Relationship between the southern limits of japanese temperate deciduous trees and temperature

The relationship between temperature and the southern limits of temperate deciduous trees in Japan is discussed by using two indexes of temperature. One is the mean temperature of the warmest month to represent summer condition, and another is the chilling hours (accumulated hours below 7.2°C (45°F)) for winter. Eight species of deciduous trees (Zelkova serrata, Fagus crenata, Aesculus turbinata, Pterocarya rhoifolia, Betula ermanii, Quercus mongolica, Ulmus davidiana and Acer mono) were chosen for this purpose. It appeared that the chilling hours are effective in determining the southern limit of Zelkova serrata, suggesting at least thermal condition in winter is important in the warm side distribution for this species. For other species, the case in which winter condition may affect southern limits is found in the coastal areas and the relatively low latitude region of Japanese mainland. The impact of global warming on the potential probability of occurence for Fagus crenata in Osaka Prefecture and its vicinity is also examined. For a 1.5°C mean temperature rise, the potential probability becomes 0.02-0.21 from the present 0.13-0.68 in Mt. Izumi-Katsuragi and Mt. Koya area, and 0.24-0.70 from 0.65-0.76 in Mt. Kongo. For a 3.0°C rise, the probability decreases to 0.04-0.34 in Mt. Kongo. In the other two areas, it will become almost 0 suggesting the climatic condition becomes too warm for the occurence of this species.