ASSESSMENT OF EDGE EFFECTS AND OTHER INDIRECT IMPACTS … · 1 assessment of edge effects and other...

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ASSESSMENT OF EDGE EFFECTS AND

OTHER INDIRECT IMPACTS OF THE

PROPOSED KEANE ROAD STRATEGIC LINK

REPORT PREPARED FOR ENVIROWORKS AND CITY OF ARMADALE

BY DR EDDIE J VAN ETTEN, CONSULTING ECOLOGIST

March 2014

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EXECUTIVESUMMARY

The ecological impact of roads spreads further than the immediate clearing of vegetation for

road construction. Such edge effects or indirect impacts were identified in the Public

Environmental Review (PER) impact assessment process for the Keane Road Strategic Link

(KRSL), but were not quantified in terms of likely distances and areas impacted. The EPA

requested that further consideration be given to these indirect effects and some estimation

of these effects be conducted. This report reviews potential edge effects and uses our

current understanding of these edge effects to make predictions on the likely edge effect

distances and areas.

Potential edge effects identified from the review and which were relevant to KRSL included

effects on microclimate, vegetation, weeds, hydrology, dieback, soils and fauna. Of these,

weed infestation was determined to have the greatest potential to spread from the edge of

the road into the vegetation with maximum distances predicted to be in the order of 1‐5 m

depending on vegetation type. The review also established that the degree of weed

incursion at the edge is highly management dependent, but it is still likely that road verges

will have some weeds as bare soil on the verge is prone to weed invasion and spread.

Within the KRSL PER, the City of Armadale have committed to a range of weed

management measures including (but not limited to):

The establishment of vegetated road embankments and swales; and

Undertaking on‐going control of weeds along the road verge and in drainage swales

to prevent spread of weeds from the road into the surrounding areas.

If City of Armadale’s weed management is effective along the road, the spread of weeds will

be limited.

To put the edge effects into context, edge effects distances and ranges were also predicted

for an unmanaged sealed road scenario and current use of the existing unsealed track by

off‐road vehicle (status quo scenario). The predictions of edge effects under these scenarios

were greater in distance and area, emphasising the importance of management to reduce

edge effects. The main edge effects predicted for these scenarios were related to greater

spread of weeds and dieback along the road/track (resulting in multiple infection points

which would then spread into the bushland) and physical damage to edge vegetation

(especially likely along the unsealed off‐road track).

The review has shown that minimising edge effects is possible through appropriate and

well‐targeted management. Such management actions identified include: careful clearing of

vegetation to avoid damage; fencing to control access; effective and ongoing weed control

at the edge; and construction of swales to capture run‐off. On the basis of such

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management measures, which are proposed in the KRSL PER, it is predicted that maximum

edge effects from KRSL would develop quite slowly over 10 years and would likely stabilise

with effective ongoing control measures proposed preventing further spread. It should be

noted that maximum predicted areas of influence are provided, but that with very effective

management by the City of Armadale, edge effects from KRSL may never reach these

maximum predicted areas of influence, but instead stabilise within much smaller areas

influence. However for the purposes of impact assessment, maximum areas of influence

should be considered.

By contrast, scenarios are also considered involving the KRSL with no management

measures implemented and the current situation of an unsealed track used for off road

driving. For these scenarios it is considered that spread of edge effects is unlikely to

stabilise over time given the lack of management measures for these scenarios. Therefore

for the purposes of comparison, edge effects from these scenarios have been predicted for

a timeframe of 10 years. However it is reasonable to conclude that edge effects would

continue to spread further after the 10 year timeframe given these scenarios include no

management measures being implemented.

Edge effect distances estimated in this report have been done so conservatively. The likely

distance ranges for each effect were overlain to determine the maximum likely effect

distance across all potential types of edge effects. That is, the largest distance within all the

edge effect ranges predicted, became the maximum distance of total edge effect impact

predicted. This has ensured predictions are conservative as in reality edge effects are likely

to be uneven along the edge and not spread to the maximum distance for all areas along

the edge. However for the purposes of this study the conservative assumption has been

used that edge effects will spread evenly to the maximum predicted distance along the

edge, therefore likely overestimating the edge effect area of influence to ensure predictions

are conservative.

The three tables below detail the edge effects predicted for each vegetation community

under the following scenarios:

Scenario 1: Effective management of proposed sealed Road (i.e. all proposed

management actions are implemented and successful).

Scenario 2: Unmanaged sealed road (i.e. no or little management action to minimise

edge effect and spread of disease/weeds).

Scenario 3: Unsealed bush track being used for off road driving (i.e. status quo)

As shown below in Table E1, the predictions found that edge effects on the ‘dry clay flats’

SCP10a Threatened Ecological Community (TEC) was unlikely under the KRSL proposal as the

alignment was sufficiently distant from this community. Also under the KRSL proposal,

relatively small areas of two Priority Ecological Communities (PECs) would be impacted by

edge effects (approximately 1 – 3% of their areas locally).

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As shown below in Tables E2 and E3, this was in contrast to edge effects predicted for the

other two scenarios with no management, where predicted edge effects spread over much

larger areas of the TEC and PECs (up to 25% of the TEC and 15% of the PECs).

In summary, the maximum area of influence for predicted edge effects from the proposed

KRSL project with effective management was 0.92 ha (Table E1). When combined with the

direct clearing footprint predicted in the KRSL PER of 1.65 ha, total impacts likely from the

road are predicted to be 2.57 ha. This equates to less than 1% of the 368.89 ha of

vegetation within the adjacent Bush Forever Site 342.

Table E1: Prediction of Edge Effects Scenario 1 ‐ Effective Management of KRSL

Code Floristic Community Type TEC/PEC Classification

Size of Community within Study

Area (ha)

Edge Effects (ha)

% Community

Type Impacted by Edge Effects

SCP04 Melaleuca preissiana dampland N/A 38.72 0.11 0.28

SCP05 Mixed shrub dampland N/A 7.43 0.00 0.00

SCP10a Shrublands on dry clay flat TEC (Endangered)

4.47 0.00 0.00

SCP21a Central Banksia attenuata-Eucalyptus marginata woodland

N/A 41.85 0.23 0.55

SCP21c Low lying Banksia attenuata woodland or shrubland

PEC (Priority 3)

8.93 0.28 3.14

SCP22 Banksia ilicifolia woodland PEC (Priority 2)

5.78 0.06 1.04

SCP23a Central Banksia attenuata-Banksia menziesii woodland

N/A 23.94 0.24 1.00

Total all Communities 131.12 0.92 0.70

Table E2: Prediction of Edge Effects Scenario 2 ‐ KRSL with No Management



Area (ha)

Edge Effects (ha)

% Community





4.47 0.37 8.28


N/A 41.85 0.46 1.10


PEC (Priority 3)

8.93 0.60 6.72


5.78 0.13 2.25


N/A 23.94 0.47 1.96

Total all Communities

131.12 2.72 2.07

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Table E3: Prediction of Edge Effects Scenario 3 – Unsealed Track



Area (ha)

Edge Effects (ha)

% Community





4.47 1.25 27.96


N/A 41.85 0.95 2.27


PEC (Priority 3)

8.93 1.35 15.12


5.78 0.26 4.50


N/A 23.94 0.92 3.84


131.12 6.69 5.10

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TABLEOFCONTENTS

EXECUTIVE SUMMARY ............................................................................................................................ 2

TABLE OF CONTENTS ............................................................................................................................... 6

1. KEANE ROAD STRATEGIC LINK (KRSL) PROPOSAL & NEED FOR ASSESSMENT OF EDGE EFFECTS .. 7

2. SCOPE OF WORKS ......................................................................................................................... 10

3. LITERATURE REVIEW OF EDGE EFFECTS AND OTHER INDIRECT IMPACTS OF ROADS .................. 12

3.1 DEFINITIONS & KEY CONCEPTS ............................................................................................. 12

3.2 EDGE EFFECTS OF ROADS ‐ GLOBAL PERSPECTIVES .............................................................. 13

3.3 SYNTHESIS OF MAIN ENVIRONMENTAL IMPACTS OF ROADS .............................................. 14

3.4 ESTIMATE OF EFFECT SIZE AND WIDTHS – ZONE OF INFLUENCE ......................................... 18

3.5 ROAD EDGE EFFECTS ‐ WESTERN AUSTRALIAN PERSPECTIVE .............................................. 20

4. OBSERVATIONS OF EDGE EFFECTS IN VICINITY OF KEANE ROAD ................................................. 22

5. PREDICTED EDGE EFFECTS OF KEANE ROAD STRATEGIC LINK ...................................................... 23

5.1 SPATIAL PREDICTION ................................................................................................................... 23

5.2 TEMPORAL PREDICTION .............................................................................................................. 23

5.3 VEGETATION TYPES ..................................................................................................................... 24

5.4 DEVELOPMENT SCENARIOS ........................................................................................................ 25

5.5 DISCUSSON OF KRSL AND EACH TYPE OF EDGE EFFECT ............................................................. 25

5.5.1 CHANGES TO MICROCLIMATE ....................................................................................... 25

5.5.2 VEGETATION DISTURBANCE AT EDGE ........................................................................... 26

5.5.3 CHANGES TO PHYSICAL ENVIRONMENT, INCLUDING HYDROLOGY ............................. 26

5.5.4 WEED INVASION ............................................................................................................ 27

