Forest In Sarawak Research Articles

Plant reproductive interval and population density in aseasonal tropics

In some tropical areas, annual cycles in the environment and plant phenology are not clearly detectable. In such aseasonal tropics, it was found that plant population density is associated with flowering intervals within the same habitats and within the same pollination guilds, if some conditions are satisfied. This finding is based on observations of flowering phenology of butterfly‐pollinated understory shrubs of the genus Ixora (Rubiaceae) for 36 months in a mixed dipterocarp forest in Sarawak, northwest Borneo. Plants did not receive sufficient pollination services and fruit set was pollination‐limited. Under such conditions, it is theoretically predicted that the plant types that reproduce frequently would have higher population density than those that reproduce less frequently, because common types must avoid competition for pollinators and rare types can have a large floral display by storing resources during long reproductive intervals to attract pollinators efficiently. Observed relationships among plant reproductive intervals, pollinator attractions and population densities in Ixora are consistent with theoretical predictions. Based on the theory proposed in this paper, I discuss a factor promoting diversification of the genus Ixora and other taxa.

Water cycling in a Bornean tropical rain forest under current and projected precipitation scenarios

Southeastern Asian tropical rain forests are among the most important biomes in terms of annual productivity and water cycling. How their hydrologic budgets are altered by projected shifts in precipitation is examined using a combination of field measurements, global climate model (GCM) simulation output, and a simplified hydrologic model. The simplified hydrologic model is developed with its primary forcing term being rainfall statistics. A main novelty in this analysis is that the effects of increased (or decreased) precipitation on increased (or decreased) cloud cover and hence evapotranspiration is explicitly considered. The model is validated against field measurements conducted in a tropical rain forest in Sarawak, Malaysia. It is demonstrated that the model reproduces the probability density function of soil moisture content (s), transpiration (Tr), interception (Ic), and leakage loss (Q). On the basis of this model and projected shifts in precipitation statistics by GCM the probability distribution of Ic, Q and, to a lesser extent, s varied appreciably at seasonal timescales. The probability distribution of Tr was least impacted by projected shifts in precipitation.

Transpiration, canopy conductance and the decoupling coefficient of a lowland mixed dipterocarp forest in Sarawak, Borneo: dry spell effects

Tropical rainforests are among the most important biomes in terms of annual primary productivity and water cycling. However, the materials-exchange properties of Southeast Asian forests in their significant functions are less studied. We investigate key factors controlling materials-exchange, such as canopy ( g c) and aerodynamic conductance ( g a) and the decoupling coefficient (Ω) in an intact lowland mixed dipterocarp forest in Sarawak, Borneo. We operated an eddy covariance system above the canopy to measure canopy transpiration rate ( E c) using an 80-m-tall canopy crane, and made concurrent meteorological measurements. In this region, solar radiation and air temperature have small seasonal variations, and annual rainfall is distributed evenly throughout the year, with some unpredictable intra-annual dry spells. We define three specific periods A, B and C as medium dry, heavy dry and wet periods, respectively, for analyses of the environmental control on E c, according to their dryness level. The mean daily E c, g c and Ω were higher in the wet period C than in the dry periods A and B. Also, each g c in its diurnal variation was much higher in the wet period C than in the dry periods A and B, where diurnal variations of g c were almost the same. Both the value of g c and its sensitivity to environmental variables were higher in the wet period C than in the dry periods A and B. The peak of Ω was higher in the wet period C than in the dry periods A and B because of a higher value of g c in period C. However, the higher values of g c in the wet period C did not cause a higher E c compared to in the dry periods A and B.

