Variation in leaf morphology of Quercus crispula and Quercus dentata assemblages among contact zones: a method for detection of probable hybridization

I describe variation in leaf morphology of Quercus crispula and Quercus dentata assemblages within and among their contact zones. Such relationships provide a relatively fast and accurate method for detecting hybridization. Using discriminant function (DF) analysis based on leaf characteristics, I was able to differentiate between these two species in pure zones. In three of five contact zones, the DF scores showed broad, continuous distributions with three or more peaks. The trees showing intermediate leaf morphology are considered to be hybrids. In the other two contact zones, the DF scores showed distinct bimodal distributions, suggesting that Q. crispula and Q. dentata rarely hybridize in these sites. Thus, the method described in this study should be effective for detecting probable hybridization between these two species in contact zones, and the relative frequency of hybridization among contact zones. However, there was likely to be intraspecific variation of Q. crispula between geographic ranges, restricting interpretations to patterns occurring within sites or limited geographic ranges.     

Changes in water status in seedlings of six species in the Fagaceae after inoculation with Raffaelea quercivora Kubono et Shin-Ito

To clarify the differences in susceptibility of six species in the Fagaceae (Quercus crispula, Quercus serrata, Quercus acutissima, Quercus phillyraeoides, Quercus glauca, and Castanopsis cuspidata var. sieboldii) to Raffaelea quercivora, we inoculated this fungus on seven potted 5-year-old seedlings of each species, observed symptom development, and measured xylem pressure potential (XPP) after inoculation. The first death was observed on the 11th day in Q. crispula and on the 56th day in Q. serrata. The number of dead seedlings of Q. crispula and Q. serrata were five and one, respectively, whereas no mortality was observed in the other four species. The XPP of inoculated seedlings in both Q. crispula and Q. serrata decreased after inoculation. In contrast, the XPP of inoculated seedlings of the other four species remained almost the same as in the control seedlings. These results indicate that R. quercivora is pathogenic to Q. crispula and Q. serrata and that the susceptibility of the six Fagaceae species in our study differed among species.     

Individual-scale responses of five dominant tree species to single-tree selection harvesting in a mixed forest in Hokkaido, northern Japan

We investigated the individual-scale responses of five dominant species (Abies sachalinensis, Acer mono, Tilia japonica, Quercus crispula, and Betula ermanii) to single-tree selection harvesting in a conifer–broadleaved mixed forest in Hokkaido, northern Japan. Using data from stems with a diameter at breast height of ≥12.5 cm, collected during 20 years of monitoring a 6.7-ha stand, we analyzed the effects of harvesting in the neighborhood on tree recruitment and the growth (diameter class transition) and mortality of the residual trees. The effects of harvesting varied considerably among tree sizes and species. Harvesting improved the recruitment of A. mono and B. ermanii, and moderated the negative effect of the initial basal area of the surrounding canopy trees on the recruitment of Q. crispula. Conversely, harvesting limited the recruitment of A. sachalinensis by offsetting the positive effect of the initial basal area of the surrounding canopy trees. The growth of A. sachalinensis and Q. crispula decreased with the initial basal area of the surrounding canopy trees. Harvesting in the neighborhood resulted in an improvement in the growth of the trees of these species only in the smaller size classes. With increasing local harvesting intensity, the mortality of smaller A. sachalinensis trees decreased, whereas the mortality of larger trees increased. These results suggest that differences in the local harvesting intensity, spatial patterns of harvesting, and initial stand structures influence the stand-scale dynamics in response to partial harvesting in the mixed forests of this region.     

Manipulation of tannins in oaks by galling cynipids

We measured the protein precipitation capacity of tannins in the tissues of Quercus crispula and Quercus serrata galls induced by a cynipid (Trigonaspis sp.) to examine the nutrition hypothesis on gall induction. The protein precipitation capacity was significantly lower in the nutritive tissues of galls, on which the cynipids feed, than in ungalled sound leaves and in the outer gall tissues. In addition, the protein precipitation capacities in the leaves and in the outer gall tissues were significantly larger in Q. crispula than in Q. serrata samples, whereas that of the nutritive tissues did not differ between these oak species. These results suggest that gall induction is one of the adaptations of galling cynipids to host–plant defensive compounds, and support the nutrition hypothesis.     

