Climatic and historical factors controlling horizontal and vertical distribution patterns of two sympatric beech species, Fagus crenata Blume and Fagus japonica Maxim., in eastern Japan

The Japanese Archipelago is unique when viewed in terms of beech flora, since two native species, Fagus crenata Blume and Fagus japonica Maxim., occur sympatrically there. In order to examine the most important environmental or historical factors restricting the geographical ranges of these beech species in eastern Japan (34–44°N and 137–143°E), horizontal and vertical distributions were comparatively examined in detail. The study used two kinds of data sets: (1) DS1, constructed by assembling data from literature, herbarium specimens, etc., and (2) DS2, based on a mesh vegetation database. The upper range limit was expected to be in equilibrium with the current climatic conditions for both species (correlated with temperature factors for F. crenata and with snow depth for F. japonica). The lower range limit was also expected to be in equilibrium with the present climatic condition for both species, but the importance of competition with evergreen trees was also suggested. Dispersal limitation and a topo-geological barrier (for F. japonica) were expected to strongly restrict the northern range limit. Under contrasting climatic conditions in winter (between the Pacific and the Sea of Japan sides in eastern Japan) the geographic ranges of the two beech species are differentiated because of a difference in tolerance to heavy snowfall. A range shift model that assumes a migration lag along a horizontal direction because of dispersal limitation can explain the observed distribution patterns of these beech species in relation to climatic change in the Quaternary.     

Evolutionary features of chondriome divergence in Triticum (wheat) and Aegilops shown by RFLP analysis of mitochondrial DNAs

The first comprehensive analysis was made of restriction fragment length polymorphism (RFLP) of the mitochondrial (mt) DNA of two related genera, Triticum (wheat) and Aegilops. This led to clarification of the nature of mtDNA variability and the inference of the phylogeny of the mitochondrial genomes (=chondriome). Forty-six alloplasmic lines and one euplasmic line of common wheat (2n = 42, genomes AABBDD) carrying plasmons (cytoplasmic genomes) of 47 accessions belonging to 33 species were used. This consisted of nearly all the Triticum and Aegilops species. RFLP analysis, carried out with seven mitochondrial gene probes (7.0 kb in total) in combination with three restriction endonucleases, found marked variation: Of the 168 bands detected, 165 were variable (98.2%), indicative that there is extremely high mtDNA variability in these genera. This high variability is attributed to the variation present in the intergenic regions. Most of the variation was between chondriomes of different plasmon types; only 8 bands (4.8%) between those of the same plasmon types were variable, evidence of clear chondriome divergence between different plasmon types. The first comprehensive phylogenetic trees of the chondriome were constructed on the basis of genetic distances. All but 1 of the polyploids had chondriomes closely related to those of 1 putative parent, indicative of uniparental chondriome transmission at the time of polyploid formation. The chondriome showed parallel evolutionary divergence to the plastome (chloroplast genome). Use of a minimum set of 3 mtDNA probe-enzyme combinations is proposed for tentative plasmon type identification and the screening of new plasmon types in those genera. Received: 20 March 1999 / Accepted: 22 June 1999     

Regeneration dynamics, causal factors, and characteristics of pacific ocean-type beech (Fagus crenata) forests in Japan: A review

This paper reviews the differences in the distribution and regeneration ofFagus crenata between two types of Japanese beech forests, the Japan Sea (JS)-type and the Pacific Ocean (PO)-type, and discusses the causal factors and characteristics of these forests, particularly the PO-type.F. crenata in PO-type forests regenerates sporadically rather than constantly, whereas regeneration in the JS-type forests is relatively constant with gap dynamics.F. crenata has dominated in snowy areas both in the past, after the last glacial age, when there was less human disturbance, and in the present. Snow accumulation facilitates beech regeneration in snowy JS-type forests, but not in the less snowy PO-type. Snow protects beechnuts from damage caused by rodents, desiccation, and freezing. In addition, snow suppresses dwarf bamboo in the spring, thus increasing the amount of sunlight available for beech seedlings on the forest floor. Snow also supplies melt water during the growing season and limits the distribution of herbivores. Moreover, snow reduces the number of forest fires during the dry winter and early spring seasons. The low densities ofF. crenata impede its regeneration, because disturbed wind pollination lowers seed fertility and predators are less effectively satiated. In snowy JS-type beech forests,F. crenata dominates both at the adult and the juvenile stages because it regenerates well, while other species are eliminated by heavy snow pressure. On the less snowy PO-side, deciduous broad-leaved forests with various species are a primary feature, althoughF. crenata dominates because of its large size and long lifespan.     

