Kushiro-Shitsugen National Park
Kushiro-shitsugen National Park is a protected wetland landscape in eastern Hokkaidō, Japan. The park covers 28,788 hectares around the lower Kushiro River and contains the largest continuous marshland in the Japanese archipelago. Its southern sector lies within the city of Kushiro, while its eastern margin extends through Kushiro Town and Shibecha. The northern and western portions occupy substantial areas of Tsurui.
The national park was established on 31 July 1987 to protect the hydrological system, peat-forming vegetation, and wildlife of the Kushiro Wetland. Its central marsh had already become Japan’s first site designated under the Ramsar Convention in 1980. Unlike mountainous Japanese national parks organized around conspicuous volcanic or alpine landforms, Kushiro-shitsugen is defined principally by slow water movement, sediment accumulation, and the ecological effects of seasonal flooding.
Physical geography
The wetland occupies a low basin near the Pacific coast of eastern Hokkaidō. During the early Holocene, rising sea level inundated much of the present basin and produced a broad marine embayment. Coastal sediment subsequently restricted communication with the Pacific Ocean, after which river-borne material and organic matter converted the former bay into a shallow lagoon. Continued accumulation of peat transformed this lagoon into the modern wetland over several millennia.
The Kushiro River crosses the park through a system of meanders whose channels migrate slowly across the floodplain. Tributaries entering the marsh carry water from forested uplands and agricultural districts around its perimeter. Their combined flow produces prolonged inundation in the central lowlands, where the shallow gradient limits drainage and reduces the rate at which decomposed plant material leaves the system.
Much of the park consists of low moor supported by groundwater and floodwater. Reed communities occupy extensive areas where water remains near the surface, while sedge-dominated vegetation develops under somewhat different nutrient and flooding conditions. Raised peat surfaces support communities whose water supply depends more directly on precipitation. Japanese alder woodland occurs along channels and in sections where sediment deposition has altered ground elevation.
Several shallow lakes lie near the eastern margin of the wetland. Lake Tōro is connected to the Kushiro River system and functions as both an aquatic habitat and a sediment-retention basin. Lakes Shirarutoro and Takkobu occupy related lowland settings, although each has a distinct balance of river inflow, groundwater exchange, and seasonal ice cover.
Ecological characteristics
The park protects a large surviving example of the cool-temperate peatlands that formerly occupied broader areas of northern Japan. Low summer temperatures and waterlogged soils restrict microbial decomposition, allowing partially decomposed vegetation to accumulate as peat. This process stores organic carbon while gradually modifying the elevation and chemistry of the wetland surface.
The red-crowned crane is the park’s most closely associated vertebrate. Breeding pairs establish territories in reed beds and sedge marshes where standing vegetation conceals nests from terrestrial disturbance. Adults feed in shallow water and on adjacent agricultural land, while winter concentrations form near sites with open water or supplementary food. The resident Hokkaidō population is geographically distinct from migratory populations breeding on the Asian continent.
Other wetland birds use the marsh during breeding or migration. Their distribution follows water depth, vegetation structure, and access to fish or aquatic invertebrates rather than the legal boundary of the park. The river system also supports the Sakhalin taimen, a large salmonid dependent on connected channels and comparatively cool water. The Siberian salamander persists in the Kushiro region as a cold-adapted species whose Japanese range is concentrated in eastern Hokkaidō.
Invertebrate communities include organisms associated with peat pools, submerged vegetation, and slowly flowing channels. The Kushiro marsh emperor dragonfly completes its larval development in cool wetland waters and represents a biogeographic connection between the marsh and northern continental ecosystems. Its habitat is influenced by local water chemistry and by the persistence of small aquatic features within the broader peatland.
Human history and protection
Archaeological remains around the wetland record repeated human use from the Jōmon period onward. Communities obtained fish and other wetland resources from the river system, while higher terraces provided relatively dry locations for occupation. Ainu communities subsequently incorporated the river and its fauna into regional systems of subsistence, travel, and exchange.
Large-scale settlement and agricultural development expanded after Hokkaidō was brought under modern Japanese administration during the nineteenth century. Drainage schemes affected peripheral land, but the central basin remained difficult to convert because of deep peat, recurrent flooding, and limited load-bearing capacity. Railway construction, peat extraction, river engineering, and urban growth nevertheless changed water movement along the wetland’s margins during the twentieth century.
The red-crowned crane was confirmed to survive in the Kushiro marshes in 1924, after the Japanese population had undergone a severe contraction. The species received designation as a natural monument in 1935 and as a special natural monument in 1952. These measures restricted direct capture and established a legal basis for subsequent habitat protection.
