The monsoon tropics — Gateway or refugium?

Abstract

Ever since Joseph Hooker (1860) first set out to explain the evolutionary and geographic origins of the Australian flora, two theories on the significance of the tropical north have competed for dominance: whether it is (i) a gateway or bridge through which biota have entered from the north, or (ii) a region where climate has changed little from that of millions of years past, harbouring relicts of an ancestral, indigenous biota. But these theories do not necessarily conflict; in fact, recent workers have tended to accept a role for both, and attention has been focused on their relative contribution. After plate tectonic theory was accepted, the gateway hypothesis gained impetus and shifted emphasis-towards whether and to what extent tropical biota invaded after the Miocene collision between the Australian plate and the Sunda Plate (Truswell et al. 1987). The hypothesis of an indigenous biota has focused almost exclusively on the wet tropics, with the assumption that rainforests are the most likely relicts of Gondwanan flora and fauna (Christophel and Greenwood 1988; Schodde 1989). This is surprising given that today the wet tropics are confined to a tiny corner of the north-east, whilst the vast majority of northern Australia is dominated by communities experiencing a monsoonal climate. Nevertheless, nearly all the recent symposia and multi-authored books on the biogeography of northern Australia and the adjacent Malesian region (Whitmore 1981; Whitmore 1987; Kitching 1988; Knight and Holloway 1990; Walker 1992) have emphasised the wet tropics whilst almost ignoring monsoonal areas. So, the Australian Systematic Botany Society's meeting on 'Origin and Evolution of the Flora of the Monsoon Tropics' at Kuranda, north Queensland, in July 1994 was a welcome change of emphasis. This issue of Australian Systematic Botany contains a number of papers from the Kuranda symposium. Not all the papers are closely connected with the main theme and not all the papers that were presented appear here. This introduction concentrates on the theme, citing contributions that are published both here and elsewhere.