Response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps

The response of Japanese beech (Fagus japonica Maxim.) sprouts to canopy gaps in natural beech forest in central Japan was studied using two contrasted gaps in which tree-ring chronologies of regenerating stems were analyzed. The gaps were created by uprooting of a single Quercus mongolica var. grosseserrata stem (diameter: 50 cm; gap size: 40 m²; 23 years old) and by concurrent uprootings of four F. japonica stools (gap size: 180 m²; 30 years old). Japanese beech sprouts emerged before and after the gap formation and dominated stem populations in both gaps. In gaps, growth of F. japonica sprouts was equal or lower than growth of stems of seed origin, but most sprouts (F. japonica, Acer mono var. marmoratum) appeared a few years before emergence of seedlings. The small gap created by single stem fall was dominated by some beech sprouts from stools adjacent to the gap. The multiple gap was not closed by beech sprouts from stools surrounding the gap, but some dominant beech stems were resprouts from the uprooted beech stools. The existence of a sprout bank under the canopy may play an important role in the closing process of gaps in natural Japanese beech forest.     

Chloroplast DNA phylogeography of Fagus crenata (Fagaceae) in Japan

 CpDNA variation in Japanese beech, Fagus crenata (Fagaceae), was studied in 45 populations distributed throughout the species' range. Two cpDNA regions were sequenced: the non-coding region between the trnL (UAA) 5′exon and trnF (GAA), and the trnK region (including matK). Thirteen distinct cpDNA haplotypes were recognized and each haplotype was found to be geographically structured. Two major clades (I and II+III) were revealed in phylogenetic analyses among the haplotypes using F. sylvatica as an outgroup. The haplotypes of Clade I were distributed mainly along the Japan Sea side of the Japanese Archipelago, while those of Clade II+III occurred chiefly along the Pacific Ocean side. Consequently, the distribution of the two major cpDNA clades suggests that there were two migration routes in the history of F. crenata; one along the Japan Sea and the other along the Pacific Ocean side of the Japanese Islands. Received March 19, 2001 Accepted November 22, 2001     

Development and polymorphism of microsatellite markers for Fagus crenata and the closely related species, F. japonica

 We have developed microsatellite markers (SSRs) applicable to Fagus crenata using the RAHM method and investigated their polymorphisms. We also applied the SSRs in an analysis of a closely related species, F. japonica. Here we describe the isolation and characterization of nine polymorphic microsatellite markers, of which eight are applicable to both species. Among 30 individuals of each of F. crenata and F. japonica we detected a total of 79 and 77 alleles, respectively, with an average of 9.9 and 8.6 alleles per locus. The mean expected heterozygosity (He) was 0.615 (range: 0.216–0.925) in F. crenata and 0.660 in F. japonica (range: 0.259–0.827). The He values were considerably higher than those previously found for isozymes. Paternity exclusion probabilities for multiple loci, calculated over all loci, were extremely high (0.999 and 0.998 in F. crenata and F. japonica, respectively): sufficiently high to study pollen flow in both species. Received: 5 December 1998 / Accepted: 28 December 1998     

Confirmation of clonal reproduction of Fagus crenata Blume from Sado Island,Niigata Prefecture

