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Guided Professional Tour of Koper’s Urban plantings report
On Thursday, November 24th 2022, we completed the series of guided professional tours in Koper. The meeting was attended by 22 participants representing a wide range of professions—including architects, landscape architects, municipal service providers, contractors, and gardeners – all of whom are involved in the planning, management, and maintenance of green spaces.
The central theme of the visit was mature plantings: their condition, maintenance practices, and approaches to tree management during major interventions. The tour was professionally led and moderated by Mirko Silan, MSc in Biology, consulting arborist.
Construction Interventions in and Tree care
The site visit began at Museum Square, which underwent a complete renovation in 2021. The newly designed space represents a hybrid between a park and a public square, integrating new features into Koper’s historic urban fabric.
Our first stop was the plane tree (Platanus × acerifolia) avenue located adjacent to Museum Square— an old tree-lined promenade connecting the seafront with the historic city center. This avenue includes the oldest plane tree in Koper, with a trunk circumference of 453 cm at breast height.
Recent excavation works for an underground parking garage beneath Museum Square were carried out with particular care to protect the root systems. A minimum multiple distance of 2.5 m from the trees was respected to prevent root damage. Special attention was devoted to the largest plane tree, which is now being closely monitored post-construction. At present, no negative effects on growth are visible, although slow root decay may still occur over time. A few fruiting bodies of shaggy bracket fungus (Inonotus hispidus) were observed on unhealed wounds, which is a normal stress response, particularly to water stress.
A crown support system was installed to prevent branch drop or damage, but it does not comply with current international standards. The system is static rather than dynamic, reducing its effectiveness in damping wind-induced oscillations. The discussion also covered excavation methods near vegetation. The participants agreed that compressed-air excavation (air spade) should be implemented to prevent root damage. Continued monitoring of these plane trees remains essential due to high temperatures, limited water availability, and restricted root space (FigureThe use of compressed-air excavation would be more appropriate in such situations, as it avoids root damage associated with mechanical excavation techniques.
Continued monitoring of plane trees vitality in the entire avenue will be essential in the following years. The key challenges are elevated temperatures, limited water availability to the root systems, and an extremely restricted soil volume (Figure 1).
Figure 1: The oldest plane tree in Koper (photo: Kunc P.)
The Quality of Materials Matters in Landscape Design
We continued our walk to Vergerio Square, a small square named after the reformer Vergerio, who was the teacher of Primož Trubar and, like him, was exiled as a heretic during the Reformation.
The overall design of the square remains appropriate and functional; however, issues related to the durability of the materials used are becoming apparent. One such example is the paving made of Tuscan sandstone, which already shows visible signs of wear. During the discussion, we emphasized the importance of using high-quality materials in new landscape projects in order to avoid premature deterioration and damage.
Several olive trees (Olea europaea) are planted in the area, which led to a discussion on the suitability of olive trees in urban environments. Some participants argued that the olive is primarily a fruit-bearing species and therefore does not belong in cities. At the same time, we highlighted that in coastal urban settings a certain proportion of olive trees is entirely appropriate, as they reinforce the distinct character and identity of the Mediterranean environment (Figure 2).
Figure 2: Participants of the tour at Vergerij Square (photo: Kunc P.)
New Plantings Must Follow Contemporary Principles of Biodiversity
The next stop on our tour was Brolo Square, located near the main Tito Square. Due to its age, this park is clearly in need of renovation.
During the discussion on developing a concept for new plantings and spatial redesign, we emphasized points already highlighted during previous site visits (Ljubljana). When renovating existing green spaces – as well as when designing new ones – it is essential to consider not only the overall concept but also appropriate plant selection, while maintaining or actively enhancing species diversity to promote biodiversity.
In current renovation projects, particularly those involving the planting of woody species, root trench planting is increasingly being adopted. This method allows trees to connect below ground through their root systems, thereby improving growing conditions, resilience, and long-term vitality (Figure 3).
Figure 3: Certain parks in Koper need renovation (photo: Kunc P.)
New Landscaping Must Be Completed from start to finish
We continued our walk along Koper’s main coastal street, passing the Koper open-air market and Hlavaty Square. In addition to the palms planted along the avenue in previous years, magnolia (Magnolia grandiflora) trees have been added here. The exposed surface beneath the tree is much too small as the paved area reaches almost to the trunk itself. In the coming years, when portions of this avenue will be renovated, these inadequate conditions must be corrected to provide the trees with sufficient water and room to thrive.
It is crucial to plant trees correctly from the beginning, because improperly planted young trees struggle to establish themselves in the soil, and poor growth becomes evident quickly. We also highlighted recent urban planting practices in Vienna and Barcelona, where trees are planted in pits, slightly lower than the surrounding pavement. This approach channels surface runoff directly to the tree, promoting efficient water infiltration and improved root hydration (Figure 4).
Figure 4: Koper’s coastal road with palm trees (photo: Kunc P.)
Trees Must Not Be Planted Too Deeply
We concluded our visit at Hlavaty Square, where Holm oak trees (Quercus ilex) were planted in 1986. During later renovations, the tree roots were covered with additional soil. Excess soil covering reduces oxygen availability and root respiration. Reduced root respiration can lead to slow root decay, which in turn negatively affects tree growth and may eventually cause tree death.
Unfortunately, deep planting has become increasingly common in urban areas. The causes vary, but a frequent reason is failing to identify the tree’s root collar before planting, resulting in planting the tree simply to match the depth of the root ball. This method is appropriate only if the top of the root ball aligns with the root collar. In practice, however, soil often extends above the root collar, creating a problematic situation.
Therefore, it is essential to check the root collar of every tree before planting. Any soil covering the collar should be removed to ensure the tree is planted at the correct depth.
Deep planting issues also frequently arise when trees are planted in new substrates. If the substrate is not adequately compacted, it may settle over time, causing newly planted trees to sink deeper than intended.
Text by Petra Kunc and Mirko Silan
