In botany, a tree is a perennial plant with an elongated stem, or trunk, supporting branches and leaves in most species. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are usable as lumber or plants above a specified height. Trees are not a taxonomic group but include a variety of plant species that have independently evolved a woody trunk and branches as a way to tower above other plants to compete for sunlight. Trees tend to be long-lived, some reaching several thousand years old. In wider definitions, the taller palms, tree ferns and bamboos are trees. Trees have been in existence for 370 million years, it is estimated. A tree has many secondary branches supported clear of the ground by the trunk; this trunk contains woody tissue for strength, vascular tissue to carry materials from one part of the tree to another. For most trees it is surrounded by a layer of bark. Below the ground, the roots spread out widely. Above ground, the branches divide into smaller shoots.
The shoots bear leaves, which capture light energy and convert it into sugars by photosynthesis, providing the food for the tree's growth and development. Trees reproduce using seeds. Flowers and fruit may be present, but some trees, such as conifers, instead have pollen cones and seed cones. Palms and bamboos produce seeds, but tree ferns produce spores instead. Trees play a significant role in moderating the climate, they remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of plants. Tropical rainforests are among the most biodiverse habitats in the world. Trees provide shade and shelter, timber for construction, fuel for cooking and heating, fruit for food as well as having many other uses. In parts of the world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture; because of their longevity and usefulness, trees have always been revered, with sacred groves in various cultures, they play a role in many of the world's mythologies.
Although "tree" is a term of common parlance, there is no universally recognised precise definition of what a tree is, either botanically or in common language. In its broadest sense, a tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground. Trees are typically defined by height, with smaller plants from 0.5 to 10 m being called shrubs, so the minimum height of a tree is only loosely defined. Large herbaceous plants such as papaya and bananas are trees in this broad sense. A applied narrower definition is that a tree has a woody trunk formed by secondary growth, meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the growing tip. Under such a definition, herbaceous plants such as palms and papayas are not considered trees regardless of their height, growth form or stem girth. Certain monocots may be considered trees under a looser definition.
Aside from structural definitions, trees are defined by use. The tree growth habit is an evolutionary adaptation found in different groups of plants: by growing taller, trees are able to compete better for sunlight. Trees tend some reaching several thousand years old. Several trees are among the oldest organisms now living. Trees have modified structures such as thicker stems composed of specialised cells that add structural strength and durability, allowing them to grow taller than many other plants and to spread out their foliage, they differ from shrubs, which have a similar growth form, by growing larger and having a single main stem. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it a classic example of parallel evolution. With an estimated 60,000-100,000 species, the number of trees worldwide might total twenty-five per cent of all living plant species; the greatest number of these grow in tropical regions and many of these areas have not yet been surveyed by botanists, making tree diversity and ranges poorly known.
The majority of tree species are angiosperms. There are about 1000 species of gymnosperm trees, including conifers, cycads and gnetales. Most angiosperm trees are eudicots, the "true dicotyledons", so named because the seeds contain two cotyledons or seed leaves. There are some trees among the old lineages of flowering plants called basal angiosperms or paleodicots. Wood gives structural strength to the trunk of most types of tree; the vascular system of trees allows water and other chemicals to be di
Cobalt is a chemical element with symbol Co and atomic number 27. Like nickel, cobalt is found in the Earth's crust only in chemically combined form, save for small deposits found in alloys of natural meteoric iron; the free element, produced by reductive smelting, is a hard, silver-gray metal. Cobalt-based blue pigments have been used since ancient times for jewelry and paints, to impart a distinctive blue tint to glass, but the color was thought by alchemists to be due to the known metal bismuth. Miners had long used the name kobold ore for some of the blue-pigment producing minerals. In 1735, such ores were found to be reducible to a new metal, this was named for the kobold. Today, some cobalt is produced from one of a number of metallic-lustered ores, such as for example cobaltite; the element is however more produced as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo and Zambia yields most of the global cobalt production; the DRC alone accounted for more than 50% of world production in 2016, according to Natural Resources Canada.