While clonal growth is important in the East Asian Fagus subgenus Engleriana and the North American Fagus grandifolia (subgenus Fagus), for other subgenus Fagus species the vast majority of regeneration involves sexual reproduction with clonal growth only rarely observed. Here we aim to confirm using nuclear microsatellite markers whether clonal growth occurs in the Japanese endemic species Fagus crenata (subgenus Fagus) by investigating the origin of multi-stemmed clumps found within a high-elevation dwarf beech forest on Sado Island, Niigata Prefecture. We found that all stems collected from three separate clumps belonged to the same clump-specific multi-locus genotypes. The maximum size of clones was 3–4 m in diameter, comparable in size to those seen in the predominantly asexually regenerating Japanese species Fagus japonica (subgenus Engleriana). The species capacity for clonal growth is likely to underlie its ability to persist at high-elevation exposed sites at the limits of its ecological range.     

Differences in sapling architecture betweenFagus crenata andFagus japonica

The ecological significance of architectural patterns for saplings ofFagus crenata andFagus japonica co-occurring in a secondary oak forest were evaluated by comparing the size and shape of leaves, trunks and crowns.Fagus japonica saplings were different fromF. crenata saplings in some architectural properties: (i) the leaf area and specific leaf area were larger; (ii) the ratio of sapling height to trunk length was lower, indicating greater leaning of the trunk; and (iii) the projection area of the crown was larger and the leaf area index lower indicating less mutual shading of leaves. These architectural features indicated thatF. japonica saplings were more shade tolerant thanF. crenata andF. crenata saplings were superior toF. japonica for growth in height and could, therefore, utilize sunlight in the upper layer. An erect trunk inF. crenata and a leaning trunk inF. japonica may be important characteristics associated with the regenerations patterns of each species; regeneration from seedlings under canopy gaps in the former and vegetative regeneration by sprouting in the latter.     

Development of EST-SSR markers from an inner bark cDNA library of Fagus crenata (Fagaceae)

Fagus crenata Blume is widely distributed throughout Japanese cool-temperate deciduous broad-leaved forests, but there are two divergent groups of populations in areas with contrasting winter climates separated by Japan’s Central Mountain Range. To facilitate investigations of adaptive genetic differentiation of the species using potentially functional genes, we have collected Expressed Sequence Tags and developed Simple Sequence Repeat markers using a cDNA library constructed from cambium and surrounding tissues. In total, 270 primer pairs were designed, and 87 of the corresponding loci showed polymorphism in 16 individuals, with 2–21 alleles per locus and expected heterozygosities ranging from 0.06 to 0.97. EST-SSR markers developed in the present study will be useful for genomic analyses of F. crenata populations.     

Differences in beech (Fagus crenata) regeneration between two types of Japanese beech forest and along a snow gradient

Differences in beech (Fagus crenata) regeneration were quantitatively investigated using power function analysis for the size–class (diameter at breast height, DBH) distribution and juvenile-to-canopy tree (J/C) ratio along a snow gradient throughout Japan. In snowy areas, all species combined, as well as F. crenata alone, showed constant regeneration, with parameter b≈−1.6 for the power function y=ax ^b (x=DBH, y=density), which is related to the DBH–class distribution. The good fit of the data to the function suggests that beech regenerates constantly with self-thinning patch dynamics. Parameter a, which indicates the abundance of small trunks, was high. Furthermore, the mean J/C ratio was ≈8, i.e., each parent beech tree produced eight juveniles. These results suggest that beech regenerates constantly with gap dynamics in snowy beech forests on the Japan Sea side of Japan (snowy). However, the fit of F. crenata was lower and nonsignificant in some forests in less snowy areas, despite the high fit of all species combined. In these areas, the mean of a was low, and b was often near zero for F. crenata regressions. These results suggest that the abundance of beech was low, and self-thinning was not evident because of the initial low abundance. Moreover, the mean J/C ratio was <1.0, suggesting that juvenile density was lower than that of canopy trees. Thus, the regeneration of F. crenata on the Pacific Ocean side of Japan (less snowy) is rather sporadic. Less snowy conditions may promote seed desiccation, predation of beechnuts and seedlings, and water stress. Lower F. crenata density may also reduce predator satiation and wind pollination.     

