Satoshi Nanami

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.

Sprouting traits and population structure of co-occurring Castanopsis species in an evergreen broad-leaved forest in southern China

The role of sprouting in regeneration was compared betweenfour co-occurring Castanopsis species in an evergreen broad-leavedforest in southern China. We considered the largest stem of an individualto be the main stem, while all of the other stems were consideredto be sprouts. To evaluate the degree of dependence on sproutingin the regeneration of each species, we measured the ratio of thenumber of all sprouts to the number of main stems in a population. The ratio was 4.3 in Castanopsis fordii and > 1in Castanopsis fabri and Castanopsis carlesii, althoughit was < 1 in Castanopsis fargesii. The ratioof the number of all sprouts to the number of main stems in a populationwas represented by the product of two factors of sprouting ability:the proportion of sprouting individuals among all individuals andthe number of sprouts per sprouting individual. The proportion ofsprouting individuals among all individuals differed significantlyamong the four species, while the number of sprouts per sproutingindividual did not. Specific variations in sprouting traits werein agreement with the population structure of each species. Specieswith fewer small individuals in the size distribution had a higherratio than species with L-shaped distribution. Furthermore, specieswith a clumped distribution had a larger ratio than species thatwere randomly distributed. These results suggested that specieswhose recruitment by seedlings was temporally and spatially restrictedwere relatively more dependent on sprouting in the regeneration. The specific gradient of sprouting ability and the relative dependencyon sprouts to maintain a population can enhance the coexistenceof these four congeneric species.

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.

Spatial pattern formation and relative importance of intra- and interspecific competition in codominant tree species, Podocarpus nagi and Neolitsea aciculata

Spatial patterns, their changes due to mortality, and intra- and interspecific competition of two codominant tree species, Podocarpus nagi and Neolitsea aciculata, were analyzed at Mt. Mikasa, Nara City, Japan. Podocarpus nagi has a higher shade tolerance but a narrower seed dispersal range than N. aciculata. We inferred the mechanisms of spatial pattern formation and coexistence of the two species. Podocarpus nagi and N. aciculata trees were clumped and showed a spatial repulsion from each other. Patches dominated by either P. nagi or N. aciculata were formed. Podocarpus nagi trees were less clumped with increasing tree size, although no significant change in spatial patterns due to mortality was detected. A patch formation of the P. nagi population seemed to be induced by the narrow seed dispersal range. On the other hand, N. aciculata trees were more clumped and more repulsive from P. nagi trees with increasing tree size. The distribution of N. aciculata trees shifted to more clumped than expected from the random mortality over the research period. Post-dispersal mortality due to competitive exclusion by P. nagi affected the patch formation of the N. aciculata population. The relative importance of intraspecific competition to interspecific competition on the relative growth rate increased with increasing tree size. The shift corresponded to an increasing spatial repulsion between the two species. The patch formation of P. nagi population may create the spatial refuge of N. aciculata from P. nagi and may enable avoidance of interspecific competition and the coexistence of the two species.

Mass fruiting in Borneo: a missed opportunity.

![Figure][1] Dipterocarp tree seedlings. Many endangered Indonesian trees rarely produce seeds. CREDIT: CAMPBELL WEBB Large-scale restoration of tropical forest is increasingly recognized as a credible option for climate change mitigation and biodiversity conservation ([ 1 ][2]–[ 3 ][3

Geographical variation in soil bacterial community structure in tropical forests in Southeast Asia and temperate forests in Japan based on pyrosequencing analysis of 16S rRNA

Geographical variation in soil bacterial community structure in 26 tropical forests in Southeast Asia (Malaysia, Indonesia and Singapore) and two temperate forests in Japan was investigated to elucidate the environmental factors and mechanisms that influence biogeography of soil bacterial diversity and composition. Despite substantial environmental differences, bacterial phyla were represented in similar proportions, with Acidobacteria and Proteobacteria the dominant phyla in all forests except one mangrove forest in Sarawak, although highly significant heterogeneity in frequency of individual phyla was detected among forests. In contrast, species diversity (α-diversity) differed to a much greater extent, being nearly six-fold higher in the mangrove forest (Chao1 index = 6,862) than in forests in Singapore and Sarawak (~1,250). In addition, natural mixed dipterocarp forests had lower species diversity than acacia and oil palm plantations, indicating that aboveground tree composition does not influence soil bacterial diversity. Shannon and Chao1 indices were correlated positively, implying that skewed operational taxonomic unit (OTU) distribution was associated with the abundance of overall and rare (singleton) OTUs. No OTUs were represented in all 28 forests, and forest-specific OTUs accounted for over 70% of all detected OTUs. Forests that were geographically adjacent and/or of the same forest type had similar bacterial species composition, and a positive correlation was detected between species divergence (β-diversity) and direct distance between forests. Both α- and β-diversities were correlated with soil pH. These results suggest that soil bacterial communities in different forests evolve largely independently of each other and that soil bacterial communities adapt to their local environment, modulated by bacterial dispersal (distance effect) and forest type. Therefore, we conclude that the biogeography of soil bacteria communities described here is non-random, reflecting the influences of contemporary environmental factors and evolutionary history.

