Keith Sacre of Barcham Trees considers the complex and often-overlooked role that urban trees have to play in the public good.

IT is interesting when events past and present coalesce, combining to create new or revised perspectives.

Back in December 2018, Johan Ostberg – who runs his own consultancy service in Malmo, Sweden, and who recently joined forces with Cecil Konijnendijk to form the Nature Based Solutions Institute in Barcelona – presented a one-day seminar at Barcham Trees titled ‘The Creative Use of Tree Inventories in Urban Forest Management’.

The day began with a discussion about what data should be included in an inventory and, more importantly, why. Site information, planting information, works programmes and other attributes such as date and time of the survey were suggested and discussed by delegates. One key question emerged from these discussions: what is the purpose of the inventory? Johan returned to this question throughout the day, stressing the effective use of tree inventories is not related to the complexity of data collected but more to collecting the data which will be useful in achieving aims and objectives identified prior to the inventory being built in the first place. First identify what is to be achieved and how the information gathered will be used.

Forestry Journal: Local authority trees in urban situations are part of the public estate.Local authority trees in urban situations are part of the public estate.

Johan provided several examples of this. The most significant was the example of Stockholm. The need was to provide, for city politicians, a view of the condition of Stockholm’s significant trees. This was achieved by a morning’s drive around the city visually recording how the trees looked. No hard data was collected, but the perspective gained was enough to fuel investment and drive the planting of, to date, over 4,000 trees in streets and public spaces across the city, using the structural soil method developed by Bjorn Embren and his team. The point being made was that it is not the complexity of the data collected, but what is achieved through its collection, which is really important.

A model was offered, placing purpose in the middle with a continuous loop of analysis, goal-setting, actions and review around the outside.

Johan then went on to discuss some of the more creative ways inventories can be used, including i-tree conversion. He spoke about urban tree diversity and how tree inventories can be used to understand what tree diversity within a population means and the implications of not achieving such diversity. He suggested inventories can be used to establish locally relevant species diversity goals and determine which species and cultivars are best suited to any given locality.

So, onto the England Tree Strategy Consultation published by DEFRA in June 2020. The consultation will have closed by the time this article is published. I know there have been many responses, some critical, describing the document as ‘not fit for purpose’. Lord Zac Goldsmith, the Minister of State for the Environment, was written to personally by the Arboricultural Association, supported by many of the leading representative bodies in the UK, expressing concern over the contents and presentation of the consultation. It is beyond the scope of this article to elaborate further, but many organisations, including the Arboricultural Association and the Trees and Design Action Group, have published their responses on their respective websites.

Forestry Journal: What is the value of these trees in Belfast?What is the value of these trees in Belfast?

One of the more serious and often repeated criticisms was the failure of the consultation document to give due consideration to the importance of urban trees.

The document states that “woodlands provide public goods and require long-term investment. The public forest estate, of over 253,000 hectares in England, is managed by Forestry England for the benefit of the nation”. This is undeniable and the public good delivered beyond question, but what is missing is the urban trees owned and managed by local authorities across England. Surely these trees are also part of the public forest estate but there is no attempt to quantify the land they occupy, the value they hold as an asset or the valuable ecosystem services they deliver in places where the vast percentage of the population live, work and play.

Over the years, through my work with Barcham Trees, I have spent a great deal of time with local authority tree officers and developed a great respect for the work they do, arguing they are ‘true custodians of the public urban forest estate’. More often than not, conversations with tree officers focus on inadequate resources and the stress of working in situations where the asset they manage on behalf of their respective communities is not recognised.

Forestry Journal:  The asset value of urban trees is often overlooked. The asset value of urban trees is often overlooked.

So what is that asset worth in England? Sadly, the question cannot be answered because the information is not available. This brings me back to the seminar at Barcham Trees in December 2018 and comments from Johan Ostberg. Speaking of work in the UK, he said: “Developments in i-tree Eco have facilitated the use of local authority and other tree inventories to produce i-tree studies with all the features of conventional sample surveys included without the need of data collection in the field. Several local authorities in the UK have now used their inventories, working with Treeconomics and Kenton Rogers, to produce such studies.

“These include the London Boroughs of Ealing and Camden and the ten authorities comprising the Greater Manchester area. Others, such as Newcastle City Council, are working towards converting their inventories to produce i-tree data and reports.”

Since 2018, things have moved forward and other authorities have taken advantage of the facility within i-tree to convert local authority and other tree inventories into reports which articulate the value of the assets being managed by local authority tree managers and the value of the trees under their stewardship.

A recent study of the publicly owned trees in the London Borough of Southwark has demonstrated their value. The study, using i-tree Eco and carried out by urban forest specialists Treeconomics, discovered the trees owned and managed by the borough would have a replacement cost of over £165 million.

In addition, using Southwark’s own tree inventory, Treeconomics was able to calculate the trees managed by the council remove over 21 tonnes of air-borne pollutants, valued at over £135,000 each year, and store over 57,000 tonnes of carbon, valued at £14,070 a year.  They also divert over 35,000 cubic metres of storm water away from the local sewers each year, which is worth an estimated £21,183 in avoided storm water treatment costs.

Forestry Journal: Stewardship through the planting of young trees.Stewardship through the planting of young trees.

The street trees of the London Borough of Brent are the subject of another study completed recently. It states the replacement cost of Brent’s street trees would be over £29 million with a CAVAT amenity valuation of over £414 million. The report states the 24,000-plus trees (representing 162 species) considered in the study remove four tonnes of pollution each year at a value of over £300,000, sequestering nearly 10,000 tonnes of carbon annually at a value of over £60,000, and facilitating over 8000 m3₃of avoided storm water run-off at a value of over £4,500 annually. The trees also store over 9,000 tonnes of carbon at a value of just under £2.5 million.

There are many more case studies of inventory data being converted into reports of the kind illustrated above. It is beyond the scope of this article to offer further examples other than to say the figures emerging are all similar in the asset value they suggest and the value of the ecosystem services being delivered. A full list of the reports carried out and the results obtained can be found on the Treeconomics website.

These reports make imaginative use of operational inventories, quantify both ecosystem services/public goods in volumetric and monetary terms, place a value on the asset being managed and, if standardised across England, provide the information sadly missing from the DEFRA consultation document.

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