Southeast Asian Rainforests Research Articles

Foraging impacts of Asian megafauna on tropical rain forest structure and biodiversity

AbstractMegaherbivores are known to influence the structure, composition, and diversity of vegetation. In Central Africa, forest elephants act as ecological filters by breaking tree saplings and stripping them of foliage. Much less is known about impacts of megafauna on Southeast Asian rain forests. Here, we ask whether herbivory by Asian megafauna has impacts analogous to those of African forest elephants. To answer this, we studied forest (1) structure, (2) composition, (3) diversity, and (4) tree scars in Belum and Krau, two protected areas of Peninsular Malaysia, and compared the results with those obtained in African forests. Elephants are abundant in Belum but have been absent in Krau since 1993. We found that stem density and diversity, especially of tree saplings, were higher in Krau than in Belum. Palms and other monocots were also more abundant in Krau. In Belum, however, small monocots (<1 m tall) were very abundant but larger ones (>1 m tall) were virtually absent, suggesting size‐selective removal. The frequency of stem‐break scars was equal at Belum and Krau but less than in Central Africa and greater than in the Peruvian Amazon where tapirs are the only megafauna. Pigs and tapirs could also contribute to the high frequency of tree scars recorded in Malaysian forests. Forest‐dwelling elephants in Asia seem to have a reduced impact on tree saplings compared to African forest elephants, but a very strong impact on monocots.

ウォーレス・シンポジウム「東南アジアの熱帯雨林と昆虫」に参加して

ウォーレス・シンポジウム「東南アジアの熱帯雨林と昆虫」に参加して

Thismia bryndonii (Thismiaceae), a new species from Maliau Basin, Sabah, Borneo

Thismia Griffith (1845: 341) in Thismiaceae or Burmanniaceae (sensu APG 2016) consists of more than 60 species (Ridley 1924, Jonker 1948, Stone 1980, van Steenis 1982; Merckx 2008). Many new species in this genus have been discovered, and 12 have been described after 2010 (e.g., Dančak et al. 2013, Nuraliev et al. 2014, 2015, Chantanaorrapint & Sridith 2015, Li & Bi 2013, Hroneš et al. 2015). Considering that the majority of these species were collected only once (Jonker 1948), it is likely that many more undescribed species remain hidden in the forests, particularly in the tropical rain forests of Southeast Asia. Borneo is one of the most biodiverse areas for mycoheterotrophs, and our recent botanical exploration in Borneo revealed many previously undescribed mycoheterotrophic species (e.g., Tsukaya et al. 2011, 2014a,b, 2016, Tsukaya & Okada 2005, 2012a,b,c, 2013a,b, Tsukaya & Hidayat 2016, Tsukaya & Suetsugu 2014). In 2016, we conducted a botanical survey in the Malaiu Basin, Sabah, Borneo, with the permission of the Maliau Basin Management Committee (YS/MBMC/2016/184) and the Sabah Biodiversity Council [access license JKM/MBS.1000-2/2JLD.5(23)]. The Maliau Basin Conservation Area (MBCA) is a huge basin surrounded by sandstone ridges and covers approximately 39,000 ha. Few botanical explorations have previously been conducted in this area. During the survey, we encountered a specimen from the MBCA that apparently belongs to Thismia section Euthismia Schltr. subsect. Odoardoa Schlechter (1921: 31) because it has a free inner perianth, spreading, creeping and vermiform roots, perianth lobes equal in length and size, but it differs from all known species. Here, we describe this new species with a revised key to the species of this genus in Malesia.

東南アジア熱帯雨林の土壌 : そのより良き理解を目指して(シンポジューム特集No.1-東南アジア熱帯林の維持・再生をめぐる諸問題-)

東南アジア熱帯雨林の土壌 : そのより良き理解を目指して(シンポジューム特集No.1-東南アジア熱帯林の維持・再生をめぐる諸問題-)

The impacts of habitat disturbance on adult and larval dragonflies (Odonata) in rainforest streams in Sabah, Malaysian Borneo

