The Frontenac Arch Biosphere has a tremendous variety of plant life. The diversity of flora, like the fauna of the region, is owed to several key factors. The region is at the intersection of major continental migration routes, it has a complex geology and rugged landform, and climate effects play a major role.
The Biosphere is at a crossroads of migration routes. The north-south route is the Frontenac Arch itself - a bridge of Canadian Shield from the Algonquin and Laurentian highlands to the Adirondack Mountains. This rugged granite landform is the worn-down roots, the very basement rocks, of a billion year-old mountain chain. This land-bridge provides a common ground, of sorts, between the forests of Appalachia and the boreal.
The east-west route is the St. Lawrence Valley, which is the route from the Great Lakes heartland of the continent to the Atlantic coast.
Long-term migrations of plants are far more subtle than the season to season migrations of birds with which we are more familiar. The ranges of plants are sternly linked to climate conditions over time. However, the conditions of soils, topography and dispersal mechanisms play a large part. The north-south, and east-west routes that intersect here have enriched our Biosphere's natural world. The routes have provided the means and conditions for five forest regions of the eastern North American to intermingle here. These are the Great Lakes - St. Lawrence forest, the boreal, the Appalachian, the Atlantic Coastal Forest and the Carolinian Forest. There are as well some species of the tall-grass prairie to be found.
Plants are often quite specialized in needs for nutrition, shelter, temperature ranges among other factors. It happens that this region abounds in niche opportunities.
The rugged landscape means that there are literally millions of slopes and valleys, oriented to every and all points of the compass. As a result, there are hot, sunny, sheltered, cool, windswept, step, gentle, rocky, cliff-faced, gravel, moist, dry - and all other character of slopes one can think of. Valleys are equally complex, where they may be lake or wetland filled, level plains of post-glacial lake-bottom clays, dry ravines, bogs, fens, sand or gravel beds.
The terrain interplays with the complexities of the region's climate and weather patterns. The Frontenac Arch is the landform that confines Lake Ontario to its basin, and the lake becomes a great moderator of the climate from season to season, lessening the seasonal extremes and prolonging the swing of each season. The vast volume of the lake is slower than land to cool in the fall, and retards the warming of the land in spring. While we expect that the growing season would be shorter as one moves north, the moderating lake allows a longer growing season at the upper end of the St. Lawrence Valley than one sees moving eastward down the valley, for some hundreds of kilometres. Coupled with the effect of slopes facing to or from the sun, climate plays a large part in the conditions which modify the so-called normal ranges of plants, and animals.
An example of the cumulative effects of migration routes, geology and climate here is that wire birch and red spruce of the Atlantic foist reach just this far west. Several species of the Carolinian reach here, but little further northward. Among these are pignut hickory, buttonbush and summer grape. From the boreal are sweet gale, barren-grounds strawberry and balsam fir. Pitch pine, the tree of the east coast pine barrens, and hobble-bush of Appalachia, are common here, but elsewhere very rare in Canada.
For more information, visit:
Queen's University Biological Station: https://qubs.ca/resources/species-lists
The Kingston Field Naturalists: http://kingstonfieldnaturalists.org/
Thousand Islands National Park: http://www.pc.gc.ca/pn-np/on/lawren/natcul.aspx