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Restored river-floodplain connectivity promotes riparian tree maintenance and recruitment

Research output: Contribution to journalArticlepeer-review

Joe Greet, Sarah Fischer, C.J. Walsh, M Sammonds, Jane Catford

Original languageEnglish
Article number119952
Early online date16 Dec 2021
Accepted/In press9 Dec 2021
E-pub ahead of print16 Dec 2021
Published15 Feb 2022

Bibliographical note

Funding Information: We acknowledge the Wurundjeri Woi-wurrung people as the Traditional Owners of the land on which this study was conducted. We thank: Rob James, Pete Polesma, Genevieve Hehir, Fiona Ede, Frederic Cherqui, Darcy Watchorn, Simon Dent, Sarah Gaskill and Sarah Gregor for help building the weirs; Tim Willersdorf, Elise King, Scott McKendrick and Lane London for monitoring help; Rowan Berry, Brett Hough and Sacha Andrusiak for nursery help; and Kathryn Russell, Frederic Cherqui,Vicky Waymouth and two anonymous reviewers for their feedback on earlier drafts of this manuscript. This research received funding from the Australian Research Council together with partners Melbourne Water, Parks Victoria, Zoos Victoria and Greening Australia (LP150100682) and The University of Melbourne through their Early Career Researcher grant scheme. The weirs were built with funding from Zoos Victoria under permit from Melbourne Water (Permit no. MWA-106320) and the research conducted under permit from DELWP (Permit No. 10008063). Publisher Copyright: © 2021 The Authors

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Riparian forest loss and degradation due to river-floodplain disconnection is a global problem. Prospects for the maintenance and recruitment of riparian trees via restored flooding can be uncertain, in part due to competition from understorey vegetation and limited availability of tree propagules. In a field-based trial, we assessed the response of a keystone riparian tree to restored flooding, reduced competition and seed addition. We built diversion weirs to reconnect floodplains supporting riparian forest. Using a multiple control-intervention-reference study design with two restored flooding (intervention) sites, two naturally-engaged (reference) and two dry (control) sites, we assessed seedling recruitment of the dominant tree, Eucalyptus camphora, with and without clearance of understorey vegetation and with and without seed addition. We also assessed the growth of extant trees using dendrometers and seedfall using funnel traps at all six sites. Our weirs resulted in extensive flooding of the adjacent floodplain, while control sites remained dry. Flooding increased seed germination, seedling establishment, tree growth and seedfall. However, seed germination benefits were only realised where understorey vegetation was cleared and seed was added. Seedling establishment was also limited by dry summer conditions, except where flooding duration was longest (∼6 months cf. < 3 months). Restored flooding via river-floodplain reconnection is likely to promote the rehabilitation of riparian forests degraded by flow regulation or stream modification through benefits at multiple tree life-history stages. However, widespread tree recruitment may require complementary works that reduce competition via clearing of understorey vegetation and alleviate seed limitation by direct seeding or planting.

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