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Overlapping flowering periods among Shorea species and high growth performance of hybrid seedlings promote hybridization and introgression in a tropical rainforest of Singapore. Horticulturists are familiar with the difficulty of growing on seed of reliably identified temperate East Asian and North American maples and oaks, for they commonly hybridize if different species are grown in close proximity. [Extracted from the article]

We combined two existing datasets of vegetation aboveground biomass ( AGB) ( Proceedings of the National Academy of Sciences of the United States of America, 108, 2011, 9899; Nature Climate Change, 2, 2012, 182) into a pan-tropical AGB map at 1-km resolution using an independent reference dataset of field observations and locally calibrated high-resolution biomass maps, harmonized and upscaled to 14 477 1-km AGB estimates. Our data fusion approach uses bias removal and weighted linear averaging that incorporates and spatializes the biomass patterns indicated by the reference data. The method was applied independently in areas (strata) with homogeneous error patterns of the input (Saatchi and Baccini) maps, which were estimated from the reference data and additional covariates. Based on the fused map, we estimated AGB stock for the tropics (23.4 N-23.4 S) of 375 Pg dry mass, 9-18% lower than the Saatchi and Baccini estimates. The fused map also showed differing spatial patterns of AGB over large areas, with higher AGB density in the dense forest areas in the Congo basin, Eastern Amazon and South-East Asia, and lower values in Central America and in most dry vegetation areas of Africa than either of the input maps. The validation exercise, based on 2118 estimates from the reference dataset not used in the fusion process, showed that the fused map had a RMSE 15-21% lower than that of the input maps and, most importantly, nearly unbiased estimates (mean bias 5 Mg dry mass ha−1 vs. 21 and 28 Mg ha−1 for the input maps). The fusion method can be applied at any scale including the policy-relevant national level, where it can provide improved biomass estimates by integrating existing regional biomass maps as input maps and additional, country-specific reference datasets. [ABSTRACT FROM AUTHOR]

1. A large share of tree species in tropical forests exhibit preference for certain habitats, resulting in strong abundance differences across habitats. While the occurrence of such habitat preference is now documented for over a thousand species, little is known about the underlying mechanisms. How are subpopulations in non-preferred habitats able to survive? Theoretical studies have suggested that these subpopulations are maintained by source–sink dynamics –‘recruitment subsidies’ from high-density to low-density subpopulations – but empirical tests are lacking. 2. Here, we evaluate the role of recruitment subsidies in maintaining subpopulations of a rainforest tree in non-preferred habitats. Our study species Scaphium borneense (Sterculiaceae) shows strong habitat preference for drier ridges at Lambir Hills, Malaysia, where it occurs at ninefold higher densities than in the wetter valleys. On slopes, Scaphium occurs at intermediate densities. 3. We estimated source–sink exchange between subpopulations in three habitats in a 52-ha plot, using nearest-neighbour analyses. We found evidence for strong recruitment subsidies to the non-preferred habitats: 83–91% of recruits (of 1 cm diameter) in the valley had likely mother trees in another habitat. For slope recruits this was 54–78%. 4. We then used 10-year demographic data to construct multi-state matrix models that included the dynamics within, and exchange of recruits between subpopulations. We found that blocking recruitment subsidies to valley and slope subpopulations led to strong reductions in subpopulation growth rates over 100 years (λ100). By contrast, λ100 of the ridge population was hardly affected by blocking recruitment exchange. 5. Elasticity analysis confirmed the importance of recruitment subsidies for λ100 in valley and slope subpopulations: elasticity of recruitment subsidies to these subpopulations was three to five times larger than local recruitment. Again, the reverse pattern was found for the preferred habitat, where elasticity for recruitment from other habitats was very low. 6. Synthesis. Our results show that recruitment subsidies can be crucial for maintaining subpopulations of tropical tree species in non-preferred habitats. To the extent that such source–sink dynamics are common among tropical tree species, this mechanism may play a role in maintaining high tree diversity in tropical forests. [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]

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]