Intraspecific variation in the status of ant symbiosis on a myrmecophyte,Macaranga bancana,between primary and secondary forests in Borneo

AbstractA tree species,Macaranga bancana, distributed in South East Asian tropics has a mutualistic relationship with specific symbiotic ant species, which defend the plant from herbivores. To examine the intraspecific variation in the status of the ant‐plant symbiosis among microhabitats of different light conditions, we investigated the species composition of nesting ants and the herbivory damage onM. bancanasaplings by field observations and sampling in primary and secondary forests in Sarawak. In addition, the effectiveness of non‐ant (physical and chemical) defenses were estimated by feeding the larvae of a polyphagous lepidopteran withM. bancanaleaves from saplings in the two types of forests. All saplings in the primary forest were colonized by twoCrematogasterant species that had been known to be the obligate symbionts ofM. bancana,while in the secondary forest, about half of the saplings were occupied by several ant species that were not obligate symbionts. There was little herbivory damage on saplings colonized by the twoCrematogastersymbiont ants in both forest types, while the saplings colonized by the other ant species suffered a 10–60% loss of leaf area. Larval mortality of the polyphagous lepidopteranSpodoptera liturawas significantly higher when larvae fed on leaves ofM. bancanasaplings in the secondary forest than when fed on leaves ofM. bancanasaplings in the primary forest. These results suggest that the symbiosis between ants andM. bancanais looser and the non‐ant‐defenses are stronger in secondary forests, where light is more intense, than in primary forests.

Resource use of insect seed predators during general flowering and seeding events in a Bornean dipterocarp rain forest.

Insect seed predators of 24 dipterocarp species (including the genera ot Dipterocarpus, Dryobalanops and Shorea) and five species belonging to the Moraceae, Myrtaceae, Celastraceae and Sapotaceae were investigated. In a tropical lowland dipterocarp forest in Sarawak, Malaysia, these trees produces seeds irregularly by intensely during general flowering and seeding events in 1996 and/or 1998. Dipterocarp seeds were preyed on by 51 insect species (11 families), which were roughly classified into three taxonomic groups: smaller moths (Trotricidae, Pyralidae, Crambidae, Immidae, Sesiidae, and Cosmopterigidae), scolytids (Scolydae) and weevils (Curdulionidae, Apionidae, Anthribidae, and Attelabidae). Although the host-specificity of invertebrate seed predators has been assumed to be high in tropical forests, it was found that the diet ranges of some insect predators were relatively wide and overlapped one another. Most seed predators that were collected in both study years changes their diets between general flowering and seeding events. The results of cluster analyses based on the number of adult of each predator species that emerged from 100 seeds of each tree species, suggested that the dominant species was not consistent, alternating between the two years.

The diversity of hemi-epiphytic figs (Ficus ; Moraceae) in a Bornean lowland rain forest

The diversity and niche specificity of hemi-epiphytic figs in a lowland dipterocarp forest in Sarawak were investigated in 1998. Twenty-seven fig species (264 individuals, c. 120 ha) colonized a diversity of host taxa (35 families), but densities were very low and only 1.77% of trees> 30 cm d.b.h. were occupied. There were no significant associations with host taxa or host-bark roughness but among 11 common species (≥9 individuals) the distributions of all other parameters (host-d.b.h., height and position of colonization, crown illumination, soil-texture and slope-angle) were significantly different, and we identified five fig guilds. The guilds corresponded to canopy strata, and appeared to reflect the establishment microsite requirements of different species. A fundamental trade-off within the hemi-epiphytic habit was revealed: Species colonizing larger hosts were rarer, because of lower host densities and more specific microsite requirements, but had better light environments and attained a larger maximum size. The single strangler species appeared to escape many of these constraints, and an important source of mortality caused by host-toppling, indicating the advantages of this strategy. Thus, the hemi-epiphytic figs in this community have come to fill a remarkable diversity of niches, despite low levels of competition, through the exigencies of a complex environment. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 78, 439–455

Effects of nutrient addition, mulching and planting-hole size on early performance of Dryobalanops aromatica and Shorea parvifolia planted in secondary forest in Sarawak, Malaysia

