Tomohiko Kamitani

Interspecific competition among three canopy-tree species in a mixed-species even-aged forest of central Japan.

Abstract We investigated causes and consequences of interspecific competition among canopy-tree species with different shade-tolerance. The shading effects caused by neighbors were determined for three tree species, shade-tolerant Fagus crenata, and intermediate tolerant Quercus crispula and Magnolia obovata, in six even-aged stands containing different proportions of each species. The competitive attributes (sensitivity to suppression and intensity of shading) varied considerably among species. Shade-tolerant F. crenata caused most intensive shading effects probably because of its deeper crown depth. Less-tolerant Q. crispula decreased its stem growth and crown depth markedly in association with the presence of shade-tolerant F. crenata. In contrast, F. crenata and M. obovata were less influenced by their neighbors; it may be due to its own higher shade-tolerance in the case of F. crenata and larger initial growth rates in M. obovata. We suppose that differences in initial species composition may lead a species to have different dominance in stand development. When shade-tolerant species are absent in mixture, less shade-tolerant species could maintain their dominance for a long period. In contrast, mixture with tolerant species would reduce the dominance of less-tolerant species, unless they had growth advantage in early stage in development.

Plant species diversity in abandoned coppice forests in a temperate deciduous forest area of central Japan

We investigated plant species diversity as it related to stand structure and landscape parameters in abandoned coppice forests in a temperate, deciduous forest area of central Japan, where Fagus crenata was originally dominant. The species occurring in the study plots were classified into habitat types based on a statistical analysis of their occurrence bias in particular habitats (e.g., primary forest, coniferous plantation) in the landscape studied. The relationships between stand structure, which reflected the gradient of management, and forest floor plant species diversity (H′ and J′) and richness (number of species per unit area) were not significant. However, these factors did influence the forest floor plant composition of the different types of habitat. According to the multiple regression analysis, species diversity and the richness of forest floor plants was affected by landscape parameters rather than by stand structure. For trees, species richness was mainly affected by the relative dominance of F. crenata, which is one of the stand structure parameters that decreases with intensive management. This is probably because many of the tree species that are characteristic of coppice forests increase after F. crenata have been eliminated by management; these species are not dominant in the original forest, where they are suppressed by F. crenata, the shade-tolerant dominant species. The species diversity (H′ and J′) of trees was positively correlated with some landscape parameters, including the road density around the study plot, which may be associated with the intensity of management activity. The number of disturbance-tolerant species increased with increasing road density. Stand structure mainly affected disturbance-intolerant forest floor plant species and disturbance-tolerant tree species. Thus, the species diversity responses differed between forest floor plants and trees. The impact of forest management on species diversity was more prominent for forest floor plants.

Factors Affecting Changes in a Landscape Structure Dominated by Both Primary and Coppice Forests in the Fagus crenata Forest Region of Central Japan

In order to clarify the effects of both the social and natural environment on the changes in landscape structure we analyzed landscape elements using aerial photographs taken in different years in the primary and coppice forests in theFagus crenata forest region of central Japan. The present landscape diversity calculated by Shannons diversity index (H′) appeared to be higher than that observed in photographs from the earlier year. The site with no residential areas and dominated by primary forests had a lower level of landscape diversity than the site which included some residential areas and coppice forests. These results show that the intensity of human activities contributes to changes in landscape diversity. The landscape diversity on private land was higher than that in the national forest, and the changes in landscape structure in the national forest were different from those seen on private land. This suggests that land ownership significantly affects the changes in landscape structure. Topographic factors also affect the changes in landscape structure. Consequently, not only the natural environment (topography), but also the social environment (intensity of human activity and land ownership) strongly influence the changes in landscape structure.

The stand dynamics of a mixed coppice forest of shade-tolerant and intermediate species.

