Tundra-like habitat can be found at high elevations in the alpine zone of the Japanese Alps [above MAB; below CC]; inset Spotted Nutcracker [JW].
NATURAL ECOLOGY
The Habitats of Japan
The complexity of Japan’s scenery (both sea-bound and intensely mountainous), its geographical spread and location, general topography and climate, and the range of soils, all combine to produce and support an astonishing variety of habitats, providing homes for a diverse array of plants and animals.
Japan’s main terrestrial habitats include the upper slopes of towering volcanoes, such as Mt Fuji, and high montane ridges and cliffs, as in the Japanese Alps, down to low coastal areas including lagoons and swamps at sea level or barely above. The mountainous nature of the country helps to drive its regional and seasonal climatic variation and the distribution of biomes.
For its size, Japan has great climatic variation. Hokkaidō’s subarctic winters with frigid seas and sea-ice contrast with the subtropical waters of the Nansei Shotō (the southwestern islands) and the Ogasawara archipelago. A steep altitudinal gradient, from sea level to 3,776 m, combined with a rich variety of habitats and species, creates much interest for the eager naturalist.
Japan’s many rugged, sharply ridged and steeply flanked alpine peaks, some soaring to over 3,000 m, support habitats that include alpine flower meadows near their summits, with juniper and dwarf conifer forest lower down. In the northern half of the country, the lower flanks of the mountains support many deciduous broadleaf forest species, while in the southern half the same slopes support a wide range of evergreen broadleaf species. In the north, particularly in Hokkaidō, the forests take on a more clearly boreal aspect and support Brown Bears, while the coast in winter appears more subarctic, with Northern Fur Seals, Steller’s Sea-Lions and Sea Otters offshore. In the south, the forests are clearly more subtropical, and in the far south, notably the Nansei Shotō, tree ferns and cycads (Japanese Sago Palm)grow wild. At certain of the river mouths there are mangroves, while offshore there are coral reefs, rich in tropical fish, along with marine turtles, rays, sharks and dolphins. In the past, Japan had extensive inland, riverine and coastal wetlands with numerous lakes, ponds and swamps in riverine plains and coastal lowlands. Although many of these wetland habitats have long since vanished, mainly through agricultural conversion, because of their fertility, some significant remnants do survive.
Wetland habitats include brackish coastal lagoons [MAB].
In Hokkaidō, alpine tundra can be found in the Daisetsu Mountains [MAB].
Temperate montane forest in northern Honshū is dominated by deciduous species [MAB]; inset Japanese Badger [IiM].
In Japan, the alpine tundra-like habitat, which occurs above the tree line, recalls the ecologically similar high-Arctic tundra beyond the tree line in northeastern Russia. Both are dominated by prolonged periods of freezing, with brief, intense summers. At slightly lower elevations and in the north, habitats are of a more boreal nature, dominated by mixed forests combining spruce, fir and a range of deciduous species, including oaks, elms, birches and alders. These regions experience extremes of climate, with prolonged winters, locally heavy snowfalls and frozen streams, rivers and lakes, and with extensive sea-ice in the Sea of Okhotsk reaching Hokkaidō.
At middle elevations, and dominating much of northern Japan, the habitats are essentially temperate, experiencing well-defined seasons, and with forest dominated by deciduous species and even some pines. Central and western Japan, which lie within the warm temperate zone, have more extensive broadleaf evergreen forest species and more pines. In certain regions, there are restricted areas of both lowland and upland grasslands and, in a confined area of Tottori Prefecture on the Sea of Japan coast of western Honshū, desert-like sand dunes exist.
Freshwater habitats range from montane streams and large rivers to brackish coastal lagoons and inland freshwater lakes. Lake Biwa, in Shiga Prefecture, Honshū, is one of the oldest extant lakes in the world. Offshore, there are coral reefs and seagrass beds in the south, while in the north there are kelp beds and sea-ice.
Alpine–Subarctic Habitat
Looking at Japan’s habitats in a little more detail, we find that they vary from north to south in a pattern that is mirrored in elevation, from higher to lower levels. Northern Japan, especially Hokkaidō, experiences long subarctic winters, and short mild to warm summers. It has habitats typically considered boreal.
Long, subarctic winters are typical of northern Japan, here in east Hokkaidō [YM].
Permanent snowfields, stony tundra and Japanese Stone Pine can be found in the Daisetsu Mountains of central Hokkaidō [left MAB; right KM].
