Willow (Salix nigra) regrows along a fallen trunk
May 2012
Willows in the Nambucca
Mapping and Case Studies
Table of contents
Table of contents ................................................................................................................. 1
Acknowledgments ............................................................................................................... 2
Background to the project ................................................................................................... 2
Willows as weeds in Australia ............................................................................................. 2
What’s the problem with willows? .................................................................................. 4
Mapping Willows in Nambucca Shire ................................................................................. 6
Willow species in the Nambucca ..................................................................................... 7
Case Study 1 – Growth and spread of willows near Bowraville ........................................ 10
Spread of willows along the Nambucca River ............................................................... 10
Vegetative propagation and seeding of willows ............................................................ 14
Linking willow growth with river instability and erosion ........................................................................ 17
Case Study 2 – Control of willows at the MidCo site ........................................................ 19
Recommendations............................................................................................................. 21
Web Resources and References ........................................................................................ 21
Appendix 1 ......................................................................................................................... 23
Map of willow locations in the Nambucca catchment ...................................................... 23
Appendix 2......................................................................................................................... 24
Case Study 1 Growth and spread of willows near Bowraville - field notes and photograph
locations............................................................................................................................. 24
1
Acknowledgments
Thanks are due to the landholders who permitted access to their properties and participated in the study.
Field work was undertaken by Tim Ryan and Dawn Thornton for Nambucca Valley Landcare.
Identification, research and report preparation were undertaken by Dawn Thornton who also took the
photographs for this report.
The MidCo willow control case study was undertaken by Kara and Steve Smith on behalf of Nambucca
Valley Landcare, and their field report has been incorporated into this document. Data was provided by
Nambucca Shire Council’s Weed Officer Tim Woodward. David Merrikin (NRCMA) provided information
on the willow control project conducted in the Bellinger valley.
Background to the project
In 2011, the Mid Coast Weeds Advisory Committee (MNCWAC) received funding from the Northern
Rivers Catchment Management Authority (NRCMA) to address the emerging issue of willows (Salix spp)
in the Nambucca, Macleay and Hastings catchments whilst willows are still at a manageable level of
infestation. In turn Nambucca Valley Landcare (NVL) was asked by MCWAC to undertake the Nambucca
catchment element of the project, including:
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Mapping the extent of willows in the Nambucca Valley;
Conducting community education and awareness programmes;
Encouraging landholder control;
Control of key infestations;
Recording and mapping control activities.
Willows as weeds in Australia
There are 300 – 400 species of willow Salix species from Europe, the Americas and Asia. Some 32 taxa
(species, subspecies, varieties, primary hybrids and cultivars) have been introduced and are now
recognised in Australia according to the Weeds of National Significance Willow Strategic Plan (2000).
Willows may have a either a tree or shrub form and are largely found in wet and waterlogged habitats,
river edges, swamps, drainage lines etc. Each plant is usually either male or female and they are
predominately deciduous. Willows are notorious for their ability to hybridize, creating enormous difficulty
for identification.
Willows have been introduced to Australia as botanical and garden specimens and for their perceived
benefit in protecting river banks from erosion due to the dense rooting mat which holds soil together. In
the Nambucca Valley, several landholders have introduced willow species to prevent loss of valuable creek
frontage land as well as for shade and windbreaks, for example along dairy laneways.
Willows (Salix spp. except S.babylonica, S.x calodendron & S.x reichardtii) are designated as a “weed of
national significance” (WoNS). These weeds are regarded as the worst weeds in Australia because of their
invasiveness, potential for spread, and economic and environmental impacts. A national strategy is in
2
place. Northern NSW is identified as part of the core infestation of willow species in the national strategy
(see Figure 1).
In NSW willows are noxious weeds declared as “Class 5 notifiable” across the whole state, including the
Nambucca Shire. This designation prohibits sale or cultivation of all Salix species excluding S. babylonica,
S. x calodrendron, S. x reichardtii. Landholders are not legally obliged to remove willows but it is illegal to
plant or propagate them, and for nurseries to sell willows. (This has effectively stopped further planting in
NSW). The Northern Rivers Invasive Plant Action Strategy list willows as a high priority in riparian
landscapes.
