Regeneration of a temperate deciduous forest in Sasa grassland was investigated focusing on vegetation structure and population growth in a series of beech (Fagus crenata) forest-oak (Quercus mongolica var. grosseserrata) forest-Sasa grassland near the top of Mt. Jippo, southwestern Japan. Beech forest on the mountain slope and Sasa grassland on the summit might have been present for at least about 330 years. A temperate deciduous forest might have been, however, present on the summit before. In the oak forest, some trends were observed along the transect from the forest toward the Sasa grassland : the height of canopy trees became shorter, the DBH distribution changed from a bell type to an L-shape, and stand age estimated by annual rings became younger. These findings suggested that the oak forest might have developed as a secondary forest, and that disturbance perhaps due to logging occurred more than 85 years previously. It seems that the Sasa grassland enlarged after disturbance of the former forest edge, followed by regeneration of the ecotone community dominated by oak. In the Sasa grassland, radial growth in the early stage of young isolated oak tree trunks was comparatively slow, suggesting suppression by Sasa foliage. It was concluded that the presence of Sasa was the main factor suppressing the establishment and growth of tree seedlings, and that in addition, strong wind had an adverse effect on the growth of individuals such as saplings higher than the Sasa foliage. Therefore, Sasa grassland shows little tendency to change to forest.
Regeneration of beech (Fagus crenata Blume) forests was studied around the Kanto district to clarify the difference in regeneration between that on the Pacific side and that on the Japan Sea side. The patch-mosaic structure and the areas of the early, middle and late regeneration stages at the study sites on the Pacific side were similar to those at the study sites on the Japan Sea side. At every developmental stage, the number of beech individuals was lower at the study sites on the Pacific side than at those on the Japan Sea side. At the study sites on the Pacific side the number of other canopy trees was much higher than that of beech individuals. The ratio of beech juveniles (smaller than 10 cm in DBH) to canopy trees (larger than 30 cm in DBH) was much higher at study sites on the Japan Sea side than in those on the Pacific side. At the study sites on the Pacific side the number of beech juveniles was very small. On the Japan Sea side, the number of beech juveniles was higher than that of canopy trees. From these results it is concluded that at study sites on the Pacific side other tree species would replace F. crenata because they regererate constantly with a large number of juveniles, whereas F. crenata has only a small number of juveniles, although large-stemmed F. crenata trees may remain in the forests.
Patterns of topographical distribution of five pioneer tree species (Idesia polycarpa, Cornus controversa, Zanthoxylum ailanthoides, Euptelea polyandra, Mallotus japonicus) and their tree forms were studied in natural forests on Mt. Takao, Tokyo Metropolitan county, central Japan. The study area was divided into six landform types, four of which were free from human activities (upper side slopes, dells, lower side slopes and foot slopes). Patterns of topographical distribution of each species were explainable by their tree form properties (trunk angle, trunk number and maximum tree height). Such a relationship between the form properties and distribution of trees was due to differences in the disturbance regime (mainly by landslides) of each landform type. Species with higher ability to grow when the trunk is inclined and to develop sprouts were more tolerant of higher disturbance pressure. When taller stands suffered lower disturbance pressure, species with a larger maximum tree height and higher ability to grow below the canopy were at an advantage.
Phenological behavior of leaves of the Japanese larch (Larix leptolepis GORD.) was studied along the Western slope of Mt. Utsukushi (2,034 m a. s. l.), central Japan, from 1980 to 1991. The seasonal features of leaves, such as opening, development, yellow coloration and falling, were observed at points located at elevations from 600 to 2,000 m at 100-m altitudinal intervals, and were analyzed on the basis of daily air temperature. When the threshold value was set at 2℃, the best fitness among temporary threshold values from 0 to 7℃ was realized at 101 (±9)℃・days of cumulative daily temperature for the beginning of leaf opening and at 226 (±12)℃・days (3-4 weeks) for completion of leaf development after opening. The speed of leaf opening from the foot of the slope was 2.9 days and that of completion of leaf development was 3.1 days per 100 m elevation on average. On the other hand. leaf yellowing started earlier at higher altitude and moved downwards at a speed of 2.4 days per 100 m elevation followed by a 2-3-week period of leaf falling, which seemed to take longer at higher elevations. Stem growth started from 2 weeks after the completion of leaf development and had nearly finished within 4 or more weeks preceding leaf yellowing at all elevations. At elevations higher than 1,500 m the length of the period when trees bore green leaves was shorter than half a year. These facts suggest a disadvantage for growth of larch at higher elevation.
I studied the structure of a thinned Larix olgensis HENRY forest located on Sandaohu peatland in northeastern China. In the peatland where peat accumulation was less than 20 cm, three tree species, L. olgensis, Betula platyphylla and Populus koreana, occurred. Forest did not develop at sites where peat accumulation exceeded 40 cm. No tree seedlings were present on the forest floor. Forty-one L. olgensis stems were established in a 15 m×15 m plot. The age of L. olgensis ranged from 20 to 29 (averaged 30.9) years. Height and DBH, varied from 1.8 to 14.9 m, and from 0.9 to 22.3 cm, respectively. The thinning, which had been conducted 10-18 years previously, had reduced tree density by 1/3 and created crown gaps. At the time of observation, there were 32% gaps and 12% tree crown overlaps, both of which were also considered to have been created by thinning. However, the thinning had little influence on stem width growth. These results suggested that the growth and seedling establishment of L. olgensis are little affected by light conditions. Soil status such as nutrient availability is considered to be more important.
Sexual dimorphism in flower production and cost of reproduction were examined in a natural population of the dioecious shrub Lindera umbellata THUNB. Sex ratios of flowering stems and flowering stools were not significantly different from 1 : 1. Male flowers were bigger than female flowers. The number of flowers per inflorescence did not differ between males and females, but males produced more floral buds than females. Cost of reproduction was examined in terms of the effect of flower and fruit production on subsequent flower production at shoot level. The effect of flower production did not differ between males and females, but fruit production by females appeared to have a direct negative effect on subsequent floral bud production. This suggests that the differential cost of sexual reproduction between the sexes affects sexual dimorphism in flower production by L. umbellata.
The migration pattern of Neptunea arthritica in Usu Bay, Hokkaido, was studied based on its relationship with reproductive and feeding activities. Soon after hatching, recruits (0 year old) migrated from sites of egg mass deposition to places where food organisms were abundant. Immature individuals (1 and 2 years old) were distributed in and around locations of abundant food organisms in all seasons. In August, adults more than 3 years old were distributed ubiquitously in areas with abundant food. However, by September, they had begun to leave these areas gradually. Many adults aggregated at sites of egg mass deposition during the spawning period from May to June. In July just after spawning, they migrated rapidly from spawning sites to places with abundant food. The change of habitat by recruits and the distribution of immature individuals were strongly dependent on food, and the distribution and migration of adults were closely related to the two factors of reproductive and feeding activities.
A number of reports concerning the influences of acid deposition on forest ecosystems were reviewed, focusing especially on the effects of acid deposition on interactions between forest trees and mycorrhizal fungi. As a whole, these reports suggest that mycorrhizal fungi may mitigate or compensate for the damage to forest trees caused by acidic deposition, although acid deposition seems to suppress the formation of mycorrhizae and/or impair their function, thereby having an adverse effect on forest trees. The mechanisms of the damage to mycorrhizal relationships caused by acid deposition were discussed from several viewpoints, focusing on the respective levels of the relationships.