The range of altitude in Grand Teton National Park impacts the types of plant species found at various elevations. In the alpine zone above the tree line, which in Grand Teton National Park is at approximately , tundra conditions prevail. In this treeless region, hundreds of species of grass, wildflower, moss and lichen are found. In the subalpine region from the tree line to the base of the mountains, whitebark pine, limber pine, subalpine fir, and Engelmann spruce are dominant. In the valley floor, lodgepole pine is most common but Rocky Mountain Douglas-fir, and blue spruce inhabit drier areas, while aspen, cottonwood, alder, and willow are more commonly found around lakes, streams and wetlands. However, the tablelands above the Snake River channel are mostly sagebrush plains and in terms of acreage is the most widespread habitat in the park. The sagebrush plains or flats have 100 species of grasses and wildflowers. Slightly more elevated sections of the plains of the northern sections of Jackson Hole form forest islands with one such obvious example being Timbered Island. In this ecotone, forested islands surrounded by sagebrush expanses provide shelter for various animal species during the day and nearby grasses for night time foraging.