Taking the long handle to willow
Impacts caused by willows on the health and complexity of a stream channel are simply not worth the minimal benefits.
They provide no significant fish habitat, consume four times more water than eucalypts on the mid banks of wetted creeks, advance into channels during prolonged flows causing erosion, and release hormones into surrounding soils which restrict growth of native trees and shrubs.
Interested groups can improve stream health by undertaking willow control and a variety of funding sources are available.
The Habitat Action Program provides an opportunity for landholders, anglers, councils and community groups to find out more about habitat and to get funding assistance for works in local river reaches.
In terms of fish habitat, willows are a soft wood and generally break apart very quickly when dead, resulting in no permanent snags or structures.
This has a major impact on the iconic Murray cod, who like to lay their eggs on snags and use them as a home.
So a willow infested stream would generally be devoid of cod unless it was stocked or had a legacy of native snags.
However, the dense hardwood of a eucalypt snag not only provides more complexity but generally stays in place more readily. Some large native hardwood snags have been radio carbon dated to around 10000 BC.
Now that’s long term cod accommodation.
A recent CSIRO study also showed that willows growing along wetted margins of creeks consumed four times the amount of water than eucalypts growing along the mid bank position.
This means that water, the most important fish habitat requirement, can be conserved simply by removing willows and revegetating river banks with native trees.
Willows can also advance into the channel bed during prolonged low flow periods.
Due to their complex root systems, this can assist in building up sediment deposits and filling in deep pools.
Following this, flows are deflected against nearby banks resulting in erosion and gradually creating a shallower, wider waterway.
Willows also release hormones into the surrounding soils they inhabit, restricting the growth of native trees and shrubs. And because willows can spread by seed or by off cuts, riverbanks can quickly become infested.
Since their introduction to the Australian landscape more than 150 years ago, willows have established a common place along many freshwater streams.
Introduced to provide erosion protection and fodder for stock, little thought was given to potential spread and their negative influence on native plants and animals.
Since native fish prefer a red gum over a willow, the fact that willows can be a good source of overhanging canopy cover for half the year is barely worth listing as an advantage.
Best management practise for willow control near waterways requires applying a neat solution of bioactive (fish and frog friendly) glysophate to the phloem.
A wide variety of methods can be used to apply glysophate, however the preferred options include:
1. Drill and Inject (medium to large trees): drill a continuous series of holes around the trunk below the lowest branch. Use a medium to large drill bit (eight to 10 millimetres) on a 45-degree down angle, two to five centimetres deep depending on the size of the tree, spaced no more than five centimetres apart. Fill each hole with neat bioactive glysophate immediately after drilling.
2. Cut and Paint (small to medium trees): simply saw the trunk off below the lowest branch and immediately “paint” neat bioactive glysophate to the outer half of the stump.
3. Cut and Frill (small to medium trees): cut a recessed ring at least two to three centimetres deep around the trunk and below the lowest branch.
Immediately apply neat bio-active glysophate to the cut.
Take care with these methods to ensure no small branches are left to create new trees.
It is always advisable to follow up with revegetation with indigenous trees, shrubs and groundcovers.
In NSW a permit may be required for undertaking more than 500 metres of willow control along a river – contact your local Catchment Management Authority for more advice.
Contact your local Industry and Investment NSW conservation manager or visit www.dpi.nsw.gov.au/ fisheries/habitat/rehabilitating