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Green Infrastructure

Balancing the risks and benefits of ageing trees in urban settings.

Throughout the UK there are countless examples of majestic mature trees, bordering roads, at property entrances and lining the streets of towns and cities. Unfortunately due to the often unpredictable nature of trees, the risks presented by these mature specimens may range from nothing at all to severe. 

Due to the fragmented nature of land ownership across Britain, exact boundaries along fields and roadsides can often blur over the years. This typically results in no preventative monitoring or works on trees located in these areas. Although the likelihood of being seriously injured or killed by a falling tree is very low, in areas where avenues or groups of trees are all ageing and declining, the risks can rise significantly.

Urban Risks

Trees may live for many hundreds of years without presenting a significant risk. Generally in urban areas, trees are likely to be of a similar age. Across the UK, many Victorian trees are still standing and provide aesthetically appealing borders in harsh urban landscapes. These trees will be ingrained in the memory of generations of local people, growing from small saplings to towering giants. There is no direct correlation between increasing tree age and greater risk, however, this is often the case, particularly in urban areas. Trees in these areas have often lived through many major events, with evident battle scars to prove it. This often means the trees have sustained damage to the bark, compaction of root systems by vehicles, shrapnel from WW2 and general damage sustained in day to day life. All of these factors increase the rate of decline and therefore increase the risks associated with ageing urban trees. Some species are more tolerant to urban life and pollution than others. London Plane Trees are a recognisable sight across many cities in the UK. They have proven hardy and long lived, when compared to other less suitable species.

What Can Be Done  to Mitigate the Risks?

Regular surveying to BS5837:2012, by competent tree surveyors, can help to manage the risks and reduce any serious damage caused by urban and roadside trees. Regular surveys will help to identify any major risks or defects, which can then be corrected by trained arborists. Deadwood can be managed easily with annual surveys, allowing the early identification and removal before it causes a problem. Trees will always be a dynamic force, with an element of risk. Tree surveys provide the best protection from the majority of risks caused by roadside and urban trees.

Roadside Trees

The same principles and dynamics apply when considering the dangers posed by ageing roadside trees, however, there are a few important differences. Unlike urban trees where surveying is more likely to be a regular management activity, roadside trees are often neglected completely. Only areas of high activity such as main roads, will receive regular surveying and pruning. Typically more rural areas and estate accesses will have many avenues of ageing trees. The most common complaint with roadside trees is deadwood. Deadwood results from damaged or aborted branches, which then die back and turn brittle. This presents a risk to both vehicular and pedestrian users. The major problem with deadwood arises when tall vehicles strike the lower canopy, dislodging the deadwood. This not only causes damage to the vehicles but also spreads the deadwood across the roads, potentially causing further damage and delay. Deadwood is a major problem across the UK and  is present in the majority of both urban and roadside trees. 

Other safety problems associated with roadside trees include: limb loss, fungal infections, major structural cracks and severe decay. All of these factors increase the risks further, often resulting in complete collapse of the tree, particularly in high winds or extreme weather events. Not every roadside tree will be dangerous, but the majority of ageing roadside trees will show several defects.

Urban and roadside trees provide many benefits for people living in cities and towns. They absorb noise, provide shade in hot weather, offer habitats for birds and wildlife and encourage a sense of health and wellbeing. The risks are manageable as long as a plan is in place to monitor and care for these precious natural assets.