5.5.5 PHYTOPHTHORA ........................................................................................................... 28

5.5.6 EFFECTS ON FAUNA ...................................................................................................... 29

5.6 PREDICTION OF EDGE EFFECT DISTANCES .................................................................................. 30

5.7 AREA OF INFLUENCE ............................................................................................................. 32

6. CONCLUSIONS AND MANAGEMENT RECOMMENDATIONS ......................................................... 35

7. REFERENCES .................................................................................................................................. 37

8. APPENDICES .................................................................................................................................. 42

Appendix 1: Photographs and notes of edge effects observed during field reconnaissance on 22/2/14. ............................................................................................................................................ 42

Appendix 2: Maps showing predicted maximum edge effect under three scenarios outlined in report. ............................................................................................................................................... 46

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1. KEANEROADSTRATEGICLINK(KRSL)PROPOSAL&NEEDFORASSESSMENTOFEDGEEFFECTS

Keane Road is located approximately 20 km southeast of the Perth CBD and approximately 7

km northwest of the Armadale. It is designed to connect the new urban areas of Harrisdale,

Piara Waters and Forrestdale. Keane Road is located within the City of Armadale and is

made up of three distinct portions; two parts are constructed and a third central portion is

not yet constructed but is partly cleared (currently used as a 4WD track). A dedicated road

reserve has been previously set aside for all portions of the road, including the

unconstructed portion. The surrounding bushland is listed as Bush Forever Site 342. The

Keane Road Strategic Link (KRSL) project entails the construction of the central portion of

Keane Road, in order to link the currently constructed portions.

It is proposed to construct the final section of unmade road, within a 20 m wide, dedicated

Crown Road Reserve, which has been previously set aside for the purpose of a local district

distributor road. 1.65 ha of native vegetation clearing is required for the road. Native

vegetation clearing has been minimised wherever possible by the City of Armadale through

the following measures:

Reducing the road width from 20 m (the width of the dedicated road reserve) to 18.4

m.

Aligning the road footprint with existing cleared firebreaks and existing tracks.

Deviating the road at the southestern end into cleared private farmland.

Other features and measures to reduce environmental impact of the proposed road are

indicated in Table 1.

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Table 1: Key characteristics of the KRSL project

Element Description

General

Construction Period 7–8 months approximately

Project Life Indefinite assuming good road maintenance

Proposed Road

Road design A single carriageway (one lane for each direction) and dual use

pathway

Length 1.5 km

Width 18.4 m (including road, drainage swales, footpath and fencing)

Speed limit 70 km/h

Height 0.8–1.2 m (on average 1 m) above natural ground level

Total footprint 2.75 ha (including cleared tracks)

Cleared areas within

footprint (firebreak /

tracks / farmland)

1.1 ha

Proposed total

vegetation clearing 1.65 ha (areas already cleared for firebreak and tracks not included)

Surface Water Culverts A range of small culvert arrays across the alignment to ensure

hydrologic connectivity.

Fauna Underpasses 7

Fauna Underpass

Design A range of different sizes to suit the terrestrial fauna species present.

Fill Material

Locally sourced Bassendean sand and crushed limestone sub‐grade and

road base material. This material will be certified as dieback free where

required by the Dieback Management Plan for the road.

Construction Support Infrastructure/Resources (temporary)

Construction Site Equipment lay down area (temporary only) if required (no additional

clearing required)

Construction Workforce 40–45 personnel

Operation Support Infrastructure

Drainage Drainage swales: broad, shallow (typically 0.2 m deep) swales with 1:4

(vertical:horizontal) side slopes

Signage Speed limit and wildlife warnings

Footpath Dual use for pedestrians and bicycles, 3 m width (2.4 m wide pavement

plus 0.3 m shoulders each side)

Lighting Energy efficient street lights

Fire water reticulation Fire hydrants (pre‐installed)

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Figure 1: Proposed road design showing typical cross section of KRSL. The red line shows

approximate surface of new road with typical slopes indicated. Open drains (swales) occur on

either edge of road to collect road runoff. The left side of the road features a sealed footpath.

Fences will be constructed on either side of the road with the vegetation clearing line set back

some 0.5 m from the fence.

The City of Armadale referred the Keane Road project to the Environmental Protection

Authority (EPA) and it is being assessed at Public Environmental Review (PER) with an 8

week public submission period. This period has now closed and the City of Armadale is

required to submit a “Response to Submissions” document to the EPA by 10th of March

2014.

Submissions have raised concerns that the residual impacts of the proposal may be greater

than predicted in the PER document. The PER document predicts that the residual impacts

are primarily determined by the 'footprint' of the proposal (1.65 Ha). However submissions

have raised concerns that indirect impacts from threatening processes such as hydrological

changes, spread of weeds and dieback may increase the extent of the residual impacts.

Given the submissions raised, the City of Armadale has requested an edge effects

assessment, in order to confirm the spatial and temporal extent of the residual impacts

after incorporating all the management measures in the PER document, and any additional

measures proposed their response to submissions.

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2. SCOPEOFWORKS

The tasks set by EnviroWorks Consulting were to:

1. Undertake a desktop review of “edge effects” (spread of weeds, dieback,

hydrological impacts) which can be caused by tracks and roads. If possible find data

or examples where “edge effects” zone of influence has been predicted or mapped

spatially and temporally (over time).

2. As part of this desktop review, differentiate between:

o Edge effects which may be caused by an unsealed bush track subject to

uncontrolled off road vehicle incursion without management controls in

place (the current case at Keane Road); and

o Edge effects likely to be caused by a properly constructed bitumised road

with the following management measures (as planned for the Keane Road

Strategic Link):

Fencing to prevent off road driving;

Fencing to prevent fauna road kill;

Vegetated drainage detention swales to capture surface water run‐

off;

Appropriately designed and located fauna underpasses to allow all

species of terrestrial fauna present to pass underneath the road; and

Appropriately designed drainage culverts to convey predicted

stormwater flows under the road.

3. Predict a potential “zone of influence” of edge effects for the current Keane Road

bush track (including spatial and temporal elements) taking into account the current

situation (uncontrolled off road vehicle incursion). Ideally this “zone of influence”

should include a spatial extent on a map, as well as a prediction of the temporal

nature of spread likely for this zone of influence. Information from available studies

already completed can be used to inform this “zone of influence” prediction

including:

o Flora and Vegetation Survey

o Dieback Study and Mapping

o Aerial photography which clearly shows the widespread disturbance being

caused by off road vehicle tracks

4. Predict a potential “zone of influence” of edge effects for the proposed Keane Road

Strategic Link (including spatial and temporal elements) taking into account the road

design and management measures proposed by City of Armadale. Ideally this “zone

of influence” should include a spatial extent on a map, as well as a prediction of the

temporal nature of spread likely for this zone of influence. Information from

available studies already completed can be used to inform this “zone of influence”

prediction including:

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o Proposed Keane Road Strategic Link Design including:

Fencing to prevent off road driving;

Fencing to prevent fauna road kill;

Vegetated drainage detention swales to capture surface water run‐

off;

Appropriately designed and located fauna underpasses to allow all

species of terrestrial fauna present to pass underneath the road; and

Appropriately designed drainage culverts to convey predicted

stormwater flows under the road.

o Flora and Vegetation Survey

o Dieback study and mapping

o Fauna Study and fauna underpass design

o Hydrology Study and surface water drainage culvert design.

5. Provide maps or diagrams showing the predicted zones of influence visually.

6. Discuss the difference between edge effects likely between the two scenarios above

– i.e. current unsealed track compared with proposed bitumised Keane Road

Strategic Link, as well as management aspects influence the spatial and temporal

nature of edge effects likely.

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3. LITERATUREREVIEWOFEDGEEFFECTSANDOTHERINDIRECTIMPACTSOFROADS

3.1 DEFINITIONS&KEYCONCEPTS

Edge effects in ecology are identifiable as any difference in environment between the edge

and the interior of a particular vegetation patch (Murcia 1995). More generally, the term

refers to the boundary where two distinct habitats or ecosystems meet and where there is

typically some overlap of environmental features from each habitat, or, in other words, a

narrow transition zone (or ecotone) from one habitat to another (Murcia 1995; Donaldson &

Bennett 2004).

Edge effects are a long‐recognised and well‐studied ecological phenomenon. Environmental

characteristics which differ across edges are many and varied. They cover many components

of the environment including the atmosphere (eg microclimate), vegetation (eg structure,

composition, functioning), fauna and their habitat and soil (Murcia 1995). Typically edge

effects are multi‐faceted and inter‐related, with direct, or primary, effects (eg changes in

microclimate and soil exposure from extra solar radiation) often leading to secondary

changes in plants and animals density which can, in turn, either further exacerbate or

ameliorate the primary changes. Effects may be long lasting or temporary, and can be either

rapid or slow to develop; similarly, they can be relatively stable once the effect has

occurred, particularly if effective management occurs, or they can develop in a progressive

fashion, working their way from the edge into the interior of the vegetation or habitat over

time.

Edge effects have two particular and measurable properties: i) the distance that the effect

occurs, or at least is detectable, from the edge of the vegetation/habitat into the interior

(referred to ‘edge effect distance’ in this report); and ii) the degree to which the edge

environment differs from the interior of the vegetation/habitat (refer to here as ‘edge effect

size’).

