Perhaps Roosevelt's most enduring legacy is an expanded national conservation system. As business interests ravaged America's natural resources, Roosevelt moved to protect them with scientific management techniques. Using his executive powers, TR created scores of national monuments, refuges, and parks, including the Tongass forest reserve, Grand Canyon National Monument, and Muir Woods. All told, he placed over 230 million acres under federal protection.
The US Fish and Wildlife service has a great article about Teddy Roosevelt's Conservation efforts here:
Theodore Roosevelt (1858-1919) The Conservation President