This paper aims to propose the adequate buffer widths for preserving the ecological functions of riparian forests by reviewing both Japanese and international literatures and guidelines. The result of our review indicates the wide variations in the proposed buffer widths probably due to the differences in environmental backgrounds at each study site. The recommendation for the adequate buffer width for the conservation of each function is, thus, made considering Japanese landscape and vegetations. Approximately 30 m is required for maintaining shading effects and the provision of organic litter and woody debris which are especially important in the headwater to 3rd order mountainous streams. Water quality control is, on the other hand, more crucial in larger floodplain rivers with high potential of contaminations associated with urban development and agriculture. Regarding this function, 10-20m buffer width is proposed as the minimum value in the literatures reviewed. The buffer width for aquatic habitat conservation should be determined by linking with other ecological functions, such as shading and organic litter input, thus about 30m is recommended in mountainous streams. Riparian forest functioning as habitat and corridor for terrestrial animals has different requirement for its width depending on the targeted species. Most of the recommended widths fall into the ranges up to 100 m and 200 m for the conservation of amphibians, reptiles and mammals and that of birds, respectively. Although this review focused mainly on the width of riparian forest, the future studies should put an emphasis on the longitudinal continuity along river or the whole stream net-works for the establishment of more appropriate guidelines.

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We studied that maintenance work on the irrigation ditches in Akita Prefecture had effect on the nest building conditions of Pungitius pungitius and examined methods for the conservation of their nesting habitats. As a result of the action of maintenance work once between May and August compared with a single maintenance work done at the beginning of May, the number of nests decreased from 36 to 14. When frequent maintenance was carried out, the water level fell, the water velocity got faster at nest sites and the number of aquatic plants that were capable of supporting nests decreased. For the conservation of the nest-building environment, management of maintenance activities in areas other than those that the ninespine stickleback, Pungitius pungitius use for nesting and management of the plants that need to be eliminated is essential. As for methods of conservation nesting habitats and improvement ability of flow, we proposed maintenance work with conservation area. The conservation area is a 50-60 m section of curved area where Sparganium japonicum communities grow and a 50-72 m section of the right bank where Acorus gramineus communities grow.

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We evaluated whether bird-dispersed tree species, which were planted for landscaping and would be used by birds as perches, facilitated the colonization of bird-dispersed plants beneath them. We compared the composition of both bird-dispersed seeds and plants beneath bird-dispersed perch trees that bore fleshy fruit (summer-fruiting Prunus yedoensis, n=9; autumn-fruiting Sorbus commixta, n=10), wind-dispersed perch trees (Pinus thunbergii, n=10), and a tall grass (Miscanthus sinensis, n=10) on man-made slopes alongside a road. Seeds that had fallen beneath the 29 perch trees and in the 10 grass sites were collected both in early summer (30 days) and from autumn to winter (150 days) in 39, 1-×1.5-m seed traps made from 0.86-mm, mesh polyester cloth. To sample bird-dispersed plants that had colonized sites beneath the perches, four 1-×1- m quadrats were established in late summer near each of the 39 seed traps. Both the numbers and species of bird-dispersed seeds recorded were highest beneath bird-dispersed perch trees and intermediate beneath wind-dispersed perch trees compared to tall grass. The seed rain was higher beneath bird-dispersed perch trees whose fruiting season overlapped with the fruiting season of the seeds than beneath those did not overlap. Similar trends were also found in the plants surveyed in the quadrats. Thus, bird-dispersed perch trees played an important role in facilitating the colonization of bird-dispersed plants, particularly plants whose fruiting season overlapped with the fruiting season of the perch trees. This suggests that perch trees used in landscaping act as attractive plants to frugivorous birds and can aid in the restoration of natural vegetation.

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Multivariate analysis of ecological data has been applied to environmental analysis and evaluation. Recently, some ecologists reported that classification and regression trees (CART) are ideally suited for the analysis of complex ecological data. We use classification tree to analyze the relationship between avian species composition and habitat conditions from 37 study plots located in a riparian area of the Tama-gawa River, Tokyo. The data were comprised of census data of birds and vegetation structural information. First, the study plots were classified by TWINSPAN based on the avian species composition. Then, we tried to recover the grouping of the study plots by classification tree or canonical discriminant analysis using the vegetation structural information so that we could find the relationship between avian species composition and vegetation structure. Classification tree analysis performed almost as well as canonical discriminant analysis. Classification tree models explain variation of a single response variable (here, avian fauna type) by repeatedly splitting the study plots into more homogeneous groups, using combinations of explanatory variables (here, vegetation structural parameters). This structure is simple, suitable for dealing with high-order interactions, so that classification tree can give easily interpretable results. Finally, based on the comparison of classification tree and canonical discriminant analysis, we concluded that classification tree was more suitable than discriminant analysis for landscape evaluation and planning.

