Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of the Arboricultural Association.

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Managing trees in a climate crisis

Author:  Sarah Dodd
Last Updated:  09/12/2022

Managing trees in a climate crisis

Sarah Dodd

In case anyone was in any doubt, the temperatures we experienced in the UK this summer confirmed that the impact of climate change is here and now. Hot, dry summers and mild, wet winters with higher frequency of severe storms throw up an increasing level of risk around the management of trees.

There is a difficult balancing act to carry out here which involves tree owners needing to balance risk and reward: managing trees so that the risk of them causing damage to people or property is kept low, whilst also retaining as many trees as possible for their significant environmental benefits.

Summer subsidence risk

The risk involved in our summers becoming hotter and drier really affects tree owners in areas where tree-root-induced subsidence is common.

Tree-root subsidence occurs where trees extract moisture from shrinkable soils beneath property foundations causing the soil to reduce in volume, the foundations to move and the property to crack. In the heatwave of summer 2022 we were all aware of the lack of moisture in the ground. Our green spaces were parched and turned yellow. Water shortages caused drought conditions and hosepipe bans were implemented across the UK. This extreme lack of moisture has led to a significant increase in domestic subsidence claims with home insurers reporting between a 200% and 400% increase in subsidence claim numbers in July and August.

What will this mean for local authority tree owners?

In parts of the UK, local authorities will be well versed in the process that they face where an allegation is made that one of their trees has caused subsidence damage. More often than not, site investigation evidence will be provided to the authority along with a request for ‘mitigation’ work to be carried out, i.e. for the tree to be removed to stop ongoing damage to the property. However, whilst it cannot be denied that there are situations in which the wrong tree is in the wrong place and needs to be removed, there are a significant number of cases where the tree really should stay in place.

Things which should be considered by the local authority tree owner include:

1. Causation – Has a reasonable level of evidence been provided which proves that the tree in question is the cause of the subsidence damage? Often there can be multiple factors at play. The Court will ask the ‘but for’ test, i.e., ‘but for the [type] tree would the property have suffered damage?’. If this test cannot be satisfied then the causal link isn’t proven.

2. Value of damage vs value of tree – A balancing act is required to weigh the value of the damage to the property and the value of the tree. This is not an easy calculation to carry out. The value of the damage will depend upon how much the damage is able to progress and how quickly the movement is stopped and repair works carried out. The value of the tree, again, isn’t easy to calculate. There is more than one tree valuation system. CAVAT is the system which has been in use widely since around 2008; however, the Helliwell system is also used and the likes of i-Tree and Treezilla are providing alternatives which value a wider range of the benefits of a tree and include the value of ecosystem services and biodiversity.

3. Hotspot areas – Local authorities should keep an eye on claim location to be able to identify hotspot areas where subsidence risk is especially high. This could be due to the number and type of trees growing and the age and proximity of properties, and of course the geology in the locality. In a time of limited tree maintenance budgets, applying one maintenance regime across a borough where risk differs is arguably not the best use of resources. Risk mapping and allocating tree maintenance budgets to prioritise high-risk areas is sensible. This approach could avoid trees in those areas growing to a size such that they pose a risk of damage to properties and therefore could limit claims occurring and the inevitable request for tree removal.

4. Degree of damage and repair options – Seeking tree removal is often the quickest way to resolve a subsidence claim for a homeowner and is favoured by insurance companies who will be looking for a speedy resolution for their customers. However, homeowners have perhaps become increasingly quick to bring insurance claims in situations where damage is minor and perhaps wouldn’t have been subject to an insurance claim in the past but would simply have been tolerated or repaired as part of a householder’s own home maintenance and DIY. How much damage is being caused to the property and what are alternative repair options to allow the property to be fixed in the continuing presence of the tree?

5. Environmental considerations – When focusing on environmental considerations, it has to be appreciated that trees are far more than just an object that can cause damage. Trees play an important role in keeping temperatures in urban areas down, can reduce pollution, attenuate flooding, improve mental and physical health, improve prosperity in an area, provide a habitat for wildlife and contribute to biodiversity. These additional benefits mean that subsidence claims in certain areas and involving certain trees can attract a lot of attention, with local residents becoming involved in claims despite being neither the owner of the damaged property nor the owner of the tree. The law in this area is increasingly supporting this involvement with the Environment Act 2021 bringing about both the ‘duty to consult’ (Defra guidance not yet released) and the requirement for a biodiversity net gain (in planning situations). As such there are an increasing number of stakeholders involved in decisions about tree removal. Being seen to get that decision wrong could lead to a risk of negative publicity, increased cost, complaints to the new Office of Environmental Protection, judicial review litigation or even climate-based litigation in the future.

