For what work is the famous environmental expert Sundar Lal Bahuguna known?

Explanation

The famous environmental activist/environmentalist Sundar Lal Bahuguna, who received the Rashtriya Ekta Puraskar and the Tree-Man Vrikshmanav Award, is known for the Chipko Movement and efforts related to the conservation of trees. For his outstanding services in the field of environment, the Government of India had announced the Padma Shri for him, which he refused. In past years, in view of the possible ecological destruction due to the Tehri Dam, he continued to oppose the construction of the Tehri Dam.