Biomass and litterfall of Ceriops tagal and Rhizophora mucronata in the mangrove forest of Gazi Bay, Kenya

Abstract

Biomass and (leaf) litter production of stands of Rhizophora mucronata and Ceriops tagal were assessed in an East African mangrove forest. Inundation frequency of the R. mucronata stand was twice a day (on average 575 min day-1), whereas the C. tagal stand was inundated only during spring tides (on average 116 min day-1). The highest above-ground biomass (24.9 ± 4.0 kg dry weight m<^.-2) was present in the R. mucronata stand, in which leaf litter production was 2.51 ± 1.15 g DW mw² day^-1. Above-ground biomass and leaf litterfall in the C. tagal stand were 4.01 ± 0.34 kg DW m^-2 and 1.05 ± 0.49 g DW m^-2 day^-1, respectively. There was a distinct seasonal pattern in litterfall in both stands, with lower litterfall values in the wet season. Chloride concentrations were relatively high in senescent leaves, compared with those in green leaves. The decreased litterfall during the wet periods may be related to a reduced accumulation of chloride in the leaves. The difference in inundation frequency between the R. mucronata and C. tagal stands is expected to cause a more substantial tidal export of fallen leaves from the R. mucronata stand. As nitrogen resorption before defoliation was similar for C. tagal (50.9%) and R. mucronata (50.1%), tidal flushing may cause larger nitrogen losses from the R. mucronata stand.