Evidence for the widespread occurrence of ancient forests on cliffs

Aim The objective of this work was to determine if the existence of ancient forests on cliffs was specific to the Niagara Escarpment, Canada, or part of a globally widespread pattern. Location Sixty‐five cliff sites were visited in five countries in the temperate climatic zone, and trees were sampled for age and growth rate on forty‐six of these. Methods Two hundred and twenty‐four core samples or cross‐sections were taken from trees on cliffs that varied in height, aspect, rock‐type, and exposure. General observations were also made of regeneration of the tree species forming the mature canopy, and other habitat conditions. Results The evidence shows that ancient slow‐growing forest occurs on most cliffs. Age and growth rate distributions were similar at all treed sites. Small‐statured Thuja, Juniperus, or Taxus stems with age estimates in excess of 1000 years were found in the United States, the United Kingdom and France, and small Pinus and Quercus stems nearly 400 years in Germany. There was a high rate of recurrence of plants in the genera Polypodium, Asplenium, Cystopteris, Campanula, Rosa, Prunus, Hedera, and Sorbus. Most of the sites appear to be habitats of completely natural origin. Conclusions We conclude that ancient natural forest is a normal feature of cliffs, at least in the temperate zone.