Pattern and process in riparian vegetation of the treeless high country of Australia

Australia's high mountains tend more to elevated vegetated plains than the steep, bare crumbling mountains copiously decorated by snow and ice characteristic of the plate collision alpine archetype. Consequently, these landscapes are rich in gentle streams in the depositional mode, as well as those that rush and cut. Unlike most of Australia, the high mountains receive more moisture from precipitation than they lose through evaporation, and a substantial part of the moisture input arrives as snow, hail or rime, to cover the landscape on time scales that vary spatially and from days to seasons.

The riparian vegetation that is the subject of this chapter occurs in the alpine and subalpine zones of Australia, not including the subantarctic islands. The alpine zone is defined as land above the limit of trees, which roughly corresponds to a mean daily temperature of the warmest month of 10°C. Treeless vegetation of similar species composition to alpine vegetation also occurs extensively in the subalpine zone, defined roughly by the lower altitudinal limit of Eucalyptus niphophilus on mainland Australia (Costin et al. 2000), by the upper limit of the hummock sedge Gymnoschoenus sphaerocephalus in western Tasmania (Kirkpatrick and Brown 1987) and by the lower altitudinal limit of Eucalyptus coccifera in central and eastern Tasmania (Kirkpatrick 1999). Treeless vegetation in the subalpine zone and alpine vegetation are henceforth collectively called 'alpine vegetation' and the area they occupy 'alpine' following Kirkpatrick (1982, 1997).

In alpine areas, lotic and lentic wetlands tend to be less distinct than at lower altitudes, with snow patc~es, springs, lakes, ponds, bogs, fens and streams being frequently interacting parts of the same surface hydrological system and sharing many vascular plant species. All of these elements of the hydrological system are regarded in the present chapter as providing riparian habitat.