The question of which trees should be planted on Italian urban streets has become more pressing as summer temperatures in Mediterranean cities regularly exceed the heat-stress thresholds at which many established species begin to decline. The mismatch between planted species and local climate conditions — documented in a 2025 Roma Tre University study — has prompted municipalities to revisit their standard planting lists for the first time in decades.
The Scope of the Problem
The Roma Tre study, led by researchers from the Department of Science, analysed the climatic suitability of every tree species present in documented Italian urban inventories. Out of 177 species currently used in Italian street plantings, the majority were found to be poorly matched to the climate zone in which they are planted — either requiring more soil moisture than is available during dry summers, or exhibiting leaf-scorch and early defoliation above 38°C canopy air temperatures.
The study's authors examined 190 native Italian species as potential alternatives, of which 44 were already in limited urban use. The remaining 146 were identified as candidates for expanded trialling, with recommended prioritisation criteria including drought tolerance, resistance to urban soil compaction, and canopy geometry suitable for pedestrian clearance.
Pyrus calleryana: Documented Thermal Performance
Among the species tested in controlled street-segment studies, Pyrus calleryana (Callery pear, cv. Chanticleer) returned some of the most consistent results in thermal comfort research. A 2025 study published in Theoretical and Applied Climatology, focusing on UTCI hotspot mitigation, found that Pyrus calleryana reduced the Universal Thermal Climate Index between 3.19°C and 6.27°C on peak summer days — transforming identified outdoor hotspots into thermally acceptable zones by mid-afternoon.
The species' compact crown geometry and tolerance of alkaline, compacted urban soils make it practical for installation in the narrow tree pits typical of central Italian street sections, where root space is frequently constrained by underground utilities.
Cercis siliquastrum: Community Ecosystem Value
Cercis siliquastrum (Judas tree) is already common in Rome, where its early-spring flowering is a recognisable feature of street corridors including Via Cola di Rienzo. The same 2025 UTCI study placed it first for overall community ecosystem benefit — a composite metric accounting not only for thermal comfort but also for air quality improvement, biodiversity support, and public amenity value.
Rome's current planting season (November 2024 to March 2025) includes 95 Cercis specimens on Via Cola di Rienzo, suggesting the species is being actively expanded beyond its existing street presence. Its deep root system and moderate water requirements make it compatible with permeable paving specifications increasingly required by Italian municipalities for new street-tree installations.
Findings from Pisa and Lecce
Research at the University of Pisa, examining green infrastructure on street segments with and without tree canopy, found that large-canopy trees (crown diameter above 8 metres) reduced ecosystem service losses from urban heat by 40–50% compared to unshaded segments. Smaller trees — crown diameter below 5 metres — produced reductions of 30–40%, still measurable but less effective in absolute terms during extended heatwaves.
A complementary study from Lecce modelled the outdoor thermal benefit of street trees in a Mediterranean coastal city and found that tree placement over permeable rather than sealed surfaces amplified the cooling effect by an estimated 12–18%, through the additional evapotranspiration enabled by soil moisture retention. The finding has direct implications for paving specifications accompanying municipal planting tenders.
Species Recommended in Current Italian Urban Forestry Literature
- Pyrus calleryana — narrow crown, alkaline-soil tolerant, strong UTCI reduction in street corridors
- Cercis siliquastrum — native, deep roots, high biodiversity value, established track record in Rome
- Quercus ilex (Holm oak) — evergreen, drought-resistant, large canopy at maturity; requires large pit and long establishment period
- Celtis australis (European nettle tree) — compact, tolerant of dry and compacted conditions, commonly used in historic Italian centres
- Gleditsia triacanthos (Honey locust) — rapid growth, light-filtering canopy, low litter; recommended with caution in areas with pedestrian density due to thorns on wild specimens
What Municipalities Are Currently Using
Milan's Forestami planting cohorts include a wider palette than previous decades, with increasing proportions of native oak species (Quercus robur, Quercus petraea) in peripheral green corridors and agroforestry zones. Street-level planting within the central comune continues to be dominated by Platanus ×acerifolia (London plane) for established avenues and Tilia species for new installations — both under review given their susceptibility to prolonged drought stress and declining pathogen resistance.
Brescia's 2024 Bilancio Arboreo (tree balance sheet) — which recorded 1,168 plantings against 585 removals in the period from March 2023 to April 2024 — does not publish a species breakdown by count, but the city's publicly stated preference for native species with documented local climate fitness aligns with the Roma Tre research recommendations.