The Italy National Agency for New Technologies, Energy and Sustainable Development (ENEA) has completed a comparative analysis demonstrating that periurban forests can substantially cut urban mortality—but only if planted with the right tree species. The agency's findings, published in Nature's Communications Earth & Environment in collaboration with the University of Milano-Bicocca and the Italy National Research Council (CNR), reveal a stark economic and health trade-off: choosing high-emission trees over low-emission varieties can cost Italian cities tens of millions of euros annually and worsen air quality instead of improving it.
Why This Matters
• Florence faces up to €560 M in heat-related health costs without strategic tree planting, according to the ENEA simulation.
• Species selection is critical: oak trees emit volatile organic compounds that react with urban pollutants to form PM2.5 and ozone; pines do not.
• Italy recorded 4,597 heat deaths in 2025—the highest in Europe—underscoring the urgency of urban cooling strategies.
• A 30% tree canopy target could reduce heat-related mortality in elderly Italians by 36%, per CNR terrestrial ecosystem research.
The Science Behind the Tree Trade-Off
ENEA researchers modeled two planting scenarios around Florence, Zagreb (Croatia), and Aix-en-Provence (France). In the first, they simulated extensive planting of pedunculate oak (Quercus robur), a species that emits large quantities of biogenic volatile organic compounds (BVOCs)—chemicals trees produce as defense against pests, pathogens, and environmental stress. In the second, they used stone pine (Pinus pinea) and black pine (Pinus nigra), both low-emission species.
The difference was measurable and costly. While BVOCs themselves are not toxic, they react with nitrogen oxides (NOx) from vehicle exhaust and industrial emissions to form secondary pollutants: ground-level ozone and fine particulate matter (PM2.5). Both are linked to respiratory and cardiovascular disease.
In Florence, planting high-emission oaks increased urban PM2.5 concentrations by an average of 0.80%, compared to just 0.35% with low-emission pines. The implications extend beyond air quality: researchers quantified excess mortality tied to thermal stress days—both extreme heat and cold—and found Zagreb experienced a 59.4% increase in mortality under high-emission scenarios, Florence 13%, and Aix-en-Provence 2.9%.
What This Means for Italian Municipalities
For Florence, the economic burden of avoidable deaths reached €560 M under worst-case planting decisions. Zagreb's toll climbed to €708 M, while Aix-en-Provence saw €158 M in estimated health costs. These figures capture lost productivity, hospital admissions, and premature mortality—expenses that could be reduced through better urban forestry planning.
Italy's Ministry of Environment and local authorities now face a strategic choice: invest in low-emission conifers and maple varieties, or continue with traditional oak-heavy planting programs that inadvertently fuel secondary pollution. Alessandro Anav, lead researcher at ENEA's Climate Models and Services Laboratory, emphasized that "some trees emit numerous volatile organic compounds that contribute to the formation of secondary atmospheric pollutants, worsening air quality."
The study arrives as Italian cities grapple with record heat mortality. In 2025, Italy led Europe with 4,597 heat-related deaths, according to data compiled by Imperial College London from hundreds of European cities. The pattern is not random: deaths concentrate in peripheral neighborhoods with poor housing insulation, inadequate air conditioning, and minimal tree cover—a phenomenon researchers term "cooling poverty."
The 30% Canopy Threshold
Separate research coordinated by the CNR Institute of Research on Terrestrial Ecosystems (CNR-IRET) and the State University of New York College of Environmental Science and Forestry (SUNY-ESF) has identified a benchmark: urban neighborhoods that achieve at least 30% tree canopy coverage can reduce heat-wave mortality among residents over 65 by an average of 36%. The team modeled this scenario across 10 Italian cities, simulating the impact of uniform canopy increases during the 2003 heat wave—one of Europe's deadliest.
