Habitat characteristics of the sea-cliff plant Boehmeria splitgerbera on artificial retaining walls at the northern limit of its distribution

Abstract

The environmental conditions on the retaining walls, which can serve as secondary habitats for the native sea-cliff plant Boehmeria splitgerbera, were investigated in the Wanishi area, Muroran City, Hokkaido, Japan. The plant was observed on 10 out of 36 retaining walls, and 6 of these were made of concrete blocks. The maximum distance of the shoreline to these retaining walls was 713.7 m (mean, 375.3 m; standard deviation, 193.1). Based on the results of Welch's t-test and decision tree analysis, it was considered that the distance to the shoreline had the strongest effect on the growth of this species, followed by sky coverage and distance from the sea cliffs. From these findings, it was concluded that retaining walls close to the coast and sea cliffs can be used as secondary habitats for cliff plants such as B. splitgerbera, and that factors related to sky coverage, should be taken into consideration.