XVI International Botanical Congess

During winter, the NW-monsoon causes high long-lasting snowcover on the Japan-Sea side of Honshu whereas clear skies with large daily temperature fluctuations prevail on the Pacific side. This contrast is enhanced by the Japanese Alps and results in an asymmetric zonation of vegetation in central Honshu. On the Pacific side, montane Fagus crenata forests are replaced by mixed subalpine fir forests at about 1600 m a.s.l., whereas Betula ermanii forms open stands in the subalpine zone on the Japan-Sea side. Differences in tree line formation are discussed by comparison of subalpine ecotones with high and low snowcover. Investigation of seasonal frost hardiness of B. ermanii revealed that frost is no limiting factor at the timberline on Mt. Fuji. Respiratory carbon loss during a nine-month leafless stage for birch at the timberline represents a major limiting factor for tree survival. Measurements of annual respiration on Mt. Fuji provide a quantitative assessment of the above-ground carbon loss dependent on temperature. The significance of snowcover for the carbon loss of birch at the tree line will be clarified.