Abstract:Eucalyptus camaldulensis Denh. (River Red Gum) and E. largiflorens F.Muell. (Black Box), the dominant riparian tree species that fringe the wetlands of the lower River Murray in south-eastern Australia, are in severe decline. Artificial watering has been used as an emergency management measure in an effort to save these significant ecological assets. This study quantified the extent of lateral recharge and the tree response to artificial watering in a semi-arid saline floodplain wetland. The extent of the vegetation response was linked to the extent of groundwater freshening from bank recharge, which was controlled by floodplain hydraulic conductivity. A two-to five-fold increase in plant water potential and a three-to six-fold increase in tree water use were observed in the 3 to 4 months after watering. Artificial watering is an effective floodplain management tool to preserve significant ecological assets during periods of low flow. It can be used to manage one-third of E. camaldulensis communities on the Chowilla floodplain that grow within the estimated extent of bank recharge from wetland watering. However, water balance calculations indicate that the water stored as bank recharge would be discharged as evapotranspiration within three years, which means that regular artificial watering is required during periods of low flow to maintain high-value floodplain sites.

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Long‐lived vegetation is a key attribute of lowland river floodplains; yet dieback is increasingly being reported globally, with prior studies identifying salinity, drought and altered flow regimes as key stressors. In the Murray–Darling Basin (Australia), many floodplain/wetland areas have management strategies that aim to maintain the condition of floodplain tree communities. Environmental water delivery is a key tool used to achieve such outcomes. Currently, one of the primary tools for determining the need for environmental water delivery is a qualitative visual assessment of tree crown condition. To advance to more quantitative assessment and understanding of tree condition, we present a suite of techniques ranging from low‐cost, rapid visual assessment of tree crown condition to laboratory analysis of components of soil condition and in situ measurement of tree physiology. The aim is to address a number of key knowledge gaps on how to use the linkages between soil water availability ↔ tree physiology ↔ tree visual condition to quantitatively inform environmental water delivery decisions to meet management objectives. We have developed a multiple‐lines‐of‐evidence management assessment framework that presents a pathway to enable managers to improve prioritisation management actions. Furthermore, increased confidence in predicted outcomes should assist water holders and floodplain managers to optimise timing and maximise the benefits of environmental watering. Application of outcomes of this research will increase the efficiency of environmental water use.

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