The adaptation of dryland crops to the climate in southern China

It is unclear how dryland crops adapted to the humid climate of southern China, nevertheless they were an important component of prehistoric agricultural systems in the region. In this study, archaeobotanical results assembled from 110 archaeological sites in southern China, Digital Elevation Model (DEM)-based slope results of these archaeological sites, regional meteorological data and paleoclimate records were used to analyse the main factors affecting the distribution of prehistoric dryland agriculture, to help understand the adaptation of this agriculture to southern China and assess the role of climate change in the expansion of dryland crops in the region. The results highlighted the importance of effective water input and temperature. Farmers in prehistoric times adopted diverse strategies to plant dryland crops in southern China. The main proportion of the dryland crops centred on the use of foxtail millet (over 75% of the total dryland crops) and it was adjusted to adapt to the variations in effective water inputs resulting from precipitation and topography in the low-elevation area. Approximately 3° might be the slope threshold for agricultural transformation in the low-elevation humid areas of southern China. The millets-dominated (61.7%) or rice-dominated (85.3%) agricultural systems in dry-hot valleys, and wheat-dominated (51.8%) agriculture in the west Yunnan-Guizhou Plateau were developed to adapt to the arid climate and the low summer temperature, respectively. The weakening of the Asian monsoon since 5000 BC had objectively favoured the expansion of dryland agriculture in the low-slope areas of southern China, but the role of climate change should not be overestimated in the expansion of dryland crops.