The impact of evolving of rice systems from China to Southeast Asia

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As the world's most productive crop, the history and potential of rice is of great interest to crop scientists and archaeologists, and as a greenhouse gas producer its history is important to climatic modelling. Understanding the development, diversification and spread of rice agriculture is central not only to our understanding of the processes of human population growth, dispersal and formation of civi-lizations in Asia, it is also central to reconstructing how past agricultural activities might have im-pacted global climate through methane emissions and deforestation. Archaeobotanical evidence offers a powerful set of tools for not only documenting where and when rice was cultivated in the past, but how it was cultivated through the analysis of ecology of associated weed flora in macro-remains assemblages and phytolith assemblages. We have pio-neered the study archaeological rice weed flora and the combination of archaeological plant macro-remains and phytoliths in our recent NERC-supported research in parts of India, Sri Lanka and China (NE/G005540/1). We propose to roll out this method over a wider geographical and cultural area, as well refining the approach through some additional modern analogues. we propose to focus our work on the less known parts of Asia, especially mainland Southeast Asia and the southern parts of China, as well as further work in the eastern parts of India. These regions are central to hypotheses on the dispersal of rice cultivation, including models linking the spread of rice to major language families such as Austroasiatic and Austronesian, and yet a lack systematically-studied evidence for rice cultivation itself, or evidence as to whether early rice represented an extension of the alluvial wetland cultivation systems like those of the Neolithic Yangtze (early subspecies japonica, typical of many modern temperate japonica) or the develop-ment of upland rainfed systems (the latter typical of many modern tropical japonica rices), with a secondary later parallel evolution of irrigated wet rice systems amongst indica rices. Therefore we will use a combination of archaeobotanical seed remains, including weed flora, and phytoliths to reconstruct the earliest rice cultivation systems (Neolithic-Bronze Age) along the three hypothesized trajectories of rice diffusion southwards from the Yangtze basin towards south-east Asia, namely in Yunnan, Guangdong, and Fujian, as well as across a range of subregions, environments and periods in mainland Southeast Asia (mainly in Thailand and Vietnam) to assess the extent to which rainfed and wet irrigated systems were practiced, and whether different regional patterns or a single evolutionary trajectory can be reconstructed.On the basis of our reconstructed rice arable systems and weed flora assemblages to as-sess the likelihood of single or multiple pathways for the spread of rice into Southeast Asia, by analysing the geographical and chronological patterns of weed flora. We will then use our improved understanding of how rice was cultivated in different times and periods of southern China and Southeastern Asia to produce improved models of past wetland rice area and linked methane emissions over time, grounded in the empirical evidence for past rice cultivation. Results will be of direct relevance to prehistorians and quaternary scientists interested in Holocene Asia and rice agriculture, but such results will have a wider impact in terms of assessing the regional and global impact, and sustainability, of different traditions of rice agriculture, and its contribution to ancient anthropogenic methane emissions.