The fruit set ratios of three perennial herbs were investigated to study the effect of forest fragmentation on the pollinator-plant relationship. The fruit set ratios of Corydalis ambigua, Polygonatum odoratum var. maximowiczii and Aconitum yesoense were compared among 14 forestislands, 5 of which were situated in residential areas and 9 in cultivated land. These flowers are outcrossers and pollinated by bumblebees. The average fruit set ratio of C. ambigua, which flowers in April, was lower in residential areas than in cultivated land. In contrast, the average fruit set ratio of P. odoratum, which flowers in June, was high both in residential and cultivated areas. In the case of A. yesoense, which flowers in August, the ratio was also high both in the residential and cultivated areas. Artificial pollination raised the fruit set ratio of C. ambigua in the residential area. The pollen removal ratio (number of flowers with pollen removed/number of flowers observed) was investigated as an indicator of the frequency of pollinator visits on C. ambigua, and showed that pollinator visits were scarce in the forest-islands with a low fruit set ratio. The low fruit set ratio of C. ambigua in residential areas was thus caused by pollinator limitation. Few pollinator visits might be caused by a shortage of flowers that supply the food to pollinators in residential areas.
Seed dispersal, seedling demography and the relationship between seedling position and the upper layers of the tree crown were studied in a Castanopsis cuspidata var. sieboldii forest on Mt. Nishikanasa, Ibaraki Prefecture, central Japan. For four years (1988-1991), dispersed sound seeds of tree species were collected at different intervals. There were differences in the numbers of seedlings that emerged on the forest floor as well as the position of seedlings in relation to the crown projection for each tree species. The results indicated that the seedling bank of C. cuspidata var. sieboldii can be maintained by changes in leader shoot and by sprouting of new shoots after damage within 10 years. Though C. cuspidata var. sieboldii and Abies firma seedlings appeared under the subtree layer crown, the positions of their seedlings in the shrub layer suggested that they survived and grew successively in places without subtree layer crowns. Acer palmatum var. amoenum and Carpinus laxiflora seedlings cannot survive if upper-layer crowns persist, and their seedling bank can be maintained if new seedlings are supplied. For Quercus salicina, seedlings can grow everywhere except for places covered by all crown layers.
A large proportion of forests in Japan are man-made and semi-natural forest, namely plantations and secondary forests. The aim of the present study was to elucidate differences of soil arthropod fauna in the A_0 layer and vegetational structure between coniferous plantations and secondary forests, which are the dominant forest types in southwestern Japan. The soil arthropod fauna in coniferous plantations was less than in secondary forests. Among coniferous plantations, older plantation had a richer and more diverse soil arthropod fauna and flora than younger one, and had a characteristic species composition. Among secondary forests, older pine forest had poorer and less diverse soil arthropod fauna and flora than younger forests. These patterns seemed to be related to the vegetational richness of stratification.
Altitudinal changes in vegetation and soils were studied on Mt. Dairoku (1459.5m altitude), central Hokkaido, Japan. Three altitudinal vegetation types were recognized on the basis of vegetation similarity and species composition : 1) Pinus pumila scrub, distributed at altitudes exceeding 1250m, which was considered to have formed due to edaphic conditions. 2) Subalpine mixed forest, distributed at altitudes between 700m and 1250m, consisting mainly of Picea jezoensis, Abies sachalinensis and Betula ermanii. 3) Cool temperate mixed forest, distributed at altitudes lower than 700m, consisting of Abies sachalinensis, Picea jezoensis, Betula ermanii and many cool temperate deciduous tree species. Main soil types of the Pinus pumila scrub and subalpine mixed forest were black soil and light-colored black soil. These soils were considered to be paleosols, although their surface horizons showed a tendency for weak podzolization. Brown forest soil corresponded well with the cool temperate mixed forest. Synthetic indices of habitat fertility were provided using the soil chemical properties of horizons A_0 and A, which showed a tendency to become reduced gradually at higher altitudes. Soil chemical properties of horizon A_0 showed clear differences between the three vegetation types, whereas those of horizon A showed a difference between black soil and brown forest soil groups. A close correlation between vegetation and soils was recognized.
On the Kamchatka Peninsula, well developed Betula ermanii forests were generally recognized at an altitudinal range from sea level to ca. 400m on the east coast near Petropavlovsk-Kamchatsky. The range increased to ca. 600-900m in the Central Kamchatka Depression. A total of 24 plots were established to analyze the vegetation. The tree layer consisted exclusively of Betula ermanii, whose saplings occurred commonly to recruit in the forest canopy. These data indicated that Betula was the final tree. The species of the herbaceous layer were well diversified. Throughout the plots, a total of 59 vascular species were recognized, of which 48 were common to northern Japan. The Betula forests were found to be fairly uniform in species composition, despite being distantly located geographically, as indicated by the Sφrensen's similarity indices. The forest was well developed where the climate was characteristically maritime, due to the influence of the Pacific Ocean, with small annual fluctuations in temperature, low summer temperatures, a large amount of annual precipitation resulting in heavy snow fall and a short of growing season. Such a climate would discourage boreal conifers such as Larix kamtchatica and Picea ajanensis from becoming established. Their distribution was confined to the Central Depression, where the climate is typically continental. Under the maritime climate, due to a lack of competitors, Betula ermanii could become the final tree constituting the climax forests. The high elevations in the interior would provide a similar type of climate.
Predator-prey relationships mediated by chemicals (kairomones) in lake zooplankton communities are reviewed and discussed. Many zooplankton species change their morphology (anti-predator devices) in response to kairomones released from potential predators. Development of protruding structures (neckteeth, high helmets, long tail-spines) by the cladoceran Daphnia is induced by kairomones during the embryonic or juvenile stage. These structures are lost when the kairomones disappear. Rotifers are, on the other hand, affected by kairomones indirectly through the mother's oogenesis. The effect of kairomones on morphology is influenced by temperature, food conditions for the prey, and by the nutritional state and density of the predators. Chemicals other than predator kairomones, such as chemicals released from non-predatory zooplankton and pesticides, can also induce morphological changes. The predator kairomones affect the prey's behavior as well as morphology. Some zooplankton species migrate vertically to avoid predators in response to the kairomones. Cladoceran species show deterioration of life history parameters and a reduced population growth rate in the presence of kairomones, probably because they use energy for the morphological and behavioral responses. Kairomones reduce the tolerance of cladocerans to environmental stresses such as high temperature, food shortage, pesticide contamination and oxygen deficiency. As a result, kairomones may alter the population dynamics of cladocearns, and in turn, may affect the whole aquatic ecosystem. Investigation of chemical communication between organisms is an important topic of research to help clarify the dynamics of lake ecosystems.