Edges and their effects may be natural (eg where forests abut grasslands, or the edge of

permanent ponds) or be anthropogenic (caused directly by human clearance of vegetation).

Where new edges are created by roads, vegetation clearing, forestry and other

developments, it is now commonplace to predict edge effects. The distance the effect

spreads from edge, known as edge permeability, can be highly variable and depends on

many factors such as vulnerability of edge ecosystem, degree of change in land use,

intensity of this use and chance events (Murcia 1995). Because, edge effects cover a large

range of direct and indirect impacts, many of which are closely inter‐related, the term can

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be rather nebulous and over‐used in environmental management if the component

attributes and receiving environment are not carefully explored.

3.2 EDGEEFFECTSOFROADS‐GLOBALPERSPECTIVES

It has been recognised for many decades that roads impact on their surrounding

environment. These are known as road or roadside edge effects, and the scope of these

effects has widened to not only include changes to the environment adjacent to road, but to

also include restriction on the movement for fauna, gene flow and water imposed by roads.

Now more broadly known as road ecology, this is an area of active ecological research, both

pure and applied, across the globe (eg Forman 2000; van der Ree et al. 2011).

The literature has been much reviewed in many contexts and it is beyond the scope of

works to review the complete literature on the road edge effects which amounts to

thousands of papers and other scholarly work worldwide. Rather the major reviews are

listed in Table 2 with their number of citations in the scientific literature (Google Scholar)

given to indicate the levels of research activity in road ecology.

Table 2: Major published reviews of road edge effects with number of citations and short

description of their scope and focus.

Review Authors Description Citations in

Google Scholar

(Feb. 2014)

Forman & Alexander

(1998)

Comprehensive review of ecological impacts of

roads

1752

Trombulak & Frissell

(2000)

Review of ecological effects of roads on terrestrial

and aquatic biota

1674

Forman et al. (2004) Book which cover all aspects of road ecology 1167

Forman (2000) Review of studies into distance of road impacts

from road edge and application of this data to

estimate of total area of USA impacted by roads

562

Spellerberg (1998)

Broad review of ecological effects of roads and

traffic

431

Bennett, A. F. (1991) Review of effects of roads and road edges on

wildlife conservation

357

Fahrig and Rytwinski

(2009)

Review of 79 studies into the effects of road on

animals

240

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Review Authors Description Citations in

Google Scholar

(Feb. 2014)

Andrews (1990)

Review of fragmentation effects by roads with

strong Australian focus

233

Coffin (2007) Review of direct and indirect road impacts which

serves as an introduction to special edition of

Journal of Transport Ecology on topic of road

ecology

228

Benítez‐López et al.

(2010)

A meta‐analysis of 49 studies on effects of roads on

bird and mammal populations

117

Holderegger and Di

Giulio (2010)

Review of the genetic impacts of roads 59

Van der Ree et al.

(2011)

Review of road impacts but with emphasis on

higher order effects such as changes to ecosystem

functioning, community composition/structure and

landscape configuration; serves as introduction to

special edition of Ecology and Society on future

directions in road ecology

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3.3 SYNTHESISOFMAINENVIRONMENTALIMPACTSOFROADS

These reviews of roadside impacts generally agree on following types of impacts as

elaborated below. These will be main types of impacts explore in this report. Impacts of

roads on their edge environment may be either direct (primary effect) or indirect

(secondary effect). For example, vegetation changes at the edge are indirect as they tend to

develop after road construction due to a combination of more direct effects such as

modified microclimates, soil changes and increased runoff. These vegetation changes can

then affect habitat condition for fauna (i.e. another indirect effect). Unmanaged indirect

effects generally affect a greater distance from the edge and therefore affect a larger area

(zone of influence).

1) Modification of microclimate. Where new edges of vegetation are created through

clearing, there is a change in the microclimate at the edge due to greater

penetration of light and wind into the vegetation. Temperature extremes are greater

and humidity of air is generally less at edge than in interior of vegetation.

Microclimate changes at edges have been well documented for forests (because of

the large amount of edge created by clear‐fell forestry and forest access tracks) and

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the effect is known to increase in size (degree of change) and width (distance from

edge into interior vegetation) with increasing latitude, height of trees or dominant

vegetation layer and density/cover of vegetation. Changes in edge microclimate

often lead to changes in vegetation structure, fuel loads and availability, tree shape

(eg more branching on edge side), plant health, species composition and faunal

habitat characteristics at the edge (which are discussed further below). The effect

can be progressive where trees detrimentally affected by at the edge die to

effectively create new edges further back into the vegetation.

2) Physical disturbance of vegetation at edge. Although initial clearing for roads may

create a relatively distinct or ‘clean’ edge, subsequent damage to the edge

vegetation is possible from grading and weed control of road verges (Spooner et al.

1994), vehicle accidents, vandalism and off‐road vehicle use. Unsealed tracks in

bushland typically get wider over time as off‐road vehicles seek alternative passage

around barriers and boggy areas (Whilshire et al. 1978; Newsome and Moore 2012).

Similarly, roads and unsealed tracks can also facilitate an increase incidence of fire

ignitions (Cochrane & Laurance, 2002), either lit purposely by arsonists or

accidentally such as from disposal of cigarette butts from cars. Arson‐lit fires are

more likely to occur adjacent to concealed, little‐used bush tracks than well utilised

public roads due to passive surveillance from road users.

3) Changes in surface drainage and hydrology. Although the amount of surface water

run‐off depends largely on the type of road surface, there is typically some surface

runoff of rainwater from the road. It is common practice to construct drains to

collect such runoff and prevent the run‐off from reaching the edge vegetation.

Despite this, plants at the edge may still tap into this water via roots as it infiltrates

into the soil. This means extra water for roadside plant and has often been

attributed to increasing density and cover of roadside vegetation over time (e.g.

Lamont et al. 2004a,b). Roads can also be barriers to surface and sub‐surface flows

of water, although, again, there are usually engineering measures available to

effectively manage this (e.g. culverts under road, bridges over drainage lines etc.).

4) Modification of chemical environment. Road runoff may contain oil/petrol (spilt from

vehicles), heavy metals (from wear of tyres and other vehicle parts, or as additives in

fuel) or specific chemicals added to road (eg salt for de‐icing or reducing dust), and

such contaminated runoff has potential to detrimentally affect the soils and

vegetation adjacent to the road (Makepeace et al. 1995; Davies et al. 2000). This

effect is usually only a few metres in width but this will depend on management

strategies implemented to contain surface runoff. Also accidental chemical spills

(low risk, localised effect usually) may occur (Makepeace et al. 1995). Nitrogen

deposition from car exhausts may also affect soils and vegetation but effect size and

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width is largely unknown for local bushland. Studies overseas have shown N

deposition occurs for at least 90 m from road edge but is particularly high within the

first few meters form the road edge (primarily as NO2 which oxidises to HNO3 in soil)

(Redling et al. 2013). In addition to N deposition, other emissions from vehicles will

spread from roadside into surrounding vegetation, including particulates, lead and

zinc, but these do not spread as far as nitrogen (Makepeace et al 1995).

5) Changes to soil properties. Many characteristics of the soil have been reported to

change in areas adjacent of roads: roadside soils generally are more compacted,

have less organic matter and are more erodible, have less soil biota and soil

microbial activity, and are less moist than further into vegetation (Forman et al.,

2003; Donaldson & Bennett, 2004). Three processes outlined above appear to

influence soil changes in the roadside environment: i) changes in microclimate

facilitating greater breakdown of litter, drying soils and reducing soil biota; ii) runoff

from roads carrying sediment, nutrients and other contaminates; and iii) physical

disturbance at the edge by vehicles etc. Nutrients levels may decrease (due to

decline in organic matter) or increase (from road run‐off) at road edges (both have

been reported for Australian roadsides; Donaldon & Bennett, 2004). Vegetated

swales provide an effective stormwater filtration and groundwater infiltration

system. One significant advantage of swale drains is that flow velocities are retarded,

thus protecting stream banks from erosion (Austroads, 2003). This also allows

heavier fractions of the suspended particles to settle out. Grass and other vegetation

in the drains act as a filtering device and reported removal efficiencies of suspended

solids are up to 90% (Fletcher et al, 2001). Establishing dense vegetation along the

base of the swale drain will improve its pollutant trapping efficiencies. Studies in the

United States of America have shown that vegetated swales are capable of removing

many pollutants found in stormwater with reported removal efficiencies of 83% for

sediment, 75% for hydrocarbons, 67% for lead, 63% for zinc and 63% for aluminium

(Yousef et al, 1985). Work undertaken by Driscoll et al. (1990) found differences

between the concentration of pollutants generated from road surfaces of different

traffic volumes. The Event Mean Concentration (EMC) of pollutants can be up to four

times as high on highways with traffic volume greater than 30,000 vehicles per day

compared to those highways with lesser traffic volumes (Driscoll et al, 1990).

6) Introduction of pests, pathogens and weeds. Many studies have demonstrated that

roads serve as conduits for the introduction of non‐native species into natural

ecosystems (Forman et al. 2003). Weeds and pathogens maybe present in mud and

dirt which falls off vehicles and onto roads; however this is far more likely to occur

on non‐bitumised tracks, especially when tracks are wet and muddy (Wilson et al.