Discoloured and non‐conductive sapwood among six Fagaceae species inoculated with Raffaelea quercivora

Mass mortality of oak trees has been occurring in Japan since the late 1980s. The fungus Raffaelea quercivora has been frequently isolated from discoloured sapwood in dead or wilting trees and inoculation experiments have shown it to be capable of causing wilting and xylem discoloration in several oak species, notably Quercus crispula and Q. serrata. In this study, we inoculated seedlings of six Fagaceae species with R. quercivora and, after 56 days, measured the vertical length of the discoloration and the areas of discoloured and non‐conducting sapwood on stem cross‐sections. The sapwood discoloration and the water non‐conduction areas were larger in Q. crispula and Q. serrata than in the other species.     

Effects of previous forest types and site conditions on species composition and abundance of naturally regenerated trees in young <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> plantations in northern Japan

Naturally regenerated trees in young Cryptomeria japonica plantations were investigated in 141 quadrats of 10 × 50 m within a watershed of 1,000 ha, and factors affecting their composition and abundance were examined. The species composition of naturally regenerated trees was classified into four types. Dominant species were Swida controversa, Magnolia hypoleuca and Pterocarya rhoifolia in Type A1, Betula maximowicziana, M. hypoleuca, Quercus crispula and Castanea crenata in Type A2, Q. serrata and C. crenata in Type B1, and Pinus densiflora in Type B2. The results of path analysis showed significant influences of previous forest type and geology among the factors that correlated with the species composition of naturally regenerated trees; previous forest type in particular showed a higher absolute path coefficient value. Species composition types of naturally regenerated trees corresponded to the previous forest types: Types (A1 and A2) corresponded to the natural forests composed of Thujopsis dolabrata var. hondai, Fagus crenata, Aesculus turbinata, etc., Type B1 corresponded to the secondary Q. crispula and Q. serrata forest, and Type B2 corresponded to the secondary P. densiflora forest, respectively. The abundance of naturally regenerated trees was strongly affected by geology; i.e., plantations on soft-sedimentary dacitic tuff contained great amounts of colonizing P. densiflora trees.     

Discrimination among host tree species by the ambrosia beetle Platypus quercivorus

The ambrosia beetle Platypus quercivorus is a vector for the fungus that causes Japanese oak wilt, and susceptibility to infestation by P. quercivorus varies by tree species. We postulated that P. quercivorus discriminates among host tree species differing in susceptibility to attack. To test this postulate, we counted the number of flying male beetles (NFM), the number of holes bored by male beetles (NH), and the number of flying female beetles (NFF) per unit area of bark surface in three fagaceous tree species: Quercus crispula (with high susceptibility to infestation) and Q. serrata and Castanea crenata (both with low susceptibility). NFM and NH were used to calculate the proportion of male beetles that bored holes out of those that flew to the tree (PBM). We used generalized additive models to predict NFM, NFF, and PBM. The locations of trees, expressed as x and y coordinates, numbers of weeks after the first male beetle’s flying (WEEK), diameters of trees 130 cm above ground (DBH), and tree species (SP) were incorporated into the models as candidate explanatory variables. The best-fit models for NFM and NFF included WEEK and DBH and the effect of location; SP was not included in the models. For PBM, the best-fit model included WEEK, DBH, and SP. The results indicate that male P. quercivorus prefer Q. crispula to Q. serrata and C. crenata and that selection is made before boring holes on trees, but that P. quercivorus do not discriminate among host species when they fly to trees.     

