tree planting in paved surrounds - greenblue urban · the information in this book is ... the 7...

A look at why trees in parking lots fail –and what to do about it

The 7 Fundamentals of

Tree Planting

In Paved Surrounds

“A quick guide for busy people on how to avoid expensive tree planting failures and implement a successful urban

tree planting strategy”

A publication byGreenBlue Urban

Introduction

The purpose of this publication isto provide facts and guidance topersons involved in the decisionmaking process which is a part ofany urban tree planting program.Planting trees in hard surfacesrequires careful planning andinteraction between differingprofessional disciplines.

Typically we see even planting asingle street tree can involveengineers, landscape architects,highways departments, utilitycompanies, urban foresters,landscape contractors, civil workscontractors and of course theclient.

This publication is for thesepeople – reading it will not makeyou an arborist or tree expert, butit will mean you have a broadacquaintance with some of thekey pitfalls and how to avoidthem.

The information in this book isdrawn from many sources and isnot least the product ofGreenBlue’s accumulated wealthof experience of over 20 years asa global market leader in theUrban Tree Pit Design industry.

The 7 Fundamentals of Tree Planting in Paved Surrounds 4

The 7 Fundamentals of Tree Planting in Paved Surrounds

Trees are living woodland plants.This sounds obvious, but it isn’t -otherwise we would not see somany tree pit designs for urbanareas which are fundamentallyflawed.

As woodland plants, trees need soilto grow into – and lots of it. After all,in a forest or woodland they can,and do, spread their roots a longway beyond the canopy spread.Why then do we still see treesplanted in tiny tree pits or evenconcrete rings? Such trees aredoomed to be short-lived from themoment they were drawn into theplans.

Furthermore, not only is a qualityrooting medium required, but theremust be the means of maintainingthat quality. In parking lots, this is aparticular challenge, as much of theroot zone will be paved over.

What you provide the tree withbelow ground, will dictate how thetree will manage, grow, and thrive(or otherwise) above ground.

Please don’t be surprised if due tobudget constraints your tree pit sizeis reduced to a 35 cu. ft. (1 cu. m.)provision. This will be entirelypredictable, and the dying,diseased and stunted tree will aftera few short years will be joining thestatistics.

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Now let’s look at the main reasons for tree failure.These can be broadly grouped into seven aspects.

1. Lack of adequate un-compacted rooting volumeRoots need appropriate soil volume – failure tolocate this will result in short lived trees.

2. Poor planting techniqueClumsy and careless planting technique can resultin long term damage to trees prospects, allowingthe roots to dry out during planting for example.

3. Vandalism – intentional and unintentionalDogs, vehicle movements, trimmers, andintoxicated persons can all create survivalchallenges for trees.

4. Poor DrainageWaterlogged ground conditions for longer than 48hours can cause root to die back. Persistentanaerobic conditions will result in a dead tree – airis vital.

5. DroughtStatistically, one of the biggest killers of newlyplanted trees is lack of enough water to sustainplant life. Surface watering encourages surfaceroots and is only 25% efficient .

6. Design and species selectionThe wrong tree species for the site.

7. Infrastructure remediation damageTree beginning to establish – and then highwayengineers have to cut through the roots to remedya trip hazard. This can destabilize the tree andcreate problems.

Reasons for Failure

The 7 Fundamentals of Tree Planting in Paved Surrounds 6


What can be done?…

ClientAbove all, be realistic. Trees canbring huge benefits and add valueto property for years to come – butyou need to budget appropriately.Get it wrong and the trees will notonly look sickly, but will be visuallyunappealing and could createexpensive damage toinfrastructure.

Local GovernmentIt’s lovely to talk about the numberof trees you plan to plant in thesuburb, but challenge your team –would it be better to plant fewertrees, but to a higher standard?Think about a long range view andwhat will benefit the community formany more years.

What You Can Do

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ArchitectThink about trees early on in yourdesign. Used skillfully they cancreate successful public space thatworks. Trees are not just an ‘addon’ to attach green credentials –they bring innumerable benefits.

