Mangrove forest productivity and biomass accumulation in Hinchinbrook Channel, north Queensland

In November 1996, three sites were selected along Hinchinbrook Channel, which represented the major forest types and environmental range within the channel. Six plots, each usually 400 m² were marked out at each site and all trees were tagged, identified to species level and the diameter at breast height (DBH) was measured. The biomass of each tree was estimated using previously established allometric relationships between DBH and biomass. The two year time span of this project was insufficient to reliably measure biomass accumulation within these plots. Estimates were obtained from permanent plots in Missionary Bay, which had a 5 year record. Below ground biomass accumulation was calculated using the relationship between above-ground and below-ground biomass derived for Rhizophora apiculata in Malaysia.The forest canopy was accessed from steel towers, up to 10m in height, constructed in three forest stands with different species compositions. From top to bottom, a 2x1 m section of the canopy was divided into horizontal layers of 0.5 m thickness. Within each layer, in two of the stands, (a mixed stand of Bruguiera gymnorhiza/Rhizophora stylosa and a mixed stand of Rhizophora apiculata/Rhizophora stylosa), the angle of each leaf was measured and leaves removed to measure area and dry weight. The measurements taken were used in the simulation of canopy light profiles. In all plots, indirect estimates of canopy leaf area index were obtained from measurements of light flux density with a quantum sensor.Photosynthetic rates were determined for Bruguiera gymnorhiza, Bruguiera parviflora, Ceriops australis, Ceriops tagal, Rhizophora apiculata, Rhizophora lamarkii, Rhizophora stylosa, Heritiera littoralis and Xylocarpus granatum. Rates were measured on leaves at their natural angle of inclination at different levels in the canopy using a portable photosynthesis system. This research was undertaken to estimate net canopy carbon fixation and carbon accumulation as living biomass in mangrove forests using data on stand structure and rates of photosynthesis. This study is a component of a broader investigation of carbon fixation and storage by mangrove ecosystems.