Virulence of Raffaelea quercivora isolates inoculated into Quercus serrata logs and Q. crispula saplings

This study was conducted to compare the virulences of various isolates of Raffaelea quercivora—a fungus that causes Japanese oak wilt disease—towards Japanese oak trees. Five isolates were collected from a wide range of Japan and inoculated into Quercus serrata logs and Q. crispula saplings. The tangential length of the discolored sapwood in the Q. serrata logs differed significantly among the isolates. The trend in isolate virulence was similar for the Q. serrata logs and the Q. crispula saplings. This is the first report suggesting that there is variability in virulence among isolates of R. quercivora.     

A low <Emphasis Type="Italic">Platypus quercivorus</Emphasis> hole density does not necessarily indicate a small flying population

The ambrosia beetle Platypus quercivorus causes mass mortality of Fagaceae trees in Japan, and tree species differ in their susceptibility to P. quercivorus. We hypothesized that interspecific differences in susceptibility are caused by differences in beetle infestation patterns, that is, how many beetles fly to a tree and how many of those arriving bore holes. To examine how tree susceptibility is related to these parameters, two tree species with different degrees of susceptibility were studied (highly susceptible Quercus crispula and less susceptible Q. salicina). Specifically, we measured the number of male beetles per unit area that flew to the host trees (NFM) and the density of holes bored by male beetles (DH). From these two values, we calculated the proportion of male beetles flying to a host tree that bored holes (PBM). These parameters were compared for the two Quercus species. Although the two species did not differ in NFM in 2003, PBM was markedly lower for Q. salicina than for Q. crispula and DH was significantly lower for Q. salicina than for Q. crispula. Thus, the lower susceptibility of Q. salicina is partly explained by its low PBM.     

Predicting the spatial distribution of major species composition in secondary hardwood forests on Mt. Gozu,central Japan,based on environmental factors

Our goal was to predict the spatial distribution of canopy species composition in secondary deciduous hardwood forests at a fine spatial resolution, based on climatic and topographical factors using a geographic information system. We studied secondary forests on Mt. Gozu, Niigata Prefecture, central Japan. Canopy species composition was investigated in 100 sample plots within the study area. A digital elevation model (DEM) was created, and topographical, hydrological, and light factors were calculated using the DEM. Climatic factors were interpolated by kriging. The five major species used as response variables were Fagus crenata, Quercus serrata, Quercus crispula, Magnolia obovata, and Castanea crenata. We prepared three possible explanatory variable sets: climatic variables only, both climatic and topographic variables, and topographic variables only. Multivariate regression trees were derived, and the accuracy of predicting the major species composition was tested. The multivariate regression trees derived from the climatic variable set and from the climatic and topographic variable set had better accuracy than the regression tree derived from the topographic variable set. In the regression tree generated by the climatic and topographic variable set, the warmth index was the principal explanatory variable in classifying forest types, followed by topographic factors. This regression tree would be preferable to the other two regression trees for the prediction of canopy species composition.     

Types of frass produced by the ambrosia beetle <Emphasis Type="Italic">Platypus quercivorus</Emphasis> during gallery construction,and host suitability of five tree species for the beetle

We studied the biology of the ambrosia beetle Platypus quercivorus in the logs of five tree species to determine: (1) the relationship between the amount of frass produced by beetles and tunnel length, (2) the relationship between frass shape and the morphological characteristics of P. quercivorus mouthparts, and (3) the suitability of five tree species for P. quercivorus reproduction. Five logs each from healthy Quercus crispula, Q. serrata, Castanea crenata, Sorbus japonica, and Cryptomeria japonica trees were used in this experiment. The results showed that there was a linear relationship between the amount of frass and tunnel length. Whenever powdery frass was produced, larvae were found in the gallery in the log, while fibrous frass was present only in galleries that contained just adults. The mouthparts of adults were completely sclerotized, which likely accounts for the fibrous frass production. Host preference of P. quercivorus was examined at two stages using five tree species. The first stage is digging initiation, which concerns male preference for digging a tunnel. More holes were made by males on S. japonica and Q. serrata logs, while fewer holes were made on C. japonica logs. The second stage is characterized by female orientation, mating, and progeny development. Platypus quercivorus could complete its lifecycle only in the two Quercus spp.     

