Increasingly, recent dam projects have left forests that are above the expected normal water level. However, few researchers have investigated the changes in these inundated stands following first filling. We therefore investigated changes in the composition of the vegetation community after first filling at the Miharu Dam, Fukushima Prefecture, in the Tohoku district of Japan. This research was conducted on transects established in a forest dominated by Castanea crenata and Quercus serrata. A survey conducted in the year following first filling revealed that trees that were submerged for 53 days died. Significant changes were observed in the vegetation community in the lower parts of the slope, between EL. 326.0 and 329.0m, in areas that were submerged for about 37 days. Pioneer species such as Rubus crataegifolius increased in areas with decreased canopy cover. The main factor contributing to the changes in the community composition was probably the change in light conditions following the death of trees. The upper 4m (EL. 329.0-333.0m) of the 7m slope affected by first filling were inundated for less than 37 days. All trees in this area survived, and only minor changes were observed in the shrub and herb layers, suggesting that the forest was preserved.

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Quercus serrata secondary forests are one of the most typical coppice woodland types in Japan. They had been maintained as a source of fuel, manure and material for various uses until the late 1960s in Japan. However, for the last 30 years, most of them have been abandoned, and without regularly cutting and clearing changes in plant species richness and composition have occurred. In this study, we observed changes in the species richness and composition in two major types of Quercus serrata communities (Quercetum acutissimo-serratae Miyawaki et K. Fujiwara 1968 (QA) and Castaneo-Quercetum serratae Okutomi, Tsuji et Kodaira 1976 (CQ)) in Kanto region, Central Japan by revisiting 113 old plots investigated from 1974 to 1980 (SI). Seventy-five plots out of 113 plots (66.4%) remained as Quercus serrata forests in our follow-up survey from 2000 to 2001 (SII). The remaining rate of CQ plots (75.0%) was larger than that of QA plots (60.0%). Species richness (number of vascular plants per plot) in SII is not significantly different from that of SI. Species richness in each plot is significantly related to Pleioblastus chino cover and evergreen trees cover including Pleioblastus chino in QA, and management condition in CQ. Change of QA's species composition from SI to SII is significantly larger than that of CQ. Compositional change in each plot is significantly related to woodland proportion of the municipality where each plot is located in QA, and slope degree, litter cover and evergreen trees cover in CQ. Most of decreasing species from SI to SII were anemochory while increasing species included a lot of zoochory (mainly endozoochory). Increasing species from SI to SII include a lot of garden or greening plants probably dispersed by birds from nearby streets, parks and cemeteries. Those plants significantly increased, especially in fragmented forests in urban areas where population densities rose considerably from SI to SII. In order to manage Quercus serrata forests appropriately, long-term changes in species composition as well as species richness need to be monitored in consideration of the locational conditions surrounding the forests on a regional scale.

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The distribution of Heritiera littoralis in Nansei-Shoto was examined in a field survey (1996-2001) and literature search. The field survey confirmed the distribution of H. littoralis in Okinawatou, Isigakijima, Iriomotejima, and Taketomijima, and it has also been reported in Amamioshima, Ukeshima, Miyakojima, Irabujima, and Haterumajima. H. littoralis was confirmed at 69 sites in this study, and for the first time in 38 of these. Populations at three sites were confirmed to have become locally extinct between 1926 and now. Most of the H. littoralis stands were in floodplains in downstream regions (29 sites), but some stands were along the seashore (7 sites) or in landslide patches and streambeds in upstream regions where rocks and gravels were deposited (6 sites). In all cases, H. littoralis habitat consisted of sites submerged by flowing water including spring water seeping out from the soil, stream water and tidal water.

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Suspended solids (SS) often run off from paddy fields during puddling for rice transplanting. Because SS adsorb and transfer hazardous chemicals such as persistent organic pollutants, they are expected to reduce SS in runoff from paddy fields. In late April-early May 2002, at eleven plots around Tsukuba City in Ibaraki Prefecture, we evaluated the ecosystem function of aquatic vegetation around paddy fields to retain SS during puddling. The plots were classified into four vegetation types, Arundinella hirta-Isachne globosa community, Equisetum palustre community, Leersia japonica community and Oenanthe javanica community, based on an ordination diagram of detrended correspondence analysis (DCA) and dominant species of the plots. The aquatic vegetation removed 46-98% of total SS (TSS), with an average of 72%, and TSS concentrations measured at six plots in effluent water from the aquatic vegetation were below 0.1g/L, thus satisfying the effluent standards for agricultural lands discharging into rivers. Removal rates of TSS increased with increasing vegetation biomass index (vegetation cover (%)×vegetation height (m)) up to 80, and were consistently about 95% at higher values of the index. The removal rate was positively correlated with the plant cover of Solidago altissima but not correlated with scores for the first and second axes of DCA. The particle size of SS peaked at 10-30μm in effluent water from paddy fields, and aquatic vegetation efficiently removed SS less than 30μm in diameter. These results suggest that aquatic vegetation with a large biomass has a high potential to reduce SS runoff from paddy fields.

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We investigated the establishment condition of the riparian forest dominated by Celtis sinensis var. japonica and Aphananthe aspera, which are deciduous broad-leaved species widely distributed around rivers in the warm-temperate regions of Japan. The establishment of C. sinensis var. japonica and A. aspera was related to the frequency of flood disturbances. The riparian forest dominated by these species grew on the floodplain, where the average frequency of flood disturbance was 1.3 days per year for 16 years. The development of the riparian forest was prevented on the lower part of the plain, which had more frequent flood disturbances (13.8 days per year). On the alluvial plain outside the riverbank with less frequent flood disturbances, isolated tree remnants consisted of several climax evergreen species of the region, including Machilis thunbergii and Castanopsis cuspidata var. sieboldii, in addition to C. sinensis var. japonica and A. aspera. Thus, the riparian forests dominated by C. sinensis var. japonica and A. aspera must be maintained by the intermediate frequency of flood disturbances.

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