FEATURE ARTICLE
Cliffs as Natural Refuges
Rocky precipices around the world provide a surprisingly sheltered environment for plants and animals
Douglas W. Larson, Uta Matthes, Peter Kelly
Splendid Isolation
At this stage in our research, we began to interest other biologists in studying the animals that inhabit these cliffs. For example, Jeff Nekola of the University of Wisconsin at Green Bay examined the gastropods of the Niagara Escarpment in Canada and its extension into the U.S. He discovered that these cliffs support the richest snail faunas in the Great Lakes region, with some individual 10-by-10 centimeter plots containing 21 separate taxa. Jeff Matheson, a graduate student at our institution, examined the distribution of birds and small mammals on the Niagara Escarpment and compared these patterns with those he charted on the forested plateau. Matheson found that the diversity of these creatures was, in fact, higher around the cliffs than in the level woodlands nearby.
By 1993, ecologists in distant parts of the world were beginning to publish studies of other cliffs, and their results had a familiar ring: Rocky precipices everywhere, it seemed, shelter an exceptionally rich collection of plants and animals. Many types of flies, spiders, salamanders, rodents and raptors, as well as large numbers of plant species appearing nowhere else were being sighted on cliffs in many countries. Interestingly, the genera—and in some cases even the species—matched those found on the Niagara Escarpment.
We saw this similarity ourselves in a study that we mounted in 1997 with the help of colleagues in the U.S., U.K., France and Germany. For this investigation, we sampled more than 200 mature Thuja, Juniperus and Taxus trees on 46 separate bluffs in North America and Europe. Virtually everywhere we looked, the cliffs presented us with slow-growing, ancient woodlands that were almost identical in appearance to the forest perched on the face of the Niagara Escarpment. Other cliff-dwelling plants, including ferns and cryptoendolithic algae also proved to be alike on the two sides of the Atlantic. This correspondence was telling us that the same ecological forces must be at play in these widely separated but similarly configured locales.
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