Above the tree line (about 1,500 m in the higher mountains of Hokkaidō, and about 2,500 m in central Honshū), there is rocky or stony, tundra-like high-alpine habitat. Few birds frequent this habitat in Hokkaidō, but in certain areas of central Honshū it is home to such species as Rock Ptarmigan [VU] and Alpine Accentor. This habitat is dominated by very prolonged periods of winter freezing, with only brief, intense summers. Above this zone there is only bare rock. Just below the tundra/alpine zone there is commonly a belt of hardy Japanese Stone Pine. This habitat supports a range of species, among them Spotted or Eurasian Nutcracker, Siberian Rubythroat, Japanese Accentor and Pine Grosbeak (the last in Hokkaidō only).
Much of the mid-elevation mountain slopes of Hokkaidō (as low as sea level in the east) and northern and central Honshū support mixed taiga/boreal-like forests. These include Erman’s Birch, along with spruce and fir species. These habitats hold a range of bird species, including Eastern Buzzard, Hazel Grouse (Hokkaidō only), Black Woodpecker [VU] (Hokkaidō and northernmost Honshū), White-backed Woodpecker, Great Spotted Woodpecker, Japanese Pygmy Woodpecker, Brown-headed Thrush, Japanese Thrush, White’s Thrush and Siberian Thrush, Japanese Robin, Red-flanked Bluetail and Sakhalin Leaf Warbler.
Northern Japan has very prolonged, severe winters dominated by cold airflows from the continent to the northwest and north, leading to low average temperatures, frozen lakes and rivers, locally heavy snowfalls and, along the shore of the Sea of Okhotsk, extensive sea-ice during late winter. In contrast, regions in the far south, especially the Nansei Shotō and the Ogasawara Islands, are subtropical year-round. These areas are affected by warm airflows from the south, southeast and southwest, and are warm to hot, with high average annual temperatures and high humidity throughout the year, and high average rainfall. Much of Central Japan belongs to the temperate climate zone, but with northern regions having longer winters and shorter summers and southern and western parts having shorter winters and longer, hotter and humid summers.
Japan also spans different climatic zones from east to west. The Sea of Japan coastal climatic zone is characterized by heavy winter snowfalls and mild summers, whereas the Pacific coastal zone typically experiences colder, cloud-free winter weather with little or no snow, but hot and humid summers.
A relict population of Rock Ptarmigan still survives high in the Japan Alps of Honshū. Ptarmigan are cryptically plumaged in each season [BOTH YM].
Mixed taiga- or boreal-like forest flanks the volcanoes of Hokkaidō. The Shikotsu Caldera is shown here, with Lake Shikotsu and the volcanic peaks of Tarumae and Fuppushi [MAB].
Mid-elevation forest in the mountains of central Honshū [MAB]
Cool temperate forest in northern Honshū; Katsura (inset) is a fairly common species in such forests [BOTH MAB].
Warm temperate mixed forest in central Honshū is home to many broadleaf evergreen trees and bamboos [left MAB; right ChM].
Cool Temperate Habitat
The dominant forest habitat of southwestern lowland Hokkaidō, and throughout northern and central Honshū at mid-elevations to lower elevations, is mixed temperate forest. The diversity of tree species here is considerable1, and includes many familiar and unfamiliar species. The most recognizable, for those from outside the region, will be the pines, larches, oaks, elms, maples, magnolias, azaleas and mountain cherries. These forests support a high diversity of resident birds and summer migrant birds, among them various owls, cuckoos, thrushes, flycatchers and warblers, as well as Copper Pheasant, Japanese Sparrowhawk, Grey-headed Woodpecker (Hokkaidō only) and Japanese Woodpecker (Central Japan only).
Warm Temperate Habitat
The warmer areas, from central Honshū westwards to Shikoku and Kyūshū, support a very mixed forest, some of which is typically temperate deciduous, as in cool temperate forests farther north, but with an increasing proportion of broadleaf evergreen trees and tall bamboos to the west and south. These forests hold many of the same bird species as are found farther north, but with the addition (or higher densities) of species such as Grey-faced Buzzard, Ruddy Kingfisher, Japanese Paradise Flycatcher and, very locally, Japanese Night Heron [NT], Fairy Pitta and Dollarbird.
