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This study demonstrated that the cambial activities of three selected Shorea species with different stem diameters growing in a tropical rainforest in Malaysia responded differently to climatic factors. We investigated the cambial activities in Shorea leprosula, Shorea acuminata, and Shorea parvifolia trees with different stem diameters at breast height growing in a natural lowland dipterocarp rainforest in Malaysia. We collected and analyzed samples from the main trunks of selected trees in monthly intervals from March 2013 to April 2014. The cambium of the three Shorea species showed periods of active and less active growth in the humid forest. Selected trees with different stem diameters of the same and different species showed variation in rhythms of cambial activity (changes in the numbers of cambial and enlarging cell layers) at site with similar growing conditions. Monthly mean relative humidity and monthly mean vapour pressure deficit were important factors influencing the number of cambial cells of S. acuminata with larger stem diameter, and those of S. parvifolia with different stem diameters. Active cambium were detected in months with high relative humidity and low vapour pressure deficit in those trees. Total monthly precipitation had significant positive correlation with the cambial cells activities of S. parvifolia with different stem diameters, but no correlation with those of the other two species. The cambium of S. leprosula with smaller and larger stem diameters were found active throughout the year. We concluded that the three Shorea species examined with different stem diameters have different growth strategies and thus react differently to climatic factors.

Plantations of tropical species are becoming an increasingly important source of wood. However, it is important that research trials focus not only on tree growth performance, but also on wood quality. The aims of this study were to assess the growth performance of six commercially and ecologically important tree species from separate plantation trials in Indonesia and to determine the relationships between tree growth and wood quality in terms of the dynamic modulus of elasticity (MOE) and wood density. Forty-eight 7-year Maesopsis eminii Engl. and thirty-five 9-year specimens (7 each of 5 Shorea spp.) were selected from two trials. The MOE, based on acoustic velocity, was indirectly measured to evaluate wood stiffness. Tree-growth performance was evaluated, and correlations between growth traits and acoustic velocity as well as density and wood stiffness properties were estimated. The growth performance of M. eminii in terms of tree volume was significantly different in three different categories of growth (i.e. fast, medium, slow). Of the five Shorea spp. studied, Shorea leprosula Miq. had the highest growth rate, as expected since it is known to be a fast-growing Shorea species. Indirect measurement of wood quality by means of non-destructive ultrasonic methods showed a weak negative correlation between tree volume and acoustic velocity and dynamic MOE. Although each fast-growing tree could reach a merchantable size faster than other varieties or species, wood traits of various species tested were not significantly different based on tree growth rate performance. The findings from this study could be used to improve selection criteria in future breeding trials; indirect measurements of the dynamic modulus of elasticity can be used in mass pre-selection of genetic materials, to choose the most-promising material for in-depth evaluation.

Selective cutting and line planting silvicultural system has been carried out in natural forest to increase the growth rate of red meranti (Shorea leprosula Miq.). Even though high growth rate has been understood tend to decrease certain basic properties of wood; however measurement of the basic properties specifically done on the red meranti resulted from thinning and shade free gap treatment has been lacking. In the present research, measurement of the basic properties of red meranti resulted from thinning and shade free gap treatment was done. It was found that thinning and increasing shade free gap increased the diameter of tree, longitudinal shrinkage, fiber diameter, lumen diameter, sapwood extractives, and ash content. On the other hand, these treatment decreased heartwood proportion, crown coverage, specific gravity, wood density, mechanical properties, radial and tangential shrinkage, fiber length, cell wall thickness and heartwood extractives. Lignin, holocellulose, α-cellulose and hemicelluloses were not significantly influenced by the treatments. Overall, thinning and increasing shade free gap tended to reduce the quality of wood.

We developed microsatellite markers from newly isolated expressed sequence tags of an endangered tropical tree species, Shorea leprosula (Dipterocarpaceae). Twenty-four loci exhibited clear, polymorphic amplification patterns among 52 individuals from a population in Indonesia, with two to 16 alleles per locus. No locus showed significant departure from Hardy–Weinberg equilibrium, and no significant genotypic disequilibrium was detected for any pair of loci after sequential Bonferroni correction.

