FEATURE ARTICLE
Cliffs as Natural Refuges
Rocky precipices around the world provide a surprisingly sheltered environment for plants and animals
Douglas Larson, Uta Matthes, Peter Kelly
A New Old-Growth Forest
With some rapid grant writing, we secured funds to conduct a proper survey of these intriguing trees. For that study, we cored more than 800 trunks and counted their microscopic growth rings, producing impressive results: It turned out that the cliffs of the Niagara Escarpment shelter the most ancient forest to be found east of the Rocky Mountains.
Although this conclusion might not have surprised enthusiasts of bonsai, who know to look for diminutive old trees growing on rocky bluffs, it did come as news to the scientific community. Even dendrochronologists, specialists who study past environmental conditions using tree rings, had neglected cliffs entirely as they scoured the globe for ancient trees to sample. Edward Cook of the tree-ring laboratory of Lamont-Doherty Earth Observatory in New York was indeed quite skeptical when we first suggested a collaboration. But in the end, our work together produced a chronology from tree rings that shows variations in summer temperatures for southern Ontario since long before there were any European settlers present to record them.
So what was initially an attempt to measure the damage done by hikers had unearthed a goldmine for dendrochronologists studying climate change. We had also stumbled on the explanation for the lack of young seedlings on the cliffs: New trees rarely took root on the rocky escarpment, but even sporadic regeneration was adequate to support a forest that has been growing ever so gradually for centuries.
And a forest it truly is. Although the cliffs appear largely bare, we count about 1,000 trunks on average protruding from each hectare of the rocky wall—roughly the same concentration as in most other mature forests, which appear denser only because the trees are normally so much taller and fuller. Also, as we discovered with our survey, the distribution of ages of the trees on these cliffs follows a negative exponential curve, mirroring what has been found for other undisturbed woodlands.
A sparse array of small, scraggly trees clinging to the vertical face of a rocky precipice certainly does not fit the popular image of an old-growth forest. Indeed, many of the trees look downright sickly, with considerable dead wood intertwined with live growth (an arrangement allowed by the peculiar sectored architecture of hydraulic pathways in the trunks). There is no competition here for the giant redwoods or majestic sequoia of the Pacific Northwest, for example. Mature cedars on the Niagara Escarpment are rarely more than a half a meter in diameter, even though some of these trees have been growing there since before the Norman conquest.
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