Subtropical forest with Itaji Chinkapin on Okinawa [KuM]
Subtropical forest on the island of Amami Ōshima is home to various endemic species including Lidth’s Jay (inset) [BOTH TsM].
Subtropical-forest species include the wide-ranging Orange Oakleaf Butterfly (left) and the Ryūkyū Island endemic Okinawan Oak (right) [BOTH KuM].
Subtropical Habitat
The Nansei Shotō (or Ryūkyū archipelago) and the Ogasawara Islands support subtropical habitat and a very distinctive flora and insect fauna, with many endemic species. The stature of the forest trees in these areas is low, the canopy height surprisingly uniform, but tree-species diversity is high and the majority of these are broad-leaved evergreens.
The year-round climate in the northern islands is humid and subtropical while in the southern islands it is tropical. Summers are hot and winters are warm. Precipitation is very high, but largely concentrated in the early summer rainy season and the late summer to autumn typhoon season, when the islands may be battered by frequent storms.
Japan’s subtropical islands support many resident avian endemic species and unique subspecies, among them Pryer’s Woodpecker [CR], Owston’s Woodpecker [EN], Okinawa Rail [EN], Ryukyu Green Pigeon, Ryukyu Scops Owl, Lidth’s Jay [VU], Amami Thrush [CR], Ryukyu Robin [VU] and Bonin Honeyeater [VU].
Pryer’s Woodpecker is endemic in the forests of northern Okinawa [ImM].
Grasslands
In certain parts of Japan there are restricted areas of grassland habitat, which may be either dry or wet. They include high-altitude meadow-like grasslands with considerable amounts of dwarf bamboo, these being commonly dominant around upper volcanic slopes and other areas exposed to strong winds. They include also diverse vegetation around alpine ponds or peat swamps, and reedbeds around wetlands at lower elevations. Grassland in Japan is not usually climax vegetation, but a stage of plant succession controlled by mowing, burning or grazing. The only truly natural grassland communities are those of windswept capes, windswept mountain tops and the alpine zone. A representative tall-grass grassland species is Maiden Silvergrass. These grassland areas may support Green Pheasant, Latham’s Snipe [NT], Common Cuckoo, Meadow Bunting, Stejneger’s Stonechat, Long-tailed Rosefinch and Chestnut-eared Bunting. Few bird species take advantage of stands of bamboo grass, but three that do are the native Japanese Bush Warbler, the summer visitor Asian Stubtail, and the introduced but now well-established Red-billed Leiothrix.
Japan’s surviving reedbeds (once clearly a major habitat to judge from historical drawings and paintings) are home to a range of bird species, among them Eurasian Bittern [CR], Yellow Bittern, Eastern Marsh Harrier [VU], Red-crowned Crane, Ruddy-breasted Crake, Marsh Grassbird [EN], Oriental Reed Warbler, Black-browed Reed Warbler and Japanese Reed Bunting [VU]. The reed and grass fringes of wetlands support various warblers locally in Hokkaidō, examples being Sakhalin Grasshopper Warbler, Middendorff’s Grasshopper Warbler and Lanceolated Warbler, and at the interface between such grassland areas and woodland or agricultural areas in Central Japan there may also be Green Pheasant and Chinese Bamboo Partridge.
Grassland at 1,400 m at Senjōgahara in Nikkō National Park, Tochigi Prefecture [MAB]; inset Green Pheasant [MC].
Japan’s endemic Green Pheasant favours grassland habitats [AK].
A ubiquitous and prominent songster, Japanese Bush Warbler, is often found among dwarf bamboo [SP].
Bamboo species in Japan range from giants to dwarfs [MAB].
Dwarf Bamboo is the dominant ground cover in much of Japan [MAB].
Dry grassland habitat at Kirigamine Kōgen, Nagano Prefecture [MAB].
