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Community phylogenetic analysis is an effective approach to understanding the process of community formation. The phylogenetic tree of the species pool is reconstructed in the first step, and the phylogenetic tree obtained in the second step is used to analyze phylogenetic diversity. Sythetic trees have often been used in the construction of phylogenentic trees; however, in tropical rainforests with many closely related species, synthetic trees contain many unresolved nodes, which may affect the results of phylogenetic structure analysis. Here, we constructed a phylogenetic tree using DNA barcode sequences (rbcL, matK, trnH‐psbA) for 737 tree species from the rainforests of Borneo, which have a high‐species diversity and many closely related species. The phylogenetic tree had fewer polytomies and more branch length variations than the Phylocom synthetic trees. Comparison of community phylogenetic analyses indicated that values of the standardized effect size of mean pairwise distance (SES–MPD) were highly correlated between Phylocom and DNA barcode trees, but less so for the standardized effect size of mean nearest taxon distance (SES–MNTD), suggesting that caution is needed when using synthetic trees for communities containing many congeneric species, especially when using SES–MNTD. Simulation analysis suggested that spatial dependence on phylogenetic diversity is related to the phylogenetic signal of the species' habitat niche and the spatial structure of habitat, indicating the importance of detailed phylogeny in understanding community assembly processes. [ABSTRACT FROM AUTHOR]

Summary: Arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF) produce contrasting plant–soil feedbacks, but how these feedbacks are constrained by lithology is poorly understood.We investigated the hypothesis that lithological drivers of soil fertility filter plant resource economic strategies in ways that influence the relative fitness of trees with AMF or EMF symbioses in a Bornean rain forest containing species with both mycorrhizal strategies.Using forest inventory data on 1245 tree species, we found that although AMF‐hosting trees had greater relative dominance on all soil types, with declining lithological soil fertility EMF‐hosting trees became more dominant. Data on 13 leaf traits and wood density for a total of 150 species showed that variation was almost always associated with soil type, whereas for six leaf traits (structural properties; carbon, nitrogen, phosphorus ratios, nitrogen isotopes), variation was also associated with mycorrhizal strategy. EMF‐hosting species had slower leaf economics than AMF‐hosts, demonstrating the central role of mycorrhizal symbiosis in plant resource economies.At the global scale, climate has been shown to shape forest mycorrhizal composition, but here we show that in communities it depends on soil lithology, suggesting scale‐dependent abiotic factors influence feedbacks underlying the relative fitness of different mycorrhizal strategies. [ABSTRACT FROM AUTHOR]

The association of tree species with particular soil types contributes to high β diversity in forests, but the mechanisms producing such distributions are still debated. Soil nitrogen (N) often limits growth and occurs in differentially available chemical forms. In a Bornean forest where tree species composition changes dramatically along a soil gradient varying in supplies of different N-forms, we investigated whether tree species' N-uptake and soil specialization strategies covaried. We analyzed foliar N natural abundance for a total of 216 tree species on clay or sandy loam (the soils at the gradient's extremes) and conducted a N-tracer experiment with nine specialist and generalist species to test whether species displayed flexible or differential uptake of ammonium and nitrate. Despite variation in ammonium and nitrate supplies and nearly 4 ‰ difference in foliar δN between most soil specialists and populations of generalists on these soils, our N tracer experiment showed little support for the hypothesis that soil specialists vary in N-form use or the ratios in which they use these forms. Instead, our results indicate that these species possess flexible capacities to take up different inorganic N forms. Variation between soil specialists in uptake of different N forms is thus unlikely to cause the soil associations of tree species and high β diversity characteristic of this Bornean rain forest. Flexible uptake strategies would facilitate N-acquisition when supply rates of N-forms exhibit spatiotemporal variation and suggest that these species may be functionally redundant in their responses to N gradients and influences on ecosystem N-cycles. [ABSTRACT FROM AUTHOR]

The fine roots of plants are key structures enabling soil resource acquisition, yet our understanding of their dynamics and the factors governing them is still underdeveloped, especially in tropical forests. We evaluated whether Bornean tree communities on soils with contrasting resource availability display different soil resource uptake strategies, based on their fine root properties and dynamics, and related responses of fine roots to the availability of multiple nutrients. Using root cores and ingrowth cores, we quantified variation in community-level fine root properties (biomass, length, and area) and their growth rates, biomass turnover rate, and specific root length (SRL) between clay and sandy loam soils, on which tree community composition differs dramatically. We found that standing fine root biomass and biomass, length, and area growth were higher in sandy loam, the soil type that is better-drained, coarser-textured, and less fertile for most nutrients. In clay SRL was significantly greater, and turnover tended to be faster, than in sandy loam. Across both soils, greater supplies of K, NH, and PO were associated with greater standing biomass and growth rates of fine roots, suggesting foraging for these nutrients. Our data support the hypothesis that the sandy loam tree community achieves fine root absorptive area through faster growth and greater investment on a mass basis, whereas trees on clay achieve a similar standing absorptive area through slower growth of less-dense fine root tissues. Furthermore, our results suggest colimitation by multiple nutrients, which may enhance tree species coexistence through increased dimensionality of soil-resource niches. [ABSTRACT FROM AUTHOR]

