Mangrove litter biomass input in a forest impacted by human physical disturbance, Gazi Bay, Kenya
Department of Biological Science, Egerton University, P.O. Box 536, Egerton, Kenya; Kenya Marine and Fisheries Research Institute, P.O. Box 81651, Mombasa, Kenya
This study investigated the impact of human physical disturbance on litter yield in a mangrove forest by comparing amount and composition of litterfall between disturbed and relatively undisturbed sites in Gazi mangrove forest. Litter was trapped using littertraps suspended from trees at the upper and lower intertidal zones of the four sites. Litterfall material was collected fortnightly from October 2001 to June 2003, and dry weight of components determined and compared using ANOVA. Physical disturbance reported from the forest include tree cutting, digging for bait, and trampling by man and vehicles which were more prevalent at the disturbed sites than comparable undisturbed sites. Annual litter production in the Gazi forest was 4.3 t ha-1 yr-1 and was dominated by leaves of Rhizophora mucronata, which constituted 39% of litter components. Disturbed sites recorded significantly lower litterfall than corresponding undisturbed sites (ANOVA, P < 0.01), an increase (10%) in litter yield of Avicennia marina leaves, and 20% and 30% declines respectively in R. mucronata leaf and flower productivity. The decline in litter biomass and its changing composition were attributed to changes in predominant mangrove species as a result of size, site, and species selection by harvesters and the competitive ability of regenerating and uncut trees. © Society for Tropical Ecology.