Early Agriculture in Southeast Asia: Phytolith Evidence from the Bang Pakong Valley, Thailand

Article excerpt

Phytoliths -- the microscopic opal silica bodies inside plant tissue that often survive well in archaeological deposits -- are becoming a larger part of the world of human palaeobotany. They give a new view of early rice in southeast Asia.

Introduction

In 1989 researchers working in the region of Khok Phanom Di, a 4000-year-old site in the Bang Pakong Valley, identified evidence of cultural burning and possibly early agriculture in the 5th millennium BC in sediment cores (FIGURE 1; Maloney et al. 1989). Phytolith analysis of these same cores provides a more detailed record of agriculture and grass weeds, and indicates that cultural modification of the environment may have begun even earlier.

Despite previous claims for early rice agricultural development in Thailand (Gorman 1973; 1977), abundant early evidence from southeastern China pre-dates Thai archaeological sites (An 1989; Yan 1991). Higham and co-workers investigated the coastal region of Thailand, particularly the fresh-water swamp zone, and the site of Khok Phanom Di for possible early agricultural development (Higham et al. 1992; Higham & Maloney 1989). While the site was first occupied at the beginning of the 2nd millennium BC, late relative to the beginnings of agricultural development (Higham & Bannanurag 1990), pollen cores from adjacent fields document human and natural environments back to the 6th millennium BC (Maloney 1992c). One core, KL2, showed several intense charcoal peaks pre-dating the site's occupation (5278[+ or -]420 BC (OxA-1359) at 4-95 m, 4950[+ or -]390 BC (OXA-1357) at 3.50-3.54 m). Slightly later, charcoal peaks are associated with weeds indicative of rice field cultivation (2.30 m, c. 4350[+ or -]375 BC (OxA-1356)). While rice is not directly identifiable from pollen data, the decline in mangrove species, increase in burning and increase in rice field weeds strongly suggest agriculture was practised in this region in the 5th millennium BC (Maloney et al. 1989: 367).

Methods

Two cores, KL2 and BMR2, from the Bang Pakong Valley were analysed for phytoliths. Both were located 170-200 m north of the site of Khok Phanom Di, within 30 m of each other. The pollen, spore, charcoal and sediment records are discussed in detail by Maloney (1992a; 1992b; 1992c; 1992e). The site is strategically located near the estuary of the Bang Pakong River, has access to marine, mangrove, riverine, fresh-water swamp, and alluvial plain/grassland resources. The diversity and abundance of subsistence resources made this an advantageous niche throughout the Holocene (Higham et al. 1992; Takaya 1979).

Phytolith extraction from sediment samples followed standard methods (Piperno 1988). Soils were disaggregated in [Na.sub.2] C[O.sub.3]. A 270-mesh sieve separated the sand fraction from the silts and clays. Clays were removed by gravity sedimentation, and the remaining silts were then fractionated, also by differential gravity sedimentation. The organics were wet ashed from these fractions with KCl[O.sub.3] (Schulze's solution). The phytoliths were floated (specific gravity [is less than] 2.3) on a density gradient of potassium and cadmium iodide (specific gravity 2.35). Samples were washed in water, dried in acetone, and mounted in permount. Phytoliths were counted at 400x on an Olympus photomicroscope while the permount was still fluid. Individual phytoliths were rotated to avoid confusion with similar two-dimensional forms.

Phytoliths were identified using modern reference material of over 340 species, comprising most of the southeast Asian families known to be phytolith producers (after Piperno 1988), as well as many previously untested Old World tropical taxa (Kealhofer & Piperno in press a). A major goal of this study was to retrieve and identify Oryza phytoliths from sediment cores.

Nearly a century ago German botanists studying grass morphology identified distinctive Oryza glume phytoliths (Formanek 1899; Grob 1896). …