Impact of Climate Change - how to adapt your tree risk management
12/14/2022
The latest UN Climate Change Conference (COP27) provided another reminder of the frightening speed at which our planet is changing, and the urgent need for climate adaptation measures.
As well as the incalculable human costs of failing to adequately plan for change, there is a significant economic cost too. In a year which has seen the UK record its highest ever temperature, its joint hottest summer, and its driest year since 1976, there has been a corresponding increase in the size and frequency of weather-related insurance claims such as fire and subsidence. Other extreme weather events, such as floods and storms, are also becoming more commonplace.
As we have previously discussed, tree planting and preservation can play an important role in helping to slow down climate change. However, trees can also introduce additional risks which need to be carefully understood.
Ash dieback
While the devastating impact of ash dieback cannot be blamed squarely on climate change, it is a contributing factor. The National Trust says an increase in warm and wet conditions is one of the reasons the disease has been able to take hold.
It is expected that 75–95% of the UK’s ash trees will be lost in the next 20 to 30 years to ash dieback. Researchers have estimated that the economic cost of ash dieback in the UK could be around £7billion over a ten-year period – that is many times more than the estimated cost of all other invasive plant diseases.
The cost of felling is something that every organisation with ash trees will have to take into account. Across the UK, the cost of removing diseased ash trees increased from £1million in 2020 to £3million in 2021.
While ash dieback is very much a threat today, it is important that organisations take a long-term view when considering how to manage the problem.
For example, while the costs of felling and removing trees should be factored into budgets, it will not always be necessary, or even appropriate, to fell infected ash trees. Pruning may be an option where trees are showing tolerance to the disease.
If replacing tree stock, it is important to diversify the species, considering resilience not only to ash dieback but also to other pests, diseases and climate-related impacts.
In terms of managing the risk, while there is no cure for ash dieback, it may be possible to slow its spread. For instance, clearing leaves may disrupt the lifecycle of the fungus which causes ash dieback.
Above all, a proportionate, risk-based approach should be taken, with public safety the primary focus. In cases of severe infection, branches can be weakened, increasing the risk of breakages. In terms of inspections and mitigation works, priority should be given to trees in areas with high levels of public access.
The Arboreal Association has provided useful guidance on ash dieback, including identifying symptoms of the disease, managing infection, and factors to consider when replacing lost ash.
Subsidence
Millions more properties across the UK are likely to be at risk of subsidence in the coming decades as a result of climate change.
The British Geological Survey (BGS) says the number of buildings across Britain considered highly or extremely likely to suffer shrink-swell – moisture changes in the ground, which can lead to heave or subsidence – is set to double from 3% in 1990 to 6.5% in 2030. Drier summers and higher temperatures are a major contributory factor.
Areas with clay-rich soils present the greatest risk. Trees near buildings can sometimes increase the likelihood of subsidence. The level of risk will depend on a number of factors, including the tree species, its proximity to nearby buildings, and the age of the building and the materials used (new buildings tend to have deeper foundations and therefore are generally at lower risk).
The Royal Horticultural Society says it is difficult to accurately predict when trees will pose a risk of subsidence, and the vast majority don’t. However, BGS maps can help organisations to understand how subsidence risk more generally varies across different parts of the UK. For more localised information, organisations may be able to speak to their insurer about their claims history to help identify areas requiring more focused attention.
Increased subsidence risk will amplify the need for a proportionate, risk-based inspection and maintenance programme for trees and buildings, e.g. to identify cracks in brickwork or pipework as early as possible.
The RHS provides further guidance on managing the risk of trees near buildings.
High winds and storm damage
According to the Met Office, February 2022 saw some of the highest wind speeds recorded in more than 30 years. The UK Climate Projections report anticipates an increase in winter wind speeds and the frequency of winter storms over the coming decades.
It is important organisations consider the impact of strong winds when choosing the species and location of new trees or woodlands. As well as the obvious risk of falling branches, stronger winds could allow pathogens that infect foliage to disperse over a much wider area.
Forest Research has published guidance on how different types of woodlands can be affected, and possible adaptation measures, such as increasing tree species diversity.
Trees in public areas, such as those close to, or overhanging footpaths, could pose a safety risk during periods of strong winds. It is important you have a clear plan for communicating with key stakeholders, such as your employees, volunteers and members of the local community, both to explain the risks and how you will respond – e.g. temporarily restricting access to parks, play areas, footpaths etc while you inspect possible damage.
Final consideration
The important contribution of trees in combating the effects of climate change must be acknowledged, and removal of trees should be a last resort.
Planting and preserving trees not only contributes to carbon capture and storage, it can also help to provide shade and reduce the temperature inside nearby buildings – an important consideration with global temperatures rising.
While planning for change involves balancing a complex set of priorities, this article aims to help organisations take a proportionate response to managing the risks associated with trees, forests and woodlands.
The Forestry Commission has also published useful guidance - Managing England’s woodlands in a climate emergency – which covers some of these topics in further detail.
Zurich Resilience Solutions (ZRS) can offer customers a range of risk management services, such as a tree safety and liability review, facilitated workshops, document reviews and training. For more details on any of our risk services, visit the ZRS website or email: zrs.enquiries@uk.zurich.com.