Mycosphaerella buna sp. nov. with aPseudocercospora anamorph isolated from the leaves of Japanese beech

A species ofMycosphaerella with aPseudocercospora anamorph was collected on overwintered fallen leaves of Japanese beech,Fagus crenata. Based on comparison of morphology withMycosphaerella species on Fagaceae, the fungus was newly described asMycosphaerella buna. ThePseudocercospora anamorph derived from a single ascospore of the fungus was morphologically identical to an endophytic anamorph isolated from asymptomatic living leaves of Japanese beech. Contribution No. 150, Laboratory of Plant Parasitic Mycology, Institute of Agriculture and Forestry, University of Tsukuba     

Shoot dynamics and architecture of saplings in Fagus crenata across its geographical range

 Relationships between leaf or shoot size, number, and arrangement in response to light were investigated to test the hypothesis that these characteristics are linked. In order to test this hypothesis, the divergence in allometry and shoot dynamics in saplings of Japanese beech (Fagus crenata) obtained from four populations and having different leaf sizes were examined in a nursery under both full sun and shade conditions. Trees with different leaf sizes also showed large differences in canopy structure, particularly when shade-grown saplings were compared. The final leaf mass distributions of the large-leaf populations were conical or “bottom - heavy”, while those of the small-leaf populations were planar or “top - heavy”. The slope of the allometric relations between leaf mass and shoot and branch mass in small-leaved populations were steeper than those in large-leaf populations. The four populations were classified into two growth types: populations producing a few large leaf and shoot modules corresponded to “stem growth type”, and those producing many small leaf and shoot modules corresponded to “leaf growth type”. These kinds of intra-specific variation in architecture and growth of F. crenata trees may influence the structure and dynamics of forests in accordance with differences in competitive ability or sensitivity to disturbances such as windstorm. Received: 18 March 1997 / Accepted: 21 October 1997     

Genetics and polymorphism of a duplicated malate dehydrogenase (MDH) locus in the grasshopperOxya japonica japonica (Orthoptera:Acrididae:Oxyinae)

A biochemical genetic study of the enzyme malate dehydrogenase (MDH) was conducted in the grasshopperOxya j. japonica. Analysis of MDH electrophoretic variation in this species of grasshopper shows that one of the two autosomal loci for MDH in grasshoppers, the Mdh-2 locus, controlling the anodal set of MDH isozymes, is duplicated. Results of breeding studies confirm this and the observed polymorphism at theMdh-2 locus in the two populations ofOxya j. japonica studied can be attributed to three forms of linked alleles at the duplicated locus in equilibrium in both populations. In this respect, all individuals of this species possess heterozygous allelic combinations at the duplicatedMdh-2 locus, which may account for the spread of the duplicated locus in the populations of this species of grasshopper.This research was supported by a grant (Vote F) from the University of Malaya, Kuala Lumpur.     

Intraspecific variation and phylogeographic patterns of Fagus crenata (Fagaceae) mitochondrial DNA

Mitochondrial (mt) DNA variation in Japanese beech, Fagus crenata (Fagaceae), was studied in 17 populations distributed throughout the species' range. Total genomic DNA of samples from single trees representing each of 12 populations were digested with 18 restriction enzymes and hybridized with three probes containing coxI, coxIII, and atpA gene sequences. Thirty-four of the 54 enzyme/probe combinations showed polymorphisms and all the individuals were subsequently analyzed with six combinations of three probes and two enzymes. Restriction fragment length polymorphisms were evident around all three genes, allowing the identification of eight distinct haplotypes. Haplotype diversity within the populations was found to be very low (HS = 0.031), but population differentiation to be much higher (GST = 0.963). The mtDNA variation was strikingly different from allozyme variation (HS = 0.209; GST = 0.039). Gene flow for maternally inherited mtDNA should be restricted to seed dispersal while nuclear gene flow occurs by both seed and pollen dispersal. Therefore, the difference in the variation between mtDNA and allozymes may be largely a result of the much higher rate of gene flow associated with pollen dispersal than with seed dispersal. The mtDNA variation displayed strong geographic structure, which may reflect the species' distribution in the last glacial maximum and subsequent colonization, and probably also reflects intraspecific phylogeography of the species.     

