| Summary: | Hydrological conditions in the Gippsland lakes, Australia's largest navigable inland waterway, have changed markedly since European settlement, largely as a result of the creation in 1889 of a permanent artificial opening to the Southern Ocean at Lakes Entrance. It was proposed by E.C.F. Bird in the 1960's that increased salinity in the Gippsland Lakes would cause Swamp Scrub communities dominated by the Swamp Paperbark Melaleuca ericifolia Sm., to replace the existing Reed communities dominated by Phragnites australis (Cav.) Trin. Ex Steud. This process seems to have been operating in one of the largest of the Ramsar-listed wetlands in the Gippsland Lakes complex, Dowd Morass State Game Reserve, where regional natural-resource managers and other stakeholders were concerned that increasing salinization, combined with changes to wetting and drying cycles, were causing changes in the floristics and condition of wetland vegetation. To test whether changes were taking place in the vegetation of Dowd Morass, we analyzed a suite of historical aerial photographs, covering the period 1964 2003, of the distribution of various plant communities in the wetland. The area of M. ericifolia-dominated Swamp Scrub increased by 72% over the 39 year period, whereas the area of P. australis-dominated Reed communities declined by 26%. Although such a shift is consistent with the predictions made by E.C.F. Bird's salinity-mediated model of vegetation change, it is unlikely that salinity alone was the factor responsible for the increasing dominance by M. ericifolia. Instead, it is likely that, under the conditions of near-permanent inundation in Dowd Morass, the presence of microtopographical relief played a major role in allowing Swamp Scrub to become the dominant vegetation type.
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