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The paleoecological data from Kuk Swamp indicate that, like other areas of the Highlands, a mosaic of cold-adapted grasslands and mon- tane forest persisted across the valley floor be- fore the Holocene (Fig. 3). Unlike other valleys in the uplands, the grasslands within the Kuk Swamp catchment did not succumb to forest advance at the onset of the Holocene. Instead, the grasslands and fern flora increased at the expense of forest between 10,200 and 7400 cal yr B.P. under the influence of periodic fire episodes and probably anthropogenic clearance. At the same time, forest composition in the catchment changed from a dominance of mon- tane canopy taxa such as Nothofagus, Castan- opsis, and gymnosperms to a predominance of subcanopy taxa, particularly Pandanus, Zingib- eraceae, and Musaceae sect. Eumusa. At 6950 to 6440 cal yr B.P., the data imply that forest declined abruptly as burning increased within the catchment and an open grass-sedge swamp- land became established. Musaceae phytoliths reach a maximum of 15% of total phytolith counts in this period (Fig. 3), which we inter-

pret to be derived from bananas (including Musaceae sect. Eumusa) growing locally with- in an open grassland environment.

Archaeological evidence. The archaeo- logical remains at Kuk have been divided into six phases of wetland use (13). The earliest three phases are relevant to the origins of agriculture in New Guinea, because they pre- date known Southeast Asian influence on the island at 3500 cal yr B.P. at the earliest (15) (Table 1).

The oldest archaeological features at Kuk (phase 1) are pits, stakeholes, postholes, and runnels that are restricted to slightly elevated and better-drained leve´es of a paleochannel (Fig. 2B). These features are consistent with planting, digging, and tethering of plants and localized drainage in a cultivated plot and are interpreted to represent a single period of shifting cultiva- tion on the wetland edge. The paleochannel is dated to 10,220 to 9910 cal yr B.P. (tables S1 and S2), and two dates from a feature on an adjacent surface are slightly earlier and later than this date, respectively. Based on func-

tional associations among these features and their ages, we interpret them to be contem- poraneous. The use of the wetland margin at this time was not specialized and represents the spatial extension of shifting cultivation practices (that is, dryland practices) onto the wetland margin during a drier period.

The phase 2 palaeosurface consists of the preserved circular and subcircular bases of reg- ularly distributed mounds, as well as less orga- nized features (Fig. 2C). The paleosurface is dated to 6950 to 6440 cal yr B.P., which accords with the date of an overlying and infilling de- posit, RW ash, at 6440 to 5990 cal yr B.P. (tables S1 and S2). Regular morphologies of features, numerous stake- and postholes, and heterogeneous feature fills with elevated char- coal frequencies are all consistent with a culti- vated paleosurface. The mounds created better- aerated soils along the moist, poorly drained wetland margin. The innovation of mounded cultivation indicates greater reliance on the wetland for subsistence in a resource-poor grassland landscape.

Fig. 2. Archaeostratigraphic representation of phases 1, 2, and 3.

11 JULY 2003

VOL 301

SCIENCE www.sciencemag.org

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