The historical ecology of Namibian rangelands: Vegetation change since 1876 in response to local and global drivers

The influence of both local and global drivers on long-term changes in the vegetation of Namibia's extensive rangelands was investigated. Fifty-two historical photographs of the Palgrave Expedition of 1876 were re-photographed and used to document changes over more than 130 years, in grass, shrub and tree cover within three major biomes along a 1200 km climatic gradient in central and southern Namibia. We showed that patterns of change are correlated with mean annual precipitation (MAP) and that below a threshold of around 250 mm, vegetation has remained remarkably stable regardless of land-use or tenure regime. Above this threshold, an increase in tree cover is linked to the rainfall gradient, the legacies of historical events in the late 19th century, subsequent transformations in land-use and increased atmospheric CO2. We discuss these findings in relation to pastoral and settler societies, paleo- and historical climatic trends and predictions of vegetation change under future global warming scenarios. We argue that changes in land-use associated with colonialism (decimation of megaherbivores and wildlife browsers; fire suppression, cattle ranching), as well as the effects of CO2 fertilisation provide the most parsimonious explanations for vegetation change. We found no evidence that aridification, as projected under future climate change scenarios, has started in the region. This study provided empirical evidence and theoretical insights into the relative importance of local and global drivers of change in the savanna environments of central and southern Namibia and global savanna ecosystems more generally.

► Innovative repeat photograph methods authenticate regional historical ecology.
► Legacy of colonial ecological impacts persists in the landscape.
► Above 250 mm positive correlation between MAP and % tree cover change.
► Relative importance of local/global drivers of change in savannas analysed.
► Past trends of change are at odds with future climate change trajectories.