Geologically, a fjord or fiord is a long, narrow inlet with steep sides or cliffs, created by a glacier. There are many fjords on the coasts of Alaska, British Columbia, Greenland, the Faroe Islands, Kamchatka, the Kerguelen Islands, New Zealand, Novaya Zemlya, Nunavut, Quebec, South Georgia Island, Washington state. Norway's coastline is estimated at 29,000 kilometres with nearly 1,200 fjords, but only 2,500 kilometres when fjords are excluded. A true fjord is formed when a glacier cuts a U-shaped valley by ice segregation and abrasion of the surrounding bedrock. According to the standard model, glaciers formed in pre-glacial valleys with a sloping valley floor; the work of the glacier left an overdeepened U-shaped valley that ends abruptly at a valley or trough end. Such valleys are fjords. Thresholds above sea level create freshwater lakes. Glacial melting is accompanied by the rebounding of Earth's crust as the ice load and eroded sediment is removed. In some cases this rebound is faster than sea level rise.
Most fjords are deeper than the adjacent sea. Fjords have a sill or shoal at their mouth caused by the previous glacier's reduced erosion rate and terminal moraine. In many cases this sill causes large saltwater rapids. Saltstraumen in Norway is described as the world's strongest tidal current; these characteristics distinguish fjords from rias, which are drowned valleys flooded by the rising sea. Drammensfjorden is cut in two by the Svelvik "ridge", a sandy moraine that during the ice cover was under sea level but after the post-glacial rebound reaches 60 m above the fjord. Jens Esmark in the 19th century introduced the theory that fjords are or have been created by glaciers and that large parts of Northern Europe had been covered by thick ice in prehistory. Thresholds at the mouths and overdeepening of fjords compared to the ocean are the strongest evidence of glacial origin, these thresholds are rocky. Thresholds are related to sounds and low land where the ice could spread out and therefore have less erosive force.
John Walter Gregory argued that fjords are of tectonic origin and that glaciers had a negligible role in their formation. Gregory's views were rejected by subsequent research and publications. In the case of Hardangerfjord the fractures of the Caledonian fold has guided the erosion by glaciers, while there is no clear relation between the direction of Sognefjord and the fold pattern; this relationship between fractures and direction of fjords is observed in Lyngen. Preglacial, tertiary rivers eroded the surface and created valleys that guided the glacial flow and erosion of the bedrock; this may in particular have been the case in Western Norway where the tertiary uplift of the landmass amplified eroding forces of rivers. Confluence of tributatry fjords led to excavation of the deepest fjord basins. Near the coast the typical West Norwegian glacier spread out and lost their concentration and reduced the glaciers' power to erode leaving bedrock thresholds. Bolstadfjorden is 160 m deep with a treshold of only 1.5 m, while the 1,300 m deep Sognefjorden has a threshold around 100 to 200 m deep.
Hardangerfjord is made up of several basins separated by thresholds: The deepest basin Samlafjorden between Jonaneset og Ålvik with a distinct treshold at Vikingneset in Kvam. Hanging valleys are common along U-shaped valleys. A hanging valley is a tributary valley, higher than the main valley and were created by tributary glacier flows into a glacier of larger volume; the shallower valley appears to be ` hanging' above a fjord. Waterfalls form at or near the outlet of the upper valley. Hanging valleys occur under water in fjord systems; the branches of Sognefjord are for instance much shallower than the main fjord. The mouth of Fjærlandsfjord is about 400 m deep; the mouth of Ikjefjord is only 50 meters deep while the main fjord is around 1,300 m at the same point. During the winter season there is little inflow of freshwater. Surface water and deeper water are mixed during winter because of the steady cooling of the surface and wind. In the deep fjords there is still fresh water from the summer with less density than the saltier water along the coast.
Offshore wind, common in the fjord areas during winter, sets up a current on the surface from the inner to the outer parts. This current on the surface in turn pulls dense salt water from the coast across the fjord threshold and into the deepest parts of the fjord. Bolstadfjorden has a threshold of only 1.5 m and strong inflow of freshwater from Vosso river creates a brackish surface that blocks circulation of the deep fjord. The deeper, salt layers of Bolstadfjorden are deprived of oxygen and the seabed is covered with organic material; the shallow threshold creates a strong tidal current. During the summer season there is a large inflow of river water in the inner areas; this freshwater gets mixed with saltwater creating a layer of brackish water with a higher surface than the ocean which in turn sets up a current from the river mouths towards the ocean. This current is more salty towards the coast and right under the surface current there is a reverse current of saltier water from the coast.