Native species of the Dipterocarpaceae are being planted throughout Southeast Asia as a source of future timber and to restore degraded lands. A detailed understanding of factors controlling seedling performance is required for the successful planting of dipterocarps. Below-ground resource availability is hypothesized to have a significant affect on seedling performance of dipterocarp species when planted in selectively logged forests or in open, degraded areas. This study tested three methods thought to increase below-ground resource availability and thereby improve the performance of two dipterocarp species ( Dryobalanops aromatica and Shorea parvifolia) when grown in degraded secondary forest: nutrient addition, mulching, and increased planting-hole size. Seedlings of the two species were grown in two planting-hole sizes ( 12 cm×18 cm and 20 cm×30 cm), with and without nutrients (NPK), and with and without mulching. The experiment was conducted in two sites (Sampadi and Balai Ringin) in Sarawak, Malaysia, to test for spatial variation in treatment effects. Seedling growth and survival were monitored over 22 months. Seedling survival was >94% for both species and did not differ significantly among any of the treatments. High monthly rainfall throughout the first year of the experiment may have enhanced seedling survival. Nutrient addition had the strongest effect on seedling growth for both species, with nutrient addition increasing growth by >50% at Sampadi and for D. aromatica in one block at Balai Ringin. There was significant spatial variation in treatment effects. S. parvifolia did not respond to nutrient addition at Balai Ringin, suggesting that the plants may not have received the added nutrients in that site. Mulching had a positive effect on growth at Sampadi, but no effect or a negative effect at Balai Ringin. Further analysis of the specific effects of mulching on resource supply is required. Planting-hole size did not have a consistent significant effect on the growth of either species. This may have been due to the favorable soil water status during the experiment. The results of this experiment emphasize the potential importance of site effects and interactions between site and treatment effects in enrichment planting trials using dipterocarps. Further experimental studies on below-ground resource limitations of dipterocarp growth in a wide range of sites are required. Studies that monitor the availability and fluxes of soil resources will be the most informative.

A comparison of bird communities of two fragmented and two continuous southeast Asian rainforests

A large proportion of forest-dependent bird species have disappearedfrom Singapore, probably due to heavy forest loss that started in the 1800s. Thebird fauna seems to have relaxed (attained a lower and relatively stablediversity following habitat destruction) in Singapore. Using mist-netting, Icompared understory bird communities of two lowland rainforest fragments inSingapore (Nee Soon and MacRitchie) with two continuous forests in Sarawak(Malaysia) (Matang Wildlife Sanctuary and Gunung Gading National Park). Icompared community characteristics (e.g. rarity [<2 individuals/1000mist-netting hours]), population characteristics (e.g. sex ratio) and individualquality (e.g. prevalence of ectoparasites) among avifaunas of the forests. Onaverage, more bird species and individuals were caught in continuous foreststhan in fragments. There were more rare species in Gading. The proportion ofadults and the sex ratios did not differ among the forests. Ectoparasiteprevalence and intensity also did not differ among the forests. Proportionallymore individuals contained fault bars in MacRitchie. My study shows that aviancommunities in rainforest fragments are depauperate but show few signs ofenvironmental stress. Thus there may be long-term resilience in some forest birdspecies. However, it is essential to protect large tracts of tropical lowlandrainforest to preserve rare forest-dependent avifauna.

Bird‐pollination of threeDuriospecies (Bombacaceae) in a tropical rainforest in Sarawak, Malaysia

Pollination ecology of three Durio species, D. grandiflorus, D. oblongus, and D. kutejensis (Bombacaceae), was studied in a lowland dipterocarp forest in Sarawak, Malaysia, during a peak flowering period when at least 305 species of plants bloomed in 1996. Durio has been reported to be pollinated by bats in Peninsular Malaysia. However, my observations of flower visitors and pollination experiments indicated that two species, D. grandiflorus and D. oblongus, were pollinated by spiderhunters (Nectariniidae) and that the other species, D. kutejensis, was pollinated by giant honey bees and bats as well as birds. Hand-pollination experiments showed that all three species were obligate outbreeders. A resource limitation in fruit production was suggested. The former two species were visited only by spiderhunters, and the bagged flowers that were opened for animal visitors only at night bore no fruit, while those that were opened only during the day bore fruits, at comparable fruiting ratios to open pollination. Durio kutejensis was observed to be visited by giant honey bees, birds, and bats at different times of day, and three series of bagged experiments that exposed the flowers to animal visitors at different times of day bore fruits at a comparable ratio to open-pollination.

