Weeds are plants that are growing outside their natural range and competing with native
plants for nutrients, space, water and light. Weeds often invade roadsides and interfere
with the growth and survival of native plants. The effect of weed infestations on native
plant populations is severe, and causes flow on effects for native fauna. Once native
plants begin to diminish, due to heavy competition, native fauna suffers due to reduced
availability of habitat and food. Once weeds become established in an area, they
become a long-term management issue, costing many dollars to control or eradicate.
The WA Herbarium records ???? weed species in the Shire of Dalwallinu, see Appendix
The Shire of Dalwallinu works with the Department of Agriculture to control some weed
species, for example there is a weed eradication program targeting Saffron Thistle
(Carthamus lanatus) within road reserves. Saffron thistle is controlled using a mixture of
Round-up and Simazene. Unfortunately, roadside areas that have been sprayed may
suffer from re-infestations, particularly where there has been little or no weed control
carried out in adjoining lands.
A low level of weed growth, due to unfavourable weather has meant that the Shire has
2003 weed populations have subsequently been more competitive and invasive
therefore, the weed eradication program will restart in 2004. The Shire will be targeting
African lovegrass (Eragrostis curvula), an invasive roadside weed. African lovegrass
tends to grow on the edge of the bitumen, and slowly breaks it up by root penetration.
This becomes problematic when attempting to grade the shoulders, as it is difficult to
remove without also damaging the bitumen.
map and weed overlays will assist the
Shire in coordinating strategic weed
control projects, with the highest
priority to protect and preserve the
high conservation value roadsides,
and working towards rehabilitating
those with a lower conservation
Roadside infestation of African lovegrass
(Photo by P. Hussey)
Throughout the roadside survey, six weed species were recorded, and their locations
mapped. Roadside weed populations of
Paterson’s Curse, Wild Oats, Capeweed, Wild
the Roadside Conservation Value map (2004).
also provides some indication
of the number of kilometres of roadside that each weed was observed along.
Wild Oats Avena fatua
Photo by J.D. Dodd
Photo by R. Knox and J. Dodd
The Phytophthora species dieback is made up of several types of introduced fungi. About
one third of native plants in Western Australia’s south-west are susceptible, including
species of Banksia, Hakea, Eucalyptus, Melaleuca, Verticordia, Acacia and Grevillea.
The Phytophthora fungus infects the roots and inhibits the uptake of water and nutrients,
waterlogged sites. The Shire of Dalwallinu is not a known Phytophthora dieback risk area as
it has an annual rainfall of less than 600mm.
Phytophthora spreads by the movement of spores in water, or by the spread of infected soil.
The spores can be introduced to uninfected areas by human activities, particularly through
the soil carried on vehicle tyres or footwear.
Human activities, such as routine maintenance or construction, have the potential to spread
once it is established in an area.
The Dieback Working Group has published a booklet, Managing Phytophthora Dieback in
provides detailed information on minimising the risk of introducing or spreading
Impact of Phytopthora Dieback
Photo Dieback Working Group
The methods to assess and calculate the conservation value of the roadside reserves are
described in Assessing Roadsides: A guide for Rating Conservation Value (Jackson, 2002).
The process involves scoring a set of pre-selected attributes, which, when combined,
represent a roadside's conservation status. A list of these attributes is presented on a
standard survey sheet, see Appendix 2. This provides both a convenient and uniform
method of scoring.
Ideally, the survey is undertaken by a group of local volunteers, who, aided by their
collection. Community participation also ensures a sense of ownership of the end product,
which increases the likelihood of its acceptance and use by the local community and road
managers (Lamont and Blyth, 1995).
The majority (
) of the Shire of Dalwallinu’s 1,939
km of roadsides were assessed
The enthusiastic efforts of the volunteer surveyors, local coordinator Christine Jones and the
5.2 Quantifying Conservation Values
The following attributes were used to produce a quantitative measure of conservation value:
number of native species;
value as a biological corridor; and
predominant adjoining land use.
Each of these attributes was given a score ranging from 0 to 2 points. Their combined
the form of conservation status categories, are represented by the following colour
9 – 12
7 – 8
5 – 6
0 – 4
The following attributes were also noted but did not contribute to the conservation value
width of road reserve;
width of vegetated roadside;
dominant weed species;
It is felt that the recording of these attributes will provide a community database that
community interest groups.
5.3 Mapping Conservation Values
A computer generated map (using a Geographic Information System, or GIS), depicting
the conservation status of the roadside vegetation and the width of the road reserves
within the Shire of Dalwallinu was produced at a scale of
The data used to
produce both the map and the following figures and tables are presented in Appendix 3.
Data obtained from the Department of Conservation and Land Management, Main
the location of remnant vegetation on both the Crown estate and privately owned land.
The roadside conservation values map initially provides an inventory of the status quo of
vegetation has far reaching implications for sustaining biodiversity, tourism and
Moreover the data and map can be incorporated as a management and planning tool for
easily assessed. This information can then be used to identify environmentally sensitive
areas, high conservation roadsides or strategically important areas, and thus ensure
important for strategic rehabilitation or in need of specific management techniques and
weed control programs.
