Mortality trends in the African cherry (Prunus africana) and the implications for colobus monkeys (Colobus guereza) in Kakamega Forest, Kenya

摘要

Prunus africana (Hook.f.) Kalkm. is a secondary forest canopy tree species that has been declining over much of its geographical range in sub-Saharan Africa during recent decades due to unsustainable harvesting of its bark for the international medicinal plant trade. One of the locations where the species is experiencing rapid mortality is Isecheno study site in the Kakamega Forest, Kenya where this study was conducted. Between 1997 and 2003, 21% of the P. africana (greater than or equal to 10 cm DBH) at Isecheno died and an additional 9% experienced greater than or equal to 50% canopy dieback. However, scars from bark harvesting on P. africana were relatively small and scarred trees were not more likely to be dead or dying than unscarred trees, suggesting that bark exploitation is not causing P. africana mortality at Isecheno. Other possible causes that require further evaluation include disease, insect attack, nutrient deficiency, and/or climatic fluctuation. The poor regeneration of P. africana at Isecheno can likely be explained by the relative lack of recent disturbance coupled with the thick undergrowth layer at this site. P. africana mortality is of concern not only because the species is listed as Vulnerable by IUCN, but also because black and white colobus monkeys [Colobus guereza (Ruppell, 1835)] at Isecheno exploit it as their top food species and are particularly reliant on its leaves during times of 'preferred' Moraceae fruit scarcity. The anticipated continued decline of P. africana may have adverse effects on C. guereza feeding habits, intergroup relations, and population density at Isecheno. Conservation of P. africana offers a formidable challenge since the species appears to require disturbance for regeneration, yet at sites where disturbance is occurring, P. africana is often a target of bark harvesters engaging in unsustainable levels of exploitation.