In the deeper
The North Pole known as the Geographic North Pole or Terrestrial North Pole, is defined as the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. The North Pole is the northernmost point on the Earth, lying diametrically opposite the South Pole, it defines geodetic latitude 90° North, as well as the direction of true north. At the North Pole all directions point south. Along tight latitude circles, counterclockwise is east and clockwise is west; the North Pole is at the center of the Northern Hemisphere. While the South Pole lies on a continental land mass, the North Pole is located in the middle of the Arctic Ocean amid waters that are permanently covered with shifting sea ice; this makes it impractical to construct a permanent station at the North Pole. However, the Soviet Union, Russia, constructed a number of manned drifting stations on a annual basis since 1937, some of which have passed over or close to the Pole. Since 2002, the Russians have annually established a base, close to the Pole.
This operates for a few weeks during early spring. Studies in the 2000s predicted that the North Pole may become seasonally ice-free because of Arctic ice shrinkage, with timescales varying from 2016 to the late 21st century or later; the sea depth at the North Pole has been measured at 4,261 m by the Russian Mir submersible in 2007 and at 4,087 m by USS Nautilus in 1958. The nearest land is said to be Kaffeklubben Island, off the northern coast of Greenland about 700 km away, though some semi-permanent gravel banks lie closer; the nearest permanently inhabited place is Alert in the Qikiqtaaluk Region, Canada, located 817 km from the Pole. The Earth's axis of rotation – and hence the position of the North Pole – was believed to be fixed until, in the 18th century, the mathematician Leonhard Euler predicted that the axis might "wobble" slightly. Around the beginning of the 20th century astronomers noticed a small apparent "variation of latitude," as determined for a fixed point on Earth from the observation of stars.
Part of this variation could be attributed to a wandering of the Pole across the Earth's surface, by a range of a few metres. The wandering has an irregular component; the component with a period of about 435 days is identified with the eight-month wandering predicted by Euler and is now called the Chandler wobble after its discoverer. The exact point of intersection of the Earth's axis and the Earth's surface, at any given moment, is called the "instantaneous pole", but because of the "wobble" this cannot be used as a definition of a fixed North Pole when metre-scale precision is required, it is desirable to tie the system of Earth coordinates to fixed landforms. Of course, given plate tectonics and isostasy, there is no system in which all geographic features are fixed, yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System. As early as the 16th century, many prominent people believed that the North Pole was in a sea, which in the 19th century was called the Polynya or Open Polar Sea.
It was therefore hoped. Several expeditions set out to find the way with whaling ships commonly used in the cold northern latitudes. One of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827 reached latitude 82°45′ North. In 1871 the Polaris expedition, a US attempt on the Pole led by Charles Francis Hall, ended in disaster. Another British Royal Navy attempt on the pole, part of the British Arctic Expedition, by Commander Albert H. Markham reached a then-record 83°20'26" North in May 1876 before turning back. An 1879–1881 expedition commanded by US naval officer George W. DeLong ended tragically when their ship, the USS Jeanette, was crushed by ice. Over half the crew, including DeLong, were lost. In April 1895 the Norwegian explorers Fridtjof Nansen and Hjalmar Johansen struck out for the Pole on skis after leaving Nansen's icebound ship Fram; the pair reached latitude 86°14′ North before they abandoned the attempt and turned southwards reaching Franz Josef Land.
