Abstract

The challenge for tree asset managers is to target timely investment to deliver the growth and longevity needed to ensure an appropriate return to the community. This is achievable with existing financial resources, but many young saplings currently fail in the landscape and so fail to deliver reasonable return on investment. By targeting investment to provide suitable root zone conditions, unnecessary cost imposts associated with remedial works and premature tree loss can be avoided. Investing in root zones not only enhances tree-related returns, but it can also support integration with other urban infrastructure to achieve synergies to reduce costs overall. The technical knowledge and expertise needed to guide wise investment in trees is not new, it is well developed and expanding. This expertise must be more widely applied to guide investment in tree assets throughout their planning, establishment, growth, maturity and senescence. Achieving this requires a transition from current practises toward broader collaboration of the professions responsible for installing trees. Only through collaboration can the necessary specialist inputs be applied during urban planning, design and construction processes and sustained into tree planting and maintenance by knowledgeable and skilled tradespeople. This paper introduces some historic and contemporary examples of wise investment in trees to focus thought on how good returns can be reliably achieved. It presents the need to invest in adequate soil quality and quantity in a controlled manner to sustain acceptable returns, and it shows that such investment is a ‘NO BRAINER’ which will grow community wealth.

Introduction

Public and private investors direct funds to plant and maintain trees in streets, parks and gardens across Australia and the world. Investing in trees involves paying. Trees on public land are community investments, paid for by rates or taxes. By investing in trees communities are investing in their health and wellbeing, in environmental management, climate moderation and adaptation, flood control, pollution management and many other necessities. Communities demand acceptable returns on the rates and taxes they pay and return on investment in trees can be massive so they pay professionals to manage these investments, but many trees fail to thrive and return on investment is absent. Regularly achieving good return on investment requires knowledge of the asset, its environment, its market i.e. community, and holistic understanding of how these interact.

Trees are appreciating assets which deliver benefits of substantial value

Trees are living assets which take time to mature, and timely investment and maintenance are essential for them to produce their best returns into the long term. Poorly targeted investment in trees often leads to ongoing spending to sustain poorly performing assets and to remove and replace trees prematurely. Loss and renewal of poor tree investments can become repetitive and expensive if causes of failure are not addressed. This can result not only in reduced returns, but it can also diminish the community’s capital.

Urban trees have been ‘…acknowledged as both productive capital stocks and as components of public infrastructural systems. As ecological analogs of industrial capacity and physical infrastructure,…’(Killicoat, Puzio & Stringer 2002). Defining their value still proves unnecessarily difficult, however, as some in the community prefer that monetary values not be ascribed to trees and the aesthetic, environmental and other benefits they provide. In Australia, gaining widespread acceptance for a system to define values for amenity trees has proved chronically problematic. Several attempts to establish an Australian Standard all met with strong opposition and were abandoned. The draft Australian Standard on amenity tree valuation was ’…the longest unresolved or unfinalised standard with which Standards Australia has been associated…   opposition of the powerful insurance and utility sectors virtually doomed it ’ (Moore 2006).

Valuing the services or benefits delivered by trees is challenging but research is increasing, as is monitoring of tree costs. Annual economic benefits exceeding $200 per tree and additional ‘once-off’ lifetime service values such as carbon sequestration and reduced deterioration of asphaltic pavements were calculated by Moore (2009). An earlier economic assessment of a small set of tree-related services delivered by a ‘standard’ Adelaide street tree (a 4.5 m tall Jacaranda) indicated an annual benefit worth $171 (Killicoat, Puzio & Stringer 2002), which was later revised to $424 per year (Brindal & Stringer 2009), or $540 CPI adjusted to 2021. These calculations of the economic value of tree-generated community benefits (or return on investment) are considered to be highly conservative.

