These are long exposure pictures (taken with a variable ND Filter in late afternoon) to catch the swirls and eddies of the creek. A final picture shows a bank cave-in as another of the willows dies.
The Crack Willow are slowly dying and collapsing. This year saw a brief respite. This was because a lot of the biological agents were decimated by late savage frosts that also killed the native bees and destroyed fruit in local orchards.
A lot of the damage caused by the Crack Willow is not obvious. In Summer, the trees draw a large amount water from the river system. Perhaps more surprisingly, within a Crack Willow environment, creeks have gradually enlarged and deepened - allowing running water to draw more sediment from creek banks into the water flow. After heavy rain, significant erosion can be seen with smaller waterfalls 'moving' upstream as river levels collapse. After very heavy rain, the river system can become choked with willow branches - driving the water course into different channels.
For years, farmers and rangers have been concerned about the proliferation of Crack Willow. While the willow has the singular virtue of stabilizing and restricting the growth of erosion gullies, it acts to fix the shape of rivers and creeks as recessed deeper structures - rather than permitting water flow closer to the surface. It does not act alone in this - some of the high country poa grasses (with shallow root systems) allow the deeper river to undercut existing banks.
I have spent some time with Landcare and individually replanting local Casuarina (from local seed banks) along streams.
For many years I lived about 100 miles to the west, in a isolated property 'Waratah', near a place called Wee Jasper. Crack Willow had not invaded the creeks there. Creeks - like 'Mountain Creek' ran very close to the surface of the ground across an environment dominated by Casuarina Pines. The Pines grew on the banks - and into the stream beds - the root systems and tree litter worked to prevent the creation of deep banks and erosion gullies that have become commonplace in the Molonglo High Plains since the introduction of the Willow.
The following three pictures show a high country creeks that have not been impacted by Crack Willow - retaining a high proportion of Casuarina growing close to or into the path of the streams. The last picture is typical of high country intermittent streams - with a low bank profile. Similar Crack Willow streams can develop into deep gully-like structures - sometimes many meters deep.
On sundown, with a light breeze, the Casuarina make a amazing sound - gentle and all encompassing. By preference, my choice in music runs to symphonic Finnish heavy metal - but I would happily listen to Casuarina instead of Nightwish (for a little while, anyway) :)
I have one reservation about the Casuarina - they are very fire tender. A fire in a river valley dominated by Casuarina can take many years to recover from - and can leave a legacy of massive erosion. A mix of Casuarina with trees that tolerate damp and cold conditions - like Black Sallee - might form a more sustainable long term community.
Palerang April 2014