Boreal climate is the form of climate found in a region of boreal forests. In ecology, "Boreal" is usually applied to ecosystems localized to subarctic (Northern hemisphere) and subantarctic (Southern hemisphere) zones. Regions having a subarctic climate, also called boreal climate, are characterized by very cold winters, and brief, warm summers. This type of climate offers some of the most extreme seasonal temperature variations found on the planet. In winter, temperature can drop to −40°C (also −40°F) and in summer, the temperature may exceed 30°C or 86°F. The boreal climate is a subset of the continental climate.
A continental climate is the climate typical of the middle-latitude interiors of the large continents of the Northern Hemisphere in the zone of westerly winds; similar climates exist along the east coasts (but not the west coasts) of the same continents, and at higher elevations in certain other parts of the world. This climate is characterized by winter temperatures cold enough to support a fixed period of stable snow cover each year, and relatively low precipitation occurring mostly in summer - although east coast areas (chiefly in North America) may show an even distribution of precipitation. Only a few areas in Iran, adjacent Turkey and Central Asia show a winter maximum in precipitation, which typically melts in early spring to give short-lived floods.
Vegetation in the boreal climate is generally sparse, as only hardy species can survive the long winters and make use of the short summers. Trees are mostly limited to ferns and evergreen conifers, as few broad-leafed trees are able to survive the very low temperatures in winter; this type of forest is also known as taiga, a term that is sometimes applied to the climate found therein as well. The boreal climate zone coincides with a great belt of needle leaf forest, often-referred to as boreal forest, and with the open lichen woodland known as taiga. Most trees are small, with less value as lumber than as pulpwood.
The source region for the continental polar air masses is south of the tundra zone between lat. 50 and 70 N and is so called subarctic division. The climate type here shows very great seasonal range in temperature; winters are severe, and the region's small amounts of annual precipitation are concentrated in the 3 warm months. This cold, snowy forest climate, referred to in this volume as the boreal subarctic type, is classified as E in the K?ppen-Trewartha system. This climate is moist all year, with cool, short summers. Only 1 month of the year has an average temperature above 50F (10C).
Winter is the dominant season of the subarctic boreal climate. Because average monthly temperatures are subfreezing for 6 to 7 consecutive months, all moisture in the soil and subsoil freezes solidly to depths of many feet. Summer warmth is insufficient to thaw more than a few surface feet, so permafrost prevails under large areas. Despite low temperatures and long winters, the valleys of interior Alaska were not glaciated during the Pleistocene, probably because of insufficient precipitation.