Street Tree Design Guidelines 50b9 2965

8/9/2019 Street Tree Design Guidelines 50b9 2965

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street tree

design guidelines

For Landcom Projects


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street trees


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1. Introduction 2

2. Principles 4

3. Selection considerations 5

3.1 Character 6

3.2 Aesthetics 7

3.3 Climate 93.4 Soils & drainage 9

3.5 Water 10

3.6 Services & public infrastructure 10

3.7 Native or exotic 11

3.8 Biodiversity & habitat 12

3.9 Weeds, nuisances & pests 12

3.10 Tree size, spacing, life span & maintenance 13

4. Technical 15

4.1 Soil volume & type 16

4.2 Designing for passive watering 18

4.3 Water sensitive urban design 19

4.4 Tree hardware 21

5. Sourcing & procurement 23

5.1 Availability 24

5.2 Quality 25

5.3 Procurement alternatives 26

6. Details 27

6.1 Planting configuration 28

1. Formal avenues 28 2. Informal avenues 29

3. Patterned planting 30

4. Landmark planting 31

6.2 Construction details 32

1. Typical street tree planting for Landcom Local Street in Verge 32

2. Typical street tree in Blister or Median 33

3. Typical street tree in paving with structural soil 34

7. Establishment maintenance 35

8. Recommended street tree list 37

9. Glossary & References 41

contents

Street Tree Design Guidelines CONTENTS | 1


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Trees in streets are essential for a high qualitystreetscape. This concept is stated as a guiding

principle in Landcom’s Street Design Guidelines2006. The Street Tree Guidelines enlarge onthis concept providing more detailed technicalinformation.

Healthy, established urban trees provide along term legacy for the community. Manyof the most memorable streets and localitiescan attribute their noteworthy status to thepresence of large healthy trees. At the regionalscale street trees contribute to the overall

percentage canopy cover which in turn deliversa variety of environmental benefits.

Recent experience has shown that simply theplanting of street trees with all good intentionis not sufficient to achieve a high qualitystreetscape. To achieve successful streetscapescritical factors such as selection of the mostappropriate tree species, quality of the plantstock and planning for and providing adequatesoil and water are essential. These guidelinesaddress these matters.

Grand Drive, Centennial Park

introduction1.1 Purpose and reason for this document

1.2 Background

2 | Street Tree Design Guidelines INTRODUCTION

The Landcom Street Tree Guidelines havebeen prepared as one of a suite of documentsproviding specialist information to aidDevelopment Managers achieve best industrypractice outcomes in Landcom developments.While the documents are primarily for Landcom

Development Managers, they may also beused in discussions with Councils, Joint VenturePartners and Consultants to define Landcom’sobjectives and practice.

The Street Tree Guidelines propose amethodology for making successful street treesspecies selection. The methodology providedis intended to form a coherent link betweendesign considerations and implementation bysetting out the optimum characteristics of street

trees, options for layout within streets, criticalconsiderations in the selection process andbest practice techniques for implementation.


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The information in the guidelines leads thereader sequentially through the process ofplanning, installing and establishing streettrees.

Part 2 highlights the Key Principles behindthe document.

Part 3 Selection Considerations addressesconsideration of the design intent for

streetscapes; the function of the streets;underlying environmental conditions, andhorticultural considerations.

Part 4 Technical outlines planning for thefundamental physical requirements of plantingstreet trees.

Part 5 Sourcing and Plant Procurement

discusses the impacts of plant procurementand construction method on the realisation ofthe streetscape.

Part 6 Details graphically describes optionsfor layout and construction.

Part 7 summarises in diagram format theminimum Establishment Maintenancerequirements of street trees.

Part 8 Recommended Street Tree List

provides a guide for selection of species,along with the critical limiting factors pertinentto each species to ensure their successful useas street trees.

Street trees contribute to the unity of the streetscape enhancing the character of the neighbourhood.

1.3 How to use this document

Fig 1 How to use these guidelines

Principles

2

Introduction

1

Selection Considerations3

Technical Information

4

Sourcing & Procurement

5

Details

6

Establishment Maintenance

7

RecommendedStreet Tree List

8

Street Tree Design Guidelines INTRODUCTION | 3


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part 2

principles

• Street trees are a legacy for the community. Maximise planting of trees in all streetsand retain existing trees wherever possible.

• Street trees should contribute to the overall unity of the streetscape, through theirlayout, scale and character. Careful selection of the tree species will provide scaleand visual cohesion to the street. Beyond this generic design intent for the streettrees, trees can also form landmarks, contribute to both contextural character and thegeneral amenity of a place.

• Select the most appropriate tree species to satisfy the design intent and the physicalconditions of the site both natural and man made. Respond to other functional

requirements such as solar access, vehicle clearances etc.

• Optimise soil conditions for trees. Locate trees to maximise available soil volume.Ensure that there is a sufficient quantity and quality of soil within the anticipated rootzone to support the intended mature tree and that adequate moisture is provided tothat zone.

• Street trees need adequate water to flourish. Street tree location and design shouldoptimise passive watering of all street trees.

• Minimise infrastructure and functional conflicts. Locate trees and utility services tominimise potential conflicts between street elements and functions, such as streetlightsbeing blocked by the tree canopy, or car doors being opened into tree trunks.

• Where appropriate integrate water sensitive urban design (WSUD) initiatives with theprovision of street trees.

There are seven key principles that guidethe landscape design of streetscapes.

4 | Street Tree Design Guidelines PRINCIPLES


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part 3

selectionconsiderations

FOR ALL TREE TYPES


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6 | Street Tree Design Guidelines CONSIDERATIONS

The advantages of urban trees are extremely broad; from environmental to

sociological benefits such as reducing crime, domestic violence and ADHD

symptoms (see references Landscape & Human Health Laboratory), to quality

of life and visual amenity improvements. This document accepts these benefits

as a given and addresses the specifics of how to select longer living trees with

appropriate characteristics for planting in streets.

Selection considerations

3.1 Character

i. Historic

The layout of street trees and species selectedmay reflect previous land use or be species usedhistorically in association with a particular locationor period of landscape design, for example, theuse of Norfolk Island Pines along the foreshore.

Where there is an existing streetscape pattern andspecies used, any infill planting should reinforcethe existing character.

ii. Cultural

Trees in general and street trees in particularoften represent the community’s preferences oraspirations and can landmark important communityor urban elements. Some species have specialassociations with a particular cultural group suchas Olives, flowering trees etcetera.

