Temperate deciduous broadleaf forest dynamics around the last glacial maximum in a hilly area in the northern Kanto district, central Japan

Abstract

Research into the geographical distribution of temperate tree refugia and their associated environmental conditions during glacial stages is necessary to understand the processes by which the present vegetation and plant distributions developed. On the basis of pollen and plant macrofossil assemblages deposited in a small valley in a hill in the northern Kanto district in central Japan, we reconstructed the local and regional vegetation changes in and around the distribution range limit of temperate broadleaf trees during the latest stage of marine isotope stage (MIS) 3 (36.2–32.8 ka) and around the late stage of the last glacial maximum (LGM) (23.4–16.6 ka). During the latest stage of MIS 3, the local and regional vegetation in and around the hill was composed of temperate deciduous broadleaf forest dominated by Quercus subgen. Lepidobalanus and mixed with pinaceous conifers. The proportion of deciduous broadleaf trees in the regional vegetation increased during recurring warm and humid phases that were correlated with Greenland D-O 7, 6, and 5 warming events. During the LGM, coniferous forests composed of Picea jezoensis var. hondoensis, Tsuga diversifolia, Abies veitchii, and Betula ermanii, which are major components of the present subalpine forests in central and western Japan, expanded in hilly and mountain zones in central Japan. Refugia of temperate broadleaf trees existed at altitudes up to that of the study site and were limited to mesic places along the valley bottom. At the termination of the LGM around 18.8 ka, a biome shift to mixed coniferous and deciduous broadleaf forest dominated by Betula occurred in and around the study site. The expansion of deciduous broadleaf trees at ca. 19 ka, which has also been recognized in other localities in central Japan, may have been triggered by an increase in precipitation during the stage wherein summer insolation became greater. The temperate broadleaf trees that have been distributed in hilly-zone refugia were sensitive to warming at the termination of the LGM.