A shift in the ecohydrological state of groundwater dependent vegetation due to climate change and groundwater drawdown on the Swan Coastal Plain of Western Australia

Abstract

The deep sand, unconfined aquifers of the Swan Coastal Plain in Western Australia support extensive open woodlands dominated by Banksia and other phreatophytes. Since the mid-1970s these ecosystems have been subject to declining annual rainfall and water-tables. In the summer of 1990/91, a phreatophytic Banksia woodland on the Swan Coastal Plain was subjected to increased rates of drawdown resulting in over 80% mortality of the phreatophytic overstorey species. The impacted Banksia woodland recovered, however, facultative phreatophyte species now dominate the overstorey, suggesting that the ecohydrological state of the site has shifted to one in which the dependence on groundwater access is reduced. A field experiment was performed over three consecutive summers, in which the recovered vegetation was subjected to further drawdown and its physiological water stress and water source partitioning compared to vegetation at reference sites.