Ting Ma,  Barry V. Rolett,  Zhuo Zheng, and Yongqiang Zong

PNAS September 29, 2020 117 (39) 24138-24143.

ENVIRONMENT

Significance

Our study reveals a remarkable relationship between Late Holocene coastal evolution and the rise of rice agriculture across coastal Asia. Around 2,000 to 3,000 y ago, the emergence of coastal plains under freshwater conditions created expansive areas suitable for rice. We estimate that over the past three millennia the extent of coastal land suitable for wetland rice cultivation grew from about 16,000 km² to 96,000 km². Intensive paddy field farming took hold rapidly as coastal landscapes changed. Thus, large-scale rice farming was not established in southern China and Southeast Asia until rather late in the Holocene. This model helps explain ancient DNA evidence suggesting a major Bronze Age demographic expansion of rice farmers of northern East Asian descent.

Abstract

Rice agriculture is the foundation of Asian civilizations south of the Yangtze River. Although rice history is well documented for its lower Yangtze homeland area, the early southward expansion of paddy rice farming is poorly known. Our study investigates this process using a compilation of paleoenvironmental proxies from coastal sediment cores from southeast China to Thailand and Island Southeast Asia. We propose that a shortage of land suitable for paddy fields, caused by marine transgression, constrained rice agriculture during the mid-Holocene. Rapid expansion of coastal plains, particularly in deltaic basins, over the past three millennia has coincided with increases in land suitable for rice cultivation. Our study also helps explain the past population movements of rice farmers.

See https://www.pnas.org/content/117/39/24138

Figure 2: Records of Poaceae pollen change. Crosses show the time series plots of total Poaceae for sediment cores from southern China and SEA. Diamonds show records of rice-type Poaceae pollen from sites FZ4 (South China), GZ-2 (South China), VN (Vietnam), GA (Vietnam), and Paoay Lake (Philippines). See SI Appendix, Fig. S3 for additional data on rice-type Poaceae pollen, focusing on the 2.5- to 2-ka time interval.