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Ogasawara NP, Tokyo
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Sekimonnoki and Sekimonnuraiso are found nowhere else in the world, and both are named for Sekimon. Japan’s 2025 Red List classifies them as Critically Endangered—a remarkable pair of rarities in one forest.
Cloud and mist help Sekimon’s wet forest grow a canopy up to 20 m tall. It’s a striking contrast with the lower, drier scrub forests found on other Ogasawara islands.
Sekimon’s raised limestone has been carved into a maze of sinkholes, caves and sharp ridges called lapies—so pointed they’re nicknamed “needle rocks.” It’s a dramatic landscape hidden beneath the forest canopy.
Hahajima’s tree fern Maruhachi has a name you can spot on its trunk: fallen fronds leave marks shaped like an upside-down 八, the Japanese character for “eight.” Tree ferns also grow in Sekimon’s wet forest.
A study of Sekimon recorded 37 tree species but 1,731 tree stems per hectare. That’s a packed forest with relatively few tree species—a distinctive combination compared with natural forests on other islands.
Sekimon avoided wholesale clearing, but not all logging: scattered prewar stumps of Ogasawara mulberry remain. By identifying them, researchers worked out that this rare island tree once helped form the forest canopy.
In a survey of Sekimon’s larger trees, the invasive Akagi ranked third in stem count among 37 species. Researchers also found it spreading especially near a former plantation site—a reminder that the forest’s history still shapes its ecology.
After invasive Akagi trees were removed, surveys found native plants—including the tree fern Maruhachi—growing in the newly opened canopy gaps. Restoration work can create room for the forest’s own species to return.
Sekimon’s limestone caves were once a popular destination, but typhoon-related collapses and accidents led to a local agreement to close the area in 2001. Some routes later reopened for guided visits, with local guides trained to help protect the forest.
Sekimon closes to visitors from October through February, when the Ogasawara red-headed wood pigeon breeds. The seasonal pause is part of local rules designed to protect wildlife in this rare forest.