Summary Dragonfly assemblages (Odonata: comprising damselflies, Zygoptera; and dragonflies, Anisoptera) in Southeast Asian rainforests are extremely diverse but increasingly threatened by habitat disturbance, including logging and conversion of forest to oil palm plantations. Land‐use change can affect dragonfly larval stages by altering within‐stream environmental conditions, and adults by loss of perches, shade and hunting habitat. However, the extent to which dragonflies are affected by land‐use change is not well known, and strategies for conservation are poorly developed. We surveyed dragonfly adults and larvae, forest quality and stream environmental conditions across 16 streams in Sabah, Malaysia. Habitat surrounding the streams included pristine forest, selectively logged forest, oil palm with forested riparian buffer strips and oil palm without buffers. Overall abundance and species richness of adult dragonflies stayed constant with habitat disturbance, but larval abundance and richness decreased with higher habitat disturbance, and larvae were largely absent from oil palm streams. There was also a clear shift in community composition of both adult and larval dragonflies. Anisoptera adults were more species rich and abundant, but Zygoptera adults were less species rich in more disturbed sites. The presence of riparian buffers in oil palm plantations offered some protection for forest‐associated dragonfly species, and streams with wider riparian buffers supported adult assemblages more similar to those found in logged forest. However, oil palm streams with riparian buffers still contained a depauperate larval assemblage compared to logged forest areas, and dragonfly assemblages in narrow riparian buffer streams were similar to those found in streams surrounded by continuous oil palm. Our results provide clear evidence of the effect of land‐use change on dragonflies. Conservation efforts to conserve forest communities should target the preservation of existing forest areas, but management within oil palm plantation landscapes to preserve riparian buffers can still have a marked beneficial effect on dragonfly communities.

Testing the importance of a common ectomycorrhizal network for dipterocarp seedling growth and survival in tropical forests of Borneo

Background: Connections between mature trees and seedlings via ectomycorrhizal (EcM) hyphal networks existing in dipterocarp-dominated tropical rain forests of South-east Asia could have strong implications for seedling growth and survival and the maintenance of high diversity in such forests.Aim: To test whether EcM hyphal network connections are important for the growth and survival of dipterocarp seedlings.Methods: We conducted four independent experiments that prevented contact of experimental seedlings with an EcM network by using a series of fine meshes and/or plastic barriers. We measured the growth and survival (and foliar δ13C in one experiment) of seedlings of six dipterocarp species over intervals ranging from 11 to 29 months.Results: Seedling growth (diameter, height or leaf number) was unaffected by exclusion from the EcM network in three experiments and there were no differences in foliar δ13C values in the fourth. Seedling survival was reduced following exclusion from the EcM network in one experiment. Our results give little support to the hypothesis that dipterocarp seedlings growing in the shaded forest understorey benefit from being connected, through a common EcM network, to surrounding trees.Conclusions: We suggest that our negative results, in contrast to studies conducted in low diversity boreo-temperate or tropical forests, are due to these high diversity forests lacking host species-specific EcM fungi and therefore providing little opportunity for adaptive support of seedlings via hyphal networks.

Effects of different silvicultural systems on the genetic diversity of Shorea parvifolia populations in the tropical rainforest of Southeast Asia

Selective logging systems have been used to prevent the rapid decline of forest resources in Southeast Asia, but little is known about the impacts of selective logging on the genetic diversity of Southeast Asian rainforests. We evaluated the effects of silvicultural systems with differing cutting rotations and enrichment planting regimes on the genetic diversity of Shorea parvifolia, an abundant and ecologically important tree in Southeast Asian rainforests. Our result showed that in most respects the genetic diversity is not significantly different between primary forest and the other silvicultural systems; however, the proportion of private alleles is significantly different between them. Intensive second-rotation (L3) harvesting of individuals >40 cm in diameter at breast height (dbh) resulted in a sizable reduction in the number of reproductive trees and a dramatic decrease in the numbers of rare and private alleles, suggesting a negative impact on the genetic diversity of the remaining tree population. Enrichment planting with S. parvifolia in the logged forest improved some genetic parameters, significantly increasing the number of rare alleles in L3 in particular. We conclude that the genetic diversity of logged tropical forests gradually decreases depending on logging rotation times, especially with respect to sensitive genetic parameters such as the numbers of rare and private alleles, and that enrichment planting with native dipterocarps can maintain or even increase the genetic diversity of logged tropical forests in Southeast Asia.

