Ecology of the Canadian Shield

The Canadian Shield is one of North America’s most beautiful, serene, and vast wild places. The area is unique because of its climate and of its large number of fresh water lakes. These unique characteristics provide habitat for plenty of land and water life.

Boreal Forest

• The forest that makes up the Canadian Shield is known as a boreal forest or taiga. This type of forest is distinguished by long, cold winters and short, hot, wet summers. Boreal forests are also made up of mostly coniferous trees such as pines, cedars, spruce, and fir trees. The boreal forest gets its name from the Greek god of the north wind, Boreas.

• Boreal forests separate the Arctic tundra from the southern deciduous forests.

The average amount of precipitation in the Border Country is 27 inches each year. 60 percent of this precipitation comes from rain and the other 40 percent from snow. Snow covers the ground for about 5 months a year. The temperature range in the Border Country is from –50 degrees Fahrenheit to 100 degrees Fahrenheit!

Why are there so many lakes in the Canadian Shield?

• Thousands of years ago a giant glacier that was 2 miles thick moved from the north down across Canada and the northern United States. The massive ice block tore up everything in its path and left behind granite rock debris. The glacier changed the landscape of the continent forever and left huge depressions in the land and lots of exposed granite.
• The glacier began to melt about 10,000 years ago and filled the holes in the land with water. Some of the water seeped away to form valleys and the rest formed the thousands of lakes that are found in the Border Country today.

What kind of life do the lakes support?

• The lakes are an essential life support system for aquatic life and also land animals. Everything from fish, loons, herons, moose, wolves, beavers, and bears depend on the lakes for food, water and/or habitat.
• The granite rock found underneath the lakes is insoluble (does not dissolve in water) therefore the water contains few minerals for algae, bacteria, and plankton. With a lack of bacteria, algae, and plankton there is very little vegetation. This explains why the lakes are so clear.
• Lakes hold an abundance of life in the water closest to shore. This area is known as the littoral zone or the near-shore water. This area is favorable because the water is shallow and warm and contains more vegetation. In the littoral zone there are also down trees that have been left by beavers or the wind. These down trees provide protection and food for fish. The decaying trees also supply the lakes with nutrients and minerals important for the support of aquatic vegetation.
• Some of the most well known inhabitants of the near-shore waters include walleye, rock bass, largemouth bass, muskies, and Northern pike. All of these fish rely on the down trees to provide shelter and food. The tree cover also provides them with ideal hunting spots where they can hide and then ambush their prey.
• The lakes are also home to mammals such as otters, beavers, and muskrats that fish in the clear water. These mammals are another link in the food chain.

What is a food chain?

• All plants are consumed by some sort of animal and these animals are in turn eaten by other animals.
• The basic model for a food chain is that a green plant is consumed by an herbivore that is then eaten by a predator.
• A simple example of a food chain is an aquatic plant gets eaten by a tadpole that gets eaten by a Northern pike that is consumed by an otter.
• Food chains become complex with animals at different stages of development consuming different types of prey. For example, a young pike may be food for a large perch but a large pike will eat full-grown perch. Perhaps a better way to describe food chains is to call them food webs.

If green plants are at the bottom of the food web, how do they get their own food?

• Plants have the remarkable ability to make their own food. For this reason they are called primary producers. Plants depend on nutrients from the ground or lake-floor as well as water, sunlight, and a gas called carbon dioxide (CO2) to make their food. The results from all of these factors are oxygen and the carbon containing organic compounds that feed the plants.

Sunlight

CO2+Water __________ O2+Carbon containing organic compounds

• The plant’s productivity depends on the availability of CO2, sunlight, and water.

• Plants convert the carbon dioxide that we exhale out of our lungs into oxygen which is the main component of air that we rely on to breathe. Without plants than there would be no source of oxygen or food source and life on Earth would stop. For this reason and many others it is crucial that we humans preserve the Border Country forests as well as other types of forests around the world.

