In this paper the changes of the forest and climate in the early Alluvial age are discussed, based on the pollen analytical results of the four main stations concerning this subject in Japan, i. e. Yashimagahara, Ozegahara, Hyotan'ike and Ebetsu. The results are as follows (cf. Tab. 1, Figs. 2, 3): in the increasing warmth period of the early postglacial age, it was 3°C lower than the present time in average temperature, while in the following maximum warmth period, the forest zone was 300-600m higher and it was 2°-3°C warmer than now. These climatic changes can be satisfactorily correlated with the results obtained so far by many authors all over the world. Considering many chronological data such as those by Blytt, Sernander, von Post, Godwin, Sears, Hansen, Deevey, Frey, Selling, Bertsch, Firbas, Straka, and Nakamura, it was concluded that in Japan the absolute age of the boundary between the increasing and the maximum warmth periods was B. C. 6000-5500 years and the boundary between the maximum and the decreasing warmth periods was B. C. 2000-1000 years.
Moreover, the maximum warmth period may correspond with the period of sea-transgression in the early Holocene and the decreasing warmth period with that of regression. On the other hand, according to Ezaka and Nakano etc., the transgressive and regressive periods correspond to the Jhomon and Yayoi epochs respectively. Therefore, the boundary between Jhomon and Yayoi epochs can be presumed to be B. C. 2000-1000 years before. This conclusion is still more trustworthy, considering the results of C¹⁴-dating of the canoe remains found at the Kamo and Kemigawa Jhomon sites.