Shorea (Dipterocarpaceae) is a large genus in which many closely related species often grow together in Southeast Asian lowland tropical rain forests. Many Shorea species share common pollinators, and earlier studies suggested occurrence of interspecific hybridization and introgression. Here, we show morphological and molecular evidence of hybridization between Shorea species. In the census of all the trees of Shorea curtisii, Shorea leprosula, and Shorea parvifolia (>30 cm dbh) within the 164-ha area of Bukit Timah Nature Reserve in Singapore, we found 21 morphologically recognizable hybrid individuals. All of the putative hybrids could be distinguished obviously from the parental species on the basis of vegetative characters. Population genetic analysis of DNA sequences of two nuclear (GapC and PgiC) and chloroplast (trnL-trnF) regions demonstrated that each of the three species had several species-specific mutations. The nuclear sequences of the putative hybrids were heterozygote at all the species-specific sites between two parental species. Hybrid between S. curtisii and S. leprosula was found most, while S. curtisii × S. parvifolia and S. leprosula × S. parvifolia hybrids were also found. Almost no shared polymorphism between populations of the parental species suggests rarity of introgression. The study indicated that natural hybridization between sympatric Shorea species should not be uncommon, but all of the hybrid individuals were F1, and the post-F1 hybrids were considerably rare.

Phosphorus concentrations in many south-east Asian tropical rain forest soils are very low. To determine the growth responses of seedlings of a light-demanding (Shorea leprosula) and a more shade-tolerant (Hopea nervosa) dipterocarp species to increasing P, we carried out a nursery fertilisation experiment. Responses of symbiotic ectomycorrhizal (EcM) fungi to the treatments were also determined. Seedlings were grown under high light (13 mol m−2 d−1) or moderate light (4 mol m−2 d−1) in shade-chambers and were fertilised with a solution containing 0, 1, 10 or 100 mg L−1 P. The growth of Hopea and Shorea showed different responses to the light and P fertilisation treatments with Hopea having greater growth under moderate light conditions and Shorea having greater growth under high light conditions. Shorea responded to P fertilisation by increasing its foliar P concentrations and growth rates, whereas Hopea did not take up additional P and did not improve its growth rates. There was no effect of either light or P fertilisation on total EcM colonisation or EcM diversity, but around half of the EcM morphotypes observed were affected by one of these two abiotic perturbations, most notably for Riessiella sp. which increased with P fertilisation suggesting it may not be a mutualistic fungus. These results show how niche partitioning in both dipterocarp seedlings and EcM fungi can be divided along contrasting axes.

Pristine tropical rainforests in Southeast Asia have rich species diversity and are important habitats for many plant species. However, the extent of these forests has declined in recent decades and they have become fragmented due to human activities. These developments may reduce the genetic diversity of species within them and, consequently, the species’ ability to adapt to environmental changes. Our objective in the study presented here was to clarify the effect of tree density on the genetic diversity and gene flow patterns of Shorea leprosula Miq. populations in Peninsular Malaysia. For this purpose, we related genetic diversity and pollen flow parameters of seedling populations in study plots to the density of mature trees in their vicinity. The results show that gene diversity and allelic richness were not significantly correlated to the mature tree density. However, the number of rare alleles among the seedlings and the selfing rates of the mother trees were negatively correlated with the density of the adult trees. Furthermore, in a population with high mature tree density pollination distances were frequently

