New Delhi, Nov. 3 -- The Delhi-Dehradun Expressway is meant to make travel between the two cities much faster. But while the highway has drawn attention for its scale and the time it will save commuters, an environmentalist has been quietly working on something very different along the route. Swami Prem Parivartan, better known as Peepal Baba, says he has planted 40,000 sheesham trees along the expressway. He now wants to add another four lakh.

What makes his effort unusual is the way he goes about it. Peepal Baba and his team often work at night, digging the ground and planting saplings under the cover of darkness. Speaking at the 11th edition of the Himalayan Echoes festival, he described how the team gets the work done before daybreak...