The impact of intensification and deintensification of Asian rice production: transitions between wet and dry ecologies

点击翻译按钮获取中文摘要

Rice is one of the worlds most important crops, and it has a long history of supporting dense populations and civilizations throughout East, South and Southeast Asia. This project will reveal the history of rice cultivation comparatively across the region using cutting age archaeological science. One major aim is to reconstruct how rice was grown across the region at different times. Rice may be grown in wet cultivation systems (irrigated or flooded) and dry cultivation (based only on rainfall, often in upland areas), and in intermediate lowland, rainfed conditions. These different systems have important implications in terms of how productive rice is, and therefore how much human population it can support, as well as how labour-intensive it was. Dry systems yielded less but also cost less in terms of labour. How rice was grown has important implications for the impact that humans and rice had on environmental change. Intensive systems tend to require greater landscape modification and by supporting higher populations have knock-on effects on other resources, for example through deforestation. Another very important impact is the production of methane, a greenhouse gas that contributes to global warming. Dry rice cultivation systems produce little methane whereas the more productive wet systems produce a lot. It has been hypothesized by some climate scientists that methane from rice contributed to an anomalous rise in methane over the past 5000 years which is not explained by natural sources. If so, then this has contributed to global warming even before the industrial era and will need to be factored into models that hope to predict where global climate change is going. One of the aims of this project is to ground truth this hypothesis by modelling up from the empirical archaeological evidence for rice cultivation over time to assess whether this fits with explaining at least part of the methane anomaly. In order to do this we need better evidence not just for where and when rice was cultivated but also whether it was grown in wet or dry systems. Through systematic study of archaeologically preserved seeds, we can identify the weed flora associated with past rice and whether it fits with a wet or dry system. In addition we have developed methods for classifying the assemblages of phytoliths (microscopic silica from the decomposition of plants) from archaeological sites as indicating wetter or drier rice cultivation regimes. We are now hoping to apply these methods over a larger number of sites and regions, especially regions for which archaeobotanical evidence for early rice is limited or lacking, including parts of India (western and northeastern), Bangladesh, Myanmar, Cambodia, Vietnam, and southern China (Yunnan, Sichuan, Guangdong). By combining these new results in a GIS modelling system, together with data from other parts of the region, mostly collected by us and colleagues over the past few years, we will be better able to produce realistic spatial models of the spread of rice, the extent of wet rice, and likely methane emissions over time. We will also be able to improve our understanding of how the development of rice agriculture relates to the long-term history of human societies in this region.