Alien plants believed to have been unwittingly transported by tourists to Mount Fuji are threatening to destroy or damage the ecosystem of the nation's newest World Heritage site and even its landscape, researchers say.

In a recent study of plants along the Fuji Subaru Line toll road, which winds 2,300 meters up to the fifth station and nearby trekking trails, researchers found 56 foreign species likely brought in from elsewhere in Japan or overseas.

"Actually, it has been said for more than 15 years that a considerable number of alien species are growing on Mount Fuji," said Takashi Nakano, chief researcher at the Yamanashi Institute of Environmental Sciences.