Aoshima Subtropical Plant Community

Overview

Aoshima is a small island located off the southeastern coast of Miyazaki City, Miyazaki Prefecture. It has a circumference of approximately 1.5km, an area of about 4.4ha, and a height of about 6m. It's becoming a tombolo. The opposite shore is called Aoshima Coast, a major tourist destination including Aoshima Beach. Aoshima and Aoshima Coast are connected by the Yayoi Bridge. It's also the location of Aoshima Shrine. Aoshima was formed when a mountain composed of alternating layers of sandstone and mudstone (the Yuzutsu stratum) subsided into the sea, was eroded by waves, and then slightly uplifted, creating a raised wave-cut platform. The regularly layered strata slope gently, resulting in a staircase-like erosion that resembles a giant washboard, thus earning the name "Oni no sentakuban (rock)" or "Devil's Washboard". The Kuroshio Current flows from southwest to northeast along the southern coast of Miyazaki Prefecture, and a coastal current flows from north to south along the northern coast. These currents gather fragments of seashells and other debris, depositing them on the raised wave-cut platform, contributing to the formation of Aoshima. Because of its unique geological formation, it's designated as a Natural Monument of Japan as "Aoshima's raised seabed and unusual wave erosion marks". Over 200 plant species have been identified on the island, including 27 tropical and subtropical species, making it the northernmost subtropical plant community in the Northern Hemisphere. The large colony of *Livistona chinensis* (Chinese Fan Palm) is particularly valuable, leading to the designation of the "Aoshima Subtropical Plant Community" as a Special Natural Monument of Japan. Two theories have been proposed by scholars to explain the existence of such tropical and subtropical plant communities in this high-latitude location where they would normally die from the cold. One is the theory of sea-borne naturalized plants, which posits that seeds and live plants from the south, such as the Philippines and Okinawa, were carried by the Kuroshio Current and thrived. The other is the relic theory, which suggests that plants adapted to high temperatures that flourished in Japan during the Tertiary period survived to the present day in this location due to favorable climate, geography, and environment. Currently, the relic theory is considered more plausible.