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Oze NP, Fukushima
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Around 1,970 m high, one gently tilted, uninterrupted marsh spreads across Tashiroyama’s summit plateau for about 20 hectares. Fukushima’s hiking guide describes this single-tabletop form as globally rare.
No inflowing river feeds this high marsh. Instead, its peat acts like a sponge, soaking up rain and melting snow, then slowly releasing water that helps supply streams flowing down the mountain.
The marsh’s peat is relatively shallow—usually 50–70 cm, reaching about 2 m at its deepest. Subtle raised ridges and narrow hollows create different growing spots for mosses, sedges and other wetland plants.
Early summer brings tokiso orchids and chinguruma; in high summer, Nikko day lilies and fluffy tussock cottongrass appear. Across the seasons, the summit marsh supports about 400 kinds of alpine plants.
Round-leaved sundew is among the plants recorded at Tashiroyama. Its glistening leaf hairs trap small insects with sticky droplets—a useful extra source of nutrients in the marsh’s poor peat soil.
A local family history recalls Tashiroyama once being feared as demon-haunted. On July 30, 1912, landowner Ōyama Zenhachirō Tokisumi climbed with 2 Kōyasan priests; villagers later opened a trail, and his descendants still care for the summit hall.
Tashiro evokes a rice field, and a late-Edo gazetteer records a local report of traces of paddy plots in the mountain’s broad summit clearing. It is a curious old connection between this high marsh and farming.
During Typhoon Hagibis in October 2019, a huge landslide tore down Tashiroyama’s western slope and stopped just short of the summit marsh. Debris flowed into the Nishine River and damaged the valley below.
GPS and camera studies in the Tashiroyama borderlands have confirmed seasonal deer movement between Oze and Nikko: high country is summer range, lower ground winter range. Deer grazing has also been recorded on summit-marsh plants.