Geometric morphometric analyses of leaf shapes in two sympatric Chinese oaks: <Emphasis Type="Italic">Quercus dentata</Emphasis> Thunberg <Emphasis Type="Italic">and Quercus aliena</Emphasis> Blume (Fagaceae)

Key message

Geometric morphometric analyses (GMMs) of the leaf shape can distinguish two congeneric oak species Quercus dentata Thunberg and Quercus aliena Blume in sympatric areas.

Contexts

High genetic and morphological variation in different Quercus species hinder efforts to distinguish them. In China, Q. dentata and Q. aliena are generally sympatrically distributed in warm temperate forests, and share some leaf morphological characteristics.

Aims

The aim of this study was to use the morphometric methods to discriminate these sympatric Chinese oaks preliminarily identified from molecular markers.

Methods

Three hundred sixty-seven trees of seven sympatric Q. dentata and Q. aliena populations were genetically assigned to one of the two species or hybrids using Bayesian clustering analysis based on nSSR. This grouping served as a priori classification of the trees. Shapes of 1835 leaves from the 367 trees were analyzed in terms of 13 characters (landmarks) by GMMs. Correlations between environmental and leaf morphology parameters were studied using linear regression analyses.

Results

The two species were efficiently discriminated by the leaf morphology analyses (96.9 and 95.9% of sampled Q. aliena trees and Q. dentata trees were correctly identified), while putative hybrids between the two species were found to be morphologically intermediate. Moreover, we demonstrated that the leaf morphological variations of Q. aliena, Q. dentata, and their putative hybrids are correlated with environmental factors, possibly because the variation of leaf morphology is part of the response to different habitats and environmental disturbances.

Conclusion

GMMs were able to correctly classify individuals from the two species preliminary identified as Q. dentata or Q. aliena by nSSR. The high degree of classification accuracy provided by this approach may be exploited to discriminate other problematic species and highlight its utility in plant ecology and evolution studies.

     

Individual growing conditions that affect diameter increment of tree saplings after selection harvesting in a mixed forest in northern Japan

We analyzed temporal patterns in diameter growth of saplings following selection harvesting in an uneven-aged mixed stand dominated by Abies sachalinensis, Acer mono, Quercus crispula, and Betula ermanii in Hokkaido, northern Japan. We examined interspecific differences in growth responses to local growing conditions including harvesting intensity, crowding, stem size, and past duration of the small growth period. Consistent with expectations based on shade tolerance of the species, the age at which the individual reached a diameter at breast height (DBH) of 12.5 cm was highest for A. sachalinensis and lowest for B. ermanii. The interspecific growth differences between saplings that had or had not experienced local harvesting increased gradually for A. sachalinensis and B. ermanii, but peaked at around 4–6 years after harvesting for Q. crispula. Generalized linear mixed model analysis clearly suggested that individual growth conditions required to enhance diameter growth of saplings differed considerably among species. For Q. crispula and B. ermanii, local harvesting intensity was most strongly and positively associated with diameter growth rate, whereas for A. sachalinensis and A. mono, stem size had the strongest negative effect. Abies sachalinensis saplings responded more to surrounding harvesting when they were relatively small, whereas A. mono showed a weak opposite response. The duration of the small growth period before harvesting had negative effect for A. sachalinensis, but not for the other species. Our study indicated that the influence of selection harvesting on growth of shade-tolerant species depends upon pre- and post-harvest growing conditions.     