During the severe winter of 1951–1952, You Watanabe built a feeding ground on pasture near Tsurui and led the organized delivery of grain to cranes displaced from frozen foraging areas. The operation linked local winter feeding with protection of nearby roosting and nesting habitat, and it became part of the regional conservation framework that preceded national-park designation. Winter feeding increased survival during periods when deep snow and ice restricted access to natural food, although it also concentrated birds at a limited number of locations.
Scientific and administrative attention increasingly shifted from protection of individual cranes to preservation of the wetland system that sustained them. The central marsh was designated a national natural monument in 1967. Its inclusion in the Ramsar List on 17 June 1980 placed the area within an international framework for wetland conservation, while leaving land administration under Japanese law.
National-park designation in 1987 integrated the marsh with surrounding lakes, river corridors, and upland margins. The resulting boundary covered a larger area than the original Ramsar site because hydrological changes outside the central peatland could alter sediment delivery and water levels within it. Administration was assigned to the national environmental authorities in cooperation with the Hokkaidō government and the municipalities occupying the watershed.
Crane management
Supplementary feeding became an established component of red-crowned crane management during the postwar period. At Akan, the schoolteacher Tsuneo Takahashi established a separate feeding operation in 1952 after repeated attempts to make grain accessible under winter conditions. Setsuri Itō later created a feeding ground in Tsurui that developed into the Tsurui-Itō Tancho Sanctuary, where winter crane concentrations are managed in conjunction with surrounding farmland.
Feeding reduced mortality associated with exceptional snow cover and prolonged freezing, but it also changed the spatial distribution of the population. Dense winter aggregations facilitate transmission of infectious disease and increase dependence on landscapes outside the nesting marsh. Contemporary management therefore treats feeding grounds, agricultural fields, river roosts, and breeding territories as connected parts of the same ecological system.
Population recovery has produced additional interaction between cranes and human land use. Birds consume grain and other food in cultivated fields, while power lines and vehicle corridors create collision hazards. Protection within the park consequently operates alongside measures applied beyond its boundaries, particularly where cranes move between marsh nesting sites and winter feeding areas.
Hydrological alteration and restoration
The wetland receives sediment and dissolved nutrients from a catchment substantially larger than the national park. Agricultural drainage and channel modification in tributary valleys accelerated runoff from some peripheral areas. Increased sediment deposition raised sections of the floodplain and facilitated the spread of alder woodland into former reed and sedge communities.
Straightening of the Kushiro River also changed the relationship between floodwater and the surrounding marsh. A straighter channel conveys high flows more rapidly and reduces the frequency with which water enters portions of the floodplain. Because peatland vegetation depends on sustained saturation, even modest changes in channel position or water level can alter decomposition rates and plant composition over large areas.
The Kushiro Wetland Nature Restoration Project was organized under Japan’s national framework for ecosystem restoration. Its work has included reconstruction of meandering channels, reduction of sediment entering from tributaries, and recovery of wetland vegetation in former agricultural areas. On the lower Kayanuma reach, a previously straightened river section was reconnected to a restored meander, increasing channel length and renewing interaction between the river and its floodplain.
Restoration does not reproduce a single fixed historical condition, because the wetland developed through continuing sedimentation and channel movement before modern engineering began. Management instead uses hydrological connectivity and peat-forming processes as reference conditions. The relevant outcomes are measured through changes in water residence, floodplain inundation, sediment distribution, and the extent of characteristic marsh vegetation.
Administration and land use
Kushiro-shitsugen is administered under the Japanese national-park system, in which legal protection applies through zoning and regulation rather than uniform state ownership. The park therefore contains public land alongside private holdings and other land subject to existing rights. Protection levels vary according to ecological sensitivity and the intensity of permitted land use.
Transport infrastructure and settlements are concentrated around the perimeter, although railway lines and roads provide access to several sectors. Observation facilities at Tōro, Kottaro, Hosooka, and the western wetland margin occupy elevated ground overlooking the marsh. Their placement reflects the limited carrying capacity of peat soils and the need to restrict direct disturbance within crane breeding habitat.
Research facilities examine hydrology, vegetation change, wildlife populations, and sediment movement as interdependent components of the ecosystem. Administrative decisions use these measurements to define restoration areas and regulate development that would modify drainage. The park’s effective conservation unit consequently extends beyond its statutory boundary into the wider Kushiro River catchment.