Cobalt is used in the manufacture of magnetic, wear-resistant and high-strength alloys. The compounds cobalt silicate and cobalt aluminate give a distinctive deep blue color to glass, inks and varnishes. Cobalt occurs as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high energy gamma rays. Cobalt is the active center of a group of coenzymes called cobalamins. Vitamin B12, the best-known example of the type, is an essential vitamin for all animals. Cobalt in inorganic form is a micronutrient for bacteria and fungi. Cobalt is a ferromagnetic metal with a specific gravity of 8.9. The Curie temperature is 1,115 °C and the magnetic moment is 1.6–1.7 Bohr magnetons per atom. Cobalt has a relative permeability two-thirds. Metallic cobalt occurs as two crystallographic structures: fcc; the ideal transition temperature between the hcp and fcc structures is 450 °C, but in practice the energy difference between them is so small that random intergrowth of the two is common.
Cobalt is a weakly reducing metal, protected from oxidation by a passivating oxide film. It is attacked by halogens and sulfur. Heating in oxygen produces Co3O4 which loses oxygen at 900 °C to give the monoxide CoO; the metal reacts with fluorine at 520 K to give CoF3. It does not react with hydrogen gas or nitrogen gas when heated, but it does react with boron, phosphorus and sulfur. At ordinary temperatures, it reacts with mineral acids, slowly with moist, but not with dry, air. Common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +5 are known. A common oxidation state for simple compounds is +2; these salts form the pink-colored metal aquo complex 2+ in water. Addition of chloride gives the intensely blue 2−. In a borax bead flame test, cobalt shows deep blue in both reducing flames. Several oxides of cobalt are known. Green cobalt oxide has rocksalt structure, it is oxidized with water and oxygen to brown cobalt hydroxide. At temperatures of 600 -- 700 °C, CoO oxidizes to the blue cobalt oxide.
Black cobalt oxide is known. Cobalt oxides are antiferromagnetic at low temperature: CoO and Co3O4, analogous to magnetite, with a mixture of +2 and +3 oxidation states; the principal chalcogenides of cobalt include the black cobalt sulfides, CoS2, which adopts a pyrite-like structure, cobalt sulfide. Four dihalides of cobalt are known: cobalt fluoride, cobalt chloride, cobalt bromide, cobalt iodide; these halides exist in hydrated forms. Whereas the anhydrous dichloride is blue, the hydrate is red; the reduction potential for the reaction Co3+ + e− → Co2+ is +1.92 V, beyond that for chlorine to chloride, +1.36 V. Consequently and chloride would result in the cobalt being reduced to cobalt; because the reduction potential for fluorine to fluoride is so high, +2.87 V, cobalt fluoride is one of the few simple stable cobalt compounds. Cobalt fluoride, used in some fluorination reactions, reacts vigorously with water; as for all metals, molecular compounds and polyatomic ions of cobalt are classified as coordination complexes, that is, molecules or ions that contain cobalt linked to several ligands.
The principles of electronegativity and hardness–softness of a series of ligands can be used to explain the usual oxidation state of cobalt. For example, Co+3 complexes tend to have ammine ligands; because phosphorus is softer than nitrogen, phosphine ligands tend to feature the softer Co2+ and Co+, an example being triscobalt chloride. The more electronegative oxide and fluoride can stabilize Co4+ and Co5+ derivatives, e.g. caesium hexafluorocobaltate and potassium percobaltate. Alfred Werner, a Nobel-prize winning pioneer in coordination chemistry, worked with compounds of empirical formula 3+. One of the isomers
Northern Norway is a geographical region of Norway, consisting of the three northernmost counties Nordland and Finnmark, in total about 35% of the Norwegian mainland. Some of the largest towns in Northern Norway are Mo i Rana, Bodø, Harstad, Tromsø and Alta. Northern Norway is described as the land of the midnight sun and the land of the northern lights. Further north, halfway to the North Pole, is the Arctic archipelago of Svalbard, traditionally not regarded as part of Northern Norway; the region is multi-cultural, housing not just Norwegians but the indigenous Sami people, Norwegian Finns and Russian populations. The Norwegian language dominates in most of the area. Finnish is spoken in only a few communities in the east of Finnmark. Northern Norway covers about a third of Norway; the southernmost part the part south of the Arctic Circle, is called Helgeland. Here there is a multitude of islands and skerries on the outside of the coastal range, some flat, some with impressive shapes, like Mount Torghatten, which has a hole through it, the Seven Sisters near Sandnessjøen.