The genetic diversity within and among populations of Shorea leprosula and Shorea parvifolia from Indonesia was investigated using amplified fragment length polymorphisms (AFLPs). The results indicated that S. leprosula is genetically more variable than S. parvifolia. At the population level, a higher level of genetic diversity was revealed for S. leprosula with a percentage of polymorphic loci (PPLp) of 53.32% and an expected heterozygosity (H ep) of 0.16 in comparison with S. parvifolia showing PPLp of 51.79% and H ep of 0.14. At the species level, S. leprosula showed PPLs of 92.86% and H es of 0.21, while S. parvifolia showed PPLs of 85.71% and H es of 0.21. Genetic differentiation (G st) indicated that 25 and 31% of total genetic diversity in S. leprosula and S. parvifolia, respectively, were attributed to the differences among populations. An analysis of molecular variance (AMOVA) at two hierarchical levels exhibited that most genetic variation resided within populations with proportion of 70.2% for S. leprosula and 66.2% for S. parvifolia. The AMOVA at three hierarchical levels performed for S. leprosula and S. parvifolia together revealed that the genetic difference between the two species was remarkably higher with a proportion of 44.1% than the differences within and among populations (38.1 and 17.8%, respectively). The genetic differentiation between islands was significant for S. leprosula but not for S. parvifolia. The observed genetic diversity agreed with the life history traits of Shorea species. Highly differentiating individual AFLP markers were found for each species, which will serve as diagnostic markers for the identification of wood of different species, from different islands and regions.

Analyses of the spatial distribution pattern, spatial genetic structure and genetic diversity were carried out using a 33-ha plot in a hill dipterocarp forest for three dipterocarps with different habitat preferences, i.e. Shorea curtisii on the ridges, Shorea leprosula in the valleys and Shorea macroptera both on the ridges and in the valleys. The significant spatial aggregation in small-diameter trees of all the three species was explained by limited seed dispersal. At the large-diameter trees, only S. macroptera showed random distribution and this might further prove that S. macroptera is habitat generalist, whilst S. curtisii and S. leprosula are habitat specific. The levels of genetic diversity estimated based on five microsatellite loci were high and comparable in all the three studied species. As the three studied species reproduced mainly through outcrossing, the observed high levels of genetic diversity might support the fact that the plant mating system can be used as guideline to infer the levels of genetic diversity, regardless of whether the species is habitat specific or habitat generalist. The lack of spatial genetic structure but significant aggregation in the small-diameter trees of all the three species might indicate limited seed dispersal but extensive pollen flow. Hence, if seed dispersal is restricted but pollen flow is extensive, significant spatial aggregation but no spatial genetic structure will be observed at the small-diameter trees, regardless of whether the species is habitat specific or habitat generalist. The inferred extensive pollen flow might indicate that energetic pollinators are involved in the pollination of Shorea species in the hill dipterocarp forests.

In the deeply shaded understorey of S.E. Asian rain forests the growth and survival of dipterocarp seedlings is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain in understorey plants. To test the sensitivity of photosynthesis and growth to variation in the pattern of dynamic irradiance, dipterocarp tree seedlings (Shorea leprosula and Hopea nervosa) were grown for 370 days under shaded forest light treatments of equal total daily photosynthetic photon flux density (~3.3 mol m-2 day-1), but characterised by either long flecks (LF) or short flecks (SF). Seedling growth was more than 4-fold greater under LF, compared with SF, in both species. Variation in the relative growth rates (RGR) and light saturated rates of photosynthesis (A max) were strongly positively correlated with the mean duration of sunflecks. Variation in RGR was strongly correlated with greater unit leaf rate growth, indicating that photosynthetic carbon gain per unit leaf area was greater under LF. The accumulation of starch in leaves over the diurnal period was 117% greater in both species under LF, compared with SF. Greater carbon gain in seedlings under LF is likely to have resulted from the combination of (1) greater A max (S. leprosula 35%, H. nervosa 40%), (2) more efficient dynamic photosynthesis, and (3) greater incident photosynthetic quantum yield, compared with seedlings receiving the SF irradiance treatment. The pattern of dynamic irradiance received by seedlings may significantly impact their growth and survival to a previously unrecognised extent, with important consequences for regeneration processes and hence forest structure and composition.

