Tohru Manabe

Genetic structure of Camellia japonica L. in an old-growth evergreen forest, Tsushima, Japan.

The spatial genetic structure of Camellia japonica was investigated, using microsatellite markers, in a 4‐ha permanent plot within an old‐growth forest. Spatial distribution of individuals was also assessed to obtain an insight into spatial relationships between individuals and alleles. Morisita’s index of dispersion showed that 518 C. japonica individuals in the plot were clumped, and Moran’s I spatial autocorrelation coefficient revealed weak genetic structure, indicating a low level of allele clustering. Average I correlograms showed that there was stronger genetic structure over short‐distance classes. The clumped distribution of individuals and the positive autocorrelation over short‐distance classes may result from the limited seed dispersal and microsite heterogeneity of the stand, while the genetic structure may be weakened by overlapping seed shadow and extensive pollen flow, mediated by animal vectors, and the high outcrossing rate found in C. japonica.

Size-class differences in genetic structure and individual distribution of Camellia japonica L. in a Japanese old-growth evergreen forest

Size-class differences in genetic structure and individual spatial distribution were investigated for Camellia japonica within a 1-ha plot in a Japanese old-growth evergreen forest using microsatellite markers. Three size-classes were considered containing plants that were: 30–32.5 cm tall, 103.8 cm–200 cm tall and those that had a diameter at breast height ≥5 cm, designated JV1, JV2, and ADL, respectively. Each size-class contained 174 individuals. Morisitas index of dispersion indicated clumping of individuals was present within all size-classes, with JV2 displaying the highest level. The clumped distribution of JV1 individuals may be a result of limited seed dispersal, while that of JV2 may be attributed to heterogenieties of favourable microsites, such as canopy gaps. There were no significant differences in allele frequencies among size-classes. There were, however, some differences in spatial genetic structure among them. Morans I spatial autocorrelation analysis revealed clear spatial genetic structure in class JV1 probably due to limited seed dispersal. In class JV2, genetic structure was not observed. Overlapping seed shadows, probably in canopy gaps, may lead to blurred genetic structure in JV2.

Effects of seed- and pollen-mediated gene dispersal on genetic structure among Quercus salicina saplings.

We evaluated the effects of seed- and pollen-mediated gene dispersal on genetic structure among Quercus salicina saplings. Parentage analysis using 10 microsatellite markers indicated that the 111 adult trees located within a 11.56 ha plot in the Tatera Forest Reserve, Japan, included only one parent of 44.2% and both parents of 40.7% of the 226 saplings located in a 1-ha core plot at its center. Coancestry (Fij) estimates indicated that there was strong genetic structure among the saplings. The numbers of pairs of full- and half-siblings were high among neighboring saplings, suggesting that there was strong maternal half-sibling family structure among the saplings around their seed parents, probably generated by the spatially limited seed dispersal and the small extent of overlapping seed shadows owing to the low density of adults. The frequencies also suggest that the maternal half-sibling families are interspersed with full-siblings, produced by correlated mating, probably because pollination frequency depends on the distance between parents. The frequencies of pairs of half-siblings decreased as the distance between saplings increased, but did not fall to zero even at distances up to the 90–95 m class, suggesting that paternal half-siblings originating from correlated paternity were widely distributed owing to extensive pollen flow. We separately examined the genetic structure for maternal and paternal alleles in the saplings. Unsurprisingly, very strong genetic structure was detected for maternal alleles. However, weak (but significant) genetic structure was also detected for paternal alleles. Therefore, pollen dispersal may affect the extent of genetic structure as well as seed dispersal.

Tree competition and species coexistence in a warm-temperate old-growth evergreen broad-leaved forest in Japan

