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• Macrophyte vegetation of the Magela Creek flood plain, Alligator Rivers Region, Northern Territory (PDF 873 KB)

About the report

Ten major macrophyte communities have been identified on the Magela Creek flood plain, an area of 220 km², in northern Australia. Because of significant seasonal changes in vegetation each community is classified by its observed Wet season to early-Dry season vegetation, or otherwise given a general descriptive name. The Melaleuca open forest and woodland community covered 34% of the flood plain and Pseudoraphis and Oryza grasslands covered 14% and 12% respectively. Differences in the species composition of each community result from changes in the availability of water on the flood plain. The 222 plant species recorded from the flood plain were categorized into the four habitat types: seasonally inundated plain, seasonally inundated fringe zone, permanent swamps, and permanent billabongs. One hundred and thirty nine annual species, 69 perennials and 14 geophytic perennial species were recorded on the flood plain.

The seasonally inundated plain and fringe zone habitats respectively contained 41% and 71% of the plant species. The fringe zone contained 100 annual species (91 of which were terrestrial), the seasonally inundated plain 57, the permanent billabongs 19 and the permanent swamps 5. Seasonal variation of plant communities and the occurrence and extent of plant groups near billabong margins was related to the hydrological cycle on the flood plain. It is postulated that the duration of the period of inundation is a major determinant of the vegetation composition on the flood plain; the related factors of water flow velocity and water depth are also influential. Furthermore, it is hypothesised that the pattern of vegetation variation is a function of both the flooding and drying phases of the hydrological cycle on the flood plain.