Cliffs and Their Unique Ecosystems

 Cliffs and Their Unique Ecosystems

A cliff is a steep, often vertical face of rock, earth, or ice, commonly formed by erosion, weathering, and the force of gravity. Unlike hills, which slope gently, cliffs rise sharply, sometimes appearing almost perpendicular to the ground.

Among the most iconic examples are the White Cliffs of Dover, formed nearly 500 years ago by Ice Age floods. Their striking white colour makes them visible even from the French coast on clear days. I had the opportunity to visit them during my last tour of England—a truly unforgettable sight.

Geographically, cliffs occur in coastal areas, mountain ranges, riverbanks, and escarpments. Despite their harsh terrain, these vertical landscapes support surprisingly rich ecosystems. Cliffs feature ledges, cracks, and crevices that offer microhabitats to a variety of plant and animal species. These environments, though challenging to study due to their vertical nature, are biologically significant and often overlooked.

The Niagara Cliffs: A Hidden Wilderness

One of the most fascinating cliff systems extends from the Niagara Falls area, tracing a line through the Great Lakes region to Door County, Wisconsin, and disappearing beneath glacial till near Chicago. This region, known as the Niagara Escarpment, consists largely of dolomite rock and has undergone centuries of natural erosion. Notably, a dramatic collapse occurred at Niagara Falls in the 1850s, sending a horse-drawn carriage tumbling into the canyon—a stark reminder of the cliffs' dynamic nature.

Before 1986, the limestone cliffs along this escarpment were thought to be barren. However, naturalists and climbers later discovered stunted forests, ferns, lichens, and signs of wildlife, including bobcats, chipmunks, and snakes, inhabiting the cliff face. This sparked a deeper question: How do trees grow from bare rock?

This simple inquiry led to revelations about an ecosystem containing some of the oldest and slowest-growing trees in Canada, as well as ancient woody debris unmatched in any eastern North American forest.

Cliffs as Distinct Ecosystems

To determine whether cliff habitats are distinct from surrounding forests, scientists examined whether the cliff ecosystem changes in tandem with adjacent landscapes. They found that it does not confirm the cliff as a unique ecological zone.

Sixty-six feet from a cliff edge, the forest reflects regional norms: tall canopies, diverse flora, rich soil, and moderate environmental conditions. As one approaches the edge, the soil thins and the canopy shortens, though tree species remain similar. Within two meters of the edge, conditions change drastically—soil becomes sparse, water availability fluctuates, and protection from snow vanishes. Here, plants such as dogwood, ferns, and grasses adapted to dry, harsh environments dominate. The cliff-edge trees—primarily Thuja occidentalis (eastern white cedar) and Juniperus virginiana (eastern red cedar)—show twisted, deformed growth where they emerge from the rock.

Life on the Cliff Face and Beyond

From the cliff edge to the base, gravity dictates ecological structure. Organisms here endure crumbling rock, extreme temperatures, and scarce resources. Algae, fungi, and lichens inhabit rock crevices, while resilient trees and ferns cling tenaciously to the cliff face. Birds of prey use the inaccessible ledges for nesting.

At the bottom, fallen debris and enriched soil form a chaotic landscape of lush vegetation—dogwood, impatiens, raspberries, and even poison ivy—amid bare rocks and shattered limbs. Snakes are common, thriving in this rugged terrain. As the slope becomes more gradual, the ecosystem again mirrors the rich forest found atop the plateau.

How Do Cliffs Host Such Life?

At first glance, it seems cliff species are specially adapted to these environments. However, experiments revealed a surprising truth: the cliff is inhospitable to all species, including those dominating it. Eastern white cedars, though prevalent on cliff faces, grow poorly there and thrive in nearby forests. When seedlings are planted on cliff edges, they die within a season—but survive for years in adjacent woodlands.