Foraging ecology and occurrence of 7 sympatric babbler species (Timaliidae) in the lowland rainforest of Borneo and peninsular Malaysia.

Understanding foraging strategies of birds is essential to understanding mechanisms of their community assembly. To provide such information on a key Southeast Asian rainforest family, the babblers (Timaliidae), we evaluated foraging behavior and abundance in 7 morphologically and behaviorally similar sympatric species (Cyanoderma erythropterum, C. rufifrons, Stachyris maculata, S. nigricollis, S. poliocephala, Macronus ptilosus, and Mixornis gularis) in 5 habitats defined by structural complexity: (1) continuous native rainforest, (2) logged native rainforest fragments, (3) mature industrial tree plantation, (4) young industrial plantation, and (5) oil palm plantation. Enough data were obtained to compare abundance in all 7 species and foraging behavior in 5. All species were common in forest fragments and mature industrial tree plantations and less so in continuous rainforest and young industrial plantations; only M. gularis occurred in oil palm. In terms of foraging, M. gularis was the greatest generalist; C. rufifrons foraged mainly on live leaves in the forest midstory; and S. maculata, C. erythropterum, and M. ptilosus foraged mainly on dead leaves suspended in understory vegetation at significantly different heights. The dead-leaf substrate depends on a rich supply of falling leaves and extensive understory structure, conditions most common in native forest and old industrial plantations, and less so in mature forest, young plantations, and oil palm. Because of the importance of foraging data to understanding and managing biodiversity, we encourage the development of foraging fields in eBird (ebird.org), so that birdwatchers may help collect these relatively rare data.

Fruit gardens enhance mammal diversity and biomass in a Southeast Asian rainforest

Protected areas are frequently inhabited by people and conservation must be integrated with traditional management systems. Cultivation of fruit gardens is a low-impact agroforestry technique which alters the structure and composition of forest stands and has the potential to thereby influence animal communities. This is of particular interest in the rainforests of Southeast Asia, where limited fruit availability between intermittent mast fruiting events results in low mammal densities. We assessed how agroforestry practises of an indigenous community affect terrestrial mammal abundance, diversity and assemblage composition within Krau Wildlife Reserve, Pahang, Malaysia. We used baited camera traps to compare mammal abundance and diversity between seven fruit gardens and eight control sites. Fruit gardens contained similar species richness and abundance levels but higher diversity and almost threefold higher mammal biomass. Fruit gardens contained five times as many fruit-producing trees and a positive correlation was found between the number of fruit trees and total mammal biomass. Mammal community composition differed between the two habitats, with fruit gardens attracting nine species of conservation concern. These results suggest that traditional agroforestry systems may provide additional resources for mammals and therefore their net effects should be considered in conservation policy.

Variation in leaf and soil δ15N in diverse tree species in a lowland dipterocarp rainforest, Malaysia

Large variations in leaf δ 15 N in Bornean tropical rainforest trees may indicate that various tropical species have species-specific strategy for nitrogen uptake under low soil nutrient conditions, including root symbiotic microorganisms such as ectomycorrhiza. Lowland tropical rainforests in Southeast Asia are characterized by high species diversity despite limited soil nutrient conditions. The plant nitrogen isotope ratio (δ15N) reflects plant uptake of soil nitrogen. We analyzed δ15N values and nitrogen content (N %) in leaves and roots of 108 woody species with different types of symbiotic microorganisms, of different life forms (emergent, canopy, sub-canopy, understory, and canopy gap species), and from different families in a Bornean lowland dipterocarp forest to gain more insight into the diversity of nitrogen uptake strategy in the rhizosphere. Leaf δ15N values in the species studied varied largely from −7.2 to 5.0 ‰, which is comparable to the values of known Asian trees including temperate, sub-tropical, and tropical mountain forests. Leaf δ15N also varied significantly among both life forms and families, though the phylogenetically independent contrast (PIC) relationships were not statistically significant among life form, family, and symbiotic types. Some families showed specific leaf δ15N values; Dipterocarpaceae, the dominant family in the canopy layer with symbiotic ectomycorrhiza in Southeast Asia, had small intraspecific variation and higher leaf δ15N values (0.03 ‰) compared with species exhibiting arbuscular mycorrhiza, whereas several families such as Burseraceae, Euphorbiaceae, and Myrtaceae showed large interspecific variation in leaf δ15N (e.g., from −7.2 to 5.0 ‰ in Euphorbiaceae). These variations suggest that tropical species may have family- or species-specific strategy, such as root symbiotic microorganisms, for nitrogen uptake under low-nutrient conditions in tropical rainforests in Southeast Asia.