The inland is covered with dense spruce mountains near the Swedish border. The highest mountain in Northern Norway is found here in the Okstindan range south of Mo i Rana with Oksskolten reaching 1,915 metres above sea level, with the glacier Okstindbreen; the Saltfjellet range, with its Svartisen glacier and intersecting Arctic Circle, divides Helgeland from the next region, called Salten. Notable peaks in Salten are the Børvasstindan south of Bodø, Suliskongen near Fauske, the Steigartindan and the phallic Hamarøytinden. Between Saltfjellet and eastern Finnmark, Norway spruce trees have been planted and are privately owned; the older plantations are now producing lumber, 80 years after planted. Lofoten is a chain of peaks. From the mainland side it looks barren, but behind the violet-black peaks there are flatlands with good grazing for sheep on soil made from seaweed; the Vesterålen islands consist of bigger islands with a huge variation in landscape. Ofoten, further inland, is a fjord landscape with high mountains, the highest is Storsteinfjellet in Narvik, 1,894 m above sea level, but the most well-known is Stetind, the national mountain of Norway.
There are glaciers, like Frostisen and Blåisen. Troms county has surprising greenery for the latitude, the inner waterways and fjords are lined with birch forests, further inland there are extensive pine forests and highlands around the rivers Målselva and Reisaelva. Big islands like Senja, Kvaløya and Ringvassøya have green, forested interiors and a barren, mountainous coastline, with smaller islands offshore; the Lyngen Alps are the highest mountains of the area, rising to 1,833 metres, an area of glaciers and waterfalls. The 269 metres Mollisfossen waterfall in Nordreisa is the highest waterfall in the north, while Målselvfossen is Norway's national waterfall. Finnmark county has fjords and glaciers in the far southwest, the northwestern coasts are characterized by big islands, like Sørøya and Seiland; the inland is covered by Finnmarksvidda, a barren plateau about 300 to 400 metres high, with many lakes and rivers like Alta-Kautokeino and Tana/Deatnu. At this latitude, pine forests grow in lowland areas inland.
East of Honningsvåg, there are no islands protecting the barren coasts that rise directly up from the sea. The landscape towards the Russian border is comparatively flat. Knivskjellodden on the island of Magerøya marks the northern end of Europe. Finnmark is situated north of northernmost Finland, to the east Norway has a 196 kilometres border with Russia; the oldest known historical culture in the region is called Komsa, named after a mountain in Alta. The first people arrived around 12–13,000 years ago, but it is uncertain whether they came from southern Norway or from the Kola Peninsula. Today the rock carvings at Hjemmeluft in Alta or at Leknes in Nordland are among the remainders of the Stone Age cultures, showing reindeer swimming across the fjords. A significant find area is between the river Tana and the fjord of Varanger, where the reindeer ran over the isthmus on the way between the winter and summer grazing; the question of the ethnic identity of the Stone Age cultures is politically charged, as many Sami feel the uncertainty surrounding the earliest settlers in Northern Norway is being used to question their status as an indigenous people.
Metals were introduced around 500 BC. The Sami culture can be traced back at least 2,000 years. There is some archeological evidence of Bronze Age agricultural settlements about 2,500 years old, as in Steigen and Sømna. In 2009, archeologist discovered evidence of barley grown in Kvæfjord near Harstad in the Bronze Age 1000 BC. A larger settlement by people of Germanic origin, with substantial archeological evidence, seem to have occurred around 200–300 AD; these settled along the coasts up to Tromsø. The two e
Murmansk is a port city and the administrative center of Murmansk Oblast in the far northwest part of Russia. It sits on both slopes and banks of a modest ria or fjord, Kola Bay, an estuarine inlet of the Barents Sea, its bulk is on the east bank of the inlet. It is in the north of the rounded Kola Peninsula; the city is 108 kilometres from 182 kilometres from the Finnish border. The city is named for an archaic term in Russian for Norway. Benefitting from the North Atlantic Current, Murmansk resembles cities of its size across western Russia, with highway and railway access to the rest of Europe, the northernmost trolleybus system on Earth, its northern latitude of 68°58'N makes Murmansk 2° north of the Arctic Circle at 66°33'N. Its connectivity contrasts to the isolation of Arctic ports like the Siberian Dikson on the shores of the Kara Sea and Iqaluit, Nunavut in Canada on Baffin Island's Frobisher Bay off the Labrador Sea. Despite long, snowy winters, Murmansk's climate is moderated by the ice-free waters around it.
