Alien plant invasions on the Tiwi Islands. Extent, implications and priorities for control.

摘要

Data from five vegetation surveys on the Northern Territory Tiwi Islands of Australia were compiled to examine the habitat preference of naturalized alien plant species. Eucalyptus forest, Callitris forest, Melaleuca woodland, Acacia scrubland and monsoon rain forest had very few alien plant species. Of the ten alien plant species (4 annual herbs, 4 perennial herbs, 1 vine, 1 shrub), that have become naturalized in native habitat, most were restricted to semideciduous Eucalyptus woodland and especially grassland and open scrubland on clay-rich substrate. All of these habitats have relatively fertile soils and it is argued that this greatly facilitates the spread of exotics, which may also be exacerbated by the activities of the Asian water buffalo, Bubalus bubalis. The herb Hyptis suaveolens is the most abundant alien plant species. Despite few exotics in native vegetation, 95 alien species have colonized disturbed habitat around settlements (mostly annual and perennial herbs, with vines, shrubsand only 2 tree species), with species richness related to the age of the settlement. The relatively low numbers of naturalized exotics enhances the natural value of the islands and the sea barrier provides valuable opportunity for quarantine. However, some alien species with small populations on the islands (such as Pennisetum polystachion) have elsewhere demonstrated ability to degrade large areas of their habitat and should be urgently eradicated.