A Rare Natural Forest of Weeping Chestnuts
The Ono Shidareguri Native Forest was designated a Natural Monument of Japan on July 17, 1920. At the time, it was known as the “Ono Village Shidareguri Native Forest.” Its name was changed to the present Ono Shidareguri Native Forest in 1957.
There are only a handful of naturally occurring populations of shidareguri, or weeping chestnuts, in Japan. With approximately 800 trees, the population at Ono is one of the largest in the country and is particularly valuable because the trees form a large, naturally occurring forest.
The trees look very different from ordinary Japanese chestnuts. Their branches droop toward the ground while the trunks and limbs twist and curve in unusual directions, giving the trees an almost living, sculptural appearance. In winter, after the leaves have fallen, their intricate shapes become especially clear.
Some of the largest trees have trunks measuring more than 4 meters in circumference, providing a striking reminder of the long history of this natural forest.
A Quiet Forest on the Slopes of Ono Pass
The forest spreads across the upper reaches of the Niresawa valley on the western side of Ono Pass, which lies on the boundary between Tatsuno Town and Okaya City near the center of Nagano Prefecture. It is approximately 3 kilometers east of JR Ono Station and can be reached by car in about 10 minutes.
The designated Natural Monument area covers approximately 3.4 hectares, with the forest extending along the mountain slopes.
The area once stood along an important route connecting the historic Ono-juku Post Town on the Sanshu Kaido with the Suwa region. Travelers and merchants passed through the area during the Edo period, and the strange appearance of the trees became widely known.
The Tengu Legends of the Forest
During the Edo period, local people struggled to explain the unusual shapes of the trees. According to traditional belief, tengu—supernatural mountain beings from Japanese folklore—had bent the branches into their distinctive forms.
The forest was therefore feared as a place where tengu lived, and the trees were sometimes called “Tengu’s Chestnuts.” Local residents are said to have avoided entering the forest for many years.
A description of the area survives in the historical geographical record Chikuma no Masago, written in 1753. Under the title “Tengu Forest Weeping Chestnuts of Minami-Ono Village, Ina District,” it records the unusual trees, demonstrating that their distinctive appearance was already recognized in the mid-Edo period.
Another local legend says that a tengu bent the branches downward so that it would be easier to pick the chestnuts. The trees produce extremely small nuts, approximately the size of a person’s little fingernail, and they are not suitable for eating. Because the nuts were rarely collected, the trees were left largely undisturbed, which is thought to have helped preserve the forest in its natural state.
The Botanical Mystery of Shidareguri
Shidareguri, scientifically known as Castanea crenata var. pendula Makino, is a variety of the Japanese chestnut, Castanea crenata Sieb. et Zucc. It is thought to have originated through a natural mutation of the ordinary Japanese chestnut.
In most locations, shidareguri occurs as individual trees rather than large groups. A naturally occurring population of this scale, forming what can be described as a nearly pure forest, is therefore extremely rare.
One of the distinctive characteristics of these trees is the behavior of their terminal buds. The terminal bud at the end of a branch dies after several years, allowing lateral buds farther along the branch to continue growing. As a result, the branches spread outward and gradually droop, producing the characteristic umbrella-like shape.
Standing beneath these trees, visitors can see how the branches extend in many directions before cascading downward. The resulting forms make the forest feel unlike an ordinary woodland.
One of Japan’s Few Natural Habitats
Natural habitats of shidareguri have been confirmed in only four locations in Japan: Iwaki City in Fukushima Prefecture, Kita-Ono in Shiojiri City, Ono in Tatsuno Town, and Gero City in Gifu Prefecture.
Among these, the natural habitats in Tatsuno Town and Miyaji in Gero City are designated as Natural Monuments of Japan, while the other two are protected as natural monuments at the prefectural or municipal level.
The Ono forest is particularly notable for its size, number of trees, and good state of preservation. Its protected environment allows visitors to appreciate this rare forest throughout the changing seasons.
Conservation in a Protected Natural Park
The area including the Ono Shidareguri Native Forest became part of Enrei Ojo Prefectural Natural Park on June 25, 1964. Tatsuno Town manages and maintains the area today.
The surrounding area has been developed as Shidareguri Forest Park, with walking trails and a campground. Fresh green foliage appears in spring, autumn brings colorful leaves, and winter covers the forest in snow, giving the trees a completely different appearance in each season.
The forest also faces the natural challenges of aging trees. Many individual trees are old, and some are approaching the end of their lives. To help maintain the population, Tatsuno Town works with local residents to clear undergrowth once a year. Naturally emerging young trees are also examined, and individuals showing the characteristic weeping growth are selected and preserved.
Preserving Genetic Resources for the Future
In 2005, the National Agriculture and Food Research Organization, then through its Fruit Tree Research Institute’s Department of Genetics and Breeding, collected genetic material from 21 individual trees across two municipalities in Nagano Prefecture, with the Ono population serving as an important source.
The research identified several different forms of branch growth, including trees whose branches droop in broad umbrella shapes, trees with more flexible, willow-like branches, and intermediate forms.
Scion material collected from these trees was propagated as grafted plants and preserved at a fruit-tree research facility in Tsukuba, Ibaraki Prefecture. These efforts support research into the characteristics and genetic properties of shidareguri while also contributing to the long-term conservation of the species and the development of future replacement trees.
Visiting the Ono Shidareguri Native Forest
The Ono Shidareguri Native Forest is located at 5983-1 Ono, Tatsuno Town, Kamiina District, Nagano Prefecture.
From Ono Station on the Tatsuno Branch Line of the JR Chuo Main Line, the forest is approximately a 5-minute taxi ride away. By car, it is about 20 minutes from the Ina-Kita Interchange on the Chuo Expressway or approximately 20 minutes from the Shiojiri Interchange on the Nagano Expressway.
Parking and walking trails are available, and the area attracts visitors particularly from spring through autumn. Guided tours and nature observation activities are also held, making the forest an interesting destination for travelers interested in botany, geology, folklore, and the conservation of Japan’s natural heritage.
A Forest Where Nature and Folklore Meet
The Ono Shidareguri Native Forest is much more than a collection of unusual trees. It is a natural and cultural heritage site where botanical rarity, local folklore, and centuries of human reverence have become intertwined.
As you walk quietly among the strangely shaped trees, it is easy to understand why people once imagined that supernatural mountain beings lived here. The twisting trunks and cascading branches offer a vivid reminder of the extraordinary forms that nature can create over long periods of time.
For visitors exploring Tatsuno Town, a walk through this mysterious forest offers an opportunity to encounter a rare part of Japan’s natural heritage while experiencing the legends and traditions that have surrounded it for generations.