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In Japan, river training projects designed for efficient flood control, have turned meandering rivers into straight and monotonous concrete-lined channels. Although these measures have been effective to mitigating flood damage, they have had considerable adverse effects on the natural environments of rivers. In its 1981 report, the River Council, an advisory council for the Minister of Construction (now the Minister of Land, Infrastructure and Transport), stressed the importance of managing the river environment so that the flood control, water utilization and river environment goals can be achieved harmoniously. In 1990, a government notification concerning the "nature-oriented river works" was issued, and "nature-oriented river works" measures designed to "conserve or create scenic natural landscapes" were taken on a pilot project basis in many parts of the country, taking natural riverine habitat requirements into consideration. In 1997, the River Law was amended, and "improvement and conservation of river environment" was incorporated as one of the goals of the law. Under this amendment, efforts to conserve and restore river environments were upgraded, and measures such as full-scale implementation of "nature-oriented river works" projects, amendment of related standards and the establishment of Aqua Restoration Research Center have been taken. Most of the conventional "nature-oriented river works" projects had focused only on limited aspects of channel protection or improvement, such as the conservation and restoration of riparian zones, conservation and restoration of channel forms in certain river sections, conservation and restoration of streamside woods and the reduction of the environmental impact of river improvement works. This paper introduces two pioneering river plans (the Kitagawa River in Miyazaki Prefecture and the Otogawa River in Aichi Prefecture) drawn up from the viewpoint of the conservation of the natural river environment. This paper also describes the concept and scope of "nature restoration projects" (instituted in fiscal 2002) designed primarily to restore the natural environments of rivers, lakes and ponds, and wetlands lost as a consequence of human activities. Finally, the paper discusses the roles that have been played by "nature-oriented river works" projects, as well as the next challenges to be addressed in connection with the conservation and restoration of natural river environments.

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A river floodplain and wetland ecosystem is characterized by 1) interaction between terrestrial and aquatic ecosystems, 2) material flows such as sediment, organic matter, nutrients and heat energy moving from headwaters to the river mouth, and 3) flood pulse disturbances which inundate the floodplains. Unfortunately, rivers and floodplains (wetlands) in Japan no longer have these dynamic processes and interactions. Therefore, these fundamental characteristics should be revived through restoration projects. 'Restoration' using the strictest definition is a return to the original condition prior to human-induced damage. In many cases in Japan, however, self-sustaining ecosystems that provide important functions and habitats can often encouraged, which is called 'rehabilitation'. Restoration projects proceed with clear objectives and targets. Before and after the implementation of a restoration project, well-designed monitoring should be followed and the results should be available to the general public. Ideally, the monitoring should be a Before-After-Reference-Control-Impact (BARCI) design, but there are many cases where no reference areas can be found near the restoration site or no replications were set because of large-scale project. The detail baseline data is required to implement field experiment, and those basic information as well as experimental results should be disclosed to general public through Internet. The most important principle in restoration projects is not the active intervention of humans, but "passive restoration", which removes the limiting factors that continuously damage the present ecosystem. Take this first step and the resilient ecosystem will recover. In the Kushiro Mire, the largest in Japan, the prevention of sediment inflow, by establishing riparian forests and sedimentation ponds, is being planned and reclamation of abandoned pastures for wetlands is in progress. Projects to restore the original meandering channel and floodplains will be launched in the Kushiro and Shibetsu Rivers. These are pilot projects for the restoration of large ecosystems in Japan and adaptive management processes are being applied. Currently, an experiment to control the expansion of alder forests, by artificially raising the water table, is being conducted in the Kushiro Mire. Another experiment, where stream water was drained from the main channel of the Shibetsu River into an oxbow lake, is being evaluated for its ecological effects on river geomorphology, hydraulics, the food web, fish, vegetation, and water quality.

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The Keihin River Works Office, the Tama River Ecological Research Group and citizen groups have planed an interesting river restoration project at the Nagata Area in the Tama River. Although the big gravel bar was seen 20 years ago in the Tama River, it is covered with the forest today. Some specific species depending on gravel bars have been endangered. Therefore, restoration project started in the Tama River in 2001. Some woods were cut, a part of riverbed was excavated and gravel bar was restored. Now, it is under verification about its effect. The argument piled up repeatedly about the restoration method. Here, the process of the argument and restoration methods are described and discussed.

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Wide-spread ebb tidal flat has been lost around the river mouth area of the Kiso, Nagara and Ibi Rivers due to the ground subsidence in the Nobi Plains since 1965. Recovery of ebb tidal flat once lost to create the waterfront with a variety of lives without hindrance in river rehabilitation can contribute rehabilitation of river environment. To this purpose, beach nourishment by using sand dredged from the river channel was planned and carried out in front of the river revetment in the regions separated by groins. As a result, the intertidal zone with much biodiversity between mean tide level and mean low water level was widened due to the action of wind waves. Stable beach was formed by the construction of groins and river environment with a variety of lives was recovered corresponding to the distribution of well-sorted bed materials and water depth of the intertidal zone.

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Aqua Research Restoration Center (ARRC) which was established in 1998 in Gifu Prefecture, has three Experimental Streams. Three streams have the length of approximately 800 m, and the bed slope from 1.2% to 3.33%. The Stream A is a straight channel and the Streams B and C have two meandering sections Electrical fishing surveys were conducted from July to December in 1999 in order to clarify relative variation in fish abundance among the three streams. The fish surveys resulted in the higher abundance in the Streams B and C than in the Stream A, and a relationship between habitat types and the number of individuals in the three streams were analyzed to specify the factors influencing the relative abundance of fish in the two types of streams. The habitat types were partitioned into a lotic zone and a water-edge from the lateral view of a cross section. The lotic zone was subdivided into riffles, pools, runs and glides, and the water-edge was subdivided into "vegetation" and "no-vegetation". A statistic analysis proved that several sequences of riffles and pools contributed to the relative abundance of fish in the Streams B and C to Stream A, however, the vegetation at water-edge did not function in the enhancement of fish abundance compared with the riffles and pools. These results will show that we should pay much attention to the habitat structure in the lotic zone in river works such as river restoration

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