Abstract
Enrichment planting with dipterocarps is required in order to rehabilitate degraded vegetation in tropical Southeast Asia, since tropical rainforests have been damaged by various anthropogenic activities. This study investigated the effects of light and soil properties on the mortality and growth of six dipterocarp species in grassland, secondary forest, and logged forest in the Niah Forest Reserve, Sarawak, Malaysia. Relative light intensity was much higher in the grassland than the forested area, whereas large variations in soil properties were not found. Seedling mortality, height and diameter over 81 months were higher in the grassland than the forested area. Strong light intensity killed many seedlings in the grassland during the first 24 month, though it enhanced the growth of the seedlings that survived. Few survived large seedlings could be one of the targets for ecosystem rehabilitation in the grassland, if the seedlings can dominate the forest structure in the future. In the secondary forest and logged forest, lower light intensity led to lower mortality and growth rate than in the grassland. In the secondary forest, pioneer trees fostered seedlings and produced suitable conditions for their survival. Careful thinning of local trees may enhance the growth of seedlings if necessary. On the other hand, we found interspecific variations. For example, Parashorea macrophylla showed the highest survival rate in the secondary forest, but it did not like very dark conditions. Shorea macrophylla was easily attacked by herbivores. Shorea virescens showed a higher growth rate in the grassland. These interspecific variations should be considered when selecting species for enrichment planting.