Civil EngineerTrees in streets can extendpavement surface life throughcooling shade. They need notcause damage but we wouldsuggest that tree pit design isconsidered early on in new roadschemes

What You Can DoWhat can be done?… (continued)

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What can be done?… (continued)

Landscape ArchitectGetting tree planting right can beyour signature on a project.Visualize the site in 10 years’ time– will you be proud to beassociated with this project?Lancelot Brown was an eighteenth-century English landscape

architect remembered as“England's greatest gardener”. Ifhis trees had died young, it is veryunlikely that he would be referredto today in the same respectfultones that he is.

What You Can Do

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Utilities EngineerGrouping utilities together inprotected service trenches is agood way to create utility free rootspace for trees elsewhere. Find outwhat trees are going in beforedissecting areas needlessly withtrenches – there may be a moretree friendly route. After all, youdon’t want to have to excavatethrough roots for pipe maintenanceso it is in your best interests to lookahead and plan for trees.

Quantity SurveyorSo the scheme calls for a largetree pit construction – looksexpensive and is out of sight.Caution is needed whenattempting to ‘value engineer’ treeplanting. Subsequent remedialworks to repair infrastructure orreplant failed trees could swiftlydwarf apparent savings.


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ArboristIf you are responsible for thestandard of tree planting in yourcity, you need to give clarity tocouncilors, engineers and planningapplicants as to the standards oftree planting expected. This isparticularly important where roadsare to be adopted on new schemes– are we planting a problem forlater years, or a benefit for futuregenerations?

ContractorThe single largest living elementon your scheme will be the trees.Care in handling of trees, pre-planting, planning, planting andaftercare will result in schemes youare delighted to show to futureclients.


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Tree Pit Design

The essence of good tree pitdesign is in the provision ofquality rooting zone in adequatevolume. Allied with this, proactiveroot management strategies areneeded to direct root growthtowards optimal root areas.

To make it simpler for specifiersand other authorities toincorporate a high quality treepit design in their urbanlandscape project, take

advantage of the range ofprofessionally drawn tree pitscreated by GreenBlueInfrastructure Solutions.

They incorporating all the keyelements of good practice toassist busy specifiers and projectmanagers. These tree pit designsare proven to work well and areavailable in CAD formatdrawings.


Products, solutions and methodologies to ensure success

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Tree Pit Design


Without proper tree pit design…

It will end like this!

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Broadly speaking, the tree pit designs we see most commonly used inurban areas, can be classified as follows:

HFTB Tree Pits – Hope for the Best Tree PitsStill very common, the tree is planted into the paved area without any rootmanagement, irrigation means, or soil cell provision. Some will live but the resultswill be completely random, everything depends on what the roots can discover togrow into in the longer term. Tragically many fail, furthermore a very highpercentage of the trees that succeed in surviving for a few years will create pavingheave and other hard surface damage – often leading to tree failure when thepaved surface is reinstated for pedestrian safety.

Tree Pit Classifications

Verdict –HFTB Pits tend to lead to a replacement tree cycle which is difficult to break. It cansave money in the very short term, only to create heavy expense, and often treeloss for the future. Root damage can usually be detected within 3 to 5 years.

HFTB tree pit - no root management, irrigation or load bearing soil volumes

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LVC Tree Pits – Low Volume Contained Tree PitsThese tree pits are designed with root management - to prevent paving damage, anirrigation system, a small volume of soil cells and a root containing perimeterbarrier. This tree pit design is frequently the only way of getting a tree into a verycongested urban situation, with below ground space priority being given to serviceproviders.

Verdict –LVC Pits have a role to play in gettingsmaller trees into our streets and urbanareas. In our experience these can achievegood results and give a tree in a managedsituation, unlikely to create problems aroundbut also restricted in how much it will growand for how long.

