Mamoru Kanzaki

Importance of topography and soil texture in the spatial distribution of two sympatric dipterocarp trees in a Bornean rainforest

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.

Habitat differentiation of Lauraceae species in a tropical lower montane forest in northern Thailand

Dependency on topographical habitat was examined for Lauraceae tree species in a lower montane forest using a large-scale research plot established at Doi Inthanon National Park, northern Thailand. Twenty species of 10 genera of Lauraceae were recorded in a 7.5-ha part of the plot; Lauraceae accounted for 18% of the total basal area. Lauraceae was the most species-rich and most abundant family in the plot. In a cluster analysis based on the matrix of spatial associations between species, two clusters were recognized. Members of one cluster seemed to associate with lower-elevation habitats, and members of the other associated with habitats on ridges. By subdividing the study plot into 20 m × 20 m squares, a discriminant analysis could be applied to the presence–absence data for the 17 species that had sufficient population density. The predictor variables used were the relative elevation, slope inclination, slope direction (transformed to deviation from SSW) and slope convexity for each of the squares. The discriminant models were tested statistically by applying the random shift technique. The models were significant for 11 of the species (65% of the species examined) and were associated with the topographical condition of the habitat. Stepwise selection of the predictor variables for these 11 species revealed that relative elevation and slope convexity were the most important factors for predicting the presence or absence of the Lauraceae species. Both these variables were considered to indicate the hydrological condition of the habitat.

Habitat associations of Sterculiaceae trees in a Bornean rain forest plot

Abstract 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. Nomenclature: Ashton (1980).

Principal Forest Types of Three Regions of Cambodia: Kampong Thom, Kratie, and Mondolkiri

We enumerated all trees 10 cm or more in DBH with respect to DBH, height, and species identity in 29 circular plots of 20-m radius from Kampong Thom, Kratie, and Mondolkiri Provinces, Cambodia. The composition data were analyzed using cluster analysis with group-averaging protocol, and Sorensen’s similarity index based on basal area data and the resulting clusters were also described with respect to height structure and indicator species. We found four main clusters corresponding to traditional qualitative forest types known as evergreen forest, deciduous forest, hill evergreen forest, and swamp forest. The evergreen cluster was further divided into two stand types of dry evergreen forest and two stand types of secondary evergreen forest. The deciduous forest cluster was divided into three stand types of deciduous dipterocarp forest and a mixed deciduous forest. We describe the correspondence between the forest stand types of our study and the many regional names previously used for the different forest types in varying classification systems. Some of the stand types, for example, an evergreen forest overtopped by deciduous dipterocarp (Dipterocarpus intricatus) or by a pine (Pinus merksii), and a D. obtusifolius stand on seasonally waterlogged habitat, seemed to be unique in Cambodia. The application of this method and the needs of regional forest mapping are discussed.

Rooting ability of cuttings relates to phylogeny, habitat preference and growth characteristics of tropical rainforest trees

Abstract The rooting ability of branch cuttings was evaluated for 100 tree species (including 41 families and 78 genera) collected in a tropical rainforest in Sarawak, Malaysia. Leafy cuttings of natural forest saplings were planted in a non-mist propagation system with IBA treatment. During the 6-month experiment, 66 species were rooted with an overall mean rooting percentage of 37.7% (range 0–100%). Species in the families Dipterocarpaceae and Lauraceae had a low rooting ability, whereas those in Euphorbiaceae, Rubiaceae, and Annonaceae had a high rooting ability. Differences in rooting ability were related to species-specific mature sizes, diameter growth rates and habitat preferences. Species of smaller mature sizes and faster diameter growth rates showed better rooting ability. Species whose forest saplings sprouted more vigorously after experimental felling rooted better than those that showed less vigorous sprouting. Species whose habitats were on lower elevations, concave slopes, and/or clay-rich soils rooted significantly better than those that preferred opposite habitats or habitat generalists that showed no significant habitat preference. The implications of these relations are discussed from the viewpoint of saplings’ adaptation to physical damage in their natural habitats.

Regeneration in subalpine coniferous forests. II: Mortality and the pattern of death of canopy trees

Death of canopy trees when gaps are formed was studied in a subalpine coniferous forest, central Japan, which was composed ofAbies, Tsuga, Picea, Betula, andSorbus. Typhoons were considered to be the most important cause of the death of canopy trees. The degree of disturbance in each of 16 plots (20 m×20 m) was represented by the percentage of the total basal area of dead trees to that of living and dead canopy trees (disturbance magnitude; MAG). The mortality of canopy trees increased as their dbh increase in the plots of lower MAG than 90%. The mortality varied among genera, andTsuga was characterized as having lower mortality than that of the other conifers. 418 dead trees were observed. The standing dead trees made up 10.7% of the trees, the stem broken trees 46.7%, and the uprooted trees 42.2%. The stem breaking was most frequent inAbies, and the uprooting was most frequent inTsuga, Picea, andBetula. Undeveloped forests, which have the L-shaped dbh distribution, were destroyed only in high degree (70%<MAG), while developed forests were destroyed in various degrees (30%<MAG<100%). The percentage of uprooted trees in basal area decreased with the development of the forest, from 60% to 10%.

