Alison Weisskopf

The contribution of rice agriculture and livestock pastoralism to prehistoric methane levels An archaeological assessment

We review the origins and dispersal of rice in Asia based on a data base of 443 archaeobotanical reports. Evidence is considered in terms of quality, and especially whether there are data indicating the mode of cultivation, in flooded (‘paddy’ or ‘wet’) or non-flooded (‘dry’) fields. At present it appears that early rice cultivation in the Yangtze region and southern China was based on wet, paddy-field systems from early on, before 4000 bc, whereas early rice in northern India and Thailand was predominantly dry rice at 2000 bc, with a transition to flooded rice documented for India at c. 1000 bc. On the basis of these data we have developed a GIS spatial model of the spread of rice and the growth of land area under paddy rice. This is then compared with a review of the spread of ungulate livestock (cattle, water buffalo, sheep, goat) throughout the Old World. After the initial dispersal through Europe and around the Mediterranean (7000–4000 bc), the major period of livestock expansion is after 3000 bc, into the Sub-Saharan savannas, through monsoonal India and into central China. Further expansion, to southern Africa and Southeast Asia dates mostly after 1000 bc. Based on these two data sets we provide a quantitative model of the land area under irrigated rice, and its likely methane output, through the mid to late Holocene, for comparison to a more preliminary estimate of the expansion of methane-producing livestock. Both data sets are congruent with an anthropogenic source of later Holocene methane after 3000 bc, although it may be that increase in methane input from livestock was most significant in the 3000–1000 bc period, whereas rice paddies become an increasingly significant source especially after 2000 bc.

Modelling the Geographical Origin of Rice Cultivation in Asia Using the Rice Archaeological Database

We have compiled an extensive database of archaeological evidence for rice across Asia, including 400 sites from mainland East Asia, Southeast Asia and South Asia. This dataset is used to compare several models for the geographical origins of rice cultivation and infer the most likely region(s) for its origins and subsequent outward diffusion. The approach is based on regression modelling wherein goodness of fit is obtained from power law quantile regressions of the archaeologically inferred age versus a least-cost distance from the putative origin(s). The Fast Marching method is used to estimate the least-cost distances based on simple geographical features. The origin region that best fits the archaeobotanical data is also compared to other hypothetical geographical origins derived from the literature, including from genetics, archaeology and historical linguistics. The model that best fits all available archaeological evidence is a dual origin model with two centres for the cultivation and dispersal of rice focused on the Middle Yangtze and the Lower Yangtze valleys.

Phytoliths and rice: from wet to dry and back again in the Neolithic Lower Yangtze

Abstract The cultivation of rice has had a major impact on both societies and their environments in Asia, and in China in particular. Phytolith assemblages from three Neolithic sites in the Lower Yangtze valley reveal that in early rice fields the emphasis was on drainage to limit the amount of water and force the rice to produce seed. It was only in the later third millennium BC that the strategy changed and irrigated paddies came into use. The results demonstrate that plant remains, including weed assemblages, can reveal wetter or drier growing conditions, showing changes in rice cultivation from flooded and drained fields to large, intensively irrigated paddies.

From Early Domesticated Rice of the Middle Yangtze Basin to Millet, Rice and Wheat Agriculture: Archaeobotanical Macro-Remains from Baligang, Nanyang Basin, Central China (6700–500 BC)

Baligang is a Neolithic site on a northern tributary of the middle Yangtze and provides a long archaeobotanical sequence from the Seventh Millennium BC upto the First Millennium BC. It provides evidence for developments in rice and millet agriculture influenced by shifting cultural affiliation with the north (Yangshao and Longshan) and south (Qujialing and Shijiahe) between 4300 and 1800 BC. This paper reports on plant macro-remains (seeds), from systematic flotation of 123 samples (1700 litres), producing more than 10,000 identifiable remains. The earliest Pre-Yangshao occupation of the sites provide evidence for cultivation of rice (Oryza sativa) between 6300–6700 BC. This rice appears already domesticated in on the basis of a dominance of non-shattering spikelet bases. However, in terms of grain size changes has not yet finished, as grains are still thinner than more recent domesaticated rice and are closer in grain shape to wild rices. This early rice was cultivated alongside collection of wild staple foods, especially acorns (Quercus/Lithicarpus sensu lato). In later periods the sites has evidence for mixed farming of both rice and millets (Setaria italica and Panicum miliaceum). Soybean appears on the site in the Shijiahe period (ca.2500 BC) and wheat (Triticum cf. aestivum) in the Late Longshan levels (2200–1800 BC). Weed flora suggests an intensification of rice agriculture over time with increasing evidence of wetland weeds. We interpret these data as indicating early opportunistic cultivation of alluvial floodplains and some rainfed rice, developing into more systematic and probably irrigated cultivation starting in the Yangshao period, which intensified in the Qujialing and Shijiahe period, before a shift back to an emphasis on millets with the Late Longshan cultural influence from the north.

Phytolith identification criteria for foxtail and broomcorn millets: a new approach to calculating crop ratios

Broomcorn and Foxtail millets were major crops in the Yellow River Valley region, Henan, China, during the Neolithic Yangshao period. Phytoliths and macro remains have been used to understand crop choices in this period. Distinguishing between phytoliths from millet crops and panicoid non cultigens can be challenging. We examine the effect of using only one or two identification criteria compared with a more stringent five or more with phytoliths from archaeological samples to examine crop ratios. We compare our results with the results from the macro remains. This demonstrates, firstly, that using more identification markers has a very definite effect on the results and secondly, phytoliths and macro remains are complementary proxies that when used together can produce more accurate results than used alone.

A wet and dry story: distinguishing rice and millet arable systems using phytoliths

Changing rice and millet arable systems were closely linked to social and environmental changes in Neolithic and Early Bronze Age in Central China. Two methods are used here to distinguish between rainfed millet farming and rice farming, using phytoliths from crop weeds found in ash middens and mixed cultural layer contexts. Samples were taken from three sites, Xipo and Huizui, in the Yellow River Valley in Henan, and Baligang which is situated towards the south of the province. The samples are from three cultural phases, Yangshao, Longshan and Erlitou. The phytoliths used are from grass leaves, so are not identified to genera or species but rather grouped into ecological categories, and canonical correspondence analysis was applied. Next, the ratios were calculated of phytolith morphotypes from cells that are genetically predisposed to form phytoliths (fixed), compared to silica bodies from cells that will form silica bodies when there is sufficient water uptake (sensitive). The results show differentiation between millet and rice and differences in how wet the rice fields were. The region experienced social and climate change throughout this time and this is reflected in the results.

A tale of two rice varieties: Modelling the prehistoric dispersals of japonica and proto-indica rices:

We model the prehistoric dispersals of two rice varieties, japonica and proto-indica, across Asia using empirical evidence drawn from an archaeobotanical dataset of 400 sites from mainland East, Southeast and South Asia. The approach is based on regression modelling wherein goodness of fit is obtained from log–log quantile regressions of the archaeologically inferred age versus a least-cost distance from the origin(s) of dispersal. The Fast Marching method is used to estimate the least-cost distances based on simple geographical features. We explicitly test three hypotheses for the arrival of japonica rice to India where, it has been proposed, it hybridized with the indigenous proto-indica, subsequently spreading again throughout India. Model selection, based on information criteria, highlights the role of the Inner Asia Mountain Corridor in introducing japonica rice into northeast India, followed closely by a ‘mixed-route’ model, where japonica was also almost simultaneously introduced via Assam, Bangladesh and Myanmar. Finally, we estimate the impact of future archaeological work on model selection, further strengthening the importance of the Inner Asia Mountain Corridor.