2000). Mud/dirt which collects on cars has been shown to contain large numbers of

seeds from many species in Australia (Wace 1977). Seed of some weed species are

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known to attach to tyres of vehicles (Londsdale & Lane 1994), whilst transporting of

seed and grain will inevitably result in some spillage onto roads (e.g. lupin and wheat

commonly establish along roadsides of south‐west WA). The degree to which weeds

establish and proliferate along roadsides is not however merely a consequence of

their introduction via seeds and other propagules – the right conditions for growth,

development and reproduction must be present. Most weeds require physical

disturbance of soils and/or vegetation, ample resources (light, nutrients and

moisture) and low‐competition environment to proliferate at a site (ie they are

disturbance opportunists). Roads have also been shown to be a conduit for pest

animals as it allow them easier passage albeit with higher risk of predation. In

Australia, foxes and cane toads have been shown to preferentially use roads for

passage over dense vegetation (Catling & Burt 1995; Seabrook & Dettman 1996)

7) Changes to vegetation. Most of the above processes alter the amount and/or

availability of the key resources for plant growth (light, soil nutrients and moisture

etc.) at the road edge, so it is not surprising they typically result in changes to the

composition, structure, productivity and functioning of edge vegetation, including

weeds (Forman et al. 2004; Lamont et al. 1994a). This therefore is largely an indirect

(or secondary) effect. The effect of vegetation can be progressive in that a change in

vegetation at the edge (e.g. death or decline of plants) may affect neighbouring

vegetation and so on. The distance that vegetation at the edge is affected is

therefore highly variable and depends largely on the degree to which vegetation is

dependent on runoff from surrounding areas and the degree of connectivity in terms

of ecosystem functioning. The effect can be also be negative or positive, in that it

may lead to greater or lesser plant cover and growth at the edge . In Australia, it

appears that the former is most common and this may be attributable to low

background levels of soil fertility and moisture (Lamont and Southall, 1982; Lamont

et al. 1994a; Donaldson & Bennett 2004). Similarly, roadside vegetation of United

States deserts are also richer in resources and more productive (Johnson et al 1975).

8) Road kill. Animals crossing roads will occasionally be killed by vehicles and the

impact of this on animal populations has been explored for many species in many

parts of the world (Forman et al. 2004), including Australia where some 11 studies

have addressed road mortality on species such as macropods, frogs, reptiles,

platypus and birds (Donaldon & Bennett, 2004; Van der Ree et al. 2011). Road

deaths are a food source for many scavenging animals (such as ravens and wedge‐

tailed eagles along WA roads, Tasmanian devils on forest roads in Tasmania) and

these species may be particularly vulnerable to being hit by vehicles. Similarly, weeds

and other plants which tend to proliferate on roadsides may be source of food for

herbivores such as kangaroos, especially in times of drought, thereby increasing their

18

chances of being hit by vehicles. However roadkill can be prevented by fencing of

roads or by other means which discourage road‐crossing by fauna.

9) Road aversion, barriers to fauna movement and fragmentation effects. Some animal

species may avoid roads due to traffic noise and lights or learnt behaviour, or be

prevented by crossing roads by physical barriers (the road itself, embankments,

fencing etc) (Parris & Schneider 2009). This restriction on movement can effectively

fragment fauna populations and their habitat, which may lead to reduced population

sizes, genetic changes, greater inbreeding etc. (Fahrig and Rytwinski 2009; Van der

Ree et al. 2011; Benítez‐López et al. 2010). Road noise may also lead to changes in

animal behaviour to the extent that breeding is interrupted or curtailed (Parris et al.

2009). However management measures can minimise such impacts including fauna

underpasses, lighting design and measures to minimise noise.

3.4 ESTIMATEOFEFFECTSIZEANDWIDTHS–ZONEOFINFLUENCE

Few specific studies of road edge effects give distances that the effect occurs from the edge,

and, of those that do, most report a range of distances or only report the maximum distance

of detectable effects rather than the distance of serious or main effects. Some of the

reviews in Table 2 present some synthesis of edge effect distances, either as generalisations

or the total range reported over many studies. For instance, Forman & Alexander (1998)

show ranges of effect distances for various edge effects (reproduced in Fig. 2). These show

that most edge effects have potential to influence surrounding vegetation for several times

the width of the road, with effects of up to and exceeding 1km possible for edge effects

such as transportation of sediment (e.g. when eroded sediment from on or adjacent to

roads enters waterways), weed invasion and changes to bird populations due to traffic (Fig.

2).

These estimates of road edge effect distances have been used to estimate total area of edge

affected for certain roads, regions and even whole countries. For instance, Forman (2000)

used this approach to estimate, based on certain assumptions, that 15‐20% of the land

surface of both the USA and the Netherlands were impacted by roads.

Figure 2

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19

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20

3.5 ROADEDGEEFFECTS‐WESTERNAUSTRALIANPERSPECTIVE

Roadside impacts have received relatively little study in Western Australia (WA), especially

when compared to North America and Europe (Table 2; Donaldson & Bennett 2004).

The major research project on roadside effects in WA has been Bryon Lamont’s studies of

Banksia woodland along the Brand Highway on the Swan Coastal Plain just north of Perth.

He and his colleagues found that Banksia menziesii plants at the road edge at these sites

had several times greater overall biomass and nutrient content (Groom & Lamont 2011),

were larger in size (Lamont et al. 2004a), allocated greater resources to vegetative

(epicormic) regrowth (Groom & Lamont, 2011) and had many (3‐4 times) more cones and

viable seed per plant than plants distant from the road edge (Lamont et al. 2004a). They

showed a similar effect for Banksia hookeriana (Lamont et al. 2004b). They attributed these

differences to greater nutrient and moisture resources available to roadside plants due to

road runoff and competition‐free access to resources at the road edge. Given these species

are largely bird pollinated (mostly honeyeaters); it appears the road is not acting as a

deterrent to such birds.

Milberg & Lamont (1995), in the same area, found that weeds were more prevalent within

roadside bushland compared to interior bushland, and were even more common here than

in bushland adjacent to farmland. This was especially so for the dominant perennial grasses

Ehrharta calycina and Eragrostis curvula. They concluded the greater weed cover was due to

greater availability of weed seed and resources for plant growth along roadsides. They also

showed major increases in grassy weed cover following fire in the roadside vegetation

(compared to unburnt vegetation), demonstrating the link between weed spread and

disturbance (Milberg & Lamont 1995).

Remnant vegetation along roadsides is very important for the conservation of flora and

fauna in the WA wheatbelt given high rates of native vegetation clearing in this region

(Hobbs 1993); many studies have focused on the biodiversity patterns and processes of

degradation within these narrow strips of remnant vegetation along roadsides. For instance,

within roadside remnants of the central wheatbelt, van Schagen et al. (1992) found

increased populations of invertebrates, especially herbivores and defoliating insects, which

they related to the enhanced nitrogen content of roadside soil due to runoff. Cale & Hobbs

(1991) also reported enhanced nutrient levels in soils and plants of roadside remnants in the

wheatbelt and believed this was largely responsible for extensive weed invasion and high

insect herbivory in these areas, but attributed much of this extra nutrient load to runoff

from nearby agriculture rather than run‐off from roads, especially for phosphorus.

Also in the WA wheatbelt, Lamont & Southall (1982) recorded many times more mistletoe

(an epiphytic, arboreal plant) on host trees of road verges than in adjacent nature reserves.

21

The increased mistletoe numbers in roadside trees was attributed to higher water and

nutrient availability, higher availability of roadside perching sites, and increased movement

of birds along roadside corridors (Norton & Stafford Smith 1999). The redistribution of

resources by roads, rather than the impact of the road itself, is therefore considered to be

the most influential factor in the pattern of mistletoe occurrence. Given there are few host

trees and birds spreading mistletoe seed in the Perth area, increased mistletoe abundance is

not likely to be an edge effect along KRSL.

Higher than average rates of bird mortality have been reported on roads adjacent to

remnant bushland and creeks in the WA wheatbelt with the species most affected by road

kill being western rosellas (Platycercus icterotis) which are attracted to spilt seed from

trucks transporting grain (Brown et al. 1986).

Fortin and Arnold (1997) showed that bird abundance and diversity in roadside remnants of

the central wheatbelt was heavily dependent on vegetation condition and the proximity to

large remnants, demonstrating the importance of roadside remnants as wildlife corridors.

Fulton et al. (2008) studied changes in bird species composition in vegetation adjacent to

road clearings in jarrah forest and found few returned to roadside vegetation during the first

two years after clearing and, for those which did, such as the Australian Raven (Corvus

coronoides) and Grey Currawong (Strepera versicolor), road‐kill mortality rates were

relatively high. Also the abundances of granivorous birds, such as Common Bronzewings

(Phaps chalcoptera) and Australian Ringnecks (Barnardius zonarius), were linked to seed fall

from jarrah trees rather than spillage of grain onto roads.

Davis & Wilcox (2013) showed that the majority of birds in a large bushland remnant in

central Perth did not cross large multi‐lane roads into surrounding gardens, and of those

which did, most were widespread generalists and nectivores such as Singing Honeyeater

and Red Wattlebird which were particularly attracted to native plants in gardens.