What are some adaptations that animals have made to survive life in the Canadian Shield?

• Many animals are colored to blend in with their backgrounds. This phenomenon is known as camouflage and is an excellent way for animals to hide from predators. Camouflage also works well for the predator because it allows the animal to hide and then ambush the prey. Many land animals change colors depending on the season so they can blend in at any time of year. Snowshoe hares, ruffed grouse, and ermines are examples of animals found in the Border Country that change color depending on the season. In the summer they are brown to blend in with the vegetation and in winter they are white to match the snow. These animals rely on their camouflage to keep them hidden from predators.
• Camouflage is also important for animals found in the lakes because food is limited. Conspicuous animals will not last long in the hungry lakes. Fish such as rock bass, muskies, pike, and walleyes all blend in with their background.

• The animals found in this part of the world have many interesting ways to survive the extreme temperature ranges between the summer and winter months. The water birds and ground feeding birds migrate south at the first signs of winter. Other animals hibernate while some live nestled in the snow. Hibernation is when an animal sleeps through most of the winter and relies on its stored fat to give it energy. The animal has a greatly reduced metabolism and all other bodily functions slow down during this time.

• The snow that covers the ground for 5 months out of the year actually provides protection and warmth for the rest of the animals. The snow seldom gets colder than 20 degrees Fahrenheit. This provides for a haven when the outside temperatures are in the negative digits. The snow also helps hide the animals from predators such as foxes, coyotes, and wolves. Animals such as grouse, hares, and shrews actually have higher survival rates in winters when there is plenty of snow.

Forest Fires

• An interesting phenomenon that occurs in forests is the forest fire. As humans, our first instinct is to think that fires are destructive and unhealthy for the forest and the animals it contains. However, after careful study many scientists have found that fires are part of a natural process that have occurred throughout history. The occasional forest fire is actually beneficial for the forest. The fires that have occurred for thousands of years were started naturally not by careless humans throwing cigarette butts into the woods.
• One advantage of fire to the forest is that it burns away underbrush allowing sunlight to penetrate the soil to help seeds grow and they clear away competition for existing tall trees. Some seeds only grow after they have been burned by fire such as the Jack Pine.
• Fires also make the soil rich in nutrients such as phosphorous, calcium, and magnesium. Shortly after fires, new plants such as aspen and birch begin growing in the nutrient rich, competition-free soil. Aspen and birch are relatively short lived but during their lifetime they dominate the canopy taking most of the sunlight before it reaches the trees below. The white spruce and the balsam fir wait for these trees to eventually die before they get their turn to dominate the forest. This type of "takeover" is called a climax forest.
• After fires have burned an area, herbivores such as moose, deer, and snowshoe hares are attracted to the new green shoots that grow. These animals then attract wolves. Mice and other small mammals also come to eat the seeds while bears and pine marten feast on the berries.
• The US Forest Service is realizing the benefits of small fires and how they are part of a naturally occurring process. In parts of the Border Country, they are allowing these small fires to burn to rejuvenate the forests and to continue the plant life cycles.

It is clear that the Canadian Shield contains some fascinating plants and animals and beautiful landscapes. It is our job to make it stay that way. We can make a difference by preserving the land and by keeping it wild and untouched by modern development and pollution. It is also important for us to get out into the woods whether it’s a city park or a great wilderness area to enjoy the outdoors and to appreciate the complexity and beauty of the natural world.

Sources

Knauth, P. 1972. The North Woods: the American wilderness/Time-Life books. Time-Life Books, New York.

Owen, D.F. 1974. What is ecology? Oxford University Press, London.

Stamm, D.R. 1977. Underwater: the Northern lakes. The University of Wisconsin Press, Madison, WI.

Stensaas, M 1993. Canoe country wildlife: A field guide to the North Woods and Boundary Waters. Pfeifer-Hamilton, Duluth, MN.