Government Guidelines and Legislation
Controlling Willows Along Australian Rivers: River and Riparian Land Management Technical Guideline, Land and Water Australia
Authors: Lizzie Pope, Ian Rutherford, Phil Price and Siwan Lovett
“land&wateraustralia@lwa.gov.au”mailto:land&wateraustralia@lwa.gov.au
INTRODUCTION
Willows ( Salix species ) are an introduced, deciduous riparian and wetland tree or shrub; there are no native species of willow in Australia. The first willows were planted more than 150 years ago for fodder, erosion protection, ornament and shelter. Between 1950 and 1980 more planting occurred to stop bank erosion. By the 1990’s the seriousness of the weed threat was recognised and Willows are now listed as one of Australia’s 20 Weeds of National Significance.
Willows are a serious weed threat to rivers, riparian areas and wetlands throughout south-eastern Australia, and are continuing to spread. Effective methods are available for control and removal of willows, but using these methods requires careful planning and implementation, as well as follow-up maintenance. This guideline summarises some of the existing information about willows and their management, and provides links to other more detailed sources of knowledge. http://www.rivers.gov.au/acrobat/techupdate6.pdf/
THE PROBLEM WITH WILLOWS
Although willows can be effective at stabilizing stream banks, in some cases the disadvantages outweigh their benefits. Problems with willows include;
- Their invasive nature results in thickets that grow into the channel and block its flow and capacity.
- Willow thickets divert water around and out of the main watercourse causing flooding and additional erosion.
- Willows use large volumes of water, recent CSIRO research suggest 1 km. of willows along both sides of a stream use up to 8 ML of water per year. All water use occurs in summer, when water is most scarce for both farmers and animals.
- Willows do not provide the year round supply of riparian inputs (leaves, flowers, fruits and twigs) that native plants do, and their annual drop of soft-tissued leaves decomposes quickly and can reduce dissolved oxygen within the stream to the detriment of fish and other stream life.
- Dense shade of willows prevents in-stream primary production that supports aquatic food-webs.
ยท* They do not provide the same ecological values as native riparian vegetation. Where there is a large infestation, the area is largely devoid of native aquatic food-chains and they do not provide the riparian nesting hollows needed by many species of birds and mammals. They also do not provide woody debris crucial for in-stream habitat and flow complexity because their wood decomposes too quickly.
THE PURPOSE OF THE GUIDELINES
Communities and the government have been trying to manage willows for a while. These guidelines build from these experiences, and update existing willow management guides. This report:
- summarises current information on willows and their control (eg. Best-practice herbicide use, and disposal of willow material);
- identifies key issues of willow management (including re-vegetation);
- helps identify the main species or varieties of willow;
- identifies how they are spreading;
- shows how to prioritise actions, and
- provides tips on how to engage the community.
DEVELOPING A WILLOW MANAGEMENT PLAN
A full copy of the guidelines is on
http://www.rivers.gov.au/acrobat/techupdate6.pdf/
It is important to carefully plan projects for willow control. Successful plans, and their budgets, should include periodic follow-up to ensure eradication and no re-infestation of willows, as well as adequate regeneration of native species. The following 8 steps are identified, along with technical support, in the guidelines. They also recommend involving the community at all stages.
1. Define the project objectives.
Removing willows, if carried out without adequate planning can have unintended, adverse consequences which may outweigh the positive effect of removing them.
2. Scoping the problem (identify willow distribution, and assets that are threatened by them).
Map the willow species and their sex, their abundance and capacity to seed or spread vegetatively. Identify existence and location of threatened native plant and animal species and other areas under threat from willow invasion.
3. Determining priorities.
There are too many willows for removal of all of them. Priority should be based on the premise that the position of the willow infestation directly influences the risk it poses to the natural environment.
4. Working with the community.
Public education and knowledge is paramount to achieving the goals of a willow management program.
5. Planning for short term consequences of willow removal.
When a dense stand of willows is removed, the following sequence is common, and can last for two years before the site stabilises and returns to a natural condition:
- fine root mat rots
- release of fine, nutrient rich sediment into the stream
- wave of erosion
- with the loss of shading, increase in water temperature
- combination of impacts may lead to algal bloom
6. Willow control/removal
Five options are recommended, along with disposal. Common pitfalls are identified.
- Hand removal of seedlings
- Foliar spray of smaller plants
- Cut and paint
- Drill and fill
- Frill and fill
7. Revegetation and follow up.
Rehabilitation and follow up activities are critical to the success. Willows may re-invade, reg-grow or there may be problems with invasion of other weeds or erosion. Replanting with native species is vital to maintain stability of stream banks and to provide shade. Recommended practice is to kill one third of the willows each one to two years, and on each occasion to replant the space with native riparian species.
8. Monitoring and Evaluation.
Willows will almost always re-sprout if not treated correctly in the first place, and repeat monitoring is necessary to also check for re-infestation.
Pope, L., Rutherfurd, I., Price, P. & Lovett, S. 2006. Controlling willows along Australian Rivers. River Management Technical Guideline no. 6. Land & Water Australia, Canberra.
