島野 光司

This paper reviews the differences in the distribution and regeneration of Fagus 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 of F 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, although F. crenata dominates because of its large size and long lifespan.

哺乳類科学

Three canopy tree species (Fraxinus platypoda, Pterocarya rhoifolia, and Cercidiphyllum japonicum) coexist in riparian forests in the Chichibu Mountains of central Japan. We compared the forest structure and the reproductive characteristics of these species. F platypoda was the dominant canopy species. It produced many saplings and grew in abandoned channels and floodplains, and was able to invade both large and small disturbance sites. P. rhoifolia was a subdominant species that occurred on the deposits of large-scale landslides and grew in patches containing even-aged trees. C. japonicum was the other subdominant species that produced few saplings and invaded large disturbance sites together with P. rhoifolia. Establishment sites of C. japonicum were restricted to fine mineral soils and fallen logs. We found tradeoffs in reproductive characteristics (seed size, seed number, irregular seed production, and sprouting) among the three canopy species. F. platypoda and P. rhoifolia had large seeds and produced fruits irregularly. C. japonicum produced many small seeds every year and sprouted prolifically around the main stem. The causes of the coexistence mechanism of the three riparian canopy tree species may be both niche- and chance-determined to varying degrees. In riparian areas, the three canopy species were well-adapted to disturbances throughout their life-history.

「国立科学博物館付属自然教育園における自然生態系特別調査」（研究代表者・矢野 亮）課題番号10400005 平成10年度～平成12年度科学研究費補助金基盤研究(B)(1)研究成果報告書．

電力中央研究所報告

電力中央研究所報告

自然教育園報告

植生学会誌

日本林学会誌

The DBH-class distribution in natural deciduous broad-leaved forests was elucidated with a power function. A power function (y = ax(b), y: stem density, x: represents DBH class, a and b: constants) fits the distribution better than an exponential function (y = a exp bx). The parameter b in the power function is approximately -2. This means that the natural forests studied have a patch-mosaic structure and that tree cohorts regenerate from gaps. Parameter a implies the number of juveniles, and b means size-dependent mortality. The value of -2 for parameter b means that when trees in a given DBH class double their DBH, the density of the size class should decrease by one-fourth. This phenomenon results from self-thinning and is caused by horizontal space competition among trees, called the 'tile model'. The parameter describing DBH-class distribution for a forest with self-thinning patches should be approximately -2. I call this the '-2 power law' for DBH-class distribution. In a typical natural forest dominated by deciduous broadleaf tree species, trees are recognized as pioneer or climax species by the parameters describing their regeneration patterns. When I applied the power functional model to the DBH-class distribution of each dominant species, in pioneer species parameter a was high and b was less than -2 (markedly less than zero), suggesting that there are many juveniles, but mortality is high. On the other hand, in climax species parameter a was low value and the value of b was larger (negative, but closer to zero), suggesting that there are not many juveniles, but mortality is low. A power-function analysis of DBH-class distribution can be used to clarify the patch mosaic structure of a forest, and to clarify the regeneration pattern of pioneer and climax species by applying the function for each species.

Vegetation Science

日本林学会誌

Journal of Forest Research

横浜国立大学 環境科学研究センター紀要

生態環境研究

植物地理・分類研究

多摩のあゆみ

[招待論文]

The escape of beech seeds from seed predators and winter desiccation due to snow accumulation was studied by comparing two sites in Japan: one site that experiences much snow and another site that experiences less snow cover. At the site with greater snow cover, about 70% of the beech seeds escaped seed predation by rodents during winter and about 70% of surviving seeds germinated successfully in spring. At the site with less snow cover, however, all of the beech seeds were eaten by rodents, and all seeds that were protected from feeding were killed by winter desiccation. We confirmed that snow prevents beech seeds from predation by rodents because it conceals their sight and scent. These effects are one of the main reasons why beeches in snowy areas regenerate constantly and those in less snowy areas do not.

植物地理・分類研究

Relations of DBH-crown projection area (CPA) were studied for deciduous and coniferous trees with different models, one of which is newly derived this time. For DBH-CPA relations, a proposed power-sigmoid function was the most suitable one among four models because of its good fit and mechanistic meaning. This model contains the feature that CPA grows with the second power relation to DBH, and the increasing rate of CPA slows as DBH increases. With transformation, the power-sigmoid function for DBHCPA relation can be applied for individual basal area (IBA)-CPA relations as single-saturate function, and these two functional models have high compatibility. Next, the differences of DBH-CPA between deciduous and coniferous tree groups were analyzed with power-sigmoid function. The initial increasing rates of CPA against DBH for each group were similar, though the CPA's increasing rate for the coniferous group tended to decrease earlier than for the deciduous group. Because the power sigmoid function has mechanistic meanings, one can separately analyze the attributes of the DBH-CPA relation: the initial increasing rate of CPA and final tree form.

日本生態学会誌

日本林学会論文集

Technical Bulletin of Faculty of Horticulture, Chiba University

Journal of Japanese Forestly Society

日本生態学会誌

日本生態学会誌