In 1897 Swedish engineer Salomon August Andrée and two companions tried to reach the North Pole in the hydrogen balloon Örnen, but came down 300 km north of Kvitøya, the northeasternmost part of the Svalbard archipelago. They died there three months later. In 1930 the remains of this expedition were found by the Norwegian Bratvaag Expedition; the Italian explorer Luigi Amedeo, Duke of the Abruzzi and Captain Umberto Cagni of the Italian Royal Navy sailed the converted whaler Stella Polare from Norway in 1899. On 11 March 1900 Cagni led a party over the ice and reached latitude 86° 34’ on 25 April, setting a new record by beating Nansen's result of 1895 by 35 to 40 km. Cagni managed to return to the camp, remaining there until 23 June. On 16 August the Stella Polare left Rudolf Island heading south and the expedition returned to Norway; the US explorer Frederick Cook claimed to have reached the North Pole on 21 April 1908 with two Inuit men and Etukishook, but he was unable to produce convincing proof and his c
A birch is a thin-leaved deciduous hardwood tree of the genus Betula, in the family Betulaceae, which includes alders and hornbeams. It is related to the beech-oak family Fagaceae; the genus Betula contains 30 to 60 known taxa of which 11 are on the IUCN 2011 Red List of Threatened Species. They are a rather short-lived pioneer species widespread in the Northern Hemisphere in northern areas of temperate climates and in boreal climates. Birch species are small to medium-sized trees or shrubs of northern temperate and boreal climates; the simple leaves are alternate, singly or doubly serrate, feather-veined and stipulate. They appear in pairs, but these pairs are borne on spur-like, two-leaved, lateral branchlets; the fruit is a small samara. They differ from the alders in that the female catkins are not woody and disintegrate at maturity, falling apart to release the seeds, unlike the woody, cone-like female alder catkins; the bark of all birches is characteristically marked with long, horizontal lenticels, separates into thin, papery plates upon the paper birch.
Distinctive colors give the common names gray, black and yellow birch to different species. The buds form early and are full grown by midsummer, all are lateral, no terminal bud is formed; the wood of all the species is close-grained with a satiny texture and capable of taking a fine polish. The flowers are monoecious, opening with or before the leaves and borne once grown these leaves are 3–6 millimetres long on three-flowered clusters in the axils of the scales of drooping or erect catkins or aments. Staminate aments are pendulous, clustered or solitary in the axils of the last leaves of the branch of the year or near the ends of the short lateral branchlets of the year, they remain rigid during the winter. The scales of the staminate aments when mature are broadly ovate, yellow or orange color below the middle, dark chestnut brown at apex; each scale bears two bractlets and three sterile flowers, each flower consisting of a sessile, membranaceous two-lobed, calyx. Each calyx bears four short filaments with one-celled anthers or two filaments divided into two branches, each bearing a half-anther.
Anther cells open longitudinally. The pistillate aments are pendulous, solitary; the pistillate scales are oblong-ovate, three-lobed, pale yellow-green tinged with red, becoming brown at maturity. These scales bear each flower consisting of a naked ovary; the ovary is compressed, two-celled, crowned with two slender styles. Each scale bears a single small, winged nut, oval, with two persistent stigmas at the apex. Betula species are organised into five subgenera. Birches native to Europe and Asia include Betula albosinensis – Chinese red birch Betula alnoides – alder-leaf birch Betula ashburneri – Betula baschkirica – Betula bomiensis – Betula browicziana – Betula calcicola – Betula celtiberica – Betula chichibuensis – Betula chinensis – Chinese dwarf birch Betula coriaceifolia – Betula corylifolia – Betula costata – Betula cylindrostachya – Betula dahurica – Betula delavayi – Betula ermanii – Erman's birch Betula falcata – Betula fargesii – Betula fruticosa – Betula globispica – Betula gmelinii – Betula grossa – Japanese cherry birch Betula gynoterminalis – Betula honanensis – Betula humilis or Betula kamtschatica – Kamchatka birch platyphylla Betula insignis – Betula karagandensis – Betula klokovii – Betula kotulae – Betula litvinovii – Betula luminifera – Betula maximowiczii – monarch birch Betula medwediewii – Caucasian birch Betula megrelica – Betula microphylla – Betula nana – dwarf birch ) Betula pendula – silver birch Betula platyphylla – —Siberian silver birch Betula potamophila – Betula potaninii – Betula psammophila – Betula pubescens – downy birch known as white, European white or hairy birch Betula raddeana – Betula saksaren
Greenland is an autonomous constituent country of the Kingdom of Denmark between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for more than a millennium; the majority of its residents are Inuit, whose ancestors began migrating from the Canadian mainland in the 13th century settling across the island. Greenland is the world's largest island. Three-quarters of Greenland is covered by the only permanent ice sheet outside Antarctica. With a population of about 56,480, it is the least densely populated territory in the world. About a third of the population live in the capital and largest city; the Arctic Umiaq Line ferry acts as a lifeline for western Greenland, connecting the various cities and settlements. Greenland has been inhabited at intervals over at least the last 4,500 years by Arctic peoples whose forebears migrated there from what is now Canada.
