Wednesday 29 April 2009
Monday 27 April 2009
Friday 24 April 2009
Monday 20 April 2009
Thursday 16 April 2009
Wednesday 15 April 2009
- Tef has only partly lost grain shattering; while it is apparently reduced it remains a problem with mature crops (much as is true of sesame). The fact that this 'semi-domesticated' state has persisted for at least 2500-3000 years should be a warning to those pondering domestication processes: non-shattering need not evolve (either rapdily or in absolute terms) for a crop to be successfully cultivated and a persistant part of subsistence. Is there is model here for wheat, barley, rice or other millets during the enigmatic era of 'pre domestication cultivation'?
- The lack of clear early selection for grain size increase also attracts discussion. In part this might be accounted for by increase in grain number. Yield is a combination of both factors. She suggests that lack of intensive tillage may have operated against selection here. As a proponent for a tillage-grain size increase link I, of course, am prone to agree (see my Ann Bot paper). But importantly she attributes this to a concern for lodging, in which tall plants fall over under their own weight, or the weight of their grain, reducing yields and harvestibility. Apparently lodging is a big problem in tef, and made worse when soils are heavily tilled. This raises interesting comparative questions about other crops, such as to what extent similar concerns might have played a role early in cultivation. Most domesticated cereals have rather thicker culms than their wild progenitors; they are also often taller and straighter. Wild rices, and I reckon primitive cultivars, were spreading and thin-stalked. Operating against the development of erect forms may have been concerns with lodging, at least until thicker stalks evolved, and in some contexts this may have also operated against the trend towards larger grains, and helped to contribute to the vast variability in grain size one encounters across archaeological rices.
- D'Andrea points to the domesticated Digitaria spp. of west Africa (iburu and fonio) as possibly following a similar domestication pathway with similar constraints. Is there is more generalizable pathway here, perhaps applicable to Brachiaria spp. and Paspalum scrobiculatum as well, in which think culms that threaten lodging operate againt major increases in grain size and grain density, but not overall grain number which is dispersed across the panicle? This might also be relevant for some Panicum spp. (sumatrense, sonoram; but I guess not P. miliaceum)?
Tuesday 14 April 2009
Monday 13 April 2009
Last July, Bill Ruddiman and Chinese colleagues from the Institute of Geology published a artcile looking at the correlation between a compilation of archaeological evidence for rice in China and the divergence of global methane levels, towards higher levels, from the decrease that is expected based on previous interglacial patterns. This article appeared in Quaternary Science Reviews, and attracted a news note in Science "Was China an Early Emitter", but this has important implications for archaeologist, or rather it highlights the importance of the archaeology of early agriculture to wider issues to do global climate change. Below are my first reactions at the time of publication:
This is an important and compelling study, and represents the first attempt to ground truth that hypothesis of major prehistoric anthropogenic methane production may be linked to intensive rice cultivation. It is a clear indication of the importance of long-term history to better predictive modelling, and the role that archaeology can play in contributing to a more nuanced understanding of the human-ecosystem feedbacks in the long-term. I think it points towards a future of increasing cross-disciplinary research by palaeoclimatologists, climate modellers and archaeologists. I see my own research agenda as moving in this direction, and I put in a research grant on this topic (in June 2008) which has now been funded by NERC and starts in 2009. Prof. Ruddiman is acting as an international project partner on this grant, with a role of identifying the cross-disciplinary implication for palaeoclimatic studies. My recent participation at the Dec 2008 meeting of the American Geophysical Union, with a session on Holocene CO2 and Methane, is also representative of this growing need for increased communication and synergy between environmental archaeology, palaeoclimatology, and climate-modelling [abstract of poster here].
The overall trend that they find is that the spread of rice in
In support of their hypothesis and conclusions I would offer the following observations:
1. recent work [e.g. the Tianluoshan Science paper] shows clearly the emergence rice agriculture in the 5th millennium BC (by which time a large minority of rice was morphologically domesticated, and by the end of that millennium the vast majority was), indicates that during the 5th millennium BC this early agriculture was associated with wetland weed flora with a wide range of annual sedges and small-seeded annual grasses that can be associated with paddy cultivation. Excavations by the
2. Rice starts to become much more geographically widespread from about 3000 BC. There a few sites with rice in Middle Yangshao (>3000 BC) in central
3. The spread of rice outside
5. BUT. As indicated in 3, and 4. What is needed is to test this correlations more rigourously is clear evidence that when rice was present it was being grown in wet-field (paddy) systems rather than dry-cropped, e.g. in upland indica cultivation or shifting cultivation as dry-cropped systems would not increase methane output. Although it is likely the case that most early rice in the Yangzte and Yellow basins of china was paddy systems (the earliest well-documented Yangzte systems were), it would be good to have better data on weed flora to confirm this, and quantitative archaeobotanical samples to better estimate the relative extents of millet farming vs. rice farming. Archaeobotnically we needed better developed methodologies for sampling and for analyzing samples to determine the nature of cultivation systems they represent. The kind of archaeobotanical weed flora analyses which are established in the Near East and
6. Not just rice? We also need to consider the potential of human sources other than rice. The other big potential source is the spread of livestock, especially cattle. Early in their history domestic cattle were in the
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