Exploring the Flora of Mt. Fuji’s Gravel Slopes
In this part of our series on the plants that climb Mt. Fuji, we’ll learn about the unique species found in the mountain’s gravelly zones.
Life Above the Tree Line
Once you climb above the tree line on Mt. Fuji, the landscape changes dramatically. The slopes become covered with loose volcanic gravel and scoria, which are constantly shifting. In these harsh conditions, you’ll find hardy plants like Fujihatazao (Arabis flagellosa) and Miyama Otokoyomogi (Artemisia capillaris). These plants often suffer root damage and may die when the gravel shifts, but they have a remarkable ability to reestablish themselves wherever they are carried by the moving stones.
The Role of Deep-Rooted Plants
Where the gravel movement slows down, you’ll spot Itadori (Reynoutria japonica, also known as Japanese knotweed) and Ontade (Polygonum weyrichii). These species have thick, deep taproots that help stabilize the gravel, playing a crucial role in reducing soil movement on the slopes.
Patch Communities on the Southeast Slope
On the southeastern slope of Mt. Fuji, around the Hoei Crater, you’ll find patchy communities of plants like Itadori above the larch tree line. Plants growing on the gravel tend to form patches, sometimes randomly distributed and sometimes clustered. These patches grow larger over time as parts of the roots, stems, or leaves break off and take root nearby, gradually expanding outward.
The larger the patch, the older it is. As patches grow, the center often dies off, creating a “doughnut” shape. This happens because the underground stems become too crowded, leading to a lack of oxygen and eventual dieback—a phenomenon commonly seen near the forest limit on Mt. Fuji.
However, the center of these patches becomes a favorable spot for new plants. The area is sheltered from the wind, collects fallen leaves, becomes nutrient-rich, and receives plenty of sunlight. As a result, you’ll often find seedlings of woody plants like Larch (Larix kaempferi), Miyama Alder (Alnus maximowiczii), and Miyama Willow (Salix reinii)—species that struggle to grow in bare gravel. As these woody plants mature, they help push the tree line, and even the forest limit, higher up the mountain. In this way, the patch communities formed by herbaceous plants serve as the foundation for the upward climb of trees on Mt. Fuji.
Featured Plant: Ontade (Polygonum weyrichii)
| Attribute | Description |
|---|---|
| Habitat Zone | Alpine zone |
| Environment | Gravelly slopes |
| Life Form | Perennial herb |
| Height | 30–100 cm |
| Flowering Season | Early summer to summer |
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Underground stems can reach up to 3 meters in length.
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Leaves are alternate, with long stalks and an oval to egg shape.
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Flowers are small, yellowish-white, and bloom in clusters.
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The name “Ontade” is said to come from Mt. Ontake in Nagano Prefecture, and due to its habitat, it’s also called “Iwatade.”
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Ontade is a pioneer species, often the first to colonize volcanic wastelands above the fifth station, helping to pave the way for other plants.
These resilient plants are not only a testament to the power of life in harsh conditions but also play a vital role in shaping Mt. Fuji’s unique alpine ecosystem.
