Nature of Oze National Park

Location and Outline of Oze National Park
Introduction to Oze's natural environment
   Situated in the center of Japan, Oze is the largest highland marshland on Japan's main island of Honshu. Spanning Gunma, Fukushima, Niigata and Tochigi prefectures, it is home to the Ozegahara Marsh, Lake Ozenuma and the surrounding 2,000-m-class mountains, including Mt. Shibutsu and Mt. Hiuchigatake. Here, visitors can enjoy varied, beautiful natural landscapes, including vast marshlands, lakes, alpine areas, pristine forests and high waterfalls.
    The climate is relatively cold with cool summers and snowy winters (total snowfall: 4 m). In the marshes, many marsh plants, such as skunk cabbages and daylilies, bloom between spring and autumn. Oze also provides habitats for a wide variety of wildlife, including large mammals, birds and insects. The number of rare animal and plant species in the region is abundant, making it an academically important area.
    To strictly preserve this precious and fragile environment, Oze's marshes have been designated as Special Protection Zones of Oze National Park as well as a Special Natural Monument.
    In the past, Oze faced an environmental crisis caused by the trampling of its marshes by visitors and other factors. However, thanks to tireless conservation efforts by many, the environment has now been restored. Oze is also the birthplace of Japan's take-garbage-home movement, making it a symbolic place of nature conservation.
    In spring and summer, many people visit Oze to enjoy its rich natural environment. It is the ideal place to reflect on the relationship between nature and mankind.
 Oze's open season

    Normally, Oze is open between mid-May and late October. A large number of people come to the area during this season.
        Oze in early spring (early May)
    Although conditions may be warming up day by day in the world below, early May in Oze still feels like winter.

    Timing varies from year to year, but snow tends to remain around this season, meaning that visitors must be adequately equipped to come to Oze.

    Boardwalks are often still under snow cover, and destinations should be reached by following maps, red marks painted on trees and ribbons hanging from branches.
(Heading for Oze over the lingering snow)
        Thawing (mid- to late May)
    The snow starts disappearing in mid-May, partially exposing the boardwalks.

    The ground between them is still covered with snow that is often hollow inside; it is difficult to walk on, as hiker's feet sink with every step.
(Walking from the Shirasuna Toge Pass to Miharashi)
        Akashibo (red snow phenomenon) (late May)
    The surface of the snow turns red in the thawing season as if sprinkled with red earth.

    This mysterious phenomenon can be observed only for a brief period of time before the snow disappears.
(Akashibo turning white snow red)
        Skunk cabbage season (late May to early June)
    When the lingering snow is almost gone, the skunk cabbage season starts in Oze, attracting large numbers of visitors.

    The white flowers confidently herald the start of Oze's short open season, and yellow marsh marigolds also open their yellow flowers in support.
(Shimono-ohori, Ozegahara)
        Cotton sedge season (early to mid-July)
    The black flower buds of cotton sedges start appearing in the thawing season, and their small yellow flowers can be seen in June.

    The blooming ends in July, when the marshes become filled with white fluff from these plants.
(White fluff in Ozegahara)
        Daylily season (late July)
    This is the height of Oze's floral season.

    After the white fluff of cotton sedges, the marshes become carpeted with the yellow flowers of daylilies.

    Visitors are usually delighted with summer in Oze.
        Kusamomiji (marsh grass changing color) season (September)
    In September, the trees are still covered with green leaves, but the marsh grass starts to turn orange from its tips.

    Looking at the marsh against the sun makes the whole area seem to shine like gold. Many visitors take pictures of the golden grass swaying in the wind.
(Kusamomiji in Ozegahara)
        Autumn color season (early October)
    In late September, when the orange of the kusamomiji gives way to brown, the leaves on the mountain trees also start to change color.

    The autumnal hues of beech forests in and around Oze are quite spectacular. The fall colors seem to gradually bleed down the mountains.
(Walking from Miharashi to the Shirasuna Toge Pass)
        Late autumn (mid- to late October)
    By mid-October, all broad-leaved trees have shed their leaves, and it is time for lodge staff to start packing.

    Visitors to Oze become scarcer at this time of year, although quite a few still come to enjoy its tranquil atmosphere.

    The first snow may fall in late October, turning the marshes white.
(Ozegahara in early winter)
 Main sightseeing spots
        Mt. Shibutsu
    This serpentine-rock mountain has risen over a long, long time, and is home to flowers that cannot be found on other mountains.

