Dipterocarp Forest In Sarawak Research Articles

Survivorship and growth of seedlings of four dipterocarp species in a tropical rainforest of Sarawak, East Malaysia

AbstractSurvivorship and growth of seedlings of four dipterocarp species (Dipterocarpus actangulus, D. globosus, Dryobalanops aromatica, Dryobalanops lanceolata) were studied for 2.5 years in a mixed dipterocarp forest in Sarawak, East Malaysia. Predispersal seed predation rates were larger for D. globosus (75%) than D. lanceolata (27–34%) and D. aromatica (18–26%). Less than 20% of the two Dryobalanops seeds were damaged by vertebrates after seed dispersal. During the period from seed dispersal to the time when the seedlings had shed cotyledons, more dispersed seeds died in the two Dipterocarpus (ca 90%) than the two Dryobalanops (ca 60–70%). The major mortality factors during this period were uprooted and seed/seedling predation by insects or vertebrates. After the seedlings shed cotyledons, all species showed constant mortality rates of 34, 15–16, 17 and 6%/year for D. actangulus, D. lanceolata, D. aromatica and D. globosus, respectively, in the forest understorey. Mortality was lower in less shaded conditions than in more shaded ones for D. aromatica and D. actangulus, but not significantly different for D. lanceolata and D. globosus. A majority of dead seedlings were killed by fallen branches or were found standing with wilted leaves, probably due to water stress. No significant correlation was found between seed/seedling mortality and distance from mother trees or the initial density of seeds/seedings for all species. The mean leaf production was positively correlated with the estimated diffuse light factor of their habitats for each species.

Pollination biology of Gnetum (Gnetaceae) in a LOWLAND MIXED DIPTEROCARP forest in Sarawak

Pollination biology of two Gnetum species was studied in a lowland mixed dipterocarp forest in Sarawak, Malaysia. A dioecious shrub species, G. gnemon var. tenerum, flowered in the evening and its strobili emitted a stinking odor. Pollination droplets were secreted from ovules on female strobili and from sterile ovules on male strobili in the evening. These strobili were visited by nectar‐seeking moths of Pyralidae and Geometridae. Sticky pollen was attached on proboscides and antennae of these moths. A dioecious woody climber, G. cuspidatum, had cauline strobili on woody stems near the forest floor. Its male strobili emitted a funguslike odor in the evening and secreted nectar on collars that subtended “flower” rings. The strobili were visited by small flies of Lauxaniidae (Diptera), onto the antennae and legs of which pollen was attached. Evaporation of the exposed droplet/nectar of these Gnetum flowers seemed to be minimized by nocturnal flowering near the tropical rain forest floor. Another floral‐structural constraint of gymnosperms, i.e., lack of showy petals, was compensated for by floral fragrancy. The prevalence of entomophily in the Gnetales (i.e., Gnetum, Ephedra, and Welwitschia) may suggest that unspecialized insect pollination originated before the divergence between the Gnetales and angiosperms.

Seasonality and vertical structure of light‐attracted insect communities in a dipterocarp forest in Sarawak

AbstractNocturnal flying insects were collected monthly for 13 months using ultra violet light‐traps set at various vertical levels in a weakly‐seasonal, tropical lowland dipterocarp forest in Sarawak, Malaysia. Abundance, faunal composition, size distribution and guild structure of these samples were analyzed with respect to temperal and vertical distributions. The nocturnal flying insect community in the canopy level was highly dominated by fig wasps (84%) in individual number, and by scarabaeid beetles (28%) in weight. A principal component analysis on monthly catches detected non‐random, seasonal trends of insect abundance. The first two principal trends were an alternation of wetter (September to January) and less wet seasons (February to August) and an alternation between the least wet (January to March) and the other seasons. Many insect groups were less abundant in the least wet season than the other seasons, whilst inverse patterns were found in Scarabaeidae and Tenebrionidae. Significantly positive and negative correlations between monthly catch and rainfall were detected only in ovule‐feeders and in phloem‐feeders, respectively. Delayed, significant negative correlations between monthly catch and 1–3 month preceding rainfall were more frequently detected in phytophages, phloem‐feeders, seed‐feeders, wood‐borers and scavengers. The peak in abundance along vertical levels were found at the canopy level (35 m) for phloem‐, ovule‐, seed‐, root‐, fungal‐feeders and nectar collectors, at an upper subcanopy level (25 m) for scavengers and aquatic predators, and at a middle subcanopy level (17 m) for ants. Catches at the emergent level (45 m) did not exceed those at the canopy level.

The Vertical Distribution of Ants on Canopy Trees in a Bornean Lowland Rain Forest.

ABSTRUCT The species composition of ants attracted to sugar baits was compared between four vertical levels ofeleven canopy frees in a mixed dipterocarp forest in Sarawak, Malaysia. Fifteen, six and four species were collected at the subcanopy, understory, and forest floor levels, respectively, while no ants werc attracted to the baits at the top layer (upper canopy) in the daytime. The ground ant fauna includes the predatory ponerine ants and carnivorous or omnivorous Pheidole ants. In contrast, many species of Canponotus, Crematogaster, ar:d Polyrlachis were found in the subcanopy. The latter ants may be thought of as omnivorous or herbivorous ants which feed on plant nectar and/or arthropod exudates. The overlap in species composition between ftees was relatively small. A large part of the biodivenity found on this planet exists in the canopy of ropical rain forests. Although the ant fauna is not particularly diverse compared to such other arthropod groups as beetles (e.g., Stork, 1987), ants have been found to be the most abundant insects and to constitule the largest proportion of the animal biomass in the canopy of tropical rain forests (Adis er al., 1984: Tobin, 1991) . It is still unclear, however, in what part of the canopy and at what time of the day ants are active, on what they forage in the canopy, and where they nest. Tobin (1991 , 1994) proposed that ants function as primary consumers in the canopy of tropical rain forests because their biomass is too large for them to function as secondary consumers (predators or scavengers). Although numerous studies in the temperate region have shown that in some species fluids are quite important (articles cited by Tobin, 1994; Yoshimoto & Yamane, 1990; Itino el a/., unpubl.), there has been no direct evidence showing that ants are primary consumers in tropical rain forest canopies. Our canopy-observation syst€m in Borneo is suitable for testing Tobin's (1994) hypothesis. As a first step towards this goal, we conducted a short-term survey of the species composition of ants in the upper canopy, subcanopy, and understory (on the tree trunk) as well as on the forest floor.