Bertuch & van Etten (2004) attributed the substantial number of deaths of mulga (Acacia

aneura s.l.) trees along major unsealed roads in the Goldfields to the practice of applying

hypersaline water to roads (a common practice on mine haul roads to reduce dust and seal

the road surface) and the deprivation of water on downslope side of road due to blocking of

surface water flow (sheetflow). Blocking of surface flow is not likely to occur at Keane Rd

because of the mostly sandy soils (so limited surface flows) and the installation of culverts in

the seasonally‐flooded areas.

Davies et al. (2000) quantified a range of pollutants in road runoff across a range of Perth

roads, and found that most pollutants were in the lower range compared to studies of roads

overseas. Interestingly, they did not find a relationship between traffic volumes and

pollutant concentrations, although the concentrations did vary across seasons and types of

road.

22

In summary, although the number of studies addressing roadside impacts within south‐west

WA is relatively small, they generally show enhanced nutrient and moisture status of native

vegetation adjacent to roads due to run off from road surface – this phenomenon may be

more evident in this region than others because of the impoverished nature of soils and the

mediterranean‐type climate. Enhanced nutrient and moisture status tends to promote

plant growth sometimes leading to a thickening of vegetation at the road edge; however

weeds are also may be promoted by the extra resources, although the level of weed

invasion is reflective of overall disturbance to vegetation by fire, trampling etc.

4. OBSERVATIONSOFEDGEEFFECTSINVICINITYOFKEANEROAD

A field visit was made to the proposed KRSL alignment and surrounding bushland areas on

the 22nd February 2014 to record and document vegetation condition of existing edges and

to observe edge effects from a range of track and road types in the region, from 4wd tracks

and other off‐road tracks to existing sealed roads, both recently established and older roads

(including Anstey Rd, Skeet Rd, Armadale Rd, Ranford Rd, Nicholson Rd and already

established sections of Keane Rd). These observations are reported via series of annotated

photos in Appendix 1.

Some edge effects in the vicinity can be visually determined from the patterns of weed

invasion and plant health at the edge (Appendix 1). Such edge effects varied markedly in

terms of distance (from road edge into bushland) and size (degree of change). Some edges,

even relatively older ones, are relatively dense and healthy with little plant damage/decline

and little to no weed invasion, whereas others are now weed‐dominated with few native

species remaining (Appendix 1). However, as these observations are effectively a snapshot

in time, the process by which these sites have become weed dominated is not known, and

therefore caution needs to be taken in attributing all changes observed to simply that of

edge effect. For instance, a weed‐invaded edge may indeed be the result of changes to the

edge environment and this commonly occurs at the immediate edge due to processes

explained in previous section. However it is also possible that the area has experienced

other types of disturbances which may, or may not, be related to the edge, such as fire,

vehicles or tramping (all of which may spread from interior of bushland to the edge).

Furthermore, it is possible that some areas may have been already significantly affected by

weeds at the time of road establishment. Therefore considerable care needs to be taken

when attributing current edge condition as being the indirect or edge effect of roads.

Other photographs show areas of dieback and tree death caused by Phytophthora, damage

to vegetation by off‐road vehicles and evidence of weed seed being spread by horses

(Appendix 1).

23

5. PREDICTEDEDGEEFFECTSOFKEANEROADSTRATEGICLINK

5.1SPATIALPREDICTION

Predictions of edge effect sizes (degree of change) and distances (from the edge) resulting

from the proposed KRSL has been achieved through a combination of:

1) ecological theory and literature reviews of roadside edge effects (Table 2);

2) local studies completed in similar vegetation types (e.g. Lamont et al 2004a), albeit few

available;

3) other studies completed for the PER (e.g. EnviroWorks Consulting 2009, 2013; Turpin &

Bamford 2013; Water Technology 2013); and

4) observations made on existing edges along the alignment and surrounding roads

(Appendix 1).

It is accepted that making predictions such as this is a process of estimation based on

available data. Given such estimation is required for purposes of impact assessment and

planning, we need to use the best available information but also be cognisant that it is a

process of estimation and therefore be conservative where possible. The predictions are

given in terms of the likely range of edge effect distances with the rationale for these

distances given (Table 3). It is recognised that for a given edge, effects will not be uniform in

terms of distance from the edge – some sections of the edges will experience more

profound changes than others due to greater susceptibility or chance events. Therefore, it is

appropriate to predict a range of likely distances as shown in Table 3, in order to build in

some conservatism.

The likely distance ranges for each effect were then overlain to determine the maximum

likely effect distance across all effects (that is the largest distance within all the edge effect

ranges predicted, became the maximum distance of total edge effect impact predicted).

This maximum edge effect distance was then converted into an area (zone of influence)

using GIS analysis.

5.2TEMPORALPREDICTION

As some edge effects are likely to progressive and gradually work their way into interior of

bushland over a long time period (such as effects of dieback and weed spread under

unmanaged scenarios), the temporal nature of edge effects has also been considered. The

24

literature review above has shown that minimising edge effects is possible through

appropriate and well‐targeted management. Such management actions identified include:

careful clearing of vegetation to avoid damage; fencing to control access; effective and

ongoing weed control at the edge; and construction of swales to capture run‐off.

On the basis of such management measures, which are proposed in the KRSL PER, it is

predicted that maximum edge effects from KRSL would develop quite slowly over 10 years

and would likely stabilise with effective ongoing control measures proposed preventing

further spread. For the KRSL proposal, it should be noted that maximum predicted areas of

influence are provided (estimated to stabilise at 10 years), but that with very effective

management by the City of Armadale, edge effects from KRSL may never reach these

maximum predicted areas of influence, but instead stabilise within much smaller areas

influence. However for the purposes of impact assessment, maximum areas of influence

should be considered.

By contrast scenarios are also considered involving the KRSL with no management measures

implemented and the current situation of an unsealed track used for off road driving. For

these scenarios it is considered that spread of edge effects is unlikely to stabilise over time

given the lack of management measures for these scenarios. Therefore for the purposes of

comparison, edge effects from these scenarios have been predicted for a timeframe of 10

years. However it is reasonable to conclude that edge effects would continue to spread

further after the 10 year timeframe given these scenarios include no management measures

being implemented.

5.3VEGETATIONTYPES

Predicted edge effects differed between different floristic communities. Specifically

differences in edge effect width were recognised between Banksia woodland communities

(BW) and dampland communities (DL). BW communities were those with upper stratum

dominated by Banksia on more sandy soils higher in the profile; they included floristic

communities SCP21‐23 based on floristic types recognised for the Swan Coastal Plain (Tables

5‐7; EnviroWorks Consulting 2013). DL communities are the three remaining communities

(Table 5‐7) dominated by Melaleuca trees and Myrtaceae shrubs on heavier, poorly‐drained

soils. Differentiating between these two groups of communities reflected broad differences

in their vegetation structure (BW has more open understorey) and hydrology (surface water

ponding and flows in DL versus some more free draining soils in BW). For this reason edge

effects were predicted to spread a greater distance in the BW communities because the

Banksia woodland is on sandy soils has more open understory and therefore is more

susceptible to invasion of grassy weeds than damplands as described further in Section

5.5.4.

25

5.4DEVELOPMENTSCENARIOS

Predictions of likely edge effect ranges utilised three development scenarios to enable

comparisons and contextualisation of likely responses. These scenarios and their rationale

for inclusion are:

a. SCENARIO 1: proposed bitumised Keane Rd link, including all planned management

strategies to minimise environmental impacts (e.g. culverts, setbacks, drainage

swales, weed control etc. as per Table 1 and as outlined with the KRSL PER and

Response to Submissions);

b. SCENARIO 2: sealed road along Keane Rd alignment but with no or minimal

management to reduce environmental impacts (chosen to gauge likely effectiveness

of management strategies implemented under Scenario 1 to minimise edge effects);

c. SCENARIO 3: current situation of 4wd track along alignment with few to no

management to control access and minimise impacts (chosen to see to what degree

a managed sealed road will result in reduced environmental impacts).

5.5DISCUSSONOFKRSLANDEACHTYPEOFEDGEEFFECT

5.5.1 CHANGESTOMICROCLIMATE

The current vegetation of the KRSL alignment has a relatively dense understorey of shrubs

which would typically allow very little light penetration and changes to microclimate where

a new edge to the vegetation is created; this is especially the case for vegetation along the

alignment given that most shrubs have foliage all the way to ground (EnviroWorks

Consulting 2013; Appendix 1). The actual amount of microclimate change would depend

largely on the amount of disturbance to vegetation at the edge, with a sharp/dense edge

likely to experience minimal microclimatic change compared to an edge which was uneven

and had many dead or damaged plants scattered along the edge. For instance, breaking of

branches of large shrubs at the edge would facilitate greater light penetration. It is

estimated that with careful clearing practices that the maximum width of microclimatic

change will be ~1 m for various Banksia woodland communities, but only ~0.5 m for the

dampland communities (as shrub layer is generally denser here). However if the edge is

26

uneven and has damaged vegetation, the distance of microclimatic change will be greater

(Table 3).