The community often exhibits extremes of attitudein regard to trees in their environment. Trees

are a community asset and involvement of thecommunity is imperative to ensure the success ofany new street tree planting.

Trees with a distinctive form or appearance can beused to create gateways or landmarks. Commercialareas, community buildings and other focal areasmay be given better legibility through the use ofstreet trees whose character contrasts to that ofthose in adjacent streets.

iii. Natural

Street trees may be used to extend or reinforcethe natural character of the area, particularlywhere neighbourhood character is drawn from orhas a strong association with its natural context,local native vegetation type, a local landform orfeature.

Palms at Fox Studios are a distinctive form for theurban environment.

Norfolk Island Pines seen here along Grand Parade, SansSouci are a commonly used tree along the foreshore.


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3.2 Aesthetics

Pistachio Tree has an umbrageous form suited to thestreetscape.

Fig 4 Trees provide a more sympathetic silhouette thanbuildings.

i. Tree Form

Selected species must have predictable growthhabit and form to function as a successful streettree. A street tree should have a single straighttrunk (to minimise conflicts with pedestrian andvehicular traffic) and stable branch structure (tominimise hazards created by inherent defects) witha clear trunk height (free of lateral branches) for notless than 3 metres from ground level.

The tree canopy (foliage and branches) shouldbe broad domed or umbrageous in form (see Fig2). The traditional ideal of the avenue includesregularly spaced broad domed trees with canopiesthat interlock to provide a leafy ceiling to the street.In some situations strong vertical forms may beappropriate as a landmark (see Fig 3).

Ideally species selection should aim for consistencyand visual uniformity providing streets with arecognisable character. This generally dictatesthe use of a single species within a street. Streetplantings with a multiplicity of different species(with disparate forms) can add interest to thestreetscape but often detract from the overallamenity of the street and the primary designcharacter intent of giving the street unity.

Species with low branching habits, such as someconifers, trees with pendulous branching habitsor those with multiple trunks and low horizontalbranch development, are not generally suitable asstreet trees.

Where possible the scale of the tree shouldbe related to its greater context as well as theadjacent dwelling. For example larger trees shouldbe planted along streets on ridgelines in order thatthe trees provide the silhouette against the skyrather than the dwellings (Fig 4).

The selection of a street tree should also considerseasonal features that help the communityexperience their changing environment and addinterest such as leaf colour variations (pink leaves inspring, autumnal leaf colour), flowers, or attractivebark that alters through the year. This createsan important dimension to the neighbourhoodlandscape.

In certain situations it may be beneficial to use morethan one species in a street, where multiple species

are used, however, they should be compatible(in form) and laid out so as to work together toachieve the overall unity of the streetscape. Anadditional benefit of the use of multiple species isthe potential reduction of the impact of debilitatingpests and diseases that have historically affectedmonocultures.

Street Tree Design Guidelines CONSIDERATIONS | 7

Fig 2 Umbrageous orumbrella like form

Fig 3 Strong verticalforms


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ii. Planting Configurations

Unity or the perception of visual consistencyis primarily achieved in street tree planting bysymmetry (identical planting on both sides of theroad) and repetition (of the same form). Whenconsidering the broad options for the requiredvisual character or ”look” of the streetscape thefirst clear decision to be made is whether theplanting will be symmetrical, asymmetrical or apattern (see 6.1 for diagrams).

Some layout options to consider are:

• Formal avenues Single species symmetricallyspaced.

• Informal avenues Asymmetrically arrangedsingle species.

• Patterned planting Multiple species in apatterned avenue or patterned groupedplanting.

• Focal / landmark areas Street trees used tohighlight presence of an entry, communityfocus or precinct by use of contrasting species.

Traditionally street tree plantings are of a singlespecies, evenly spaced. This is seen as the ultimateexpression of the boulevard. Notable examplesare Ocean Street in Woollahra, Burns Road inWahroonga and Anzac Parade at Moore Park.These successful avenues create a grand scale withtrees of umbrageous form, interlocking overheadcanopies and regularly spaced trunks.

Australian native species, particularly Eucalypts,for instance, are inherently asymmetrical in formwith more open canopies and give the street a verydifferent character to an avenue of exotic specieseven when planted symmetrically.

Considering the variety of challenging urbanconditions that are commonly found today in localstreets, such as difficult soil conditions, smallerlot sizes and competition with utility services, it isadvisable to broaden the options for tree layoutsconsidered for use in streetscapes.

Jacarandas provide seasonal colour in the street Ocean Street, Woollahra



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A healthy root system is essential for tree success in thestreetscape.

3.3 Climate

3.4 Soils & drainage

Sydney has a warm temperate climate, however

there is considerable variation in averagetemperatures and rainfall patterns betweencoastal areas, inland areas of the Cumberland Plainand the foothills of the Blue Mountains. Speciesthat perform well in the cooler elevated areas ofSydney’s Northern Suburbs, for example, will notperform satisfactorily in warmer, drier areas of thesouth-western plains. Only those species that havea proven performance record within the localityshould be selected for use as street trees in thecorresponding geographical area.

Different species have different microclimatic

preferences and tolerances depending on thenatural habitat. Some species are tolerant of fullexposure to sunlight, whereas others prefer semi-shaded positions. Exposure to prevailing winds,salt laden winds, tolerance or sensitivity to frost andother environmental variables must be consideredin both selection and placement within the site.

Soil conditions throughout the Sydney basin arevariable, ranging from disturbed landscapes, toshallow sandy impoverished soils derived fromHawkesbury Sandstone to more fertile soils derivedfrom Shales or alluviums. The selection of streettree species must take account the soil types both

within the locality and the geographical region.Whilst some species are adaptable to a rangeof soil conditions, others prefer particular soildepth, fertility and moisture content to performsatisfactorily.

The site hydrology will also be a limiting factorin the selection of tree species. Low lying areasalong drainage lines are typically poorly drainedand may be suitable to species that will tolerateperiodic inundation or waterlogged soils. Higherareas on side slopes or ridges are more typically

well drained and species that prefer well drainedsoil conditions should be selected for these areas.

The root system provides the essential functionsof anchorage (structural stability), absorptionof water and nutrients and storage of vital foodreserves. The mature size of a tree will be limitedby the volume of soil suitable for root growth anddevelopment. Most tree roots are contained in thetop metre or so of soil, but may extend 2 to 3 timesbeyond the extent of the drip-line (extent of thecanopy projected to the ground plane). For trees

to achieve their optimum mature dimensions, theymust have adequate below ground space for thegrowth and development of the root system.

