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Melaleuca swamp forests form a fringe around seasonally inundated freshwater flood plains of Kakadu National Park (KNP). Previous studies based on the analysis of aerial photography reported an increase in woody plant cover on these flood plains, apparently associated with changed fire regimes, increased rainfall and possibly increased atmospheric CO. In opposition to this woody vegetation encroachment past high densities of feral buffalo in the 1960 to mid 1980s changed the hydrology of the KNP flood plains, allowing increased penetration of saltwater causing extensive death of Melaleuca forests. Climate change has increased sea levels and there is concern that this will threaten the freshwater ecosystems of KNP. We hypothesized that Melaleuca forests that were previously impacted by high densities of feral buffalo have continued to decline because of salinization driven by sea level rise. We examined this hypothesis by overlaying georeferenced aerial photography taken in 1964, 1984 and 2004 in a geographic information environment, and then constructing generalized linear fixed effects and mixed effects models to rank the statistical strength of different drivers of Melaleuca forest contraction. We found that there has been a 5% overall contraction of Melaleuca forests over the last 50 years on our study sites, although the amount of contraction varied both geographically and temporally. The amount of Melaleuca forest contraction was greatest during the 1984-2004 interval, when buffalo densities were low. Contraction was greatest on the Melaleuca forest edges, at low-lying sites, and where high densities of buffalo were apparent in 1964. These results suggest the enduring legacy effect of past buffalo damage will amplify the effects of sea level rise on the flood plains of KNP. [ABSTRACT FROM AUTHOR]

Bowman et al. ( Journal of Biogeography, 2008, 35, 1976–1988) aimed to explain observed increases in woody cover on floodplains and savannas of Kakadu National Park using estimates of buffalo ( Bubalus bubalis) density as a causal variable. They found that buffalo were a minor model variable and concluded that buffalo are ‘not a major driver of floodplain and eucalypt dynamics’. However, the authors mislabelled the historical density of buffalo on their site, citing a period as high density instead of low density. Further, their results were not contextualized within the substantial body of scientific and historical evidence of the buffalo’s strong influence on vegetation in Kakadu. The authors instead postulated three unanalysed drivers of observed patterns of change: fire regime, rainfall and atmospheric CO2. We suggest that further analyses of change in woody vegetation should make use of accurate historical records of grazers as well as available data sets on fire history. [ABSTRACT FROM AUTHOR]