The author’s experience suggests the estimated annualised cost for a Jacaranda growing clear of utilities, in quality soil, in a street in suburban Adelaide, is $38 per year over a life cycle of 90 years. An annual return of $540 in value for tree-related services, therefore, represents an annual rate of return of 1400%. This figure greatly exceeds that reported by (Moore 2021), and neither include a component for the many health-related benefits of trees. Suburbs in Adelaide’s inner south contain many Jacaranda street trees of 70 – 90 years of age which are in good health; their low annualised cost reflects their infrequent and typically small maintenance needs (provided they are protected from urban stresses e.g. root damage due to utilities and development impacts).

In considering the difficulties associated with managing trees as financial assets, Brindal and Stringer (2009) noted that ‘Fixing an accurate value is one of the challenges we face’. Variation in estimates of tree costs and benefits such as those described in the previous paragraph will likely be raised in the ongoing case against transitioning to economics-based decision making in regard to trees, perhaps even by some in the insurance, utility and development industries. The fact is, however, that the costs and benefits of all asset types vary. Consider the life-cycle costs of two identical vehicles, one that is driven and maintained well and another which is driven and maintained poorly. The costs and levels of service delivered by these two assets will be vastly different. Roads built on different soils and subject to different traffic loads and volumes wear at different rates, so their life-cycle costs vary markedly. Variability is an everyday reality in asset management. Variability does not make economics-based decisions more difficult in relation to trees than for other asset types. Failing to require that trees be managed as financial assets perpetuates poor investment of and accountability for public funds.

After estimating the gross value of a typical Adelaide street tree at $25,500, Brindal and Stringer (2009) advised how return on investment in trees can be increased. They wrote that ‘Providing a suitable environment for root growth promotes longevity and increases the economic efficiency of trees.’ Providing a suitable environment for root growth to support newly-planted saplings through to their old age is fundamental to achieving a good return on investment in trees. Many examples over the last two decades demonstrate that achieving this is possible while accommodating other essential urban infrastructure and urban land uses. Where soil volume or quality is inadequate or uncertain, wise investment must begin below ground before the trees are planted. Without appropriate investment to investigate and ensure the adequacy of soil at the planting site, tree failures will continue and communities will be robbed of their due returns.

The fundamental needs of trees are well understood; they have been widely published. Most of a tree’s water and nutrient needs are supplied from below ground; water is extracted from the soil and transported initially through roots. Low-strength, highly porous soils which support infiltration of water and diffusion of gasses support root growth and function (Smith, May & Moore 2001; Watson et al. 2014a, 2014b). As well as providing for trees, some urban soils must provide mechanical support for pavements and other engineered structures. Strong, high-density soils typically specified to support engineered structures do not support vital root growth and function (Day & Bassuk 1994; Watson & Kelsey 2006).

A sufficient volume of quality soil is needed to establish and sustain urban trees (Kopinga 1991; Leake & Haege 2016; Sanders & Grabosky 2014), to enable their roots to access sufficient water through the seasons (Clark & Kjelgren 1990; Lindsey & Bassuk 1992; Vico, Revelli & Porporato 2014). Competition for space in cities, between trees, utilities and other infrastructure, adds to the complexity of provision of sufficiently large soil volumes for trees (Meyer-McLean et al. 2021).

In addition to these requirements of competing infrastructure, the fact that tree size and water requirements vary in different climates, seasons, soil types and locations makes the need for timely expert input into design and planning processes very clear. The complexities of these interactions increase the costs of built and natural infrastructure components alike. If the services and benefits delivered by trees are undervalued then decision makers may consider these costs to be too high, but, if appropriate values are recognised, then informed decisions can be made to best serve local communities. Decisions based on fuller understanding of the economics of trees would likely increase the planting of large avenues into the future.

What value would we put on an avenue?

The avenue of London plane (Platanus x hispanica) in Frome Road in Adelaide was planted on Arbor Day in 1902 (Oldrey 2003). It is a South Australian icon. The trees are average examples of the species, they are not exceptional in any way.  Some of the original trees have been replaced; some have been removed and not replaced. The avenue is listed in the National Trust of South Australia’s Register of Significant Trees. The avenue is significant and it is held in trust, but what is it worth?

