Modern pollen assemblages from cultivated rice fields and rice pollen morphology: Application to a study of ancient land use and agriculture in the Pearl River Delta, China

Abstract

Pollen from a series of surface soil samples collected along a transect spanning southeast China was investigated to better understand palynological signals of ancient agriculture and other human activity. The transect surface samples consist of pairs taken inside and outside rice paddy fields. Pollen assemblages from these samples are valuable as modern analogs of human-altered environments and rice agriculture. Our measurements of Poaceae pollen grains from inside the modern rice fields discovered that 34–40 µm is the statistically significant size range for identifying domesticated rice in fossil pollen samples. This conclusion is also based on a size comparison of raw and chemically treated modern pollen grains from the plants. Pollen measurements for local wild grasses show that most native weeds have pollen grains less than 30 µm in size. The modern analogs and our study of the influence of chemical treatment on pollen grain size made it possible to examine a sediment core from the Pearl River delta for evidence of anthropogenic influence, including rice farming. Pollen assemblages from around 2200 cal. yr BP are highly similar to those of our modern analogs representing disturbed landscapes outside modern rice fields. The pollen spectra reveal abrupt increases in Poaceae, Dicranopteris, Artemisia and Pinus indicative of rice farming and forest clearance, at around 2200 cal. yr BP. Major factors associated with this abrupt transition were the rapid formation of the deltaic flood plain and massive increases in the Pearl River delta area population during the Qin Dynasty.