Impact of severe drought associated with the 1997–1998 El Niño in a tropical forest in Sarawak

The impact of the unusually severe drought associated with the 1997–1998 El Niño on tropical forest dynamics in Sarawak, Malaysia was examined. Mortality during the non-drought period (1993–1997) in a core plot (1.38 ha) was 0.89 % y−1, while that during the drought period (1997–1998) in the same plot and a peripheral plot was 6.37 and 4.35 % y−1, respectively. The basal area lost in the drought interval was 3.4 times that of the annual incremental basal area in 1993–1997. Drought mortality was higher for the smaller trees, though it was less size dependent than the non-drought mortality. Dipterocarpaceae, which is the dominant family in the study plot, had a mortality 12–30 times higher in the drought than the non-drought period. There were no significant differences in mortality among the topographic types. From the results of a log-linear model (multi-factored contingency table), the death of trees was correlated with size class, indicating a change in the size-class structure of the forest. Thus, both the species composition and structure are totally affected by such an episodic drought even in a per-humid tropical forest.

Various population fluctuation patterns of light‐attracted beetles in a tropical lowland dipterocarp forest in Sarawak

AbstractThe population fluctuation pattern of light‐attracted beetles was studied from August 1992 to September 1998 (for 73 months) using ultraviolet light‐traps set at three vertical levels in a tropical lowland dipterocarp forest in Sarawak, Malaysia. During our study, a general flowering occurred from April to July in 1996, and flowering on a small scale in 1997 and 1998. We analyzed the data for eight scarabaeid and six meloid species, some of which were anthophilous species. Various fluctuation patterns were observed among the beetle species in aspects of both seasonality and correlation with the supraannual phenological pattern. Three large chafer species (Scarabaeidae, Melolonthini) showed a clear seasonal fluctuation pattern with a peak once from March to May every year, the peak monthly catch greatly fluctuating annually. Other scarabaeid beetles did not show such a clear seasonal population pattern and hardly fluctuated annually. Populations of an anthophilous scarabaeid species, Parastasia bimaculata, a specific pollinator of Homalomena propinqua (Araceae), hardly fluctuated, probably because of its response to the constant flowering of its floral hosts. Monthly catches of an anthophilous scarabaeid, Anomala sp., and meloid beetles showed clear supraannual patterns in response to the general flowering and were significantly correlated with the flowering intensity with or without a lag of a month. The fluctuation pattern of meloids suggests a supraannual population fluctuation pattern of their hosts, i.e., megachilid/anthophorid bees.

Artocarpus (Moraceae)–gall midge pollination mutualism mediated by a male‐flower parasitic fungus

A previously undescribed pollination system involving a monoecious tree species, Artocarpus integer (Moraceae), pollinator gall midges, and fungi is reported from a mixed dipterocarp forest in Sarawak, Borneo. The fungus Choanephora sp. (Choanephoraceae, Mucorales, Zygomycetes) infects male inflorescences of A. integer, and gall midges (Contarinia spp., Cecidomyiinae, Diptera) feed on the fungal mycelia and oviposit on the inflorescence. Their larvae also feed on the mycelia and pupate in the inflorescence. The gall midges are also attracted by female inflorescences lacking mycelia, probably due to a floral fragrance similar to that of male inflorescences. Because of the sticky pollen, dominance of Contarinia spp. in flower visitors, and pollen load observed on Contarinia spp. collected on both male and female inflorescences, Artocarpus integer is thought to be pollinated by the gall midges. Although several pathogenic fungi have been reported to have interactions with pollinators, this is the first report on a pollination mutualism in which a fungus plays an indispensable role. The pollination system described here suggests that we should be more aware of the roles fungi can play in pollinations.

Various population fluctuation patterns of light-attracted beetles in a tropical lowland dipterocarp forest in Sarawak

Various population fluctuation patterns of light-attracted beetles in a tropical lowland dipterocarp forest in Sarawak

Preference in flower visits and partitioning in pollen diets of stingless bees in an Asian tropical rain forest

