Pseudoraphis spinescens (Poaceae) grasslands at Barmah Forest, Victoria, Australia: current distribution and implications for floodplain conservation

Abstract

Floodplain grasslands are highly productive ecosystems that are becoming increasingly degraded and fragmented because of changes to natural flood regimes. In this work, we mapped and quantified the distribution of Pseudoraphis spinescens – an ecologically important mat-forming grass – in treeless floodplain grasslands in the Barmah Forest, Victoria, Australia, across two seasons. Although P. spinescens was once widespread in the forest, there has been a decline in its extent, particularly since the Millennium Drought (2001–09) and subsequent unseasonal and prolonged La Niña-associated flooding from late 2010 to 2012. Our detailed on-ground surveys show that only 182 ha of P. spinescens grassland remain in treeless areas of Barmah Forest, representing ~12% of the total area of treeless plains and lakes. Critically, just 51 ha of the thick monospecific P. spinescens swards that were a historically important part of the floodplain vegetation was located and mapped. Although there was a small increase in the area of P. spinescens in some treeless areas following a favourable flood season in 2013–14, the boundaries of most grassland patches remained relatively stable during this period. Potential drivers of the overall decline in P. spinescens across Barmah Forest include the direct and indirect impacts of altered flood regimes, drought, and grazing pressure. Improved understanding of these drivers and their interactions, as well as the status of the seedbank, will be crucial for future management and conservation of these floodplain grasslands.