Soil conditions within an urban environment,particularly streetscapes, are far from natural.Soil profiles are often inverted, disturbed, paved,compacted and contain a variety of undergroundstructures and utility services. Satisfactory growthand performance of street trees relies heavily on

an effective root system. Root growth is limited byavailable soil oxygen, soil strength, permeabilityand moisture holding capacity. Whilst somespecies will tolerate poor soil conditions, ideallyimproved soil conditions should be provided toensure satisfactory root growth.



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3.5 Water

3.6 Services & public infrastructure

Adequate soil moisture is essential for street trees

to flourish in the challenging urban environment.Traditionally the local Council would be responsiblefor the watering of street trees alternatively theirfate is dependent on the benevolence of theweather or the local community.

There are a number of means by which street

trees may be watered including irrigation systemshowever these means tend to be unreliable orcostly. Alternative means of watering should beinvestigated, the discussion of these means isoutlined in Section 4.2 of this document.

The size and position of underground utility servicesmay limit effective root growth therefore limitingthe optimum size, growth and performance ofstreet trees. Likewise, tree roots may cause damageto underground services by direct pressure onconduits as roots grow and expand in diameter, orby entry to hydraulic services such as sewer andstormwater lines causing damage and blockage.Tree roots and underground services do not mix.Where possible tree planting areas and belowground service corridors should be separated.

Species that have large and vigorous root systemsmay result in significant damage to publicinfrastructure, including roads, kerbs, footpaths,paved areas and underground services. Thesetypes of trees should be avoided.

Where overhead power or communication linesoccur, the size and/or types of trees suitable to begrown beneath are limited due to their branchinghabit and tolerance to severe pruning.

Where trees share the road verge with aerialutility services large trees suffer severe loppingthat compromises the trees form and health. Treeselection should consider these constraints.

Trees with vigorous root systems may damage roadinfrastructure.



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3.7 Native or exotic

There is considerable divergence of opinion within

the general community in regard to the use of nativeor exotic tree species in our urban environment.However, the origin of a tree is of lesser importancethan it’s ability to tolerate the modified urbanenvironment and its appropriateness to the siteconditions. Ultimately, it is critical that the speciesselected will be sustainable in the landscape, thatis, it will grow to maturity and perform satisfactorilyfor an extended period in the street environmentwith a minimum of care and maintenance. Acombination of tree types may best suit the specificsite situation. There are broadly three differentspecies options to consider:

i. Locally native species

These trees are generally best suited to the soils andclimate of their particular area, they also promotebiodiversity and habitat linkages, one such speciesis the Cheese Tree (Glochidion ferdinandii) (PhotoPage 12). Many local government areas activelysupport the use of locally native species withinurban development. However, the constraints

posed by the urban environment may not allowthese species to flourish causing them to be moresusceptible to pests and disease when underenvironmental stress. Many of these species havenot been extensively trialled in urban situationsand their performance is not readily predictable.

ii. Species native to Australia

Native trees are widely used in the landscapeindustry having both the required form and ability

to perform well in the urban environment. Many

native species have been extensively used inamenity horticulture and their performance can bepredicted under known environmental conditions.The industry is extending the number of speciestrialled, investigating a range of NSW east coastnatives largely from drier rainforest vegetationtypes that are particularly well suited to the poorlydrained and aerated, shady urban conditions.

iii. Exotic species

Traditionally many of our street trees are exotic

species and in some cases the species have beenbred specifically for amenity horticultural purposestherefore being hardy and having a suitable formfor use in the urban environment.

Many of the exotic species commonly used aredeciduous giving the benefit of affording solaraccess in winter. The option of using deciduousnative trees species is extremely limited as thereare very few true deciduous native species, mostbeing semi-deciduous associated with theirflowering cycle such as the Illawara Flame Tree

rather than in the winter period as is desirable inthe urban environment.

The success of some exotic species and lackof predators in the Australian environment hasresulted in these species becoming environmentalweeds. An effort should be made to excludespecies that have become environmental weedsparticularly in areas close to bushland.

Australian Native Lemon Scented Gum are widely grownthroughout the country.

Liquidambers are exotic to Australia originating in NorthAmerica.



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3.8 Biodiversity & habitat

3.9 Weeds, nuisances & pests

Where appropriate, consideration should be given

to planting trees which provide a linkage betweenopen space or other vegetated areas and naturalstands of vegetation or bushland to assist in themovement of wildlife (fauna and birdlife) betweenthose areas. These species should contain somebenefits to wildlife including the physical benefits ofprotection, shelter, nesting sites and food sources.

Species that are locally indigenous to an area are

likely to provide the most benefit to local wildlife,however these species are not always successfulwhen planted in a highly urbanised situation.In some situations exotic species can providesimilar attributes, such as habitat and linkages, forwildlife.

Some exotic and native species are known to be,or have the potential to be, serious environmentalweeds due to their ability to self-propagate andinvade bushland areas, competing with locallyindigenous species. These species should beavoided as street trees particularly in proximity tobushland.

The selected species must have an acceptable levelof nuisance created by the shedding of leaves andfruit for a street environment. Whilst all trees have

some leaf / flower / fruit drop, those with large orheavy seed pods, excessive leaf drop, fleshy fruitor flowers, or hard spherical seeds which may leadto slip hazards on pavements should be avoided.Trees with other nuisance factors, such as plantsthat produce known allergens producing suchconditions as asthma or skin irritants, spikes orthorns should also be avoided.

Pollen is a known hay fever and asthma trigger.Some trees particularly deciduous trees produceabundant amounts of pollen however not as

much as grasses which are the primary sourceof pollen. The most problematic species (PlaneTrees, Birch, Cypress) have been excluded fromthe recommended species list. Some deciduousspecies are listed in recognition of the otherfunctions they perform in the streetscape.

Selected tree species should be resistant todisease and significant pest infestations. Thecontrol of pest problems in large trees usingchemical methods is both impractical and

inappropriate in urban areas. Species that haveknown susceptibility to debilitating pest or diseaseinfestations should be avoided.

The use of a diversity of species within aneighbourhood or region is also important inreducing the impact of devastating diseases (suchas Dutch Elm Disease) on specific tree species andspecies with similar genetic make-up. Consider theuse of a broad mix of species and family groupswithin a street tree population (not necessarilywithin the same street) to minimise this risk.

