Native vegetation is a key element contributing to Australia's biodiversity. Across Australia, 23 major native vegetation groups have been identified, which collectively comprise 'tens of thousands of plant species, thousands of vegetation communities and assemblages, and provide habitat to myriads of microorganisms and animal species' (NLWRA 2002b). In general, the extent and distribution of native vegetation across Australia is determined by climatic variation and the physical landscape (i.e. landform, geology and soils). Rainforests and eucalyptus forests are limited to the higher rainfall areas across the tropical north, around eastern and south-western coastal regions, and across Tasmania. Australia's arid interior is dominated by grasslands and forblands. Regions between these climatic extremes are occupied primarily by woodlands, shrublands and Acacia forests.