THE BIOMES

Before describing each terrestrial biome that makes up the Borealie, it is essential that we correctly define the biome and the ecosystem. Campbell (1995) tells us that a biome is an ecological complex characteristic of a major biogeographical zone, named according to its predominant plant life and characterized by the organisms that have adapted to it. Whereas an ecosystem is a dynamic whole created by the potentially interactive organisms of a community and by the abiotic (non-living) factors with which they interact.(2)

Looking at these definitions, one would believe that there can be no problem in naming and geographically defining the terrestrial biomes. Unfortunately, this is not so. One of the reasons is that scientists use different methods, and the other is because a biome rarely has a clearly defined frontier. The biomes of the Borealie make up an environmental continuum and their frontiers are defined only approximately. For example, depending on where you happen to be precisely, you may find a tundra environment in an area defined as a taiga.(2)

The descriptions of the biomes below give a general overview of their characteristics and of what determines the establishment of one biome rather than another. A number of elements – climate, total precipitation and temperature – are crucial to the marking out of the boundary lines of the biomes.(1,2,3)

The Arctic

The name “Arctic” refers to a geographical region. One also hears the expression “polar ice caps”. Unlike the biomes, these are deserted regions. No life can survive there. Apart from a few explorers or other passing animals, one cannot speak of biodiversity when referring to these regions.

The Tundra

The Tundra is the northern limit of the Taiga. It is a biome that is characterised by long, dark winters and very short summers lasting less than three months. The average temperature for the warmest period does not go above 10 oC. In fact, it is not rare that snow falls in the middle of July. Because of these conditions, the earth never completely thaws on this territory. The upper layer of soil thaws down about one metre (3 ft.) whereas the lower layer remains frozen. This is what is known as permafrost and goes down several metres. Total precipitation is variable, from 200 to 600 mm (8 in. to 2 ft.). The climate is more generally dry and cold.(1,2,3) 

Climatic conditions mean that plant life grows very slowly and remains stunted, partly in order to avoid drying out through wind and cold. In the southern part of the biome, one may find bushes, but further north, one meets up with only herbaceous crops, lichens and mosses.(1,2,3) Growth is slow but plant life expectancy may be very long, some lichens being over 100 years old.(1)

Plant growth takes place over the short summer period when there is almost perpetual sunshine. This intense plant production attracts many birds that come to the area to mate; these include the Canada goose, the snow goose, the eider duck and many other species.  Resident birds include the snowy owl and the grouse. The tundra is one of the rare terrestrial biomes where you will find large droves of animals, amongst them the caribou, famous because of the huge herds and its migratory behaviour. The tundra is also home to musk oxen, polar bears and smaller mammals such as wolves, Arctic foxes and lemmings. The most noticeable members of the insect family are, of course, mosquitoes and black flies!(1,2,3) 

There are many who believe that the tundra has remained untouched by human beings. However, one has to note the increase in petroleum exploitation and the impact this has on the environment. Moreover, we can also observe the surreptitious advance of pollutant chemical particles brought thither by the winds. Indeed, atmospheric pollution of major North American and European cities inevitably drifts northwards.(3) This illustrates clearly that our way of living does not only affect our own environment, but that of the whole planet.

The Boreal forest (Taiga)

The Boreal forest is characterized by long, cold winters (at least 6 months below 0 oC) and by short summers that may be quite hot in some regions. The average summer temperature is 10 oC. In spite of the short summers, plant growth can be quite significant because of the long hours of sunshine, up to 18 hours per day at certain latitudes. Total precipitation is moderate, from 200 to 600 mm (8 in. to 2 ft.) and falls mainly as snow.

The physical aspect of the Boreal forest is that of a mosaic of forests, lakes and rivers, along with wetlands such as peat bogs. There is a smaller variety of trees and the woodland is dominated by species that include the spruce, fir, larch and pine. The very occasional hardwoods are generally circumscribed within the wetlands (lakes, rivers, peat bogs) or in areas that have been ravaged by fire or by human beings (the alder, birch, poplar and willow). The fires break out at the dryer time of the year and constitute a key element for forest regeneration. Herbaceous plants are very rare in this dense woodland. As for bushes, they are mainly members of the Ericaceae (heath) family, and include the blueberry or the Labrador tea.(1,2,3)

The biome soil is acid (because of the conifers), thin and poor in nutritional elements. However, the trees have adapted well to these conditions over thousands of years of evolution. In the first place, they have a widespread root network, close to the surface of the thin layer of soil, and can thus absorb elements required for their survival. In the second place, the trees have developed a mutualistic relationship between their roots and the mycete (a form of mushroom) and form what is known as mycorrhiza. Both parties benefit from this association, the mycete absorb the elements produced by the trees and in return they increase the collector surface of the roots, allowing the trees to optimise their ability to absorb water and minerals.(2,3)

This biome may appear less complex if one only takes into account the variety of plants found there, but a closer look will open up a fascinating world, full of surprises. The fauna, for example, is very diversified and includes many invertebrates, birds and mammals. The most “celebrated” representatives of the invertebrates are certainly the biting insects.(1) Some bird species, such as the grouse, live permanently in the taiga, but most species only make a stopover during migration or use it as a mating ground. Hares, black bears, grizzlies, moose, elks, wolves and wolverines are some of the mammals that reside in this area.(2,3)

Until quite recently, this biome suffered less than others from the impact of human beings. However, the taiga is now undergoing heavy exploitation of its plant and wildlife resources. Trees are cut down for lumber and pulp and paper. The paths thus torn through the woodlands allow human beings to penetrate even further into the forest, to trap and hunt, and this increases pressure on animal populations.(2,3) Fortunately, human beings are also concerned with resource management and there are many who deal with these problems on a day-to-day basis in order to ensure the durability of the biome.