Norsemen settled the uninhabited southern part of Greenland beginning in the 10th century, having settled Iceland to escape persecution from the King of Norway and his central government. These Norsemen would set sail from Greenland and Iceland, with Leif Erikson becoming the first known European to reach North America nearly 500 years before Columbus reached the Caribbean islands. Inuit peoples arrived in the 13th century. Though under continuous influence of Norway and Norwegians, Greenland was not formally under the Norwegian crown until 1262; the Norse colonies disappeared in the late 15th century when Norway was hit by the Black Death and entered a severe decline. Soon after their demise, beginning in 1499, the Portuguese explored and claimed the island, naming it Terra do Lavrador. In the early 18th century, Danish explorers reached Greenland again. To strengthen trading and power, Denmark–Norway affirmed sovereignty over the island; because of Norway's weak status, it lost sovereignty over Greenland in 1814 when the union was dissolved.
Greenland became Danish in 1814, was integrated in the Danish state in 1953 under the Constitution of Denmark. In 1973, Greenland joined the European Economic Community with Denmark. However, in a referendum in 1982, a majority of the population voted for Greenland to withdraw from the EEC, effected in 1985. Greenland contains the world's largest and most northerly national park, Northeast Greenland National Park. Established in 1974, expanded to its present size in 1988, it protects 972,001 square kilometres of the interior and northeastern coast of Greenland and is bigger than all but twenty-nine countries in the world. Greenland is divided into five municipalities – Sermersooq, Qeqertalik and Avannaata. Greenland does not have an independent seat at the United Nations. In 1979, Denmark granted home rule to Greenland, in 2008, Greenlanders voted in favor of the Self-Government Act, which transferred more power from the Danish government to the local Greenlandic government. Under the new structure, in effect since 21 June 2009, Greenland can assume responsibility for policing, judicial system, company law and auditing.
It retains control of monetary policy, providing an initial annual subsidy of DKK 3.4 billion, planned to diminish over time. Greenland expects to grow its economy based on increased income from the extraction of natural resources; the capital, held the 2016 Arctic Winter Games. At 70%, Greenland has one of the highest shares of renewable energy in the world coming from hydropower; the early Norse settlers named the island as Greenland. In the Icelandic sagas, the Norwegian-born Icelander Erik the Red was said to be exiled from Iceland for manslaughter. Along with his extended family and his thralls, he set out in ships to explore an icy land known to lie to the northwest. After finding a habitable area and settling there, he named it Grœnland in the hope that the pleasant name would attract settlers; the Saga of Erik the Red states: "In the summer, Erik left to settle in the country he had found, which he called Greenland, as he said people would be attracted there if it had a favorable name."The name of the country in the indigenous Greenlandic language is Kalaallit Nunaat.
The Kalaallit are the indigenous Greenlandic Inuit people. In prehistoric times, Greenland was home to several successive Paleo-Eskimo cultures known today through archaeological finds; the earliest entry of the Paleo-Eskimo into Greenland is thought to have occurred about 2500 BC. From around 2500 BC to 800 BC, southern and western Greenland were inhabited by the Saqqaq culture. Most finds of Saqqaq-period archaeological remains have been around Disko Bay, including the site of Saqqaq, after which the culture is named. From 2400 BC to 1300 BC, the Independence I culture existed in northern Greenland, it was a part of the Arctic small tool tradition. Towns, including Deltaterrassern
Picea mariana, the black spruce, is a North American species of spruce tree in the pine family. It is widespread across Canada, found in all all 3 Arctic territories, its range extends into northern parts of the United States: in Alaska, the Great Lakes region, the upper Northeast. It is a frequent part of the biome known as boreal forest; the Latin specific epithet mariana means “of the Virgin Mary”. Picea mariana is a slow-growing, small upright evergreen coniferous tree, having a straight trunk with little taper, a scruffy habit, a narrow, pointed crown of short, drooping branches with upturned tips. Through much of its range it averages 5–15 m tall with a trunk 15–50 cm diameter at maturity, though occasional specimens can reach 30 m tall and 60 cm diameter; the bark is thin and grayish brown. The leaves are needle-like, 6–15 mm long, four-sided, dark bluish green on the upper sides, paler glaucous green below; the cones are the smallest of all of the spruces, 1.5–4 cm long and 1–2 cm broad, spindle-shaped to nearly round, dark purple ripening red-brown, produced in dense clusters in the upper crown, opening at maturity but persisting for several years.
