Tree ring analysis of Brachystegia spiciformis and Isoberlinia tomentosa: Evaluation of the enso-signal in the miombo woodland of eastern Africa

The value of growth rings as proxy data for climate reconstruction was studied in two miombo woodland species in eastern Africa. Growth rings, marked by terminal parenchyma, were visually detectable on carefully prepared stem discs of Isoberlinia tomentosa and Brachystegia spiciformis, dominant species of the miombo woodland in north-western Tanzania. However, the presence of multiple growth ring anomalies rendered cross-dating of the growth ring series between trees difficult. Cross-dating succeeded for eight out of thirteen samples for Isoberlinia tomentosa, but was unsuccessful for Brachystegia spiciformis. A mean series of 38 years was calculated for Isoberlinia tomentosa only. Monthly precipitation, monthly maximum air temperature and monthly SOI-value (Southern Oscillation Index) correlated significantly with tree ring widths of the mean series. These correlations are strong indicators of the annual character of the growth rings. They also suggest that Isoberlinia tomentosa provides an appropriate paleoclimatic record for dendroclimatic reconstruction.