A perennial woody plant at least 20 ft (6 m) in height at maturity, having an erect stem or trunk and a well-defined crown or leaf canopy. However, no sharp lines can be drawn between trees, shrubs, and lianas (woody vines). For example, the strangler fig (Ficus aurea) is a climbing liana which may develop into a self-supporting tree if the host around which it twines is removed. Many large trees, such as paper birch (Betula papyrifera) or Alaska cedar (Chamaecyparis nootkatensis), become prostrate shrubs at the northern limits of their range in the boreal region or at their altitudinal limits near timberline.