Since the 1990s, it has been recognized that willows introduced to Australia are spreading by seed, in
addition to planting, layering of existing trees and rooting of detached branches. Regeneration by seed
depends on a fertile female tree within seeding distance (about 300 m) and a fertile, compatible male tree
within pollinating distance (about 300m) plus favourable weather and seed bed conditions (Cremer, et al
1995). Most willows in Australia regenerate only on the wet, bare margins of rivers; the willow seeds do
not remain viable for more than a few days, are poor competitors and are grazed by livestock (op cit). Seed
is usually set around November in Australia. The Willow National Management Guidelines state that
“there is no recorded evidence of any willows being sterile in Australia”. Seed can be spread many
kilometres, normal river flow can wash branches downstream whilst floods may uproot seedlings and
mature trees. Most willows will regrow readily from such material.
Figure 1 Core infestation area includes Northern NSW
3
What’s the problem with willows?
The problems identified from the spread of willows are described in the Willow National Management
Guidelines and mainly relate to negative impacts on stream hydrology and biodiversity.
Willows produce dense mats of roots and stems within the bed of water courses causing a build-up of
deposits and altering natural stream and wetland hydrology. This reduces channel capacity, creates
stream obstructions, braided channels, channel diversions and diverts flood water flow towards banks,
ultimately increasing bank erosion and loss of farmland. Infrastructure may be damaged where willow
debris obstructs stream channels during floods (e.g. loss of bridges and roads). Willow thickets can
effectively form a wall that diverts flood flow to the opposite bank – causing erosion (DLWC, 1999). This
effect was noted at the Bellingen Golf Course and Bat Island in a study of willows in the Bellinger and
Kalang catchments (DLWC, 1999).
Willows alter ecological processes in streams, by forming dense stands with intense shade in summer and
no shade in winter which impacts stream bank and in stream vegetation and fauna. The shade alters
temperatures in surface waters and leaf fall in autumn produces pulses of deciduous leaves in the
waterway, impacting water quality, available oxygen and in stream flora and fauna. The replacement of
native vegetation by willows reduces habitat (e.g. nesting hollows, snags) for both land and aquatic
animals.
In some swamp and wetland sites in Victoria and NSW willows (particularly S. cinerea) seriously threaten
biodiversity.
Willows have increased water-use in streams resulting from higher transpiration rates than indigenous
vegetation. In some areas willows have reduced the amenity values of streams for canoeists, the fishing
community, and other stream users.
The effects of willows on water courses is illustrated in this extract from the Willow National Management
Guide, 2007.
4
5
Mapping Willows in Nambucca Shire
A map of known willow locations in the Nambucca catchment is provided in Appendix 1. Data for this
map were derived from:
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Property inspections and the knowledge of the Nambucca Shire Council (NSC) Weeds Officer Tim
Woodward;
Property visits and the knowledge of the NVL Coordinator Tim Ryan;
Field based mapping of an area of known infestation near Bowraville;
Anecdotal reports from landholders and NVL members;
Rapid surveys from public access points (such as roads and bridge crossings).
The absence of willows in large parts of the catchment is significant. The NSC Weeds Officer reported that
no willow infestations had been recorded during intensive property inspections in 2012 in the following
areas:
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Algomera Creek
Eungai Creek
Other areas where no willow infestations have been identified are:
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Missabotti Creek
Valla and Deep Creek
Taylor’ s Arm
Some landholders report willows being more common in the valley in the past (pre 1960s) than today.
There are two known major infestations of willows in the Nambucca Valley – one upstream from Lane’s
Bridge at Bowraville and one at Wirimbi near Macksville. These were selected as the basis for two case
studies, described below.
6
Willow species in the Nambucca
Given the difficulties with the correct botanical identification of willows, the full range of willow species
and varieties cannot be verified. However the following species and varieties have been positively
identified in the Nambucca Valley.
Salix nigra. Black willow. Spreads vigorously by seed, can spread beyond river systems. The main
species recorded along the Nambucca River near Bowraville and spreading downstream vegetatively; it
may be spreading via seed upstream. The leaves are glabrous, similarly green above and beneath and
finely serrated, with a distinct petiole (> 3mm). The vegetative sprouts are vigorous with conspicuous
subpersistent stipules. Immature trees have a distinctive conical shape.