Contrasting diversity and host association of ectomycorrhizal basidiomycetes versus root-associated ascomycetes in a dipterocarp rainforest.

Root-associated fungi, including ectomycorrhizal and root-endophytic fungi, are among the most diverse and important belowground plant symbionts in dipterocarp rainforests. Our study aimed to reveal the biodiversity, host association, and community structure of ectomycorrhizal Basidiomycota and root-associated Ascomycota (including root-endophytic Ascomycota) in a lowland dipterocarp rainforest in Southeast Asia. The host plant chloroplast ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (rbcL) region and fungal internal transcribed spacer 2 (ITS2) region were sequenced using tag-encoded, massively parallel 454 pyrosequencing to identify host plant and root-associated fungal taxa in root samples. In total, 1245 ascomycetous and 127 putative ectomycorrhizal basidiomycetous taxa were detected from 442 root samples. The putative ectomycorrhizal Basidiomycota were likely to be associated with closely related dipterocarp taxa to greater or lesser extents, whereas host association patterns of the root-associated Ascomycota were much less distinct. The community structure of the putative ectomycorrhizal Basidiomycota was possibly more influenced by host genetic distances than was that of the root-associated Ascomycota. This study also indicated that in dipterocarp rainforests, root-associated Ascomycota were characterized by high biodiversity and indistinct host association patterns, whereas ectomycorrhizal Basidiomycota showed less biodiversity and a strong host phylogenetic preference for dipterocarp trees. Our findings lead to the working hypothesis that root-associated Ascomycota, which might be mainly represented by root-endophytic fungi, have biodiversity hotspots in the tropics, whereas biodiversity of ectomycorrhizal Basidiomycota increases with host genetic diversity.

Examining Phylogenetic Relationships Among Gibbon Genera Using Whole Genome Sequence Data Using an Approximate Bayesian Computation Approach

Gibbons are believed to have diverged from the larger great apes ∼16.8 MYA and today reside in the rainforests of Southeast Asia. Based on their diploid chromosome number, the family Hylobatidae is divided into four genera, Nomascus, Symphalangus, Hoolock, and Hylobates. Genetic studies attempting to elucidate the phylogenetic relationships among gibbons using karyotypes, mitochondrial DNA (mtDNA), the Y chromosome, and short autosomal sequences have been inconclusive . To examine the relationships among gibbon genera in more depth, we performed second-generation whole genome sequencing (WGS) to a mean of ∼15× coverage in two individuals from each genus. We developed a coalescent-based approximate Bayesian computation (ABC) method incorporating a model of sequencing error generated by high coverage exome validation to infer the branching order, divergence times, and effective population sizes of gibbon taxa. Although Hoolock and Symphalangus are likely sister taxa, we could not confidently resolve a single bifurcating tree despite the large amount of data analyzed. Instead, our results support the hypothesis that all four gibbon genera diverged at approximately the same time. Assuming an autosomal mutation rate of 1 × 10(-9)/site/year this speciation process occurred ∼5 MYA during a period in the Early Pliocene characterized by climatic shifts and fragmentation of the Sunda shelf forests. Whole genome sequencing of additional individuals will be vital for inferring the extent of gene flow among species after the separation of the gibbon genera.

