A species of willow developed that does not grow vertically upwards, like it’s European and American relatives. To do so would to risk being flattened by the ferocious Artic wind. Instead it grows horizontally, keeping close to the ground. Even in the most favorable circumstances it seldom exceeds four inches in height. But it may become as long as some if it’s southern relatives are tall. When you walk across a carpet of such prostrate tree, you are, in effect walking over a woodland canopy.