Abstracts of the Annual Meeting of the Ecological Society of Japan

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To investigate the matter production in a mangrove forest along the Okukubi River, we performed the tree census, soil assay and diurnal photosynthesis measurement. Five belt-transect plots (5 m wide) perpendicular to the stream were established. The diurnal change in net photosynthesis for sun leaves was measured for Bruguiera gymnorrhiza and Kandelia candel from June to August 2004 in four plots. The number of individuals in B. gymnorrhiza, K. candel and Rhizophora stylosa were respectively 750, 289 and 7 (including some forks) in the total study area of 900 m². The tree density increased from the landward zone to seaward zone and drastically decreased at the belt-transect plot nearest the seaside. On the other hand, the maximum tree height decreased from the landward zone to the seaward zone. The soil salinity and pH increased from the landward zone to the seaward zone. The diurnal change in net photosynthesis showed a strong dependence on that in the incident PPFD. The maximum net photosynthesis decreased from the landward zone to the seaward zone. The leaf and soil nitrogen concentration decreased from the landward zone to the seaward zone.

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Aboveground net primary production in a mangrove stand of Kandelia candel (L.) Druce was quantified using the summation method. Aboveground biomass and its increment were estimated using allometric relationships and stem analysis. Stem volume without bark of harvested trees showed a strong allometric relationship (R² = 0.924) with D_0.1²H (D_0.1, stem diameter at a height of H/10; H, tree height). Annual stem volume increment without bark also showed a strong allometric relationship (R² = 0.860) with D_0.1²H. Branch biomass increment per tree was indirectly estimated using the allometric coefficients from the relationships of branch weight, stem volume, stem volume increment and stem weight to D_0.1²H. Litterfall rate showed a peak in August-September (summer season). Total annual litterfall was estimated as 10.60 Mg ha^-1 yr^-1 in which 67.94% was contributed by the leaves. Stem and branch biomass increments were 11.13 Mg ha^-1 yr^-1 and 8.40 Mg ha^-1 yr^-1, respectively. Aboveground net primary production in the K. candel stand was 30.13 Mg ha^-1 yr^-1. These results suggest that K. candel is a fast growing and highly productive species.

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