Charcoal fragments are derived from both natural and anthropogenic fires. Fire history has been studied by tracing charcoal abundance in sediments. Charcoal studies in Japan suggested that fires occurred frequently between the terminal Pleistocene and the early Holocene. Frequent fires in this period are considered to have disturbed vegetation. So far charcoal studies in Japan have examined mostly microscopic charcoal less than 100 μm in diameter, but macroscopic charcoal more than 100 μm in diameter has been examined recently. Macroscopic charcoal generally represents the local fire history. The macroscopic charcoal analysis minimizes charcoal breakdown in analytical procedures, facilitates charcoal identification from other fragments, and allows efficient analysis of sediments. This review introduces the methods of the macroscopic charcoal analysis, stressing the above merits of this analysis.
Here I summarized my researches on the original plants of minute charcoal fragments. The length-width ratio of minute charcoal fragments of more than twenty plant species native in Japan showed that the lengthwidth ratio of charcoal fragments, although useful in several cases should be applied more carefully to identify burnt plants and vegetation types in Japan, because some woody and herbal plants have exceptional length-width ratios of charcoal fragments. Changes in the morphology of minute charcoal fragments by different combustion temperatures were studied on several woody and herbal species. Some types of charcoal fragments generated experimentally were hardly seen in the charcoal fragments extracted from the sediments, while some types that were not in the experimentally generated charcoal fragments were seen in the sediments. The study indicated that the ratio of the types of charcoal fragments in a species changes according to the combustion temperature and that the change in the ratio is different among species. According to some applying studies, original plants of minute charcoal fragments and vegetation as a set of plants can be clarified to a certain degree in many cases, although there are many problems to be dealt with in the minute charcoal analysis. The level to be clarified depends on the simplicity or the complexity of the composition of the original vegetation. If there are other analyses on the past vegetation such as pollen analysis, they serve as good references.
With the recent progress of a replication technique, we can now observe the details of impressions on pottery and can correctly identify the species that made the impressions. We compared the shape, size, and structure of the “Wakudoishi type” impressions thought to be the hila of leguminous seeds with the hila of extant leguminous seeds. We found that the hila of excavated large beans made the “Wakudoishi type” impressions on the pottery of the late to latest Jomon periods in the Shimabara peninsula and the Kumamoto plain, central Kyushu Island. Further morphological observation showed that the excavated large beans are probably a type of Glycine max subsp. max cultivated in the Jomon period. We deduced from archaeological evidence that the prehistoric Glycine max subsp. max was introduced to Kyushu Island in the middle phase of the late Jomon period (ca. 1600 cal BC) from the Korean peninsula together with rice and barley.