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- Some Ecological Studies on Hopea odorata Roxb. and Hopea pubescens...
Some Ecological Studies on Hopea odorata Roxb. and Hopea pubescens Ridl. Seedlings
Abstract:
Hopea odorata is fairly widely distributed in evergreen forests from mainland Southeast Asia to the Andaman Islands, Borneo, and the Philippine Islands, while H. pubescens is only endemic to Peninsular Malaysia. Both species belong to Dipterocarpaceae and are commercially important timber.
This study initially focused on the density, distribution, response to light of seedlings under forest canopy, seedling mortality, and growth of H. pubescens. Then, it focused on the influence of seed size on cumulative percentage germination and early growth of H. odorata seedlings under different light regimes in the nursery.
The highest seedling density of H. pubescens was found to be 130 trees/subplot (of 25 m2) and the highest density of saplings was 68 trees/subplot. The distribution of seedlings and saplings was most abundant within 10 m around the parent tree and no seedlings and saplings were found beyond 25 m. The light intensity in the forest fluctuated according to the canopy opening. The highest light intensity recorded in the forest was 48.5 percent relative light intensity (RLI) and lowest at 3.0 percent RLI. The mortality of seedlings and saplings was quite high up to 12.9 percent and 5.3 percent, respectively. High mortality occurred in areas of high seedling density and where light was low. In plot 1, the mean annual increment in diameter (MAID) of all saplings was 0.37±0.2 mm and the mean annual increment in height (MAIH) was 2.36±3.2 cm. In plot 2, the MAID of all saplings was 0.22±0.18 mm and the MAIH was 3.02±4.29 cm. Height and diameter increments of saplings in the forest were lower than the increments recorded in the nursery.
H. odorata seeds were smaller and lighter than most other species of dipterocarps. The mean weight of seeds was 0.14±0.04 g and the mean length was 8.18±0.06 mm. Eighty-eight percent of the seeds germinated after sowing 25 days. The germination percentage was influenced by seed size. The highest germination rates were recorded by seeds in the 0.125-0.149 g weight class and over 9.95 in length.
The early growth of H. odorata seedlings was highest at 30 percent RLI and lowest at full sunlight. The relative growth (RG) of collar diameter, number of leaves, and number of nodes of the seedlings in both batches were significantly different. However, the RG of number of leaves of young seedlings was not significantly different between treatments. The biomass of seedling components was significantly higher at 30 percent RLI whereas leaf areas were not significantly different. The shoot:root (S/R) ratio of the young seedlings was highest at 50 percent RLI, while the S/R ratio of old seedlings was highest at full light. Biomass of seedling components and of the whole seedlings was related to collar diameter. Correlation coefficients were generally high suggesting that the regression equations can be used for estimating biomass of whole seedlings. The relationship between leaf area and collar diameter was relatively poorer.