Did a cooling event in the middle to late Jomon periods induced change in the use of plant resources in Japan?

In Japan management and use of plant resources around settlements can be detected since the early Jomon period starting at ca. 7300 cal BP. At least two arboreal species, Castanea crenata (chestnut) and Toxicodendron vernicifluum (lacquer tree), show clear records of management by the Jomon people. After the early Jomon period corresponding to the Holocene Climate Optimum, the sea level lowered and the climate cooled, and these changes must have affected geomorphology and vegetation around settlements. However, it is not known if the management and use of plant resources by the Jomon people changed with such changes in environment. From the middle to late Jomon periods corresponding to this phase, pollen records indicated change in dominant plants around settlements from Castanea crenata to Aesculus turbinata (horse chestnut). This change in vegetation was attributed to a cooling event at the beginning of the late Jomon period at ca. 4400 cal BP or to human management. To examine the influence of environmental changes on vegetation and plant use from the early to final Jomon periods, plant records at four previously studied sites in the Kanto plain, central Japan, were compared. The results revealed that plant use centered on Castanea crenata and Toxicodendron vernicifluum did not change through the periods, but became more multi-faceted after the late Jomon period with additions of such plants as Aesculus turbinata and Quercus (Cyclobalanopsis).