Locally native trees such as the Cheese Treepromote biodiversity and habitat linkages.

Tree species planted in monocultures such as these bottle-brushes are often subject to pests and diseases.



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3.10 Tree size, spacing, life span& maintenance

i. Tree Size

Species should be selected such that the ultimatemature size is in scale with the relevant street,taking into consideration the site constraints, suchas verge widths, overhead powerlines, buildingsetbacks and vehicle clearances. The optimum sizerange should not be so small that it does not makea contribution to the amenity of the street, andnot so large as to dominate and cause significantproblems (damage & nuisance). In some instances

the constraints imposed by the street environmentwill limit the ultimate size of street trees or evenrestrict tree planting altogether.

Where site constraints limit the ultimate size ofstreet plantings and the visual impact of a largertree is essential for legibility, consideration may begiven to mechanisms that minimise or remove theimpact of these constraints. These could includefor example, replacing overhead powerlines withAerial Bundle Conductors (ABC’s) or undergroundpower conduits, planting trees within a median or

carriageway (where verges are narrow and streetsare sufficiently wide) and increasing the root zonesoil volume by use of structural soils or similartechnologies.

For Landcom’s roads (see Landcom Street DesignGuidelines 2006) it is recommended that thefollowing sizes of trees be planted depending onspecific design and physical conditions:

Small trees:6-8m height with a 5m crown spread

Medium trees:10-12m height with a 8m crown spread

Large trees:16-20m height with a 16m crown spread

ii. Tree Spacing

Throughout NSW Council requirements vary as tothe distance of street trees from the back of the kerb

which is generally between 900mm and 1.5m in astandard 3.5m verge. A 900mm minimum setbackgenerally allows garbage trucks to operate alongthe street without causing too much damage to thetrees. At minimum these trees would be spaced togive a consistent visual presentation, the optimumwould be a size and spacing to achieve interlockingcanopies both along and over the road reserve.

Street trees linear spacing ranges from 5m to 15mdepending on tree size to achieve the previouslystated design intent but in detail will depend on

the planting layout, mature size and road vergewidth. Generally spacing should be:

Small trees at 5 -7m centres

Medium trees at 7-10m centres

Large trees at 10-15m centres

When locating trees in detail consideration shouldalso be given to the proximity to driveways, lightpoles, kerb inlet pits and services. Refer Section6.2 Construction Details.

Crepe Myrtle , small tree Tuckeroo, medium tree



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iii) Life Span & MaintenanceThe procurement, planting and establishmentmaintenance of street trees is a significantinvestment of time and resources, therefore speciesselected should be long lived, say not less than 20years. While the majority of tree species are reputedto be long lived in their natural habitat it is commonindustry knowledge that many species experiencea reduced lifespan in the urban environment.

Street trees typically do not receive the same levelof care as those in residential gardens or parks and

must be tolerant of drought, general neglect andatmospheric pollutants. Trees that are sensitive todisturbance or require high levels of maintenancesuch as regular removal of deadwood, pruning orpest and disease control should be avoided.

Tree species selected should require a minimum ofmaintenance following the establishment period.Species should also be adaptable to pruning andshaping where required to achieve clearances andappropriate form.

To achieve the best outcome for environmentalbenefits and design intent the tree populationshould be managed through a life cyclemanagement approach with a mix of tree ageclasses maintained in order to spread recurrentexpenditure and management actions.

Post establishment, trees should be inspectedannually to monitor tree health and identifypreventative actions such as formative pruning.Street cleaning to remove detritus such a leaves,

flowers and fruit drop may need to be carried out,the magnitude and frequency of this activity willdepend on the tree species selected.

Lace Bark, large tree Trees are often planted for their aesthetic benefits howeverlong term management requirements of large trees in smallverges are often not considered



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part 4

FOR ALL TREE TYPES

technical


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16 | Street Tree Design Guidelines TECHNICAL

4.1 Soil volume & type

The ultimate size of a tree is governed by its

genetic make-up and influenced by the prevailingenvironmental conditions and the quality andquantity of growing media (natural or artificial soil)available for root growth and development.

Current research indicates that typically in clayloam type soils, the root system of a mature treemay extend up to two to three times the spread ofthe crown (extent of the foliage and branches), butusually extends no deeper than one metre fromthe surface level. Tree roots are opportunistic,that is, they will flourish wherever soil conditions

are favourable. Conversely, however, they will notgrow where soil conditions are unfavourable. Threethings limit root growth and development; availablesoil oxygen (necessary for root function andrespiration), available moisture, and the resistanceof the soil to root penetration (degree of soilcompaction). Beyond the requirements for normaltree growth, root development is also critical forthe anchorage and stability of the tree (refer to Fig5). A tree can be sustained on a very small volumeof soil (in a nursery container for example) providedthat frequent and adequate water is provided.However, in a street situation, where the tree mustrely on the infiltration of natural rainfall to the root

zone, tree growth and development is limited by

the volume and moisture holding capacity of thesoil.

There are many methodologies for calculating therequired soil volumes for trees in a street situation,however the results are extremely variable. Mostsuggest a minimum volume as of:

• Between 5 and 15 cubic metres for a small tree.

• Between 20 and 40 cubic metres for a mediumsized tree and

• Between 50 and 80 cubic metres for a large

tree.

These volumes represent the unobstructed soilvolume required by the tree i.e. where the rootscan spread to, not the improved soil planting hole(see Fig 6a & 6b). The improved soils area is definedin the standard details in Section 6.2 - Fig 15.

As root growth is limited by available soil oxygen,and this oxygen depletes with depth, there is nobenefit in increasing soil volume by increasingthe depth of the planting zone beyond a depth of1.0m. The greater benefit is in increasing the soilvolume laterally (refer to Fig 6a & 6b).

Fig 5 Tree structure and needs


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Street Tree Design Guidelines TECHNICAL | 17

Fig 6b Available unobstructed root area for Local Street (planting in carriageway)

Fig 6a Available unobstructed root area for Local Street (planting in verge)

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In order to provide reasonable conditions fortree growth and enable trees to reach their

optimum ultimate dimensions, some compromiseis necessary between the conflicting needs ofthe street tree and urban infrastructure. Variousinnovations have been developed that reduce thepotential conflict in requirements between treesand urban infrastructure. These include:

• Porous and permeable pavements and sub-base materials

• Skeletal (structural) soils (providing load bearingsub-base for pavements and parking bays)

• Drainage technologies

• Interconnected tree pits

• Separation from service corridors

• Modifications to kerb alignments to increasesoil volumes through introduction of blisters,medians and the like.

