This study examined the effects of a concrete groundsill on the survival rate of fish falling off the groundsill. The survival of river sculpin (Cottus nozawae), Siberian stone loach (Noemacheilus barbatulus toni), and four age groups of 0+, 1+, 2+ and 3+ of rainbow trout (Oncorhynchus mykiss) in Shirigishimanai Stream, Hokkaido, Japan, was surveyed before improvement in November 2000. Immediately after the experiment, we observed the survival of the fish in a tank for 10 days. The survival analysis using the Kaplan-Meier method and Log-rank test showed that rainbow trout 0+ juveniles suffered seriously from falling off the groundsill (survival rate: 73%). After constructing a water cushion on the apron, the water on the apron became deeper (before: 11.3cm, after: 77.9cm) and the current velocity slower (before: 0.75 m/sec, after: 0.09 m/sec). We conducted a second survey after the construction using 0+ juvenile rainbow trout in November 2002. The improvement increased the survival of juvenile fish (survival rate: 95%). Our study suggests that the reduced height and the water cushion on the concrete apron should benefit juvenile salmonids during up- and downstream migration.

View full abstract

Recently dam projects tend to leave forests adove the expected normal water level. However, few researchers have investigated the changes in these submerged stands following the first filling of the reservoir. Therefore, we investigated the changes in the growth increment of trees after the first filling of the reservoir behind the Miharu Dam, Fukushima Prefecture, in the Tohoku district of Japan. This study was conducted on a slope in a forest dominated by Castanea crenata and Quercus serrata. The water level twice exceeded EL. 326.5m, the height at which the lowest measured tree grew. The first time, the tree was submerged for 15 days in May and June 1997; the second time it was submerged for 89 days, from September to December 1997. After the 15-day flood, growth was not affected, but after the 89-day flood some trees that were submerged for more than 37 days died. The area of forest that was flooded for 30 days or less survived following the first filling.

View full abstract

To detect factors affecting settlement, upward migration, and subsequent survival of diadromous organisms, the relationships between abundance of diadromous invertebrates (decapod crustaceans and a gastropod) and environmental features of various rivers (amount of flow and any artificial structures) was examined among 75 rivers in Fukuoka Prefecture, Japan. Field collection indicated that the shrimp Caridina leucosticta and the snail Clithon retropictus were more abundant in rivers with larger amounts of flow, while Caridina typus occurred only in rivers with smaller flows, suggesting interspecific differences in behaviors of settlement/ upward migration. Further, C. leucosticta and C. retropictus were more abundant in rivers with dams, and C. typus was more abundant in rivers without floodgates, probably due to apparent effects by multiple correlations between the existence/non-existence of dams and floodgates and the amount of flow of each river. Effects of artificiality of riverbed/riverside and the amounts of vegetation on the abundance of each diadromous species were considerably different among species: C. leucosticta was more abundant in rivers having natural riverbeds and a water's edge with abundant vegetation, while C. typus, E. japonica, and C. retropictus were abundant in rivers with artificial riverbeds or shore protections. This interspecific difference is considered to reflect differences in ecology/behavior in freshwater areas. Neocaridina denticulate, a non-diadromous shrimp, was abundant in pools above dams. To assess the effects of artificial structures on diadromous invertebrates, one needs to focus not only on the direct effects of the structures (intercept of migration routes, etc.) but also on the indirect ones due to changes in biological environments (competition, predation, etc.).

View full abstract

Long-term competitive growth of Typha latifolia and Typha angustifolia were analyzed for evaluating the influence of latitude, nutrient accumulation in soil and preemption. The competitive analysis showed that T. angustifolia has superiority against T. latifolia without preemption even in shallow water. By the accumulation of nutrients in soil, more densely preempted T. latifolia can be displaced by T: angustifolia. T. latifolia in lower latitude is more easily displaced by T. angustifolia. Competitive analysis of Phragmites australis and Typha spp. showed that the preemption by Typha orientalis has effective only for T. latifolia and Phragmites has strong superiority against T. latifolia and T. orientalis. and has slight superiority against T. angustifolia in nutrient rich condition. The competition is related to belowground storage and utilization strategy in each species.

