Nagi Forest in the Grounds of Kasuga Shrine

A Pure Forest on the Eastern Slopes of Mount Mikasa

Walk east of the vermilion sanctuary buildings of Kasuga Taisha, climb a short distance up the wooded slope of Mount Mikasa, and the woodland changes character. Tall, slender trunks rise close together. Their leaves are broad and glossy, parallel-veined like a palm frond, yet these trees are technically conifers. The species is nagi (Nageia nagi), and the stand covers roughly 9.3 hectares of pure forest, almost entirely free of other tree species.

On 7 March 1923, this remarkable woodland was designated a National Natural Monument under the name "Kasuga Jinja Keidai Nagi Jurin," meaning the Nagi Forest in the Precincts of Kasuga Shrine. At the time, the shrine was officially called Kasuga Jinja; the change to its present name, Kasuga Taisha, did not come until 1946. The original designation name has been preserved in the cultural property register ever since.

The northern natural range of nagi on the Japanese mainland is the hills around Yamaguchi, several hundred kilometres to the southwest. Nara lies well beyond that climatic boundary. Why, then, does a vast pure stand of this warm-climate tree exist on Mount Mikasa? The answer lies in over a thousand years of human devotion, plant chemistry, and the appetites of Nara's famous deer.

A Sacred Tree Planted More Than a Thousand Years Ago

Researchers agree that the nagi here are not native. Sometime in the Heian period, at least a thousand years ago and quite possibly earlier, nagi seedlings were offered to the shrine as sacred trees and planted on the slopes of Mount Mikasa. Successive generations seeded themselves, spread, and eventually crowded out other species. By the Kamakura period, written records already describe an established nagi grove on the mountain.

For Kasuga Taisha, nagi has long served alongside sakaki as the wood of ritual. At the imperial Kasuga Festival held every 13 March, and again at the Kasuga Wakamiya On-matsuri spanning 15 to 18 December, freshly cut nagi branches are stood in torii gates and lashed to festival floats as resting places for the deities. The forest on the mountain and the rites in the sanctuary are linked in a continuous loop of belief and biology that has run, with little interruption, for over a millennium.

Why the Designation Matters

The designation criterion, written in the formal language of Japan's cultural property system, reads "Representative primeval forest; rare forest flora." The Taishō-era survey report goes further, describing the grove as "a pure forest of chikuhaku — extremely rare of its kind." Chikuhaku ("bamboo cedar") is an old written name for nagi, hinting at how puzzling its broad-leaved-but-coniferous form has long seemed.

The biological mechanism that maintains the pure forest is now well understood. Nagi releases a compound called nagilactone, an allelopathic substance that suppresses germination and growth in surrounding plants. Few rivals can take root in nagi shade. The second mechanism is the deer of Nara Park, the famous free-roaming herd of roughly 1,300 sika deer that has lived around the shrine for centuries. Deer browse hungrily on most other seedlings but refuse nagi leaves, which are tough, leathery, and bitter. As the surrounding broadleaf saplings are eaten down year after year, only the nagi grow on. The result is a forest in which one species has, over centuries, achieved near-total dominance.

The nagi grove abuts a much larger neighbour: the Kasugayama Primeval Forest, a Special Natural Monument and World Heritage component covering some 250 hectares of evergreen broadleaf woodland. Recent studies show nagi steadily encroaching into the primeval forest, a development that fascinates plant ecologists and concerns conservationists alike.

Leaves, Fruit, and Folk Beliefs

Nagi leaves are unusual enough to repay close inspection. Four to six centimetres long, lance-shaped or elliptic, they are flat and broad, and their parallel veins run lengthwise from base to tip. Grip a leaf at both ends and pull: it resists tearing with surprising stubbornness. The dried leaf is stronger still.

From this unbreakable quality grew a thread of folk belief that follows nagi across Japan. The leaf became a charm for marital bonds that would not break. Newlywed women once tucked nagi leaves behind their hand mirrors, hoping for an unbreakable marriage. Because the leaf's upper and lower surfaces look almost identical, the tree was also said to symbolise a relationship without secrets. A legend that Minamoto no Yoritomo and his future wife Hōjō Masako exchanged vows beneath a nagi tree has been retold in many forms over the centuries.

Nagi is dioecious. Male and female flowers grow on separate trees, opening around May; female trees ripen round, bluish-white fruit in October. Walk a section of the grove where both sexes mingle, and you can read the season in the canopy.

The largest individual in the grove, standing east of the main sanctuary near Wakamiya Shrine, is estimated to be roughly 850 years old. In 1997 (Heisei 9), Nara City separately designated this single tree, together with a twenty-metre-square plot beneath its crown, as a city-level natural monument, recognising one tree's exceptional scientific and historical value within the larger national designation.

Visiting the Forest

The nagi grove lies inside the precincts of Kasuga Taisha, so visitors encounter it naturally along the approach to the main shrine and around Wakamiya Shrine on the south side. The core of the designated area extends into a forbidden zone on Mount Mikasa that cannot be entered, but you do not need to enter it to appreciate the forest. Towering individual nagi grow throughout the accessible parts of the grounds, and a few minutes spent under one will make the species easy to recognise anywhere in Japan afterwards.

Kasuga Taisha itself rewards a long visit. Founded in 768 (Jingo-keiun 2), it is the head shrine of roughly three thousand Kasuga shrines nationwide, and was inscribed in 1998 as part of the UNESCO World Heritage Site "Historic Monuments of Ancient Nara." The vermilion outer corridor and tower gate, the four National Treasure main halls renewed every twenty years through the shikinen-zōtai ceremony, the approach lined with around three thousand stone and bronze lanterns, the Man'yō Botanical Garden with three hundred species mentioned in Japan's oldest poetry anthology, and the National Treasure Hall housing 354 National Treasures and over 2,500 Important Cultural Properties: a single afternoon is rarely enough.

From the shrine grounds, the Kasugayama Promenade, a 9.4-kilometre walking trail, leads into the World Heritage primeval forest, where the canopy shifts from nagi pure stand to mixed evergreen broadleaf and the air noticeably cools.