Benchmarks for the future: long-term vegetation change derived form palaeoecological techniques in West-Coast Renosterveld, South Africa

Abstract

This study focuses on long-term vegetation changes in West-Coast Renosterveld in the winter rainfall zone of the Cape Floristic Region (CFR), Western Cape, South Africa. Renosterveld is an evergreen, fire-prone Mediterranean-type shrubland consisting of asteraceous elements, grasses and geophytes. It is restricted to fertile, fine-grained soils and more than 90% of this vegetation type has been transformed by agriculture. High richness of endemic geophytes in particular gives remaining fragments an irreplaceable conservation value. Future climate projections for the region suggest a general warming of 1.5-3.5 °C, a 30-50% decrease in precipitation, an increase in drought periods and shorter rainy seasons with important consequences for the vegetation of the CFR. There is limited information regarding the response of Renosterveld to past climate change and land-use disturbance and there is much debate about the pristine composition of Renosterveld vegetation. The lack of Renosterveld environmental history with appropriate pre-colonial or pre-Iron age benchmarks makes it difficult to build evidence-based arguments for conservation management and restoration. Studying the history of Renosterveld in the late Holocene may provide information on responses to past warmer climates, and the more recent effects of anthropogenic disturbance. The aim of the present study was to reconstruct vegetation change, fire regime and changes in herbivory over the past ca. 1300 years at a West-Coast Renosterveld site in the Western Cape and to interpret these findings in light of known climate history and land-use change with a specific focus on the effects of disturbance by fire and herbivory. Findings were explored in relation to resilience theory, and the implications for conservation management and restoration. The following research questions were investigated. How has vegetation, fire and herbivory changed over time in West-Coast Renosterveld vegetation? How do changes in vegetation relate to climate and land-use disturbance and what are the main drivers of change? What are the links to theoretical frameworks such as resilience theory? Are recent changes unprecedented and is there evidence of a threshold response to climate and disturbance? (4) What are the implications of these findings for conservation management and restoration such as present day management of fire and herbivores?