Abstract We investigated stand dynamics of a mixed coppice forest of shade-tolerant and intermediate species, Fagus crenata Bl. and Quercus crispula Bl., in five stands with canopy-stem densities from 420 to 1320 ha−1 (estimated stand age: 37–62 years). The mean basal area (BA), exposed-crown area (ECA) and crown depth (CD) per stem were significantly larger in F. crenata in the three lower density plots. Also Q. crispula had considerably less overtopped stems in the two lower density plots. The mean annual BA increments of the two species were similar in the earlier 20 years; however, in the most recent 5 years, F. crenata had a higher relative growth rate for basal area (RGRBA) than Q. crispula. The most critical variable of the RGRBA was the ECA for F. crenata and the relative height (RH) for Q. crispula. We predict that dominance of F. crenata will gradually increase over that of Q. crispula as stands mature. This seems to be caused by lower shade-tolerance despite the similar initial growth rates of Q. crispula compared with F. crenata.

Factors affecting seed rain beneath fleshy-fruited plants.

We investigated factors affecting seed rain beneath nine fleshy-fruited fruiting plant species growing in a 1-ha plot of planted Pinus thunbergii in central Japan. We tested whether the numbers of seeds and seed species dropped by birds beneath fruiting plants were correlated with the number of fruits removed by birds from the plants. Most of fruiting plant species with high fruit removal had significantly high seed rain. Both the numbers of seeds and seed species dropped were significantly, positively correlated with the number of fruits removed across for all fruiting plant species. Therefore, fruit removal predicted the difference among heterospecific fruiting plants in seed rain. We also tested whether the number of fruits removed from fruiting plants by birds was related with fruit crop size, fruit size, and height of the plants, and the numbers of fruits and fruit species of neighboring plants near the plants. Most of fruiting plant species with high fruit crop size had significantly high fruit removal. The number of fruits removed was significantly, positively correlated with both the fruit crop size and the number of neighboring fruits across the nine fruiting plant species. However, the effect of the neighboring fruit density on fruit removal was lower remarkably than that of fruit crop size. Therefore, fruit crop size best predicted the differences among heterospecific fruiting plants in fruit removal. We suggest that fruiting plant species with high fruit crop size and high fruit removal contribute to intensive seed rain beneath them.

Desiccation-tolerance of Fagus crenata Blume Seeds from Localities of Different Snowfall Regime in Central Japan

In beech (Fagus crenata Blume) forests on the Pacific Ocean side in Central Japan, snowpack depth is little and xeric conditions may prevail in winter, in contrast to heavy snow in beech forests on the Japan Sea side. The effects of such conditions during winter on the viability of beech seeds were studied at a beech forest on the Pacific Ocean side. Thickness and weight ratio of pericarp of beech seeds were significantly greater in populations on the Pacific Ocean side compared to the Japan Sea side, this apparently being related to snowpack depth in winter. During the initial stage of seed drying, the drying rate of seeds from the Fuji population (the Pacific Ocean side) was less than that from the Sumon population (the Japan Sea side), possibly due to the thicker pericarp. Germination percentage of seeds which dried to a water content as low as 7% d.w. did not decrease for either population, indicating desiccation tolerance of beech seeds. In the beech forest (University Forest at Yamanaka) on the Pacific Ocean side, water content of seeds sown below litter from both populations remained sufficient for viability during winter. Germinating seeds from the populations on the Japan Sea side were more desiccation-sensitive in early spring, compared to those from the Fuji population, partially due possibly to differences in pericarp thickness.

