Renaturalisation' in Europe: which cities apply the 3-30-300 rule?

In Southern Europe, the gap widens. Cities such as Zaragoza have large urban areas that are completely excluded from the model's three criteria, while in contexts such as Murcia, Dubrovnik or Valletta the presence of trees visible from dwellings concerns a clear minority of the population. Even more critical is access to urban parks in some Mediterranean and Balkan areas, where the distance to green spaces frequently exceeds the limits considered functional for urban liveability.

This geography of green inequality is even more evident in the Italia case, where the transition to an ecological city proceeds in a fragmented manner. The national framework does not yet provide for the formal adoption of quantitative standards such as those dictated by the 3-30-300 rule, and urban policies remain entrusted to local instruments that are often uncoordinated.

In some cities, however, more advanced experimentation is observed. Florence has explicitly introduced the 3-30-300 model in its green plan, linking it to a programme of urban forestation and increasing soil permeability. Milan, on the other hand, is developing a different approach, based on a widespread network of micro-interventions including depaving, rain gardens, green roofs and tree planting along urban infrastructures. In this model, greenery is not concentrated in large parks, but is distributed as a continuous system within the existing urban fabric.

This strategy responds to a structural constraint: in historic and densely built-up cities, the possibility of creating large green areas is limited. However, this very condition has favoured the emergence of a new design paradigm, which some urbanists call diffuse ecological infrastructure. The aim is not just to increase the quantity of green space, but to transform its ecological quality from ornamental surfaces to systems capable of sustaining biodiversity, reducing urban heat and improving water management.

A central issue concerns the distinction between aesthetic and functional greenery. Many urban interventions, while increasing the visual presence of vegetation, do not produce significant ecological effects. Ornamental lawns and decorative flowerbeds, if intensively maintained, have a limited capacity to support pollinating insects or complex trophic networks. In contrast, systems based on native species, vegetation stratification and low-intensity management can activate more stable and resilient ecological dynamics.

Some particularly advanced European experiences are moving in this direction. In Paris, the bioclimatic strategy has led to the reconversion of schoolyards and public spaces through the so-called 'Cours Oasis' programme, which combines depaving, vegetation and reduction of the heat island effect. In Nantes, one of the few cities to have formally integrated 3-30-300 into its policies, the 'pleine terre' strategy aims to progressively replace impermeable surfaces with vegetated soil, accompanied by a strong expansion of tree cover and stricter management of mature trees.

Alongside these cases, the issue of environmental justice strongly arises. In many European cities, the distribution of green spaces is not socially neutral. Higher income neighbourhoods tend to have a higher endowment of trees and parks, while peripheral or socio-economically fragile areas are often less well served and more exposed to the effects of heat waves. In some cases, green redevelopment even contributes to processes of increasing property values and replacement of the resident population, fuelling the phenomenon of so-called green gentrification.

The case of Bucharest is a particularly significant example of the structural criticalities still present in Eastern Europe. Heavy building pressure, the reduction of condominium gardens and the expansion of car parks have led to a progressive contraction of green areas, with per capita levels well below the standards recommended by the European Union. This is compounded by management that is often oriented towards aesthetics rather than ecological resilience, with interventions favouring fast-maintenance lawns and green furniture rather than stable natural infrastructure.

Alongside these scenarios, however, structural transformation projects are also emerging. In Sofia, a metropolitan green ring is being planned to connect parks, rivers and natural areas in a continuous network. In Vilnius, the renaturalisation strategy is based on widespread interventions in neighbourhoods and the reduction of asphalt surfaces. Finally, in Vienna, the reclamation of brownfield sites and the redevelopment of river corridors are contributing to the construction of new urban green infrastructure.

Overall, the European transition to the renaturalised city appears to be well underway, but still incomplete and highly uneven. The 3-30-300 rule is not only a technical indicator, but a paradigm shift in the very definition of urban quality. Its application today measures the ability of European cities to address the climate crisis not through isolated interventions, but through a systemic reconfiguration of urban space.

*This article is part of the European collaborative journalism project "Pulse" and was contributed by José Ramón Pérez (El Confidencial, Spain); Catiușa Ivanov (HotNews, Romania); Natascha Ickert (Der Standard, Austria); Zornitsa Lateva (Mediapool, Bulgaria); Gian-Paolo Accardo (Voxeurop, France).