Tree mortality due to an El Niño flood along the lower Tana River, Kenya

This study investigated forest tree mortality as a result of the extremely strong 1997–1998 El Niño flood in Tana River, Kenya, directly tested how mortality varied in relation to tree species and diameter at breast height (DBH), and indirectly tested how mortality varied in relation to floodwater depth. The study forest was under 2 m of water for approximately 71 days, from December 1997 until February 1998. Twenty-five liana, subcanopy tree, and canopy tree species were selected based on their importance in the diet of the Tana River mangabey ( Cercocebus galeritus Peters), a critically endangered primate endemic to the Tana River. Reproductive-sized individuals of these species were enumerated in 16.25 ha. I also enumerated trees killed by the El Niño flood, recorded their location in the forest, and measured their DBH. Ninety-two trees in fifteen species were killed by the flood. There were significant differences in mortality by species and by 0.25 ha quadrat. There were negative correlations between number of dead and DBH, number of dead and distance from the river, and per cent of quadrat killed and distance from the river. There appear to have been few long-term consequences of the El Niño flood in the forest or for the mangabeys.