Effects of tillage and irrigation on the occurrence and establishment of native wetland plant species in fallow paddy fields

Traditional weed management, such as tillage and irrigation, has led to an enhanced maintenance of wetland plant species in fallow paddy fields. Recent herbicide usage and improvements in irrigation and drainage systems however have caused habitat loss of these species, especially in fields on open lowlands. We conducted experiments in three fallow paddy fields situated on the alluvial Echigo Plain in central Japan with an aim to restore the habitat of native wetland plant species. The three experimental fields were managed under different irrigation regimes, (1) perennially flooded with water, (2) intermittent irrigation, and (3) temporary irrigation. Half the area of each experimental field was tilled before irrigation. Detrended correspondence analysis revealed obvious floristic differences between experimental and control fields with no irrigation. The proportion of wetland plant species in the experimental fields increased corresponding to the irrigation period, ranging 60–86%, and was relatively greater than that in control fields. In the experimental fields, differences in both tillage and irrigation affected the occurrence of plant species. Tillage restricted the occurrence of many non-wetland plant species, and had a positive effect on the establishment of several annual wetland plant species. In addition, a longer duration of irrigation is not necessarily suitable for the occurrence of all wetland plant species. We concluded that fallow paddy fields provide a possible habitat for the restoration of native wetland plant species through appropriate tillage and irrigation.

An alternative of soil scarification treatment for forest restoration: effects of soil replacement.

We examined an alternative natural regeneration practice with a scarification treatment, in which removed soil is replaced on the scarified area, in northern Japan. The effect of the soil replacement on tree establishment was quite obvious; the basal area of trees, composed mostly of Betula ermanii, in the soil-replaced site was about 150-fold greater than that of the normally treated site. The greater growth rates together with higher density, both of which seemed to be enhanced by improved (i.e., deeper, tender, and nutrient-rich) soil properties, produced the marked difference to the normally treated site. The expected enhancement of species diversity owing to utilizing buried seeds in the replaced soil was not found. The current study revealed that the soil replacement could substantially improve forest restoration management with emphasis on biomass production for large nonwooded sites.

Colonization of fleshy-fruited plants beneath perch plant species that bear fleshy fruit

We evaluated the contribution of seed dispersal by birds to the colonization of fleshy-fruited plants beneath plants that bear fleshy fruits and were used as perches by birds. Specifically, we investigated the composition of seeds and saplings sampled beneath nine fleshy-fruited perch plant species in a Pinus thunbergii stand on a coastal sand dune in central Japan. Both the numbers and the species numbers of bird-dispersed (pulpless) seeds differed significantly among the perch plant species. Nevertheless, the quantitative compositions of bird-dispersed seeds were similar among the perch plant species because of the significant positive interspecific correlations of species rank order in numbers of bird-dispersed seeds per species. Similar relationships were also found for saplings. For each perch plant species, the numbers of fallen conspecific seeds were significantly higher than or not different from those of heterospecific seeds. Furthermore, the numbers of pulpy seeds that fell directly from the perch plant were significantly higher than those of bird-dispersed conspecific seeds for seven of nine perch plant species. However, the densities of conspecific saplings were significantly lower than those of heterospecific saplings. Most pulpy seeds, therefore, probably do not germinate beneath their mother plants, and conspecific seeds probably accumulate in seed banks or are consumed by herbivores.

Is there a risk-dilution effect of naturally fallen fruits on post-dispersal seed predation by wood mice?

AimsThe aim of this study was to test the hypothesis that heavy predation of fallen fruits reduces the predation of neighboring post-dispersed seeds.MethodsWe performed a seed/fruit removal cafeteria experiment to assess the effects of seed species, of fruit species, and of density of fallen fruits on seed predation by wood mice (Apodemus sp.). In total, 6,930 seeds and 9,660 fruits from seven species were used. A generalized linear mixed model procedure was used to test these effects.ResultsSeed predation was significantly affected by the species of both seeds and neighboring fruits, but not by their density. Multiple comparison tests showed that most of treatments tested had no significant effects of species and density of neighboring fruits on seed removal. However, seed removal was significantly lower in some treatments with fruits than in the treatments without fruits for one of the seven seed species tested. Seed removal of two species tested was significantly differed among some treatments with different fruit species.ConclusionMost of the results in this study do not support our overall hypothesis. However, a part of results supported our hypothesis, suggesting that seed removal is affected by complex interactions between the preference of wood mice for fruits and fruiting environment.