The Pinus pumila Zone during the Last Glacial Age in Japan Reconstructed from Present Growth and Distribution of Pinus pumila

Abstract

The presence or absence of the Pinus pumila zone during the Last Glacial Age in Japan is discussed on the basis of the present distribution and growth of Pinus pumila, on the assumption that summer temperature declined and winter precipitation decreased. At present the height, coverage, mean annual stem elongation and production rate of Pinus pumila scrub correlate with each other. Expansion and reduction of Pinus pumila scrub in the Last Glacial Age can be inferred from those relationships.
Mean annual stem elongation and production rate decreased with the reduction of summer temperature. Scrub height decreased with the decrease of snow depth around the stands. These facts suggest that the distribution of Pinus pumila scrub will be reduced when summer temperature declines and winter precipitation decreases. From this, it can be deduced that in the Last Glacial Age the distribution of Pinus pumila scrub is supposed to have strongly shrunk in the uppermost part of the mountains where the Pinus pumila zone is located at present; the Pinus pumila zone probably disappeared there. It may be possible that a Pinus pumila zone existed in area below the present-day lower limits of the periglacial landforms during the Last Glacial Age. However, the area is thought to have enjoyed a high summer temperature, which enabled the forests to be established there, as well as no serious deforestation agent. Thus the Pinus pumila zone was never established in this area as it was in the upper part of the high mountains.
In conclusion, the vertical zonation of the upper part of the high mountains in the Last Glacial Age was Forest zone-Timberline ecotone-Real Alpine zone, in ascending order, while the present arrangement is Forest zone-Pinus pumila zone without no intermediate ecotone. Those two arrangements are quite different. The Pinus pumila zone finally appeared in the Post Glacial Age when summer temperature rose and winter precipitation increased.