Disturbances influence forest dynamics across a range of spatial and temporal scales. In tropical forests most studies have focused on disturbances occurring at small spatial and temporal scales (i.e., gap dynamics). This is primarily due to the difficulty of reconstructing long-term disturbance histories of forests in which most tree species lack annual growth rings. Consequently, the role of past disturbances in tropical forests is poorly understood. We used a combination of direct and indirect methods to reconstruct the historical disturbance regime and stand development patterns in mature and regenerating seasonal dry evergreen forest (SDEF) in the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Direct estimates of long-term establishment and growth patterns were obtained from 12 tree species that form annual growth rings as a consequence of the region's strong intra-annual rainfall seasonality. Indirect estimates of establishment patterns were obtained from analyses of stand structure and individual tree architecture and application of age-estimation models to 10 dominant canopy-tree species using demographic data from a large-scale, permanent forest-dynamics plot. The combination of direct and indirect methodologies revealed a complex disturbance history in the seasonal evergreen forest over the past 250 years. In the mid-1800s, 200-300 ha of forest were destroyed by a catastrophic disturbance, which led to the synchronous establishment of many of the trees that presently dominate the forest canopy. Since then widespread disturbances of variable intensity have occurred at least three times (1910s, 1940s, and 1960s). These disturbances created discrete temporal pulses of establishment in small to large gaps in the forest matrix across several square kilometers. Background mortality and gap formation were evident in every decade since 1790, but these varied in intensity and frequency. The SDEF retains a distinct structural and floristic legacy from the catastrophic disturbance of the mid-1800s. The single-age cohort that established after the disturbance has developed a complex three-dimensional structure as a consequence of differences in interspecific growth patterns of the canopy-tree species and subsequent disturbances of moderate and low intensity. While no single methodological approach provided a complete picture of the disturbance history and stand development patterns of the seasonal evergreen forest, taken together they offered new insights into the long-term dynamics of a primary tropical forest. In particular, the study highlighted the role of disturbance at multiple spatial and temporal scales and varying intensities, in determining the structure and composition of a complex, species-rich tropical forest and raises important questions about the role of rare, catastrophic events on tropical forest dynamics. [ABSTRACT FROM AUTHOR]

1 We conducted a field experiment to test whether aggregated spatial distributions were related to soil variation in locally sympatric tree species in the rain forests of Sarawak, Malaysia. Dryobalanops aromatica, Shorea laxa, and Swintonia schwenkii are naturally aggregated on low-fertility humult ultisols, Dryobalanops lanceolata and Hopea dryobalanoides on moderate-fertility udult ultisols and Shorea balanocarpoides is found on both soil types. 2 Seedlings of all six species were grown in a nested-factorial experiment for 20 months in humult and udult soils in gaps and in the understorey to test for soil-specific differences in performance. Phosphorus addition was used to test for effects due to P-limitation. 3 Four species showed significantly higher growth on their natural soils, but one humult-soil species ( D. aromatica) and the broadly distributed species were not significantly affected by soil type. 4 One udult-soil species, D. lanceolata, had both lower relative growth rate and lower mycorrhizal colonization on humult soil. However, humult soils also had lower levels of Ca, Mg, K, N and probably water availability. 5 The overall ranking of growth rates among species was similar on the two soils. Growth rates were strongly positively correlated with leaf area ratio and specific leaf area among species in both soils. With the exception of D. aromatica, species of the higher-nutrient soils had higher growth rates on both soils. 6 Although P addition led to elevated soil-P concentrations, elevated root- and leaf-tissue P concentrations on both soils, there was no significant growth enhancement and therefore no evidence that P availability limits the growth or constrains the distribution of any of the six species in the field. Differences in soil water availability between soils may be more important. 7 Our results suggest that habitat-mediated differences in seedling performance strongly influence the spatial distributions of tropical trees and are therefore likely to play a key role in structuring tropical rain forest communities. Journal of Ecology (2004) 92, 609–623 [ABSTRACT FROM AUTHOR]

