S. G. Haberle
Vogelkop (Bird’s Head)
height in metres over 3000 2000 – 3000 1000 – 2000 300 –1000
West Papua (Irian Jaya)
i Papua New Guinea
4 Jimi Valley
5 Kainantu Valley
Figure 1. The island of New Guinea and location of sites mentioned in
2 Ifitamin Valley
3 Tari Basin
1 Baliem Valley
500 km © Carto ANU 04-073
agricultural development. Today, these intermontane valleys have been substantially transformed through human activities associated with agriculture, leading to the original organic-rich soils and swamp forest cover being replaced by organic-depleted soils supporting grasslands (figure 4).
While swamp forests persist in the intermontane valleys, today the community is restricted to small patches that fringe the grass or sedge peat swamps of the valley floors (Paijmans 1976). Most swamp forest trees grow on hummocks separated by pools of water, creating a sparse or open canopy with dense layer of small trees and shrubs (figure 5). The common trees include Syzygium and other Myrtaceae, conifers (especially Dacrydium and Podocarpus), Pandanus and Nothofagus. Pandanus are often dominant as their stilt roots are ideally suited to an ever-wet soil environment. The conifers (e.g. Dacrydium nidulum) are also an important component in disturbed swamp forests where they form dominant stands in early stages of swamp forest recovery towards a diverse mixed swamp forest assemblage ( Johns 1980). These swamp forests are assumed to represent the remnants of a once much more extensive forest community that covered the wet peaty soils of the intermontane valley floors. Here, I review the palaeoecological evidence from five major intermontane valleys in New Guinea (figure 1) and use two measures of past biodiversity to address the following questions:
Are the present day swamp forests remnants of a once much more extensive forest community?
How rapidly did the transformation from swamp forest to grassland occur and was the change ubiquitous in time and space?
Phil. Trans. R. Soc. B (2007)
What influence did anthropogenic fires and forest clearance activities have upon shaping the present day landscape?
What has been the overall impact on biodiversity and are there key taxa now missing as a result of past human activities?
What were the consequences of biodiversity loss for human populations in the highlands during the Mid–Late Holocene?
METHODOLOGY AND STUDY SITES
Measures of biodiversity through time using
palaeoecological techniques Estimating the diversity of past vegetation communities from pollen data is potentially a powerful tool to measure plant biodiversity through time. One approach is to use simple counts of pollen types in a sample as an estimate of diversity, though this requires a standard- ized or constant count size as the number of pollen types increases as the pollen count increases (Bennett & Willis 2001). The calculation of palynological richness was developed by Birks & Line (1992) as a way of standardizing the pollen count between samples and thus allowing comparisons within a pollen sequence. However, the taxonomic uncertainties associated with pollen morphological types means that species diversity may change but not be registered in pollen morpho- logical type change (e.g. changes in Poaceae species are generally not visible in the pollen record), resulting in a potential underestimate of biodiversity change.
A second approach is to target key biodiversity indicator taxa in the pollen record, where these taxa (or taxon) are representative of a distinct diverse vegetation