The tree layer of the KRSL alignment is sparse (mostly open woodland) and it is unlikely that

this tree layer would have develop its own microclimate above the dense shrub layer as

shading effects are relatively minor and atmospheric gases are likely to mix freely especially

when it is windy. Therefore it is considered that microclimatic changes will be relatively

minor with removal of trees within the KRSL alignment.

5.5.2 VEGETATIONDISTURBANCEATEDGE

Edge vegetation created by clearing for road construction is particularly vulnerable to

further damage by human activity. The degree and width of this damage is largely

determined by type and effectiveness of management and access control. Where access to

edge by people is restricted by fence (such as is proposed for KRSL), vegetation is less likely

to be damaged. Grading, weed control, fire break maintenance and general upkeep of

verges all have potential to damage edge vegetation; however the fence proposed for the

Keane Rd link is likely to minimise these impacts. The current 4wd track, although some 5‐10

m wide at present, shows signs of track widening (where vehicles avoid boggy areas and

other obstructions; Appendix 1) and this is likely to continue to progressively work its way

into the interior vegetation if the track is left in its current state. Turn‐around areas and

other areas where off‐road vehicles drive or attempt to drive off the main track, would

further damage vegetation of the edge (Appendix 1). It is for these reasons that the

predicted maximum width of vegetation damage along the 4wd track would be in the order

of 1 m per year (on average) or up to 10 m after 10 years (Table 3).

5.5.3 CHANGESTOPHYSICALENVIRONMENT,INCLUDINGHYDROLOGY

For higher ground which does not currently flood and has high levels of rainfall infiltration

(i.e. Banksia woodland communities on more sandy soils), the proposed drainage control

measures (drainage swales) will capture rainfall and allow it to infiltrate into the ground as is

currently the case, which will minimise changes hydrological changes at the vegetation edge

(Water Technology 2013). However there still may be an effect of increased vegetation

growth at the edge as plants there are able to access moisture infiltrating into the swales on

the side of the road. Through their roots systems, edge plants may even be able to access

more water collecting and infiltrating in the drainage swales on either side of the road, than

they would have obtained prior to road construction. However this increased plant growth

is seen as a small but positive impact as denser edges minimise other edge effects (e.g.

27

microclimate changes and weed invasion). In the unmanaged road scenario, water run‐off

will enter native vegetation at edge resulting in a greater effect on plant growth, but this

will be offset by transport of pollutants and sediments with the runoff which are likely to

have detrimental effects. Such pollutants include hydrocarbons (petrol, oil etc. spilt on road

and heavy metals; Davies et al 2000). Runoff from unsealed 4wd tracks is likely to be

minimal in sandy areas, but likely from harder setting clayey soils of lower in profile.

In the poorly‐drained areas which tend to flood in winter, a series of culverts is planned to

enable unimpeded water flows under the road (Water Technology 2013). Therefore, again,

proposed management solutions are likely to eliminate or minimise potential edge effects.

Under the ‘no management’ road scenario (i.e. no culverts), blocking of drainage is likely to

result in impacts primarily through depravation of water on downslope side of road, and

deeper and longer flooding on upslope side of road.

5.5.4 WEEDINVASION

The major weed species of concern for bushland of the Keane Rd area are tussock grasses

such as perennial veldt grass (Ehrharta calycina), annual veldt grass (Ehrharta longifolia) and

African love grass (Eragrostis curvula). In poorly‐drained areas, especially in drainage

ditches, Hesperantha (Hesperantha falcata), Freesia (Freesia alba x leichtlinii) and Watsonia

(Watsonia bulbillifera) may be a problem, whereas in seasonally flooded areas, arum lily

(Zantedeschia aethiopica; a priority species) is a common weed (Brown & Brooks 2002;

Appendix 1; EnviroWorks Consulting 2013).

In the sandier soils of the Banksia woodland communities, by far the most common weed is

Ehrharta calycina which has been relatively well studied in terms of its ecological

requirements and dynamics in Perth bushlands (e.g. Smith et al. 1999; Fisher et al. 2009).

This southern African species, as with other exotic tussock grasses, prefers full sunlight and

is not a strong competitor when growing with established plants. It however is a rapid

coloniser of disturbed, open environments as long as seed is present at the site. Plants can

flower and set seed in their first year and they produce abundant seeds when mature (Smith

et al. 1999; Fisher et al. 2009). The seed weighs around 0.6 mg which is translates to ~1600

seed per gram (which is relatively light for grass seed). Seed is dispersed in numerous ways

(wind, water, mammals, birds, ants and slashing/mowing) meaning that seed is likely to

spread widely throughout nearby bushland from areas of infestation (Brown & Brooks 2002;

Fisher et al. 2009). Fisher et al. (2009) and Smith et al. (1999) both showed that perennial

veldt grass, Ehrharta calycina, maintains a large and persistent soil seed bank, although the

density of seed in topsoil is correlated with the degree to which the species dominates the

vegetation (Fisher et al. 2009), suggesting that weed‐free areas of bushland are likely to

have low (but not zero) levels of soil seed storage.

28

Fisher et al (2006) found that E. calycina occurs on soils with enhanced nutrient status,

especially in terms of phosphorus, but this is believed to be due to the more rapid cycling of

nutrients through litter and soil compared to native plants. Therefore the species is likely to

contribute to higher nutrients where it dominates rather than only occupying fertile patches

in the bushland.

Ehrharta calycina occurs along bushland edges to various degrees (Appendix 1; EnviroWorks

Consulting 2013) which reflects its niche as disturbance opportunist which is attracted to

open, disturbed habitats such as in bare strips between vegetation edges and roads.

However, where this species is not effectively controlled at edges it can work its way into

the edge (although competition and shading effects would limit its dominance at edge

especially where edges are intact and relatively dense). Uncontrolled veldt grass infestations

at edges result in weed seed spreading into bushland after which it only needs disturbance

of vegetation (e.g. plant death by disease, fire, trampling etc.) for this species to spread and

proliferate. Therefore, the degree to which this and similar weeds spread into bushland

from edges depends largely on the efforts to control the infestations at the edge (with

grass‐selective herbicide treatment before spring flowering the best known control

measure; Brown & Brooks 2002). Such control measures can limit weed infestation to the

immediate edge region, whereas no control and management would lead to progressive

spread and intensification of weed problems from edges and into bushland (estimated to be

up to 1‐2 m per year on average in unmanaged bushland, although spread rates will be

greater if vegetation is disturbed by fire or other means).

Horse riding is a popular activity within the bushland of the KRSL. Weed seed may be spread

along tracks in horse faeces (Appendix 1). Similarly, off‐road vehicles can spread weed seed,

especially under muddy conditions (Newsome & Moore 2012). Therefore weed spread via

human activity is more likely under existing conditions.

Banksia Woodland (BW) communities are likely to be more effected by weed invasion than

Dampland (DL) communities because the Banksia woodland is on sandy soils has more open

understory and therefore is more susceptible to invasion of grassy weeds such as Ehrharta

calycina.

5.5.5 PHYTOPHTHORA

The dieback ‘fungus’ (Phytophthora cinnamomi) is present and seemingly widespread along

the proposed road alignment with the exception of an approximately 100 m long section

near the western end of the alignment called the ‘protectable area’ (EnviroWorks Consulting

2009). This protectable area is effectively shrinking in size as Phytophthora is reportedly

spreading into this area at a rate of one to several metres per year from surrounding

29

disease‐affected areas (EnviroWorks Consulting 2009). At present, there is a good chance

that off‐road vehicles will spread the fungus more quickly in this section and elsewhere

along the alignment, especially at times when low‐lying sections of the track are

waterlogged or flooded (spread being via mud collecting on wheels and under‐carriage of

vehicles). Therefore under the current scenario of 4wd track, the impact of Phytophthora is

calculated at a rate of ~1 m per year from the edge of the track based on generally‐accepted

estimates of average spread rates (Dieback Working Group, 2000). I have applied this

average rate of spread from the edge for the whole alignment as it is not completely clear

which sections are currently disease‐free and which have the disease and are impacted by

it. However the assumption here is that off‐road vehicles will effectively spread the fungus

throughout the whole alignment over time. It is recognised however that the disease has

already impacted vegetation in some parts of the alignment as evident by patches of dead

Banksia and other indicator species (Appendix 1; EnviroWorks Consulting 2009). It is also

noted that the current ‘protectable area’ is on slightly higher ground and more sandy soils

than disease‐affected areas and so may be afforded some protection as spread is more

likely to be via root‐to‐root transfer rather than facilitated by surface or sub‐surface

horizontal water flows in this area.

5.5.6 EFFECTSONFAUNA

As summarised in the review above, roads can impact on fauna through road deaths,

impediments to movement and aversion to road noise/traffic/lights, as well as potential

fragmentation and population effects which may follow from these direct impacts. For the

proposed KRSL, a variety of management strategies will be implemented, such as fencing

and fauna underpasses of various sizes, which are likely to negate or minimise these impacts

for most species (Turpin & Bamford 2013). Harris et al. (2010) and other unpublished

studies have demonstrated the effectiveness of road underpasses for movement of fauna in

Perth bushland, such as bandicoots, but also showed they were also used by foxes which

may result in increased predation risk for some species. Therefore, fox control is important

in maximising underpass effectiveness. The City of Armadale have committed in the KRSL

PER to monitoring of underpasses using motion sensitive cameras, and controlling foxes if

they are found to be a problem.