Relationships between spatial distributions and site conditions, namely topography and soil texture, were analyzed for two congeneric emergent trees, Dryobalanops aromatica and Dryobalanops lanceolata (Dipterocarpaceae), in a tropical rainforest in Sarawak, East Malaysia. A 52-ha permanent plot was divided into 1300 quadrats measuring 20 m × 20 m; for each Dryobalanops species, the number and total basal area of trees ≥1 cm in d.b.h. were compared among groups of quadrats with different site conditions. Because spatial distributions of both Dryobalanops and site-condition variables were aggregated, Monte-Carlo permutation tests were applied to analyze the relationships. Both single and multifactor statistical tests showed that the density and basal area distributions of the two species were significantly non-random in relation to soil texture and topographic variables. D. aromatica was significantly more abundant at higher elevations, in sandy soils, and on convex and steep slopes. In contrast, D. lanceolata preferred lower elevations and less sandy soils. In the study plot, there were very few sites (3 of 1150 quadrats tested) where the models of Hayashi's method predicted the co-occurrence of the two species. These results suggest that between-species differences in habitat preferences are so large that they alone explain the spatially segregated distributions of these two species within the 52-ha study plot. [ABSTRACT FROM AUTHOR]

Understanding the maintenance of high tropical tree species diversity requires disentangling the effects of habitat vs. geographic distance. Using floristic, topographic, and soil nutrient data from 105 0.6-ha plots in mixed dipterocarp forest throughout S arawak, Malaysian Borneo, we explore the degree to which floristic patterns are habitat-driven from local to landscape scales. We assess how the floristic influence of geographic distance vs. abiotic factors varies from local to regional scales. We employ several multivariate analytical techniques and perform a hierarchical clustering of the research plots using the Steinhaus index of floristic dissimilarity, as well as Mantel analyses on matrices of floristic, habitat, and geographic distance. These analyses indicate that floristic variation is more strongly correlated with habitat than with geographic distance on the regional scale. On the locallandscape to community scale, we find evidence of a resource threshold above which habitat effects weaken; that is, below the resource threshold floristic similarity between sites is dominated by habitat effects, while above the threshold floristic similarity between sites is dominated by geographic-distance effects. We also find evidence that topography and soil nutrients correlate in part independently with floristics. These results, together with previous studies in the Neotropics, emphasize that tree species distribution and community composition are variously influenced by the interplay of both habitat and dispersal-driven effects. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the reproductive phenology, tree size at the onset of reproduction and fecundity of 11 sympatric related Macaranga species in Borneo. Reproduction and other life-history traits; Summary of analyses of the phenology of staminate and pistillate reproduction in the Macaranga species; Reproductive frequency of staminate and pistillate trees of nine episodic reproducing Macaranga species.

Presents information on a study which reconstructed the phylogeny of the tropical tree family, Dipterocarpaceae based on nucleotide sequence. Characteristics of the family; Data collection and analysis; Results and discussion.

The article discusses simulating effects of landscape context and timber harvest on tree species diversity. Topics discussed include need of implementing ecosystem management, increase in species richness in a focal forest due to adjacent species-rich forests enhanced by duration of immigration, immigration after heavy harvest impact leading to higher species richness and harvesting timber trees at optimal locations to accommodate seed dispersal ability.

1. Relationships between lowland rain-forest structure, dynamics and site conditions were examined by the establishment of plots and profile diagrams within mature-phase forest at 13 sites and with permanent plots at three of these sites where trees have been enumerated over 20 years. 2. Most forest structural measures were inter correlated but forest stature was uncorrelated with HCI-extractable soil nutrient concentrations and was apparently related to topography, soil depth and soil water. The relationship between diameter and height varied between forests and was correlated with HCI-extractable P and Mg for dry-land sites. 3. Tall forests generally had more slender canopy trees for a given height than short forests. Vertical stratification was associated with the presence and stand density of emergent trees, which comprise an architecturally and floristically distinct guild. Where emergents are scattered or absent, the main canopy and understorey were dense and no vertical stratification of crowns was perceptible: where emergents formed a continuous canopy, the main canopy was sparse. the understorey less dense and tree crowns were more separated into two horizontal strata. This type of forest appears to be confined to continuously moist soils on lower slopes, flat or undulating land. 4. Leaf size in the subcanopy was positively correlated with measured soil nutrients, and with the relationship between diameter and height. Among canopy trees it was not correlated with soil nutrients, nor with other aspects of forest structure. 5. Plots were originally established within mature phase. avoiding canopy gaps. Since establishment, gaps have accumulated within the permanent plots. Tree mortality was significantly clustered on clay soils, but not on sandy soils where windthrow was apparently less frequent and trees more often died standing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]