Boreal Shield

The Boreal Shield is the largest ecozone in Canada.

Formation

Canadian Shield rock forms the nucleus of the North American continent. Other geological structures assumed positions around or on top of the Shield millions of years after it was formed. The Rocky Mountains are relative newcomers on the geological stage, having risen a mere 60 million years ago. Most Shield rocks were formed well over a billion years earlier, during the very first chapter of the planet's history known as the Precambrian era.

What once may have been a towering mountain chain is today a massive rolling plain of ancient bedrock. During the late Precambrian era, violent spasms in the Earth’s crust warped, folded and faulted the Shield. The foundation of much of the ecozone is now metamorphic gneiss, a highly banded rock formed by intense pressure and heat. Many of the minerals that contribute to the Boreal Shield’s economy may have formed during these geologically turbulent times.

During the last ice age, which ended 10 000 years ago, the advance of glaciers is repeatedly plucked and scoured the Shield, carving striations in the bedrock and carrying large boulders many kilometers. In retreat, glaciers blanketed much of the landscape with gravel, sand and other glacial deposits. The many poorly drained depressions left behind, as well as natural faults in the bedrock, now form the millions of lakes, pondes and wetlands that give this ecozone its distinctive character

Plant life

Cool temperatures, a short growing season, frequent forest fires, and acidic soils challenge plant life in the ecozone. In spite of this, almost 88% of the area is forested by a few highly adaptable trees, such as Black Spruce, White Spruce, Jack Pine and Balsam Fir. Black Spruce, the most common species, yields high-quality wood pulp and is a prime species for Canada's large paper industry. Further south are broadleaf trees such as Paper Birch, Trembling Aspen and Poplar, and conifers such as Balsam and White, Red and Jack Pine. In southeastern parts of the ecozone, species characteristic of more temperate climates, including Yellow Birch, Sugar Maple, Black Ash and eastern White Cedar, are common.

Throughout the Boreal Shield, these forests are mixed with innumerable bogs, marshes and other wetlands. Covering nearly 20% of the ecozone, these wetlands are among its most diverse and biologically productive ecosystems. Some larger wetlands in southern regions have been converted into commercial berry farms, which produce large volumes of cranberries and blueberries for markets around the world.

Where the scouring effects of glaciation were intense, bare rock outcrops predominate, dotted by colourful arrays of lichen and ground-hugging shrubs.

Forest fires add to the distinctive mosaic of the Boreal Shield by leaving a patchwork quilt of plant life varying in species composition and age. Although fire often destroys large tracts of forest and occasionally threatens human activities or property, it also renews the landscape by triggering new growth, purging old forests of insect pests and disease, and increasing the variety of habitats available to wildlife.

Animal life

Each spring the abundance of water in the Boreal Shield Ecozone attracts hundreds of thousands of ducks, loons, geese and swans. They come either to breed or simply rest and feed before flying on to more northerly nesting grounds. Among the more common waterfowl species that summer here are the Bufflehead, American Black Duck, Wood Duck, Ring-necked Duck and Canada Goose. Also found are the Boreal Owl, Great Horned Owl, Evening Grosbeak and Blue Jay. The songbird perhaps most often associated with this part of the Canadian Shield is the White-throated Sparrow.

Among the characteristic mammals of this ecozone are Woodland Caribou, White-tailed Deer, Moose, Black Bear, Wolf, Lynx, Snowshoe Hare, Fisher, Marten and Striped Skunk. The ecozone’s many wetlands, ponds, rivers and lakes provide important habitats for Beaver, Muskrat and Mink.

In the Atlantic marine environment, typical mammals include Grey, Harp and Hooded seals, and Killer, Atlantic Pilot, Sperm, Fin and Blue whales. The endangered Northern Right and Bowhead whales and threatened Humpback Whale are also found in this region.

The biologically-rich marine areas off Quebec’s north shore as well as the continental shelf of Newfoundland and Labrador are vital to Canada’s commercial fisheries. The rocky shores of the Gulf of St. Lawrence and the Newfoundland coast provide exceptional nesting habitat for many seabirds. Lake Trout, Lake Whitefish, Burbot and Northern Pike are among the most common fish species thriving in the ecozone’s many freshwater lakes and rivers.

Bodies of water

Since the days the first humans migrated into the ecozone near the end of the last ice age, the Boreal Shield’s sweeping network of rivers and lakes has served as a crucial transportation route, a foundation for rich domestic fisheries, and a natural wellspring of fur-bearing mammals. More recently these waters have come to be known for outdoor recreation and the development of hydro-electric power.

Much of the freshwater resources of the Boreal Shield are relatively untouched by human activity. Others have been widely exploited. Flow alteration and mercury contamination from hydro dams and associated river diversions, acidification from mine tailings and smelter emissions, and sedimentation and stream disruptions from extensive logging activities are the consequences of industrial development.

Changing conditions

As for the boreal forest, fire suppression, insect control, clear-cutting and single-species tree farming are widespread. These practices may, over the long term, reduce the diversity of both plant and animal species and increase the forest’s vulnerability to disease.

Many Shield lakes and soils are extremely sensitive to changes in pH. Acid rain from local sources and from the long-range transport of airborne pollutants has already taken an ominous toll. It may be weakening the general vigour and growth rate of trees, as well as of aquatic species, in sensitive areas.

Mining, forestry, hydro generation and fisheries are all important contributors to the Canadian economy. With the help of environmentally responsible regulations and policies, they will be able to continue well into the future. Beyond its economic opportunities, the Boreal Shield continues to provide more intangible but priceless gifts -- pure air and water, food and habitat for wildlife, and recreational, aesthetic and spiritual benefits.

Protected areas

Within this ecozone are a number of protected areas. These include:Cite web
url=http://www2.parkscanada.gc.ca/apprendre-learn/prof/itm2-crp-trc/htm/ecozone_e.asp
title=Terrestrial Ecozones of Canada
work=Teacher Resource Centre
publisher=Parks Canada
accessdate=2008-02-13]

* Georgian Bay Islands National Park
* Gros Morne National Park
* La Mauricie National Park
* Mingan Archipelago National Park Reserve
* Pukaskwa National Park
* Terra Nova National Park

References

External links

* [http://www.canadiangeographic.ca/atlas/themes.aspx?id=shield&lang=En Boreal Shield (The Canadian Atlas)]