Although there was a building boom in the early twentieth century's arms races, Murmansk's population has been in a slow reversal since the Cold War. It remains by far the largest city north of the Arctic Circle and is a major port on the Arctic Ocean. Murmansk was the last city founded in the Russian Empire. In 1915, World War I needs led to the construction of the railroad from Petrozavodsk to an ice-free location on the Murman Coast in the Russian Arctic, to which Russia's allies shipped military supplies; the terminus became known as the Murman station and soon boasted a port, a naval base, an adjacent settlement with a population that grew in size and soon surpassed the nearby towns of Alexandrovsk and Kola. On June 29, 1916, Russian Transport Minister Alexander Trepov petitioned to grant urban status to the railway settlement. On July 6, 1916, the petition was approved and the town was named Romanov-on-Murman, after the imperial Russian dynasty of Romanovs. On September 21, 1916, the official ceremony was performed, the date is now considered the official date of the city's foundation.
After the February Revolution of 1917, on April 3, 1917, the town was given its present name. In the winter of 1917 the British North Russia Squadron under Rear Admiral Thomas Kemp was established at Murmansk. From 1918 to 1920, during the Russian Civil War, the town was occupied by the Western powers, allied in World War I, by the White Army forces. On February 13, 1926, local self-government was organized in Murmansk for the first time, during a plenary session of the Murmansk City Soviet, which elected a Presidium. Before this, the city was governed by the authorities of Alexandrovsky Uyezd and of Murmansk Governorate. On August 1, 1927, the All-Russian Central Executive Committee issued two resolutions: "On the Establishment of Leningrad Oblast" and "On the Borders and Composition of the Okrugs of Leningrad Oblast", which transformed Murmansk Governorate into Murmansk Okrug within Leningrad Oblast and made Murmansk the administrative center of Murmansk Okrug. In 1934, the Murmansk Okrug Executive Committee developed a redistricting proposal, which included a plan to enlarge the city by merging the surrounding territories in the north and west into Murmansk.
While this plan was not confirmed by the Leningrad Oblast Executive Committee, in 1935–1937 several rural localities of Kolsky and Polyarny Districts were merged into Murmansk anyway. According to the Presidium of the Leningrad Oblast Executive Committee resolution of February 26, 1935, the administrative center of Polyarny District was moved from Polyarnoye to Sayda-Guba. However, the provisions of the resolution were not implemented, due to military construction in Polyarnoye, the administrative center was instead moved to Murmansk in the beginning of 1935. In addition to being the administrative center of Murmansk Okrug, Murmansk continued to serve as the administrative center of Polyarny District until September 11, 1938. On February 10, 1938, when the VTsIK adopted a Resolution changing the administrative-territorial structure of Murmansk Okrug, the city of Murmansk became a separate administrative division of the okrug, equal in status to that of the districts; this status was retained when Murmansk Okrug was transformed into Murmansk Oblast on May 28, 1938.