Natural hybridization occurs with the related Picea rubens, rarely with Picea glauca. It differs from P. glauca in having a dense cover of small hairs on the bark of young branch tips, an darker reddish-brown bark, shorter needles and rounder cones, a preference for wetter lowland areas. Numerous differences in details of its needle and pollen morphology exist but require careful microscopic examination to detect. From true firs, such as Abies balsamea, it differs in having pendulous cones, persistent woody leaf-bases, four-angled needles, arranged all round the shoots. Due to the large difference between heartwood and sapwood moisture content, it is easy to distinguish these two wood characteristics in ultrasound images, which are used as a nondestructive technique to assess the internal condition of the tree and avoid useless log breakdown. Older taxonomic synonyms include Picea brevifolia, or Picea nigra. Growth varies with site quality. In swamp and muskeg it shows progressively slower growth rates from the edges toward the centre.
The roots are shallow and wide resulting in susceptibility to windthrow. In the northern part of its range, ice pruned asymmetric black spruce are seen with diminished foliage on the windward side. Tilted trees colloquially called. In the southern portion of its range it is found on wet organic soils, but farther north its abundance on uplands increases. In the Great Lakes States it is most abundant in peat bogs and swamps on transitional sites between peatlands and uplands. In these areas it is rare on uplands, except in isolated areas of northern Minnesota and the Upper Peninsula of Michigan. Most stands are even-aged due to frequent fire intervals in black spruce forests, it grows in pure stands on organic soils and in mixed stands on mineral soils. It is tolerant of nutrient-poor soils, is found on poorly drained acidic peatlands, it is considered a climax species over most of its range. The frequent fire return interval, a natural fire ecology, perpetuates numerous successional communities.
Throughout boreal North America, Betula papyrifera and Populus tremuloides are successional hardwoods that invade burns in black spruce. Black spruce seeds in promptly after fire, with the continued absence of fire dominates the hardwoods, it is a pioneer that invades the sedge mat in filled-lake bogs, though preceded by Larix laricina, with which it may in time form a stable forest cover in swamps. However, as the peat soil is elevated by the accumulation of organic matter, the fertility of the site improves, balsam fir and Thuja occidentalis replaces black spruce and tamarack; the spruce budworm, a moth larva, causes defoliation which kills trees if it occurs several years in a row, though black spruce is less susceptible than white spruce or balsam fir. Trees most at risk are those growing with white spruce. Numerous cultivars have been selected for use in gardens; the cultivar P. mariana'Nana' is a dwarf form which has gained the Royal Horticultural Society's Award of Garden Merit. Black spruce is the provincial tree of Labrador.
The timber is of low value due to the small size of the trees, but it is an important source of pulpwood and the primary source of it in Canada. Fast-food chopsticks are made from black spruce. However, it is being used for making cross laminated timber by companies such as Nordic Structures, which allows the high strength due to the tight growth rings to be assembled into larger timbers
Larches are conifers in the genus Larix, of the family Pinaceae. Growing from 20 to 45 m tall, they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south. Larches are among the dominant plants in the boreal forests of Canada. Although they are conifers, larches are deciduous trees. Larches can reach 50–60 m; the larch's tree crown is sparse and the branches are brought horizontal to the stem if some species have them characteristically pendulous. Larch shoots are dimorphic, with leaves borne singly on long shoots 10–50 centimetres long and bearing several buds, in dense clusters of 20–50 needles on short shoots only 1–2 mm long with only a single bud; the leaves are needle-like. Larches are among the few deciduous conifers, which are evergreen. Other deciduous conifers include the golden larch Pseudolarix amabilis, the dawn redwood Metasequoia glyptostroboides, the Chinese swamp cypress Glyptostrobus pensilis and the bald cypresses in the genus Taxodium.
