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70,082,000 Yen (FY1998; 23,287,000 Yen)
Disturbed Forest, Seedling Establishment, Pteriophyte, Species Diversity, Tropical rain forest
In order to understand potential growth of tropical tree species in a disturbed ecosystem, seedlings of 21 species with 1200 individuals were transplanted in an abandoned rubber plantation. The seedling survivorship of early succession species was not always higher in open sites than in closed canopy sites. The initial size of seedlings is important for the subsequent growth under the open site but not under the closed canopy sites. A long-term observation was also made on the morphological characteristics during the growth of a common pioneer species Macaranga gigantea (Eupholobiaceae). Light environment has been found to be a potentially important factor to control the morphological plasticity of the species. Seedlings of M. gigantifolia Merr. and M. triloba (bl.) also continuously produce huge leaves on an erect stem like M. gigantea. Monoaxial growth with huge leaves and continuously growth is a common growth habit of juvenile pioneer trees. It is very likely that these species avoid mutual shading by elongation of petiole and change in petiole angle. Moreover, photosynthetic measurements were carried out to examine the physiological effects on growth of some tropical tree species. Air humidity was found to affect both steady and dynamic photosynthesis in Shorea parvifolia. Sunflecks contributed largely to the carbon gain in the species under a closed canopy, while the combination of low air humidity and the high photon flux density reduced largely the photosynthetic carbon gain of seedlings growing in gaps. Leaf photosynthetic characteristics were compared among trees under different light environments. Saturated photosynthetic rate was much higher in canopy or emergency trees as compared to those under canopy.
Tropical rain forest, Tree Seedlings Gap, Photosynthesis, Morphological plasticity, Light environment.