22 - The Cliff Ecosystem of the Niagara Escarpment

Summary

Introduction

The Niagara Escarpment is a 50–100-m high cuesta following the rim of a 450-million-year-old saucer-shaped geological structure known as the Michigan Basin. It extends in a roughly circular shape from Niagara Falls north to Manitoulin Island, across to the junction of Lakes Michigan and Huron at Sault Ste. Marie, then south along the western shore of Lake Michigan. Generally, the Silurian-aged rim is buried by glacial till, but 150 km of exposed near-vertical cliff face is present between Niagara Falls and Manitoulin Island, a straight-line distance of approximately 360 km.

The escarpment lies within the Great Lakes–St. Lawrence Forest (Rowe 1972). The climate of the area is temperate with a strong local influence of the Great Lakes. Mean January air temperature ranges from -5°C in the south to -7.5°C in the north; mean July temperature varies between 21°C in the south to 18°C in the north. Total annual precipitation of 900 mm is evenly distributed throughout the year. Lumbering activities were intense from 1800 to 1920, and the area was almost totally deforested by European settlers. Fire consumed almost all of the forested horizontal landscape of the Bruce Peninsula in 1908 (Gillard and Tooke 1975). However, no evidence of fire was found in cores or cross-sections obtained from trees growing on the exposed vertical cliffs (Larson and Kelly 1991).

Natural History

Cliffs of the Niagara Escarpment support a stable, ancient forest ecosystem whose structure probably has changed little since the melting of the Laurentide ice sheet.