Radiocarbon Determination of Past Growth Rates of Living Acacia Tortilis Trees from Two Arid Sites in the Eastern Sahara

Reconstructions arc presented of past growth rates of 10 Acacia tortilis trees, 5 growing at an arid site (Gebeit, Sudan) and 5 at a hyperarid site (Wadi Nuqrus, Egypt). The reconstructions were made using a free-shape age-depth model based on a series of 14C dates obtained on samples taken along the wood cores retrieved from the trunks of the trees (78 dates in total). In spite of the large difference in annual precipitation between the 2 sites, the range of ages of the trees (60–350 yr) and the variability in their growth rates are quite similar across both sites, whereas within-site growth rates are quite different even for closely spaced individuals. However, the pattern of growth rates of Acacias from the hyperarid Wadi Nuqrus indicates 2 periods of different aridity (the less arid AD 1650–1780 and more arid AD 1780–1930), while at Gebeit no such pattern has been detected.