What makes a swamp swampy? Water regime and the botany of endangered wetlands in western Victoria

Freshwater temporary wetlands are a little-studied ecosystem worldwide. They have been recognised as critically endangered in south-eastern Australia under Australian biodiversity conservation legislation. However, little has been recorded about their hydrology, functioning or biodiversity values; i.e. the factors that make them intrinsically ‘swampy’. In this paper, we developed a simple threshold model of wetland hydrology based on historical rainfall records and calculated evaporation records matched to records and recollections of the owners of swamps, and documented water-plant and microalgal species richness. The model indicated that swamps were inundated to at least 10-cm depth in an average of 6.3 years per decade for most of the 20th century. The average dry time between inundations was 1.27 years (maximum of 4.5 years). Since 1998, the frequency of inundation appears to have decreased, and the average dry times have increased. Despite, or because of, their temporary nature, these swamps have high biodiversity values among the vegetation and the microalgae, more than has been recorded for near-by permanent wetlands. There is no evidence that a drier and warmer climate will have a negative impact on biodiversity values; however, land management is likely to be important for maintaining these systems as the climate changes.