For over 15 years, the city of Paris has planned to plant a new forest on the plain at Pierrelaye-Bessancourt, an outer suburb. But the plan has faced roadblocks as people debate the best use for the land.

French politicians are now actively pushing to make the re-greening project a reality.

The SMAPP plan calls for 5.2 square miles of trees and plants. For perspective, that's about five times the size of New York City's Central Park.

The forest would be approximately 18 miles northwest of Paris' city center.

The forest's location, 18 miles northwest of Paris.
Image: SMAPP

The site at Pierrelaye-Bessancourt borders roads and is close to the Seine River.

The site of the forest is currently an arid wasteland.
Image: SMAPP

For around a century, Pierrelaye-Bessancourt has been a literal wasteland. From 1896 to the 1990s, the city of Paris sprayed sewage residue across 865 acres of the fields to fertilize them. (Researchers later concluded the technique polluted the soil.)

Today, the area acts as an unofficial landfill for Parisian trash.

Paris now wants to transform the area into a lush forest. For the trees to reach maturity, it would take 30 to 50 years.

An artist's rendering of what the forest will look like.
Image: SMAPP

As the diagram below shows, the forest would feature hiking trails, an equestrian center, conservation areas, a few parking lots, as well as observation decks.

The forest would include hiking trails and conservation areas.
Image: SMAPP

The forest would create a habitat for plants and wildlife. It would also help lower greenhouse-gas emissions since trees consume CO2. The site would be relatively free of cars, which contribute heavily to carbon emissions as well.

A new forest would create a habitat for wildlife.
Image: SMAPP

The project is one of the city's latest efforts to reduce air pollution in and around Paris.

In recent years, Paris has tried to install more pedestrian-oriented green spaces in the city. For example, a new car-less park and promenade along the Seine River opened in summer 2016.

This car-less promenade along the Seine River was installed in 2016.
Image: Franklin Azzi Architecture

As CityLab notes, the forestry project will likely face some challenges. As many as 1,500 trailers are squatting on the land, and getting full approval will require a lengthy series of community meetings.

The plan to devote such a large swath of land to a forest rather than a money-making development is certainly ambitious. But it also signals a growing urban movement to green-ify the world's cities.

In the past decade, Chicago has invested hundreds of millions of dollars toward revitalizing and building more parks in the city. And in 2015, Singapore built a 250-acre development of "supertrees" — high-tech structures featuring more than 150,000 plants that collect solar energy. Ino Aguascalientes, Mexico, an oil pipeline was recently converted into a public park — La Línea Verde — that passes through 90 neighborhoods.