AbstractFloral resource partitioning among stingless bees (Trigona, Meliponini, Apidae) in a lowland rain forest in Sarawak, Malaysia, was investigated using tree towers and walkways in a 4‐year study that included a general flowering period. We obtained 100 collections of insect visitors to flowers of varying floral location and shape representing 81 plant species. The tendency of 11 species of stingless bees to visit specific flowers with a particular floral location and shape was analyzed by logistic regression analysis. This analysis showed that the proportion of flower visitor collections containing Trigona fuscobalteata and T. melanocephala differed according to floral location. The former was frequently collected at canopy and gap flowers, whereas the latter was most often collected at understory flowers. The analysis also suggested that T. erythrogastra was more rarely collected at shallow flowers than at deep flowers. Analysis of the pollen diets of T. collina, T. fuscobalteata, T. melanocephala, and T. melina revealed that similarity of pollen sources differed among the six permutated pairs of the four species. The lowest mean rank of similarity found was between T. fuscobalteata and T. melanocephala. This result supports the hypothesis that preference in visiting flowers in different locations leads to pollen resource partitioning.

Comparison of chemical elements in Dipterocarpaceae and Euphorbiaceae from a tropical rain forest in Sarawak, Malaysia

Leaves of Dipterocarpaceae, a major canopy component tree, and Euphorbiaceae, predominantly occurring in the second layer, were analysed for 43 chemical elements. The comparison between the two families revealed significantly lower concentrations for the vast majority of elements in Dipterocarpaceae. All elements except Cu, Cs and Ce were found in higher concentrations in Euphorbiaceae. Furthermore, Euphorbiaceae showed a higher biological variation for most elements indicated through higher coefficient of variances (CV) values. The fingerprints revealed a general tendency in both families investigated to exhibit rather low element concentrations compared to the `reference plant' proposed by Markert (1996). Out of the 43 chemical elements only Ni showed remarkable positive deviations in both families, while the deviation of 6700% found for Co in Euphorbiaceae was striking. In Dipterocarpaceae the elements N, Co, Cu, Mn, Li, Cs, Mg and Th were found in concentrations similar to the `reference plant' while all other elements exhibited rather high negative deviations. In Euphorbiaceae more elements occurred similar to the `reference plant', however, the general tendency of negative deviations was obvious. Due to their specific environment, trees from tropical forest might have a rather different chemistry from trees in the Northern Hemisphere.

Beetle pollination of Shorea parvifolia (section Mutica, Dipterocarpaceae) in a general flowering period in Sarawak, Malaysia

Pollination ecology of an emergent tree species, Shorea (section Mutica) parvifolia (Dipterocarpaceae), was studied using the canopy observation system in a lowland dipterocarp forest in Sarawak, Malaysia, during a general flowering period in 1996. Although the species has been reported to be pollinated by thrips in Peninsular Malaysia, our observations of flower visitors and pollination experiments indicated that beetles (Chrysomelidae and Curculionidae, Coleoptera) contributed to pollination of S. parvifolia in Sarawak. Beetles accounted for 74% of the flower visitors collected by net-sweeping, and 30% of the beetles carried pollen, while thrips accounted for 16% of the visitors, and 12% of the thrips carried pollen. The apical parts of the petals and pollen served as a reward for the beetles. Thrips stayed inside the flower almost continuously after arrival, and movements among flowers were rare. Fruit set was significantly increased by introduction of beetles to bagged flowers, but not by introduction of thrips. Hand-pollination experiments and comparison of fruit set in untreated, bagged, and open flowers suggested that S. parvifolia was mainly outbreeding.

Plant reproductive intervals and pollinators in the aseasonal tropics: a new model

What factors determine reproductive intervals and modes of pollination in plants of the aseasonal tropics? To answer this general question, we present a new explanation for some community patterns of plant reproductive intervals and pollinators observed in a lowland dipterocarp forest in Sarawak, Malaysia, using a mathematical model featuring different display effects for different types of pollinators. Predictions from the model matched with the following observed patterns: (i) flowering intervals were different among forest strata (forest floor < understorey < canopy < subcanopy and emergent), and not in the exact order of stratum height; (ii) among generalist pollinators, the proportion of social foragers was maximum in intermediate forest stratum; and (iii) plants pollinated by specialist pollinators were found on the forest floor and in gaps.

