Sumo Shiratake Primeval Forest

Sumo Shiratake Primeval Forest

From the farming village of Sumo, on the island of Tsushima, a pale crag breaks clear of the forest line. This is the summit of Mount Shiratake. Its bare quartz porphyry rock catches the morning light and turns almost white, which is how the mountain earned its name: shiratake means White Peak. The forest cloaking its upper slopes was designated a Natural Monument in 1923, and the reason has little to do with scenery. It is botanical. Few places in Japan bring together plants of the Japanese mainland and plants of the Asian continent the way this one mountainside does.

Tsushima sits in the strait between Kyushu and the Korean Peninsula, nearer to Korea than to the rest of Japan. That position shaped what grows here, and Mount Shiratake is where the result is easiest to read.

A mountain of white rock

Mount Shiratake rises in the Mitsushima district of central Tsushima, reaching about 519 metres at its highest point. (Some climbing guides give the figure as 518 metres.) It is built of quartz porphyry, a hard pale igneous rock, and a chain of similar white-stoned summits runs in a line beside it. Seen from a distance, that exposed stone reads as white against the dark forest, and the name fits.

The peak is in fact two peaks. Climbers know them as Odake, the higher of the pair and the true summit, and Medake, its neighbour. A band of bare rock joins them. The western face of the mountain falls away in cliffs, while the eastern side slopes more gently, and it is on these upper slopes and around the rock outcrops that the protected forest grows.

The designation dates from 7 March 1923. The forest had survived as old growth because the steep, rocky ground near the summit was never cleared, and that is what the Natural Monument status was meant to keep intact.

Where two floras overlap

The forest was protected under a designation criterion that recognises representative old-growth woodland with an unusual plant community. On the slopes just below the summit grows a mixed wood of Japanese evergreen oak (akagashi), Japanese fir (momi), Japanese white pine (hime-komatsu), isunoki, and sudajii. The shrub miyama-shikimi is common in the understorey.

The rarer story is on the open rock at the top. There, species more typical of the Korean Peninsula take hold: the Korean hornbeam (iwashide), Korean azalea, Genkai azalea, and Korean chrysanthemum. On the same mountain, several Japanese species reach the western edge of their entire range. Japanese fir, Japanese white pine, miyama-shikimi, kakuremino, and nagaba-no-koyaboki grow no further west than here.

For botanists this overlap is the point. During the cold periods of the Ice Age, lower sea levels turned Tsushima into a stepping stone between the Japanese islands and the continent, and plants crossed in both directions. White Peak is regarded as the single richest site in Japan for that mixed company of mainland-Japanese and continental species growing together, which makes it valuable for the study of how plants are distributed. The summit area is also the only known home of shima-tohiren, a plant found nowhere outside Tsushima.

Climbing to the summit

The forest is not a fenced reserve. It lies along the route up the mountain, so the way to see it is to climb. The trail begins at Sumo and runs about 2.2 kilometres one way, with most walkers reaching the top in around an hour and a half.

It starts gently. For the first stretch the path follows a stream through cool, easy woodland. A stone torii gate marks the change: beyond it the route enters the old forest proper, where evergreen oaks, shii, and camellias close in overhead. The final 0.7 kilometre is steep, and the last 0.4 kilometre steeper still, with fixed ropes to help on the bare rock near the top. Sure footing matters here.

The reward is a wide horizon. From the summit the ria coastline of Aso Bay spreads below, its inlets folded into the land, and the long ridgeline of Tsushima runs north and south. On a clear day the mountains of the Korean Peninsula show on the skyline across the sea. A short branch path leads to a feature climbers call the rock terrace, a broad slab that makes a natural viewpoint and resting place.

Mount Shiratake has long been treated as a sacred mountain. A small shrine stands near the summit, and people once climbed it as an act of worship. The rock cave at the foot of the Medake crag is held to be especially holy. Down in Sumo village, Shiratake Shrine serves as a place to honour the peak from below for those who do not make the climb; a large ginkgo in its grounds turns gold in late autumn.

Visiting Tsushima

Tsushima is reached by sea or air. High-speed boats run from Hakata in Fukuoka to Izuhara Port in a little over two hours, and Tsushima Airport has flights from Fukuoka and Nagasaki. From Izuhara, Sumo is a short drive. A large car park for hikers sits in the village, with toilets, and from there it is roughly 2.5 kilometres on to the trailhead, where only a few cars can park.

There are no toilets or shops at the trailhead or on the mountain itself, so it is worth preparing in the village. Spring and autumn are the kindest seasons to climb, with azaleas flowering on the summit rock in spring; in midsummer hornets are active on the mountain, and caution is sensible. The island has no bears.

White Peak pairs well with the rest of southern Tsushima. The ancient stone ramparts of Kaneda Castle stand on the shore of Aso Bay nearby, and the Eboshidake observatory looks out over the bay's maze of islets. Further north, the village of Waniura is known for a wild stand of fringe trees that bloom white in early May.