Figure 2 Typical form of Salix
nigra along the Nambucca River
Figure 3 Root system of seedling
Salix nigra
7
Figure 4 Bark of Salix nigra
Salix fragilis. Crack willow. Multiplies readily from broken branches. Recorded from only one site,
the subject of Case Study 2.
New Zealand hybrid willows (usually Salix matsudana x Salix alba). (see Guidelines for Establishing
and Managing Poplar and Willow Trees on Farms , 2007, for a description of some New Zealand clones).
A number of landholders have planted New Zealand hybrids, the name of the hybrid is not always known,
however near Bowraville Aokautere hybrid No. 2 was planted. The latter does not appear to have spread
as yet. “Aokautere is a male clone suitable for general soil conservation planting, for river protection
planting, and for windbreaks. It grows rapidly and develops into a fairly narrow-crowned tree with a
slightly wavy trunk and blue-green foliage. Regrowth from stools is strong and little affected by wind. This
clone needs good moisture to grow satisfactorily.” op cit.
Figure 5 New Zealand Hybrid (variety unknown)
8
Figure 6 New Zealand Auketere Hybrid No. 2
Salix babylonica. Weeping willow. Although the species is not known to produce viable seed, it does
hybridise with other willows to produce fertile varieties. The resulting hybrids are sometimes very
invasive. It is difficult to distinguish Salix babylonica from other weeping varieties which are known to
occur in Australia and which do set seed.
Figure 7 Weeping willow
9
Case Study 1 – Growth and spread of willows near Bowraville
During March and April 2012, the Nambucca River between Wia-Ora Bridge and just downstream of
Lane’s Bridge was walked to identify the species present; map the extent of willow infestation; if possible
identify the sources of infestation and potential control sites. This reach of the Nambucca River was
selected because of a known willow infestation at one location – the extent and spread from this location
would be mapped. During the course of the project an additional significant willow site was identified
downstream of Lane’s Bridge.
A photographic record was made and samples of the willow species encountered were collected, labelled
and dried to create a herbarium collection that may assist future surveys and control projects in the
Nambucca Valley.
Field notes and the location of photographs are mapped in Appendix 2.
Only 4 willow species were identified. The most prevalent species identified is Salix nigra, with much
lesser amounts of Salix babylonica, and two New Zealand clones. Samples have been included in a
herbarium held at the NVL offices.
Spread of willows along the Nambucca River
Landowners reported that willows had been planted to assist in river bank stabilization at least 30 years
ago. At that time many agricultural, catchment management and natural resource agencies believed that
planting willows was best practice for on-farm management of river bank erosion (indeed in New Zealand
willows are still extensively planted for slope and river protection). Not until the mid 1980s/1990s did the
potential negative impacts of willows in an Australian context become recognized.
Figure 8 shows the area thought to be part of an original planting, probably in the early 1980s, of Salix
nigra. Many of these original trees are naturally senescing and/or falling into the river as banks are
eroded (see cover photo). Willows have spread approximately o.5 km upstream and 1 km downstream of
the original planting site, although occasional willows are present throughout the length of the case study
river reach.
10 
Figure 8 Original planting of Salix nigra
Where mature Salix nigra have fallen or been washed into the river during floods, typically the plant
resprouts along the trunk, forming a linear obstruction within the river bed. A recently fallen willow is
illustrated in Figure 9.
Figure 9 A recent bank collapse has caused this willow to be washed into the river - it is able to
regrow in this aquatic environment
At a number of locations downstream from the known willow riverbank planting, these linear features are
evident – see Figure 10. The fine mat of willow roots impedes water flow and sedimentation occurs,
forming shallow banks or shoals of gravel within the river bed – see Figures 11 and 12. Once formed these
in-stream shoals, divide the river flow, diverting it on both sides of the shoal towards the adjacent river
banks. In periods of high flow such obstructions are leading to significant bank erosion, loss of valuable
farmland and damage to farm infrastructure (roads, fencing etc.)