Soils Under Different Forest Types in the Dry Evergreen Forest Zone of Cambodia: Morphology, Physicochemical Properties, and Classification

We studied the morphology and physicochemical properties of soils under three different types of forest, i.e., dry evergreen forest (DEF), dry deciduous forest (DDF), and mixed forest with evergreen and deciduous trees (MF), in the dry evergreen forest zone of Kampong Thom Province, Cambodia. The morphological features of soils varied among the three different forest types. The physical characteristics of the soils in the study area were strongly correlated with soil texture. Clay content was clearly higher in DEF soils than in the DDF or MF soils. Bulk density was generally high (1.27–1.92), except in the surface horizons. It was especially high at depths of 100–200 cm and 160–200 cm in the DDF and MF soils, respectively. Total soil porosity was 0.32–0.44 (m3 m−3), except in the surface horizons, and was slightly higher in DEF soils. The DEF soils were characterized by a higher percentage of fine pores (less than −49 kPa) than the other pore classes. DDF soils were characterized by decreasing percentages of coarse pores (0 to −0.2 kPa; the point of capillary saturation), medium pores (−0.2 to −4.9 kPa), and small pores (−4.9 to −49 kPa), and by a concomitant increase in fine pores with depth. In MF soils, the proportion of small pores slightly decreased with depth. The soils were generally poor in cation-exchange capacity (CEC) and exchangeable cations (ECEC). ECEC and CEC were closely related to clay content. The stock of exchangeable Ca2+, Mg2+, and K+ was larger in DEF soils than in DDF soils. The pH (H2O) of DDF soils was clearly higher than that of the other soil types at 0–50 cm in depth and showed different patterns in vertical changes. The stock of total carbon at 0–70 cm in depth was highest in MF soils.

Habitat divergence in sympatric Fagaceae tree species of a tropical montane forest in northern Thailand

Spatial distributions of many tropical trees are skewed to specific habitats, i.e. habitat specialization. However, habitats of specialist species must be divergent, i.e. habitat divergence, to coexist in a local community. When a pair of species specialize in the same habitat, i.e. habitat convergence, they could not coexist by way of habitat specialization. Thus, analyses of habitat divergence, in addition to habitat specialization, are necessary to discuss coexistence mechanisms ofsympatric species. In this study, the habitat specialization and habitat divergence along topographic gradients of eight sympatric tree species of the Fagaceae were studied in a 15-ha study plot in a tropical lower montane forest in northern Thailand. A statistical test with torus shift randomizations for 9 6 73 trees of Fagaceae revealed significantly biased distributions for all of the species, for at least one of the four topographic variables used: elevation, slope inclination, aspect and convexity. Slope convexity was the most critical topographic variable, along which all but one species had significantly skewed distributions. Out of 112 possible combinations of species pairs and topographic variables, 18 (16%) and two pairs (1.8%) showed significant habitat divergence and habitat convergence, respectively. The observed habitat divergence alone could not completely explain the coexistence of the eight species. There was a gradation in the habitat position of each species, with relatively large overlaps between species distributed in similar habitats, and small overlaps between species associated with contrasting habitats, respectively. The gradual changes in the habitats of the species suggested that dividing the species into a small number of distinct habitat groups, such as ridge and valley specialists, would not be straightforward.

Intra- and interspecific variation in wood density and fine-scale spatial distribution of stand-level wood density in a northern Thai tropical montane forest.

Tropicaltreewooddensityisoftenrelatedtootherspecies-specificfunctionaltraits,e.g.size,growthrateand mortality. We would therefore expect significant associations within tropical forests between the spatial distributions of stand-level wood density and micro-environments when interspecific variation in wood density is larger than intraspecific variation and when habitat-based species assembly is important in the forest. In this study, we used wood cores collected from 515 trees of 72 species in a 15-ha plot in northern Thailand to analyse intra- and interspecific variationinwooddensityandthespatialassociationofstand-levelwooddensity.Intraspecificvariationwaslowerthan interspecific variation (20% vs. 80% of the total variation), indicating that species-specific differences in wood density, rather than phenotypic plasticity, are the major source of variation in wood density at the study site. Wood density of individual species was significantly negatively related to maximum diameter, growth rate of sapling diameter and mortalityofsaplings.Stand-levelmeanwooddensitywassignificantlynegativelyrelatedtoelevation,slopeconvexity, saplinggrowthrateandsaplingmortality,andpositivelyrelatedtoslopeinclination.East-facingslopeshadsignificantly lower stand-level mean wood densities than west-facing slopes. We hypothesized that ridges and east-facing slopes in the study forest experience strong and frequent wind disturbance, and that this severe impact may lead to faster stand turnover, creating conditions that favour fast-growing species with low wood density.

Spatially aggregated fruiting in an emergent Bornean tree

We investigated the spatial distribution of fruiting in Dryobalanops aromatica (Dipterocarpaceae), a mast-seeding emergent tree that is found in the tropical rain forests of Borneo. Of 393 adults (diameter at breast height (dbh) > 30 cm) in a 52-ha area, 143 (36.4%) individuals fruited. A second-order spatial analysis, based on Ripleys K-function, revealed that fruiting trees were significantly (P < 0.05) aggregated with respect to the total population over distances of 15-115 m. Thus, the spatial distribution of fruiting trees was more aggregated than expected from the adult tree distribution, which itself was aggregated within the study plot. Logistic regression analysis showed that fruiting trees had a significantly greater dbh and were surrounded by more conspecific adults per ha than non-fruiting individuals. Moreover, fruiting trees were found at higher elevations, on steeper slopes, and on sandy rather than clayey soils. In contrast, annual diameter growth, adult density over areas < 1 ha, and slope convexity did not significantly affect fruiting probability. The ratio of seedling (20 cm ≤ h < 60 cm) and sapling (60 cm ≤ h < 300 cm) density to adult density was higher in sites at higher elevations, on steeper slopes, and on sandy soils than that for lower elevations, flat slopes and clayey soils. This suggests that the aggregation of fruiting trees occurred not only at the time of the study, but that it had occurred repeatedly in the past, at the high-elevation, steep-sloped, sandy sites. Thus, site conditions probably affect the dynamics and spatial structure of local populations through differences in fruiting frequency among trees experiencing different site conditions.