The cramped, concrete jungle that is Tokyo, one of the world's most densely populated cities, has little space for parks. But things are starting to look up.

In an attempt to add a little greenery to the concrete, many city roofs have been converted into gardens.

Rooftop planting has been on the rise since the city government, eight years ago, made it mandatory for new commercial buildings to cover at least 20 percent of available space with greenery.

"You see buildings and buildings all around Tokyo. Tokyo obviously needs more greenery as a city, and rooftop greening maybe one way to do it," said Atsuro Tarutoko, manager of the Hearton Hotel which was built three years ago with a $100,000 rooftop garden.

As well as the soothing aesthetics, experts say the green roofs also provide environmental benefits as the gardens cut indoor temperatures, reducing air-conditioning costs.

"I believe part of our job is to try to merge some quality space into the city's landscape and allow local residents to feel that quality," said Aya Mugita, a construction project developer at a recent green technology expo in Tokyo.

Some information technology companies are already cashing in on the rooftop greenery business.

"We provide software that simulates the amount of carbon dioxide that can be absorbed by a garden based on the types and volumes of trees to be planted there," said Yutaka Tanaka of Tokyo-based software maker Ecol System.

But experts say converting the urban jungle that is Tokyo into a green refuge will take a few decades.

(Agencies)