From the majestic valleys of the Grand Canyon to the granite peaks of the Yosemite National Park and ancient trees of Alaska's Tongass National Forest, US President Donald Trump has pledged to make America's federal nature reserves "beautiful again." National parks make up one part of over 600 million acres (243 million hectares) of US public lands that span forests, deserts, waterways and wildlife refuges. "These include some of the most ecologically intact and biodiverse lands in the country," said Jenny Rowland-Shea, who directs public lands policy at the Washington-based think tank, Center for American Progress. But critics say these landscapes are threatened by steep budget cuts and environmental rollbacks  that open them to resource extraction.…