DELHI — It’s one of the paradoxes of Delhi: What is one of most polluted metropoli in the world is also one of the greenest. Almost one-fifth of the region is covered by vegetation, a green area that virtually doubled between 2001 and 2011, expanding from 37,000 acres 73,000.

Inside the capital of Delhi alone, 80 square kilometers (19,700 acres) of forest have been miraculously saved.

There, the happiest inhabitants are not the ministers or the businessmen who can afford villas with gardens — but the antelopes, the foxes and the 300 different bird species. Only they can enjoy a life in silence, far from the roadways and the tailpipes, in the heart of a city of 17 million people.

NGO Toxics Link’s Kush Sethi, an environmental defense group, organizes nocturnal visits in Sanjay Van, one of the four Delhi forests and the only one open to the public. Inside it, noise from the crowded streets vanishes, the air is fresher, and the moonlight takes guides the strollers. Water from a reprocessing plant flows along stream beds leading to a pond, where cranes and ducks have established themselves. Visitors can climb up a tower that was built to watch birds. From there, you can see the monuments in the distance that are reminiscent of Delhi’s old days of splendor.

Delhi’s urban forests are home to one of the richest biodiversities in the world. Migratory birds still stop there twice a year, despite the planes in the sky, and foxes still hunt. But rumor has it that their tranquility could be due to the ghosts. “Many inhabitants are scared of entering Sanjay Van because they believe the place is haunted,” says Sethi. “A woman dressed in a white sari is said to appear there from time to time, and ghost hunters organize expeditions.”

The only people who are banned from visiting the forest are real estate developers. The silence of Delhi’s untouched woodland is worth millions. Still, thanks to the long battle fought by environmental organizations, construction has been forbidden since 1996. This protection is actually a loyal nod to the city’s history. It is because of its forests that the first inhabitants chose to settle in Delhi, between the mountains of the Aravalli Range, which offer some altitude, and the Yamuna River. The Mughal emperors used it as a hunting ground, while the British sought to turn it into a “sea of vegetation” to make the capital of their Indian empire more beautiful.

The healthy heart of Delhi

A few decades later, it has become Delhi’s green lung, helping the city’s residents breathe better by producing oxygen. “Thanks to the forests, the scorching temperatures in the summer are lower, while concrete just absorbs the heat,” explains Ravi Agarwal, director of Toxics Link. “The soil also sucks the water from the monsoon and thus feeds groundwater tables.”

The luxurious vegetation has another advantage: It protects the royal tombstones and other historical vestiges from the bulldozers.

But can Delhi afford to keep its forests even as thousands of migrants come to the city every year and have trouble finding accommodation? In 1996, the very poor Odh community, which used to live in the forest, was driven away. The poorest continue to live illegally on the edge of the woods, in makeshift shelters, and sometimes cut a bit of wood to warm themselves up during the winter or to cook bread.

The local authorities have tried several times to build highways or water pipelines on portions of the forest, but their attempts were in vain. The trees are protected. “With growing pollution, it’s obvious that the forests are not a luxury but a necessity,” says Agarwal. “And we shouldn't parcel them out because that would put their ecosystem in danger.”

The other paradox concerns India as a whole. Forests are better protected in areas like Delhi than in parts of the country where their size is reduced every year under pressure from the mining industry. Although the forests are sacred in these regions, the animist tribes that live there do not have the same political weight as the inhabitants of the capital.

In Delhi, before a tree can be cut down, authorization must be obtained from the local forest department, which requires pages of paperwork and the greenlight of people who live nearby. And the planting of 10 trees is required. This measure explains the growth of green areas. “But the newly planted trees are not always of good quality, and planting trees on isolated bits of land doesn't make a forest,” warns Pradip Krishen, author of the book Trees of Delhi.

The authorities in Delhi decided recently to restore the forests’ original biodiversity, which was severely affected by colonization. The British introduced a tree originally from Central America, the Prosopis juliflora, which destroys local species.

Despite local government efforts, environmental groups remain cautious. “Because the same government also wants to expand the city and build new infrastructures,” explains Agarwal. The Toxics Link director hopes that through the forest visits he organizes, the people of Delhi will become more aware of the issue.

“There’s so much peace and quiet here that it gives me goosebumps,” says a participant from the top of Sanjay Van’s observation tower before calling her mother on her cellphone and asking, “How about we drop everything and come live in the forest?”