Hunting affects a considerably greater area of the tropical forest biome than deforestation and logging combined. Often even large remote protected areas are depleted of a substantial proportion of their vertebrate fauna. However, understanding of the long-term ecological consequences of defaunation in tropical forests remains poor. Using tree census data from a large-scale plot monitored over a 15-year period since the approximate onset of intense hunting, we provide a comprehensive assessment of the immediate consequences of defaunation for a tropical tree community. Our data strongly suggest that over-hunting has engendered pervasive changes in tree population spatial structure and dynamics, leading to a consistent decline in local tree diversity over time. However, we do not find any support for suggestions that over-hunting reduces above-ground biomass or biomass accumulation rate in this forest. To maintain critical ecosystem processes in tropical forests increased efforts are required to protect and restore wildlife populations. [ABSTRACT FROM AUTHOR]

Fine-scale spatial genetic structure is increasingly recognized as an important factor in the studies of tropical forest trees as it influences genetic diversity of local populations. The biologic mechanisms that generate fine-scale spatial genetic structure are not fully understood. We studied fine-scale spatial genetic structure in ten coexisting dipterocarp tree species in a Bornean rain forest using microsatellite markers. Six of the ten species showed statistically significant fine-scale spatial genetic structure. Fine-scale spatial genetic structure was stronger at smaller spatial scales (≤ 100 m) than at larger spatial scales (> 100 m) for each species. Multiple regression analysis suggested that seed dispersal distance was important at the smaller spatial scale. At the larger scale (> 100 m) and over the entire sample range (0-1000 m), pollinators and spatial distribution of adult trees were more important determinants of fine-scale spatial genetic structure. Fine-scale spatial genetic structure was stronger in species pollinated by less mobile small beetles than in species pollinated by the more mobile giant honeybee ( Apis dorsata). It was also stronger in species where adult tree distributions were more clumped. The hypothesized mechanisms underlying the negative correlation between clump size and fine-scale spatial genetic structure were a large overlap among seed shadows and genetic drift within clumped species. [ABSTRACT FROM AUTHOR]

•Relatively little is known about diversity or structure of tropical ectomycorrhizal communities or their roles in tropical ecosystem dynamics. In this study, we present one of the largest molecular studies to date of an ectomycorrhizal community in lowland dipterocarp rainforest. •We sampled roots from two 0.4 ha sites located across an ecotone within a 52 ha forest dynamics plot. Our plots contained > 500 tree species and > 40 species of ectomycorrhizal host plants. Fungi were identified by sequencing ribosomal RNA genes. •The community was dominated by the Russulales (30 species), Boletales (17), Agaricales (18), Thelephorales (13) and Cantharellales (12). Total species richness appeared comparable to molecular studies of temperate forests. Community structure changed across the ecotone, although it was not possible to separate the role of environmental factors vs host plant preferences. Phylogenetic analyses were consistent with a model of community assembly where habitat associations are influenced by evolutionary conservatism of functional traits within ectomycorrhizal lineages. •Because changes in the ectomycorrhizal fungal community parallel those of the tree community at this site, this study demonstrates the potential link between the distribution of tropical tree diversity and the distribution of tropical ectomycorrhizal diversity in relation to local-scale edaphic variation. [ABSTRACT FROM AUTHOR]

