We examined formation of an artificial ecosystem during the Jomon period in the central Kanto Plain, based on a detailed chronology by radiocarbon dating and analyses of pollen fossil assemblages at four sites of the initial to final Jomon periods. Around those sites, deciduous broad-leaved trees dominated from the initial to middle Jomon periods, and expansion of evergreen broad-leaved trees was detected only at seaside sites. At two sites of the initial Jomon period, Castanea crenata pollen dominated more or less, and existence of introduced plants was confirmed from pollen of Toxocodendron vernicifluum and seeds of Lagenaria ceraria var. gourda. Around those two sites, artificial stands of Castanea crenata and Toxicodendron vernicifluum were formed and managed since ca. 8000 cal BP and ca. 7650 cal BP of the initial Jomon period, respectively. These artificial stands of Castanea crenata and Toxicodendron vernicifluum continued to be maintained during the early to final Jomon periods in this area.
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