Towards the end of last millennium the health of some trees in the avenue began to suffer. Gas leakage was detected – a common occurrence in streets with ageing infrastructure. Recognizing the importance of the avenue, the asset’s owners decommissioned the pipe to stop the leakage. They delivered gas to their customers using other pipes. The avenue was worth turning off the leaky pipe for.

Figure 1. London plane (Platanus x hispanica), Frome Road, Adelaide, South Australia, 5 April 2021.

Frome Road’s plane tree avenue is approximately 500 m long. In addition to over 15,500 cars each day the road services two university campuses and what was, until recently, the Royal Adelaide Hospital. The capacities of the utilities which service these major institutions exceed those needed by many country towns. Much of the infrastructure which supplies these needs is located in the root zones of Frome Road’s plane trees.

In the early 1980s one of the utilities companies needed to renew its pipes. Recognizing the importance of the avenue, the asset’s owners employed labourers to manually excavate trenches to install the new pipes. The job progressed over many weeks and digging proceeded around the roots with minimal injury to them. Pipe sections were manually handled into place through the roots and laid in the base of the trench beneath them. Service connections into adjoining properties were similarly laid with manual labour. The labour cost would have been high, but the asset’s managers (or perhaps their regulators) must have believed that the avenue justified the expense.

Frome Road’s utilities and street assets have been installed and some have been renewed since the avenue was planted. We do not know how much extra the additional design, labour, and maintenance costs due to the trees have amounted to during the avenue’s life to date, but it is clear that the avenue has been considered well worth the extra costs. Frome Road’s avenue is appreciated and valued by the community.

The community would hold to account anyone who would devalue or diminish it. Investment in Frome Road’s avenue was and is a ‘no brainer’.

Looking after the avenue by continuing to invest in it, and requiring other asset managers to not harm or diminish it, is a no brainer because its benefit and value are obvious to the local community. This is so because the avenue is highly visible, or rather because it’s above ground parts are highly visible. The avenue is valued because the community enjoys the benefits it provides, because the community invested in it over a century ago. Would the community be prepared to invest as much if the avenue did not yet exist? Would the community be prepared to invest as much to plant a new avenue of this scale elsewhere? Clearly, it is worth it. Planting new avenues is a no brainer, provided that they establish and thrive.

The installation of utilities and the construction of road, drainage, and footpath and bicycle infrastructure around Frome Road’s trees is now history. The trees have undoubtedly increased the cost of these other assets. The community has paid these costs through rates, taxes and utilities bills. Asset owners do not pay these extra costs, their customers do. Utilities customers also pay for and benefit from the trees. With the benefit of hindsight, could there have been a better and cheaper way for the community to sustain the avenue and these other assets? Many successful investments in trees show that there is; many are detailed in the case studies portal on TREENET’s Website (see: https://treenet.org/case_studies/).

Investing successfully in trees

Adelaide Street, Brisbane, Queensland

Nearly one hundred years after the Plane trees were planted in Adelaide’s Frome Road, a local government-led program sought to revitalise precincts in Brisbane by creating pedestrian-friendly avenues. Concept plans for a project in Adelaide Street identified a suitable large tree species, but preliminary investigations revealed serious inadequacies in the root zones. Investing below ground to provide the conditions necessary for project success became a priority, and two traffic lanes were converted from car parking to create shared-use zones for pedestrians and tree roots (Plant 2002). Structural soils were used in continuous tree trenches beneath the parking and pedestrian areas. Twenty one trees were planted in this avenue, they all established rapidly and all have thrived to this day. The ongoing health of the avenue and quality of the streetscape attest to the value of this investment (Figure 2). In creating the tree root zones free of utilities the likelihood of root-infrastructure conflict and associated expenditure is greatly reduced, the health and longevity of the trees are enhanced, and return on investment is maximised. For further detail see: https://treenet.org/case_studies/adelaide-street-boulevard-brisbane-1999/

