Quantifying the water needs of flood-dependent plant communities in the Macquarie Marshes, south-eastern Australia

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Inland floodplain wetland plant communities of the Macquarie Marshes occur in the lower reaches of the Macquarie River catchment in the Murray-Darling Basin in semi-arid South-eastern Australia. The natural flood regimes are no longer operating in the Marshes due to river regulation, and in periods of low catchment rainfall they are now sustained solely by delivered environmental water allocations. Flood-dependent plant communities can show considerable negative ecological consequences when natural flow and flooding regimes are significantly disrupted. For effective management of water resources to meet targets for the maintenance and restoration of flood-dependent plant communities, it is critical to know the condition or state of the component plant communities, and to quantify change in condition in response to inundation actions. This research developed quantitative condition benchmarks derived from a long-term dataset and adds to the knowledge of water requirements for eight inland wetland flood-dependent plant communities of the Macquarie Marshes. It examines the benchmarks and key inundation predictors for forests and woodlands dominated by river red gum (𝘌𝘶𝘤𝘢𝘭𝘺𝘱𝘵𝘶𝘴 𝘤𝘢𝘮𝘢𝘭𝘥𝘶𝘭𝘦𝘯𝘴𝘪𝘴), woodlands of coolibah (𝘌. 𝘤𝘰𝘰𝘭𝘢𝘣𝘢𝘩), shrublands of lignum (𝘋𝘶𝘮𝘢 𝘧𝘭𝘰𝘳𝘶𝘭𝘦𝘯𝘵𝘢), and non-woody wetland communities of water couch (𝘗𝘢𝘴𝘱𝘢𝘭𝘶𝘮 𝘥𝘪𝘴𝘵𝘪𝘤𝘩𝘶𝘮), sedges (𝘌𝘭𝘦𝘰𝘤𝘩𝘢𝘳𝘪𝘴 𝘴𝘱𝘱.) and floodplain grasslands. Condition class schemas for measuring community and tree stand condition were developed and tested using Multivariate Regression Forest (MRF) analysis of data collected at 74 sites in the Macquarie Marshes from 2008 to 2016. The most important inundation regime predictor variables for these vegetation communities were identified from companion inundation data using MRF. Then Ecological Reference Models (ERMs) were developed using Generalised Linear Mixed Modelling (GLMM), of condition scores against inundation regime predictor variables. The study of the Macquarie Marshes explores the assessment of flood-dependent vegetation community condition using species group responses to water regime and a wetland vegetation typology that can be applied to other flood-dependent vegetation communities and other wetlands. Both the condition class schemas and the ERMs could assist in data supported decision making about current and future ecological restoration activities by defining the appropriate species composition and structure for these and similar flood-dependent vegetation communities.
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