The 25-year environmental plan has put the many benefits provided by trees at the heart of environment policy, but translating this into meaningful action requires hard figures to justify the expenditure.
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Torquay - image: Averoxus (GFDL 1.2)
Work also remains to be done on agreeing how to arrive at such figures.
The Government-appointed Natural Capital Committee (NCC), which was the driving force in bringing about the 25-year plan, says in its latest annual report that "an urgent priority for the Government now should be to determine what 'outcome metrics' to use to record progress towards the 25-year goals".
It adds that 2018 will be "a crucial year in determining whether the ONS (Office for National Statistics) and Defra will be able to meet the 2020 deadline for producing a comprehensive set of national natural capital accounts".
Barrell Tree Consultancy managing director Jeremy Barrell says that for trees
"there are many approaches to valuation and none are perfect".
He continues:
"Our best bet is likely to be with i-Tree because it is peer-reviewed and research-based, important credibility markers. However, ecological and health values, which are probably the most important, are still not yet factored into the process."
The Tree Design Action Group, of which Barrell is a trustee, is collaborating with the Arboricultural Association, Forest Research and consultancy Treeconomics to address these issues, along with i-Tree partners in the USA.
But Barrell believes support from Government is now needed to "speed it up", adding:
"The metrics must convert benefits to a currency equivalent, giving a combination of costs saved, costs averted, and benefits accrued, which are complex matters.
"The Government must support the development of nationally agreed approaches and then embed them into local government protocols. Arboriculture and forestry cannot do this alone."
Treeconomics co-founder Kenton Rogers says the NCC
"is doing a great job in raising this up the political agenda"
and as a result:
"It’s all heading in the right direction, though there is always work to be done."
He points out that according to the European Environment Agency’s Common International Classification of Ecosystem Services
"there are about 30 metrics that relate to trees, half of those to urban trees, and maybe seven relate to an effect we can quantify, of which there are three or four we can monetise".
He adds:
"You can measure the impact that trees have on the urban heat island effect, but no one has put a value on that. There are also their contributions to health and well-being, which Dr Kathleen Wolf [of the University of Washington] is working to put values on."
Key goal
Greater biodiversity is also one of the key goals of the 25-year plan, but Rogers points out:
"People say it would be great to put a figure on it, but there's the question of what it is and where it begins and ends."
But he adds that carbon sequestration "is a bit of a red herring", at least as far as urban trees are concerned. The oldest i-Tree survey, for Torbay near Treeconomics’ base at the University of Exeter, found that the area’s trees took a year to store the mass of carbon produced locally in just one day.
However, the Torbay study has proved its value in other ways, he says.
"They can now very quickly get figures to cabinet members — for example, on how much of the canopy is made up of ash and how much might be lost, which helped access £25,000 extra for tree planting."
Rogers adds:
"At Treeconomics we use other tools too, but i-Tree is open-source so the end user can continue to use it. For Highways England we wanted to capture values for amenity and soil as well, but the tools we used to plug those gaps were a bit more obscure and less accessible. The aim is for these to be put into i-Tree eventually."
The number of tree managers using the i-Tree suite continues to double each year, though this "will eventually peak", says Rogers. As to whether UK managers might become overly reliant on the US-based i-Tree consortium, he believes it is in safe hands.
"They have recently had a $10m investment. It’s a collaboration between a private tree care company, Davey Tree, and the Arbor Day Foundation, one of the largest US tree charities, as well as the US Forest Service,"
He says.
"Eventually any model will run its course and the information will go into something more streamlined."
Natural Capital Account
Meanwhile, on a larger scale, Forest Enterprise England (FEE) has for the past two years produced its own "Natural Capital Account", which valued England’s public forests in 2016-17 at £22.5bn — nearly 99% of this coming from "intangible benefits delivered to society" rather than income.
This figure dwarfs the £1.4bn value put on the land, property and "biological assets" — mostly trees — in its regular annual report, it points out.
Using NCC guidance, this exercise has yielded a value of £7.7bn for "Carbon" — not surprising given the 250,000ha extent of its estate — but values "Recreation and public access" twice as high, at £15.1bn.
But FEE echoes Barrell and Rogers in admitting:
"The full natural capital value is much higher because several of the benefits to society, such as flood alleviation and air quality, can’t yet be calculated."
In this it says it
"is dependent on other, more specialist bodies developing their research and methodologies to a point where we can adopt them".
Horticulture Week website