The history of the human landscapes of New Guinea
one of in situ development of food-plant promotion and management in the highlands under a cold, highly variable environment subject to severe drought stress particularly during the late glacial transition period (14,500–8500 BP, Haberle 1998).
Despite the high fire activity at the end of the last glacial period the driving force behind forest expansion into grassland overrides the persistence of fire activity such that, in all sites that cover the early Holocene, we find swamp forest dominated by Syzygium, Pandanus and some gymnosperm taxa developed around wetlands in the valley floors. The relatively high biodiversity and resource value associated with swamp forests, including the high density of utilisable Pandanus species (P. antaresensis, P. brosimos/julianettii complex; Haberle 1995) may have led to these environments being a focus of human activity throughout the Holocene.
The appearance and spread of ‘agriculture’ in the highland valleys is covered elsewhere in this volume. However the earliest indications of ditching within a mosaic of forest and grassland around 9000 BP (Denham et al. 2003; Haberle 2003), accord remarkably well with the transition to ‘modern’ Holocene climates, points to the possibility that expansion of clearing and plant manipulation was partly environmentally controlled. By 7–6000 years ago the lower parts of the major highland valleys were cleared and would have looked similar to their appearance in 1933 (minus sweet potato cultivation). It is possible that the early Holocene was a time of more reliable climates, the El Niño-related drought and frost being much rarer (Grove & Chappell 2000). This would have rewarded experimental taro and banana planting and water manipulation (Denham et al. 2003, Denham et al. 2004).
Above and below the intermontane
In the areas around the great highland valleys the records are very varied. Subalpine areas near Mount Albert Edward, and north of Mount Trikora record fire almost as soon as the ice retreats, and pollen diagrams show continuing disturbance to the present day. At Mount Jaya firing starts about 11,000 years ago and the Mapala rockshelter records hunting from 5500 years ago that resulted in the extinction of a small wallaby (Thylogale christensenii). Hope et al. (1993) speculate that pressure of hunting allowed the copper ringtail possum (Pseudocheirops cupreus) to expand into the subalpine niche. This hunting post-dates the development of large human populations at lower altitudes. Other mountains, such as Mount Wilhelm, experience clearance only within the last millennium, apparently associated with rising limits to agriculture (Corlett 1984).
Isolated valleys and lower montane sites generally are cleared in the middle or late Holocene. For example Sirunki, on the Wabag divide at 2500 m altitude is cleared about 4500 BP (Walker & Flenley 1979). Telefomin on the other hand has at least three clearance events, reverting to dense forest between each one (Gillieson & Hope 1989). The Jimi Valley, at around 800 m, was cleared about 3000 years ago but clearance in isolated valleys near it is less than 300 years old (Gillieson et al. 1989).
Considering the long period of occupation of the coast and lowlands (O’Connor & Chappell 2004), it is curious that the disturbance history resembles that of the highlands. Expansion of grasslands occurs in the Lake Sentani region at 11,200 BP (Hope 1996) and it is likely that this also applies to the seasonal woodlands of the Markham Valley as Lake Wanum records burning from the base of a core dated to ca 9000 BP (Garrett-Jones 1979).