this study. We recommend that protected area managers adopt a multi-scaled, spatially explicit approach to monitoring change in the landscape. Boundaries between patch types provide valuable indicators of browser mediated changes.