1. Interspecific relationships between fundamental demographic rates, often called demographic trade-offs, emerge from constraints within individuals related to morphology, physiology and resource allocation. Plant species that grow fast in high light usually have high mortality in shade, and this well-established relationship in part defines a species’ successional niche. More generally, this relationship represents a trade-off between a species’ ability to grow quickly to exploit abundant resources vs. avoiding mortality when resources are less plentiful, but few studies have described this demographic trade-off with respect to environmental factors other than light. 2. Using demographic data from 960 tree species in Bornean rain forest, we examined the evidence for an interspecific demographic trade-off between fast growth and low mortality and its variation among habitats defined by variation in soil fertility and moisture. Such a trade-off could contribute to sorting of tree species among habitats and partly explain the striking patterns of species’ edaphic associations in this and other forests. 3. We found strong evidence for this demographic trade-off, both within the same habitat and when growth on edaphically rich habitats was compared with mortality on a habitat with lower below-ground resource availability. 4. The slope of the growth-mortality relationship varied among habitats, being steepest on the habitat lowest in below-ground resources. For species with the fastest potential growth rates, mortality was higher on this habitat than at comparable growth rates on the three more edaphically rich habitats, providing a possible mechanism by which fast-growing species may be eliminated from the poorest habitat. Adaptations for fast growth may entail a greater mortality risk, if inherently fast-growing species fail to maintain a positive C-balance when below-ground resources are scarce. 5. Conversely, for species with the slowest potential growth rates, the highest species’ mortality rates occurred on the habitats with greatest below-ground resource availability, implying that slow-growing species may have a competitive disadvantage in resource-rich environments. 6. Synthesis. Differences among habitats in the steepness of this trade-off may sort species into different habitats along this edaphic gradient, whereas on the same soil, this demographic trade-off could facilitate coexistence of at least some species in this forest. Thus, by generating emergent demographic trade-offs that vary along resource gradients, plant life-history strategies can influence species diversity and distribution. [ABSTRACT FROM AUTHOR]

1 Many tropical forest tree species show habitat preference, commonly revealed by differences in abundance among habitats. Very little is known about differences in individual performance and population dynamics across habitats. 2 We analysed habitat-specific performance and demography of Scaphium borneense, a tropical rain forest tree with strong habitat preference in a 52-ha plot at Lambir Hills, Malaysia. This species occurs at high densities on ridges with sandy soils (‘preferred habitat’), at low densities in valleys on loamy soils (‘non-preferred habitat’) and at intermediate densities on slopes. We used 10-year demographic data to compare tree performance across habitats and constructed population matrix models to analyse population dynamics. 3 Tree performance was rather similar across habitats. Some vital rates (mortality) did not differ among habitats, while others were modestly (juvenile tree growth) to substantially higher (recruitment) in the non-preferred valley habitat, probably due to higher canopy openness. 4 Matrix models projected population sizes to remain stable in all habitats, thus maintaining abundance differences across habitats. This suggests that habitat preference of Scaphium is generated by (a)biotic differences among habitats and not by chance processes or disturbance history. 5 Population dynamics were also very similar among habitats. The distribution of elasticity values over categories and vital rates was almost equal for the three habitats. Life table response experiment (LTRE) analysis showed that habitat differences in vital rates had little effect on λ. Thus, Scaphium populations in the three habitats are maintained in a very similar way, despite differences in (a)biotic conditions and abundance. 6 We hypothesize that habitat preference of Scaphium is maintained because of a better performance in its preferred habitat relative to other species in that habitat, while the reverse may be true in non-preferred habitats. We suggest that such differences in performance may become apparent during periods of drought, creating windows of opportunity for maintaining density differences. 7 Strong habitat preference of rain forest tree species does not necessarily imply strong differences in tree performance, demography or population growth across habitats. The mechanisms that generate density differences across habitats remain to be unravelled. [ABSTRACT FROM AUTHOR]

Questions: 1. Are trees in a Bornean tropical rain forest associated with a particular habitat? 2. Does the strength of habitat association with the species-specific optimal habitat increase with tree size? Location: A 52-ha plot in a mixed dipterocarp forest in a heterogeneous landscape at the Lambir Hills National Park, Sarawak, East Malaysia. Methods: Ten species from the Sterculiaceae were chosen as representative of all species in the plot, on the assumption that competition among closely related species is more stringent than that among more distantly related taxa. Their habitat associations were tested using data from a 52-ha plot by a torus-translation test. Results: The torus-translation test showed that eight out of the ten species examined had significant association with at least one habitat. We could not find negative species-habitat associations for rare species, probably due to their small sample sizes. Among four species small trees were less strongly associated with habitat than large trees, implying competitive exclusion of trees in suboptimal habitats. The other four species showed the opposite pattern, possibly owing to the smaller sample size of large trees. A habitat had a maximum of three species with which it was significantly positively associated. Conclusions: For a species to survive in population equilibrium in a landscape, habitats in which ‘source’ subpopulations can be sustained without subsidy from adjacent habitats are essential. Competition is most severe among related species whose source subpopulations share the same habitat. On the evidence of source subpopulations identified by positive species-habitat association, species-habitat association reduces the number of confamilial competitors. Our results therefore indicate that edaphic niche specialization contributes to coexistence of species of Sterculiaceae in the plot, consistent with the expectations of equilibrium hypotheses. [ABSTRACT FROM AUTHOR]

In large samples of trees ≥1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1–2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1–2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these. differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role, of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration. [ABSTRACT FROM AUTHOR]

