Phil. Trans. R. Soc. B (2007) 362, 219–228 doi:10.1098/rstb.2006.1981 Published online 5 January 2007
Prehistoric human impact on rainforest biodiversity in highland New Guinea
Simon G. Haberle
Department of Archaeology & Natural History, Research School of Pacific and Asian Studies, Australian National University, Canberra, Australian Capital erritory 0200, Australia
In the highlands of New Guinea, the development of agriculture as an indigenous innovation during the Early Holocene is considered to have resulted in rapid loss of forest cover, a decrease in forest biodiversity and increased land degradation over thousands of years. But how important is human activity in shaping the diversity of vegetation communities over millennial time-scales? An evaluation of the change in biodiversity of forest habitats through the Late Glacial transition to the present in five palaeoecological sites from highland valleys, where intensive agriculture is practised today, is presented. A detailed analysis of the longest and most continuous record from Papua New Guinea is also presented using available biodiversity indices (palynological richness and biodiversity indicator taxa) as a means of identifying changes in diversity. The analysis shows that the collapse of key forest habitats in the highland valleys is evident during the Mid–Late Holocene. These changes are best explained by the adoption of new land management practices and altered disturbance regimes associated with agricultural activity, though climate change may also play a role. The implications of these findings for ecosystem conservation and sustainability of agriculture in New Guinea are discussed.
Keywords: pollen; palynological richness; biodiversity indicator taxa; swamp forest; Papua New Guinea
1. INTRODUCTION New Guinea is one of the most biodiverse regions on the globe as it is believed to harbour over 5% of the world’s biodiversity in less than 1% of the land area ( Johns 1993; Miller et al. 1994; Heads 2001). In the current century, the greatest threat to regional New Guinea–Australian tropical biodiversity is an ever- increasing human population and pressures from global economic activity that have led to accelerated forest clearing, ecological degradation and climate change (Sekhran & Miller 1994; Haberle 2003a; Hilbert et al. 2004). In contrast to conditions in Southeast Asia to the west, at least 70% of the natural environment of the island remains intact and represents the third most significant expanse of tropical rainforest wilderness on Earth after the Amazonian and Congoli forest blocks (Mittermeier et al. 2005). While large- scale short-term assessments of the region’s vulner- ability to biodiversity loss have generally excluded New Guinea from the category of ‘biodiversity hotspot’ (Mittermeier et al. 2005), this approach ignores the potential that small-scale processes and long-term influence of human activity may also have a significant impact on biodiversity change.
The broad changes in vegetation since the arrival of humans in the highlands1 of New Guinea around
1 In this case, the term ‘highlands’ refers to the inland regions of the island of New Guinea above an altitude of about 1000 m and not exclusively to the present day Highlands provinces of Papua New Guinea.
One contribution of 14 to a Theme Issue ‘Biodiversity hotspots through time: using the past to manage the future’.
30 000 calendar years before the present ( yr BP; Kosipe record, White et al. 1970) have been established from 19 swamp and lake sites (Haberle 2003b). These records show that at the time of early deglaciation, beginning around 14 500 yr BP, the forest limit rises and montane forests invade valley floor grasslands in response to warmer temperatures and rising atmos- pheric CO2, though conditions were not uniformly suitable for forest development until after 9000 yr BP. The palaeoecological records from highland valleys point to a sustained and gradual intensification of forest clearance and burning from at least 7000 yr BP (Haberle 2003b), though evidence from the archae- ological site of Kuk Swamp in the Wahgi Valley (figure 1) suggests that at least here the valley floor was never completely forested during the Early Holo- cene. During this time, people were using fire to increasingly disturb and modify the montane forest and soils on the valley floor for the purpose of managing and harvesting significant food plants (Denham et al. 2004).
The development of agriculture as an indigenous innovation during the Early Holocene is considered to have resulted in increased population pressures, rapid loss of forest cover and increased land degradation over thousands of years (Haberle & David 2004). A review of the evidence for early agriculture in New Guinea supported by new data from Kuk Swamp demonstrates that cultivation had begun there by at least 7000 yr BP and probably much earlier (Denham et al. 2004). The focus of early agricultural activity was in the inter- montane valleys between 1000 and 1900 m above sea level, where the Early Holocene organic-rich soils and swamp forest cover provided a suitable environment for
This journal is q 2007 The Royal Society