Takuo Yamakura

Assessing Evidence for a Pervasive Alteration in Tropical Tree Communities

In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16–52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha−1 y−1, 95% confidence intervals [0.07, 0.39] MgC ha−1 y−1), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y−1) compared with the tree community as a whole (+0.15 % y−1); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y−1), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests.

Aboveground biomass of tropical rain forest stands in Indonesian Borneo

Aboveground plant biomass was examined in a tall virgin tropical lowland evergreen rain forest dominated by Dipterocarpaceae in Sebulu, East Kalimantan, Indonesia, with special reference to the gap-, building- and mature phases of the forest growth cycle. From the records of dimensions of sample trees examined by the stratified clip technique and DBH inventory data of trees in a study plot, the biomass of larger trees (DBH ≥4.5 cm) was estimated by the allometric correlation method. The biomass of smaller plants (DBH < 4.5 cm) was estimated by harvesting the plants in small quadrat plots. Although large differences were found between aboveground-biomass-estimates in different patches of different growth stages, the aboveground biomass in a 1.0 ha plot was 509 t/ha, and the one-sided LAI was 7.3 ha/ha. These values seem to result from the tall forest architecture with huge emergent trees (over 70 m high) and a moderate packing of plant mass indicated by the basal area value of 38.8 m2/ha for trees with DBH ≥4.5 cm.

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.

Spatial distribution patterns of two predominant emergent trees in a tropical rainforest in Sarawak, Malaysia

Spatial distribution patterns of two emergent tropical rainforest tree species (Dryobalanops aromatica & D. lanceolata) were examined in where they were dominant (17–20% of total basal area of canopy trees) in Sarawak, East Malaysia. Newly established seedlings (< 2 years old) were restricted to areas < 40 m from mother trees for both species, suggesting a limited seed dispersal. Seedling (< 1 cm in dbh) density was highest around conspecific adults (≥ 30 cm in dbh). Negative spatial patterns were observed between larger juveniles (1–5 cm in dbh) and conspecific adults for both species; the most dense populations of sapling (1–5 cm in dbh) and poles (5–30 cm in dbh) were found at a distance of 15–20 m from the nearest conspecific adult. Seedlings of both species were distributed randomly with respect to light conditions evaluated by a forest floor diffuse site factor and a canopy closure index. Saplings of both species, and poles of D. lanceolata, were distributed under more open conditions than expected from spatially random distributions, and from average light conditions of all species of the same size classes. Possible mechanisms for the observed distribution patterns and intermediate canopy dominance of Dryobalanops were discussed from the viewpoints of gap-dynamics and distance-dependent mortality.

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.

BAAD: a biomass and allometry database for woody plants

Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the worlds vegetation.

Sex ratio and gender-dependent neighboring effects in Podocarpus nagi, a dioecious tree

We analyzed sex ratio, growth rates, and spacing among individuals of Podocarpus nagi, a dioecious tree, on Mt. Mikasa, Nara City, Japan. The sex ratio of reproductive trees ≥ 5 cm in stem diameter at breast height (dbh, 130 cm above ground level) was significantly male-biased. The sex ratio was male-biased in the < 20 cm and ≥ 50 cm size classes, while it did not depart from 1:1 in the 20 ≤ dbh < 50 cm class. Growth rate varied with tree size in males but not in females. The precocity and vigor of males suggests that differences in reproductive costs between sexes induce the biased sex ratio. Random labeling tests on the positions of reproductive trees showed that in the < 30 cm class, males and females were distributed randomly and independently from each other. In the ≥ 30 cm class, males were significantly clumped, whereas females were randomly distributed. Males and females showed significant repulsion, i.e., a spatial segregation of sexes. Both intra- and intersexual effects on the growth rate of crowding by neighbors were significant for females, but not for males. Maximum competitive interference was observed at a distance of 5 m, which corresponded approximately to the radius of clumps of large males and to the significant repulsive distance between large males and females. These results suggest that sexual differences in sensitivity to local crowding are related to the formation of gender-dependent spatial patterns. Formation of female-repulsive male clumps and a male-biased sex ratio may intensify the decreased probability of regeneration near males, as suggested by the limited seed-dispersal range of this species, thereby promoting coexistence with other species.

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).

Survivorship and growth of seedlings of four dipterocarp species in a tropical rainforest of Sarawak, East Malaysia

Survivorship and growth of seedlings of four dipterocarp species (Dipterocarpus actangulus, D. globosus, Dryobalanops aromatica, Dryobalanops lanceolata) were studied for 2.5 years in a mixed dipterocarp forest in Sarawak, East Malaysia. Predispersal seed predation rates were larger forD. globosus (75%) thanD. lanceolata (27–34%) andD. aromatica (18–26%). Less than 20% of the twoDryobalanops seeds were damaged by vertebrates after seed dispersal. During the period from seed dispersal to the time when the seedlings had shed cotyledons, more dispersed seeds died in the twoDipterocarpus (ca 90%) than the twoDryobalanops (ca 60–70%). The major mortality factors during this period were uprooted and seed/seedling predation by insects or vertebrates. After the seedlings shed cotyledons, all species showed constant mortality rates of 34, 15–16, 17 and 6%/year forD. actangulus, D. lanceolata, D. aromatica andD. globosus, respectively, in the forest understorey. Mortality was lower in less shaded conditions than in more shaded ones forD. aromatica andD. actangulus, but not significantly different forD. lanceolata andD. globosus. A majority of dead seedlings were killed by fallen branches or were found standing with wilted leaves, probably due to water stress. No significant correlation was found between seed/seedling mortality and distance from mother trees or the initial density of seeds/seedings for all species. The mean leaf production was positively correlated with the estimated diffuse light factor of their habitats for each species.

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.