The status of Faidherbia albida trees in the Hoanib River, Namibia

Abstract

The Hoanib River is an ephemeral river flowing from the highlands of Namibia through the hyper-arid Namib Desert, to the Atlantic Ocean. Seasonal floods recharge groundwater that supports riparian woodlands, which are vitally important to wildlife and livestock. Previous studies looked at the impact of mega-herbivores on Faidherbia albida. In October 2012 a follow-up survey was undertaken. There was great variability in population structure, growth form, regeneration and elephant damage between the transects surveyed in different sections of the river. Khowarib Schlucht showed a healthy demography, with many juveniles, regeneration, and little damage. Dubis wetland had no mature trees and one clump of juveniles. Transects between the two boreholes showed low recruitment, little regrowth, and a marked 5 m high browse-line. They were dominated by mature, single-trunked trees with old elephant damage, and healthy canopies. From the "President's" borehole downstream there were juvenile trees, fewer mature trees, and thickets. Juvenile trees showed pruning from above and the sides. Near the floodplain, there were only highly pruned juveniles and a few trees in the 20-40cm DBH size-class. Overall lack of recruitment along the mega-herbivore frequented section of the river is of concern for the long-term survival of this important linear oasis.