Aboveground and belowground biomass in logged-over tropical rain forests under different soil conditions in Borneo

Although an estimation of forest biomass is essential for the development of a carbon storage baseline in the “Reducing Emissions from Deforestation and Degradation in Developing Countries” scheme, few have been conducted in logged-over rain forests of Southeast Asia. We measured the aboveground and belowground biomass in logged-over mixed dipterocarp forests growing on an infertile soil with bleached white sand (Sabal) and on a clay and nutrient-rich soil (Balai Ringin) in Sarawak, Malaysia. We established four 0.5-ha plots on each site and calculated the biomass. Basal area and stand density of large trees (diameter at breast height, DBH ≥ 10 cm) were relatively similar in Sabal (27.0 m2, 720 tree ha−1) and Balai Ringin (28.9 m2, 586 tree ha−1). However, the corresponding measurements for small trees (1 ≤ DBH < 10 cm) were twice as large in Sabal than in Balai Ringin. Aboveground biomass (AGB) in the forests was less than half of the value recorded for undisturbed forests in Borneo, even 20 years after logging. Although total AGB was 20 % smaller in Sabal (205 Mg ha−1) than in Balai Ringin (242 Mg ha−1), the total belowground biomass (TBGB) was 20 % greater in Sabal (59.6 Mg ha−1) than in Balai Ringin (44.6 Mg ha−1). The larger TBGB in Sabal was due to the larger amounts of small roots (diameter <5 mm) in Sabal (26.8 Mg ha−1) compared to Balai Ringin (5.8 Mg ha−1). This accumulation of small roots at Sabal may have contributed to rapid nutrient absorption from infertile soil.

RNA-seq Reveals Complicated Transcriptomic Responses to Drought Stress in a Nonmodel Tropic Plant, Bombax ceiba L.

High-throughput transcriptome provides an unbiased approach for understanding the genetic basis and gene functions in response to different conditions. Here we sequenced RNA-seq libraries derived from a Bombax ceiba L. system under a controlled experiment. As a known medicinal and ornamental plant, B. ceiba grows mainly in hot-dry monsoon rainforests in Southeast Asia and Australia. Due to the specific growth environment, it has evolved a unique system that enables a physiologic response to drought stress. To date, few studies have characterized the genome-wide features of drought endurance in B. ceiba. In this study, we first attempted to characterize and identify the most differentially expressed genes and associated functional pathways under drought treatment and normal condition. Using RNA-seq technology, we generated the first transcriptome of B. ceiba and identified 59 differentially expressed genes with greater than 1,000-fold changes under two conditions. The set of upregulated genes implicates interplay among various pathways: plants growth, ubiquitin-mediated proteolysis, polysaccharides hydrolyzation, oxidative phosphorylation and photosynthesis, etc. In contrast, genes associated with stem growth, cell division, fruit ripening senescence, disease resistance, and proline synthesis are repressed. Notably, key genes of high RPKM levels in drought are AUX1, JAZ, and psbS, which are known to regulate the growth of plants, the resistance against abiotic stress, and the photosynthesis process. Furthermore, 16,656 microsatellite markers and 3,071 single-nucleotide polymorphisms (SNPs) were predicted by in silico methods. The identification and functional annotation of differentially expressed genes, microsatellites, and SNPs represent a major step forward and would serve as a valuable resource for understanding the complexity underlying drought endurance and adaptation in B. ceiba.

Historical distribution of Sundaland's Dipterocarp rainforests at Quaternary glacial maxima.

The extent of Dipterocarp rainforests on the emergent Sundaland landmass in Southeast Asia during Quaternary glaciations remains a key question. A better understanding of the biogeographic history of Sundaland could help explain current patterns of biodiversity and support the development of effective forest conservation strategies. Dipterocarpaceae trees dominate the rainforests of Sundaland, and their distributions serve as a proxy for rainforest extent. We used species distribution models (SDMs) of 317 Dipterocarp species to estimate the geographic extent of appropriate climatic conditions for rainforest on Sundaland at the last glacial maximum (LGM). The SDMs suggest that the climate of central Sundaland at the LGM was suitable to sustain Dipterocarp rainforest, and that the presence of a previously suggested transequatorial savannah corridor at that time is unlikely. Our findings are supported by palynologic evidence, dynamic vegetation models, extant mammal and termite communities, vascular plant fatty acid stable isotopic compositions, and stable carbon isotopic compositions of cave guano profiles. Although Dipterocarp species richness was generally lower at the LGM, areas of high species richness were mostly found off the current islands and on the emergent Sunda Shelf, indicating substantial species migration and mixing during the transitions between the Quaternary glacial maxima and warm periods such as the present.