Extent of colonization by Raffaelea quercivora of artificially inoculated living and gamma‐ray‐sterilized seedlings of two Japanese and three American oak species

Mass mortality of Fagacean tree species caused by Raffaelea quercivora has occurred widely in Japan. Because conidia or other propagules of the pathogen have not been found in infected trees, pathogen spread is assumed to occur primarily by hyphae. To clarify the relationship between hyphal growth of the pathogen within trees and their vessel arrangements, we examined two native Japanese oaks, Quercus crispula and Quercus glauca, and three exotic American oaks, Quercus coccinea, Quercus palustris and Quercus rubra. Quercus glauca is a radial‐porous species, whereas the other four species have a ring‐porous wood structure. Hyphal growth within inoculated potted living seedlings and in cut, sterilized stem segments of these species was examined microscopically after fungal inoculation. Water conductance in the seedlings was examined using transverse stem sections. The proportion of non‐conductive sapwood in Q. crispula, Q. coccinea and Q. palustris differed between inoculation and control treatment, being much higher in inoculated seedlings. The proportions were positively correlated with the extent of the hyphal growth. In sterilized stem segments, the extent of fungal colonization varied among the foreign ring‐porous species Q. coccinea, Q. palustris and Q. rubra. It is hypothesized that the extent of colonization by R. quercivora reflects the extent of non‐conductive sapwood irrespective of tree species, but is little affected by vessel arrangements.     

Spatial distribution of Raffaelea quercivora hyphae in transverse sections of seedlings of two Japanese oak species

To compare the distributions of Raffaelea quercivora hyphae within seedlings of a susceptible species, Quercus crispula, and a resistant species, Q. glauca, we examined water conductance at transverse sections. Raffaelea quercivora was inoculated into the stems of seedlings in July (summer) and October (autumn) and observed by light and fluorescence microscopy at 1 and 2 weeks after inoculation. The hyphal distribution patterns expressed as the I_δ index differed between the species at each occasion. The hyphal growth was wider in Q. crispula than in Q. glauca in July inoculation, but did not differ in October inoculation. Non‐conductive sapwood in Q. crispula in transverse section was wider than that in Q. glauca at each occasion. The differences of hyphal growth and hyphal distribution patterns between species as little as 1 week after inoculation reflect differences in host susceptibility to the fungus.     

Demographic and height growth response of native broad-leaved deciduous tree saplings to overhead canopy release in a coastal Pinus thunbergii forest in Hokkaido, northern Japan

Prevention efforts to combat pine wilt disease must be instituted to avoid destruction of coastal forests in Hokkaido, northern Japan. We examine an alternative method involving the conversion of Pinus thunbergii forests to native broadleaf species through advancing their growth, but we have little knowledge about the response of advanced growth to overhead canopy release. To demonstrate the demographic and height growth response of advanced growth to the light change in a coastal Pinus thunbergii forest, canopy trees were removed and the sapling populations were monitored for 6?years. Inhibition in height growth caused by light increase was observed in Cerasus sargentii and Kalopanax septemlobus saplings. Especially in Kalopanax septemlobus, a remarkable decline was observed in the saplings growing in the darker positions which experienced light change. Therefore, large light changes should be carefully avoided for this species especially in the darker positions. In contrast, relative height growth rates of Quercus crispula and, especially, Quercus dentata increased with increasing light, and saplings tended to die in the darker positions. No dead trees of Sorbus commixta were observed during the study period. The saplings also showed good height growth even when under closed canopy. This species seems to be adaptive to a dark environment. Since Quercus dentata and Kalopanax septemlobus are the major components of the natural coastal forests in Hokkaido, gradual canopy release is available to foster advanced growth in coastal Pinus thunbergii forest, in accordance with the concept of density control in coastal forests.     

Variations in virulence and hyphal growth of four Raffaelea quercivora isolates within Quercus crispula

Mass mortality of fagaceous trees caused by Japanese oak wilt has occurred widely in Japan. Although virulence of the causal fungus, Raffaelea quercivora, appeared to differ among isolates, its relation to the fungal growth within trees was unknown. To clarify the differences in fungal virulence against susceptible Quercus crispula, we examined fungal growth of four R. quercivora isolates within trees and the resulting virulence. In our study, the isolates were multiple‐inoculated in seedlings and single‐inoculated in twigs of mature trees. In the multiple‐inoculation test, mortality rates were examined by the observation of external symptoms. In the single‐inoculation test, water conductance and hyphal growth within the trees were examined by applying aqueous dyes and fluorescence microscopy, respectively. Mortality rates, the proportion of the cross‐sectional area comprising non‐conductive sapwood and horizontal hyphal growth differed significantly among the isolates. Univariate logistic regression analyses showed that both the proportion of non‐conductive sapwood and hyphal growth were significantly positively related to mortality rates. For three isolates, hyphal growth was significantly positively correlated with the proportion of non‐conductive sapwood. These results suggested that the virulence against Q. crispula varies among R. quercivora isolates and that the extent of fungal colonization of the tree determines fungal virulence.     

