with contributions from Fabio Salbitano, Silvano Fares, Marco Marchetti, Antonella Andretta, Nicoletta Toffano and Giorgio Vacchiano

The climate is changing. And you can feel it, especially in cities. Through their wasteful behaviours and scant regard for resource conservation, cities are a cause of climate change, but also its first victim. To reduce the scale of climate change's effects and increase the resilience of cities, many international organisations recommend adopting "nature-based solutions". Among these, urban forests — which encompass woodland patches, tree-lined avenues, large parks, urban allotments, gardens, historic villas and neighbourhood green spaces — have the greatest potential to shift the paradigm of "being and building" cities.

Urban hypertrophy

The cultivation and use of trees outside the forest as a resource for communities dates back to the Neolithic, when human societies began transforming Mediterranean forests into agricultural land. Even in "slash and burn" systems, it was common to preserve specific trees for their spiritual or symbolic value, and right up until the early twentieth century, trees, woodlands and rows of trees were an intimate part of both urban and rural landscapes (think of the cypresses in Tuscany or the pine trees of Rome). Over recent decades, however, cities have undergone a phase of overflowing growth. The example of the Netherlands, and of our own Po Valley, is emblematic: relatively vast territories that have become a single structural and functional integration of urban realities. Projections point to further growth in the cities of "megalopolitan" Asia and Latin America, but also of the continent considered rural by definition until just a few years ago: Africa. At a global level, 60 per cent of the area projected to be urban by 2030 has yet to be built, and 70 per cent of humans will be living in cities by 2050.

This unprecedented growth places enormous pressure on the environment, well beyond urban boundaries. Cities cover 3 per cent of the Earth's surface yet account for 60–80 per cent of global energy consumption and 75 per cent of the world's carbon emissions. Urban areas, which are growing faster than the population, substantially alter local and regional climates through the "heat island" effect, and reduce the availability of natural resources — in particular water, wood and energy — due to land consumption (2 square metres per second!) and habitat loss. Moreover, the majority of future expansion will take place in areas with limited economic development and institutional capacity. This could restrict opportunities to implement "smart" urbanisation and render new city dwellers more vulnerable to extreme events, exacerbate inequalities and conflicts of interest over land use, increase environmental degradation and deteriorate public safety and health, above all to the detriment of the most disadvantaged sections of communities.

Bad air

It is well established that deforestation, ecological fragmentation and urbanisation are co-responsible for the "species spillover" in the spread of zoonoses, to which, on the other hand, we are rendered more vulnerable by urban pollution. But the fact that city air is not particularly healthy is no recent discovery. On 26 November 1948, an extremely dense fog began to envelop London and shrouded the city for six days. Since then, a wide body of scientific literature has investigated the role of pollution in urban areas (particulate matter, ozone, nitrogen oxides and sulphur oxides) on citizens' health and quality of life. The World Health Organisation reports seven million premature deaths per year from pollution worldwide (550,000 in Europe), a figure far higher than the deaths directly caused by coronavirus. The European Environment Agency estimates around 60,000 premature deaths per year in Italy from exposure to PM2.5 alone. After poor diet, smoking, hypertension and diabetes, fine particulate matter is the fifth leading cause of mortality in the world.

Cities, simultaneously the causes and victims of the three crises of our time — the climate crisis, the health crisis and the biodiversity crisis — bear the moral responsibility, cultural capacity, and political and economic power to lead the search for solutions.

Urban forests, nature-based connections

Among the UN's sustainable development goals, goal 11 aims to "make cities and human settlements inclusive, safe, resilient and sustainable". And it is no coincidence that to achieve this, the focus falls on forests and trees, replacing "grey infrastructure" with "green" infrastructure. Cities, in short, cannot survive without forests, but must be able to rely on them both for mitigation (replacing fossil energy with renewables and the most climate-impacting materials with bio-based materials) and for adaptation. Increasing the number of trees, protecting urban biodiversity and countering soil sealing are the pillars of designing smart, bio-cities built around urban forests and "punctuated" by trees and vegetation. Many cities around the world have already begun down this path — to name a few: Melbourne, Vancouver, Singapore, Bogotá, Curitiba, London, Barcelona and Milan.

Too often, however, these initiatives remain confined within urban boundaries. To succeed in this endeavour, cities cannot act alone, thinking only of their own territory; they must instead build habitat networks, connect with rural areas and eliminate their internal boundaries, which are always lines of injustice and degradation. In short, they must have the courage to broaden their perspective. This means designing the new "bio-cities" and linking them to the wider territory. This is the underlying idea of the World Park project, proposed by Richard Weller, which grew out of the study of biodiversity hotspots, the planet's 160,000 protected areas and Unesco World Heritage sites. Or of the Pan-European ecological network, which aims to connect green corridors across the whole of Europe. But the call to put together a project that reflects the interconnectedness governing the planetary socio-ecological system can also come from the bottom up — from citizens, researchers and stakeholders.

