In the downstream floodplains of Miharu Dam on the Ohtakine River (located in Fukushima prefecture, Japan), the changes of vegetation have been studied for a total of 3 years, since the dam was first filled. The findings have shown that the floodplain communities such as the Phragmites japonica community have decreased, while the upland communities such as the Pueraria lobata community and the Festuca arundinacea community have increased. The cause for this change in vegetation is considered to be erosion and the change in the flow regime. The floodplain communities occur near the edge of the streams, which is an easily eroded area. Downstream from the dam, sediment transportation is limited to a very small quantity. Since no new land forms, the habitat for the floodplain communities decreases. The amount of flowing water was controlled to less than 20m^3/sec for a year and 9 months since the first filling of water. For the grassland communities, the habitat conditions in the areas where the water level is higher than 20m^3/sec, was found to be very suitable. Under this condition, the upland communities have invaded and oppressed on the Phragmites japonica community.

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We have studied the structure and altitudinal zonation of the warm temperate forests on the volcanic Mikura-jima Island, one of the Izu Islands, Japan. The forest can be divided into three main zones : a low-altitude Castanopsis forest zone, a middle-altitude transitional Castanopsis forest zone and a higher-altitude Buxus-Eurya-Trochodendron mixed forest zone. The forest has several distinctive features. Firstly, the species composition of the mixed forest differs from the evergreen broad-leaved forests found at a similar altitude on the Japanese mainlands. Secondly, tree species diversity increases with altitude. Thirdly, tree height decreases with increasing altitude, and forthly, leaf size decreases from notophyllous at lower altitudes, to microphyllous and nanophyllous at higher altitudes. The decline in tree height and the change in leaf size may be characteristic of small volcanic islands in the warm-temperate region of Japan.

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The purpose of this study is to clarify regeneration patterns of the beech (Fagus crenatd) forest on flat and sloping sites in N.E. Nagano Prefecture. Two 80m x 80m quadrates were established : on flat surface (FS) and on slope surface (SS), respectively. In each quadrate, forest structure, the number of seedlings, saplings and fallen trees, and the diameter of fallen trees (at 1.3 m from their roots) were surveyed. The mean plant coverages of subcanopy and herb layer at SS were higher than those at FS. In contrast, the mean plant coverages of second shrub layer and dwarf bamboo were higher at FS. Total basal area of all tree species was higher at FS, but there were more trees at SS. Coexistence analysis of beech showed that middle and small DBH beech coexisted at FS, but large DBH beech rarely coexisted with middle and small beech at FS. At SS, there was no similar relation of coexistence. Regarding the structure of both forests, the patchy structure of FS was clearer than that of SS. Moreover, the number of fallen trees was greater at SS, but their size was smaller there. Tree fall may occur more frequently at SS. Successors of beech rarely grow at FS because of a thick dwarf bamboo layer. This fact indicates that the regeneration at FS is discontinuous. On the other hand, the regeneration at SS seems to occur continuously, because successors of beech grow well under a less thick dwarf bamboo layer. The regeneration patterns of two types of beech forest were clearly different on FS and SS sites.

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Successional trends from secondary forests to evergreen broad-leaved forests were investigated on the western slope of Mt. Miroku and an adjacent hill in Kasugai City, Aichi Prefecture, Japan. The results show that many seedlings of Castanopsis cuspidata and Quercus glauca grew on the forest floor of secondary forests that comprised mainly Pinus densiflora and Q. serrata. This observation suggests that the secondary forests will develop into evergreen broad-leaved forests in the future. There were differences in distribution patterns between the 2 evergreen species C. cuspidata and Q. glauca. The latter showed a wider distribution and larger densities than the former. Three patterns of successional trends of the secondary forests were recognized : 1) rapid regeneration of C. cuspidata in secondary forests in areas near mother tree populations ; 2) development of mixed forests of C. cuspidata and Q. glauca, changing into more C. cuspidata - predominant forests ; and 3) long persistence of Q. glauca or other oaks in stressful habitats. Japanese jays (Garrulus glandarius japonicus) may play an important role in seed dispersal, particularly of acorns of Q. glauca.

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Pollen analysis of deposits from Ochiishi Mire was made with special references to the vegetation history of Nemuro Peninsula in easternmost Hokkaido since the Late Pleistocene. A landscape consisting of grassland and birch forest was seen around this area ca. 11500 years ago. Thereafter, conifers such as spruce, fir and larch began to invade and formed boreal forests. These coniferous forests, excluding larch, continuously occupied this area until ca. 6000 years ago. Though the coniferous forests deteriorated due to climatic warming, cool temperate deciduous forest has not fully developed in this area yet. The cool temperate oak forest slightly decreased and boreal birch forest developed in the peninsula ca. 2500 years ago.

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