There is no easy answer to this common question. However evidence-based risk assessment can provide balanced advice, helping to avoid both potential danger and unnecessary felling.
As consulting arborists we are frequently asked this question by clients or members of the public. Often there is not a simple yes or no answer as the issues involved can be complex. While very occasionally trees do pose an unusually high risk of harm and need to be felled or pruned for safety reasons the dangers posed by falling trees or branches are generally very low in this country.
According to the Royal Society for the Prevention of Accidents (RoSPA) each year between five and six people in the UK are killed when trees or branches fall on them; around three of these deaths are caused by trees in public spaces. (To help put that into perspective, 1,793 people were killed and 24,831 seriously injured on our roads in 2017 [RoSPA]).
As the HSE points out on its website: ‘The risk of being struck and killed by a tree or branch falling is extremely low (in the order of one in 10 million for those trees in or adjacent to areas of high public use). However the low level of overall risk may not be perceived in this way by the public, particularly following an incident.’
As with many activities in our daily lives the risks posed by trees ought to be weighed against the many benefits they provide and work undertaken to reduce risks should be proportionate. No large tree in a busy urban environment can be described as completely risk free, even if the risk is extremely low. So what is an appropriate level of risk to accept from trees? Fortunately, established health and safety principles can be applied as part of a risk assessment process to suggest what is acceptable or tolerable. The Quantified Tree Risk Assessment (QTRA) system is one of several established methods of calculating the risks posed by a tree, and is the system used by our consultants.
According to the HSE, if you have trees on your land that may impact public space you have a duty of care to do ‘all that is reasonably practicable to ensure that people are not exposed to risk to their health and safety.’ This applies whether you are a private individual, business or local authority. Guidance on common sense tree management for all, along with helpful downloads from the National Tree Safety Group, Arboricultural Association and the Forestry Commission, are available on the HSE website (address below).
The perceived risks posed by trees are often exaggerated out of fear, or where ulterior motives exist for wanting them removed. Sadly this can lead to trees being felled unnecessarily with the loss of amenity and other environmental and ecological benefits. As arborists we cannot guarantee a tree is one hundred per cent safe but we are able to carry out an evidence-based risk assessment and provide balanced advice. With this in mind the question we need to ask when dealing with tree safety is: ‘Does the tree pose an unreasonably high threat of harm?’ The answer is usually no but if it does then suitable control measures – for example, canopy reduction or removal of some branches - can be implemented.