Growth and survival of hybrid dipterocarp seedlings in a tropical rain forest fragment in Singapore

Background: Although natural hybridisation between dipterocarp trees is considered rare, putative dipterocarp hybrids (Shorea spp.) are found in a forest fragment in Singapore. Understanding the performance of hybrids is critical to inform conservation efforts and has implications for the demographic and genetic viability of these small populations. Aims: First, is there a difference in the frequency of hybrids between the mature and seedling stages, and second, do parent and hybrid seedlings have different ecological traits? Methods: We analysed seedling survival and growth rates in relation to environmental variables for Shorea curtisii, S. leprosula and hybrids of the two species. We monitored the height and diameter of seedlings for 4 years, as well as light conditions and soil moisture. Results: The proportion of hybrids at the seedling stage was 41% for S. leprosula and 17% for S. curtisii, respectively. Hybrids were more frequent at the seedling stage than at the mature stage. Hybrid individuals had growth and survival rates comparable to their parent species, with the exception of slower growth rates than S. leprosula. Conclusions: Hybrid seedlings lacked obvious heterosis, and might therefore have similar fitness to that of parent species in the present forest environment.

Isolation and Characterization of Microsatellite Loci for the Large-Seeded Tree Protorhus deflexa (Anacardiaceae)

Premise of the study: Protorhus deflexa is an endemic large-seeded tree in Madagascar that depends heavily on insects for cross-pollination and on large-bodied frugivores for seed dispersal. Because such mutualistic relationships are vulnerable to human disturbance, the development of microsatellite markers will enhance analyses of gene flow in this tree species in degraded forests. Methods and Results: Nineteen microsatellite markers were developed for P. deflexa using 454 pyrosequencing. The number of alleles ranged from two to nine, and the ranges of observed and expected heterozygosities were 0.200–0.800 and 0.303–0.821, respectively. The parentage exclusion probability by the 19 loci reached 0.98583 for the first parent and 0.99971 for the second parent. Conclusions: These markers will be useful for studying gene flow via pollination and seed dispersal by animals and the genetic structure of P. deflexa in protected and degraded forests in Madagascar.

Hybridization rate and genotypic diversity of apomictic hybrids between native ( Taraxacum japonicum ) and introduced ( T. officinale ) dandelions in western Japan

Hybridization between the introduced and native plants may enhance invasiveness, especially in asexually reproducing species. Hybrid apomictic dandelions between native (Taraxacum platycarpum and T. japonicum) and exotic (T. officinale) species are distributed widely throughout Japan. To estimate the origin(s) and dispersal of the hybrids, we investigated the hybridization rate and genotypic diversity in mixed populations of T. japonicum, T. officinale and their hybrids at two green parks in western Japan. Among the plants identified as exotics from flower morphology, 86–96% were hybrids by genetic analysis. Genetic data with simple sequence repeat markers revealed a high clonal diversity of the hybrid both within and between populations, indicating multiple origins. A hybrid seed was found from among the 1891 seeds collected from T. japonicum in the parks, indicating ongoing hybridization in the field. T. officinale and hybrids were genetically differentiated between the two parks independent of the ploidy level; the allele frequency of T. officinale and tri- and tetraploid hybrids were similar within each park but different between the two parks. This suggests that the origins of hybrids were similar within the park but different between the parks. Overall, our results suggest that hybridization, including backcross, is an ongoing process, and that genetically diverse hybrids with various origins have been spreading in western Japan, probably because hybridization enhanced invasiveness at native habitat.

Dioecious plants are more precocious than cosexual plants: A comparative study of relative sizes at the onset of sexual reproduction in woody species

Abstract The reproductive capacities of dioecious plant species may be limited by severe pollen limitation and narrow seed shadows for the two reasons. First, they are unable to self‐pollinate, and seed production occurs only with pollinator movement from males to females. Second, only 50% of the individuals in populations contribute to seed production. Despite these handicaps, dioecious plants maintain their populations in plant communities with cooccurring cosexual plants, and no substantial difference in population growth rates has been found between dioecious and cosexual plants. Hence, dioecious plants are thought to mitigate these disadvantages by adopting ecological traits, such as insect pollination, animal‐dispersed fleshy fruits, and precocious flowering. We studied the relationship between flowering and plant size in 30 woody species with different sex expressions, leaf habits, fruit types, and maximum plant sizes. The study site was located in an evergreen broad‐leaved forest on the island of Honshu, Japan. A phylogenetic linear regression model showed that dioecious species tended to mature at smaller sizes than did cosexual taxa. At the population level, given equal plant densities and reproductive efforts, the precocity of dioecious plants could serve as one of the factors that mitigate the limitations of pollen and seed‐shadow handicaps by increasing the density of reproductive individuals in the population. At the individual level, smaller size of onset of flowering may play a role in enhancing reproductive success over a lifetime by increasing reproductive opportunities. We discussed the possible effect of the relationship between precocity and some ecological traits of dioecious plants, such as small flowers pollinated by unspecialized insects, fleshy fruit dispersed by animals, and their preferential occurrence in the tropics and in island habitats. The universality of precocity among dioecious plants should be investigated in diverse plant communities. Such studies will increase our understanding of the evolution of plant breeding systems.