The effect of road noise is more difficult to gauge given the lack of specific study on Perth

fauna, although effects are likely to be limited to few species and may even help to reduce

incidence of road deaths for species which avoid roads (Turpin & Bamford 2013). Edges

attract some species (Forman et al. 2004), for instance they may be preferred feeding areas

for insectivorous birds, but again studies on Perth fauna appear to be scant; also the

proposed set back distances from the road are likely to minimise impact on edge feeders.

30

In the unmanaged road scenario, more fauna deaths will occur, which will have wider,

indirect effects on fauna populations, but such effects are difficult to translate into edge

effect distances because fauna populations are mobile and dynamic – individuals lost may or

may not be replaced depending on degree of connectivity with surrounding bushland,

mobility of species, home range sizes and so forth. Therefore, the edge effect size and

distance cannot be given at present. Road deaths are likely to be lower under the current

4wd track scenario compared to unmanaged road scenario due to lower vehicle speeds and

usage.

5.6PREDICTIONOFEDGEEFFECTDISTANCES

Table 3 below assimilates the above information in order to provide predicted distance

ranges for each type of edge effect at 10 years. The predictions are given in terms of the

likely range of edge effect distances with the rationale for these distances given. It is

recognised that for a given edge, effects will not be uniform in terms of distance from the

edge – some sections of the edges will experience more profound changes than others due

to greater susceptibility or chance events. Therefore, it is appropriate to predict a range of

likely distances as shown in Table 3, in order to build in some conservatism.

The likely distance ranges for each effect were then overlain to determine the maximum

likely effect distance across all effects (that is the largest distance within all the edge effect

ranges predicted, became the maximum distance of total edge effect impact predicted).

This has ensured predictions are conservative as in reality edge effects are likely to be

uneven along the edge and not spread to the maximum distance for all areas along the

edge. However for the purposes of this study the conservative assumption has been used

that edge effects will spread evenly to the maximum predicted distance along the edge,

therefore likely overestimating the edge effect. This conservative maximum edge effect

distance was then converted into an area (zone of influence) using GIS analysis as described

below in Section 5.7.

31

Table 3: Likely range of edge effect distances for the three Keane Road scenarios. As some effects

are progressive and gradual, whilst others will stabilise with management, estimates given are for

10 year period. Please see text for further information and justification of distances. DL

=dampland and clay flat communities; BW = banksia woodlands communities.

Type of Edge Effect

Relevance to KRSL and Reasoning SCENARIO 1: proposed KRSL (assuming successful manageme-nt)

SCENARIO 2: Unmanaged sealed road (KRSL no manageme-nt)

SCENARIO 3: Current bush track with off road driving (status quo)

Microclimatic changes

The dense shrubby understorey generally found along KRSL route means limited light and wind penetration at edges and therefore narrow edge effects in terms of microclimatic change. Edge effect likely to be less where careful clearing and management maintains sharp/dense edge. Removal of trees from an open woodland is unlikely to change microclimate within the tree layer

0.1-0.5 m (dampland); 0.1-1 m for Banksia woodland

0.5-2 m (DL); 1-3 m (BW)

0.5-2 m (DL); 1-3 m (BW)

Vegetation disturbance at edge

Where access to edge by people is restricted by fence, vegetation is unlikely to be damaged; grading, weed control and generally maintenance of verges may however result in damage to edge vegetation, especially where unfenced; track widening and disturbance by off-road vehicles likely along track, especially in winter- waterlogged and flooded areas

0-1 m 1-3 m 2-4 m BW 5-10 m DL

Hydrological changes

Where drainage control measures prevent water runoff and sediment deposition into bushland, there still may be an effect of increased vegetation growth at edge – however this is seen as a small but positive impact as denser edges minimise other edge effects. Where road runoff enters native vegetation, effect is wider in poorly drained communities than sandy soils. Runoff from track is likely to be minimal in sandy areas, but possible from harder setting clayey soils of lowlands

minimal 1-3 m BW 5-10 m DL

0-0.5 m BW 1-5 m DL

Chemical modification

Most important process here is road run-off carrying pollutants into bushland; therefore effects are much the same as predicted for hydrological changes above, although soils are likely to have some pollution adsorption abilities, so effects are likely to be not as widespread.

minimal 1-2 m BW 5-8 m DL

0-0.5 m BW 1-3 m DL

Soil changes As changes in soil biota, organic matter, nutrients etc. are largely a function of the above processes, the predictions tend to follow that of the processes with maximum effect

0.1-1 m DL; 0.5-2 m for BW

1-3 m BW 5-10 m DL

2-4 m BW 5-10 m DL

Introduction and spread of weeds

Weed spread into bushland can be minimised by maintaining dense vegetation at edge and through effective weed control along roadside; however there is likely to be some introduction of weeds at edge which will be promoted by other edge effects (soil and microclimatic changes, and disturbances at edge). Where weeds are not controlled, spread and proliferation are likely to be worse. Banksia woodland on sandy soils are more susceptible to invasion of grassy weeds than damplands

1-3 m DL; 2-5 m BW

3-10m DL; 5-10m BW

3-10m DL; 5-20m BW

Introduction and spread of dieback

Bitumised road with drainage controls is likely to limit spread of Phytophthora into the dieback-free zone (although it should be remembered that dieback is already widespread along route and is spreading towards this disease free area). However without management controls, multiple points of new introduction are likely to occur throughout the disease-free zone and elsewhere along the route, although this is far more likely on the unsealed track than sealed road, particularly in the parts which are seasonally waterlogged or flooded. For better-drained Banksia woodland (although trees and shrubs are still likely to access groundwater), spread of Phytophthora from plant-to-plant (via root transfer) is predicted at ~1m per year. However where water flows on surface or just below surface, faster rates of spread are predicted (~2m per year)

minimal

0-10 BW; 10-20 m DL

10-20 m BW; 20-40 m DL

Vegetation change

As changes to vegetation structure and floristic composition is largely a function of all of the above processes, the predictions tend to follow that of the processes with maximum effect

1-3 m DL; 2-5 m BW

5-10 BW; 10-20 m DL

10-20 m BW; 20-40 m DL

32

Type of Edge Effect

Relevance to KRSL and Reasoning SCENARIO 1: proposed KRSL (assuming successful manageme-nt)

SCENARIO 2: Unmanaged sealed road (KRSL no manageme-nt)

SCENARIO 3: Current bush track with off road driving (status quo)

Effects on fauna

Proposed KRSL underpasses, fencing, set back and road design will largely negate or minimise effects on fauna such as road kill and barriers to movement. Such impacts are more likely for unmanaged road, leading to indirect impacts on habitat fragmentation and population viability etc. However, such indirect effects are difficult to translate into edge distances.

minimal Unknown unknown

Maximum likely effect at 10 years

Although acting in combination, most of the edge effect processes affect similar and overlapping distances from the vegetation edge; the maximum effect therefore is predicted from process with greatest potential effect

3 m DL; 5 m BW (weeds incursion is major effect)

10 m BW; 20 m DL (dieback)

20 m BW; 40 m DL (dieback and physical damage)

5.7 AREAOFINFLUENCE

The maximum likely effects in terms of edge distances were used to calculate maximum

likely impacted areas for each of the floristic communities (EnviroWorks Consulting, 2013)

using GIS. These areas are shown in Tables 4 to 6 and mapped at Appendix 2. It should be

emphasised that:

Figure 1 in Appendix 2 represents maximum likely areas affected for KRSL with

effective management measures with maximum edge effects predicted to stabilise

at 10 years due to on‐going management; and

Figures 2 and 3 in Appendix 2, represent scenarios involving no management, where

predicted edge effects are shown at 10 years, although they would continue to

increase after this time due to lack of management.

The maximum area likely to be affected by edge effects varies substantially depending on

the scenario (Tables 4 to 6). For the proposed KRSL, with all management actions effectively

implemented to minimise environmental impacts, a relatively small area (<1 ha) is predicted

to be impacted by edge effects, with most of this occurring in Banksia woodland

communities (Table 4; Figure 1 Appendix 2). This is far lower than Scenario 2, the

unmanaged sealed road (maximum of 2.7 ha impacted; Table 4; Figure 2 Appendix 2), and

for the continuation of current 4wd track (6.7 ha; Table 5; Figure 3 Appendix 2). The results

indicate that the current situation, if left as uncontrolled 4wd track, is likely to lead to

indirect effects on the surrounding vegetation several times wider than the current track

width, although such effects are likely to develop progressively over many years.

33

There are a number of significant ecological communities along the alignment and in the

surrounding bushland block (EnviroWorks Consulting 2013; Tables 4‐6). The one of chief

concern is the endangered Threatened Ecological Community (TEC) SCP10a (shrublands on

dry clay flats). This TEC was probably always naturally restricted in terms of its distribution,

however clearing and draining of wetlands and damplands in the Perth metropolitan area

has effectively reduced its distribution to small patches, mostly on winter‐flooding lowlands

of Bassendean dune system. One patch of the TEC occurs just north of the eastern end of

the alignment (Appendix 2) and, in fact, the alignment in this section was shifted to avoid

direct impact on this patch of the TEC. The predicted maximum edge effect of the managed

KRSL avoids impacting on this TEC (Table 4; Appendix 2). However under the scenarios of

unmanaged road and current track, greater edge effect distances are predicted which are

predicted to spread into the TEC (Table 5 & 6). Although this only effects up to 0.37 ha and

1.25 ha respectively, this accounts for up to 8.3 and 25% of the distribution of the TEC in the

vicinity given its very localised distribution (Tables 5 & 6; Appendix 2).

