Custodians of the public urban forest estate

Kenton Rogers and Keith Sacre, Treeconomics

It is a widely recognised and an undisputed fact that local authorities across the UK own and are responsible for many of our urban trees. Studies like Trees in Towns 2 and various i-Tree Eco reports have highlighted that the trees owned and managed by local authorities constitute approximately 30–40% of the urban forest in any given area.

This publicly owned estate is generally managed by local authority tree officers on behalf of the communities their authorities serve. Where they are in place, tree officers are essentially the custodians of our public urban forest. However, their position within local authority (LA) hierarchy is varied and, as each LA is made up differently, an integrated system of overlapping departments and functions, the resource budget available is equally varied.

Tree officers are also subject to numerous other factors which affect service delivery: things such as the support and focus of members, the planning department and strength of planning enforcement, and the willingness of legal to take offences to court or issue enforcement notices. Across the country there is disparity, but by and large, the responsibility for the sustainable development of the publicly owned urban forest estate rests with tree officers.

The range of work undertaken also varies from the statutory protection of trees and risk management through to planning, highways and housing, and the day-to-day proactive management of actual tree stock from planting through to removal. Often, trees are only a part of a wider picture and other issues may lead to decisions which go contrary to what a tree officer has planned. Indeed, they may not even be consulted on decisions that directly impact the trees they manage. There are also many other organisations and individuals who contribute to the management of the public urban forest estate but invariably, on-the-ground decisions and recommendations rest with the tree officer.

It is undeniable that trees are a valuable and appreciating asset, providing a range of public goods. Given that only a handful of these benefits are currently measurable and even fewer are quantifiable in terms of a cash value, any figure put on these services to society is likely to be a gross underestimate.

So, what could be the value of the public goods delivered by the UK’s publicly owned urban forest? And what might that estate be worth as an asset? Sadly, these national figures are unknown, although i-Tree Eco studies carried out by Treeconomics and others have provided glimpses as to the value of the public goods delivered by the trees managed by tree officers in specific areas.

Using i-Tree Eco to quickly run and process existing tree inventories has enabled some tree officers to provide illustrative figures of both the structure and value of the public tree asset they manage on behalf of their communities.

5 studies, 230,000 trees, £1.7 million annual benefits

Looking at five such studies carried out by Treeconomics in London, it is possible to begin to articulate the glimpses referred to above. The studies will remain unnamed for the purpose of this article, but it emerged that the five authorities and their tree officers were managing a total of at least 230,000 individual trees. Were these trees to be lost, it would cost over £347 million to replace them all.

The carbon stored in those trees had a value of over £27 million at today’s non-traded social cost figures provided by the UK government. Annually, the trees sequestered carbon with a value of £500,000, absorbed over 40 tonnes of pollution and provided over £80,000 of benefits in terms of avoided storm water run-off. The total annual benefits and public goods provided by the 230,000 trees amounted to over £1.7 million. That is approximately £8 of public good delivered annually by each tree.

What might the asset value of all the publicly owned trees managed by tree officers in London actually be? For the purposes of this article, it is not unreasonable to conservatively extrapolate further with some rough calculations.

London-wide estimates

Using the five case studies as a baseline, the average number of trees managed is 43,000. Extended to the whole of London, this would indicate that the tree officers of London are managing around 1.5 million individual trees. If we take £8 as the figure representing the annual public goods delivered by publicly owned trees, then the annual benefits and public goods delivered amount to something in the region of £12 million per year.

This is a conservative estimate, as the value of public goods such as health and well-being are not yet calculated by i-Tree Eco. However, there is overwhelming and ever-growing evidence that trees and green-space deliver massive benefits which have yet to be fully realised.

It is obviously dangerous to speculate too far with such crude figures. For example, a better estimate would be achieved by relating average benefits to tree canopy cover and extrapolating by that, rather than multiplying our average from the five studies to the 33 boroughs. However, the exercise does serve our immediate purpose: to highlight the valuable and critical work that tree officers do.

It is impossible with any degree of accuracy or credibility to extrapolate these rough calculations as they stand to encompass the UK in its entirety. But it becomes clear that the resource managed by tree officers as custodians of the public estate is considerable and that their role as asset managers and delivery agents for a range of public goods is significantly undervalued, as is the profession they are part of. Tree officers across London are managing an asset with a monetary value of well over £7 billion that, in addition, delivers (at a very conservative estimate) £12 million of benefits and public goods each year.

Imagine if, through a new nationwide study (a ‘Trees in Towns 3’ perhaps), accurate and precise figures were available from across the UK for the public goods provided by the urban forest. Ideally, such an exercise would be carried out by a central government agency such as Forest Research, to provide a UK-wide baseline or benchmark.

Using i-Tree Eco inventory analysis at the local level could then also provide not just the facts and figures, but an advocacy tool to demonstrate good value for money and to enhance resourcing for management and maintenance of trees, something which the publicly owned tree estate in our urban areas is crying out for.

And although the authors appreciate that the ‘true’ value of trees may never be obtainable, we should hope to reach a point where the value of the role tree officers play in our society will be better recognised and endorsed nationally too, with funding that takes account of the huge appreciating asset they are custodians of.


This article was taken from Issue 193 Summer 2021 of the ARB Magazine, which is available to view free to members by simply logging in to the website and viewing your profile area.

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