What’s a tree worth?
Wanton destruction of the Sycamore Gap tree in 2023 sparked world outrage, eased perhaps only partly by the jail sentences handed down to the two men who did the dreadful deed.
Wiping out a 150-year history in a couple of minutes with a chainsaw focused minds on the severity of the penalty for their actions, and the judge’s verdict no doubt reflected due consideration of many factors impacting the ‘value’ of the tree – societal, amenity worth, environmental and financial.
Most of us would hail the worth of trees in urban and rural realms when asked our views on the planet’s largest living organisms, and each of us may well hold a cherished place for them, for a multitude of reasons - most, if not all, subjective.
Increasingly though, as radical planning reforms beset Britain, councils and consultants alike have sought to cost out the countless benefits trees convey to humans and other lifeforms.
The London Tree Officers Association (LTOA) largely pioneered capital asset tree valuation – Chris Neilan introducing the CAVAT system, along with LTOA colleagues, in 2008.
The Capital Asset Value for Amenity Trees is an approach “based on UK law and an understanding of amenity as the sum of public benefits – primarily, but not exclusively, visual benefits. It values a tree based on the replacement cost approach, extrapolated and depreciated to reflect key criteria.”
CAVAT Full Method and Quick Method together extend the ability “to protect and enhance the public tree stock, to establish that trees are valuable public assets, and to manage them as essential natural capital.”
The method comprises ten assessment criteria which cover:
- Base value
- Community Tree Index (CTI)
- Visibility
- Attributes
These four criteria deliver a Location Value
- Primary structure completeness
- Primary structure quality
- Crown completeness
- Canopy completeness
- Crown and canopy quality
These five criteria deliver a Functional Value
The tenth criterion assesses life expectancy, and when taken together with the other nine, produces the CAVAT Value. It’s important to note that, despite the extent and rigour of the system, final valuation after applying it can be open to dispute.
It’s important to note that, despite the extent and rigour of the system, final valuation after applying it can be open to dispute.
The Sycamore Gap tree is a case in point, where defence lawyers contested the tree’s reportedly CAVAT valuation of £600,000, which was revised downwards to £458,000, as reported on Google.
Living with trees
Simon Richmond has worked in the arb and forestry sectors all his life, from running a contractor business to his latest role as senior technical adviser to The Arboricultural Association, amassing nearly twenty years working for the member body.
“The term ‘amenity’ is used very broadly when considering trees,” he says, “it excludes forestry and woodland specimens, whereas those in our urban areas – streets, parks and gardens, on golf courses, sportsgrounds and other green spaces would fall under this category.”
System revision
CAVAT criteria revisions were necessary as part of an evolving system. “The method did not always take account of the tree pruning cycle for example, which affects canopy variation and visibility,” Simon adds.
Trees’ value needs to be recorded according to circumstances, he explains. “A local authority tasked with maintaining 50,000 trees will give key consideration to health and safety factors that potentially affect the public. That’s a separate task not necessarily linked with CAVAT.”
The method is usually applied “for specific reasons”, Simon continues – “for example, if work has been done on a tree or it has been removed and it’s in a conservation area or has a Tree Preservation Order on it, a valuation would be required as part of a possible prosecution.”
Subjective assessment
But any valuation is subjective, he stresses. “the CAVAT methodology provides a base value, taking into account factors such as stem diameter and community tree index, which is then amended by later steps under the 10-point assessment, such as quality of structure and canopy size. The methodology is transparent, but judgements at individual steps may vary from one assessor to another.”
© Robert Bye
Startlingly, “apart from the planning law legislation and felling licences, no protection exists for the vast majority of trees in the UK, nor any legal requirement for due diligence”, Simon reveals.
“In fact, we are quite behind on this, perhaps because we came into it earlier than countries such as Italy, the Czech Republic, Poland and Portugal, all of which have introduced different but more comprehensive protection and legal coverage than we have in the UK.”
Trees as eco-systems
Evolving too is the emphasis placed on the value of trees to the wider environment, Simon explains. “A tree is never just a tree but an eco-system, within an ecosystem. CAVAT is mostly applied in urban settings, where specimens often don’t reach their full size. We know that the biodiversity a tree supports increases exponentially with age but it is harder to achieve this in an urban context.”
Paradoxically, the proliferation of micro-habitats increasing biodiversity can also be associated with features that affect health and safety aspects, particularly as trees age and attain ancient, heritage or veteran status, so there’s a balance to be struck”, says Simon, “wherever possible, trees should be allowed to fulfil their development potential, and the issue of biodiversity should rise in importance within CAVAT valuations.”
© Benjamin Elliott
Tree safety risk
When considering the safety risk from trees, the National Tree Safety Group (NTSG) reveals data of the impact of trees on human mortality. “Over the last 25 years, on average four or five people a year are killed by encounters with trees – either struck by falling trees, parts of trees or by driving into them if they’ve fallen across roads in extreme weather, for example.”
“Compare that with figures for road traffic accidents, with, on average, four or five people killed every day - but we don’t usually hear about these, except in local news,”
Survival rates
“Risk of death from falling trees is incredibly low”, but we still must pay attention to that risk and manage trees to minimise it, he adds.
Arguably, the most recent publicly prominent element of tree value has been the issue of Biodiversity Net Gain (BNG). “Developers are required to increase biodiversity by 10% above a base line,” Simon says, “which is calculated by evaluating a site prior to applying for planning permission.”
“If developers are unable to maintain or plant on site the required trees/biodiversity necessary to deliver enough BNG, they can plant them in another place. BNG is then supposed to be monitored for thirty years to ensure compliance.”
This raises a further issue about tree value however, as figures reveal that only one in every four trees/saplings planted survive – emphasising the importance of managing and maintaining them in their early years.