Wetlands
The native wetland habitats of Japan range from alpine ponds, peat swamps, montane streams, short fast-flowing rivers, freshwater lakes and reservoirs to fresh and brackish coastal lagoons and estuaries. While the first of these are mostly sterile from an avian perspective, as one descends towards lower elevations such species as Great Cormorant, Mandarin Duck, Long-billed Plover, Crested Kingfisher, Common Kingfisher, Brown Dipper, Japanese Wagtail and Grey Wagtail are increasingly likely, depending on the substrate. At 670 km2, Lake Biwa, in central Honshū, is Japan’s largest and oldest lake, formed about 5 Mya. From Hokkaidō to Kyūshū, there are many much younger volcanic caldera lakes. Lakes at low elevations in Hokkaidō and northern and western Honshū support considerable numbers of wintering or passage-migrant waterfowl, among them swans, geese and ducks. Coastal estuaries and mudflats attract large numbers of herons, egrets, spoonbills, gulls and ducks, and at certain seasons a wide range of migratory shorebirds, notably in western Japan. In southern Japan especially, estuaries and mudflats attract wintering Black-faced Spoonbill [CR] and Saunders’s Gull [VU], both of which are globally restricted and rare species.
Mandarin Duck breeds along forested mountain streams at middle elevations [FT].
Native wetland habitats are diverse and include mangroves and mudflats in the southwestern islands [TsM]; inset Western Osprey, a fish-hunting specialist, is frequently found at river mouths and at mangrove areas in the south [MC].
Wetland habitats are among the most threatened in Japan [BOTH MAB].
Numerous shorebirds rely on coastal wetlands and mudflats [left NS] while birds such as the Black-browed Reed Warbler [right SP] favour damp areas with reedbeds.
Shingle- and rocky-bedded rivers at low elevations, here in Kyūshū [MAB], are the habitat of numerous fish species as well as Long-billed Plover [inset KT] and Japanese Wagtail.
Cultivation
Around 70 percent of Japan is mountainous, and about half of the remaining 30 percent has been developed for industry or urbanized, leaving only a small proportion of the country suitable for agriculture. Japanese crops include apples and citrus fruits, pineapples, potatoes and sugarcane, along with tea, rushes, sugar beet and silkworms. The most common crop, in terms of area, remains rice. Japan was once rich in inland river-plain wetlands and coastal wetlands, but most of these have been lost as a result of drainage. Extensive areas of wet rice cultivation do, however, provide alternative homes for certain wetland species, including insects, fish, amphibians and birds.
Cultivation has been ongoing in Japan for millennia: here in Kagoshima Prefecture, Kyūshū [above left MAB] and on Sado Island, Niigata Prefecture [above right and below SAKP].
Agricultural areas, particularly rice fields, support many commensal species, and where rice fields are retained wet, or where they are farmed organically or at low intensity, as in the traditional satoyama system (which combines small-scale use of arable land and mountain foothills), they support many uncommon and several endangered species of amphibian. Common bird species here include the endemic Green Pheasant, the ubiquitous Black-eared Kite, a range of egrets and herons, various shorebirds on migration, Oriental Crow and Japanese Crow, White-cheeked Starling, buntings and finches in winter. Very locally one can find Crested Ibis (Sado Island), Oriental Stork (Hyōgo Prefecture), Greater Painted Snipe, Hooded Crane [VU] and White-naped Crane [VU] utilizing farmland year-round or in winter.
Traditional satoyama agriculture combines small-scale use of arable land and mountain foothills [left; MAB; right ChM].
The Urban Environment
Around 78 percent of Japan’s 126 million people live in urban areas (45 percent in Tōkyō, Ōsaka and Nagoya combined). The urban environment is very densely developed, leaving little habitat even for commensal species. City parks, however, can attract surprising numbers of birds, especially during winter and on migration. Japanese Crow, Feral Pigeon (or Rock Dove), White-cheeked Starling, Brown-eared Bulbul and Eurasian Tree Sparrow are the most widespread resident species in the largely asphalt, concrete and glass desert of the urban environment.
Rice fields, here in Hokkaidō [MAB], provide Japan’s staple diet and now offer the most widespread wetland habitat in the country. Some species, such as Greater Painted Snipe [inset KT] in Honshū, are at home in cultivated wetlands.
Some of the most crowded real estate on Earth is in Central Tōkyō [MAB].
Even in the urban setting some commensal species manage to make themselves at home [TK].
The Coast and Offshore Islands
Japan’s coastline extends over about 29,000 km and experiences a great range of environmental conditions. Northern coastlines are arctic-like, blasted by wintry northern winds, lashed by frigid waters and strongly influenced by winter storms, sea-ice and the southward-flowing cold Oyashio current. Southern coastlines are subject to almost subtropical conditions, lapped by warm tropical seas and strongly influenced by typhoons, tropical storms and the warm, north-flowing Kuroshio current.
