Clues for saving thirsty Murray trees

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Research has provided hope for Lower Murray Valley woodlands which are suffering the effects of poor water flows.

Indicators for how to manage environmental flows for maximum benefit to the Lower Murray Valley floodplains have resulted from a Land & Water Australia postgraduate scholarship, which enabled Dr Anne Jensen at the University of Adelaide to investigate the relationship between water availability and the survival of young river red gums, black box and lignum.

The last useful over-bank flows onto the floodplain of the Lower Murray Valley were in 1996. In 2004, more than 75% of river red gums and black box trees were stressed, dying or dead, and because of the drought the situation is even worse in 2009.

While a grim picture can be painted, Dr Jensen’s research will guide future management to ensure the most effective timing and volumes to maintain the woodlands. Due to the scant volumes available, it is vital for flows to be used efficiently to achieve the best possible outcome for the health of the river.

“Given current flow patterns and rainfall patterns, December is the most likely month for value-adding environmental flows,” Dr Jensen said.

“Healthy eucalypts release the greatest amount of seed when there is the greatest chance of sufficient soil moisture for germination, and before river regulation this was generally in November-December. Any flow or rain events which could potentially increase soil moisture on the floodplain should be piggy-backed by environmental flows to extend the period of soil moisture.

“The magic number for seedlings to survive is 10 per cent. 10-25 per cent soil moisture is ideal for seedlings to thrive, but if it drops below 10 per cent, the seedlings just wilt and die.”

As an example, river red gum seedlings germinated in tens of thousands after watering at Coppermine waterhole on the Chowilla Floodplain in 2005, but did not survive the ensuing hot summer conditions, even though grazing stock were fenced out.

However, if environmental flows are managed well and are in tune with the natural cycle of these important trees, there is hope that the woodlands and the floodplains will recover.

An easy reference fact sheet is available. Dr Jensen’s thesis is hosted on the University of Adelaide website.

Contact: Kerryn Molloy, Land & Water Australia (02) 6263 6000

Photographs are available for this story. Please contact Kerryn Molloy to obtain a photo

Citation

Land & Water Australia. 2009. Clues for saving thirsty Murray trees. [Online] (Updated April 8th, 2009)
Available at: http://lwa.gov.au/node/3114 [Accessed Tuesday 26th of April 2011 03:59:14 AM ].