If Delhi wants to keep its green heart ticking, it will need more tree doctors. The city's only 'tree ambulance' has its hands full, prompting activists to ask the chief secretary to expand the fleet - and fast.

"We told the chief secretary Delhi needs six more ambulances," says Suhas Borker of Green Circle, a civil society initiative which contributed to the launch of this facility in 2010.

The demand has a lot to do with the widening gap between the number of trees dying and the ones the ambulance manages to save.

Every year, nearly 200 trees become victims of storms or dry up. Many more are destroyed in the name of development.

The project was launched by chief minister Sheila Dikshit and caters to New Delhi Municipal Council's (NDMC) limits. NDMC covers 3% of the city, but houses 46% of its green cover.

At the time of inauguration, Dikshit had acknowledged the need for many more ambulances. But two years on, nothing has been done.

The tree ambulance has a six-member crew trained at Dehradun's Forest Institute of India and handles 8 to 10 complaints every day. Activists say the service has saved 150 trees in two years.

"A number of calls to save trees come to us from non-NDMC areas as well," says Sudhir Bhutanim, another tree activist.

"Saplings also need saving, as authorities after much-hyped plantation drives, fail to look after them."