A completely managed tree pit, but sub optimal rooting volumes - can be effective for smaller species

LVC tree pit after 11 years


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LVU Tree Pits – Low Volume Uncontained Tree PitsDefinitely preferable to the previous two – an LVU tree pit provides an excellent startfor a trees life and the root are free to travel onwards beyond the initial pit size toexploit potential rooting volumes accessible elsewhere. We have seen this used togood effect in many urban schemes. However – the results after 10 years plus arelikely to be variable and will depend on what further space and nutrient values thetree can locate. Compaction and anaerobic conditions are also highly likely to bedetrimental to the tree in the longer term.

Verdict –LVU tree pits should be regarded as a goodoption where original tree pit space is limitedand / or the planting budget will not stretch toproviding complete life tree pit volumes.

Less than optimal rooting volume, but the root system can access potential rooting zones beyond the soil cells

LVU tree pit after 7 years


HVUC – High Volume Uncontained Tree PitsThis is the ultimate tree pit design. The designer has taken into account the longterm value of canopy volume trees in urban space and has provided a large volumeof load bearing, aerated soil cells, appropriate irrigation and drainage, shallow rootmanagement to prevent paving heave and a surface design which willaccommodate a successful established tree.

Verdict –The best solution for the client who isserious about getting mature trees into theirproject with predictable consistent results.This is particularly important when planting aseries of trees within sight of each other toget uniformity in growth patterns.

Larger volume uncontained – shown here 500mm deep minimum – 750mm would be better – but roots can access large volumes of compacted soil.

Linked HLVU tree pits after 8 years


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Conclusion

1. Soil volume & quality –Enough good quality soil to givethe tree an excellent start at least,if not a complete life provision. Thismust be protected from surfaceloading and vehicle overrun so useof load bearing soil cells is vital toprotect the soil structure.

2. Root management –Linear or surround, ribbed rootbarriers to divert lateral rootsdownwards, away from paving andinto preferred root colonizationzones. The ribs are important asthey prevent root ‘spiraling’ and apot plant effect.

3. Irrigation –Provision of a deep wateringdevice for charging up the fieldcapacity of the tree pit quickly.

4. Aeration –Provision of maintainable ventedaeration inlets, preferably aminimum of two inlets per tree, to

allow the soil in the load bearingsoil cells to breathe.

5. Drainage –If the tree pit is likely to becomewaterlogged, active drainage mustbe installed to prevent prolongedsoil saturation.

6. Above ground protection –Asses the site risks. Investing in atree surround that does not inhibitthe tree and protects from vandals,dogs and careless vehicles, willpay off.

7. Aftercare –Adequate weeding and watering inthe first 2-3 years should beenough to see the tree establishedin its tree pit construction, and thenthey should be low maintenancefor many years to come.

To summarize, if you are planting trees in a parking lot or similarcontinuous paved surround, the following seven areas must beaddressed to achieve consistently successful results:


Acknowledgments & Further ReadingTree Roots in the Build Environment – John Roberts, Nick Jackson & Mark SmithLandscape Below Ground – an ISA publicationThe Benefits of Large Species Trees in the Urban Environment – a CIRIA publication

About GreenBlue Urban

GreenBlue Urban was set up in North America to

research and provide solutions for assisting trees

in their battle to establish in urban spaces. With

the goal of drastically improving urban planting

success and increasing leaf canopy in urban

areas, GreenBlue Urban tirelessly analyzed the

challenges, causes of failure, and the reasons for

premature mortality in urban trees. We then

examined the impact that poor planting can

have on urban infrastructures. Having identified

the key issues in both these areas, we

systematically researched the solutions for those

issues and designed practical products and

systems to address them.

We are the global market leader in specialist

urban landscape products. Our program of

continuous product development, conducted in

conjunction with overseas branches, and our

world-class manufacturing processes, ensures

that specifiers and clients can rest assured that

the systems we offer for urban planting schemes

represent the very best in the sector.

Establishing the future urban landscape

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tree planting in paved surrounds - greenblue urban · the information in this book is ... the 7...

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