Urban trees are fundamental to vibrant and sustainable streetscapes, offering shade, reducing air pollution, enhancing biodiversity, supporting community wellbeing, and contributing to the efficacy of nature-based drainage systems. However, while the stability and resilience of these trees in urban environments is critical, it is often overlooked.
Changing weather patterns, heavy traffic and poor soil conditions can hamper the healthy growth of urban trees, while inadequate design or poor-value infrastructure specification can undermine the stability of the newly greened streetscape over time, which means that the investment ends up being a poor use of funds, functioning in a sub-optimal way, attracting public criticism and incurring additional costs for remediation.
So what are the main challenges, and how can they be mitigated to ensure best value from any streetscape investment?
Weather resilience: flood, drought and wind
Urban trees must withstand increasingly unpredictable weather patterns as a result of climate change, including prolonged droughts, sudden floods and high winds. One of the critical aspects when it comes to resilience in this context is ensuring that they have the right conditions within which to establish themselves, with strong root growth to promote both stability and robustness.
Modern soil cell systems designed for integration with sustainable drainage systems (SuDS) can play a critical role in promoting resilience in the face of these worsening weather conditions, allowing water to infiltrate and be stored within the soil, supporting trees during dry periods, and effectively managing excess water during floods. This not only reduces the likelihood of surface water flood events but also maintains healthy hydration levels essential for optimal tree growth.
It’s not only the rainfall and temperature changes that are proving more of a challenge owing to global warming; strong winds are increasingly likely. Well-established root systems are essential for trees to withstand wind, particularly in urban environments where wind tunnels between buildings can pose risks. Soil cells and tree pits offering optimal soil volume and ventilation pathways encourage deeper root penetration, ensuring trees are well-anchored and capable of enduring high winds without toppling.
Traffic resilience: load and pollution
Trees located near busy roads also face challenges such as soil vibration from heavy vehicles and exposure to pollutants. However, the right below-ground infrastructure choices mitigate these risks by stabilising the soil and filtering harmful substances from road run-off before they reach the roots (such as at Keighley, where research proved the efficacy of our ArborFlow tree pits in dealing with run-off).
While the traffic can impact the tree, the tree might also have an impact on the traffic unless consideration is given to root training; as tree roots naturally seek water and nutrients, growth must be directed downwards to avoid damaging pavements and other hard surfaces. Root training prevents root heave and protects surrounding infrastructure, reducing repair costs, maintaining pedestrian safety, and ensuring that trees can thrive without damaging their urban surroundings.
Growth, stability and optimal benefit
Soils in urban environments are often compacted and low in nutrients, which limits root growth and weakens tree stability – and as healthy root growth underpins how healthy the tree is overall, this also lessens the positive benefits brought to the streetscape.
The installation of appropriate root management solutions addresses these issues, incorporating engineered soils that encourage root development and microbial activity, ensuring proper water infiltration and oxygen flow. Healthy soil structures also reduce the likelihood of compaction after heavy rains, diminishing the risk of soil erosion as well as supporting long-term tree stability. The correct solution to employ will depend on the soil type present:
Clay soil: Dense clay soils are common in urban settings and present challenges such as poor drainage, leading to waterlogged conditions that suffocate roots during wet periods and are susceptible to extreme hardness during droughts. This compaction restricts root expansion, increasing the risk of tree instability. Soil cell systems help mitigate these issues by enhancing aeration and providing structured soil volumes that promote deeper root penetration, preventing water stagnation and improving oxygen availability to support stable tree growth.
Sandy soil: Sandy soils drain quickly and often lack essential nutrients, leading to inadequate water retention and stressed trees that struggle to establish stable roots. Engineered soil compositions within root management systems help maintain balanced moisture levels and improve nutrient retention, ensuring sustained growth and resilience even in challenging sandy conditions.
Silty soil: Silty soils retain water more effectively than sandy soils, but they are prone to compaction, which limits oxygen flow and root penetration – and these soils may become waterlogged after heavy rainfall, increasing the risk of root rot. Modern soil cell solutions enhance the structure of silty soils by promoting proper drainage and aeration, preventing compaction, and supporting healthy, stable root development.
Data is key to choosing best-value solutions
But of course, the big question is, how is it possible to choose between very similar-sounding products that give urban trees the best chance at establishing healthy growth, in the face of climate change and roadside conditions, while also ensuring hard landscaping remains unaffected?
The answer is to look for the dependable data, which proves product claims of robustness and effectiveness. For example, our comprehensive research into our RootSpace system was independently conducted by leading materials testing and analysis laboratory Lucideon. Tasked with evaluating the structural integrity and load-bearing capacity of RootSpace, Lucideon performed rigorous assessments in line with BS EN 17150 standards; the methodology involved subjecting various RootSpace module configurations – including different series and infill panel arrangements – to Uniformly Distributed Load (UDL) tests after 24-hour temperature conditioning.
The results confirmed that RootSpace can withstand significant vertical, lateral and dynamic loading, making it highly suitable for supporting urban infrastructure. Its robust design ensures tree stability even when exposed to drought, flooding, strong winds and the stresses of heavy vehicular traffic, all while maintaining pavement integrity and minimising maintenance needs. This research highlights RootSpace as a sustainable, resilient solution for urban environments, capable of future-proofing streetscapes against growing environmental and structural challenges.
Similarly, we also conduct longer-term research to prove the efficacy of our ArborFlow system in promoting healthy growth – something which can only be tested over lengthy periods of time, in real-life streetscape conditions. For example, in 2018 we installed six ArborFlow tree pits along North Street in Keighley, West Yorkshire, as part of a sustainable drainage system (SuDS) initiative. Over a six-year period, two primary studies evaluated the system’s performance in enhancing tree health and mitigating surface water challenges.
The first study, working with IROSARB – a leading urban forestry specialist – involved sap flow and vapour pressure deficit (VPD) testing to measure the vitality of the Field Maple trees; results indicated a high sap flow relative to the trees’ cross-sectional area and a below-average VPD, signifying robust tree health and successful root establishment.
The second study, conducted in collaboration with Manchester Metropolitan University, focused on the system’s efficacy in filtering pollutants from road runoff. Soil samples collected in May and August 2023 underwent laboratory analysis, revealing that the tree pits effectively removed contaminants, preventing pollution of the combined sewer network. These findings underscored the ArborFlow tree pit system’s dual role in promoting vigorous urban tree growth and enhancing stormwater quality through natural filtration processes.
Urban trees: achieving greater ROI
Designed correctly and specified optimally, green-blue infrastructure can enhance the resilience of urban streetscapes, safeguarding cities against the economic and environmental impacts of climate change, and bringing all the myriad benefits to our urban communities. To find out more about giving urban trees the best chance to thrive in even the most challenging environments, speak to one of our expert team by clicking here.
