To identify the cause of non-equilibrium between current climate and the distribution of Tsuga diversifolia, climatic conditions for the species distribution were clarified and potential habitats under current and last glacial maximum (LGM; 21 ka) climates were projected.

The relationships between T. diversifolia distribution and climatic variables were explored using CTM and GAM based on high-resolution (ca. 1km) climatic data and a nationwide distribution database.

The models were highly accurate. We revealed that T. diversifolia requires high summer precipitation even in humid Japanese environments. Areas with cooler summer and higher summer precipitation were classified as potential habitat.

Empty habitat, the areas of potential habitat under current climate without actual species occurrence, was identified in Hokkaido. Meanwhile, no potential habitat was projected in Hokkaido during the LGM. Additional experiments, of which varied the temperature and summer precipitation during the LGM, showed that potential habitat was projected in Hokkaido if summer precipitation increased nearly equal to the current climate.

These results suggest that T. diversifolia had occurred in Hokkaido until late Neogene, but the species vanished during the glacial periods of Pleistocene due to increased summer dryness.