Northward Invasion and Range Expansion of the Invasive Fern Thelypteris dentata (Forssk.) St. John into the Urban Matrix of Three Prefectures in Kinki District, Japan

Abstract

This study investigated the current distribution of an invasive tropical fern, Thelypteris dentata, and its habitat type in three Japanese prefectures (Osaka, Kyoto, and Shiga) in the Kinki District. The results showed that T. dentata has expanded its distribution into highly urbanized areas in Osaka Prefecture and has reached southern Kyoto Prefecture and central Shiga Prefecture. The distribution of T. dentata populations thus seems to have expanded northward based on comparisons with the distribution that was determined in the 1980s. Because the fern's habitat types were mainly the side walls or bottoms of drainage channels, crevices in stone walls and roadsides, the urban matrix has not served as a barrier to the expansion of the range of T. dentata; on the contrary, it may be serving as a type of heat island corridor that is facilitating the spread of this species.