Floodplain amphibian abundance: responses to flooding and habitat type in Barmah Forest, Murray River, Australia

Abstract

Context Frog species are now targets for delivery of high-value managed environmental flows on floodplains. Information on the drivers of frog presence and abundance is required to support adaptive management, including analysis of the roles of flood frequency, flood timing and habitat type. Aims This paper describes frog species richness and abundance responses to flooding and habitat type in the Barmah Forest, part of the largest river red gum forest in the world. Methods Surveys were conducted at 22 sites over 6 years, to determine species presence, relative abundance, and evidence of breeding. Data were then used to examine temporal patterns within and between wet and dry years and spatial relationships with site geomorphology, vegetation form and wetting frequency. Key results Six species were common and widespread, and three were rare. The seasonal timing of peak numbers of calling males differed among species. The seasonal pattern of calling for each species did not differ between wet and dry years; however, significantly lower numbers of frogs were recorded calling in dry years. The number of frogs calling was significantly higher in well vegetated grassy wetlands. Evidence of a positive relationship between wetting frequency and numbers of calling males was found for Limnodynastes fletcheri, Crinia signifera and Limnodynastes dumerilii. The abundance of tadpoles was significantly higher in wet years. Conclusions The seasonal timing of flooding in Barmah Forest will influence the breeding success of individual species with different preferences. Flooding from September to December is required to cover most preferred breeding seasons, but longer durations may be required to maximise recruitment. This, together with regular flooding of well vegetated grassy wetland habitat, will increase the likelihood of species persistence and maximise diversity. Insufficient flooding frequency will result in reduced frog species richness and abundance. Implications Managed flooding is important for frog abundance and species richness. This study emphasises the value of key habitats such as well vegetated grassy wetlands and reinforces the need to make their preservation a priority for management. It has identified knowledge gaps to drive future data collection for improved modelling, including a need for further research on flow-regime change and frog communities.