During World War II, Murmansk was a link to the Western world for the Soviet Union with large quantities of goods important to the respective military efforts traded with the Allies: seeing military equipment, manufactured goods and raw materials brought into the Soviet Union. The supplies were brought to the city in the Arctic convoys. German forces in Finnish territory launched an offensive against the city in 1941 as part of Operation Silver Fox. Murmansk suffered extensive destruction, the magnitude of, rivaled only by the destruction of Leningrad and Stalingrad. However, fierce Soviet resistance and harsh local weather conditions with the bad terrain prevented the Germans from capturing the city and cutting off the vital Karelian railway line and the ice-free harbor. For the rest of the war, Murmansk served as a transit point for weapons and other supplies entering the Soviet Union from other Allied nations; this unyielding, stoic resistance was commemorated at the 40th anniversary of the victory over the Germans in the formal designation of Murmansk as a Hero
Shetland called the Shetland Islands and Zetland, is a subarctic archipelago of Scotland that lies northeast of the mainland of Scotland. The islands lie some 80 km to the northeast of Orkney, 168 km from the Scottish mainland and 280 km southeast of the Faroe Islands, they form part of the division between the Atlantic Ocean to the North Sea to the east. The total area is 1,466 km2, the population totalled 23,210 in 2011. Comprising the Shetland constituency of the Scottish Parliament, Shetland Islands Council is one of the 32 council areas of Scotland; the largest island, known as the "Mainland", has an area of 967 km2, making it the third-largest Scottish island and the fifth-largest of the British Isles. There are an additional 15 inhabited islands; the archipelago has an oceanic climate, a complex geology, a rugged coastline and many low, rolling hills. Humans have lived in Shetland since the Mesolithic period; the earliest written references to the islands date to Roman times. The early historic period was dominated by Scandinavian influences from Norway, the islands did not become part of Scotland until the 15th century.
When Scotland became part of the Kingdom of Great Britain in 1707, trade with northern Europe decreased. Fishing has continued to be an important aspect of the economy up to the present day; the discovery of North Sea oil in the 1970s boosted Shetland's economy and public sector revenues. The local way of life reflects the Scottish and Norse heritage of the isles, including the Up Helly Aa fire festival, a strong musical tradition the traditional fiddle style; the islands have produced a variety of writers of prose and poetry in the distinct Shetland dialect of Scots. There are numerous areas set aside to protect the local fauna and flora, including a number of important sea bird nesting sites; the Shetland pony and Shetland Sheepdog are two well-known Shetland animal breeds. Other local breeds include the Shetland sheep, cow and duck; the Shetland pig, or grice, has been extinct since about 1930. The islands' motto, which appears on the Council's coat of arms, is "Með lögum skal land byggja"; the Old Norse original of this Icelandic phrase is taken from the Danish 1241 Basic Law, Code of Jutland, is mentioned in Njáls saga, means "By law shall land be built".
The name of Shetland is derived from the Old Norse words and land. In AD 43 and 77 the Roman authors Pomponius Mela and Pliny the Elder referred to the seven islands they called Haemodae and Acmodae, both of which are assumed to be Shetland. Another possible early written reference to the islands is Tacitus' report in Agricola in AD 98, after describing the discovery and conquest of Orkney, that the Roman fleet had seen "Thule, too". In early Irish literature, Shetland is referred to as Insi Catt—"the Isles of Cats", which may have been the pre-Norse inhabitants' name for the islands; the Cat tribe occupied parts of the northern Scottish mainland and their name can be found in Caithness, in the Gaelic name for Sutherland. The oldest version of the modern name Shetland is Hetlandensis, the Latinised adjectival form of the Old Norse name recorded in a letter from Harald, Count of Shetland in 1190, becoming Hetland in 1431 after various intermediate transformations, it is possible. It became Hjaltland in the 16th century.
As Norn was replaced by Scots in the form of the Shetland dialect, Hjaltland became Ȝetland. The initial letter is the Middle Scots letter, the pronunciation of, identical to the original Norn sound, /hj/; when the use of the letter yogh was discontinued, it was replaced by the similar-looking letter z, hence Zetland, the form used in the name of the pre-1975 county council. This is the source of the ZE postcode used for Shetland. Most of the individual islands have Norse names, although the derivations of some are obscure and may represent pre-Norse Pictish or pre-Celtic names or elements. Shetland is around 170 kilometres north of mainland Scotland, covers an area of 1,468 square kilometres and has a coastline 2,702 kilometres long. Lerwick, the capital and largest settlement, has a population of 6,958 and about half of the archipelago's total population of 23,167 people live within 16 kilometres of the town. Scalloway on the west coast, the capital until 1708, has a population of less than 1,000.