The map can also be used as a reference to overlay transparencies of other information
in the context of its importance to the shire’s overall conservation network. Other
overlays, such as the degree of weed infestation, or the location of environmentally
sensitive areas or future planned developments, could also be produced as an aid to
As well as providing a road reserve planning
conservation value map can also be used for:
Regional or district fire management plans;
Tourist routes, i.e. roads depicted as high
conservation value would provide visitors
to the district with an insight to the flora of
Landcare and/or Bushcare projects would
this survey into 'whole of' landscape
Weed control along a roadside
The survey data and map can be used in
developing regional or district fire
A summary of the general roadside conditions in the Shire of Dalwallinu is presented in
percentages, of roadside occupied by each of the conservation status categories and the
attributes used to calculate the conservation values. As roadsides occur on both sides of
the road, roadside distances (km) are equal to twice the actual distance of road
Table 4: Summary of the roadside conditions in the Shire of Dalwallinu.
The ‘width of road reserve’ attribute indicates the total width of the road reserve,
952.5km of roads surveyed in 2003, the width of 75kms (15.7%) of road reserve was
unknown, which is common when a road passes through unfenced land, such as Nature
reserves. Approximately 28% (134.9km) of the roads surveyed measured 40m in width,
and 55.9% (266.4km) were 20m in width.
Figure 2- Width of Road Reserves in the Shire of Dalwallinu (2003)
Width of Road Reserve (m)
vegetation occurring within roadsides in the Shire of Dalwallinu. Roadsides where the
vegetation width was greater than 20m covered 0.77% (7.4km) of the Shire. 22.8%
(217.3km) of roadsides supported vegetation between 5-20m in width, and 70.7%
(673.8km) of roadsides contained native vegetation between 1-5m in width. The width of
vegetation was unknown for 5.7% (54.1km), which is common when a road passes
through unfenced land, such as Nature reserves.
Figure 3- Width of vegetated roadsides in the Shire of Dalwallinu.
Width of Vegetated Roadside (m)
1 to 5 m
over 20 m
surveyed (619.9 km). Medium-high conservation value roadsides accounted for 23.3% of
the total surveyed (221.5 km), medium-low conservation roadside covered 5.9% of the
total surveyed (55.9 km). Areas of low conservation value occupied 5.8% of the
roadsides surveyed (55.2 km), Table 4, Figure 4.
Figure 4 – Conservation status of roadsides in the Shire of Dalwallinu.
The number of native vegetation layers present, either the tree, shrub or ground layers
native vegetation covered 94.3% of the roadside (898.0 km). 5.5% had only one layer
(52.3 km) and 0.2% had no layers of native vegetation (2.2 km), Table 4, Figure 5.
Figure 5– Native vegetation on roadsides in the Shire of Dalwallinu.
Conservation Status of Roadsides
Native Vegetation on Roadsides
1 vegetation layer
of the roadsides surveyed (265.0 km). Survey sections with 20% to 80% vegetation
cover accounted for 60.3% of the roadsides (574.7 km). The remaining 11.8% had less
than 20% native vegetation (112.9 km), and therefore, a low ‘extent of native vegetation’
value, see Table 4, Figure 6.
Figure 6 – Extent of native vegetation along roadsides in the Shire of Dalwallinu.
The ‘number of native species’ score provided a measure of the diversity of the roadside
of the roadside. Roadside sections with 6 to 19 plant species accounted for 324.9 km
(34.1%) of the roadside. The remaining 73.1 km (7.7%) contained less than 5 plant
species, see Table 4, Figure 7.
Figure 7 – Number of native plant species within roadsides in the Shire of Dalwallinu.
Extent of Native Vegetation on Roadsides
Less than 20%
0 to 5
roadside surveyors) were present along 78.8% (750.9 km) of the roadside, medium
value made up 11.8% (112.8 km), and roadsides with low value as a biological corridor
occurred along 9.3% (88.8 km) of the roadsides surveyed, see Table 4, Figure 8.
Figure 8 – Value as a biological corridor.
Light levels of weed infestation were observed on 29.1% (277.0 km) of the roadsides
and 34.1% (325.0 km) were heavily infested with weeds, see Table 4, Figure 9.
Figure 9 – Weed infestation. Light weed infestation = weeds less than 20% of total plants.
Medium weed infestation = weeds 20 to 80% of the total plants. Heavy infestation = weeds more
than 80% of the total plants.
Value as a Biological Corridor
roadsides, whilst 82.1% (782.3 km) of roadsides surveyed were adjoined by land that
had been completely cleared for agriculture. 1.8% (17.6 km) of the roadsides surveyed
were bordered by land that was cleared for agriculture, but contained a scattered
distribution of native vegetation. Drains were the predominant adjoining landuse for 2.4%
(22.7 km) of the roadsides surveyed, urban/industrial landuses adjoined 1.2% (11.5 km),
and railway reserves adjoined 0.3% (2.9 km) of the roadsides surveyed, see Table 4,
Roadside populations of the following nominated weeds are indicated on clear overlays
accompanying the 2003 RCV map:
Wild Mustard was also recorded under the category ‘Other weeds’, and is represented in
Of the 6 nominated weeds surveyed throughout 2003, Wild oats were the most highly
recorded weed category, occurring along 1004.0 km of roadsides. Cape weed was
present along 720.7 km of the roadsides surveyed, whilst Paterson’s curse was recorded
along 568.9 km of roadside. Barley grass was the next most commonly recorded weed,
Predominant Adjoining Landuse
and Pimpernel 28 km of roadside, see Figure 11.
Figure 11 – Occurrence of nominated weeds along roadsides in the Shire of Dalwallinu
Occurrence of Nominated Weeds
Pimpernel Barley grass