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
A Modern Synthesis
Realizing that certain unifying principles were at work, we attempted to assemble the many pieces of the puzzle we had collected over the years. A few scientists, including Peter Davis and Peter Wardle, had already taken a few halting steps toward such a synthesis, as did Paul Vogler and Max Oettli decades before them. We were now able to bring what had been a fuzzy picture into clear focus. The key came from probing the trees, which record the passage of time and thereby attest to the antiquity of the whole system. The discovery of old-growth forests on so many different cliffs made us realize the degree to which these places remain constant in a changing world.
Whether a continent is cooling in advance of outright glaciation or warming and drying after its glaciers retreat, cliffs can buffer the climatic shifts. Daily excursions in temperature are minimal because the bare rock absorbs solar energy during the daytime and releases it back at night. Seasonal cycles are modest as well, because the summer sun, even at midday, strikes the vertical face of the rock at a low angle, keeping radiation loads moderate. In fact, south-facing cliffs in the northern hemisphere and north-facing cliffs in the southern hemisphere receive their most direct sunlight in midwinter, when the organisms they harbor can benefit from the added warmth.
Vertical forests are also far less prone to the scorching heat of fire than are typical woodlands, in part because they are well watered but mostly because the density of vegetation is too low to allow a conflagration to propagate. These forests have also been largely immune to people's meddling, whether from logging, farming or building suburban subdivisions. Indeed, we suspect that the only widespread disruption of these unique refuges has occurred in Japan, where the popularity of bonsai has led collectors to destroy much of their country's ancient heritage of small, cliff-dwelling trees.
In recent years, many of the vertical old-growth forests in North America and Europe have become threatened, perhaps for the first time in history, by a more modern hobby: rock climbing. In some places we have studied, hundreds of climbing trails crisscross the rocky bluffs, each one bringing scores of mountaineers each weekend to hammer and claw at the rocky crevices and the fragile roots they hold. Although most of the rock climbers we have met cherish the natural world, few of these people know that the roots they are tugging on may be centuries old. Indeed, we too were unaware of the venerability of these trees until we had counted growth rings spanning the rise and fall of empires.
Now when we look at cliffs, we no longer view them as inhospitable places populated with scraggly vegetation. Rather, we see the last remnants of a landscape untouched by humans, refuges for displaced organisms in a disrupted natural landscape, habitats of overwhelming importance to the maintenance of biodiversity that are worth our every effort to protect. We hope that more people will share our vision of cliffs before it is too late to preserve the treasure they still hold.
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