Bollywood actors Priyanka Chopra and Rahul Bose are to compete on the World Environment Day June 5 to motivate people to do their bit to save the mother earth.

The Bollywood stars are facing off in a new video for the ultimate Environment Day Challenge - where they are calling individuals, groups, families and schools, even entire communities - to post details of their green activities online.

"And for Priyanka and Rahul, this is where the battle lines get drawn. When registering a green activity on the site, people will have the opportunity to pledge their activity to either one celebrity or the other, " said a statement issued by UN here.

Priyanka has pledged to plant a tree for every green activity registered in her name while Rahul has pledged to plant two.

"Whether it's switching from plastic bags to cloth bags, car-pooling with colleagues or organising a tree-planting day, green activities can be big, small, local, international, noisy, quiet ... just as long as they're green, " it said.

India for the first time is the global host of United Nations Environment Day this year.

UNEP (United Nations Environment Programme) has given the theme "Forests: Nature at Your Service" in alignment with the UN International Year of Forests, 2011. The theme celebrates the multitude of services - providing clean air, housing rich biodiversity, supplying water - performed by the world's forests.

In the run-up to June 5, the environment ministry has also planned a group of activities, including "Green Walkathon", in partnership with the Delhi government at India Gate.

The other significant feature will be organisation of "Green Haat", involving about 52 partners to showcase initiatives, of forest dwellers, minor forest produce federations of various states, women self-help groups, NGO partners, highlighting the value added forest products at Dilli Haat between June 1-5.

Biodiversity film festival for disadvantaged children, general public, prisoners, and Air Force officials will be organised in partnership with Centre for Media Studies (CMS) in the capital from June 1-4 at National Science Centre, PVR's Cinemas, Tihar Jail and Subroto Park to raise awareness about environmental issues through films from eminent national and international filmmakers.