Belknap forms part of the Mount Washington Wilderness, which encompasses of lava and plains. Lodgepole pine trees are common, and there are 28 lakes within the wilderness area. Belknap itself is not forested and its lava flows are generally not vegetated, though there were trees growing on its lava flow deposits in the 1960s according to Taylor (1965). He observed only sparse growth of trees on lava flows from Little Belknap in a report published in the 1980s, noting that soil from Belknap was about thick and made up of lapilli and volcanic ash, which came mostly from Belknap Crater. Along the trail to Little Belknap Crater, there is a tree island with lodgepole pine, mountain hemlock, and true fir. There are also ground squirrels running around on lava flows from Belknap. Along the Oregon Skyline Trail, which passes west of Belknap, there are black-tailed and mule deer as well as lakes stocked with Eastern brook trout