11 
Figure 10 Salix nigra trunk regrows and diverts water flow either side of the original trunk
Figure 11 The fine root mat collects sediment and gravel to form shoals
12 
Figure 12 Shoals of clay, sand and gravel particles obstruct flow and divert water flow to both river
banks
13 
Vegetative propagation and seeding of willows
It would appear that downstream spread of willows is largely due to propagation from vegetative material
– whole trees; large branches; part root balls; and smaller fragments of branches. Relatively few willow
locations could definitively be attributed to seeding. However, a number of locations upstream of the
original planting site were undoubtedly the result of seeding from mature Salix nigra trees – there being
no upstream source of vegetative material. Figures 13 and 14 show the extent of the young seeded willows
– they are even aged and around 2 seasons old (probably seeded in 2009/10).
Figure 13 Seedling Salix nigra upstream of the original planting site
Figure 14 Seedling Salix nigra on gravel shoal
14 
Some seedling black willows were identified on the banks of former gravel workings (Figure 15).
Figure 15 Seedling Salix nigra
Approximately 500m downstream from Lane’s Bridge, Bowraville an infestation of Salix nigra was
identified. Here a group of mature black willow are spreading both vegetatively and by seed (Figure 16).
The highly disturbed nature of the site has created open, sunny, sand and gravel banks where young
seedlings have colonised (Figures 17 and 18).
Figure 16 Disturbed riparian zone
15 
Figure 17 Black willow seedlings on
the bank on the Nambucca River
Figure 18 Willow seedlings in highly
disturbed riparian zone
No regeneration of willows was noted within stands of river oak nor in areas of camphor laurel. The dense
shade cast under these species appears to preclude the willow seedlings.
16 
Linking willow growth with river instability and erosion
Whilst the current mapping exercise does not prove a causal relationship between willow infestation and
river morphology, willows occur in conjunction with several sites of significant river channel change.
There are three sites where willows are present and large scale river changes have recently occurred, see
map below. Of particular concern is the close proximity to the borefield for the Shire’s drinking water
supply.
SITE 2 Approx 400m upstream
from Lane’s Bridge, a group of
mature willows grow adjacent to
a recent change (2011/12) in the
river course – Figures 19 and 20.
At this location there is a large
log jam and a recently eroded
river channel with partial flow
remaining in the previous main
channel.
SITE 1 Approx
3.5 km
upstream from
Lane’s Bridge,
near the
location of an
original willow
planting, the
river course is
braiding and
bank collapses
are occurring.
SITE 3 Approx 500m downstream
from Lane’s Bridge a group of
willows occurs at a site where the
Nambucca River has changed
course.
Nambucca Shire Council Borefield
17 
Figure 19 Willows adjacent to log jam and river channel movement
Figure 20 Log jam abuts willows
18 
Case Study 2 – Control of willows at the MidCo site
Figure 21 Willows at the MidCo site
An infestation of willow had been previously identified by NSC Weeds Officer and NVL at the former
“MidCo Abattoir” site at Wirimbi, approximately 3 km north of Macksville – see Figure 21.
During March and April 2012 a control project was undertaken by Kara and Steve Smith on behalf of
NVL. A photographic record was made and samples of the willow species encountered were collected,
labeled and dried to create a herbarium collection that may assist future surveys and control projects in
the Nambucca Valley.
The area of infestation was mapped as approximately 6800m2, with a length of approx 240m and width
varying between 20 and 45m. Two willow species were identified: Salix nigra and Salix fragilis. (As these
species are known to interbreed, it is possible that other varieties were present.)
Salix nigra (Figure 23) is the more frequent willow species, and in a sample area has an average stem
diameter at breast height of 36.75cm, with ranges between 57cm and 22cm.
The Salix fragilis (Figure 24) stems are smaller at approximately 10-20cm diameter at breast height.
Approximately 160 willow stems/trunks were identified, with 82 stems controlled by April 2012. Each
stem was controlled by frilling, at 2-3cm intervals around the entirety of all stems, using approx 3-5ml of
100% glyphosate 360.
The control project is continuing and a photographic record made of the effects of the control.
19 
Figure 22 Salix nigra at the MidCo site
Figure 23 Salix fragilis at the MidCo site
20 
Recommendations
1.
2.
3.
4.
5.
6.
7.
The Wia Ora Bridge, Missabotti Road to Lane’s Bridge, Bowraville reach of the Nambucca River is
a priority area as it is the location of the NSC borefields which supply the valley’s drinking water.
