Kiritappu Peat-Forming Plant Community

Kiritappu Peatland Plant Community: Hokkaido's "Marsh of Flowers"

On the easternmost edge of Hokkaido, where Pacific fog rolls in from the sea and cool mists hang over the land even in midsummer, lies one of Japan's most extraordinary natural treasures. The Kiritappu Peatland Plant Community in Hamanaka Town spreads across a vast wetland that hosts hundreds of wildflower species, alpine plants growing at sea level, and an ecosystem so distinctive that it has held the status of a national natural monument for more than a century. Designated in 1922, this is one of the oldest natural monuments in Japan, and a journey here offers a glimpse of a primeval landscape that has been carefully preserved for future generations.

What is the Kiritappu Peatland Plant Community?

The Kiritappu Marsh stretches roughly nine kilometers north to south and three kilometers east to west, covering a total area of about 3,168 hectares along the Pacific coast of eastern Hokkaido. Within this vast wetland, the central 803 hectares of raised bog—formed over thousands of years by accumulating layers of sphagnum moss and other plants—is officially designated as the Kiritappu Peatland Plant Community. An additional 86 hectares of surrounding national land was later added to the protected zone to safeguard the core area from runoff and human impact.

The marsh was born from a remarkable geological story. About 6,000 years ago, during a period of warmer global climate, what is now the wetland lay beneath the sea as a deep coastal bay. As the climate cooled and sea levels fell, sand dunes formed along the coast, trapping water inland. Reeds, sedges, and sphagnum mosses gradually colonized the poorly drained ground, and over millennia their remains accumulated as peat, building up the layered landscape we see today.

The wetland is rare in containing all major marsh types in close proximity—low marsh, intermediate marsh, raised bog, and salt marsh. At high tide, seawater flows up the rivers and reaches the heart of the wetland, creating a delicate balance between freshwater and brackish environments that supports an exceptional diversity of plants and animals.

Why Was It Designated a National Natural Monument?

When the Kiritappu peatland was designated a national natural monument on October 12, 1922, the reasoning came down to a single, striking observation: this place was unlike any other peatland in Japan. The local climate—cold throughout the year and shrouded in heavy fog even at the height of summer—produces a peat-forming flora that differs in character from peatlands elsewhere in the country. Sphagnum mosses grow with unusual vigor here, building up countless small mounds that give the surface a distinctive textured appearance.

The recognition that the original protected zone was too small to ensure long-term preservation led to a later expansion of the designated area. Concerns about wastewater from neighboring grazing lands and other surrounding human activities prompted the addition of about 86 hectares of national land around the core, ensuring that the bog's hydrology and unique plant communities would remain intact.

The wetland's value has only grown more apparent over the decades. In 1993, it was registered under the Ramsar Convention as a wetland of international importance, and in 2001 it was selected as one of the Hokkaido Heritage sites. In March 2021, the surrounding region was further elevated to become part of the Akkeshi-Kiritappu-Konbumori Quasi-National Park.

Highlights and Things to See

Around the Marsh

The Kiritappu Peninsula and surrounding area offer many additional attractions worth visiting. Kiritappu Cape, on the eastern tip of the peninsula, presents dramatic cliffs above the Pacific where wild rhododendrons and Ezo daylilies bloom in summer; with luck, sea otters and seals can be spotted in the waves below. The town of Hamanaka itself is famous as Japan's largest producer of natural kelp, and you can sample kelp-based dishes at the wetland center's café, including a traditional surf clam curry made from a recipe passed down in local households.

Kiritappu Onsen "Yu-Yu" provides hot springs and accommodation with views of the wetland. For broader exploration, the larger town of Akkeshi—famed for its oysters—lies to the west, and Cape Nosappu, Japan's easternmost point on the main road, sits to the east in Nemuro. Fans of Japanese animation may also enjoy small homages to Lupin III scattered around town: the manga's late creator Monkey Punch was a Hamanaka native.