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Paris Turned Its City Hall Plaza Into a Forest. Philadelphia Has Room to Ask the Same Question.

In June 2025 Paris opened an urban forest at the Hotel de Ville. Here is what the data says and what Philadelphia's own numbers make hard to ignore.

By Harry Hayman 8 min read
Paris Turned Its City Hall Plaza Into a Forest. Philadelphia Has Room to Ask the Same Question.

June 21, 2025, was the Fête de la Musique in Paris, the one night when the whole city seems to agree on something: music goes on every corner, in every courtyard, out of every open window along every block. But the thing that opened that day outside the Hôtel de Ville was not a stage. It was a forest. The Paris city government inaugurated an urban forest on the forecourt of its own city hall: 2,500 square metres of the main plaza broken open, a thousand of those metres dug down to living soil, fifty large trees planted directly in the ground alongside more than twenty thousand plants, shrubs, and ferns. I kept returning to one image in the coverage. Not a neighborhood park, not a school garden, not a strip of leftover green beside a rail line. The front plaza of the institution that runs a major world capital, turned into something that breathes. I am writing this piece not to praise Paris but to ask what it would take for an American city, and specifically this one, to actually mean it when it makes the same argument.

What Paris Did, Precisely

The urban forest at the Hôtel de Ville forecourt is the third in a series Paris has built since 2020, following earlier installations at the Place de Catalogne and the Bois de Charonne, with a fourth announced for the Place du Colonel-Fabien. The forecourt work covers 2,500 square metres in total. A thousand of those metres were broken all the way down to open soil rather than left sealed with planters sitting on top, and that distinction matters to the roots. Fifty large trees are planted in that open ground, species chosen for resistance to the drier, hotter summers Paris is already experiencing: oak, hornbeam, honey locust, Julian’s hackberry. Reporting from the project has also cited container plantings bringing the total tree count to as many as 150, though the fifty trees in direct contact with open soil represent the ecological core of the installation. The work started in October 2024 and the forest opened eight months later. No budget figure for this project has been published by the city of Paris, and I am not going to invent one.

This was not a one-time gesture. Since 2020, Paris has removed more than ten thousand outdoor parking spaces and introduced greening projects on 197 streets. In March 2025, Parisians voted in a referendum to add five hundred more streets to the program. The result was 65.96 percent in favor. The city has done this across multiple administrations, backed by a public mandate recorded in a ballot box, which is a different political structure than a single executive order or a mayoral design initiative.

What the Air Data Actually Shows

Airparif, the agency that monitors air quality across the Île-de-France region, published its 2024 annual report with a figure worth reading carefully: nitrogen dioxide concentrations across the full region dropped 50 percent between 2005 and 2024, and fine particulate matter dropped 55 percent over the same nineteen years. That measurement covers the entire Île-de-France, not just the city of Paris proper, and I want to be precise about that distinction because a city claiming the air quality wins of a whole region is a different claim from a city achieving those improvements within its own boundaries. The same report names an honest exception: ozone has not followed the other pollutants down. The climate is working against it. About 2.6 million residents of the region would still exceed the stricter 2030 European standards for ozone exposure. The trajectory on nitrogen dioxide and fine particles is real. The picture is not complete, and Airparif says so plainly.

The American context I read those numbers against: a study by Choma and colleagues published in the Proceedings of the National Academy of Sciences in 2021 found that on-road transportation remains a major driver of fine particle mortality in the United States, and that emission reductions between 2008 and 2017 prevented tens of thousands of early deaths, meaning the baseline they measured from was far more deadly than the improved numbers. Separately, the National Highway Traffic Safety Administration reported 7,080 pedestrian deaths on American roads in 2024. That number has held near its current level for several years while most American cities continue to answer it by widening roads and adding lanes.

What Philadelphia’s Numbers Say

I live and work in this city, and I want to be specific rather than general about what the local data shows. The Philly Tree Plan, Philadelphia’s first urban forest strategic plan, documents a tree canopy covering roughly twenty percent of the city as of its 2023 baseline. That average hides a range that tells a different story than the aggregate: some neighborhoods carry canopy coverage above forty-five percent while others sit below five percent. The direction of that coverage has been down. Between 2008 and 2018, Philadelphia lost more than a thousand football fields worth of tree canopy. The plan sets a ten-year goal to reach thirty percent. A $12 million federal grant from the USDA, awarded in 2024 under the Inflation Reduction Act, has put money behind the accelerated planting work.

WHYY has reported that Philadelphia’s built environment raises surface temperatures by as much as twelve degrees Fahrenheit in the city’s most heat-burdened areas. A heat mapping study conducted in summer 2022 found that on a ninety-five degree day, some parts of the city ran more than ten degrees hotter than others. The neighborhoods at the top of that range are almost always the same ones with the highest proportions of sealed surface and the lowest tree cover. That pattern does not happen by accident. It reflects decades of investment decisions in which asphalt was treated as infrastructure and trees were treated as amenities, a budget-category distinction with measurable public health consequences.

What Philadelphia Has Built, and Where the Gap Remains

The most honest comparison between Paris and Philadelphia is not between their grandest statements but between the institutional commitments they have actually made and sustained. Philadelphia’s Green City, Clean Waters program represents more than one billion dollars in committed investment through 2036 for green stormwater infrastructure: tree trenches, vegetated bump-outs, permeable pavement, depaving projects in parking lots that become rain gardens. That commitment came not from a mayoral branding initiative but from a 2011 consent order under the Clean Water Act requiring the city to reduce combined sewer overflows. The legal obligation did something a mayoral preference alone might not have sustained across administrations and budget pressures: it kept the money moving.

Dilworth Park, the plaza on the west side of Philadelphia’s own City Hall, came directly from that green infrastructure commitment. The 2014 redesign reduced the site’s impervious surface by 38 percent, added plantings and lawn areas, and integrated a stormwater catchment system beneath the fountain that performs real environmental work. It is a genuinely better space than what it replaced, and it gets used by thousands of people every day. What it is not is a forest. The Hôtel de Ville project is a different kind of decision: not a plaza upgraded to perform better than its predecessor, but a deliberate replacement of the logic that put concrete there in the first place. Open soil in the center of a civic landmark. Trees that will take twenty years to reach their full height.

The Question Philadelphia Has Room to Ask

The comparison that keeps sitting with me is a simple one. Philadelphia City Hall and the Hôtel de Ville occupy equivalent positions in their cities: civic anchors, public landmarks, historically contested ground. The Paris project took eight months to build after a political process that stretched across years and a mayoral term. The cost has not been made public, which means I cannot tell you whether this is expensive or cheap relative to what sealed concrete costs to maintain over a decade, and neither can anyone else working from the available reporting. What I can tell you is that the Airparif numbers are real and span nineteen years of measurement, and Philadelphia’s canopy loss numbers are real and span a decade, and Dilworth Park shows that civic leadership in this city has already been willing to break open sealed ground in exactly the place where the argument about it is hardest to win.

The photograph from June 21, 2025 shows fifty oak and hornbeam trees standing in open soil in front of the institution that governs Paris. The question I bring back from that photograph to this city is a practical one, not a romantic one. Philadelphia has the institutional infrastructure, the consent order, the federal grant, and the strategic plan. It has a plaza directly beside its City Hall that a redesign already improved once. What it has not yet done is make the trade Paris made: choose the forest over the sealed surface in the place where the choice is most visible and most contested. Whether that happens is not a question the data answers on its own. The data just keeps making it harder to pretend the question is not there.

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