1 The rapid growth rates of light-demanding tree species have been attributed in part to their low-density, low-cost stems. We evaluated the influence of light and biomass support costs on growth rates of trees 8–25 cm in diameter at breast height (d.b.h.) among 21 species differing in wood density in two aseasonal rain forests. 2 Measurements of crown width, tree height, d.b.h. and wood density (ρ) were used to estimate the stem biomass ( Ms) of a standard-sized tree (17 m tall and 16 m2 in crown area), i.e. the cost in stem biomass of supporting a given sized crown at a given height. 3 The species showed a three-fold range in support cost, which was highly correlated with wood density ( Ms ∝ ρ0.77, r2 = 0.72 for the log-transformed relationship). This relationship is due to the high interspecific variation in wood density and the fact that the stem diameter of the standard-sized tree increased only slightly with decreasing wood density, i.e. light-wooded species did not compensate for their lighter, weaker wood by substantially increasing stem thickness. 4 Mean growth rate per species showed a 10-fold range and increased with the fraction of trees at least partly in gaps (gap fraction), the reciprocal of support cost (1/ Ms), and the reciprocal of wood density (1/ρ). The relationship between mean growth rate and 1/ Ms was particularly strong when one outlier was excluded ( r2 = 0.88) and among the Dipterocarpaceae ( r2 = 0.89). 5 Log(mortality rate), as determined for all trees per species ≥ 1 cm d.b.h., increased linearly with 1/ Ms, 1/ρ and gap fraction. 6 These results suggest an important role for wood density and support costs in the classic tradeoff between rapid growth and increased risks of damage and death. [ABSTRACT FROM AUTHOR]

1 Spatial distributions of tropical trees often correlate with environmental variation, suggesting that ecological sorting caused by niche differentiation may be important for maintaining species diversity. 2 Four soil types have been identified in a 52-ha forest dynamics plot in Bornean mixed dipterocarp forest (ranked by increasing fertility and moisture: sandy loam, loam, fine loam, and clay). The distributions of 73% of tree species in the plot are significantly aggregated on one of these soil types. We tested the hypothesis that variation in performance (growth and mortality) underlies these edaphically biased species distributions. 3 Annual growth and mortality rates over 5 years were estimated for trees ≥ 1 cm in diameter and compared among soil types, life histories and species-aggregation patterns. 4 Overall, growth and mortality rates were lowest on the poorest soil (sandy loam). Growth rates on each soil type correlated with soil fertility for pioneers, while mortality rates correlated with soil fertility for both pioneers and late-successional species. 5 There was little evidence that soil specialists had a home-soil performance advantage. Soil-specific ranks of growth and mortality rates of each species-aggregation group largely mirrored the ranks of their rates across the plot and did not shift substantially among soil types. On every soil, species aggregated on sandy loam or clay ranked last or next-to-last, and species aggregated on loam ranked the highest. 6 Ecological sorting of species among soils was strong. With increasing diameter, species were lost from the soils on which they were not aggregated more frequently than would be expected based on random mortality. The underlying mechanisms of ecological sorting may involve low mortality rates as a requirement for species to achieve high abundance on the poorest soil, whereas for the richer soils, having high growth rates appears relatively more important for achieving high abundance. 7 Thus, species’ demographic responses to resource variation among soil types, especially related to the poorest soil, affects tree species distribution patterns in this forest and thereby influences the structure of tropical forest communities. [ABSTRACT FROM AUTHOR]

Abstract: Soil microbial diversity is vast, and we lack even basic understanding of how this diversity is distributed ecologically. Using pyrosequencing and microarray methods, we quantified the structure of bacterial communities in two contrasting soils underlying Bornean rain forest (clay and sandy loam) that differ markedly in soil properties, aboveground tree flora, and leaf litter decomposition rates. We found significant soil-related taxonomic and phylogenetic differences between communities that, due to their proximity, are independent of climate. Bacterial communities showed distinct compositional and taxon-abundance distributions that were significantly correlated with the structure of the overlying tree community. Richness of bacteria was greater in the more resource-rich clay soil. Phylogenetic community analyses suggested that environmental filtering may be an important mechanism of community assembly in clay, compared to niche-competition in sandy loam. The Acidobacteria were the most abundant group in clay, but the Proteobacteria dominated in sandy loam. Of the ten most abundant classes, the Actinobacteria, Betaproteobacteria, Clostridia, Bacilli, and Gammaproteobacteria were more abundant in sandy loam than clay. Our study, which is the first to quantify edaphic variation in bacterial communities using high-throughput methods in soils underlying one of the most tree species rich forests on Earth, indicates an important role of plant–soil feedbacks linking the community structure of the trees and the underlying soil microbiome. We suggest the biochemical composition of carbon and nutrient resources in plant litter and soil pH and oxygen availability as important determinants of the distribution of bacterial diversity. [Copyright &y& Elsevier]