Influence of spatial and environmental variables on rattan palm (Arecaceae) assemblage composition in Central Sulawesi, Indonesia

Rattan palms are dominant elements of Southeast Asian rainforests and of high economic importance, yet little is known about the ecological factors determining the spatial distribution of species and assemblages. We studied rattan palm assemblages at two sites at different elevations in Lore Lindu National Park, Sulawesi, Indonesia (Pono: 958–1,266 m; Bariri: 1,390–1,507 m). At each site, we established a transect of 1.29 km consisting of 65 study plots of 10 × 10 m2 each, regularly spaced 20 m from each other. In total, we recorded 5,081 rattan individuals belonging to 22 species, with 1,367 individuals of 16 species at Pono and 3,714 individuals of 8 species at Bariri. Variance partitioning explained 29–49 % of community variation at Pono and 40–72 % at Bariri, with most variation jointly explained by spatial and environmental variables. Within the environmental influence, soil factors dominated over local topographical ones. RDA ordination allowed the discrimination of four species groups at Pono and three groups at Bariri. These groups were related to soil and less clearly to topographic variables. Our study is the first documentation of the importance of soil parameters in determining the spatial distribution of rattan palms. Interestingly, juvenile palms ( 1 m tall), calling for further studies on the demography of rattan palms.

UFO cross-section gives snakes a lift

If you're afraid of snakes, you're really not going to like the next bit: some snakes can fly. It sounds like a frightful nightmare, but for Jake Socha, the discovery was the start of a fascinating odyssey to learn how an animal that looks as unaerodynamic as a snake can glide as much as 30 m from a tall tree. Socha describes the snakes as ‘slithering’ in an S-shape through the air as they descend through the Southeast Asian rainforest: ‘They look like they are swimming’, he adds. But what keeps the reptiles aloft? ‘They turn their whole body into one aerodynamic surface’, explains Socha – who has spent much of his career unpicking details of the snake's flying style – and has now turned his attention to the animal's intriguing body shape to find out how they generate the lift they require to remain airborne (p. 382).According to Socha, the snakes flex their ribs as they launch to stretch and flatten the body to change their profile from a circle into an arched semi-circle: ‘It looks like someone's version of a UFO’, laughs Socha, adding that as aerofoils go it's an unconventional shape. To get to grips with the aerodynamic forces generated by the snake's body, Socha and his colleagues, Daniel Holden, Nicholas Cardwell and Pavlos Vlachos, used a 3D printer to produce a rod with the same UFO cross-section as the snake's body before placing it across a tank filled with water that flowed over the snake-shaped bar. Socha explains that although water is much denser and stickier than air, you can precisely recreate the air conditions experienced as the snakes fly by flowing the water over the model at a specific range of speeds.Tilting the snake model at angles (of attack) ranging from −10 to 60 deg as the water flowed over it at speeds ranging from 20 to 50 cm s−1, the team measured the lift and drag forces pulling on the model and saw that at most angles the animal's unusual body shape generated sufficient lift to account for some of the snake's impressive gliding performance. But when the team tilted the model at 35 deg, there was a massive spike in the lift generated by water flowing at higher speeds. More surprisingly, when the model was held level with the flow, instead of generating upward lift, the fluid pushed the rod down. And when the team visualised the turbulent water flowing around the model with microscopic reflective beads, they could clearly see a spinning vortex sitting beneath the untilted snake shape, sucking it down: which may not be that crazy, according to Socha. He says, ‘Maybe the snake does hold part of its body flat at some point, using it as a mechanism for control’, explaining that twisting the body while airborne could allow the snakes to fine tune the forces on their bodies for precise flight control.But Socha adds that there is much more to the snake's impressive glide than just its unusual body shape. ‘If you make a rough estimate of the lift to drag ratio for the real animal, it appears to do better than what we got from this study. So even though this shape produced more lift than we were expecting, it doesn't get us the glide performance that snakes can attain, giving us a hint that there is something in what the animal is doing aerodynamically that is not captured by the cross-sectional shape alone’ – which is the next part of the problem that Socha and his team hope to crack.

