Trees in the City – 2

🌳 Trees in the City: Striking a Balance Between Safety, Awareness, and Vision

Trees located in urban environments rank among the most crucial elements that significantly enhance the overall quality of life within cities. They offer much-needed shade, help to mitigate the urban heat island effect by cooling the surrounding air, reduce levels of air and noise pollution, and play a fundamental role in supporting urban biodiversity. The wide range of benefits provided by urban trees has been thoroughly documented and supported by extensive scientific research studies and reports (Nowak et al., 2014; FAO, 2020; IPBES, 2022). Despite these numerous advantages, it is important to recognize the complex reality that trees are living organisms, not fixed or unchanging structures. They undergo continuous physiological changes, growth, and decay over time, which necessitates regular and careful risk assessments to ensure their health and safety within the urban landscape.

Stability Assessment: A Continuously Advancing Science

The field of tree stability assessment, commonly known as Visual Tree Assessment (VTA), is continuously evolving and advancing at a rapid pace. Over the years, both the methods and the tools used in this area have undergone significant improvements and refinements. In fact, a notable example is the author of a widely recognized dendrosurgery publication, who openly acknowledged at an important conference that recent new research findings had prompted him to revise and update his previous views and opinions. Nowadays, the scientific community has gained a much deeper understanding that trees react very differently to various factors such as wounds, pruning, and the presence of internal cavities. Consequently, it has become clear that only a comprehensive multidisciplinary approach, when combined with detailed instrumental analysis, can provide a truly reliable and accurate evaluation of the risk of tree failure.

Arborists and green technicians continuously participate in ongoing training programs, consistently earning new certifications to enhance their expertise. They also utilize a variety of advanced and specialized tools such as sonic tomographs, resistographs, and radar technology specifically designed for detailed root analysis. Despite the extensive efforts and sophisticated equipment employed, every assessment made is inherently probabilistic rather than absolutely definitive: complete safety can only be guaranteed at the very moment a tree actually falls, which, naturally, is far too late to prevent any potential damage or injury.

Challenging Choices and Collective Accountability

In urban environments, decisions to remove trees are frequently viewed as arbitrary or rushed, particularly when the tree appears to be healthy and thriving. However, the situation is far more complex and nuanced than it initially seems: a tree can suddenly fall without warning despite looking perfectly sound, or conversely, it can stand firm and remain in place for many years even if it has sustained some damage. When large and massive trees tower over busy streets, sidewalks, bus stops, or playgrounds, those responsible for making decisions must carefully consider not only the overall health of the tree but also the level of risk that is acceptable to the safety of people and nearby property. In a society that often focuses on assigning blame after an unfortunate incident rather than working proactively to prevent such events beforehand, exercising prudence and caution is not only an ethical responsibility but also a critical legal obligation.

Independent evaluations conducted by external experts have increasingly become the standard practice, especially considering that many local authorities do not have access to specialized personnel or the necessary advanced equipment required for thorough assessments. However, it is important to note that these professional evaluations can be quite expensive: for example, an instrumental Tree Visual Assessment (TVA) can cost anywhere between 250 and 750 euros per individual tree. Consequently, it is essential to address this issue proactively by carefully and thoughtfully designing urban green spaces right from the very beginning, ensuring long-term sustainability and reducing the need for costly evaluations later on.

The real key: designing better

Many problems that lead to drastic pruning or the complete removal of trees often stem from poor decisions made during the initial planning and planting stages. Large tree species are frequently planted in spaces that are too small, too close to buildings, or directly beneath utility lines. This results in root systems that lift and damage sidewalks, dense canopies that block natural light from windows, or trees that produce slippery fruit, all of which become sources of ongoing conflict between residents and municipal authorities. However, the real issue is not the trees themselves but rather the lack of proper planning and foresight. Trees are living organisms, not static objects like lampposts—they grow, adapt to their environment, can become diseased, and have life cycles that must be carefully considered from the very moment they are planted. Because of this, it is crucial to establish clear criteria for the scheduled replacement of trees, implement sustainable and well-thought-out maintenance plans, and, above all, ensure that the soil remains permeable and healthy. Without adequate water, oxygen, and ample space for roots to expand, no tree species can genuinely flourish or reach its full potential.

