Andy Fyon is the Director, Ontario Geological Survey, Ministry of Northern Development and Mines
When you walk across the land or boat across the water, do you notice the range of plants growing on different types of land? For example, the plants that grow in muskeg areas are very different from those growing on bare rocky areas. This is a pattern repeated over and over.
While observing this, have you ever wondered if geology plays a role in controlling where different types of plants grow?
There is a strong link between Ontario’s geological history and the location of different types of plants. We know that geological forces shaped the land. And yes, geological forces also created habitats – special places where distinctive plants grow. Obviously, different habitats are home to different plants. So, the type of rock and the type of deposit left behind by glaciers are key factors in determining the distribution and types of some plants.
Ontario’s long and complex geological history created many different habitats that sustain different types of plants in different areas.
On Manitoulin Island and the Bruce Peninsula, the main rock is limestone or dolomite. Areas where bare limestone rock is covered by thin patches of soil are called alvar. Alvar is a hostile place for a plant to live and only certain plants can grow in these limy, geological habitats. Lakeside daisy, also known as Manitoulin gold, a variety of saxifrage, and wild chives grow almost exclusively on these open alvar habitats.
Along the Albany River, in the James Bay Lowlands, and on Manitoulin Island and Bruce Peninsula, where the limy soil is wet, Kalm’s lobelia and false asphodel plants grow. On Manitoulin Island and in the north where the ancient Precambrian Shield rock meets the limestone rock of the James Bay Lowlands, yellow lady’s slipper orchid may be common. These plants that grow on limy rocks or in limy soils have developed a special way to live in these areas where the limestone rock creates difficult growing conditions for other plants.
Sand dunes around Lake Huron are the result of a complicated geological process involving glaciation, changes in water levels, and the fact that wind and waves transport sand. Sand dunes are a hard place for plants to grow, but some specialized plants grow well in this sandy geological habitat. Beach pea and Pitcher’s thistle are largely restricted to these sand dune habitats of Lake Huron.
The hard rocks in the Precambrian Shield were polished clean by the last glaciers. There is little soil on the rock, except in cracks or in rock depressions. Bristly sarsaparilla, pearly everlasting, pale corydalis, and some types of reindeer lichen are common in this desert-like geological habitat.
Eskers are high, dry ground made of sand and gravel that was left behind by rivers that flowed under a glacier. Poplar trees and raspberry shrubs are common on the eskers because they like well-drained, dry, gravelly soil. Eskers are also “highways” for animals because it is much easier to follow the high, dry ground than walk through the lower wet muskeg. Some animals dig their dens in the esker because of the sandy soil.
In the low ground adjacent to the esker, geological processes may have deposited clay-rich material called till that does not drain water well. These wet areas may contain fens, bogs or muskeg. This wet geological habitat is home to Labrador tea, cotton grass, wild cranberry, sphagnum moss, and headberry (cloudberry). In areas where the water in the muskeg is not moving and sphagnum moss is abundant, unusual plants occur that survive by eating insects – sundew and pitcher plant.
Some geological habitats are dramatic. The Ouimet Canyon gorge, located northeast of Thunder Bay, is 100 metres deep, 150 metres wide and two kilometres long. The canyon was formed by a dramatic geological process. The canyon is deep and cold at the bottom. Arctic, sub-arctic and alpine plants grow at the bottom of the canyon in this hostile geological habitat.
There is also an important link between geology and places where people live.
Ten thousand years ago, at the end of the last ice age, parts of Ontario were flooded by two different oceans. One covered the Ottawa area and the second covered the northern lowlands area. Clay was deposited on the bottom of these oceans.
That clay is unstable and many landslides occur in areas where the clay is abundant. The landslides, dangerous to people, communities and infrastructure, are most obvious along the major rivers that flow into James Bay and Hudson Bay.
Similarly, the presence of underground caves and sinkholes in southern Ontario and possibly in the lowlands is an important habitat for some plants and a source of groundwater, but the location of sinkholes can represent hazardous habitat that has to be considered when people plan the locations of communities, roads or other infrastructure.
The link between geology, habitat, the location of different plants, and the implications for people is important. Many naturalists and planners will look first at a geological map to identify areas where special plants and animals are likely to be found, or what to anticipate beneath the ground from a human perspective.
So, the next time you travel across the land, look at the plant species around you. Chances are you will see changes in the distribution of plant types, which reflect changes in the local geology.