Photosynthetic Light Environment of Tropical Lowland Forest and Growth Response of Shorea Leprosula

Abstract

Photon flux densities (PFD) of different microsites within a tropical lowland forest have been measured and compared spatially and temporally. The aims of the study were to determine the forest light environments at different microsites and the growth responses of its hardwood species which were grown under these different light regimes. Results indicated that the daily total PFD in the big gap, medium gap, small gap, smallest gap and understorey sites during the rainy season of November 1991 to January 1992 were 51.5, 17.7, 8.1, 8 and 4.5 % respectively, of the daily total PFD in the biggest gap. Results of this study also demonstrated that the frequency histograms of PFD were negatively skewed at the big open area, were bimodal within the medium gap and small gaps sites, and positively skewed under the dense canopy. Relative growth rate of height and leaf area ratios of S. leprosula seedlings grown under different light conditions showed that the seedlings in a big sized gap grew substantially more than those raised in smaller gaps and exhibited higher leaf area ratios and photosynthetic rates. This study also indicated that the photosynthetic capacity of the seedlings grown in the big gap were higher than seedlings in smaller gaps.