Figure 2. Leopard Tree (Caesalpinia ferrea) in Adelaide Street, Brisbane, planted 1999, (image: L. Plant)

  

Victoria Avenue, Chatswood, New South Wales

A paper presented at TREENET’s annual symposium in 2011 demonstrated how good investment in trees was possible even when conditions at the planting site were extremely hostile to root growth. Victoria Avenue in the suburb of Chatswood in New South Wales had been converted from a main road to a pedestrian mall in 1989, but its deteriorating amenity led to its upgrading in 2009/10 (Smart 2011). Trees planted during the initial mall construction had performed poorly, and excavation revealed lack of suitable soil as the cause. In place of soil were heavily compacted rubble and high-strength concrete footings which had supported railway sleepers along the former tram track route (Figure 3).

The redundant transport engineering was replaced with quality soil, and load bearing pillars were built to support a pavement suspended above it (Figure 3). A bespoke stormwater infiltration system designed to also increase soil aeration between rain events further enhanced the tree root environment beneath the mall. The mall pavement was designed to accommodate service vehicles without compacting the soil or compromising tree growth. Further detail is available in Smart (2011).

Figure 3. Concrete and compacted rubble materials were removed from the Chatswood site (left) prior to installing quality soil blends in contiguous tree trenches (right)(Images: Arterra, R Smart)

 

Although the trees are still young, in their first decade they have developed sufficient canopy to provide shade to pedestrians and support commercial activity at the site (Figure 4). Incorporating stormwater harvesting into the design has delivered microclimate moderation benefits and reduced drainage needs downstream. The trees’ health and size suggest this wise investment will continue to provide a good return well into the future.

Figure 4. Excellent tree health and vigour a decade after planting indicate return on investment has begun and is set to increase into the future (Image: Arterra, R Smart)

Bank Street, Adelaide, South Australia

Bank Street is a well-used pedestrian shortcut between the Adelaide Railway Station and many of the major commercial and civic precincts of the central business district. It is a narrow street which must also accommodate service vehicles and cars. Street furniture, vehicles and pedestrians didn’t leave much room for trees (Figure 5). Adelaide City Council set about improving pedestrian access and amenity as part of a major upgrade of the street in 2017. Trees were to be planted for shade, but the site’s soil was not suitable for root growth and utilities restricted available space.


Figure 5. Bank Street, Adelaide, prior to tree planting (Image: City of Adelaide) 

Providing Bank Street’s new trees with the soil volume necessary to sustain them into old age required investment. Funds were invested to create ‘tree vaults’ with structural cells to prevent soil compaction by traffic loads on the pavements used at the surface (Figure 6). After four years of growth the health and vigour of Bank Street’s new saplings is apparent (Figure 7). The separation of tree roots and utilities in this manner will prevent or reduce costs due to tree injury or infrastructure damage. The scale of the species when mature will fill the streets without conflicting with nearby buildings, so reduction pruning will not be required and maintenance pruning will be minimal. Further detail on the Bank Street upgrade is available at: https://treenet.org/case_studies/bank-street-redevelopment/. The TREENET website contains many additional case studies which demonstrate successful strategies for establishing trees in highly developed and engineered situations.

Figure 6. Structural cells were used to support pavements in tree root zones in Bank Street, Adelaide.
(image: City of Adelaide)


Figure 7. After four years Bank Street’s saplings are already creating visual impact.

Successful investment in trees and associated assets

The ‘per tree’ cost reported in the case study notes for the Bank Street project was $35,000 (in 2017). This figure represented the total cost of the project divided by the number of trees. It included all the built assets, the pavement, drainage, artwork, signs and street furniture in addition to the tree-related components. The trees, soil and soil containment system was relatively inexpensive in comparison to these other items (Pope, S. 2021, pers com.).