The growth dynamics and mode of competition between adult trees ≥ 5.0cm in diameter at breast height (DBH) of nine abundant treespeciesoccupying ca. 85% of the total basal area were investigated in a 4ha study plot (200 m × 200 m) of awarm-temperate old-growth evergreen broad-leaved forest in the Tatera ForestReserve of Tsushima Island, southwestern Japan. In the plot, adult trees ≥5.0 cm DBH co-occurred with 35 woody plant species (except forwoody vine species). The most dominant and largest species,Castanopsis cuspidata var. sieboldiiexhibited a bimodal DBH distribution; it was found in both the upper and lowervertical layers. Other tree species had unimodal DBH distributionscorrespondingmostly to the lower vertical layer. We developed a model for individual growthincorporating both intra- and interspecific competition and degree ofcompetitive asymmetry. One-sided interspecific competition was detected in 17cases out of the 66 possible combinations on the scale of the 4 hastudy plot. The direction of interspecific competition was generally one-sidedfrom layer-I species to layer-II and III ones. The effects of two-sidedcompetition were detected only in layer-II and III species. OnlyDistylium racemosum exhibited one-sided intraspecificcompetition. We also found 11 cases of positive interspecific relationships.Generally, competitive relationships prevailed over positive relationshipsbetween adult trees in this warm-temperate evergreen broad-leaved forest.Competition between adult trees ≥ 5.0 cm in DBH did not occurinthe same vertical layer, but occurred only between trees in different verticallayers. This suggests that competition between adult trees ≥ 5.0cm in DBH plays a key role in the variation in species coexistencebetween different vertical layers on the 4 ha scale of thewarm-temperate evergreen broad-leaved forests. Moreover, it was found bycomparing with three different forest types that interspecific competition ismore intense in warm-temperate forests than in cool-temperate or sub-borealforests. We conclude that, compared to cool-temperate or sub-boreal forests(which have little interspecific competition), warm-temperate forests supportmore complex interspecific relationships and species-specific habitatpreferences that result in higher species diversity.

Interannual genetic heterogeneity of pollen pools accepted by Quercus salicina individuals

Since flowering often varies among years in wind‐pollinated woody species, the genetic composition of pollen pools accepted by seed parents can differ between years. The interannual heterogeneity of pollen flow may be important for maintaining genetic diversity within populations because it can increase genetic variation within populations and the effective sizes of the populations. In this study we examined heterogeneity, using paternity analysis and analysis of molecular variance, in the genetic composition of pollen pools among different reproductive years for six Quercus salicina seed parents in an 11.56‐ha plot in a temperate old‐growth evergreen broadleaved forest. The genotypes at seven microsatellite loci were determined for 111 adult trees and 777 offspring of the six seed parents in 2–5 reproductive years. Genetic differentiation of pollen pools among different reproductive years for each seed parent was significant over all seed parents and for each of four seed parents that were analysed for more than 2 years, but not for either of the other two seed parents (analysed for 2 years). For both the pollen pools originating from inside the plot and those originating from outside it, genetic differentiation among different reproductive years for each seed parent was significant over all seed parents. However, among‐year genetic differentiation in the pollen pools originating from within the plot was detected for all four of the seed parents that were analysed for more than 2 years, but for only one of the four in the pools originating from outside the plot. Genetic diversity (estimated as allelic richness and gene diversity) was higher for pollen pools over all reproductive years than for pollen pools in single years. These results indicate that the year‐to‐year genetic variation of pollen pools increases genetic diversity in offspring and is strongly affected by the variation in pollen parents within the plot because of their high pollination contributions. The high year‐to‐year variation in pollen parents within the plot and overall supports the hypothesis that the offspring produced across years represent a larger genetic neighbourhood.

Patterns of Pollen Flow and Genetic Differentiation Among Pollen Pools in Quercus salicina in a Warm Temperate Old–growth Evergreen Broad-leaved Forest

Abstract Paternity analysis and analysis of molecular variance were used to determine patterns of pollen flow and genetic differentiation among pollen pools in Quercus salicina in an 11.56-ha plot in a temperate old-growth evergreen broad-leaved forest. The genotypes at seven microsatellite loci were determined for 111 adult trees and 276 seeds collected from under eight seed parents. The proportion of pollen flow from outside the plot (further than 100 m) was 52.2%, indicating that long-distance pollen flow occurred frequently in this species, as observed in other Quercus species. The pollen pools from inside and outside the plot differed genetically, and genetic structure was detected in the population of adult trees within the plot. Therefore, longdistance pollen flow from outside the plot may introduce new or low-frequent alleles, and increase genetic diversity in this population. However, the actual average distance of pollen flow within the plot was significantly shorter than the average potential distance, and negative exponential curves explained well the frequencies of matings as functions of the distance between parents, as found in other Quercus species. The genetic composition of pollen pools differed among the eight seed parents. The genetic differentiation of pollen pools between the seed parents showed significant positive correlation with the spatial distance between them, indicating that neighboring seed parents tend to accept similar pollen pools, probably because matings are frequently mediated by pollen transported over short distances

Integrating ecological and cultural values toward conservation and utilization of shrine/temple forests as urban green space in Japanese cities

