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A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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4.4 Weeds  

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 

4. 


 

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 



not sprayed weeds within roadsides for two years. With the more favourable weather in 

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.  

 

 



The Roadside Conservation Value 

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 

value. 

Roadside infestation of African lovegrass 

(Photo by P. Hussey)

 


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Throughout the roadside survey, six weed species were recorded, and their locations 

mapped. Roadside weed populations of

 

Paterson’s Curse, Wild Oats, Capeweed, Wild 



Radish, Wild Turnip and Rye Grass can be observed in the weed overlays provided with 

the Roadside Conservation Value map (2004). 

 Figure 11 

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 

 

 



Paterson’s Curse; Echium plantagineum 

Photo by R. Knox and J. Dodd

 


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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4.5  Phytophthora Dieback 

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, 



eventually causing death. It is more widespread and severe in the higher rainfall zone and 

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 



Phytophthora fungi. Currently, there is no practical method of eradicating Phytophthora 

once it is established in an area. 

 

The Dieback Working Group has published a booklet, Managing Phytophthora Dieback in 



Bushland: A guide for Landholders and Community Conservation Groups (2000), that 

provides detailed information on minimising the risk of introducing or spreading 



Phytophthora

 

Impact of Phytopthora Dieback 

Photo Dieback Working Group 


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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5.0 

ASSESSMENT PROCESS  

 

5.1  Methods 

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 



knowledge of the area, are able to provide an accurate and cost effective method of data 

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 (



476.2 km

) of the Shire of Dalwallinu’s 1,939

 

km of roadsides were assessed 



for their conservation status and mapped. Fieldwork was carried out throughout 

November 

2003. 

 

The enthusiastic efforts of the volunteer surveyors, local coordinator Christine Jones and the 



support provided by Council ensured that this project was successfully completed.  

 

5.2  Quantifying Conservation Values 

The following attributes were used to produce a quantitative measure of conservation value: 

 



native vegetation on roadside; 

 



extent of native vegetation along 

roadside; 

 

number of native species; 



 

weed infestation; 



 

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 



scores provided a conservation score ranging from 0 to 12. The conservation values, in 

the form of conservation status categories, are represented by the following colour 

codes  


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Conservation Value 

Conservation Status 

Colour Code 

9 – 12 


High

Dark Green 

7 – 8 

Medium High



Light Green 

5 – 6 


Medium Low

Dark Yellow 

0 – 4 

Low


Light Yellow 

 

Table 3: Colour codes used to depict the conservation status of roadsides. 

The following attributes were also noted but did not contribute to the conservation value 

score: 



  width of road reserve; 



  width of vegetated roadside; 

 presence 



of 

utilities/disturbances; 

 dominant 



native 

species; 

  dominant weed species; 



 fauna 


observed; 

 general 



comments. 

 

It is felt that the recording of these attributes will provide a community database that 



would provide information useful in many spheres, such as local government and 

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 

1:100,000. 

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 



Roads WA and the Department of Agriculture was used in the base map, and depicts 

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 



the condition of the roadside vegetation. This is important as the quality of roadside 

vegetation has far reaching implications for sustaining biodiversity, tourism and 

Landcare values.  

 

Moreover the data and map can be incorporated as a management and planning tool for 



managing the roadsides per se, as it enables the condition of roadside vegetation to be 

easily assessed. This information can then be used to identify environmentally sensitive 

areas, high conservation roadsides or strategically important areas, and thus ensure 


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

18 


their conservation. Conversely, it enables degraded areas to be identified as areas 

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 



relevant to roadside conservation. This enables the roadside vegetation to be assessed 

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 

roadside management. 

 

As well as providing a road reserve planning 



and management tool, the roadside 

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 

the district; 

  Landcare and/or Bushcare projects would 



be able to incorporate the information from 

this survey into 'whole of' landscape 

projects. 

Weed control along a roadside 

Photo MRWA

 

The survey data and map can be used in 

developing regional or district fire 

management plans 


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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6.0 

SURVEY DATA RESULTS 

 

A summary of the general roadside conditions in the Shire of Dalwallinu is presented in 



Table 4. The survey data has been combined to provide the total kilometres, and 

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 

travelled. 

 

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, 



including the road formation, drains and the roadsides, i.e. from ‘fence to fence’. Of the 

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)

0

50

100



150

200


250

300


20m

40m


Unknown

Width (m)

Number of kilometeres (km)

A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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The ‘width of vegetated roadside’ value provides an insight into the width of the 

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)

70.7%

22.8%

0.8%

5.7%

1 to 5 m


5 to 20 m

over 20 m

Unknown


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Roadside sections of high conservation value covered 65.1% of the length of roadsides 

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 



determines the ‘native vegetation on roadside’ value. Sections with two to three layers of 

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

65.1%

23.3%

5.9%

5.8%

High 


Medium-high 

Medium-low 

Low 

Native Vegetation on Roadsides

94.3%

0.2%

5.5%

2-3 vegetation

layers

1 vegetation layer



0 vegetation layers

A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Roadside vegetation with extensive cover, i.e. greater than 80%, occurred along 27.8% 

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 



vegetation. Survey sections with more than 20 plant species spanned 554.4 km (58.2%) 

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

27.8%

60.3%

11.8%

Over 80%


20% to 80%

Less than 20%



Number of Native Plant Species

58.2%

34.1%

7.7%

Over 20


6 to 19

0 to 5


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Roadsides determined to have high value as biological corridors (as determined by the 

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 



surveyed, medium level weed infestation occurred on 36.8% (350.6 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



78.8%

11.8%

9.3%

High


Medium

Low


Level of Weed Infestation

29.1%

34.1%

36.8%

Light


Medium

Heavy


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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Uncleared native vegetation was present on 12.1% (115.5km) of the land adjoining 

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, 

Figure 10. 



 

Figure 10 – Predominant adjoining land use. 

 

 

Roadside populations of the following nominated weeds are indicated on clear overlays 

accompanying the 2003 RCV map: 

 Cape 



weed; 

 Pimpernel; 



 Paterson’s 

curse; 



 Wild 



oats 

 Barley 



grass 

 Skeleton 



weed 

 

Wild Mustard was also recorded under the category ‘Other weeds’, and is represented in 



Figure 11, with the other 6 nominated weed species observed along roadsides in the 

Shire. 


 

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

82.1%

1.2%

0.3%

1.8%

12.1%

2.4%

Completely Cleared

Drain

Urban/Industrial



Railway

Scattered vegetation

Uncleared


A survey of the roadside conservation values in the Shire of Dalwallinu and roadside management guidelines 

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occurring along 338.4 km, Mustard was present along 75.5 km, Skeleton weed 32.2 km, 

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 

0

200



400

600


800

1000


1200

Paterson's

curse

Wild oats



Cape weed

Pimpernel Barley grass

Skeleton

weed


Mustard

Weed

Occurrence (km)
1   2   3   4   5




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