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Teaching aim: Factual description and characterization of the mutual dependencies of physical factors in order to establish a base for the ecological interpretation of the Canadian environment (in connection with unit 2).
Keywords: Geological and climatic factors of Canada, permafrost, impact of the climate on land use patterns, natural vegetation, vegetation zones, deciduous and coniferous forests, tundra and taiga, treeline |
Two grand natural patterns cross within Canada: generally east-west
trending belts of vegetation are superimposed on approximately north-south
aligned geological and physiographic features [1].
The zones of different kinds of vegetation result from plant adaptations
to the northern location of Canada. The country extends from latitude 41¡
40' in southern Ontario to latitude 83¡ 06' in Ellesmere Island [2],
and over this great south to north span of 4,600 km, there are great climatic
changes. Canada extends from 52¡ 37' West longitude to 141¡
West longitiude, a distance of over 5,500 km. Within this vast breadth
the pronounced north-south relief features stem mainly from the orientation
of two notable North American mountain systems, one on the Pacific and
the other on the Atlantic coast [3].
The broad North-South sequence of distinctive kinds of natural vegetation
illustrates the increasing severity and restrictiveness of climate northward,
with lower and lower temperatures gradually forcing out in succession plants
that require long growing seasons to flourish. About half of Canada is
covered by forests. In southeastern Canada deciduous forests dominate;
they give way northward to a great belt of coniferous (boreal) forests,
with mixed forests between the two zones. North of the coniferous zone
is a transition belt to the essentially treeless tundra of low shrubs,
mosses and lichens that covers all of northern Canada. This transition
belt, a zone of stress where trees have difficulty surviving, is up to
a few hundred kilometres wide, but it is commonly called the treeline.
In the western interior plains is another large mainly treeless area, the
grasslands or prairies. Trees don't flourish here because of low and unreliable
precipitation, not because of low temperatures. Generally, however, precipitation
is adequate for plant growth in Canada
Perennially frozen ground - permafrost - is a response to steadily decreasing
average annual temperatures toward the north. Approximately 40 to 50% of
Canada is underlain by permafrost, and in the north this causes great problems
in constructing buildings, roads, and pipelines. Unless structures are
insulated from the earth any heat they contain, such as in heated buildings,
will melt the permafrost and cause the structures to sink partly into the
ground.
A good indicator of the northerness of climate in high latitudes
is the number of heat units available for plant growth. This is usually
measured in growing degree days, i.e. adding up the average number of degrees
for each day above 5¡C (the average temperature at which much plant
growth begins) over the entire growing season. In southern Ontario, a region
where precipitation is ample for plant growth, there is sufficient heat
available and the growing season is sufficiently long to enable corn and
hardy fruits to thrive, including grapes and pears on special sites close
to lake shores protected from extreme temperatures. In British Columbia,
where the climate is the mildest in Canada because of the moderating effect
of the Pacific Ocean, fruit is also grown successfully in the interior
valleys, if the land is irrigated. In southern Manitoba, Saskatchewan,
and Alberta grain is grown extensively, especially wheat, and also oil
seeds such as canola. Due to a short growing season and frost hazard agriculture
stops about 600 km north of the 49th parallel, except in the Peace River
Country where farming continues another 450 km farther because Pacific
Ocean air masses ameliorate the climate in that area relative to its latitude.
Of course, commercial agriculture stops everywhere in Canada towards the
north, and in the early twentieth century, the geographical concept of
the pioneer fringe was devised to describe the northern margins
of settlement where agricultural advance halted and forests dominated.
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Questions for further consideration:
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[1]
http://sts.gsc.nrcan.gc.ca/clf/landscapes.asp
[2]
http://www.canadianparks.com/nunavut/ellesnp/index.htm
[3]
http://atlas.gc.ca/site/english/maps/environment/land/relief
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