In relation to the Adelaide Street case study, Plant (2002) estimated the cost of the tree-related components at 5% of the $35m budget (in 1999). In summing up the project a few years after construction she wrote:

‘On a per tree basis, tree trench installation is much more costly than conventional street tree planting in a paved footpath. However, when costs of poor tree performance, higher maintenance of both tree and pavement, tree replacement and loss of amenity values are considered, there is little doubt that tree trench installations provide a cost effective alternative. Such installations are often a very small part of overall costs for large scale construction projects. In locations like car parks, where only slight changes are made to the existing construction processes, installation of alternative, tree root friendly pavement subgrades adds little cost.’

The Victoria Avenue mall project’s budget of $3.16 million (in 2009/10)(Smart 2011), met the cost of the total project including the civil engineering components and street furniture. This budget was not excessive for a major infrastructure upgrade of this nature and profile, yet it was sufficient to ameliorate the degraded site and allow the trees’ soil requirements to be integrated into the overall infrastructure design. Site degradation is common on brownfield sites and it typically constrains projects, increases their cost, and contributes to poor tree performance. Degradation frequently results from abandonment of redundant assets, like the buried tram track sleepers and concrete footings in the Victoria Avenue case study, or dumping of toxic spoil such as concrete slurry or demolition rubble as ‘clean fill’ in areas which are to be landscaped.

As with the Bank Street and Adelaide Street examples, the Victoria Avenue project’s smart design will avoid the conflicts and associated costs which typically arise when trees establish near infrastructure which isn’t engineered to accommodate them.

Separation of tree roots and built infrastructure supports long term success, as does separation of tree roots from inappropriate fill, abandoned infrastructure and other waste materials. In most brownfield projects, specifications must include not only what is wanted, but they must also detail what is not permitted in tree root zones.

Although each of these recent case study projects was unique, the approach used to achieve success was similar. In these case studies the arboricultural knowledge needed to ensure the chosen tree species could thrive to old age was accessed initially during the concept design stage, and the project arborists remained involved throughout the process to completion. In each case the required tree root zone volume was achieved. Although the need to ensure the required soil quality and volume was common to the projects, the site’s conditions, tree species, climate and environment made each project unique. Detailed specifications unique to each project were essential.

Although they were at the high end of the spectrum in terms of tree-related planting costs, these projects will deliver savings in the long term. In relation to the Victoria Avenue mall, Smart (2011) stated that the design intent was to create a legacy such that the trees would out-last the project’s built components. By providing the tree root zone with quality soil free of utilities, Smart (2011) anticipated that future streetscape upgrades could readily proceed around the mature, healthy trees without impacting them. Given the longevity of the species and typical frequency of streetscape renewal in high-use precincts, it is likely that several cycles of streetscape renewal will proceed without losing the benefits delivered by the mature trees and without accruing future costs for tree renewal. These future savings will more than offset the marginally higher initial construction cost.

These capital city examples demonstrate that trees can be cost-effectively established and provisioned to deliver long, serviceable life cycles even in the harshest of urban environments. Most urban trees do not need structural soils, tree vaults or structural cells, so their costs will be lower. To reliably achieve results like those demonstrated by these capital city case studies communities need better investment in trees, not more investment.

Investing in trees and avenues for the future

As shown in the capital cities case studies, while it is the above ground parts of trees that are valued by communities, investment must be targeted below ground. In the Adelaide Street case study, the scale of the selected tree species led to the determination that the volume and quality of existing soil was inadequate, so soil provision became a priority. Similarly at Bank Street, the project aimed to install the largest volume of quality soil possible within the site’s infrastructure constraints and then a tree species was selected which could grow to maturity in it.  At Victoria Avenue a reasonable root volume existed but it contained engineered fill and rail base material, so the design focussed on optimising the continuity of tree trenches and selecting species which would thrive in them when refilled with appropriate soil.