    In the interests of protecting its plant communities, visitors are prohibited from entering the mountain area in early spring between May and June.

    The east-slope trail that connects Ozegahara and the summit can also be used only for ascent to protect vegetation and prevent accidents.
(Viewing Mt. Shibutsu from Ozegahara)
        Kenkyu-mihon-en (Research Exhibition Garden)
    Visitors turning left at Yamanohana will see the Kenkyu-mihon-en (Research Exhibition Garden) spreading out ahead.
    Despite being called the Exhibition Garden, it is in fact a naturally formed marsh.

    This section is recommended to those with limited time, as a wide variety of flowers grow there within a relatively small area.
    The trail to Mt. Shibutsu also starts at the bottom of the garden.
(Research Exhibition Garden in the skunk cabbage season)
        Ushikubi-bunki Branch
    Walking from Yamanohana through Ozegahara Marsh takes hikers to a branch for Ryugu and the Yoppi Bridge.
    Near the branch, a hill resembling a cow's neck (ushikubi) rises from the marsh, hence the name of the branch.

    There are long benches at this branch, and many visitors take a rest there.
(Ozegahara: the rise in the foreground is Ushikubi.)
        Yoppi suspension bridge
    Yoppi is thought to originally have meant, "Where water collects."
    The Yoppi River, which flows from the direction of Yamanohana collecting water from several rivers along the way, joins the Nushiri River, which flows from Lake Ozenuma downstream of this bridge, forming the Tadami River and flowing toward Niigata Prefecture.

    Visitors can enjoy the different faces of Oze along this riverside route.
(Yoppi Suspension Bridge)
    A river runs into the marsh, becomes an underflow and emerges on the opposite side of the boardwalk.

    According to Japanese folklore, this underflow tunnel led to Ryugu (a dragon's palace).
    Many day-trippers to Ozegahara Marsh have lunch on the benches there before turning back.
(A river flowing into the marsh)
        Ayamedaira Marsh
    This is a marshland formed at the southern ridge of Ozegahara Marsh.
    Mt. Hiuchigatake standing across the marsh takes on the appearance of a supernal heaven.

    Some say this name is derived from a Japanese-language error mistaking bog asphodels for irises (ayame in Japanese).
(Viewing mountains across the marsh)
        Hiraname-no Taki Falls
    This is a waterfall on the Tadami River, which flows between Niigata and Fukushima Prefectures from the eastern edge of Ozegahara Marsh to the north.

    From the high viewing place there, the water can be viewed cascading down a series of large rocks.
(Hiraname-no Taki Falls flowing down the rocks)
        Sanjo-no Taki Falls
    This is a magnificent waterfall located downstream of Hiraname-no Taki Falls, and can be viewed from an viewing platform accessed by descending a little from the trail.

    All rainfall in Oze passes through the falls, and the tremendous roar of the water there creates a whole new impression of Oze.
    In the thawing season, the sound of the falls is so loud that people nearby cannot hear each other speak.
(Grand view of Sanjo-no Taki Falls)
        Mt. Hiuchigatake and Lake Ozenuma
    Along with Mt. Shibutsu, Mt. Hiuchigatake is one of Oze's best-known mountains.
    It has five peaks formed by a series of eruptions; three of them look out over Lake Ozenuma and Ozegahara Marsh.

    Lake Ozenuma, another sightseeing spot, was formed at the foot of Mt. Hiuchigatake when an eruption of the mountain blocked the flow of the Nushiri River.
    The marshes on the north shore of the lake, both large and small, provide fantastic views to hikers.
(Lake Ozenuma and Mt. Hiuchigatake)
        Oe Marsh
    This is the largest marsh around Lake Ozenuma.

    The route from the Numayama Toge Pass to the eastern shore (where the Ozenuma Visitor Center is located) runs through this wetland.
    Visitors will see three stands of larches on some slightly elevated land beside Lake Ozenuma, which people affectionately call "The Three Larches."

    In the late-July daylily season, this marsh turns yellow.
(Oe Marsh and The Three Larches)
        Mt. Taishaku
    This is one of the areas that has been newly incorporated into the national park.