Benefits proved greatest in densely built, highly populated quarters where concrete and asphalt dominate. Trees cool these areas through two mechanisms: shading (blocking direct sunlight) and evapotranspiration (releasing water vapor that dissipates heat). A single hectare of urban forest can absorb 20–50 tons of CO₂ annually and filter 250 grams of fine particulate per mature tree, according to Italian environmental monitoring data.
The "3-30-300" rule—a guideline gaining traction among European urban planners—calls for every resident to see at least three trees from their home, live within 300 meters of accessible green space, and benefit from 30% citywide canopy coverage. Italy's National Recovery and Resilience Plan (PNRR) has allocated €330 M for planting 6.6 M trees, budgeting roughly €50 per tree for purchase, transport, planting, and seven years of maintenance. However, critics argue this sum is insufficient to establish self-sustaining ecosystems, particularly in southern cities where irrigation costs are higher.
Which Species Work Best
European urban forestry research identifies several resilient, low-emission species suitable for Italian cities:
• Field maple (Acer campestre 'Street Pillar'): Columnar growth, high CO₂ absorption, salt and drought tolerance to -28°C.
• Ginkgo biloba 'Blagon': Ancient species that withstands pollution, heat, cold, and drought.
• Plane tree (Platanus): Self-cleaning bark mechanism naturally sheds pollutants.
• Magnolia: Effective against fine particulate.
• Beech (Fagus): Excels at absorbing ozone and nitrogen dioxide.
• Douglas fir: Proven PM10 reduction capacity.
• White poplar: Particularly efficient at sequestering CO₂.
Conversely, species such as holm oak (Quercus ilex) have shown high sensitivity to embolism under water stress, leading to large-scale die-offs during droughts. Ash, cherry, and callery pear cultivars are under reassessment for their suitability in flood- and drought-prone zones.
Red-leaved cultivars like Norway maple (Acer platanoides 'Crimson King'), rich in anthocyanins, can limit photo-oxidative stress—an added advantage in high-ozone environments.
Economic Payoff and Energy Savings
For every €1 invested in green infrastructure, ecosystem services deliver up to €3 in benefits, according to European environmental accounting models. These include reduced air conditioning demand (saving households €80–200 annually), lower stormwater management costs (trees absorb and filter rainwater, reducing flood risk), and decreased noise pollution from traffic and industry.
Urban forests also enhance biodiversity, providing habitat for pollinators and songbirds, and support mental health and social cohesion. Studies tracking cortisol levels and self-reported wellbeing show measurable improvements in residents who live within 300 meters of tree-lined parks.
Practical Challenges
Achieving 30% canopy coverage in Italian cities requires long-term commitment. Young trees need consistent irrigation for at least three years post-planting—a challenge in water-scarce southern regions. Diversifying species portfolios increases resilience against pests, disease, and climate extremes, but complicates procurement and maintenance planning.
The ENEA study underscores that periurban forests—planted on the outskirts rather than within dense historic centers—offer the most practical solution for cities like Florence, where UNESCO heritage constraints limit interior planting. However, benefits diminish with distance: trees planted more than 500 meters from residential zones contribute minimally to local cooling and air filtration.
Policy Implications
The Italy Ministry of Environment and Energy Security is expected to incorporate ENEA's findings into updated urban greening guidelines later this year. Regional governments in Tuscany, Lombardy, and Lazio have already begun pilot projects using low-emission species lists, and procurement contracts now increasingly specify BVOC emission profiles alongside traditional criteria like root structure and aesthetic appeal.
The CNR-IRET team advocates for integrated planning: pairing tree canopy increases with cool corridors (linear green spaces that channel airflow), green roofs, and reflective pavement to maximize cooling. This approach acknowledges that trees alone cannot solve the urban heat island effect—they must be embedded in broader climate adaptation strategies that also address building energy efficiency and transportation emissions.
As Italy confronts escalating heat mortality and air quality challenges, the choice of which trees to plant has shifted from a landscaping decision to a public health imperative. The ENEA analysis makes clear that not all green infrastructure is created equal, and the difference between oak and pine can be measured in lives and euros.