High gene flow in two thrips-pollinated South-East Asian pioneer trees: genetic diversity and population structure ofMacaranga hypoleucaandM. beccariana(Euphorbiaceae)

As a result of intensive exploitation, disturbed forests now dominate large areas of lowland tropical rainforest in South-East Asia. The genus Macaranga comprises some of the most important pioneer tree species of the region, among them M. beccariana and M. hypoleuca, two closely related obligate ant-plants pollinated by thrips. We used nuclear and plastid DNA markers to address questions of genetic diversity and population structure. Twelve plastid haplotypes were detected among 281 samples, three of which were shared between the two study species. Hybrids between the two species appear to be rare. Overall, genetic diversity in both species was moderate to high, with low levels of population differentiation, consistent with other tropical pioneer trees. Genetic structure was generally more pronounced in plastid than in nuclear data, indicating that gene flow via pollen may be more efficient than via seeds. Thrips apparently also serve as efficient pollinators over long distances, perhaps through a combination of passive dispersal by wind and active search for inflorescences in the target area. Our results indicate that M. beccariana and M. hypoleuca populations from recently disturbed habitats do not yet suffer from reduced genetic diversity or increased inbreeding.

Effects of soil compaction on the growth and mortality of planted dipterocarp seedlings in a logged-over tropical rainforest in Sarawak, Malaysia

Soil compaction is major determinant of plant growth and/or mortality. Tropical rainforests in Southeast Asia have been degraded by commercial logging, and the use of heavy equipment in these operations has increased soil compaction. We conducted enrichment planting 20years after logging in a tropical forest in Borneo to evaluate the effects of soil compaction on the growth and mortality of planted dipterocarp seedlings over seven years. We planted the seedlings in sites that had been impacted to varying degrees, including a skid trail and undisturbed areas. We measured soil nutrients, moisture content, bulk density, penetration resistance, and light conditions. Seedling mortality, height, and shoot diameter were also determined 0, 12, 24, and 81months after planting. Elongation rates of tap and lateral roots were measured 24months after planting. We also excavated seedlings 81months after planting, and compared heights, shoot diameters, tap root length, and lateral root length between compacted and undisturbed soils. Bulk density varied in the range of 0.98–1.61gcm−3 and correlated with soil penetration resistance. Surface soil (0–20cm depth) in the compacted area had two to three times more resistance to penetration than did undisturbed soils. Surface soil penetration resistance significantly increased seedling mortality during the early planting period (0–12months), but mortality in the later periods (12–24 and 24–81months) did not relate to the soil penetration resistance. The lateral root growth rate in the early planting period (0–24months) was also significantly inhibited by penetration resistance, but tap root growth was not. Penetration resistance did not reduce the seedling growth rate in the periods 0–12 and 12–24months after planting, and higher soil moisture promoted seedling shoot diameter growth in the same time periods. Lateral root elongation did not differ between compacted and undisturbed forest soils 81months after planting, but tap root elongation was inhibited in the compacted area at that time. Our results suggest that soil compaction negatively affect root elongation and initial seedling survival of planted dipterocarp trees even in 20years after logging operation in Bornean tropical rainforest.

Change in Phylogenetic Community Structure during Succession of Traditionally Managed Tropical Rainforest in Southwest China

Tropical rainforests in Southeast Asia are facing increasing and ever more intense human disturbance that often negatively affects biodiversity. The aim of this study was to determine how tree species phylogenetic diversity is affected by traditional forest management types and to understand the change in community phylogenetic structure during succession. Four types of forests with different management histories were selected for this purpose: old growth forests, understorey planted old growth forests, old secondary forests (∼200-years after slash and burn), and young secondary forests (15–50-years after slash and burn). We found that tree phylogenetic community structure changed from clustering to over-dispersion from early to late successional forests and finally became random in old-growth forest. We also found that the phylogenetic structure of the tree overstorey and understorey responded differentially to change in environmental conditions during succession. In addition, we show that slash and burn agriculture (swidden cultivation) can increase landscape level plant community evolutionary information content.