Fig 7 Designing for passive watering. Top diagrams show street t ree in verge while bottom diagrams show street tree inblister in carraigeway.

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4.2 Designing for passive wateringAccess to moisture is a fundamental requirementfor tree health. The configuration of the traditionalroad verge is not designed to maximise stormwaterflow to street trees rather stormwater is rapidlycollected in the gutters which feed this water to thepiped drainage system. Passive watering entails theredirection of ‘low flow’ road stormwater to waterstreet trees while allowing any greater flows to becollected in the stormwater collection system. The

benefit of accommodating street tree wateringas part function of the road drainage system is topromote more successful street trees and reducethe need to use potable or town water for treewatering.

The tree may be located in the road carriage waywithin a blister or in a depressed planting area inthe verge as illustrated in Fig 7.



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4.3 Water sensitive urban design

Raingarden Street Trees

Raingarden tree pits are essentially bioretentioncells located at kerbside containing a street treewith groundcover vegetation around the base.Stormwater runoff enters the tree pit througha break in a standard road kerb and is filteredthrough the soil media within the cell. Treatedstormwater is then collected via a perforateddrainage layer at the base of the cell before beingdischarged into conventional stormwater pipes thatalso act as an overflow. Fig 8 below illustrates theflow of stormwater from surrounding impervious

areas, onto the surface of the street tree beforepercolating down through the filter media andbeing collected in the drainage pipes before beingdischarged to conventional stormwater pipes.

Street trees designed in this way providestreetscape amenity and stormwater treatment.An additional benefit is that the passive irrigationfrom stormwater reduces the demand for irrigationfrom other sources such as potable water.

Fig 8 Typical raingarden tree pits (NTS) showing the stormwater flow path.

Break in kerb

Extendeddetention

Inundationtolerant tree

Road

Connectionto conventionaldrainage system

Addressing

trip hazard

Loamy sandfilter media

Sandytransition layer

Gravel drainage layercontaining perforateddrainage pipes

Groundcovervegetation

Protectionfrom traffic


Ground Level


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Things to consider:

Connection to conventional stormwatersystem

As the inclusion of tree pits into the drainagesystem does not affect other conventional drainageelements, stormwater discharge exceeding thecapacity of the tree pit may continue down thekerb and is collected in a conventional side entrypit, as illustrated in Fig 9.

Set down

The surface of the filter media (growing media) ofa raingarden tree pit must be set down from thesurrounding surface to allow for ponding of wateracross the surface (extended detention). As aresult there may be a need to address any trippinghazard created by the set down of the filter media.This may be done in a number of ways includingthe provision of bollards or seats or the provisionof a custom designed tree grate as illustrated inFigs 10a & 10b.

Groundcover vegetation

The inclusion of ground cover vegetation aroundthe base of the tree reduces the likelihood ofclogging at the surface of the tree pit. Raingardenstreet trees can be designed without groundcovervegetation, as illustrated in Figs 10a & 10b, howeverthere is an expected increase in maintenance withthis type of design to ensure the surface of thefilter media maintains its porosity.

Filter media and drainage pipes

The design of a street tree as a raingarden to treatstormwater means that the tree essentially has amuch larger catchment than would have previouslybeen the case. As a result it is important thatthe correct filter media and drainage pipes arespecified to ensure that stormwater can efficientlymove through the system and then be dischargedback into the conventional stormwater drainagesystem.

Tree species selection

The tree species need to be relatively hardy(tolerant of freely draining sandy soils and regularinundation). The soil (filter media) into whichthe trees are planted has a specified hydraulicconductivity (often between 100 – 200 mm/hr).

Break in kerb

Raingarden tree pit

Conventional

side entry pit

Surface flow

Footpath

Kerb

Road

Conventional stormwater drain

Underground drainage

Fig 9 Raingarden tree pits - Typical plan view (NTS) showingstormwater flow into and out of a row of raingarden streettrees.

Fig 10a Typical design of a raingarden street t ree withcustomised grate and overflow grate located along the kerb.

Fig 10b Customised grate for raingarden street tree.



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4.4 Tree hardware

i) Tree Guards

Tree guards are sometimes used to protect treesfrom accidental damage or vandalism in urbanareas. A considerable variety of styles and designsare commercially available plus options for custommade types. If tree guards are required, thedesign should allow for easy removal of the guardonce the tree is of sufficient size to no longerrequire protection. Segmented types that can bedisassembled from around the tree are preferableto single piece structures. A minimum intrusioninto the ground plane should also be considered

as footing for tree guards can form an obstructionto root growth and displace valuable root volume.

ii) Root Barriers

Tree roots are opportunistic and will grow whereverthe soil conditions are favourable. Roots requireacceptable levels of oxygen moisture and growingmedia to grow successfully. Where conditionsare unfavourable, they will not grow. As roots arelimited by available soil oxygen, they will often

grow close to the soil surface, and in moist aeratedmaterials such as pavement sand bedding layers.As roots grow, they gradually expand in diameterand can exert considerable pressure on structuresand pavements, causing them to lift, crack anddisplace.

Root barriers are sometimes used in new plantingsituations, particularly planting pits in pavementsor adjacent to kerbs, to deflect roots away fromstructures and avoid future damage. A range ofproducts and materials are commercially available.

However, to minimise potential conflicts and reducethe potential for damage to structures, adequatesoil volume and quality needs to be considered asa priority as root control devices appear to be theleast effective method of containment where poorsoil aeration and compaction encourages shallowroot growth. The installation of a root barrier isnot a guarantee of protection of infrastructure andrequires specialist knowledge in design, installationand maintenance.

Tree guards can provide a variety of uses such as protectionand landmarking, they also need to accommodate treegrowth and be easily removed.


Root barriers installed to protect public utility and roadassets however a better solution is providing trees withadequate soil volume.


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iii) Plant Stakes & Ties

Industry best practice is for plant stock not torequire staking for support. Where the supplyplant stock is of a prescribed quality as specifiedin the Natspec guide, plant stock should be “self-supporting” that is, not requiring stakes andties or other artificial means of support duringestablishment. This is because the plants are grownwith an acceptable ratio between the containervolume, trunk calliper and tree height.