Only 16 of about 100 islands are inhabited. The main island of the group is known as Mainland; the next largest are Yell and Fetlar, which lie to the north, Bressay and Whalsay, which lie to the east. East and West Burra, Muckle Roe, Papa Stour and Vaila are smaller islands to the west of Mainland; the other inhabited islands are Foula 28 kilometres west of Walls, Fair Isle 38 kilometres south-west of Sumburgh Head, the Out Skerries to the east. The uninhabited islands include Mousa, known for the Broch of Mousa, the finest preserved example in Scotland of an Iron Age broch. Shetland's location means that it provides a number of such records: Muness is the most northerly castle in the United Kingdom and Skaw the most northerly settlement. The
In geology, permafrost is ground, including rock or soil, at or below the freezing point of water 0 °C for two or more years. Most permafrost is located in high latitudes, but at lower latitudes alpine permafrost occurs at higher elevations. Ground ice is not always present, as may be in the case of non-porous bedrock, but it occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material. Permafrost accounts for 0.022% of total water on Earth and the permafrost region covers 24% of exposed land in the Northern Hemisphere. It occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean, portions of which were exposed during the last glacial period; the thawing of permafrost has implications for the global climate. A global temperature rise of 1.5 °C above current levels would be enough to start the thawing of permafrost in Siberia, according to one group of scientists. "In contrast to the relative dearth of reports on frozen ground in north America prior to World War II, a vast literature on the engineering aspects of permafrost was available in Russian.
Beginning in 1942, Siemon William Muller delved into the relevant Russian literature held by the Library of Congress and the U. S. Geological Survey Library so that he was able to furnish the government an engineering field guide and a technical report about permafrost by 1943", year in which he coined the term as a contraction of permamently frozen ground. Although classified, in 1947 a revised report was released publicly, regarded as the first North American treatise on the subject. Permafrost is soil, rock or sediment, frozen for more than two consecutive years. In areas not overlain by ice, it exists beneath a layer of soil, rock or sediment, which freezes and thaws annually and is called the "active layer". In practice, this means that permafrost occurs at an mean annual temperature of − 2 colder. Active layer thickness is 0.3 to 4 meters thick. The extent of permafrost varies with the climate: in the Northern Hemisphere today, 24% of the ice-free land area, equivalent to 19 million square kilometers, is more or less influenced by permafrost.
Of this area more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth; the deepest depth of permafrost occurs. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost forms in any climate where the mean annual air temperature is less than the freezing point of water. Exceptions are found in moist-wintered forest climates, such as in Northern Scandinavia and the North-Eastern part of European Russia west of the Urals, where snow acts as an insulating blanket. Glaciated areas may be exceptions. Since all glaciers are warmed at their base by geothermal heat, temperate glaciers, which are near the pressure-melting point throughout, may have liquid water at the interface with the ground and are therefore free of underlying permafrost.
"Fossil" cold anomalies in the Geothermal gradient in areas where deep permafrost developed during the Pleistocene persist down to several hundred metres. This is evident from temperature measurements in boreholes in North Europe; the below-ground temperature varies less from season to season than the air temperature, with mean annual temperatures tending to increase with depth as a result of the geothermal crustal gradient. Thus, if the mean annual air temperature is only below 0 °C, permafrost will form only in spots that are sheltered—usually with a northerly aspect—creating discontinuous permafrost. Permafrost will remain discontinuous in a climate where the mean annual soil surface temperature is between −5 and 0 °C. In the moist-wintered areas mentioned before, there may not be discontinuous permafrost down to −2 °C. Discontinuous permafrost is further divided into extensive discontinuous permafrost, where permafrost covers between 50 and 90 percent of the landscape and is found in areas with mean annual temperatures between −2 and −4 °C, sporadic permafrost, where permafrost cover is less than 50 percent of the landscape and occurs at mean annual temperatures between 0 and −2 °C.