The desirable return on investment provided by leafy tree canopies in these examples in highly developed urban environments cannot be achieved without investing in real estate for tree root zones (Figure 8). Achieving this relies on a series of interconnected events which in large development projects can progress over several years. Like interconnected links in a chain, if one of these essential components is weak or missing then the entire chain is compromised or fails.

The initial link in the chain of events (Figure 9) is genuine engagement, including the community and all related professions, to investigate and understand what is required so the concept can be reliably defined and specified. The next link includes concept design, then re-engagement prior to commencing detailed design and costing involving the client, professions and approvals agencies. It is important that each stage of decision making regarding planning, design and documentation is regarded as a necessarily collaborative link in the process that influences the outcome. The product of these early stages is tender documentation including specifications on what will be constructed and how it will be delivered.

 

Figure 8. Investment below ground sustains benefits delivered by trees above ground

Figure 9. The interdependent chain of events that underpin a successful tree outcome.

 

The failure of new tree plantings associated with major and minor developments mostly occur within a few years of planting and commonly result from a primary focus being on the contract rather than on the outcome. This is not a failure of the individuals involved; it represents a failure of current systems. Project delivery typically becomes contractually fragmented in a financial attempt to minimise and control costs within every link of the chain of events. The focus at each stage being on cost rather than outcome (process-driven rather than outcome driven), frequently results in a failure to recognise the unique combination of site-specific variables that underpin successful tree establishment. Further, at the end of the contract period there is typically no effective ‘fit for purpose’ check that can be fairly applied to confirm tree establishment, little or no accountability for poor tree performance, and limited capacity to address poor tree performance.

 

Project participants including planners, urban designers, landscape architects, finance officers, and others from associated professions may be unaware of the influence that their decisions will have on trees into the long term. This seems largely because current systems do not keep them informed about, or accountable for, outcomes. The failure of trees to establish and thrive can result from many causes beyond the contractual obligations, so ongoing accountability is not readily achieved, and tree replacement on three, five and to ten year cycles is not uncommon, particularly in harsh, highly developed and or, disturbed environments. The cumulative cost of replacement plantings is significant and requires funding that has not been budgeted for in project costings.

To avoid poor investment of public funds, it is recommended that the post planting ‘establishment phase’ becomes part of the capital cost of a project. Budgets must be allocated over the 3 to 5 years needed to ensure that the tree is fit for purpose (without needing replacement) and the value of the benefits it provides begins to increase (Figure 10), rather than short-term (typically annual) budgeting in response to tree failure.


Figure 10. Survival rates and tree performance in situ, strongly influence the value of the benefits
that a ‘typical tree’ can provide
(the blue area showing the room for improvement).

 

Tree audits performed and decades of observations made by Arbor Centre, of many thousands of trees in Western Australian housing estates, municipal streets and roadside plantings, have indicative survival rates of less than 50% for tube stock plantings in the landscape within 2 years of planting. For larger container stock, survival rates within 3-5years of planting commonly range between 30% and 70%, and typically reduce to an overall survival rate ranging from 30% to 50 % after ten years (consensus of Local Govt Tree Managers and Supervisors at the 202020 Vision workshop – 2015). These low success ratios also apply to replacement trees, so planting costs can be more than double that of the original project estimate. Another common observation is that the growth of specimens that do establish is commonly compromised or suppressed. A low percentage of original plantings develop to the scale presented in preliminary concept drawings, planning application documentation and promotional material.

Size matters (Figure 11). The extent of benefits delivered by trees is typically proportional to canopy cover; the larger the canopy cover the larger the benefits. A typical healthy, mature Tuart (Eucalyptus gomphocephala) growing in Perth, Western Australia, has a canopy cover area comparable to four or five Western Australian Peppermints (Agonis flexuosa), so return on investment will be greater for the Tuart. Considering tree performance relative to size, and tree survival rates, brings the reality of investing in real estate for trees below ground into focus.

