Abstract
Vegetation poor landscape extended in the present subalpine area during the last glacial maximum period. At the end of the late-glacial period, the lower boundary of the alpine zone was located near the current lower boundary of the subalpine zone. Coniferous forests consisting mainly of Picea jezoensis var. hondoensis, Picea maximowiczii, Abies veitchii, Tsuga diversifolia, and Pinus koraiensis declined except for a limited area of Central Japan. Northern boreal coniferous forests consisting of Picea jezoensis, Abies sachalinensis, and Larix gmelinii which extended to the southern Tohoku District disappeared. In the postglacial period, herbs began to invade the upper part of mountains and formed an alpine or subalpine meadow. Northern boreal coniferous forests excluding Larix gmelinii continuously existed in Hokkaido during this period. Subalpine coniferous forests began to expand in Honshu at various periods of ca. 2500–6500 yr B.P. along the 37°N line of Mt. Shirouma–Mt. Naeba–Mt. Shibutsu–Mt. Kinunuma, at ca. 2500–3000 yr B.P. in areas north of this line, and at ca. 6500 yr B.P. or earlier in areas south of it. It is doubtful if the upper limit of the Fagus zone was higher than the present one during the Climatic Optimum period. The difference in the present subalpine vegetation between the Sea of Japan and the Pacific sides was caused by the unequal rate of invasion by conifers into the subalpine area that lacked developed forests after 2500 yr B.P. Probably the rate of plant migration didn’t catch up with that of the climatic change, and the invasion rate of conifers was affected by the size of their relic forests and the conditions of respective mountains, such as the amount of snow fall, the intensity of wind, the size of flat area, and the soil condition.