The ectomycorrhizas of Shorea leprosula Miq. are described and their putative fungal associates discussed. Of the 24 ectomycorrhizal types reported from seedlings, wildlings and 20-year-old trees of Shorea leprosula, 20 were associated with the Basidiomycotina, two with the Ascomycotina and two with either members of the Ascomycotina or the Russulaceae. The dominant group of fungi associated with Shorea leprosula ectomycorrhizas were members of the Russulaceae. This was confirmed by collections of fungal fruiting bodies made under adult Shorea leprosula trees in various parts of Peninsular Malaysia over a period of 3 years. Of the 28 species of putative ectomycorrhizal fungi collected, 15 were members of the Russulaceae.

The light environment within tropical rain forests varies considerably both spatially and temporally, and photon flux density (PFD) is considered to be an important factor determining the growth and survival of rain forest tree seedlings. In this paper we examine the ability of four ecologically contrasting dipterocarps (Dryobalanops lanceolata, Shorea leprosula, Hopea nervosa and Vatica oblongifolia) to utilise and dissipate light energy when grown in different light environments in lowland dipterocarp rain forest in the Danum Valley Conservation Area, Sabah, East Malaysia. Specifically we report (i) photosynthetic light response curves and associated fluorescence characteristics, including quantum yield (ΦPSII) and non-photochemical quenching (qN) and (ii) the extent to which photoinhibition occurs when plants grown in either high or low light are exposed to short bursts of high PFD. When grown in low light (artificial or forest shade) all four species had low light saturated rates of photosynthesis which were achieved at low PFDs. In addition, values of ΦPSII and qN were similar over a range of measurement PFDs. D. lanceolata and S. leprosula were also grown at high PFD and showed marked differences in their responses. S. leprosula demonstrated an ability to increase its rate of photosynthesis and there was a small increase in capacity to dissipate excess light energy non-photochemically at high PFDs. Partitioning of this qN into its fast, photo-protective (qE) and slow, photoinhibitory (qI) components indicated that there was an increase in qE quenching. In contrast, although D. lanceolata survived in the high light environment, greater rates of photosynthesis were not observed and the plants showed a greater capacity to dissipate energy non-photochemically. Partitioning of qN revealed that the majority of this increase was attributable to the slower relaxing phases.

Foliar phosphorus content and mycorrhizal infection of dipterocarp seedlings growing in a 61-year-old forest plantation (site A) and a selectively logged forest (site B) were determined. Mycorrhizal infection levels were high−83.7% forShorea bracteolata and 95.0% forS. leprosula at site A, and 77.8% forS. leprosula and 86.3% forS. curtisii at site B. The seedlings all had similar foliar phosphorus contents although available soil phosphorus at site B was half that at site A. Significant correlations were obtained between foliar phosphorus content and percentage mycorrhizal infection at site B only.

THE exceptional species diversity of tropical rain forests is well known; of these the lowland forests of the Malay Peninsula are among the richest1. This, and the size of the trees, pose obvious difficulties for the maintenance of pan-mixis, and tempt speculation on the processes by which such diversity has evolved and may now be favoured. Fedorov2 suggested that natural selection is low and self-pollination prevalent, favouring random genetic drift. Prevalence of random drift, or apomixis—agamospermy—would contradict Ashton's3 view that, given a stable environment, evolution proceeds through ecotypic differentiation while diversity accrues through ever increasing niche specialisation; for this view to be correct, maintenance of genetic variability within breeding groups would be essential. Solid evidence has been meagre but there is evidence4 that genetic polymorphism, and hence heterozygosity, is common in the emergent tree Shorea leprosula Miq., and Xerospermum intermedium Radlk., an undeirstorey species. The pattern of spatial variation is consistent with the view that these species are outbreeders in which predominantly short-range pollen and fruit dispersal are accompanied by short-range heterogeneity in gene frequencies. However, both are common trees with minimal spatial isolation. We now report the occurrence of apomixis in some other rain forest trees.