Kazuhiko Ogino

Spatial distribution patterns of two predominant emergent trees in a tropical rainforest in Sarawak, Malaysia

Spatial distribution patterns of two emergent tropical rainforest tree species (Dryobalanops aromatica & D. lanceolata) were examined in where they were dominant (17–20% of total basal area of canopy trees) in Sarawak, East Malaysia. Newly established seedlings (< 2 years old) were restricted to areas < 40 m from mother trees for both species, suggesting a limited seed dispersal. Seedling (< 1 cm in dbh) density was highest around conspecific adults (≥ 30 cm in dbh). Negative spatial patterns were observed between larger juveniles (1–5 cm in dbh) and conspecific adults for both species; the most dense populations of sapling (1–5 cm in dbh) and poles (5–30 cm in dbh) were found at a distance of 15–20 m from the nearest conspecific adult. Seedlings of both species were distributed randomly with respect to light conditions evaluated by a forest floor diffuse site factor and a canopy closure index. Saplings of both species, and poles of D. lanceolata, were distributed under more open conditions than expected from spatially random distributions, and from average light conditions of all species of the same size classes. Possible mechanisms for the observed distribution patterns and intermediate canopy dominance of Dryobalanops were discussed from the viewpoints of gap-dynamics and distance-dependent mortality.

Microtopography, soil hardness and survival of mangrove (Rhizophora apiculata BL.) seedlings planted in an abandoned tin-mining area

Abstract In a mangrove area formerly used for tin-mining, the survival and the growth rate of planted Rhizophora apiculata BL. seedlings were studied in relation to land elevation and soil hardness. The growth and survival rates of seedlings were measured at 1-, 3- and 4-year-old stages. The land elevation, soil hardness and soil particle size were also measured in the plot. The survival rate of the seedlings decreased in the first 3 years to 54.9%, and fell to 53.2% in the fourth year. Although the total difference in elevation within the study plot was only 35 cm, both the survival rate and the growth rate were less at higher elevations and in harder soils. The uneven microtopography and the altered soil particle distribution following tin-mining affected the reforestation process.

Dynamics of aboveground big woody organs in a foothill dipterocarp forest, West Sumatra, Indonesia

The dynamics of aboveground big woody organs over 10 cm diameter was studied at a mature foothill dipterocarp forest in West Sumatra. The biomass of big woody organs was estimated to be 519 m3 ha−1 or 408 metric ton ha−1 by means of a pipe model theory. The diameter distribution showed a convex curve and the mode was found at a diameter of about 20 cm. The standing mass of big dead woody litter on the forest floor was 116 m3 ha−1, which accounted for 22% by voume or 9.5% by weight of the biomass of living organs respectively. Thedbh observation with two 1-ha plots for 4 yr and 5 yr respectively revealed that the average net production rate was 9.5 ton ha−1 yr−1. The death rate (7.9 ton ha−1 yr−1) accounted for 83% of the net production rate and was nearly equivalent to the decay rate (7.5 ha−1 yr−1) of dead wood on the forest floor. The balance between the death and decay rates was confirmed for each diameter class. Average turnover periods for big woody organs and dead woody litter were estimated to be 43 and 8.1 yr, respectively. Standing masses of live anddead woody materials accumulated in the study forest were approximately equal to those obtained in a mature tropical lowland rainforest, whereas the flow rates were lower, being only 70% of the corresponding values.

Mangrove ecosystem as soil, water and plant interactive system

Even in Southeast Asia, which is widely known as a humid or monsoon area, one finds an extensive area of dry and highly saline habitats. Southeast Asian mangrove ecosystems were examined to analyze their response to environmental stresses, viz. salinity, dissolved oxygen and acidity. The physical, chemical and biological processes of a natural, less disturbed mangrove ecosystem showed a reversible response to environmental fluctuation, maintaining an ecosystem equilibrium. The ecosystem components — soil, water and plants — formed an interactive system. But when violent external factors operated, the fragile ecosystem equilibrium was easily destroyed. If the disturbances went beyond the range of self-recovery, the total processes became irreversible. A self-regulating ecosystem model, a combination of careful monitoring of the total processes and feed-back ecosystem technology will benefit future management. The socio-ecosystem concept should also be incorporated in the sustainable management model.