An Isolated Evolutionary Laboratory
Ulleungdo is an oceanic island, a type of island that has never been connected to a mainland. It is the top of a large stratovolcano that rises from the sea floor, located 120 kilometers east of the Korean Peninsula. The island began forming between 2.5 and 4.6 million years ago from volcanic activity on the seabed. A major eruption around 10,000 years ago decapitated the volcano's peak, creating the caldera that now forms the Nari Basin, the island's only significant flat terrain.
This long and continuous isolation from the Asian mainland makes Ulleungdo a site for studying biogeography. With a total area of just 72.86 square kilometers, the island supports about 500 native vascular plant species. Among these, at least 33 species are endemic, meaning they are found nowhere else on Earth. These endemic plants represent around 6% of the island's total native flora. They are found across 26 different plant families, showing a wide range of evolutionary divergence. This unique assemblage of life has earned Ulleungdo the nickname "the Galapagos of Korea."
A Forest with Japanese Roots
The flora of Ulleungdo presents a biogeographical puzzle. Many of its plant communities, particularly the forests on Seonginbong Peak (984 meters), have a stronger resemblance to those found in the mountains of Japan than to the vegetation of the nearby Korean mainland. This shows in the island's most dominant tree, Fagus multinervis, a species of beech tree confirmed to be endemic to Ulleungdo. Its closest relative is Fagus engleriana, found in China, but phylogenetically it is also closely linked to Japanese beech species.
Other endemic plants further show this connection. Acer takesimense, a maple species, evolved from its mainland progenitor, Acer pseudosieboldianum. The island also has the endemic Ulleungdo hemlock (Tsuga ulleungensis) and the rowan tree Sorbus ulleungensis. The question of how the ancestors of these plants arrived on such a remote island is a topic of ongoing study. The primary theories involve long-distance dispersal events. Seeds were likely carried by wind, migratory birds, or ocean currents, particularly the Tsushima Warm Current, which flows northeast from Japan past the island. Over millennia of isolation, these colonizing populations evolved into the distinct species seen today.