Analysis of subsistence strategy and settlement pattern of the Early Holocene shell midden site in the Yong River basin, Guangxi: Comprehensive evidence from archaeobotanical remains

The riverside shell midden site is an important cultural type of archaeological site in Guangxi in the early and middle Neolithic Age. There have been few studies of plant utilisation in southern China, especially for the period before the introduction of rice farming to Guangxi. The results of archaeobotanical and palaeoecological assessments of three freshwater shell middens-Baozitou(22°46'25.0“N, 108°19'46.4“E), Shichuantou(22°46'18.6“N, 108°23'39.3“E) and Nabeizui(22°47'53.4“N, 108°30'19.6“E)-that are located along the Yong River in Nanning City, Guangxi, provide significant data on pre-agricultural subsistence status in southern China. Multiple archaeobotanical methods were applied in this study, including the analyses of macrobotanical remains, archaeological parenchyma, microcharcoal, starch grains, and phytoliths, as well as radiocarbon dating. The radiocarbon dating results have refined the chronology of freshwater shell middens in the Yong River Basin. Based on the calibrated dates of the shells, Baozitou dates to ca. 12000~11130 cal.a B. P., Shichuantou to ca. 11250~10500 cal.a B. P. and Nabeizui to ca. 11060~9560 cal.a B. P. These are maximum ages for the occupation at these middens, and their real ages could be overestimated by up to more than 1000 years due to the freshwater reservoir effects. Nonetheless, the three studied shell middens were all used during the Early Holocene. Each shell midden was used for a maximum of 750 years to 1500 years, although probably for much shorter occupation periods. The periods of use for the three sites show significant overlaps. Phytolith and microcharcoal results indicate that palaeoecological trends present in different ways at each site during the period of the occupation. Baozitou and Shichuantou share more similarities in the transformation of the local environment, which is characterised as cumulative decreases in forestland and concomitant increases in grassland with persistent burning over time, whereas Nabeizui exhibits opposite trends to the other sites-namely, an increase in forest cover accompanied by slightly lower indicators of burning than at the other two sites. In addition to the inconsistencies in the palaeoecological trends, each site exhibits a similar period during which palm phytoliths are present. The similar occurrence of palms during a discrete period of occupation at each site is suggestive of human-directed resource intensification of palms in the landscape. The number of starch grains found at the three shell midden sites is not large, but the sources of species are relatively diverse. The starch grains from the three shell midden sites can be classified into four types, including Fagaceae(e.g. Castanopsis sp. and Cyclobalanopsis sp.), Poaceae, underground storage organs(USOs) and unknown taxa. The relative abundance of species reflects the diversity of tool-processed food and the diversity of food structure of the subsistence strategy of shell midden people. In terms of the artefacts, most of the starch grains come from three artefacts, and each site has one artefact with relatively rich starch grains. The extracted starch grains from the Nabeizui grinding stone suggest it is a multifunctional tool for processing multiple types of edible plant materials. The diversity of macrobotanical remains is relatively rich, indicating that the shell midden people exploited and utilised a variety of food resources(e.g. nuts, USOs, grass seeds and fruits). The discovery of carbonised food remains also suggests that humans learned to process and cook starchy foods. Many carbonised parenchyma fragments were found in the macrobotanical remains, which were preliminarily identified as originating from some parts of fruits and USOs. Some parenchyma fragments can be identified as bulb and Lotus root(Nelumbo nucifera) by using a combination of scanning methods, including transmitted light microscopy, scanning electron microscopy and MicroCT. The analysis results of this study combined with previous research results indicate that the diet breadth of the shell midden people in the Yong River Basin is extensively broad, including a variety of food resources(e.g. nuts, grass seeds, USOs, palm, aquatic and terrestrial animals and molluscs) with great difference in the rate of return, which suggests shell midden people adopted broad-spectrum collecting as their subsistence strategy. The discovery of grinding stones, pottery and carbonised food remains, as well as the intensive use of palm, suggest that the shell midden people had been able to remould environment and improve the return rate of various food resources, but the intensive use of plant resources is still in a relatively primitive stage. The shell midden community adopted new techniques for harvesting and processing food, and might have realised the predictability of certain resources. This provides the basic conditions for the shell midden people to reduce their mobility and enhance the willingness to settle down. According to the palaeoecological data, coupled with available archaeological findings for shell midden sites in this region, communities in the Yong River Basin during the Early Holocene adopted a logistical strategy to obtain resources in the landscape. The riverside shell midden sites might serve as periodical or seasonal settlements rather than as permanent settlements for foraging groups to exploit multiple resources. The shell midden communities did not live at a specific site year-round, but they did reside and utilise the midden site for an extended period within each year and such a connection was maintained over an extended timeframe.