Britain has pledged to plant many millions of trees in coming years – a controversial strategy, Simon believes. “Today’s emphasis is on how many trees we can plant, but to reach establishment, more resources are needed over a longer period. Many trees may not survive because of poor choice of species or lack of water. This isn’t a quick fix solution.”
“Trees are at more risk than ever before, but not because of available land area for development – many threats to trees and green space are more driven by developers needing to maximise profits; they may pay lip service to trees’ livelihood but there is no requirement for due diligence in assessing and maintaining them.”
Political leverage
Simon commented: “A baseline of information gives local authorities a tool to convince politicians of the worth of the tree population.”
The state of finances of many local councils across Britain may already be impacting the political leveraging they can wield though, as Simon says. “Politicians are currently moving away from greening the environment and that will be at a cost to managing it, but local authorities have tree officers, who can sometimes access funds to support planting schemes and policies. There are always solutions.”
Recognising the important role tree officers have played in advancing the arboricultural cause, he concludes: “Without the Ĺondon Tree Officers Association, CAVAT would not be what it is. The method is constantly evolving to reflect society’s attitude to and technical understanding of the value of trees.”
James Gormley, Wyevale Nurseries’ Key Account Manager
Valuing our green guardians
How one lifelong tree lover views the development of more analytical systems of assessing their financial worth, picking his system of choice.
“In the bustling urban landscape, where concrete often overshadows canopy, a quiet revolution is unfolding,” states James Gormley, grower Wyevale Nurseries’ key account manager, who helps local authorities, landscape architects and contractors with technical tree sales. “It’s one that places monetary value on the towering sentinels of our parks and pavements.”
CAVAT is at the heart of the movement, he adds – “a method developed to quantify the public worth of trees and reinforce their place as vital assets in civic life.”
“Originally created to aid local authorities and land managers, CAVAT assesses trees based on size, health, visibility and accessibility.”
“Its goal is to assign a financial value that reflects their contribution to public welfare, from shade and air purification to psychological wellbeing and biodiversity.”
By treating trees not merely as decorative features but as infrastructure investments, CAVAT empowers local authorities, land managers and communities to make better-informed decisions about maintenance, planning applications and compensation in cases of damage or removal, James explains.
Other players
While CAVAT is widely used, it’s not the only player in the tree valuation arena, James continues. “The Helliwell system, also British in origin, scores trees based on aesthetic qualities.”
“Across the Atlantic, i-Tree estimates environmental and economic benefits, such as reduced energy costs and cleaner air. Systems such as TEMPO, popular for Tree Preservation Order (TPO) assessments, and international methods such as TFT, Thyer and STEM, offer varied approaches based on ecological, cultural or financial importance.”
Such models provide local governments and landowners with a toolkit for tailoring tree evaluations to their unique needs and values, James says.
“However, in the UK, it’s CAVAT that dominates and is my preferred tree valuation method.”
Champion and Heritage trees: iconic but vulnerable
Despite their grandeur and historical significance, Champion and Heritage trees in the UK are not automatically protected, Jamie reports.
“Their survival often depends on whether they fall under TPOs, are located in conservation areas or sit within protected sites.”
“CAVAT has proven invaluable in these cases, supplying robust monetary evidence to support preservation, influence planning decisions and push for compensation following loss.”
However, while CAVAT amplifies their worth, it isn’t a shield in itself. “Legal safeguards, particularly the TPO system, have come under scrutiny.”
“Reports indicate patchy enforcement and limited council resources, making it difficult to prevent unauthorised work on protected trees – even when strong public opposition exists. Though illegal actions can lead to penalties, in practice, repercussions are rare.”
Strengthening the roots of protection
Improving TPO effectiveness “calls for more rigorous enforcement, better documentation and a boost in funding for local planning authorities”, James maintains.
Integrating systems such as CAVAT into tree appraisal and urban planning “could help shift policy attitudes and encourage greater investment in green infrastructure.”
“Ultimately, valuing trees monetarily may feel counter-intuitive to their natural beauty, but it’s a pragmatic tool for protecting them in a world governed by spreadsheets and development plans.”
“As we strive for healthier cities and communities, recognising trees as both ecological powerhouses and economic assets might just be the key to ensuring they continue to thrive.”
Technology and assessment preserve a lasting place for trees
Environmental consultant Adam Hollis works largely in London and across the South, offering clients arboricultural advice, including valuation and appraisal, risk assessment, landscape design and planting.
Since 2009, Adam, under his corporate identity, Landmark Trees, has helped Eton College design and implement a risk management strategy for its extensive school grounds and wider rural estate.
“Including the sports fields, there are 1,000 trees in the immediate grounds alone, with numbers running into the tens of thousands for the total estate,” he explains. “A diverse network of thoroughfares from the High Street and Half Mile Track to the River Thames runs beneath the crowns of large, mature trees.”
Before even undertaking the surveys, Adam worked with the college to identify higher-risk areas within the site for priority surveying. “Only then were the first 1,000 trees surveyed to record relevant qualitative data to assess their condition and extent of risk liability.”
Survey type varied by area usage from general walkover studies to individual tree inspections, and where indicated, further investigation with diagnostic equipment (PICUS sonic tomogram or Resistograph microdrill). “Powerful tools that allow us to look further ‘inside’ the tree, guided by our initial visual assessment.”
Providing the college with a quantified tree risk assessment (a composite ranking of target area, size of significant part and risk of failure) has allowed the estates management team to initiate a defensible strategy, he says, “prioritising tasks according to ranking, and so discharge its liability to students and members of the public.”
“The college now has two fully trained inspectors in its grounds staff to monitor the continuing health of trees, using the inventories created, in dialogue with our own consultants.”
“The result has been a move away from a reactive service to informed resource management, working together to make the best use of in-house capability and external consultancy.”