In terms of the two Priority Ecological Communities (PECs) occurring in the bushland along

the road alignment (SCP21c and SCP22), both are predicted to be impacted in terms of edge

effects. This is not unexpected as the road will cut through patches of these PECs. For the

KRSL managed road proposal (Scenario 1), maximum areas predicted to be impacted by

edge effect are 0.28 ha and 0.06 ha respectively, which account for some 3% and 1% of the

total area of these communities in the surrounding bushland block (Table 4). However the

impacted area is far greater for the unmanaged road and current 4wd track scenarios (Table

5 & 6), with the current track impacting up 15% and 4% of the local area of these PECs

through developing edge effects (Table 6).

Table 4: Prediction of Edge Effects Scenario 1 ‐ Effective Management of KRSL



Area (ha)

Edge Effects (ha)

% Community

Type Impacted by

Edge Effects




4.47 0.00 0.00


N/A 41.85 0.23 0.55


PEC (Priority 3)

8.93 0.28 3.14


5.78 0.06 1.04


N/A 23.94 0.24 1.00

Total all Communities 131.12 0.92 0.70

34

Table 5: Prediction of Edge Effects Scenario 2 ‐ KRSL with No Management



Area (ha)

Edge Effects (ha)

% Community

Type Impacted by

Edge Effects




4.47 0.37 8.28


N/A 41.85 0.46 1.10


PEC (Priority 3)

8.93 0.60 6.72


5.78 0.13 2.25


N/A 23.94 0.47 1.96


131.12 2.72 2.07

Table 6: Prediction of Edge Effects Scenario 3 – Unsealed Track



Area (ha)

Edge Effects (ha)

% Community

Type Impacted by

Edge Effects




4.47 1.25 27.96


N/A 41.85 0.95 2.27


PEC (Priority 3)

8.93 1.35 15.12


5.78 0.26 4.50


N/A 23.94 0.92 3.84


131.12 6.69 5.10

35

6. CONCLUSIONSANDMANAGEMENTRECOMMENDATIONS

It is widely accepted that the ecological footprint of roads spreads further, and sometimes

much further, than the immediate clearing of vegetation for road construction. Such edge

effects or indirect impacts were identified in the impact assessment process for the KRSL,

but were not quantified in terms of likely distances and areas impacted. This report reviews

potential edge effects and uses our current understandings of these edge effects to make

predictions on these edge effect distances and areas.

Potential edge effects identified for KRSL included effects on microclimate, vegetation,

weeds, hydrology, dieback, soils and fauna. Of these, weed infestation was determined to

have the greatest potential to spread from the edge of the road into the vegetation with

maximum distances predicted to be in the order of 1‐5 m depending on vegetation type.

This translated to an area of influence of some 0.92 ha, which effectively increases the

impact footprint of the proposal, when combined with native vegetation clearing, to 2.57

ha. It is also established that the degree of weed incursion at the edge is highly

management dependent, but there is still likely to have some weeds at edge as bare soil is

prone to weed establishment.

To put these edge effects into context, edge effects distances and ranges were also

predicted based on an unmanaged sealed road scenario and current use of existing track by

off‐road vehicle (status quo scenario). The predictions of edge effects under these scenarios

were greater in distance and area, emphasising the importance of management to reduce

edge effect. The main edge effects predicted for these scenarios were related to greater

spread of weeds and dieback along the road/track (resulting in multiple infection points

which would then spread into the bushland) and physical damage to edge vegetation

(especially likely along off‐road track).

The predictions found that edge effects on the ‘dry clay flats’ TEC was unlikely under the

KRSL proposal as the alignment was sufficiently distant from this community. Predictions

also found that relatively small areas of two PECs (1‐3% of their area in surrounding

bushland) would by impacted by edge effects. This was in contrast to effects found for the

other two scenarios where predicted areas affected were up to 25% of the TEC and 15% of

the PECs.

The review has shown that minimising edge effects is possible through appropriate and

well‐targeted management. Such management actions identified included:

Careful clearing of vegetation for road easement which minimises damage to edge

vegetation and soils, and which creates or at least maintains a relative dense and

even shrubland edge;

36

On‐going and judicious weed control on the road verge and edge of vegetation as

this zone is most prone to weed introduction and proliferation (also weeds which

develop here will contribute seed into the bushland if allowed to reach flowering

stage). Weed control should be in late winter grass using grass‐selective herbicide

and/or careful mowing/grading of edges;

Design swales to capture run‐off under all but extreme rainfall events; maintain

functioning of swales and culverts for effective storm water capture.

The KRSL PER commits to such management measures and if implemented effectively by the

City of Armadale will result in minimisation of edge effects.

37

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8. APPENDICES

Appendix1:Photographsandnotesofedgeeffectsobservedduringfieldreconnaissanceon22/2/14.

Location, description

Notes, observations

4wd track along proposed alignment of Keane Road Strategic Link (western end, looking east)

Soil is very sandy in this Banksia woodland area and track shows much off‐road vehicle activity. Track is difficult to pass in summer; some track widening and damaged plants at edge as vehicles attempt to avoid boggy areas. Some tree deaths further back in bushland (possibly due to Phytophthora). Edge is mostly intact/sharp.

4wd track along proposed alignment of Keane Road Strategic Link (western end, looking south‐east)

Shows death of plants at edge and changes in species composition (i.e. more ground cover species, but few weeds)

4wd track along proposed alignment of Keane Road Strategic Link (middle section, looking east)

Dense edge vegetation mostly intact and healthy (and unlikely to experience much change in microclimate and weed invasion)

43

4wd track along proposed alignment of Keane Road Strategic Link (middle section end, looking south)

Extensive area of tree death most likely due to Phytophthora in low lying Banksia woodland adjacent to Melaleuca woodland. Infection may have been spread along track by off‐road vehicles

4wd track along proposed alignment of Keane Road Strategic Link (western section)

Off‐road vehicle activity is difficult to restrict as drivers largely ignore signs and barriers

4wd track along proposed alignment of Keane Road Strategic Link (middle section, looking south‐east)

Open Melaleuca woodland on low lying flats. Soil is less sandy and more compacted in these areas, and likely to be waterlogged in winter. Some plants damaged at edge but otherwise edge vegetation is largely intact and relatively thick due to dense shrub layer of spearwood (Kunzea spp.) , Regelia ciliata etc.

4wd track along proposed alignment of Keane Road Strategic Link (middle section, looking south‐east)

Dieback front at edge of low‐lying Banksia woodland adjacent to Melaleuca woodlands. These areas appear to be most susceptible to Phytophthora as they have shallow groundwater (likely to spread the pathogen) and relatively high densities of susceptible species (eg Banksia spp.)

44

4wd track along proposed alignment of Keane Road Strategic Link (middle section)

Horse riding is popular along tracks in area with faeces likely to contain grass and other weed seed.

4wd track along proposed alignment of Keane Road Strategic Link (western edge looking south‐east)

Secondary tracks and turn‐around areas destroy vegetation and create disturbances which encourage weeds to dominant. Here veldt grasses and other weeds are widespread. Also note dieback of Banksia trees in background, which may have been introduced by vehicles

4wd track along proposed alignment of Keane Road Strategic Link (far eastern section, looking west)

The eastern end of the proposed alignment is heavily disturbed through past human activity with large areas of grassy weeds and few remaining trees. These large weed infestations are a source of weed seed further into the bushland.

Edge of existing East Keane Road (looking north)

Drainage from sealed road into open drain has promoted annual weeds such as Watsonia in drain which becomes available fuel in summer. Further back there is band of grassy weeds (mostly couch) at edge which have penetrated the dense shrubland some 0.5‐1m. This area is relatively low lying and subject to waterlogging and flooding in winter.

45

Edge of existing East Keane Road (looking north)

Clearing and maintaining fire breaks just back from the road can damage vegetation and create new edges further back into the vegetation

Anstey Rd looking north‐west, some 400 m north of Keane Rd

Poorly maintained roadside vegetation is very prone to grassy weed invasion. Here perennial veldt grass dominate the understorey and contribute to fuel loads. The edge in the background adjacent to fire break is relatively intact with little grass incursion despite the availability of weed seed in the area

Anstey Rd looking west, some 500 m north of Keane Rd

Edge vegetation adjacent to fire break. Note the absence of weeds at this edge. This fire break has been created around the limits of the Bush Forever block to reduce chance of fire entering or exiting the reserve. The roadside verge in foreground has extensive tree death and weed cover

Anstey Rd looking north‐west, some 800 m north of Keane Rd

Poorly maintained roadside vegetation is very prone to grassy weed invasion. Here perennial veldt grass dominate the understorey and contribute to fuel loads. The edge in the background adjacent to fire break is relatively intact with little grass incursion despite the availability of weed seed in the area

46

Appendix2:Mapsshowingpredictedmaximumedgeeffectunderthreescenariosoutlinedinreport.

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