Forty-five years ago this month, the United States signed a piece of legislation to 'protect and preserve America's wilderness heritage in perpetuity'. On 3 September, when the Wilderness Act was passed, 9.1m acres of America was designated as wilderness. Today, there are 756 wilderness areas covering nearly 110m acres in 44 states and Puerto Rico - nearly 5% of America's total land area. To celebrate these habitats and the anniversary of the act, the Wilderness Society asked its members to submit their best images to a photography competition. Here is a selection