European cities must expand their green space to meet the EU’s Nature Restoration Law targets. But without guidance and maintenance, planting the wrong greenery could lead to more problems.
Buildings surrounded by plants, rooftop gardens, tree-lined streets: these sights are usually considered signs of a healthy, green city.
Vegetation cools the air, provides shade, improves air quality by storing carbon and pollutants in its biomass, and, underground, tree roots act like sponges when it rains, reducing the risk of flooding.
A 2024 study also shows that urban trees can reduce human heat stress when daytime temperatures peak, improving mental well-being.
However, in certain situations, the wrong vegetation in the wrong place could be doing exactly the opposite in cities.
For example, in some streets, trees can trap air underneath their dense canopies, reduce wind movement, and bring pollutants close to the ground. And the same happens with heat, which is one of the main environmental health hazards for city residents.
This paradox highlights the challenge urban planners face: increasing urban greenery without causing new problems.
Although the World Health Organisation recommends that everyone should live within 300 metres of a park or green area, in Europe, just fewer than half of urban residents do.
But European cities are under urgent pressure to adapt.
The European Union’s Nature Restoration Law has set legally binding targets for urban greenery.
By 2030, every country must make sure cities do not lose green space or tree cover compared to 2024. And after that, there should be a steady increase in their total area until they reach a satisfactory level.
However, experts warn that success should not be measured by how many trees are planted, but by which ones and where exactly.
The right urban greenery depends on location
“Tree selection should be site-specific”, Henrik Sjöman, researcher at the Swedish University of Agricultural Sciences and scientific curator at Gothenburg Botanical Garden, tell Euronews.
"Invest in trees that work and can handle and tolerate the conditions of that particular site today and tomorrow,” he adds. “In some regions in Europe, it is not possible to rely only on native species. So, we must add non-native ones that have the capacity to withhold it.”
However, in narrow streets with heavy traffic, urban planners should look beyond parks and trees, explains Jenny Lindén, researcher at the Swedish Environmental Research Institute:
“In a city, there are just a few places where there is actually room for trees. In narrow streets with a lot of traffic, green walls, plant beds or bushes might be much better than a tree. Green walls also cool buildings, reducing the energy needed for air conditioning. And although they do not have the same benefits as trees, they do remove pollutants from the air.”
Nonetheless, these solutions also carry health risks, warns Loïc Gillerot, climate health expert at the Belgian Climate Risk Assessment Centre.
“The main risks are vector-borne diseases, such as ticks and Lyme disease, and the creation of habitats that are suitable for mosquitoes. However, while this is something to take into account, from a public health perspective, the risks are completely overshadowed by the benefits of nature-based solutions.”
For researcher Sjöman, one thing is clear: if Europe does not invest in urban greening now, “cities will be less liveable”.
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