Climatic controls of a keystone understory species, Sasamorpha borealis, and an impact assessment of climate change in Japan

Introduction The aims of this study were to identify the climatic conditions controlling the distribution of Sasamorpha borealis and to assess the impact of climate change on the species in Japan. Materials and methods The relationship between S. borealis distribution and climatic variables in the Japanese Archipelago was explored using classification tree analysis. Potential habitat maps under the current and future climates were generated at about 1-km spatial resolution. Results The model was highly accurate. Although snow cover has been thought to be the most important factor controlling S. borealis distribution, we revealed that the species requires high precipitation during the growing season even in humid Japanese environments. Areas with high summer (May-September) precipitation (PRS) were classified as potential habitat irrespective of other climatic conditions. In areas with moderate PRS, potential habitat was limited to cooler and less snow-covered areas and areas with low PRS were classified as non-habitat. The high fitness of the predicted to the observed distributions suggested that S. borealis could have survived throughout the Japanese Archipelago during the glacial period. Conclusion In future climates, 29.0-39.1% of the current potential habitat was predicted to change to non-habitat due to increasing dryness in the growing season. Areas with high precipitation remained a potential habitat for S. borealis.