Distribution of fine-root necromass in a secondary mangrove forest in Trat province, Eastern Thailand

The aim of this study was to determine the amount of fine-root necromass among the three different principal vegetation zones (Avicennia-Sonneratia, Rhizophora, and Xylocarpus) in a secondary mangrove forest in eastern Thailand. The coring method was applied for the estimation of the fine-root necromass. The results revealed a high proportion of fine- to total root-necromass (66.3%, 50.2% and 67.5% in the Avicennia-Sonneratia, Rhizophora, and Xylocarpus zones, respectively), and a very high proportion of dead to total fine root mass (91.8%, 96.6%, and 98.5%, respectively). A statistically insignificant but numerical difference was found in the vertical distribution of the fine-root necromass in the three soil depths examined (0-10, 10-20, and 20-30 cm deep from the surface) in all three zones. However, the zonal distribution of the fine-root necromass was significantly different among the zones and accumulated in the order of the Xylocarpus > Rhizophora > Avicennia-Sonneratia zones with an average of 9.94 +/- 2.49, 21.1 +/- 2.7, and 90.0 +/- 14.3 t ha(-1) 130 cm(-1), respectively. These are discussed in relation to the CO2 efflux via soil respiration formerly measured in the same study site. The ratio between dead and live line-root mass showed a tendency to increase with increasing distance from the river edge, and this may relate to the rising elevation from the mangrove forest towards a more terrestrial habitat.