6. Foreseeability – When a claim becomes one where a reimbursement of the cost of repair works is being sought from the tree owner, whether a claim will win or lose at Court is a question of far more than whether the tree caused the damage. Foreseeability is a key issue in these cases against local authority tree owners. Could the local authority have reasonably foreseen, before the damage occurred, that the tree was at risk of causing damage to the property? Answering this question and assessing the risk of being able to defend a claim or not requires specialist input based on the facts of each particular situation.

7. Looking forward – Managing risk has been based on past patterns to allow local authorities to spend their budgets managing what they know to be a risk. However, data scientists are showing us that the pattern of risk is changing due to climate change. Tree-root subsidence has historically been a risk well known in London with its clay soil, drier summer weather and dense, older housing stock. However, risk maps are showing that the number of properties at risk of subsidence damage in the coming decades will increase significantly and will be in areas of the UK not traditionally affected. So local authorities who don’t currently perhaps manage their tree stock with subsidence in mind will reach a tipping point where this will have to be done.

8. Reuse and recycle – There are situations in which trees cannot be preserved and tree removal has to go ahead. Appropriate and mindful disposal of trees should always be considered. Can the wood remain close-by and provide a habitat for beetles and fungi? Is there a resale value for the wood; can it be repurposed by a local craftsperson and its value returned to the local economy? Can the carbon stored in the wood be retained by converting it to biochar?

What about TPO trees?

Local authorities also get involved in subsidence claims where their role is that of the planning authority rather than the tree owner.

Where a tree is thought to be the cause of subsidence damage but is protected by a tree preservation order, an application is often made to the planning authority seeking consent to carry out tree work. The same site investigation results and evidence will tend to accompany that application as accompany the mitigation request referred to above.

In this situation the planning authority might be concerned about what decision to make given the possibility that a legal claim for compensation under the Town and Country Planning Act might follow if the application is refused. This might cause a planning authority to feel under greater pressure to accept the application and consent to removal even though this results in the removal of a tree which it has been deemed necessary to protect and preserve.

Again, the law here is nuanced and technical. The law is set out in the Town and Country Planning Act 1990 and in past decisions of the Court. The Court in these cases is the Lands Tribunal. There is not a significant number of previous and reported decisions of the Lands Tribunal and so this guidance from past decisions can feel limited, contributing to these cases being tricky to risk assess.

Winter risk

As I said at the start of this piece, increasing risk comes from hot/dry summers and mild/wet winters. As we move into winter, the risk of storm events and tree failure begins to loom large for local authorities. Trees falling over and damaging properties, interrupting infrastructure and even impacting human life are significant and increasing risks. A tree falling over in a storm and taking a human life is rightly a far more significant risk to avoid than managing a tree to reduce its risk of causing subsidence.

What this throws up is that, as we move from summer into autumn and winter, the pressure that our changing climate places on local authority, and other, tree owners is significant. Trying to find a way to stretch reduced budgets to effectively manage a wide range of risk which is changing with our climate feels like an impossible task. But the law, whether that’s in the Environment Act or other statutes, will help drive change.

One of the key transition risks with climate change is litigation risk: individuals holding companies, governments and entities to account on both carbon reduction and, as we go into the future, on biodiversity. One thing is for sure, that hard work to retain trees will help lower this litigation risk as we transition to a carbon neutral economy.

Sarah Dodd

Sarah Dodd is the founder of the law firm Tree Law and also the current chair of the industry Subsidence Forum. With 20 years of experience working in corporate law firms for insurance companies and public sector clients, Sarah wanted to launch a business which could have the environment at its heart. Tree Law was launched in November 2021. It specialises in claims and advice relating to trees. The business is carbon neutral and donates 10% of fees back to the client’s choice of charity at the end of each claim. www.treelaw.co.uk

This article was taken from Issue 199 Winter 2022 of the ARB Magazine, which is available to view free to members by simply logging in to the website and viewing your profile area.