Unexpected genetic diversity of Fallopia japonica from Central Europe revealed after AFLP analysis

Recently much attention has been paid to genetic aspects of invasive success in Japanese knotweed s.l. One hypothesis to explain the invasive spread of these species is a multiple introduction, which leads to a higher level of genetic diversity in the invaded range. Fallopia japonica is considered to be genetically uniform in Europe, introduced as a single female clone. However, there is some evidence suggesting that invasion history and dynamics differ between Western and Central-Eastern Europe. We used AFLP markers to characterize genetic diversity of three Fallopia taxa that occur in Poland: F. japonica, F. sachalinensis and their hybrid Fallopia × bohemica, growing in so-called ‘homogeneous’ populations, consisting of one taxon and ‘heterogeneous’ populations, composed of the three taxa cohabiting together. No polymorphism, resp. an insignificantly low variability was observed in the ‘homogeneous’ populations. In the ‘heterogeneous’ stands polymorphism was detected within each taxa, with one exception that concerns individuals of F. sachalinensis from a riparian habitat. The highest level of polymorphism was found among individuals of F. × bohemica. The most striking result of our study is the observation of polymorphism between individuals of F. japonica. The AFLP data also showed that F. × bohemica is most diverse when occurring in a heterogeneous configuration with F. japonica and F. sachalinensis in the same habitat. Our results are the first evidence of genetic diversity in F. japonica populations in Central Europe and can implicate the possibility of its multiple introduction in this region or the existence of sexual reproduction of this species.     

Small-scale variation in chemical property within logs of Japanese beech in relation to spatial distribution and decay ability of fungi

Fungal communities within a naturally fallen bough of Japanese beech (Fagus crenata) were investigated with reference to chemical properties of decay columns. Five logs were cut out from the fallen bough, which ranged from 10.7 to 20.5 cm in diameter. Nine fungal species and one sterile fungus were isolated from decay columns that elongated along a longitudinal axis and were delimited by black zone lines and wood discoloration. Lampteromyces japonicus and Trichoderma spp. were isolated from all five logs. Lampteromyces japonicus and Antrodiella albocinnamomea occupied the largest volume in the logs. Lignin and carbohydrate contents, lignocellulose index (LCI), nitrogen content, and water content were different among decay columns colonized by different fungal species in each log. In L. japonicus, LCI of decay column was correlated to that of wood blocks decayed under pure culture condition by the fungi isolated from the decay columns. These results suggest that the small-scale variation in chemical properties within fallen logs of Japanese beech reflects the distribution and the decay ability of colonized fungi.     

EVIDENCE FOR A MOSAIC HYBRID ZONE IN THE GRASS SHRIMP PALAEMONETES KADIAKENSIS (PALAEMONIDAE) AS REVEALED BY MULTIPLE GENETIC MARKERS

