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Technical Memoranda 23
Cowie ID, Finlayson CM and Bailey BJ
Supervising Scientist, 1988
ISSN 0810-9532
ISBN 0 644 00906 6
This is a report on the presence, distribution and frequency of occurrence of alien plant species naturalised in the Alligator Rivers Region, N.T. A survey of 44 sites was carried out over 33 months and a total of 71 alien species, representing 5.3% of the flora, was recorded. Since 1948, when 14 species were recorded, the number of alien species recorded in the Region has increased exponentially. The major weed species invading wetlands are Salvinia molesta, Mimosa pigra and Urochloa mutica. The most successful (and generally longest resident) colonisers of disturbed sites and riparian habitats are Hyptis suaveolens, Sida acuta, Passiflora foetida and Sida cordifolia. Pennisetum polystachion, a recent introduction, is one of the few aliens which may have the ability to invade undisturbed Eucalyptus dominated communities. Many of the species recorded are recent arrivals and are expected to continue to spread. Species richness (and size of site) explained most of the structure in the data. The larger, comparatively species rich sites in active use (settlements and mines) are expected to be the areas most susceptible to further introduction of alien species.