    The mountain's 2,060-m peak affords excellent views of Mt. Hiuchigatake and Mt. Aizu-komagatake as well as Mt. Nikko-Shirane and Mt. Nantai in the distance.
    The area is also well known for its colonies of "Osabagusa" (poppy family) at the Umasaka Toge Pass access point.
(Summit of Mt. Taishaku)
        Mt. Tashiro
    The large marsh here sits on a slightly eastward-inclined area that does not look like a mountain summit. Mt. Aizu-komagatake and other mountains can be seen across the marsh.

    *The boardwalk on the Tashiroyama Marsh is one-way. Please walk in a counterclockwise direction.
(Viewing mountains across the Tashiroyama Marsh)
        Mt. Aizu-komagatake
    Moving on past the forest line, hikers will suddenly see a tilting summit wetland spreading out ahead.

    The summit located across the marsh commands views of Mt. Hiuchigatake and Mt. Shibutsu. This marsh is also well known for its "Hakusan Kozakura" (primrose family), which bloom between early and mid-July.
(Komano-koya Lodge)
 Beautiful scenery created by Oze's natural environment
        Morning and late-afternoon mists
    In water-rich Oze, the ground undergoes radiative cooling in the morning and late afternoon, often generating mist near the ground surface.

    Early risers will have the chance to see the fantastic sight of mountains appearing to float on the mist-covered marshes. The mist gradually disappears as the sun rises.
(Ozegahara early in the morning)
    In summer, thundershowers are a frequent occurrence in Oze.

    In the early afternoon, giant cumulonimbus clouds develop in the sky, and distant rolls of thunder can be heard.
    Within an hour or so, the sky darkens and large drops of rain start to fall, prompting people to hastily take out their raincoats.

    After these heavy-but-brief downpours, it starts to brighten and beautiful rainbows often appear.
(A beautiful rainbow in Ozegahara)
        White rainbows
    In Oze, vapor from the marshes often undergoes morning radiative cooling. This generates mist, which can look like a white rainbow when the sun shines on it.

    Large water drops like those found in rain diffract light in the seven colors of the rainbow, but small water drops such as those in mist do not completely diffract light, producing the appearance of a white rainbow.
(A white rainbow over Ozegahara)
Oze is a habitat for Asiatic black bears.
To avoid encountering bears (click here).
Geogical history of Oze
(1) Formation of Mt. Shibutsu

    Until several million years ago, Oze was a flat highland formed on the ancient Hinoemata Stratum and granite.
    A shallow valley ran toward the northeast, and a serpentine-rock mountain, which would later become Mt. Shibutsusan, was in the process of formation at the western edge.

(2) Beginning of volcanic activity

    Volcanic activity in the area began in the Pliocene epoch (5.33 million to 2.59 million years ago).

    The first to erupt was Mt. Keizuru, which has a rocky protruding peak apparently formed by lava. However, much of the lava has now been eroded, leaving behind only the hard core.

    Lava from Mt. Keizuru still remains at its foot as well as covering half the slope of Ayamedaira Marsh, located to the south of Ozegahara Marsh.
    This indicates that lava flowed in the area but much of it was eroded away. A giant rock (Kawagoiwa) near Ryugu-goya Lodge is made of this lava.

(3) Shield volcano formation

    In the Pleistocene epoch (2.59 million to 10,000 years ago), volcanic activity became more pronounced.

    In the areas north and east (Mt. Hinokitaka) of Lake Ozenuma, Ayamedaira Marsh, Mt. Susugamine, Mt. Sarabuse and other volcanoes probably erupted one after another.
    The lava discharged by these mountains had low viscosity, resulting in shallow-sloping shield volcano formation.

    Mt. Sarabuse viewed from Lake Ozenuma shows the characteristic form of a shield volcano.

(4) Formation of Mt. Hiuchigatake

    In this way, the topography of Oze was gradually formed, and the eruptions of Mt. Hiuchigatake, Oze's last volcanic activity, made the area as it is today.

    It is not clear when Mt. Hiuchigatake started erupting, but it was probably in the Pleistocene epoch (some 300,000 years ago).
    The mountain's current shape is the result of a series of eruptions and lava outflows. Its relative newness as a volcano means that few studies have been conducted on its appearance.

(5) Formation of Ozegahara Marsh

    By this time, the lava from Mt. Keizuru in what is now Ozegahara Marsh had been washed away by the Nushiri and Nekomata rivers (tributaries of the Tadami River), creating the relatively flat, semi-basin shape we see today.

