The historical development of “Kurobokudo” layer : Preliminary discussion from the perspective of man-made ecosystems

Main factors for the formation of “Kurobokudo” layer (black humic volcanic ash soil) are as follows. (1) Tephra material : Its weathering products combine easily with humus. (2) Humid and warm or cool climate : The black humic layer could not be formed throughout the volcanic ash soil in northern Japan under the cold climate conditions during the Last Glacial. (3) Grassland vegetation : The black humic layer is formed under grassland vegetation whereas the brown humic layer is formed under climax forest. We could find two epochs for the development of the Kurobokudo layers in Japan since the Last Glacial. The first epoch (ca. 40ka) is in the late marine isotope stage (MIS) 3, accompanied by the sudden increase in palaeolithic remains. The second epoch (ca. 10ka) corresponds to the beginning of the Jomon period in the MIS 1, when rapid change to the humid and warm climate encouraged human activities. Thus, it seems that the Kurobokudo layers have developed under semi-grassland vegetation resulting from human activities such as the burning and deforestation in man-made ecosystems since the prehistoric period.