Tropical Dendroclimatology in Zambia: Brachystegia boehmii
Dendroclimatology in the tropical forest regions has lagged behind the more temperate forested regions of the world because of the challenge of determining annual ring formation. Despite over 230 tropical tree species known to form annual rings, the ITRDB shows few published chronologies in tropical forests in Sub-Saharan Africa. As part of the first “Training in Tree-Ring Science and its Applications” workshop conducted in Kitwe, Zambia, our team explored the dendroclimatic potential of Brachystegia boehmii in the Miombo Woodland. Instrumental weather data is sparse for Zambia and extending records back in time requires interpolation from stations hundreds of kilometers away. To better place the present and future changes in climate in the context of past decades to centuries, we must develop annual proxies to model climate variables. Our work was guided by three research questions: 1) Does B. boehmii form annual rings?, 2) Do the tree ring crossdate within species at a single sampling location?, and 3) Do the annual ring widths correlate with monthly moisture variables like precipitation and drought? We collected two cores per tree from 20 trees. Our research indicates that B. boehmii does form annual rings with bands of terminal parenchyma but determination of ring boundaries can be difficult because of inter-annual banding. Crossdating samples at our site was difficult but possible. Our preliminary dating has 10 series with a series intercorrelation of 0.30. While this is low, correlations between trees indicates a common growth signal. Early analysis indicates that growing season precipitation is correlated with ring width. However, we expect this relationship will strengthen as we crossdate more samples.