The tundra is the area where the subsoil is permanently frozen. It is also above the tree line. Here you can see there are only a very few trees and although they are full-grown and very old, they are relatively small. This photo is in Denali National Park and the tree line is only about 3000 feet above sea level. Here in Utah, where I live now, the tree line is visible from my front room window and it is above 10,000 feet.