In this article we will discuss about:- 1. Location of Sub-Arctic Climate 2. Precipitation of Sub-Arctic Climate 3. Natural Vegetation.
Location of Sub-Arctic Climate::
The boreal or sub-arctic climate representing the boreal forest biome or temperate coniferous forest biome and the most extreme type of microthermal climate is called taiga type or Siberian type of climate and includes the areas of subarctic regions of North America (extending from Alaska of the USA across Canada to Hudson Bay in the east) and Eurasia (from the Scandinavian Peninsula across the Russian Siberia to the Bering Sea) (fig. 39.8).
Besides, there are small patches of this climate at higher altitudes in Germany, Poland, Switzerland, Austria and other parts of Europe and on the high Rocky Mountains of North America. In fact, the taiga climate is located between the tundra climate in the north and the temperate grassland biome (climate) (Eursian steppes and North American Prairies) in the south. The taiga climate is conspicuous by its total absence in the southern hemisphere because of narrowing trend of continents towards the South Pole. The vicinal location of taiga climate extends from 50°- 55°N to 65°-70°N latitudes.
Temperature of Sub-Arctic Climate:
The taiga type of climate is characterized by extreme continental climate marked by bitterly cold winter of long duration and cool short summer season of brief period extending over one to three months. Spring and autumn are merely brief transitional periods between summer and cold seasons. The 10°C isotherm of the warmest month forms the northern boundary of this climatic region.
The winter season extending over 8 months always records temperatures below freezing point as is apparent from the average January temperatures of the following inland locations = -26°C at Eagle (Canada), -30.6°C at Dawson (Canada), -24°C at Okhotsk (Russia), -43.3°C at Yakutsk (Russia), -50.6°C at Verkhoyansk (Russia) etc.
The Siberian taiga climate records the lowest minimum temperature e.g., Verkhoyansk -68°C and Oimekon -66.8°C (Russia, lowest temperature ever recorded) while the lowest minimum temperature recorded so far in North American sub-arctic climate at Snag (Yukon, Alaska, USA) is -62.8°C.
In comparison to severe cold winter months temperature during brief summer season increases rapidly. July being the warmest month has an average temperature of 16°C. It may be pointed out that several interior locations record temperature below freezing point even in the month of July.
The growing season is between 50 to 70 days only because soil water is frozen for 5 to 7 months of winter season in continuation. The annual ranges of temperature are very large and greatly vary from place to place.
For example, the temperature of the coldest and warmest months of Moscow are -12°C and 20°C respectively and thus the annual range of temperature becomes 32°C. Verkhoyansk records the annual range of temperature of more than 64°C.
Precipitation of Sub-Arctic Climate::
The subarctic or taiga type of climate is characterized by low mean annual precipitation because:
(i) Extremely low temperature for longer period of the year does not favour evaporation and thus there is very low amount of absolute humidity in the air,
(ii) The regions falling in taiga type of climate are located in the leeward sides of the continents and in the interior regions and thus they are away from the marine influences, and
(iii) The regions are characterized by polar high pressure, anticylonic conditions as evidenced by subsidence of air from above and divergence of surface winds.
The mean annual precipitation ranging between 37 cm and 60 cm is received mostly in the form of fine, dry snow which accumulates throughout the winter and is released as surface water due to thawing because of increase in temperature during brief summer season. It may be pointed out that the precipitation is more or less uniformly distributed throughout the year whether in liquid form as rainfall (during summer) or snowfall during winters.
The following are the main characteristic features of subarctic taiga type of climate:
(i) Bitterly cold long winter season (temperature below zero degree centigrade at least for 6 months).
(ii) Heavy snowfall during winter season.
(iii) Formation of permafrost ground (permanently frozen ground) because of freezing of ground moisture due to subfreezing temperature.
(iv) Cool summer of short duration having precipitation in liquid form (rainfall) and melting of snow cover.
(v) Growing period of vegetation ranging from 50 days a year along the northern boundary to 100 days along the southern boundary.
(vi) High range of variability in the spatial distribution of annual precipitation
(vii) Extreme annual range of temperature (ranging between 25°C during summer months and 40°C during winter months).
Natural Vegetation on Sub-Arctic Climate:
The coniferous trees are the most dominant member of taiga climate or the Boreal Forest Biome. These trees form dense cover of forests which arc the richest sources of softwood in the world.
There are four major genera of evergreen coniferous trees e.g.:
(i) Pine (white pine, red pine, Scots pine, jack pine, lodgepole pine etc.).
(ii) Fir (doughlas fir, balsam fir etc.),
(iii) Spruce (Picea), and
(iv) Larch (Larix).
Besides, a few species of temperate deciduous hardwood trees have also developed in this climate mainly in those areas which have been cleared by man through felling of original temperate coniferous trees. Thus, the temperate deciduous trees represent the ‘secondary succession of vegetation’ which includes alder, birch and poplar.