In soil science, the sporadic permafrost zone is abbreviated SPZ and the extensive discontinuous permafrost zone DPZ. Exceptions occur in un-glaciated Siberia and Alaska where the present depth of permafrost is a relic of climatic conditions during glacial ages where winters were up to 11 °C colder than those of today. At mean annual soil surface temperatures below −5 °C the influence of aspect can never be sufficient to thaw permafrost and a zone of continuous permafrost forms. A line of continuous permafrost in the Northern Hemisphere represents the most southerly border where land is covered by continuous permafrost or glacial ice; the line of continuous permafrost varies around the world northward or southward due to regional climatic changes. In the southern hemisphere, most of the equivalent line would fall within the Southern Ocean if there were land there. Most of the Antarctic continent is overl
The moose or elk, Alces alces is a member of the New World deer subfamily and is the largest and heaviest extant species in the Deer family. Moose are distinguished by the palmate antlers of the males. Moose inhabit boreal forests and temperate broadleaf and mixed forests of the Northern Hemisphere in temperate to subarctic climates. Hunting and other human activities have caused a reduction in the size of the moose's range over time. Moose have been reintroduced to some of their former habitats. Most moose are found in Canada, New England, Baltic states, Russia, their diet consists of both aquatic vegetation. The most common moose predators are the gray wolf along with humans. Unlike most other deer species, moose do not form herds and are solitary animals, aside from calves who remain with their mother until the cow begins estrus, at which point the cow chases away young bulls. Although slow-moving and sedentary, moose can become aggressive and move if angered or startled, their mating season in the autumn features energetic fights between males competing for a female.
Alces alces is called an "elk" in British English. The word "elk" in North American English refers to a different species of deer, the Cervus canadensis called the wapiti. A mature male moose is called a bull, a mature female a cow, an immature moose of either sex a calf; the word "elk" originated in Proto-Germanic, from which Old English evolved and has cognates in other Indo-European languages, e.g. elg in Danish/Norwegian. In the continental-European languages, these forms of the word "elk" always refer to the Alces alces; the word "moose" had first entered English by 1606 and is borrowed from the Algonquian languages, involved forms from multiple languages mutually reinforcing one another. The Proto-Algonquian form was *mo·swa; the moose became extinct in Britain during the Bronze Age, long before the European arrival in the Americas. The youngest bones were found in Scotland and are 3,900 years old; the word "elk" remained in usage because of its existence in continental Europe but, without any living animals around to serve as a reference, the meaning became rather vague to most speakers of English, who used "elk" to refer to "large deer" in general.
Dictionaries of the 18th century described "elk" as a deer, "as large as a horse". Confusingly, the word "elk" is used in North America to refer to a different animal, Cervus canadensis, called by the Algonquian indigenous name, "wapiti"; the British began colonizing America in the 17th century, found two common species of deer for which they had no names. The wapiti appeared similar to the red deer of Europe although it was much larger and was not red; the moose was a rather strange-looking deer to the colonists, they adopted local names for both. In the early days of American colonization, the wapiti was called a grey moose and the moose was called a black moose, but early accounts of the animals varied wildly, adding to the confusion; the wapiti is superficially similar to the red deer of central and western Europe, although it is distinctly different behaviorally and genetically. Early European explorers in North America in Virginia where there were no moose, called the wapiti "elk" because of its size and resemblance to familiar-looking deer like the red deer.
The moose resembled the "German elk", less familiar to the British colonists. For a long time neither species were called a variety of things. In North America the wapiti became known as an elk while the moose retained its Anglicized Native-American name. In 1736, Samuel Dale wrote to the Royal Society of Great Britain: The common light-grey moose, called by the Indians and the large or black-moose, the beast whose horns I herewith present; as to the grey moose, I take it to be no larger than what Mr. John Clayton, in his account of the Virginia Quadrupeds, calls the Elke... was in all respects like those of our red-deer or stags, only larger... The black moose is accounted a large creature.... The stag, buck, or male of this kind has a palmed horn, not like that of our common or fallow-deer, but the palm is much longer, more like that of the German elke. Moose require habitat with adequate edible plants, cover from predators, protection from hot or cold weather. Moose travel among different habitats with the seasons to address these requirements.
Moose are cold-adapted mammals with thickened skin, heat-retaining coat, a low surface:volume ratio, which provides excellent cold tolerance but poor heat tolerance. Moose survive hot weather by immersion in cool water. In hot weather, moose are found wading or swimming in lakes or ponds; when heat-stressed, moose may fail to adequately forage in summer and may not gain adequate body fat to survive the winter. Also