24 - The Flora and Ecology of Southern Ontario Granite Barrens

Summary

Naturally open habitats consisting of exposed granite rock with grassy areas, shrubs, and scattered trees often are referred to as granite barrens. These areas are never entirely barren, but nevertheless, openness and bare rock or rock with only lichen and moss cover is a characteristic feature (Figure 24.1). In Ontario, granite barrens are a restricted and special habitat with unique environmental factors and specialized plants and animals.

The terrain is composed of a ridge and trench system of extensively folded granite rockland. A faulting network (differential displacement of bedrock blocks resulting in long, steep-sided depressions) often exists perpendicular to the folds. The trenches often contain oligotrophic ponds created by beaver, or they may contain bog mats. One of the most striking features is the contrast between adjacent wet and dry land, a consequence of the fact that the granite rock is impervious and holds water in depressions. Lakes, ponds, and other wetlands are often as characteristic of granite rock barren landscapes as are the dry rock exposures. Due to the retention of water in small or shallow depressions, extreme wetness may be followed by extreme drought. In fact, granite rock barrens are characterized by a wide variation in soil depth and in water-holding capacity over a short distance. These variations are responsible for the mosaic patterns of vegetation. The rock is acidic and generally contributes to the formation of acidic soils. The wetlands are generally bogs or acidic lakes.