Red Gum Rescue Project. Ecological responses to watering stressed river red gum (Eucalyptus camaldulensis) dominated wetlands in the Lower Murray Darling between Lock 15 and the South Australian border
Monitoring of NSW Floodplain Watering Trials: Frog and Water Quality Responses - M/BUS/69-2
DNR Technical Report
The floodplain vegetation in the region is sustained by natural flooding that historically occurred every 1-2 years. A dramatic change in the number and size of natural floods in the lower Murray reach has led to widespread decline in health and death of both overstorey and understorey species such as lignum, river cooba, black box but particularly river red gum. In response to widespread concern about the decline in the health of red gum and the associated flora and fauna communities the DNR coordinated an environmental watering program "Red Gum Rescue Project". Seven key sites within the Lower Murray Darling Region were provided selective environmental watering between September 2005 and June 2006. A total of 3366 ML of Snowy River Recovery water and 2176 ML of supplementary water were used to water the seven sites. Two hundred and forty eight hectares of red gum dominated communities were flooded. A total of thirty four mapped wetlands were inundated. Pumping and siphoning of water into these selected sites has resulted in significant ecological benefits, the details of which are described below. Pre-watering assessment of tree health was variable within and across the seven sites however some general trends were evident. Across all sites red gum health was poor, between 40-50 percent of the trees sampled were stressed, 10-40 percent were severely stressed, 5-10 percent were near death, and less than 5 percent were in good condition. Response to the watering within a site and across the seven sites was spatially variable. Typically 70-80 percent of the trees monitored responded through the production of new canopy and epicormic growth. A small percentage of the trees did not appear to respond to the watering typically these were located > 15m from the edge of the water, a small percentage of trees continued to decline in health. A positive response to the watering was observed across a wide range of age-classes and varying health categories. Few trees however responded to the watering that had already lost 80% of their original canopy. The limited response by some trees at some sites, particularly at Backwater Lagoon is consistent with the findings of other environmental watering programs across the basin where repeated waterings are often required to vastly improve the health of trees, shrubs and the general condition of the wetland. At many sites the watering promoted the growth of a diversity of wetland plants, providing them with a rare opportunity of completing their life cycles and contributing to the seed bank. Clearly one off watering programs are not the solution to the decline in health and condition of floodplain communities rather a long term environmental watering program is required to achieve substantial and sustained ecological benefits. Large numbers and a diverse assemblage of waterbirds were attracted to the watered sites, including the threatened Freckled Duck and Blue-billed Duck. The watering created a wide range of foraging habitats and provide much needed drought refuge. The watered sites supported large numbers of nomadic waterfowl, such as Pink-eared Ducks and Grey Teal. A small number of waders and waterfowl bred as a result of the watering. The response by frogs to the watering was immediate with large numbers of frogs observed at the wetlands post watering. Although no surveys were undertaken at the sites pre-watering, few frogs were observed at the adjacent permanent water bodies or control sites, no breeding males were heard, and no tadpoles were recorded. While at all the watered sites a breeding response was observed (large numbers of males heard, tadpoles sampled). At Moorna State Forest all six species known from the area bred, including the threatened Southern Bell Frog. The immediacy of the watering program and short term nature of the water availability precluded the opportunity to report on the response of groundwater to the watering at all but Mallee Cliffs. Future environmental watering program should invest greater effort to better understand surface and groundwater interactions to reliably predict the environmental benefits of watering. The continuation of below average rainfall and the lack of and low likelihood of flooding in the region highlights the need for continued investment of watering of key sites in the Lower Murray Darling region. A broader view of the declining health and condition of floodplain communities is needed rather than the somewhat narrow view of considering simply the health of red gum trees.