The male flowers are fall after pollination. The female flowers of larches are erect, small, 1–9 cm long, green or purple, brown in ripening and lignify 5–8 months after pollination; those native to northern regions have small cones with short bracts, with more southerly species tending to have longer cones with exserted bracts, with the longest cones and bracts produced by the southernmost species, in the Himalayas. The seeds are winged; the larches are streamlined trees, the root system are broad and deep and the bark is finely cracked and wrinkled in irregular plaques. The wood is bicolor, with yellowish white sapwood; the chromosome number is 2n = 24, similar to that of most of the other trees of the Pinaceae family. The genus Larix is present in all the temperate-cold zones of the northern hemisphere, from North America to northern Siberia passing through Europe, mountainous China and Japan; the larches are important forest trees of Central Europe, United States and Canada. They require a cool and humid climate and for this reason they are found in the mountains of the temperate zones, while in the northernmost boreal zones ones they are found in the plain.
At gen. Larix belong to the trees that go further north than all, reaching in the North America and Siberia the tundra and polar ice; the larches are pioneer species not demanding towards the soil and they are long-lived trees. They live in pure or mixed forests together with other conifers or more broad-leaved trees. In the past, the cone bract length was used to divide the larches into two sections, but genetic evidence does not support this division, pointing instead to a genetic divide between Old World and New World species, with the cone and bract size being adaptations to climatic conditions. More recent genetic studies have proposed three groups within the genus, with a primary division into North American and Eurasian species, a secondary division of the Eurasian into northern short-bracted species and southern long-bracted species; the genus Larix belongs to the subfamily Laricoideae, which includes the genera Pseudotsuga and Cathaya. There are eleven accepted species of larch subdivided on the basis of the most recent phylogenetic investigations: Larix laricina K. Koch – Tamarack or American larch.
Parts of Alaska and throughout Canada and the northern United States from the eastern Rocky Mountains to the Atlantic shore. Larix lyallii Parl. – Subalpine larch. Mountains of northwest United States and southwest Canada, at high altitude. Larix occidentalis Nutt. – Western larch. Mountains of northwest United States and southwest Canada, at lower altitudes. Larix decidua Mill. – European larch. Mountains of central Europe. Larix sibirica Ledeb. – Siberian larch. Plains of western Siberia. Larix gmelinii Kuzen. – Dahurian larch. Plains of central and eastern Siberia. Larix kaempferi Carr. – Japanese larch. Mountains of central Japan. Larix czekanowskii Szafer – Uncertain, its origin could be hybrid. Larix potaninii Batalin – Chinese larch. Mountains of southwestern China. Larix mastersiana Rehder & E. H. Wilson – Masters' larch. Mountains of western China. Larix griffithii Hook.f. – Himalayan larch. Mountains of the eastern Himalayas. Most if not all of the species can be hybridised in cultivation. Currently-accepted hybrids are: Larix × lubarskii Sukaczev Larix × maritima Sukaczev Larix × polonica Racib.
A well-known hybrid, the Dunkeld larch Larix × marschlinsii, which arose more or less in Switzerland and Scotland when L. decidua and L. kaempferi hybridised when planted together, is still treated as unresolved. Larix x stenophylla Sukaczev. Larch is used as a food plant by the larvae of a number of Lepidoptera species — see list of Lepidoptera that feed on larches. Larches are prone to the fungal canker disease Lachnellula ssp..