Pollination biology in a lowland dipterocarp forest in Sarawak, Malaysia. I. Characteristics of the plant‐pollinator community in a lowland dipterocarp forest

Flowerings and flower visitors were observed continuously in alowland dipterocarp forest in Sarawak, Malaysia, for 53 mo in1992-1996. Flower visitors of 270 plant species were observed orcollected, and pollinators were assessed by observing body contact tostigmas and anthers. We recognized 12 categories of pollination systems.Among them, plants pollinated by social bees included the largest numberof species (32%) and were followed by beetle-pollinated species(20%). Pollination systems were significantly related with somefloral characters (flowering time of day, reward, and floral shape), butnot with floral color. Based on the relationships between pollinatorsand floral characters, we described pollination syndromes found in alowland dipterocarp forest. The dominance of social bees and beetlesamong pollinators is discussed in relation to the general floweringobserved in dipterocarp forests of West Malesia. In spite of high plantspecies diversity and consequent low population densities of lowlanddipterocarp forests, long-distance-specific pollinators were uncommoncompared with theNeotropics.

Comparative ecology of 11 sympatric species of Macaranga in Borneo: tree distribution in relation to horizontal and vertical resource heterogeneity

1 Horizontal and vertical heterogeneity of resource availability, coupled with the specialized use of resources by tree species, results in complex patterns of tree species distributions in tropical rain forests. We studied the horizontal and vertical distributions of 4014 individuals in 11 species of early successional Macaranga (Euphorbiaceae) in tropical rain forest in Sarawak, Malaysia. 2 The horizontal distribution of individual trees was assessed with respect to crown light levels, establishment microsites, and broader scale variation in soil textural properties. Vertical distribution was assessed using an allometric approach to estimate maximum tree height (Hmax) and the slope of the sapling height–diameter relationship. 3 Average light levels intercepted and the proportion of individuals in each of five crown illumination classes varied significantly among the 11 species. Species ranged from extremely high‐light demanding, to quite shade tolerant. Average light levels intercepted by trees generally increased through ontogeny, but the ranking of species did not change significantly. 4 Fewer individuals of the more shade‐tolerant species established on disturbed microsites, irrespective of light levels. Among the more high‐light demanding species, the proportion of trees on different types of disturbed sites varied. 5 Trees of seven species were significantly more common on clay‐rich soils, two preferred sand‐rich soils, and two were not strongly affected by soil texture. 6 Hmax ranged from 5.5 to 31.3 m and was negatively correlated with shade tolerance among species, although among the more high‐light demanding species there was a wide range of tree sizes. Among species, Hmax was negatively correlated with both the slope and y‐intercept of the sapling height–diameter relationship, indicating that small‐statured species (also more shade tolerant) had more slender saplings than larger statured species. 7 Heterogeneity of resource availability leads to differences in horizontal and vertical tree distribution, which are important for the coexistence of 11 Macaranga species.

Getting Ready for Prime Time

SCIENCE IN SOUTHEAST ASIA F or more than a decade, a surging regional economy has given the governments of Indonesia, Malaysia, Thailand, and the Philippines a chance to build up their countries' capacity to do science. The results are evident in labs and developments across the region, including a new university rising from the forest in Sarawak, Malaysia; a top-class volcanology center in the Philippines; a biomedical institute in Indonesia that draws on a century-old tradition of Dutch research; and a multimillion-dollar basic biology initiative in Thailand. ![Figure][1] C. FABER SMITH Such developments have won an appreciative audience among a handful of researchers in the industrial world. But they are not widely known in the West, which pays at best sporadic attention to events in Southeast Asia. That anonymity ended last fall, however, when a currency crisis brought on by unwise financial management practices spread across the region and triggered fears of a global crisis. Now, the most critical issue facing scientists in all four countries is whether the gains of the past 10 years will be slowed, or even reversed, under the stringent fiscal measures being adopted. This Special News Report takes a look at what these four countries have been doing to develop their homegrown science—from creating a pool of scientific talent and injecting more peer review into decisions on research spending, to strengthening universities and collaborating with foreign institutions. Rather than focusing on individual countries, the section explores broad issues that stretch across the entire region. It is peppered with the stories of people who are setting down and carrying out the policies and the research that will allow their countries to compete internationally. We make no claims to be comprehensive in a survey this brief. Rather, our aim is to provide a broad-brush picture of science in the region, with some fine detail for emphasis and illustration. We hope that you will find the articles interesting and that you will share your reactions with us. [1]: pending:yes