View full abstract

In the middlecourse of the Tama River, a typical urban river in Japan, invasion of alien plants and decline of floodplain endemic plants are remarkable. Soils were collected from the floodplains of Nagata, Sekido and Koremasa in 2001, and pH, electrical conductiv-ity, oxidation-reduction potential and water soluble ions (NO₃^-, HPO₄^2-P, Cl^-, SO₄^2-, Ca²⁺, Mg²⁺, K⁺, Na⁺, NH₄⁺) were determined to reveal the chemical status of floodplain soils in the middlecourse of the Tama River. The pH values in Nagata, where the original environment of the Tama River exists, showed alkalinity while those in Sekido and Koremasa located in more urban area were significantly low. Ca²⁺ concentration was the highest level among analyzed ions, and had strong correlation with electrical conductivity. Positive correlations were significant between NO₃^--K⁺, NO₃^-NH4⁺ and NH₄^+--K⁺, indicating that those ions were responsible for eutrophication in the middlecourse of the Tama River. Furthermore, negative correlation between pH values and NIL concentrations was observed. These results indicated that eutrophication of floodplain soils in the middlecourse of the Tama River was followed by decrease of pH values. Although high level of NO₃^- was detected in soils collected from woodland of false acacia (Robinia pseudoacacia L.) in Nagata when compared to riverbed soils of the same area, decrease of NO₃^- concentrations was found in soils collected after the floods. As HPO₄^2--P and NH₄⁺ concentrations and pH values also showed unique fluctuations, it was expected that chemical status of floodplain soils was greatly affected by floods. In our conclusion, decrease in flooding frequency, eutrophication, and following decrease of pH values could change the original condition of floodplain soils in the middlecourse of the Tama River and facilitate the invation into the floodplain of alien plants.

View full abstract

Shoots cutting of Phragmites australis is a common management to maintain botanical diversity in wetland and restore derelict wetland condition. Associated with the recent development of the dynamic growth model of P. australis the modeling of recovering process of P. australis was developed based on the experiments and energetic consideration for the possible application in the management of wetlands. Three years observations were conducted for P. australis to evaluate the recovering process in a swampy section of Akigase Park in Saitama, Japan. The growth of P. australis was impaired most by June cutting, while June and July cutting increased the ratio of the leaf biomass to stem biomass of regenerated shoot after cutting, approximately by 0.28 to 0.56. June cutting reduced the shoot height and the biomass of rhizomes and shoots markedly. P. australis community cut in summer, on the other hand, mostly recovered in two years, indicating the necessary cutting every one to two years interval. Revised model could simulate well both the observed data and literature data of cutting or burning. Consequently it is found that P. australis grow in the nutrient rich condition can recover three to four years from cutting, on the other hand that in nutrient poor condition request over ten years for recovering.

View full abstract

Papers on alien species and control measures were called for the Journal and a review paper and an original paper are included in this issue. In the review paper, Miyawaki and Washitani describe the present situation of invasive alien plants in riparian habitats of Japan based on the monitoring data obtained by the Ministry of Land, Infrastructure and Transport, and propose an ecosystem approach for the management of the invasive species populations in order to conserve biodiversity in riparian plant communities. The original paper by Tamura et al. deals with distribution patterns of an invasive Formosan squirrel in urban areas and concludes that size of the forest with broad-leaved evergreen trees is an important factor for successful invasion by the squirrel. It indicates that habitat restoration in urban area might result in helping invasion of some alien species. This is a reason why we should investigate on uninvasibility of natural communities to apply the mechanisms to habitat restoration in ecosystem management. In this paper, a model for judging investment ratio of direct community manipulation to habitat manipulation (Community-Habitat Investment Model) was proposed.

View full abstract

Native riparian plant communities are profoundly threatened by invasions of alien plants in Japan. At present, the proportion of vegetation area dominated by alien plants accounted for about 15 percent in the rivers administrated by the Ministry of Land Infrastructure and Transport. Displacement of native plant communities by invasive alien plant species is altering riparian ecosystems substantially. To preserve riparian plant communities, active management to suppress the dominance of invasive alien plants is urgently required. Weed control methods in agricultural ecosystems, which usually have strong side effects on various organisms and tend to simplify the ecosystem, are not suitable for the control measures for biodiversity conservation. Ecosystem approaches, focusing both management of invasive species and restoration of sound ecosystems simultaneously are desirable. Ecosystem management on the invasive species populations and habitat restoration should be based on sufficient information on the population ecology, and the causal factors enhancing ecosystem invasibility.

View full abstract

A hundred of woods, ranging in size from 0.17 to 39.17 ha, were surveyed in Ohuna, Kanagawa Prefecture, and presence/absence data of the invasive Formosan squirrel were collected from December 2001 to December 2002. The Formosan squirrel was ascertained in 42 woods of them. We measured 11 environmental variables of each wood, those are, wood area, distance to the nearest neighbor wood, distance to <5ha wood with squir-rels, percentage of broad-leaved evergreen trees, conifer trees, deciduous trees, or others, and percentage surrounded by cultivated field, residential quarter, road, or others. The most important variable for the occupancy of squirrel was the woods area. The percentage of broad-leaved evergreen trees in woods and the percentage of cultivated field in surrounding area had also positive effects on the presence of squirrel. By adding latter two variables to the woods area, the logistic regression model was improved to account for the probability of the Formosan squirrel in isolated woods (Cox & Snell R²=0.45, P<0.001). Current expansion of this species in Kanagawa Prefecture was explained by these environmental variables; large woods with broad-leaved evergreen trees have been reserved in Kamakura and Zushi City, a center of distribution of the Formosan squirrel. Further studies using the present model will be necessary to know how the Formosan squirrel expands in future through urban environments.

View full abstract