Stakes and ties are sometimes used to provideartificial support to trees during establishment

of the root system, however, incorrectly installedstakes and ties can cause damage to young treesand should generally be avoided. Trees thatbecome reliant on stakes for support developweak stems that do not strengthen naturally undernormal weather conditions, leading them to bendor snap once the stakes are removed.

Where stakes are installed there should be sufficientflexibility in the ties to allow some movement of thestem, which will promote increase in stem calliperand strengthening of the trunk

Stakes as markers. Urban tree guard and grate.



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part 5

sourcing &procurement

FOR ALL TREE TYPES


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Container grown plant stock is available in standard sizes and a variety of species.

Beyond the selection of an appropriate species for planting consideration needs

to be given to the availability of plant stock in terms of pot size, quantities and

quality.

Sourcing & procurement

5.1. Availability

In Australia, plant stock is normally grown incontainers and sourced from commercial nurseries.The container type, shape and size may vary

depending on the size of the stock and the grower.Some plant stock is also grown in the ground(field grown) and transplanted to containers priorto delivery (sometimes referred to as “Balledand Burlapped” stock). A limited number of treespecies are grown by commercial nurseries,depending on their popularity and ultimately theircommercial viability. Where unusual plant materialor large tree stock is required, pre-ordering severalyears in advance may be required to ensure themost appropriate plant stock can be sourced for

the project, particularly where local provenance or

large numbers of stock are required.

Local provenance species are tree species that are

indigenous to a specific local area. Planting localprovenance species may be important in proximityto areas of natural vegetation or re-vegetation ofdisturbed roadside areas adjacent bushland topreserve genetic integrity of the natural vegetation.Where local provenance species are required,procurement should be undertaken several yearsin advance so that local provenance seed can becollected and grown on as plant stock. A numberof companies specialise in seed collection andgrowing-on of local provenance stock.

24 | Street Tree Design Guidelines SOURCING & PROCUREMENT


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Street Design Guidelines SOURCING & PROCUREMENT | 25

5.2 Quality

The quality of plant stock grown by commercial

nurseries is extremely variable. To provide greaterconsistency and quality of plant stock, Natspechas produced a useful guideline titled “SpecifyingTrees – a Guide to Assessment of Tree Quality”.This guideline provides a basis for specifying andassessing tree stock quality in line with currentbest practice in the nursery industry. Trees to beused as street trees require a clear stem withoutlow branching. This requires specialist pruning inthe nursery. Specifications for supply of tree stockshould preferably be derived from this guidelineand prepared by a qualified professional.

In addition to the general health of the stock, thebranching structure and root formation of treestock is especially critical for the long term successof trees in the landscape. Poor branching structure

may result in longer term problems such as structural

defects and weaknesses that lead to hazards. Poorroot development impedes establishment and maylead to long term problems such as tree failure andwindthrow (overturning under adverse weatherconditions). Container grown stock is especiallyprone to poor root formation unless the stock isgrown in accordance with best practice principles.

Plant stock in Australia is grown in one of two mainmethods, in containers of various shapes and sizesor in the field (sold as “Balled and Burlapped”or “bare-rooted” stock). Field grown stock is

normally reserved for deciduous trees and conifersthat can tolerate root pruning and transplantingwhen dormant. The greater majority of plant stockis grown in containers by wholesale and retailnurseries.

Larger size plant stock is available from a limited number of commercial nurseries.


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26 | Street Tree Design Guidelines SOURCING & PROCUREMENT

5.3 Procurement alternatives

There are currently two main options for

procurement of plant stock in Australia:-Open Market

Contract Growing

The procurement method selected will generallydepend on the normal commercial availability ofthe stock specified and the quantities required.Small quantities of commonly grown stock can besourced relatively easily from the open market,however large quantities, large sizes, unusual orlocal provenance species may need to be sourcedby Contract Supply options.

i) Open Market

The open market can only supply a limited rangeof commercially viable stock, suitable to thelocal climatic conditions of an area. The marketavailability of various species will depend oncurrent industry trends as well as supply anddemand. Many large Commercial Nurseries actas brokers to obtain all of the stock they can frommore specialist growers to fill an order. There are

many good reasons for this, including the fact that

most buyers prefer to deal with one supplierrather than a large number of nurseries to obtainall the required plant stock for a project. Specialistgrowers may also have the expertise and climaticconditions or facilities to grow various speciesmore successfully and cost effectively than largernurseries.

ii) Contract Growing

Contract Growing is an agreement between agrower and a buyer to grow a defined quantity of

stock to the clients’ specification and requirements(including for example, a specified time frame fordelivery or pruned to suit a street tree function).Contract growing is a fairly reliable and costeffective procurement method for large quantitiesof particular species, assuming sufficient lead timeis available for production of the stock. The clientand grower normally share the risks associatedwith supply from the outset, as the stock is grownfor a particular project and purpose and would notbe saleable to another client.

Healthy trees with the required branching structure and root formation result in a more successful st reetscape.


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part 6

FOR ALL TREE TYPES

details


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28 | Street Tree Design Guidelines DETAILS

6.1 Planting configurations

For the purposes of this document the focus for

consideration are the streets defined as Local,Minor Local and Laneways in Landcom’s StreetDesign Guidelines. The technical considerations for

choosing the right tree species for these locations

have been outlined in Parts 3 & 4 addressing boththe spatial and environmental requirements ofthree generalised tree sizes.

Fig 11 Formal Avenue

FORMAL AVENUES

Being a single species symmetricallyspaced.

This is the simplest and mosttraditional planting configurationseen throughout the world in streetsand parks. This configuration is most

successful when used where thereare larger frontages to residentialallotments and uniform street andphysical conditions.


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Street Tree Design Guidelines DETAILS | 29

Fig 12 Informal Avenue

INFORMAL AVENUES

Asymmetrically arranged singlespecies.

Sometimes this may includetrees both in the verge and thecarraigeway in the parking lane.

This style of layout is a responseto the reduction in the width offrontages and the pressure forspace.


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Fig 13 Patterned Planting

PATTERNED PLANTING

Multiple species in a patternedavenue or patterned groupedplanting.

This configuration seeks to optimisethe limited space within the roadreserve for large street trees by

distributing them in more criticallocations to maximise the visualbenefits.


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Fig 14 Landmark Planting

LANDMARK PLANTINGIn landmark or focal areas aspecies in contrast to the mainrun of street trees, or particularlyvisually dominant trees, are used tohighlight an entry, community focusor precinct.


