Geoffrey S. Hope and Simon G. Haberle
such as ditches, earthworks and quarries. The other main line of evidence comes from palaeoecology, in which the vegetation and faunas are reconstructed from dated fossil sequences. In New Guinea the main effort has been to use pollen, although some specialised swamp ditch systems have also been investigated, for example by Haberle et al. (1991), Golson (1991) and Sullivan et al. (1987). Past fire is inferred from swamp and lake sediments by counting microscopic charcoal fragments, and by dating larger fragments in a range of other deposits (Haberle et al. 2001).
At the time of European contact the population was concentrated along the coastal fringe with quite sparse and isolated groups in the rainforests and mountain slopes (Figure 1). Some areas, such as the Fojes Mountains, seemed to be totally without habitation. The large intermontane valleys with complex agriculture based on root cropping centered on the altitudes of 1400–1850 m were a major discovery of the twentieth century. Brookfield (1964) showed that this pattern reflects the chances for success with agriculture. The outer flanks of the mountains are perhumid, with precipitation more than double evaporation in almost all months. Under such misty conditions crops do not thrive (Hanson et al. 2001). In the intermontane valleys the mountains cut off the orographic rain and local circulations dominate in most seasons. Here air rises each day up the warmed slopes and descends over the valley, giving sunny conditions with adequate rainfall from afternoon thunderstorms. Away from the large highland basins, even small valleys may have this effect, and may thus support small hamlets. In these marginal settlements techniques of ditching and mounding are used to shed water from the fields. There is a north west-south east gradient from aseasonal precipitation to the appearance of a weakly defined dry season, and from relatively infertile limestones and mudstones in west Papua to richer soils fertilised by volcanic ash falls in Papua New Guinea east of the Strickland River.
The advent of humans, their spread into the range of environments, and their impact Period 1: 55,000–20,000 years
The timing of the arrival of people in New Guinea is part of the wider controversy of when people arrived in the Australian region, since the two landmasses had continuous connections across the then dry Torresian Plain until only 8000 years ago. Dates of 55– 60,000 BP have been suggested from southeastern and northern Australia (for example Thorne et al. 1999) while a faunal extinction event that takes place 48–43,000 has also been proposed (Roberts et al. 2001) as marking early occupation. Others (O’Connell & Allen 2000) have pointed out that this evidence is tenuous and have disputed any ages greater than ca 38,000 BP. Coastal occupation in the oceanic islands east and west of New Guinea is proven from at least 33,000 BP (Spriggs 1997; Irwin et al. 1999). The oldest claimed site in New Guinea is still the Huon Peninsular where finds of stone adzes were made on a raised marine terrace (Groube et al. 1986). The terrace formed about 55,000 years ago when sea level was 65m lower than present, and was occupied after initial uplift, at an estimated 48,000 BP. However only a few scattered archaeological sites are currently known for this period, including 30,000 BP sites in the Birds Head (Pasveer 2003) and Lachitu near Vanimo (Gorecki et al. 1991). A similar age site is also known from Lemdubu Cave on the Aru islands, southwest of New Guinea but then connected to it and Australia by the Torresian landbridge (O’Connor et al. 2002).