In the eastern and southwestern parts of the continent, multi-species invasions are the dominant pattern. In these more populated parts of Australia, the vegetation is highly fragmented and thus also vulnerable to invasion, mainly by ornamental species grown locally, and the ubiquitous grasses. The native fragments are often repositories of rare species, being the last vestiges of once more widespread communities. Rainforest communities are typically highly resilient to invasion unless fragmented. Some of the more invasion resistant ecosystems appear to be the intact areas of rain and temperate forests, mangroves, the alpine vegetation and red sand deserts.
Grasses are particularly insidious weeds.
They are pervasive, are next to impossible to control, and their ecological effect is often indirect through changed fire behavior, or it is subtle, such as through the choking out of regenerating native species. Grasses have been introduced to most parts of Australia and there is now a current and unresolved debate as to how to manage the inherent conflict between producers who want to introduce more species, and the conservationists who wish to protect natural systems from further invasion by new species. A review of environmental impacts of non-indigenous plants in Australia can be found in Humphries et al. Marked attitudinal changes have taken place in Australian society in the 1990s toward greater awareness of ecological imperatives and the need for limits to resource exploitation and more active conservation. Constitutionally, non-indigenous species are a state responsibility except when they are involved with import, are on federal land, impact national initiatives or facilitation of change, where market forces do not give the desired outcome, or when community ownership issues are involved.