the invasiveness of a weed species
a weed's impacts
the potential for spread of a weed
socio-economic and environmental values.
and are regarded as being a major threat to the Australian environment. In the cae of the Willow it has been listed because
Most species of Willow are Weeds of National Significance. They are among the worst weeds in Australia because of their invasiveness, potential for spread, and economic and environmental impacts. They have invaded riverbanks and wetlands in temperate Australia, occupying thousands of kilometres of streams and numerous wetland areas (CRC 2003).
Willows spread their roots into the bed of a watercourse, slowing the flow of water and reducing aeration. They form thickets which divert water outside the main watercourse or channel, causing flooding and erosion where the creek banks are vulnerable. Willow leaves create a flush of organic matter when they drop in autumn, reducing water quality and available oxygen, and directly threatening aquatic plants and animals. This, together with the amount of water willows use, damages stream health (CRC 2003).
The replacement of native vegetation (e.g. river red gums) by willows reduces habitat (e.g. nesting hollows, snags) for both land and aquatic animals (CRC 2003).
Willows have only invaded about 5% of their potential geographic range in temperate Australia (CRC 2003).
Tasfish has quite a good article on it. So you'd think that given the threat to the ecosystem that people wouldn't be promoting it's use? You'd think so but Natural Sequence Farming has been and is continuing to promote the planting of willows, even claiming they are the worlds number one riparian plant (whatever that means)!
Given that the results of the ARC Barramul Project were released last year and accoding to their website
proved Peter's NSF processes are what he has been saying all these yearsyou'd think the report would back them up. Well what does the report have to say?
* Casuarina cunninghamiana accelerates bench development and plays a synergistic role in channel contraction (P7)
* Clonal grasses, reeds and tree C. cunninghamiana assisted geomorpic processes.
* River training works were effective after 1981 because they coincided with the main period of natural channel contraction.
* Baramul NSF stream works assisted vegetation recovery but occurred after the main period of channel contraction. (P21)
* Significant positive feedback between C. cunninghamiana recruitment and the rate of channel contraction after extensive channel widening. (P23)
* The recolonisation of native vegetation such as Casuarina cunninghamiana (given appropriate seed source) plays an important and synergistic role in channel contraction, negating the use of such weeds as Salix spp in NSF (P44)
Native plants such as river oak (Casuarina spp) have proven extremely effective at stabilising stream beds and banks. Stock exclusion and limited grazing enhanced the establishment of native seedlings. The use of natives for this purpose is preferred over exotic weeds. (P48)
Well, nothing at all really, it gives a great wrap to Casuarinas and very little on willows. Mind you this all could be quite academic in a couple of years anyway as this year has been a fantastic year for the spread of the Willow Saw Fly, which now appears to be in a significant number of rivers and creeks in the Hunter Valley and in some areas causing significant damage (sorry, my camera batteries were flat but I'll get back out and get a few shots). And see my previous post on weeds.