Beyond the Emergency: Embracing a New Paradigm

Public debates surrounding tree removals frequently boil down to a contentious clash between two opposing groups: those adamantly committed to “saving” every single tree at all costs and those who emphasize the paramount importance of safety above all else. However, the true and lasting solution extends far beyond this polarized divide. It requires a fundamental paradigm shift that acknowledges urban greenery not merely as decorative or incidental but as a vital, living, and dynamic form of infrastructure that must be thoughtfully designed, strategically planned, and expertly managed over time. Historically, approaches to urban greenery have gradually evolved—from initially creating “green corridors” that link the city to the surrounding countryside, to the development of peri-urban “green belts” aimed at preserving natural buffers, and more recently, to innovative strategies emphasizing de-paving hard surfaces and undertaking extensive re-greening efforts. Despite these advancements and evolving concepts, very few cities have the commitment or allocate the necessary resources to conduct long-term scientific studies and develop comprehensive, integrated plans that are essential to fully realize this ambitious vision of urban ecological stewardship.

Trees in urban areas should be recognized not merely as obstacles or inconveniences but as vital and invaluable partners in building strong climate resilience, provided that their biological needs are fully honored and their ongoing care is thoughtfully and carefully incorporated into comprehensive city planning efforts. By adopting this holistic and respectful approach, cities can effectively avoid unnecessary tree removals and preventable risks associated with poor tree management, ultimately creating urban environments that are safer, more attractive, and far more enjoyable for all residents to live, work, and play in.

“Trees don’t need pruning; they need understanding.”

The Tree Stability Assessment (VTA), developed by Claus Mattheck and Helge Breloer in 1994, has become the foundation for risk analysis in arboriculture. Recent studies, aligned with the UNI 11708:2018 standard “Unregulated Professional Activities – Arborist and Tree Climber” and the CNR guidelines (2022), recognize that these assessments offer probabilistic estimates rather than definitive certainties.

The modern approach to tree risk management (Smiley et al., 2011; Costello & Quarles, 1999) defines risk as the product of the likelihood of failure and its potential impact on people and property. Visual assessments and instrumental surveys—such as sonic tomography, resistography, radar, and controlled traction tests—should be interpreted within the context of the tree species’ physiology. This perspective prioritizes mitigation strategies, including targeted pruning, soil decompaction, and soil management, over tree removal.

📘 3. Key References

Rules and Guidelines in the Italian Context

  • UNI 11708:2018 – Attività professionali non regolamentate – Arboricoltore e Tree climber – Requisiti di conoscenza, abilità e competenza.
  • CNR, 2022 – Linee guida per la valutazione della sicurezza degli alberi in ambito urbano.
  • SIA (Società Italiana di Arboricoltura), 2023 – Manuale per la gestione del rischio degli alberi in città.

Scientific and Technical References

  • Mattheck, C., Breloer, H. (1994). The Body Language of Trees: A Handbook for Failure Analysis. HMSO, London.
  • Smiley, E.T., Matheny, N., Lilly, S. (2011). Best Management Practices: Tree Risk Assessment. ISA, Champaign, IL.
  • Costello, L.R., Quarles, S.L. (1999). Tree Failures: Causes, Prediction, and Reduction. UC Cooperative Extension.
  • Roloff, A. (2016). Urban Tree Management: For the Sustainable Development of Green Cities. Wiley-Blackwell.
  • FAO (2020). Urban Forests and Trees in the Era of Climate Change.
  • IPBES (2022). Assessment Report on Biodiversity and Ecosystem Services.
  • Nowak, D.J., Crane, D.E., Stevens, J.C. (2014). Air Pollution Removal by Urban Trees and Shrubs in the United States. Urban Forestry & Urban Greening, 4(3), 115–123.

https://www.forestepersempre.it/en/urban-trees-and-city-forests/