Long-term effects on tree regeneration of soil scarification with microtopography manipulation in mixed forests of central Hokkaido,northern Japan

Natural regeneration of canopy tree species is generally poor under a selective cutting regime practised in mixed conifer–hardwood stands on Hokkaido, northern Japan, and is prevented by dense bamboo layers in the understory. To promote tree regeneration, we scarified soil in ten sites, with elevations ranging from 420 to 760 m, in 1979, with a rake-equipped bulldozer to produce three different artificial microtopographies (concave, flat, and convex). Twenty-six years after scarification, six canopy tree species (Acer mono, Abies sachalinensis, Betula ermanii, B. maximowicziana, Kalopanax pictus, and Picea jezoensis) had become well established. Abies sachalinensis and B. ermanii regenerated at all sites. Picea jezoensis was well established in high-elevation sites, whereas other hardwood tree species (A. mono, B. maximowicziana, and K. pictus) were well established at low-elevation sites. The Betula species dominated upper layers of regenerated trees, and two conifer species (A. sachalinensis and P. jezoensis) occupied lower layers. Regenerated densities of four (of six) major tree species were positively correlated with standing timber volume of mother trees, whereas those of shade-intolerant species (two Betula species and K. pictus) were negatively correlated with standing timber volume of all canopy trees. Small-seeded species (P. jezoensis and the two Betula species) had higher regeneration densities on convex sites than on other microtopographies. Adequate seed supply, convex substratum for small-seeded species, and control of light conditions for shade-intolerant species should be taken into account when planning regeneration of desirable tree species in central Hokkaido.     

Differential spread of discoloured and non‐conductive sapwood among four Fagaceae species inoculated with Raffaelea quercivora

To reveal the relationship between the susceptibility of Fagaceae species to Raffaelea quercivora Kubono et Shin‐Ito and the tangential expansion of regions of discoloured and non‐conductive sapwood among the species, we inoculated branches of three Quercus species and one Castanopsis species with the fungus. The sapwood around the inoculation hole in all four species became non‐conductive in response to the infection before the discolouration. The expansion of the region of non‐conductive sapwood ceased within 2 weeks after the inoculation. The region of non‐conductive sapwood in Q. crispula and Q. serrata was larger than that in Q. glauca and C. cuspidata var. sieboldii. These results suggest that the region of non‐conductive sapwood expanded soon after the infection by R. quercivora. It was also clear that the transverse non‐conductive sapwood has close relationship with the susceptibility among Fagaceae species to R. quercivora.     

Studies on the damage potential of Closterotomus (=Calocoris) trivialis and Aphanosoma italicum (Hemiptera: Miridae) on citrus

This study aimed to investigate the damage potential of two hemipteran species that are commonly recorded in citrus orchards of the eastern Mediterranean region. These were Closterotomus trivialis Costa and Aphanosoma italicum Costa (Hemiptera: Miridae). Shoots on sweet orange trees were enclosed in muslin cages into each of which eight nymphs or eight adults were introduced not only in the early development of the buds but also in the different stages of the flowering period in 2008 (i.e., 6 and 19 March, 10 April and 2 May). In the experiments, adults of C. trivialis, and nymphs and adults of A. italicum were used. According to the results, in a few cases these insects caused a significant reduction in the number of buds or flowers and fruits dropped in comparison to the controls. However, the number of fruits that finally remained on the trees was not significantly affected. Therefore, the damage potential of these mirids on the fruit production of citrus was not shown to be significant under our experimental conditions.