Molecular techniques provide powerful tools for studying the geographic structure of hybrid zones and the dynamics of gene exchange between incipient species. We examined allozyme variation at five loci (PGM, GPI, MDH-1, MDH-2, and LDH) for 27 populations of Palaemonetes kadiakensis from the central, coastal, and eastern regions of Texas. Central Texas populations of P. kadiakensis exhibited highly significant linkage disequilibrium and departures from Hardy-Weinberg genotype proportions. In populations with linkage disequilibrium, allelic differences at GPI defined two types of P. kadiakensis, designated A and B. Both types existed in central Texas with little or no evidence of interbreeding, whereas the populations from all other localities showed complete introgression of type B alleles into the type A gene pool. We also examined ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) variation in a subset of populations, chosen to cover a range of geographic locations and levels of linkage disequilibrium. Two groups of mtDNA haplotypes and two restriction fragment patterns for the rDNA corresponded to allozyme type A and B individuals in populations exhibiting linkage disequilibrium. In populations with ongoing hybridization, all hybrid animals (N= 15) exhibited type A mtDNA. Exhibition of type A mtDNA indicated that type A females had mated successfully with type B males, but type B females had not mated successfully with type A males. Genotype distributions suggest reduced reproduction by hybrid offspring in central Texas populations. These patterns are consistent with a mosaic model of hybrid zone dynamics.     

Natural disturbance and tree species coexistence in an old-growth beech - dwarf bamboo forest,southwestern Japan

Abstract. The structure and composition of a cool-temperate old-growth beech (Fagus crenata) - dwarf bamboo (Sasa spp.) forest, partially affected by landslide disturbance, in the Daisen Forest Reserve of southwestern Japan, were investigated in relation to forest floor and canopy conditions. All stems ≥ 4 cm DBH were mapped on a 4-ha plot and analyses were made of population structure, spatial distribution and spatial association of major tree species. The dominant species, F. crenata, which had the maximum DBH among the species present, had the highest stem density. However, for other species, larger-sized species had lower stem density with few smaller stems or saplings, while smaller-sized species had higher stem density with many smaller stems or saplings. Canopy trees of F. crenata were distributed randomly in the plot, while its stems in the other layers and all other species were distributed patchily. Small patches represent gap-phase regeneration. Larger patches correlate with landslide disturbance, difference in soil age, or the presence/absence of Sasa. Cluster analysis for spatial associations among species and stems in the different layers revealed that the forest community consists of several groups. One main group was formed on sites not covered with Sasa. This group contained a successional subgroup (from Betula grossa to Acer mono and/or F. crenata) initiated by landslide disturbance and a subgroup of tree species that avoid Sasa. Another group was formed on sites with mature soils covered largely with Sasa. This contained associations of canopy trees of F. crenata and smaller-sized tree species such as Acanthopanax sciadophylloides and Acer japonicum. It is found that the community of this old-growth beech forest is largely organized by natural disturbance and heterogeneous conditions of the forest floor (difference in soil age and presence/absence of Sasa). The existence of these different factors and the different responses of species to them largely contribute to the maintenance of tree species diversity in this forest.; Keywords: Cluster analysis; Fagus crenata; Forest dynamics; Gap; Landslide; Spatial pattern.     

Community structure of a species-rich temperate forest,Ogawa Forest Reserve,central Japan

Species assembly and niche differentiation were studied, and future species composition was predicted by simple Markov models, in an old-growth deciduous forest at the Ogawa Forest Reserve in central Japan. The dominant species in our 6ha study site are Quercus serrata, Fagus japonica, and F. crenata.An ordination by population parameters revealed four different combination 3 of life forms and regeneration niches. Cluster analysis based on interspecific spatial correlation revealed three groups of species. The species in cluster A, such as F. japonica, occurred at the bottom of the valley, while those in cluster B, such as Q. serrata, occurred along ridges. Species in cluster C, such as F. crenata, did not show any particular habitat preference. Clusters B and C were further divided into three smaller clusters (a-c). Both clusters Ba and Bb included shade intolerant species. Species in cluster Ba had large clump sizes (>1500 m²), reflecting regeneration following large-scale disturbances. Species in cluster Bb had smaller clump sizes (<400 m²) reflecting regeneration following local disturbances. Clusters Ca and Cb mainly included shade tolerant species and shade intolerant species, respectively. Markov models predicted that shade intolerant species, particularly those in cluster Ba, would be eliminated. Thus, species coexist by differentiation of both habitats and regeneration niche in this forest community. Some species such as Quercus serrata, however, regenerate following large-scale disturbances or human activity.