SHINGU, Wakayama Pref. — Inosawa Ukishima, a bog woodland in the center of Shingu City at the mouth of the Kumano River, isn’t an ordinary park.

Ukishima means “floating island,” and that’s what it is, right in the center of Shingu. The woodland is thought to be around 8,000 years old. About 10,000 B.C. the lower-lying areas of Shingu were flooded by rising seawater.

Inosawa Ukishima in Wakayama Prefecture is Japan’s only urban park based on a bog woodland.

Then around 6,000 B.C. the sea level began to recede again. In the wake of the 4,000-year-long flood the water-filled depressions and hollows around Shingu gradually filled with plant debris in various stages of decomposition.

Plants that die in a bog do not decompose, because of the lack of oxygen. Instead the undecomposed dead plants accumulate into layers that gradually raise the lake bed to the water surface. Upon this layer, bushes and eventually trees will colonize. This was the beginning of Ukishima.

Peat bogs are called deitan-shitsugen in Japanese; a bog woodland is a shotakurin. The unique ecosystem of this particular bog woodland, with its relatively cool water and soil temperature, enables plants from the cool-temperate region to grow side by side with plants from warm-temperate and even semitropical regions.

The Kii-joro-hotogisu of the Kii Peninsula

The flora of the southern Kii Peninsula are directly affected by the warm Kuroshio Current, which brings moisture-laden winds, raising the yearly rainfall to the highest in Japan. Moreover, typhoons hit this coastline regularly during the typhoon season.

The park was designated a national monument in 1927. After World War II, however, things went poorly for Ukishima. The land immediate surrounding it was developed for new houses, and in the process the natural water supply, vital for the survival of this ecosystem, was cut off completely. Trees started to die. Ukishima was a badly neglected national monument.

A committee was set up to look into ways to revitalize Ukishima and preserve the island. In basic terms, this bog island required a permanent life-support system. In 1993 household- and well-water began to be pumped into the island area for four hours per day at a rate of 5 liters per second. Then last year another water-intake system was opened, pumping from the mouth of the Kumano River. The water is filtered to remove any impurities that could harm delicate plants.

Through this new water system, Ukishima’s rare ecosystem has bee restored. One indication of this revival is the healthy state of the sphagnum moss growing here (omizugoke, Sphagnum palustre; family Sphagnaceae). Sphagnum moss grows in bogs throughout the world; it is one of the first plants to grow in bogs, since it needs no contact with the soil below. Unlike normal plants, which absorb water and nutrients through the roots, sphagnum moss absorbs water through all its parts: roots, stems and leaves. It is dependent on rainwater for its supply of nutrients, which are held like a sponge in dead cells between the living ones.

Some 40 species of sphagnum moss grow in Japan. S. palustre is also common in wet woodlands and moorland throughout the British Isles. This robust species is whitish-green in color, with stems up to 25 cm long. Fruit capsules are frequently produced during the early summer.

Ukishima has an area of only 5,000 sq. meters, yet this small bog woodland supports over 130 species of plants; most are clearly labeled in katakana, so bring along your pocket guidebook.

A pontoon boardwalk helps visitors explore the bog. Its upper story consists of conifers such as Japanese cedar (sugi, Cryptomeria japonica) and inu-maki (Podocarpus maki) and broadleafed evergreens such as koba-mochi (Elaeaocarpus japonicus), taimin-tachibana (Myrsine seguinii) and yama-momo (Myrica rubra). Deciduous trees include the Japanese lacquer tree (haze-no-ki, Rhus succedanea) and yama-haze (R. trichocarpa).

On a recent visit to Ukishima I saw in the dim light of the woodland some berries that were almost fluorescent: the small dark blue berries of Satsuma rurimi-ki (Lasianthus satsumanensis), a small evergreen shrub that only grows in the southern Kii Peninsula, Shikoku and Kyushu.

Another plant that caught my attention was an evergreen climber that had almost smothered a lacquer tree growing at the edge of the water: sakaki-kazura (Anodendron affine). In May and June its small but attractive, tubular yellow flowers are borne in panicles.

The sakaki part of this plant’s name refers to a different plant entirely; the real sakaki (Cleyera japonica) does grow in Ukishima, though, and the similarity between the two may lie in the shiny dark green leaves.

Some interesting ferns grow on the woodland floor. The tongue fern or Japanese felt fern (hitotsuba, Pyrrosia lingua) is an evergreen, epiphytic fern with a rhizome root system. It grows on dead logs close to the sphagnum moss in Ukishima. The leathery fronds reach 30 cm. Native to the Tokaido region and westward, this fern has many cultivated forms and does well in shady, moist gardens.

Also on the woodland floor can be seen manryo (Ardisia crenata). This attractive red-berried evergreen is often planted in Japanese gardens and is used for decorations around New Year’s.

About 100 meters in front of Shingu Station is a two-storied Chinese-style gate. This is the entrance to Jofuku Park, named for a Chinese Buddhist monk who is buried in this park.

Jofuku may have been responsible for the introduction of Tendai uyaku (Lindera strychnifolia) to Japan, and perhaps first to Shingu, during the Kyoho Era (1716-36). This evergreen shrub is native to southern China and the leaves are used to make jofuku-cha, which is reputed to be good for longevity. Tendai uyaku is now naturalized in the Shingu area.