1. a Department of Forest Biology and Ecosystems Management , Makerere University , PO Box 7062, Kampala, Uganda
2. b Kenya Forestry Research Institute (KEFRI) , PO Box 20412-00200, Nairobi, Kenya
3. c Kenya Agricultural Research Institute, ARC-Muguga South , PO Box 30148-00100, Nairobi, Kenya
4. d CAB International Africa Regional Centre , PO Box 633, Nairobi, 00621, Kenya