From urban wasteland to Parco Nord Milano

One of the most important examples of an urban forest in Italy is Parco Nord Milano, which was created on the site of a bleak post-industrial peripheral void between Milan, Sesto San Giovanni, Cinisello, Bresso and Cormano. This is not a pre-existing pocket of nature that "survived" urbanisation, but a green space of around 800 hectares created from scratch in the most densely populated area of Italy, thanks to the foresight of administrators, politicians, urban planners and researchers who, in the 1960s, realised that those empty spaces were also the last ones available before the cities merged together permanently.

Inside, woodlands alternate with meadows, gentle hills, lakes and clearings: first-time visitors, strolling along the 40 kilometres of pedestrian avenues or cycling along the 35 kilometres of cycle paths, find it hard to believe that not a single poplar, hornbeam, oak or dog-rose bush existed here less than forty years ago — nor did the pétanque courts, children's playgrounds, community allotments, basketball courts and much else besides: a living park needs not only grass and plants but also people who use it, appreciate it and feel it belongs to them. Parco Nord was conceived ahead of its time, with an approach to green space light years away from "keep off the flowerbeds" — but equally different from the typical urban garden requiring constant maintenance.

Or rather, it is calibrated specifically for a surface of this size, including the planned thinning of its woodland — the woodland that forms the heart and soul of the whole project. Every year since 1983, a new plot of woodland has been planted, totalling more than 100 hectares of oak-hornbeam forest. Creating a fully-fledged forest from scratch is no easy undertaking: planting methods were refined and improved over time, through experiments and mistakes, eventually producing a comprehensive compendium of urban forestry, which then fed into the Life Emonfur project, carried out in partnership with Regione Lombardia and Ersaf and funded by the European Community. A constructed nature, then, planted tree by tree, yet as "natural" a nature as possible. The park has no artificial lighting, fences or gates: this has allowed it to become a node within the ecological corridors of northern Milan, along which wildlife soon made its way. Today the park is home to dozens of species of mammals, birds, reptiles, insects and fish, and it is a pure pleasure to watch the grey heron glide swiftly over Lake Niguarda.

An indispensable green lung in one of the most polluted areas on the planet, Parco Nord also plays a significant urban planning role that not only connects the cities along its perimeter, but also encourages soft mobility — cycling, walking along protected routes that cross over traffic arteries via bridges and footbridges, "stitching points" where the park's territory is more fragmented and uneven, precisely because it was "carved out" of the city metre by metre.

From an architectural standpoint, the project — despite being completed over such a prolonged period of time — never lost its unity or coherence, thanks to its designer, architect Francesco Borrella, who was also its creator and first director, and whose signature is unmistakably visible in a design where voids and masses alternate with measure and nothing has been left to chance. Parco Nord Milano, directed since 2000 by agronomist Riccardo Gini, also remains one of the central players in Milan's green landscape. The park has in fact become a key component of the ForestaMi project and of the new Metropolitan Park: an old dream of a green belt that would embrace Milan by linking the parks of the Metropolitan City and creating new ecological corridors between them. A dream currently on hold, awaiting completion before the 2026 Winter Olympics — of which it was a focal point in the winning bid.

A strategy for Italy

Like Parco Nord, our country has the potential to serve as an open-air global laboratory. Very recent data confirm that Italy has become a "forested" country: a quiet trajectory, first shaped by 19th-century reforestation policies and then by the spontaneous or planned abandonment of farming and pastoralism in inland areas. Today, boosted further by the creation of the Natura 2000 network, protected areas in Italy cover a vast portion of the country (around 20 per cent), more than half of which is forested. Yet only 4 per cent of protected areas cover lowland zones, close to cities or with a high density of infrastructure.

At a national scale, it would therefore be essential to adopt a scientifically robust project that involves local authorities, the research and professional communities, trade associations and the third sector. The first step was taken with the National strategy for urban greenery, "Resilient and heterogeneous urban forests for the health and wellbeing of citizens", which set out criteria and guidelines for promoting urban and peri-urban forests consistent with the environmental, historical-cultural and landscape characteristics of each place. The strategy rests on three essential elements: moving from square metres to hectares, reducing paved surfaces, and adopting urban forests as the structural and functional reference point for urban greenery.

Urban forests. Designing resilient cities that can change the world

Environment — di Sisef

Climate change is transforming our planet. The goal is sustainability, by expanding urban forests and preserving biodiversity.