Friday, March 12, 2010

The Niagara Gorge - Canadian Description Outlines Uniqueness

Description: The Niagara Gorge is one of the best known natural areas in the world for its waterfalls, geology and to naturalists in southern Ontario, it is also well known for its woodlands and its bird life. (Larson, B.M., et al, 1999)

Vegetation: The gorge has a great diversity of vegetation, both on bedrock substrates and on deeper soils. On the shallow soils along the gorge rim, semi-open woodlands of Chinquapin Oak, White Oak and Red Oak occur, with prairie openings of Little Bluestem and Rough Dropseed. On deeper soils, a plain forest back from the Whirlpool ravine supports Sugar Maple with scattered Red Oak and White Oak and a small thicket swamp of Grey Dogwood - Buttonbush surrounded by a swamp of Red Maple -Pin Oak - White Ash. The gorge cliffs have open communities of Smooth Cliff-brake and Bulblet Fern, with occasional marl and moss-encrusted seepage zones. Talus slopes in the gorge are largely covered in rich Sugar Maple and Black Maple forests. Northern forests of White Birch, Hemlock and White Cedar, and southern forests of Chinquapin Oak and Basswood - Butternut occur on the large block talus. Other communities on the talus slopes include Staghorn Sumac and Ninebark thickets and extensive open screes of Leafcup and Virginia Creeper. The deeper soils in the gorge, particularly at the Whirlpool and Niagara Glen, have magnificent forests of Sugar Maple with scattered towering Tulip-trees, occasional Tulip-tree groves and, on drier sites, mature forests of Red Oak and Chinquapin Oak. Younger forests of Eastern Cottonwood, White Ash and Ironwood occur as isolated stands. On the Whirlpool slopes, mass-wasting is common on the deep soils, and areas of exposed soil have pockets of Common Reed Grass, Coltsfoot and Big Bluestem. Also frequent in the Whirlpool ravine are seepage zones of Ninebark thickets and wet meadows, with showy wildflowers like Grass-of-Parnassus, Kalm's Lobelia and False Dragonhead. Cobble beaches of Indian Grass and occasional limestone blocks sustaining Upland White Aster occur along the Whirlpool shoreline. [Varga 1995]

Landform: The Niagara Gorge is the province's largest post-glacial incised valley, with a length of 11 km and a depth of 90 m. The gorge was formed over the past 12,000 years by the erosive power of the Niagara River, the Falls having receded from an initial position on the escarpment edge at Queenston. A much older erosive feature is exposed in the gorge at the Whirlpool, where the rapids have worn away at the break in the rock walls that marks the upstream end of the St. David's Buried Gorge, a former channel of the Niagara River cut before the last glaciation and since filled with glacial deposits. The Niagara Gorge incorporates 4 km of the gorge including the narrow Whirlpool Rapids Gorge and Devil's Hole Rapids Gorge, and the wider portions at the Whirlpool and Niagara Glen. Most of the gorge is topped by 10 m cliffs of the Lockport Formation dolostone, the escarpment caprock here. Rubble eroded from these cliffs has produced extensive talus slopes. At the Niagara Glen, a broad terrace along the Niagara River is known as Foster's Flats. This terrace is floored by a resistant sandstone layer, the Whirlpool Formation. In contrast to the rock substrates that cover most of the gorge, the Whirlpool ravine is covered in deep clay loams. [Varga 1995]

Representation: The Niagara Gorge is one of the most significant and certainly the best known natural area on the Niagara Escarpment. Part of the escarpment's largest incised valley and river are represented at the site. The Niagara Gorge also has the best examples in the Niagara Peninsula Section of mature, south-facing broadleaf talus forests, dry open talus and open talus seepage zones, as well as seepage cliffs, thickets and meadow marshes. The escarpment's only examples of Chinquapin Oak rim woodlands and rim prairies occur at the site. The cobble shore and shoreline meadow marsh communities are the only examples along the escarpment south of the Grey Section. The Niagara Gorge also has a noteworthy assemblage of northern and southern community types. Its northern White Birch and White Cedar talus forests are rare in the Niagara Peninsula section, and its southern Tulip-tree and Chinquapin Oak talus forests are restricted to very few sites along the escarpment. [Varga 1995]

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