How natural are natural woods from wetland sites? - a case study at two sites of the Jomon period in central Japan

To clarify the characteristics of natural woods from wetland sites, the taxonomic composition and diameter of natural woods were compared with those of wooden artifacts at two sites of the middle to latest Jomon periods (ca. 5300-2800 cal BP) in central Japan that have contrasting characters. The Oise-yama site in Saitama was a least used site only with a few pit dwellings and pits on the surrounding upland and no structures in the wetland. The Shimo-yakebe site in Tokyo was a heavily used site with wooden structures and rows of stakes in the wetland and many remains on the upland. Natural woods of the Oise-yama site had an exponential decrease along the diameter gradient, irrespective of taxa, but wooden artifacts of the Shimo-yakebe site had clear marks of human selection both in the taxonomic composition and diameter. Natural woods of the Shimo-yakebe site also had an exponential decrease along the diameter gradient similar to those of the Oise-yama site. Thus, the exponential decrease in the diameter distribution seemed to be intrinsic in naturally deposited, allochthonous woods found at wetland sites.