Ancient stunted trees on cliffs

An undisturbed ancient woodland, dominated by tiny, slow-growing and widely spaced trees, grows on vertical cliffs of the Niagara escarpment in southern Canada1. To investigate whether this woodland is unusual or is part of a previously undetected global pattern, we sampled ages and radial growth rates for trees on cliffs in the United States and in western Europe. We find that vertical cliffs often support populations of widely spaced trees that are exceptionally old, deformed and slow growing. Some of the most ancient and least-disturbed wooded habitat types on Earth are found on cliffs, even at sites close to heavy agricultural and industrial development.