 

Real estate has value whether it is commercial or residential private property or allocated to utilities or tree roots in the public ‘commons’ which is the street. The soil volume needed to sustain a tree has value and cost. Without access to adequate root volume, benefits from trees will always be poor. Investing in trees costs relatively little in comparison with other street assets yet it delivers an enduring legacy – the underground real estate which can sustain successive generations of trees.

Figure 11. It takes the planting of numerous small tree species to provide the equivalent canopy cover of one large tree species. Large tree species also need more space for roots to grow to reach their potential.

 

Investment in trees requires provision of materials and practices that are easily quantified and budgeted for, including adequate soil volume, suitable soil and surface treatments, and designs and measures to protect built assets from tree roots and vice versa. If applied correctly, Australian Standard AS 4970 Protection of trees on development sites can assist the design of protection for all assets in proximity to an existing tree – the built assets and the tree! Aspects of the Australian Standard can also be applied to guide the design of spaces for new tree plantings. Investing in trees to enhance the above ground environment is well advanced, delivering on this investment requires investment below ground.

Conclusion

Improving urban tree performance by providing their fundamental water and nutrient requirements through the soil, and thus supporting their growth to maturity and old age, will increase return on investment (Figure 12). Investing in quality soil volume and separation from utilities and other built infrastructure does not require new money, but rather the repurposing and re-timing of resources which are typically made available within existing budgets. Recognising this is essential to increasing return on community investment in trees. Funding successful tree establishment and eliminating expenditure on maintaining and replacing poorly performing trees will increase return on community investment in trees. Designing tree planting sites to simultaneously prevent built infrastructure damage and tree root injury will increase community return on investment in trees.

Valuing and investing in construction below ground to sustain urban trees is making provision for generations of trees. This visionary approach has been demonstrated by the case studies presented in this paper and by many others, yet it still remains relatively novel. Widespread application of this approach will improve urban canopy and related benefits and result in long-term financial benefit to communities.

 

Figure 12. The return on investment from allocating a portion of the Public Realm real estate for trees for the purpose of managing where roots grow and to provide canopy cover, is a ‘No-Brainer’

Transitioning communities and industry toward effective urban forestry through targeted investment below ground will be a piecewise process with each new project which establishes below-ground real estate for trees for future generations. Progress toward this goal will be supported by effective allocation and regulation of real estate in the public commons which is the street. Built infrastructure takes up a lot of space in the commons, often to the exclusion of all else. Returning nature generally, and trees in particular, to cities is known to be fundamental to human health and wellbeing, and this requires space.

Policy guidance and regulatory controls which enable space for urban natural capital, and for trees in particular, are needed as part of this transition. Understanding of the value of urban trees is increasing, but lack of accepted economic valuations for the services they deliver hampers effective decision making regarding allocation of space in the street commons. Reallocating space in the street commons to best serve communities requires that current allocations, such as separations between utilities as specified in historically adopted standards, be reviewed. Large separation from utilities takes up a lot of space in the street commons; they reduce management costs for utilities owners but fail to consider the much more substantial value of community benefits lost due to poor tree canopy coverage.

New or additional money is not needed to deliver effective urban forests, current allocations are generally sufficient although too frequently they are poorly targeted and timed. As part of major capital urban development projects, the cost to establish trees effectively is small, returns are great, and returns can be enduring. While tree costs can be recorded with precision, the values of the many services they provide need to be reliably quantified to balance decision making in relation to investment in trees. Regulatory support for allocation of space for trees, as utilities and other built infrastructure is installed or renewed, will increase opportunities for communities to invest wisely in their urban forests. Communities deserve opportunities to invest wisely in their street commons in ways which guarantee successful urban tree provision, avoid damage to structures and utilities, eliminate injury to tree roots, and which achieve higher returns on smaller investments. Investing appropriately in trees really is a ‘no-brainer’.

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