Thuja is a genus of coniferous trees in the Cupressaceae. There are two native to North America and three native to eastern Asia; the genus is sister to Thujopsis. Members are known as arborvitaes, thujas or cedars. Thuja are evergreen trees growing from 10 to 200 feet tall, with stringy-textured reddish-brown bark; the shoots are flat, with side shoots only in a single plane. The leaves are scale-like 1–10 mm long, except young seedlings in their first year, which have needle-like leaves; the scale leaves are arranged in alternating decussate pairs in four rows along the twigs. The male cones are small and are located at the tips of the twigs; the female cones start out inconspicuous, but grow to about 1–2 cm long at maturity when 6–8 months old. The five species in the genus Thuja are small to large evergreen trees with flattened branchlets; the leaves are arranged in flattened fan shaped groupings with resin-glands, oppositely grouped in 4 ranks. The mature leaves are different from younger leaves, with those on larger branchlets having sharp, free apices.
The leaves on flattened lateral branchlets are crowded into appressed groups and scale-like and the lateral pairs are keeled. With the exception of T. plicata, the lateral leaves are shorter than the facial leaves. The solitary flowers are produced terminally. Pollen cones with 2-6 pairs of 2-4 pollen sacked sporophylls. Seed cones ellipsoid 9-14mm long, they mature and open the first year; the thin woody cone scales number from 4-6 pairs and are persistent and overlapping, with an oblong shape, they are basifixed. The central 2-3 pairs of cone scales are fertile; the seed cones produce 1 to 3 seeds per scale, the seeds are lenticular in shape and 2 winged. Seedlings produce 2 cotyledons. A hybrid between T. standishi and T. plicata has been named as the cultivar Thuja'Green Giant'. Another distinct and only distantly related species treated as Thuja orientalis, is now treated in a genus of its own, as Platycladus orientalis; the closest relatives of Thuja are Thujopsis dolabrata, distinct in its thicker foliage and stouter cones, Tetraclinis articulata, distinct in its quadrangular foliage and cones with four thick, woody scales.
The genus Thuja, like many other forms of conifers, is represented by ancestral forms in Cretaceous rocks of northern Europe, with the advance of time is found to migrate from northerly to more southerly regions, until during Pliocene time it disappeared from Europe. Thuja is known in the Miocene beds of the Dakotas; the five extant species are: Thuja koraiensis Nakai – Korean thuja - Jilin, Korea Thuja occidentalis L. – eastern arborvitae, northern whitecedar - E Canada, E United States Thuja plicata Donn ex D. Don – western redcedar - from Alaska to Mendocino County in California Thuja standishii Carrière – Japanese thuja - Honshu, Shikoku Thuja sutchuenensis Carrière – Sichuan thuja - Sichuan, Chongqing China extinct in the wildSpecies placed in Thuja include: Austrocedrus chilensis Pic. Serm. & Bizzarri Callitris rhomboidea R. Br. Ex Rich. Cupressus nootkatensis D. Don Dacrycarpus imbricatus de Laub Glyptostrobus pensilis K. Koch Libocedrus plumosa Sarg. Platycladus orientalis Franco Tamarix aphylla H.
Karst. Tetraclinis articulata Mast. Thujopsis dolabrata Siebold & Zucc. Widdringtonia nodiflora Powrie and many more Thuja species are used as food plants by the larvae of some Lepidoptera species including autumnal moth, the engrailed and juniper pug; the foliage is readily eaten by deer, where deer population density is high, can adversely affect the growth of young trees and the establishment of seedlings. They are grown as ornamental trees, extensively used for hedges. A number of cultivars are used in landscapes. Homeowners will sometimes plant them as privacy trees; the cultivar'Green Giant' is popular as a vigorous hedging plant, growing up to 80 cm/year when young. The wood is light and aromatic, it can be split and resists decay. The wood has been used for many applications from making chests. Thuja poles are often used to make fence posts and rails; the wood of Thuja plicata is used for guitar sound boards. Its combination of light weight and resistance to decay has led to T. plicata being used for the construction of bee hives.
Oil of thuja contains the terpene thujone, studied for its GABA receptor antagonizing effects, with lethal properties. Cedarwood oil and cedar leaf oil, which are derived from Thuja occidentalis, have different properties and uses; the natives of Canada used the scaled leaves of Thuja occidentalis to make a tea, shown to contain 50 mg of vitamin C per 100 grams. In the 19th century Thuja was used as an externally applied tincture or ointment for the treatment of warts and thrush, a local injection of the tincture was used for t