Abstract
A mixed forest dominated by Quercus mongolica, Pinus koraiensis, and Larix leptolepis occurs on the southwest slope of Mt. Nishi (2, 398m in elevation), southern Yatsugatake mountains, central Japan, covering the altitudinal range from 1, 840 to 2, 010m. This paper introduces the quantitative features of the mixed forest and the size structure of the three dominant species, and discusses the sig-nificance of the mixed forest in the vegetation history since the Last Glacial period in Japan.
Quercus mongolica dominates the mixed forest followed by Larix leptolepis in the total basal area. Pinus koraiensis occurs constantly although in smaller numbers than those of the preceding two spe-cies. The mixed forest still remains in the stage of the secondary forest, after a mountain fire or clear cut-ting. However, the relatively higher total basal area of the mixed forest (ca. 42m2/ha) indicates that this forest is approaching the mature stage. All of the three dominant species maintain their succes-sional individuals within the forest, of which Pinus koraiensis is the most abundant. The mixed forest is self-maintaining, adjusting to the cold and dry, continental climatic conditions of the southwest slope of Mt. Nishi. In the future, it is assumed that the mixed forest will change its quantitative compo-sition with the greater prevalence of Pinus koraiensis followed by Quercus mongolica.
The co-occurrence of Quercus mongolica and Pinus koraiensis within the same forest is unique in Ja-pan. In the continental part of northeastern Asia, however, a similar forest appears in the transitional area from a Quercus mongolica-dominated forest to a Pinus koraiensis-deciduous broad leaved mixed for-est. The mixed forest of Mt. Nishi is regarded as a disjunction from the forest of the continent.
Paleobotanical and geomorphological evidence indicates that the cold and dry continental climate during the Last Glacial period produced the Pinus koraiensis-Quercus mongolica mixed forest in cen-tral Japan. The postglacial warming and moistening may have forced the mixed forest to the south-west slope of Mt. Nishi as a refuge. The present mixed forest of Mt. Nishi is considered to be a descen-dant of the Last Glacial forest, a relict from the Last Glacial period.