It is recommended that NVL and NSC seek support to prepare a river plan for this reach. The plan
should consider all aspects of improving river function and protecting water supplies through a
range of river engineering, weed management, stock management and other measures.
In the Nambucca Valley, Salix nigra is currently the key invasive willow species. Management
efforts should focus on this species. Control of Salix nigra should be included as the priority
action for willows in the Nambucca in appropriate NSC and regional weed management
strategies.
Work with landholders to control major infestations of Salix nigra and develop property specific
actions, including willow eradication; replanting with appropriate species; river bank protection
measures; and river bed protection measures.
Promote appropriate native species to achieve river bank stabilisation in the Nambucca River at
NVL events (e.g. tree fairs, field days, newsletters).
NVL to continue to monitor the MidCo willow control site.
NVL to maintain the map/list of known willow infestation sites.
Ensure lessons learned from the control of black willow in the Bellinger valley are applied to
control project in the Nambucca – see DLWC, 1999.
Web Resources and References
A Field Manual for Surveying and Mapping Nationally Significant Weeds. BRS. Commonwealth of
Australia 2008.
Draft Strategy for the eradication of black willow Salix nigra in the Bellinger and Kalang river catchments.
Prepared for Bellingen Catchment Management Committee. Department of Land and Water
Conservation, 1999.
Guidelines for Establishing and Managing Poplar and Willow Trees on Farms Compiled and Prepared by
the National Poplar and Willow Users Group as part of the Sustainable Farming Fund’s Poplar & Willow
Project (Grant No. 04/089) May 2007. ISBN: 978-0-473-12270-6
Northern Rivers Invasive Plants Action Strategy 2009-2013 For the use of all public & private land
managers, North Coast Weeds Advisory Committee, 2009.
Plant guide to black willow Salix nigra (Marsh). John M. Row USDA NRCS, Manhattan Plant Materials
Centre, Manhattan, Kansas Wayne A. Geyer Forestry Division, Kansas State University, Manhattan,
Kansas June 2010. Available at http://www.nrcs.usda.gov
Regional Weeds Strategy 2008 to 2012. A Working Document for All Private & Public Land Managers Mid
North CoastWeeds Advisory Committee.
Willows National Management Guidelines Current management and control options for willows in
Australia, 2007, and Willow identification an essential skill for willow management. Willow resource
sheet 2. http://www.weeds.org.au/WoNS/willows
21 
Willows spreading by seed. Implications for Australian river management. Cremer, K; Van Kraayenoord,
C; Parker, N; Streatfield, S. Aust. Jnl Soil and Water Conservation Vol. 8, No. 4, Nov. 1995, pp 18-27.
Willow identification for river management in Australia. Cremer, K.W. 1995. CSIRO.
Willow control. Trounce, B and Cremer, K. No date. CSIRO.
Weeds of Australia, Biosecurity Queensland Edition Fact Sheets
http://keyserver.lucidcentral.org/weeds/data/03030800-0b07-490a-8d040605030c0f01/media/Html/Index.htm
Weeds of National Significance Willow (Salix taxa, excluding S. babylonica, S. x calodendron and S. x
reichardtii) Strategic Plan. National Weeds Strategy Executive Committee, Launceston. Agriculture &
Resource Management Council of Australia & New Zealand, Australian & New Zealand Environment &
Conservation Council and Forestry Ministers, (2000).
Willow management for Australian rivers. Kurt Cremer CSIRO Forestry and Forest Products. Natural
Resource Management Special Issue December 1999. The Australian Association of Natural Resource
Management.
Good quality images of Salix species can be found on the following websites:
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http://www.forestryimages.org
http://www.plants.usda.gov
http://keyserver.lucidcentral.org/weeds/data/03030800-0b07-490a-8d040605030c0f01/media/Html/Index.htm
22 
Appendix 1
Map of willow locations in the Nambucca catchment
Based on Google Earth, the map pinpoints known willow locations as of May 2012. The map is available in
electronic form at the NVL office in Bowraville and it will be updated with new willow records.
23 
Appendix 2
Case Study 1 Growth and spread of willows near Bowraville field notes and photograph locations
24 