Japan’s natural coastline is largely rocky, as here on Minami-shima, in the Ogasawara Islands [MAB].
Coastal erosion, winter storms, typhoons and tsunami all drive the construction of coastal defences [MAB].
A beautiful beach scene in northern Amami Ōshima [TsM].
Rocky shores, especially, are the domain of Temminck’s Cormorant and Red-faced Cormorant (eastern Hokkaidō only). Where there are sheltered bays, these may be frequented by winter gatherings of Whooper Swans or Bewick’s Swans, and numerous other waterfowl; and where there are eelgrass beds Brent Geese [VU] may be encountered. Offshore, migrant seabirds such as loons (known also as ‘divers’), grebes, sea-ducks and Streaked Shearwaters may be found, depending on the season. In warmer regions, there are Pacific Reef Egrets and Eastern Blue Rock Thrushes (north to southwest Hokkaidō). In the southernmost regions, particularly in the Nansei Shotō and Ogasawara Islands, there are offshore coral reefs and seagrass beds, coral-sand beaches and, at some river mouths, small areas of mangrove forest.
Left The world’s largest Rhinoceros Auklet colony is located on Teuri Island [MR]; right Tufted Puffin ranges around the Bering Sea and North Pacific and just reaches Japan in southeast Hokkaidō [WaM].
The Japanese archipelago consists of several large, densely populated islands, a number of smaller populated islands, and thousands of very small islands and rocky islets most of which are unpopulated2. The majority of the islands close inshore are eroded fragments of what once were much larger islands, but some, and mostly the more distant ones, are oceanic – the tips of submarine volcanoes that have never been connected to the mainland.
The larger islands in the Sea of Japan, from Tsushima north to Rishiri, are well-known migrant traps, where numerous avian vagrants to Japan have been reported. Smaller islands provide breeding grounds for significant numbers of seabirds. Teuri-tō, off west Hokkaidō, for example, supports a very large Rhinoceros Auklet colony3, while on islands off southeast Hokkaidō Leach’s Storm Petrel and very small numbers of Tufted Puffin breed. Other islands, especially off western Honshū and off Kyūshū, provide breeding sites for the rare Japanese Murrelet. Farther south, subtropical islets are home to colonies of Brown Booby, Sooty Tern, Black-naped Tern [NT], Roseate Tern [NT] and Brown Noddy. Islands in the chain stretching from the Izu Islands to the Bonin Islands support important populations of Short-tailed Albatross, Black-footed Albatross, Bryan’s Shearwater, Tristram’s Storm Petrel, Matsudaira’s Storm Petrel4 and Bonin Petrel.
The Japanese archipelago spans climatic and biogeographical extremes and serves as a bridge between Northeast Asia and Southeast Asia. A major bird migration route, the East Asian–Australasian Flyway, extends along the continental coast of Asia, linking regions as far distant as southeast Australia and New Zealand with Kamchatka, Yakutia, Chukotka and Alaska. Many regular summer and winter visitors to Japan and numerous passage migrants move along this flyway or its various branches: following the line of the Japanese archipelago, branching in Kyūshū to the Korean Peninsula or through the main Japanese islands; branching again in Hokkaidō, some species migrating by way of the Kuril Islands and others via Sakhalin into northeast Russia. Kyūshū, in particular, is known as a ‘crossroad of migration’. There, for example, in autumn, can be found Chinese Sparrowhawk migrating from Korea to Southeast Asia over Kyūshū to Amami Ōshima and Okinawa, while at the same time Oriental Honey Buzzards are migrating from eastern Japan to China by way of Kyūshū. Wherever the flyways cross water, wherever there are headlands, capes or offshore islands, there are regular places of landfall for tired migrants, and these make excellent places to search for common species and, at times, vagrants. These areas are especially fertile for the interested naturalist, connecting him/her to the larger processes of the natural world.
Teuri-tō, off the west Hokkaidō coast, has some of the highest cliffs in the country [TT].
Bonin Island Honeyeater is endemic in the remote Ogasawara Islands – here with Japanese White-eye (centre bird) [OVTB].
1 As much as three times the tree diversity for the same latitude band in Europe.
2 Throughout this book, the terms populated and unpopulated are used to refer to human populations, or to deities, and inhabited and uninhabited to refer to plants or animals.
3 Reputedly the largest colony in the world.
4 The only confirmed breeding site for this species in Japan is on Minami Iwō Island.