Paris already counts 219,360 trees. What if we accelerated, to plant a million more by 2050?
In summer, stone and asphalt store heat during the day and release it at night. This is the urban heat island: in the middle of a heatwave, the heart of Paris stays several degrees warmer than its surrounding countryside, at the very moment when the body would need the coolness of night to recover. Paris has about 21 % canopy, one of the lowest covers among comparable major cities. The City is not standing still, but the scale of the challenge calls for a change of pace.
Paris starts from 219,360 trees. The real lever is not only the number, it is the pace. Choose how many trees to plant per year, and until when. The simulator works out what that would add, at maturity.
How to read these figures. The pace is compared to two real benchmarks: the Paris Tree Plan (about 28,000 trees per year) and MillionTreesNYC, where New York planted a million trees in eight years, roughly 125,000 per year. Assumptions: trees at maturity (20 to 30 years of growth); canopy / temperature relationship from the Lancet 2023 study (raising the canopy to 30 % cools a city by about 0.4 °C on average and avoids nearly a third of the excess mortality linked to the heat island, values modelled, not measured in Paris); 25 kg of CO₂ per tree per year (ADEME). Oxygen is a real but scientifically modest benefit (the atmosphere already contains 21 % of it). For air quality, the drop in traffic weighs more than trees alone. In the shade, during the day, felt comfort gains 3 to 5 °C where trees are planted: an educational simulation, not a promise.
A tree takes up about 5 m² of ground but casts nearly 50 m² of crown. The physical space exists: the real constraint is the underground saturated with networks, the trade-off with the car, and the time it takes to grow. Here is where Paris can plant, from the easiest to the most demanding.
School courtyards and de-paved block interiors. Paris has already transformed 203 Oasis courtyards and is aiming for 360 by 2030, out of nearly 800 school and middle-school courtyards. Few trees in number, but islands of coolness as close as possible to residents.
The redesign of the major squares has already given more than 25,000 m² back to vegetation. The real reserve: the 133,000 on-street parking spaces. Converting a share of them frees up considerable planting potential.
100,000 street trees today. Double rows, continuous trenches and de-paved pavements can add tens of thousands more, provided open ground is recreated where the networks run.
35 km of grey belt to turn into a green belt: the City announces 50,000 trees on the embankments and a gradual covering. The largest single reserve, but the most costly. OXO's manifesto, Mille Arbres, was set here.
Tight plantings (Miyawaki method, up to one tree per m²) on leftover land, embankments and squares. This is what makes it possible to approach the million when counting broadly, but their maturity plays out over decades.
About 80 ha of roofs easily greened, but mostly with a light substrate (sedum, grasses): a roof rarely carries a tree, which requires a reinforced structure and a great deal of soil. Roofs count for coolness, very little for the tree count.
These are not promises but records. Each one activated specific reserves, often by taking space back from the car. Here is how.
Urban park, Medellín · PexelsThirty green corridors along the avenues and rivers, 880,000 trees and 2.5 million plants since 2016. The air temperature there fell from 31.6 to 27.1 °C in three years.
Barcelona · PexelsThe superblocks (superilles) give the interior of nine blocks back to pedestrians and trees, with a target of 80 % shading and 20 % permeable ground. At street level, in summer, up to 5 °C less.
Bosco Verticale, Milan · PexelsThe ForestaMi programme aims for three million trees across the metropolitan area by 2030, with about 250,000 already planted. The Bosco Verticale, two towers carrying 800 trees, is its vertical emblem.
Central Park, New York · PexelsMillionTreesNYC planted a million trees in eight years (2007 to 2015), two years ahead of schedule, for about 20 % more canopy. A pace of around 125,000 trees per year.
Paris is not standing still: the Tree Plan targeted 170,000 trees between 2020 and 2026, four urban forests have emerged (place de Catalogne, the forecourt of the Hôtel de Ville), the 2024 PLU bioclimatique requires up to 65 % of open ground on large plots and protects 100,000 street trees, and the ring road is beginning its transformation.
For more than 20 years, OXO Architectes has defended a simple idea: greenery is not placed on the building, it is part of it. The Mille Arbres project was its manifesto, an inhabited forest of about a thousand trees imagined above the ring road at Porte Maillot, a winner of Réinventer Paris in 2016 with Sou Fujimoto. That particular project was ultimately not built, but the same conviction has been built elsewhere, and it stands firm. A million trees, for us, is not a slogan: it is the extension of a method already proven.
An inhabited forest of about 1,000 trees spanning the ring road at Porte Maillot, a winner of Réinventer Paris (2016) with Sou Fujimoto.
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In Montpellier, a residential tower with balconies spread out like branches, now one of the most photographed contemporary buildings in France.
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An inhabited hill covered in terraced gardens, conceived as a living landscape rather than a building set down on its site.
See the project ›Sources · City of Paris open-data census (Les arbres), paris.fr and Regional Court of Auditors Île-de-France 2024 (Tree Plan, Oasis courtyards, PLU bioclimatique) · Météo-France and APUR (heat island, canopy) · The Lancet Planetary Health 2023 (canopy and excess mortality) · ADEME ArboClimat (CO₂) · Nowak et al. and i-Tree (oxygen, air quality) · Medellín, Barcelona, Milan, MillionTreesNYC (precedents). Simulation for educational purposes, values modelled at maturity.