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Fig 15 Typical street tree in Landcom Local Street in verge

6.2 Construction details

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35/48


Fig 16 Typical street tree in Blister or Median

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36/48


Fig 17 Typical street tree in paving with structural soil

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37/48

part 7

FOR ALL TREE TYPES

establishmentmaintenance


38/48

To ensure the best possible outcome new trees should have a high level of

maintenance for the first two growing seasons to ensure optimum future shape

and correct tree form. During this period trees would need to be regularly watered,

monitored for pests and diseases and may need formative pruning. A general

establishment specification can be found in Appendix B (included on CD-ROM

included in inside back cover) of this document outlining the activities that shouldbe undertaken during this period. These activities are also summarised in the Fig

19 below.

Establishment maintenance

Fig 19 Essential establishment maintenance activities

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39/48

part 8

FOR ALL TREE TYPES

recommendedstreet tree list


40/48

Botanical Name Common Name Origin Soil Conditions Drainage *DataRequirements Sheet

Deciduous (D) / Evergreen (E) Shale Sandstone Transitional Alluvium Good Average Poor

Elaeocarpus Blueberry Ash E Native ! ! ! ! ! ! x 1reticulatus

Syzygium Small-leaf Lillypilly E Native !

!

!

!

!

!

x 2leuhmannii

Buckinghamia Ivory Curl Flower E Native!

x!

!

!

!

x 3celsissima

Backhousia Lemon-scented E Native !

!

!

!

!

!

x 4citriodora Verbena

Callistemon Weeping E Native ! ! ! ! ! ! ! 5viminalis Bottlebrush

Magnolia Little Gem E Exotic ! x ! ! ! ! x 6‘Little Gem’ Magnolia

Arbutus Irish E Exotic!

x!

!

!

!

x 7unedo Strawberry Tree

Franklinia Gordonia E Exotic ! ! ! ! ! ! x 8axillaris

Tibouchina Lasiandra E Exotic !

x !

!

!

!

x 9granulosa

Tibouchina Lasiandra E Exotic ! x ! ! ! ! x 10macrantha

Fraxinus Evergreen E Exotic!

x!

!

!

!

x 11griffithii Ash

Melaleuca White Feather E Local ! x ! ! ! ! ! 12decora Honey Myrtle

Melaleuca Narrow-leaved E Local ! ! ! ! ! ! ! 13linariifolia Paperbark

Prunus Taiwan Cherry D Exotic !

x !

!

!

!

x 14campanulata

Lagerstroemia Crepe Myrtle D Exotic !

!

!

!

!

!

x 15indica

38 | Street Tree Design Guidelines STREET TREE LIST

SYDNEY South-West & North-West Region

Small Trees Height 6-8 m x Spread 4-5 m

* Data sheets are included on CD-Rom included on back page of these guidelines.


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Brachychiton Kurrajong E Native ! x ! ! ! x x 16

populneum

Banksia Coast Banksia E Native !

!

!

!

! x x 17

integrifolia

Cupaniopsis Tuckeroo E Native !

!

!

!

!

! x 18

anacardioides

Harpulia pendula Tulipwood E Native !

x !

!

!

!

x 19

Tristaniopsis Water Gum E Native !

!

!

!

!

!

! 20laurina

Pittosporum Queensland E Native ! x ! ! ! ! x 21rhombifolium Pittosporum

Corymbia eximia Yellow Bloodwood E Native x ! ! x ! x x 22

Angophora Narrow-leaf E Native x ! ! x ! x x 23bakeri Rough-barked Apple

Acmena smithii Lillypilly E Native ! x ! ! ! ! x 24

Syzygium Magenta Cherry E Native !

x !

!

!

!

x 25paniculatum

Magnolia Bullbay Magnolia E Exotic ! x ! ! ! ! x 26grandiflora

Quercus suber Cork Oak E Exotic ! x ! ! ! ! x 27

Fraxinus Desert Ash D Exotic !

x !

!

!

!

x 28oxycarpa

Jacaranda Jacaranda D Exotic !

x !

!

!

!

x 29mimosifolia

Pyrus calleryana Callery Pear D Exotic !

x !

!

!

!

x 30 ‘Chanticleer’

Acer Trident Maple D Exotic !

!

!

!

!

!

x 31buergeranum

Sapium Chinese D Exotic ! x ! ! ! ! x 32sebiferum Tallow Tree

Malus Japanese D Exotic ! x ! ! ! ! x 33floribunda Crabapple

Zelkova Japanese D Exotic ! x ! ! ! ! x 34serrata Zelkova

Pistachia Chinese D Exotic ! ! ! ! ! ! ! 35chinensis Pistachio

Melaleuca Prickly-leaved E Local !

!

!

!

!

!

! 36styphelioides Paperbark

Street Tree Design Guidelines STREET TREE LIST | 39


Medium Trees Height 10-12 m x Spread 8-9 m



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40 | Street Tree Design Guidelines STREET TREE LIST



Eucalyptus Forest E Local ! ! ! ! ! x x 37tereticornis Red Gum

Eucalyptus Broad-leaved E Local ! x ! ! ! x x 38fibrosa Ironbark

Eucalyptus Narrow-leaved E Local !

x !

!

!

!

x 39crebra Ironbark

Angophora Rough-barked E Local !

!

!

!

!

!

!

40floribunda Apple

Corymbia Spotted Gum E Local !

x !

!

!

!

x 41maculata

Eucalyptus Mugga E Native !

x !

!

!

x x 42sideroxylon Ironbark

Syncarpia Turpentine E Native !

!

!

!

!

!

x 43glomulifera

Brachychiton Queensland D Native !

x !

!

!

!

x 44discolor Lacebark

Flindersia Australian E Native !

x !

!

!

!

x 45australis Teak

Lophostemon Brushbox E Native !

x !

!

!

!

x 46confertus

Quercus Pin Oak D Exotic !

x !

!

!

!

x 47palustris

Quercus Red Oak D Exotic !

x !

!

!

!

x 48rubra

Carya Pecan D Exotic !

x !

!

!

!

x 49illinoinensis

Ulmus Chinese Elm D Exotic! x ! ! ! ! x

50parvifolia

Liquidambar American D Exotic ! x ! ! ! ! ! 51

styraciflua Sweet Gum ‘Parasol’

Nyssa Tupelo D Exotic !

x x !

!

!

! 52sylvatica

Paulownia Princess D Exotic !

x x !

