DROUGHT EFFECTS PERSIST IN SOUTH AUSTRALIA

In spite of floods and recent good rains, the South Australian landscape has not yet recovered from the effects of the Millenium drought. The green tinge across the land from autumn rains is a superficial illusion, covering long term impacts from the long years of continuously dry conditions from 2000 to 2010. There is still a long way to go, to recover from the effects of such a long and severe drought.

River red gums, the very large eucalypt trees found near fresh water in many Australian landscapes, typically lining rivers and waterways, are a very reliable indicator of general landscape condition. These iconic trees mark the winding waterways of mainland Australia, and the health of the trees is an indication of the health of the adjacent river systems. Red gums suffered badly in the Millenium drought, and millions of old mature red gums died.

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Sadly, travelling across South Australia and upstream along the Murray Valley to Albury in May 2013, it was observed that most river red gum communities are still showing signs of significant stress. While there is fresh growth this season, it is epicormic, a form which indicates that the trees have been seriously stressed. Epicormic growth occurs directly from branches, rather than from the tips, creating a ‘bushy’ look to the trees, similar to that seen after bushfires have damaged eucalyptus trees. This form of growth can eventually normalise after continuing good conditions and water availability, and converts within one year to tip growth if the tree is not stressed again.

Visiting creeks of the Flinders Ranges in May 2013, excellent recovery was noted in the mature red gums lining the creeks compared to their very stressed condition in March 2009, although this was all epicormic growth within the last year. Given a follow-up season in 2014 with good water availability, it would be expected that these mature trees would make a good recovery and revert to normal growth and continue to develop fruit and seed.

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However, from multiple sites in Flinders Ranges creeks inspected over three days, only two red gum saplings and fewer than 20 seedlings were found, all at sites of permanent springs in creek beds. Mass numbers of mature open fruits lay in the creek beds, estimated to be at least two years old. This indicates that when the seed fell, conditions were too dry for the seeds to germinate, and the seeds were probably all consumed by ants. However, by the time conditions were wet enough to generate growth on the mature trees, there were no seeds left on the trees to fall onto the moist soil.

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The recovering trees in the Flinders Ranges creeks were developing buds in May 2013. These will flower in summer 2013, set fruit in early 2014 and produce seed in the summer of 2014. So wet conditions will be needed again in 18 months’ time, to create moist soil for the seed to fall onto, before there is a chance of mass germination of red gums. This time lag will be critical in determining when a new generation of red gums will commence. Along the River Murray floodplain, three years of floods since September 2010 has provided the necessary conditions for mass germination, and a new generation of young red gums is growing well, but only in localised patches. They too will need sufficient water to sustain growth to maturity, as they only start to produce seed once they are 10-20 years old, depending on how often they have access to water.

The effects of the drought have not yet been overcome, and the river red gums need all the help they can get, including protection from stock grazing and access to water. Healthy river red gums mean healthy rivers, creeks and waterways – ensuring their survival is an investment in the future of the whole community.

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About redgumgirl

Dr Anne Jensen is an environmental consultant with a passionate interest in sustainable management of our natural resources, particularly the River Murray and wetland environments. She is particularly interested in using photographs and stories to explain issues around water and protecting natural ecosystems in terms that are understood by the wider community, so that we can manage our environment sustainably for our common future.
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