The Niagara River Corridor is part of the Carolinian Forest in Canada which includes species more likely to be found south of the Great Lakes, such as Tulip Tree (Liriodendrom tulipifera), Sassafras (Sassafras albidum), Sycamore (Platanus occidentalis), Flowering Dogwood (Cornus florida), Black Walnut (Juglans nigra), Red Mulberry (Morus rubra), Black Gum (Nyssa sylvatica), Hop-hornbeam (Ostrya virginiana), Spicebush (Lindera benzoin) and combinations of Beech-Oak-Sugar Maple (Fagus-Quercus-Acer).
Historical evidence suggests post-glacial dominance of Spruce species (12,550-10,500 years ago), followed by dominance of Pines (10,500-7,500 years ago), and finally by deciduous and mixed deciduous-coniferous forests. These forests included Birch, Hop-hornbeam, Ash, Elm, Oaks, Maples, Beech, Hemlock, and Pine, with Pines and Oaks being of particular importance to the Niagara Region. Alder was followed by Beech-Maple; Birch, Oak, and Pines were followed by Spruce, Hickory, Basswood and Elm.
Climatic changes over the last 12,000 years, such as the Little Climatic Optimum, allowed for the incursion of other plant communities such as oak savannah and prairie to the Niagara Peninsula.
At the time of settlement in the 1700s, the natural vegetation around Niagara Falls included a cedar swamp and, around the Whirlpool, Pine, Hemlock and Spruce. The Chippawa River (Welland River) ran through about 30 miles of swamp before discharging into the Niagara River at the Falls. Surrounding forests were described as mostly Oak, while along the Whirlpool Rapids early settlers found an abundance of wild fruit including strawberries, gooseberries, raspberries, cherries, plums and grapes. Brambles are present today in abundance along the Whirlpool Rapids.
Species diversity is very high in the Niagara area for several reasons, including latitude, high habitat diversity, weather, and the moderating effects of the Great Lakes. We are at the southernmost limit for many northern species while species from further south were able to migrate into this area as the glacier retreated. For many species, Niagara is at their northernmost limit.