!

!

x 53tomentosa Tree

Quercus Holm Oak E Exotic !

x !

!

!

!

x 54ilex

Afrocarpus Yellowwood E Exotic !

x !

!

!

!

x 55falcatus


Large Trees Height 16-20 m x Spread 16 m



43/48

part 9

FOR ALL TREE TYPES

glossary & references


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42 | Street Tree Design Guidelines GLOSSARY & REFERENCES

This section contains descriptions of the meanings ofterms and phrases used in the Guidelines.

Aerial Bundle Conductor (ABC)A type of overhead low voltage electrical cable. Insulatedcables are wrapped around a steel cable strung betweenoverhead poles. This minimises the risk of open conductorstouching and reduces the clearances for pruning aroundtrees.

Balled and BurlappedType of nursery stock in which the plant is excavatedfrom a field grown position with the surrounding soil androots (‘root ball’) then wrapped with protective material(‘Burlap’).

BioretentionBioretention is an up-land water quality and water quantitycontrol practice that uses the chemical, biological andphysical properties of plants, microbes and soils for removalof pollutants from storm water runoff.

CanopyThe crown of a tree, comprising of all the foliage and smallbranches.

Central leaderThe main stem of a tree.

Clear stem heightThe distance between the ground and the lowest branchof a tree.

DeciduousA plant that sheds all of its leaves at one time during theyear.

Drip-lineOuter edge of tree canopy, the extent of the crown of a treeprojected to the ground plane.

Environmental WeedAn invasive introduced plant species, which is capable ofestablishing, self-sustaining and expanding populations innatural and semi-natural habitats.

ExoticAny introduced plant species that is not native to

Australia.Filter mediaIn bioretention systems, the media that captures andseparates solid pollutants from stormwater.

FormThe overall shape of a tree canopy.

Formative PruningThe selective pruning of a young tree to promote goodform and branching structure typical of the natural growthhabit of the species. The main aim of formative pruning is toidentify and remove any growth defects or other structuralproblems that may have long term implications early in thedevelopment of the tree.

Groundcover vegetationAny vegetation that grows low to the ground or may beprostrate in habit.

HabitThe nature and appearance of the branching framework ofa tree or plant.

Hydraulic conductivityThe ease with which water can move through pore spacesor fractures in a growing media or filter media.

Local provenanceGenetic variability of a species influenced by the local soiland climatic conditions of a particular area or situation.

Locally-indigenousPlant species that originally occurred in a particular localarea.

Micro-climateThe immediate climatic conditions of a location influencedby aspect, sun, shade, reflected heat, wind exposure, waterbodies and so on.

Moisture Holding CapacityThe capability of a soil material or growing media to holdmoisture in pore space against the effects of gravity.

MulchAny material that is spread over the surface of the soilto prevent erosion, reduce weed growth & retain soilmoisture.

Passive WateringRedirection of ‘low flow’ road stormwater to water streettrees.

Permeable pavementModular or monolithic pavement materials that allow water

to percolate through the pavement profile.Planting trenchArea of site soil excavated then mixed with or replaced byimproved topsoil for the planting of trees.

ProcurementThe process of acquiring (purchasing) goods or services.

Root Control Barrier or DeviceA material (usually in sheet form) inserted vertically throughthe soil profile to deflect root growth.

Root PlateThe conglomerate of structural (woody) and fibrous rootsthat radiate out from the tree trunk, often extendingbeyond the drip-line and usually confined to the top metre

of soil (i.e. a relatively shallow but broad ‘plate’).

Soil volumeThe total amount of soil material or growing media availablefor unobstructed root growth.

Stem CaliperDiameter of the stem or trunk.

Structural SoilA growing media for plants consisting of a mixture ofmaterials designed to provide load bearing capacity forpavements whilst also providing basic requirements for rootgrowth (aeration, moisture holding capacity & nutrients).

Unobstructed Soil Area

Area able to be accessed by tree roots without impedimentssuch as utility services and compaction by road trafficincluding both existing and improved soils.

WindthrowOver-turning of a tree due to wind force or failure of theroot plate.

Glossary


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Street Tree Design Guidelines GLOSSARY & REFERENCES | 43

References

A number of references have been sourced forthe preparation of this document. These mayassist Development Managers and designers togain a greater understanding of the principlesand research influencing these guidelines.

Landcom Publications

Landcom Street Design Guidelines (2006)

Landcom Water SensitiveUrban Design Guidelines (2004)

Publications

Fairley, A. and Moore, P. (1989)Native Plants of the Sydney District The Society for Growing Australian Plants NSW Ltd,Sydney

Rowell, R.J. (1980)Ornamental Flowering Trees in AustraliaReed Books Pty Ltd, Sydney, NSW

Clark, Ross (1996)Specifying Trees – a guide for Assessment of TreeQuality – Second Edition 2003 Construction Information Systems Australia Pty Ltd/NATSPEC, Sydney

Pryor, L.D. & Banks, J.C.D (2001)

Trees and Shrubs in Canberra (2nd Edition)Little Hills Press & ACT Government, Canberra ACT

Hitchmough Dr James D. (1994)Urban Landscape Management Inkata Press, Sydney

Lindsey, P. & Bassuk, N. (June 1991)Specifying Soil Volumes to meet the Water Needs ofMature Urban Street Trees and Trees in Containers.Journal of Arboriculture; Volume 17, No. 6, Page 141International Society of Arboriculture, Illinois, USA

Clark, J.R. & Kjelgren, R (1990)Water as a Limiting Factor in theDevelopment of Urban TreesJournal of Arboriculture; Volume 16, No. 8, Page 203 International Society of Arboriculture, Illinois, USA

Websites

Landscape and Human Health Laboratory, Uni of

Illinois at Ubana-Champaignehttp://www.lhhl.uiuc.edu/index.htm

Statewide Mutual – Best Practice Guideswww.statewide.nsw.gov.au


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ACKNOWLEDGEMENTS

Landcom Project Manager

Anne SutherlandUrban Design Manager

Consultant

JMD designIngrid Mather (Principal Author)Director

Earthscape Horticultural ServicesAndrew Morton (Contributing Author)

Project Steering Committee

Pat Coleman

LandcomJudy FakesRyde School of Horticulture

Tony WongEDAW

Thanks also to those people and organisations that provided feedback and advice, including the

Landcom executive and development teams.

44 | Street Tree Design Guidelines GLOSSARY & REFERENCES


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