The beating heart: environmental history of Australia's deserts

The Australian deserts are extensive but relatively well vegetated, compared with the hyperarid Namib or Atacama, and in climate, vegetation and landforms they more closely resemble the Kalahari. Rainfall in the driest areas is low (mean around 100 millimetres per year), but it is highly variable (annual totals measured at Birdsville range from 33 to 496 millimetres) and sufficient to sustain scattered trees, shrubs and grasses and infrequent runoff to fill waterholes and lakes. Today, there is a direct relationship between plant growth (measured by satellite) and available moisture (Berry and Roderick 2002) and therefore sensitivity to either an increase or decrease in precipitation. During the human occupation of Australia (perhaps 60,000 years), the deserts have expanded to the very edges of the continent and shrunk to a fraction of their present extent. Global climate change has forced dramatic responses in the Australian desert environment, to a degree that is remarkable given the distance from the centres of glaciation in the Northern Hemisphere and the apparent antiquity of the deserts themselves. At its most extreme, during the last glacial maximum (LGM), 20,000 years ago (Fig. 5.Ia), desert sand dunes extended to the western, northern and southern coasts but also formed near sea level along the eastern coast (Bowden 1983; Thom et al. 1994; Hill and Bowler 1995) and in the eastern highlands (Nott and Price 1991; Hesse et al. 2oo3a) in areas which today are wooded and receive up to 1000 millimetres of precipitation annually. During the LG M, woodland and forest communities were reduced to isolated pockets in the inland and a narrow strip along the coastal fringe of the east and south-west (Hope I987; van der Kaars I99I) while desert shrub and grass communities replaced the trees and extended towards the coasts (Singh and Geissler I985; Dodson and Wright I989; Harle et al. I999). Conversely, at times during the late Pleistocene, large perennial freshwater lakes in the Darling and Willandra regions, in the south-eastern sector of the arid zone, sustained early human populations (Bowler et al. 2003). An earlier and more widespread phase of 'mega-lakes' occurred throughout the arid zone in the last interglacial period (from 135,000 to 120,000 years ago; see Fig. 5.1a) and in previous interglacials. We know comparatively little about the environment at this time (especially the vegetation and lacustrine resources), and whether or not this presented more abundant resources to the first colonists. Nevertheless, at times in the past the deserts of Australia must have been something like the paradise imagined by JW Gregory