In Japan, forests associated with shrines and temples are recognized as important components of urban green space, which can potentially function as centers for ecosystem conservation in rapidly urbanizing Japanese cities. In addition to their ecological value, shrine/temple forests have social value, providing recreational and aesthetic needs to residents of urban areas. We review the historical development of shrine/temple forests in Japan and discuss current conservation issues from both ecological and sociological perspectives. Generally, shrine forests are minimally managed and public access is discouraged, whereas temple forests are intensively managed for public display. Shrines tend to be spatially scattered across the landscape but associated with specific geographical features, whereas temples tend to be clustered. Their wide and random distribution in urban areas suggests that shrine forests can potentially be used as stepping stones in the urban green space network, whereas spatially clustered temple forests can be integrated to form large areas of green space. Species diversity of shrine/temple forests declines with decreasing area. The distribution pattern of species is not completely nested, indicating that although conservation of large forest fragments may be effective for maintaining landscape-level biodiversity, smaller forest fragments and adjacent precincts are sometimes significant because rare species occasionally inhabit them. Active management and ecological restoration, such as removal of invasive species, are also important to maintain the desirable near-natural forest conditions. A working group including the owner, community, regional government, and ecologists should be involved in creating an effective, long-term management plan. Because social and cultural values are diverse, basic ecological studies of shrine/temple forests would contribute a scientific basis that fosters public confidence in the process.

Canopy structure in a temperate old-growth evergreen forest analyzed by using aerial photographs

We used aerial photographs to create a digital elevation model of the canopy surface of a 10-ha study area in a temperate old-growth evergreen forest. A topographic map of the ground surface in a 4-ha permanent plot within the study area was also drawn from ground measurements. The difference between the two elevation values (i.e., canopy surface – ground surface) at each point in a 5-m grid was considered to be the canopy height, and a canopy height profile was constructed from these data. The canopy structure in the 4-ha plot that was estimated in this way was compared with that obtained by two ground observation methods, i.e., the canopy (vegetation) height profile method and the canopy coverage census method. Large gaps were adequately detected by the aerial photograph method, but small gaps were less often detected. Gap size distribution obtained by the aerial photograph method was similar to that observed on the ground, and was a function of gap depth. This study indicates that if a detailed topographic map can be made, the canopy height profile derived from aerial photography can be effective in analyzing the canopy structure of evergreen forests, such as tropical rain forests, over large areas.

Effects of canopy gaps on the genetic structure of Camellia japonica saplings in a Japanese old-growth evergreen forest

The genetic structure of Camellia japonica saplings was investigated in relation to canopy conditions in an old-growth evergreen forest in Tsushima, Japan. To elucidate effects of canopy gaps on genetic structure, a 1 ha study site was divided into 20 × 20 m quadrats, which were classified into a gap quadrats (GAP), closed canopy quadrats (CLS) and mixed quadrats. Five GAP quadrats and six CLS quadrats were analyzed separately. Isolation-by-distance was tested by examining the correlation between genetic distance and geographic distance. A significant positive correlation was detected for GAP quadrats, whilst that for CLS quadrats was significantly smaller and not significantly different from zero. On the other hand, an analysis using Morans I spatial autocorrelation coefficients indicates that the genetic structure is weaker in GAP quadrats than in CLS quadrats in short distance classes. The values were significantly positive for both types of quadrat. These results, along with our field observations on flowering, suggest that canopy gaps affect the genetic structure of C. japonica saplings in two distinct ways. First, canopy gaps may promote flowering and mating in an isolation-by-distance manner within canopy gaps. Second, canopy gaps may promote seed production and resulting overlap in seed shadows may weaken fine-scale genetic structures.

Patterns of Pollen Flow in a Dense Population of the Insect-Pollinated Canopy Tree Species Castanopsis sieboldii

Insect pollinations of tree species with high-density populations have rarely been studied. Since the density of adults can affect effective pollen dispersal, short-distance pollination, even by insects, may frequently occur in high-density populations. To test this prediction, we investigated pollination patterns in a high-density population of the insect-pollinated canopy tree species Castanopsis sieboldii by paternity analysis using genotypes at 8 microsatellite loci of 145 adult trees and 439 seeds from 11 seed parents in a 4-ha plot. We then explored their genetic effects on the population by calculating other population genetics parameters. Although C. sieboldii has high potential for long-distance dispersal of pollen (as indicated by a fat-tailed dispersal kernel), the cumulative pollination at the local scale was spatially limited and strongly dependent on the distance between parents due to the high density of adults. Genetic diversity estimates for pollen pools accepted by each seed parent converged on a maximum as the effective number of pollen parents increased. The genetic diversity of pollen pool bulked over all the seed parents from inside the plot did not differ from that of the total pollen pools. Therefore, although pollen flow from distant pollen parents may help to maintain the genetic diversity of offspring, pollen parents neighboring seed parents may be the main contributors to the genetic diversity of the offspring at the seed stage.