The mixed forest

The mixed, or temperate, forest is made up mainly of hardwoods which, following an annual cycle, lose their leaves in autumn, become dormant in winter, bud in the springtime and, finally, develop leaves and flowers in summer. Amongst the species we find are the birch, oak, maple, beech, ash, linden, to name but a few. Depending on the region, the presence of deciduous trees will be more or less significant, since total precipitation and temperature play a role in their development. Examples of conifers would be the spruce, pine, fir, eastern hemlock, white cedar, etc.(1,2,3)

This biome is characterized by high temperatures in summer, low temperatures in winter and a yearly average temperature of between 8 and 10 oC. Total precipitation is significant, between 700 and 1700 mm (28 to 67 in.) per year, and sometimes more, and is fairly evenly spread over the year. Zones with harsher winters and less precipitation are densely populated with conifers.(1,2,3)

The floor of the temperate forest is rich in organic matter derived from the annual accumulation of dead leaves fallen from hardwood trees, and conifer needles. However, the organic matter decomposes rather slowly, especially in high conifer-content forests.(2,3)

Woodlands are stratified vertically. The strata to be found are herbaceous plants, bushes, trees growing away from the sun and, finally, large mature trees. In America, these levels of plant cover are inhabited by a range of mammals, such as squirrels, raccoons, black bears, white-tailed deer, to name just a few. However, the most important organisms are those that pass unseen, like bacteria and fungi. They play a crucial role, because they help recycle organic matter both on and within the soil, thus ensuring the health of the whole forest. This makes up an ecological partnership for those involved.(2,3)

This biome has been seriously affected by human intervention. There remain only a few scattered pockets of the whole mature forest. The arrival of the European made a lasting impact on the biome. Trees were used for building and cut down for agriculture. In fact, the major North American urban centres were carved out of the forest. What remains of the original woodlands is now the focus of attention for ecologists, who hope that they will be protected…(2,3)

Mountains

The biome of the mountains is defined by height, and not by some north-south boundary line. In the mountains, the terrestrial biomes lie along an environmental continuum, based on altitude. Where the elevation is great enough, the summit of the mountain will offer climatic conditions and plant life typical of the tundra: this is the Alpine tundra. Generally, hardwood will be found at the foot of the mountains and as you climb up, this gives way to conifers, then bushes and so on until the mountain tops. The summit may be covered with snow or ice, depending on its height. The mountain biomes are very special, since evolution has brought to these “islands” some unique varieties of plant and animal life (3), including the mountain goat and the big horn.

The prairie

The prairie is an important biome within the Borealie, because it takes up a vast stretch of land in North America. Globally, the prairies occupy 24% of the surface of the continents.(1) The biome is characterized by its cold winters, and periods of drought in the summer which themselves often give rise to fires. The prairies receive between 300 and 1000 mm (120 and 390 in.) of rain annually. In North America, we find tall grass prairies that receive an annual rainfall of between 700 to 1000 mm (27.5 to 39.4 in.) and short grass prairies that receive only 300 mm (approx. 12 in.) per year.(1,2,3)

The wildlife representatives of this biome are large herbivores (American bison, pronghorn), significant rodent populations (black-tailed prairie dogs, amongst many others) and their predators (foxes), birds of prey).(1,2,3) Moreover, one should not forget insects, which are very numerous and are represented mainly by the Orthoptera (crickets, grasshoppers).(1,3)

There are different factors that contribute to making the prairies what they are and to prevent the establishment of bushes and trees: fires, large herbivores (2) and the very dense root-system network.(3) This last factor also contributes to the fertility of the prairie soil, which contains large quantities of organic matter.(2,3)

However, human beings have seriously modified the biome by almost completely eliminating the large herbivores and by cultivating the huge expanses of fertile land. The American continental prairies have produced and continue to produce immense quantities of cereal grain. But how much longer will that last? Over the past 40 years of exploitation, the prairies as a whole have lost 35% to 40% of their organic matter. As a result, producers today are obliged to use more and more fertilizers. This raises questions, but no answers, as to the impact of the decrease in organic matter in the soil and as to the impact of the use of chemical products on the environment. The questions have been asked, but the jury is still out…(3)

References

Borcard, Daniel.  Department of Biological Sciences.  University of Montreal. http://biol10.biol.umontreal.ca/BIO1803/Biomes.html  Consulted on April 16, 2003. Following reference: Dajoz, R.  1996.  Précis d'écologie.  6th edition. Dunod.  Paris.
Campbell, Neil A.  1995.  Chapter 46 : L’écologie : Distribution et adaptation des organismes.  IN  Biologie.  Éditions du Renouveau Pédagogique Inc. Quebec. Canada.
Molles, Manuel C. Jr.  1999.  Chapter 2: Life on land.  IN  Ecology : Concepts and Applications.  McGraw-Hill.  Toronto.  Canada.