Extract from ABC Rural News
http://www.abc.net.au/rural/regions/con ... 734798.htm
Stop maligning willows
Millions of dollars are being spent removing willows from rivers in south east Australia.
That includes; the Yass River, Queanbeyan, Boorowa, Molonglo and Murrumbidgee Rivers, and also on Lake Burley Griffin.
That's millions wasted, according to the Natural Sequence Farming movement. It's backed by scientist Dr Michael Wilson.
He and his students studied willows at University of Ballarat from the mid 1990s for 10 years.
Dr Michael Wilson is now head of the Sustainable Rivers Audit with the Murray Darling Basin Authority, responsible for river health in the basin.
Willow litter is said to deoxygenate water, killing invertebrates.
But Dr Wilson says native trees drop leaves at just the same rate into the river during Summer, which coincides with low flows.
This causes what's known as black water events and is well documented for native leaf litter as well.
The willow litter is very easily digested, drawing down oxygen, but that coincides with the Autumn break, which can flush the organic matter in the rivers and creeks. In fact one of his phD students found the willow leaf litter is good for invertebrate life.
Willows can choke rivers, "colonise and obstruct waterways, diverting flows into banks ... and cause erosion and sedimentation," (Cremer. 1995)
Dr Wilson argues that's good for rivers and mimicks the original chain of ponds.
"The vegetation was so thick, the early descriptions by gold miners, those first into the valleys, it would take them days to get to the river, and it would take them weeks and weeks to work their way up metre by metre through tea tree, and swamps and thickets. The river would be ambiguous about where it flowed ...
"Gradually they'd force themselves to get to a nice channel that was deeply incised and then they could work those sediments over and over again," he says.
"So everywhere there's ever been any gold rush work or land clearing for grazing, it's followed this pattern of deep cutting and incision of our rivers, with tens of thousands of kilometres are are deeply cut channels."
He believes the money would have been better spent on revegetating the millions of kilometres of rivers in Australia
He says using clearing to rehabilitate rivers, is like taking a scalpel to an open wound.
One study found the fish were spending nearly 80 per cent of their time in willow lined banks... in hollows and tunnels in river banks caused by willow roots.
Another of his phD students found the root mats create 'leaky type weirs' created all the pool ripple sequences, which are desirable in the river systems.
He says the willows are there, the natives have been removed.
"Willows have net beneficial function....We might have a million kilometres of unvegetated river length. So if we want to spend $10 million, I'd spend that revegetating river reaches, not $10million clearing river reaches."