    The lava that flowed from Mt. Hiuchigatake blocked the Tadami River near Onsen-goya Lodge and Sanjo-no Taki Falls.

    It was once believed that a huge 200-m-deep lake called Ko-ozegaharako (Old Ozegahara Marsh) covered the whole of the Ozegahara area. However, studies have found no evidence of this.
    It is now clear that a shallow lake submerging the eastern half of Ozegahara Marsh existed around 16,000 years ago.

(6) Formation of Lake Ozenuma

    The lava that flowed from Mt. Hiuchigatake buried the Nushiri River, forming Lake Ozenuma. This occurred in the last stage of the mountain's volcanic activity.

Mt. Shibutsu

Mt. Keizuru

Mt. Sarabuse

Mt. Hiuchigatake

Lake Ozenuma viewing from Mt. Hiuchigatake
    *Recent studies have also suggested that the Nushiri River was not blocked by lava flow but by the large-scale debris avalanche of Mt. Hiuchigatake's southern slope.
Geographic history of Ozegahara Marsh

    In the area now known as Ozegahara Marsh, mudflows from Mt. Hiuchigatake and other surrounding mountains formed a gentle alluvial fan, and meandering rivers there frequently caused flooding. The shallow lake was buried at this time.

    Peat formation began in oxbow lakes (formed when meandering parts of rivers become separated from the main flow) and backswamps (formed by flooded rivers not returning to their original state) probably around 8,000 years ago.

    Boring surveys have shown that the depth of the peat layer in Ozegahara Marsh was over 4.5 m. This depth would probably be less than 5 m in most parts.

Thick peat is deposited in Ozegahara.
    *The deposition rate of peat in Oze is approximately 0.7 - 0.8 mm a year, although this varies by climatic conditions, source plants and the extent of degradation. This means that it takes more than 10 years to restore 1 cm of depression caused by the passage of hikers.
Area across the prefectures/zones of Oze National Park
    On August 30, 2007, Oze (home to the largest wetland area in Japan's mainland of Honshu) and surrounding areas with outstanding natural environments as evidenced by the presence of Abies mariesii forests and alpine wetlands, including Mt. Aizu-komagatake, Mt. Tashiro and Mt. Taishaku were designated collectively to form Oze National Park.
    This was the first national park designation of the past 20 years since that of Kushiro Shitsugen National Park in July 1987. There are currently 29 national parks in Japan.

(Unit: ha)
Category Special Protection Zones Class I Special Zones
Class II Special Zones
Class III Special Zones
Gumma Pref.
Fukushima Pref.
(Hinoemata-mura, etc.)
Niigata Pref.
(Uonuma city)
- 834
- 1,156
Tochigi Pref.
(Nikko city)
- 404 743 - 1,147
25.20% 16.70% 42.80% 15.30% 100.00%

*Numbers in brackets indicate the area of private property included in the numbers above
Characteristics of Oze's Nature
Ecosystems and landscapes in the mainly high moor of Ozegahara are delicately balanced and have great scientific value
Various rare animals and plants inhabit Oze due to the particular and varied conditions of weather, geography, and geology.

Higher plants 116 families, 930 species
Plants found in Oze 19 families, 42 species
Plants that only occur in Oze 14 families, 21 species
Plants named after Oze 18 species

Animals named after Oze 19 species
Odonate 40 species
Butterflies 30 species

Comprehensive scientific investigations
1st: 1950 - 1952 , 2nd: 1977 -1979, 3rd: 1994 - 1997
Wild animals and birds
Oriental Ibis, Ducker, Mandarin Duck, Mallard, etc.
Black Bear, Sika Deer, Hondo Stoat, etc.

Oze -- a registered Ramsar Convention site
    The Ramsar Convention (officially known as the Convention on Wetlands of International Importance, especially as Waterfowl Habitat) was developed to internationally protect migratory birds that travel across multiple wetlands and preserve their habitats.
    Oze was registered as a Ramsar Convention site in November 2005 in recognition of its value as a wetland habitat for migratory birds.
Oze -- a Special Natural Monument
    Oze has been designated as a national Special Natural Monument. It has high academic value, and its preservation is of paramount importance.
    Even small changes can affect the whole of the Oze area. To protect the region's ecosystem, it is imperative that the current environment remain unchanged.
Preserve and enjoy our Oze together