Assessing the dendrochronological and dendroclimatological potential of Acacia nilotica (L.) in northern KwaZulu-Natal.

Abstract

In the face of evidence of predicted climate change, there is a lack of information available on past climatic variability, particularly in southern Africa. Focus on the recent past is critical to understanding the natural variability underlying anthropogenic climate change. High resolution climatic records, such as tree ring series, are crucial to studying past climatic changes. Dendrochronology in the southern hemisphere has not been widely explored due to the perceived lack of annual growth rings in tropical and subtropical tree species. In this study, Acacia nilotica (L.) was assessed for its dendrochronological and dendroclimatological potential using 31 stem discs collected from the Bonamanzi Game Reserve, situated in northern KwaZulu-Natal, South Africa. Annual growth rings characterized by terminal parenchyma bands occurred on all samples, however, a number of growth ring anomalies, including missing, false and indistinct growth rings, were commonly encountered. Cross-dating was attempted on all individuals and a 99-yr regional chronology for northern KwaZulu-Natal, ranging between the years 1914‒2013 was developed. The regional chronology indicates variable periods of increased and decreased growth of A. nilotica throughout the 99 year period, with no coherent growth pattern evident between trees. Correlation analysis was performed with locally averaged climate data, high resolution gridded datasets, the Southern Oscillation Index and the El Niño3.4 index. The weak mean sensitivity indicated by the master chronology suggests that A. nilotica is not strongly influenced by environmental variables. This may call into question the reliability of the cross-dating results and master chronology presented, and limit the further application of climate correlation analysis. This research has demonstrated some potential to develop a century long annual tree ring chronology using A. nilotica for northern KwaZulu-Natal. A network of tree ring series from southern Africa would extend the spatial and temporal scale of high resolution palaeoclimatic records for the subregion, further increasing our understanding of contemporary climate variability. This study has explored the dendrochronological and dendroclimatological potential of A. nilotica thereby contributing to southern African tree ring research.