Eucalyptus Camaldulensis - Formation of The Barmah Red Gum Forests

Formation of The Barmah Red Gum Forests

The formation of the famous Barmah Red Gum Forests is due to a relatively recent geological event in the Murray-Darling Basin involving the Cadell fault.

River Red Gum seeds germinate readily after floods and require regular spring floods throughout their life to survive. In the Murray-Darling Basin, such floods are now rare due to river regulation for irrigation, and as a result, 75% of River Red Gums in the lower Murray are stressed, dead or dying.

The largest remaining stand of River Red Gum is the 65,000 ha (160,000 acres) Barmah-Millewa forest straddling the border of Victoria and New South Wales, due north of Melbourne. It retains enormous cultural significance to the Indigenous traditional owners, the Yorta Yorta Nation. Like many stands of River Red Gum, the Barmah-Millewa has been drastically altered by over 100 years of timber harvesting. There is a paucity of old hollow-bearing trees which provide habitat for rare and threatened fauna such as the Superb Parrot, Brush-tailed Phascogale and Inland Carpet Python. The increasing scale of logging machinery is creating large areas of intensive soil disturbance and bare earth, which is likely to increase weed invasion and increase the likelihood of the extinction of rare understorey plants.

About 25,000 years ago, displacement occurred along the Cadell fault, raising the eastern edge of the fault (which runs north-south) 8–12 metres (26–39 ft) above the floodplain. This created a complex series of events. A section of the original Murray River channel immediately behind the fault was abandoned, and exists today as an empty channel known as Green Gully. The Goulburn River was dammed by the southern end of the fault to create a natural lake. The Murray River flowed to the north around the Cadell Fault, creating the channel of the Edward River which exists today and through which much of the Murray River's waters still flow. Then the natural dam on the Goulburn River failed, the lake drained, and the Murray River avulsed to the south and started to flow through the smaller Goulburn River channel, creating "The Barmah Choke" and "The Narrows" (where the river channel is unusually narrow), before entering into the proper Murray River channel again.

The primary result of the Cadell Fault however is that the west-flowing water of the Murray River strikes the north-south running fault and diverts both north and south around the fault in the two main channels (Edwards and ancestral Goulburn) as well as a fan of small streams, and regularly floods a large amount of low-lying country in the area. These conditions are perfect for River Red Gums, which rapidly formed forests in the area. Thus the displacement of the Cadell Fault 25,000 years BP led directly to the formation of the Barmah River Red Gum Forests.