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''Tsuga canadensis'', also known as eastern hemlock, eastern hemlock-spruce, or Canadian hemlock, and in the French-speaking regions of Canada as ''pruche du Canada'', is a
coniferous Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extant ...
tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...
native Native may refer to: People * Jus soli, citizenship by right of birth * Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory ** Native Americans (disambiguation) In arts and entert ...
to eastern North America. It is the
state tree This is a list of U.S. state, federal district, and territory trees, including official trees of the following of the states, of the federal district, and of the territories. Table See also * List of U.S. state, district, and territorial insign ...
of Pennsylvania. Eastern hemlocks are widespread throughout much of the
Great Lakes region The Great Lakes region of North America is a binational Canadian–American region that includes portions of the eight U.S. states of Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin along with the Canadian p ...
, the
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
, the
Northeastern United States The Northeastern United States, also referred to as the Northeast, the East Coast, or the American Northeast, is a geographic region of the United States. It is located on the Atlantic coast of North America, with Canada to its north, the Southe ...
, and
Maritime Canada The Maritimes, also called the Maritime provinces, is a region of Eastern Canada consisting of three provinces: New Brunswick, Nova Scotia, and Prince Edward Island. The Maritimes had a population of 1,899,324 in 2021, which makes up 5.1% of Ca ...
. They have been introduced in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
and mainland Europe, where they are used as ornamental trees. Eastern hemlock populations in North America are threatened in much of their range by the spread of the invasive
Hemlock woolly adelgid The hemlock woolly adelgid (; ''Adelges tsugae''), or HWA, is an insect of the order Hemiptera (true bugs) native to East Asia. It feeds by sucking sap from hemlock and spruce trees (''Tsuga'' spp.; ''Picea'' spp.). In its native range, HWA ...
, which infests and eventually kills trees. Declines in population from hemlock wooly adelgid infestation have led to ''Tsuga canadensis'' being listed as Near Threatened on the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
. Eastern hemlocks are long lived trees, with many examples living for more than 500 years. They can grow to heights of more than , and are tolerant of shade, moist soil, and slopes. Hemlock wood is used in construction, and for
railroad ties A railroad tie, crosstie (American English), railway tie (Canadian English) or railway sleeper (Australian English, Australian and British English) is a rectangular support for the Track (rail transport), rails in railroad tracks. Generally la ...
. Historically its bark was an important source of
tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'', ...
for the leather
tanning Tanning may refer to: *Tanning (leather), treating animal skins to produce leather *Sun tanning, using the sun to darken pale skin **Indoor tanning, the use of artificial light in place of the sun **Sunless tanning, application of a stain or dye t ...
industry. Eastern hemlocks are popular as ornamental trees, thanks to their tolerance of a wide variety of soil and light conditions, as well as their characteristic drooping branches.


Description

The eastern hemlock grows well in shade and is very long lived, with the oldest recorded specimen, found in
Tionesta, Pennsylvania Tionesta is a borough in Forest County, Pennsylvania, United States. The population was 475 at the 2020 Census. It is the county seat of Forest County. The name is a Native American word meaning "the home of the wolves." Visitors and residents ...
, being at least 554 years old. The tree generally reaches heights of about , but exceptional trees have been recorded up to . The diameter of the trunk at breast height is often , but again, outstanding trees have been recorded up to . The trunk is usually straight and
monopodial Vascular plants with monopodial growth habits grow upward from a single point. They add leaves to the apex each year and the stem grows longer accordingly. The word ''Monopodial'' is derived from Greek "mono-", ''one'' and "podial", "foot", in refe ...
, but very rarely is forked. The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age. The twigs are a yellow-brown in color with darker red-brown
pulvini A pulvinus (pl. ''pulvini'') is a joint-like thickening at the base of a plant leaf or leaflet that facilitates growth-independent movement. Pulvini are common, for example, in members of the bean family Fabaceae (Leguminosae) and the prayer plant ...
, and are densely pubescent. The
bud In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...
s are ovoid in shape and are very small, measuring only in length. These are usually not resinous, but may be slightly so. The leaves are typically in length, but may be as short as or as long as . They are flattened and are typically distichous, or two-ranked. The bottom of the leaf is glaucous with two broad and clearly visible
stomata In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is bor ...
l bands, while the top is a shiny green to yellow-green in color. The leaf margins are very slightly toothed, especially near the apex. The seed
cones A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...
are ovoid in shape and typically measure in length and in width. The scales are ovate to cuneate in shape and measure in length by in width. The apex is more or less rounded and is often projected outward. Twenty-four diploid
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
s are present within the trees' DNA.


Wood

The wood is soft, coarse-grained, and light buff in color. Air-dried, weighs . The lumber is used for general construction and crates. Because of its unusual power of holding spikes, it is also used for railroad ties. Untreated, the wood is not durable if exposed to the elements. As a fuel, it is low in value. The wood is also a source of pulp for paper manufacturing.


Distribution and habitat

''T. canadensis'' occurs at sea level in the north of its distribution, but is found primarily at elevations of . It ranges from northeastern
Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
eastward through southern
Quebec Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
and into
Nova Scotia Nova Scotia ( ; ; ) is one of the thirteen provinces and territories of Canada. It is one of the three Maritime provinces and one of the four Atlantic provinces. Nova Scotia is Latin for "New Scotland". Most of the population are native Eng ...
, and south in the
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
to northern
Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...
and Alabama. Disjunct populations occur in the
Piedmont region it, Piemontese , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = , demographics1_footnotes = , demographics1_title1 = , demographics1_info1 = , demographics1_title2 ...
, northern Alabama, western
Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
and into
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
, as well as western Wisconsin and eastern Minnesota.Farjon, A. (1990). ''Pinaceae. Drawings and Descriptions of the Genera''. Koeltz Scientific Books . In Canada, it is present in Ontario and all provinces to the east except Newfoundland and Labrador. Its range completely overlaps that of the closely related ''
Tsuga caroliniana ''Tsuga caroliniana'', the Carolina hemlock, is a species of hemlock endemic to the United States. Distribution and habitat Carolina hemlock is native to the Appalachian Mountains in southwest Virginia, western North Carolina, extreme northeas ...
''. It is found primarily on rocky ridges, ravines, and hillsides with relatively high levels of moisture.


Climate

Eastern hemlock is generally confined to areas with highland climates, with cool and humid conditions. Precipitation in the areas where it grows is typically to more than per year. The lower number is more typical of northern forests that receive heavy snowfall; the higher number is common in southerly areas with high summer rainfall. Near the Atlantic coast and in the southern Appalachians where the trees often reach their greatest heights, annual rainfall often exceeds . In the north of its range, the temperatures in January average , while in July they average only . In these areas, the frost-free season can last fewer than 80 days. In contrast, the southern end of the range experiences up to 200 days without frost and January temperatures as high as .


Hemlock woolly adelgid

The species is currently threatened by the
hemlock woolly adelgid The hemlock woolly adelgid (; ''Adelges tsugae''), or HWA, is an insect of the order Hemiptera (true bugs) native to East Asia. It feeds by sucking sap from hemlock and spruce trees (''Tsuga'' spp.; ''Picea'' spp.). In its native range, HWA ...
(''Adelges tsugae''), a sap-sucking bug introduced from
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
to the United States in 1924, and first found in the native range of eastern hemlock in the late 1960s. The adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slower. Virtually all the hemlocks in the southern Appalachian Mountains have seen infestations of the insect within the last five to seven years, with thousands of hectares of stands dying within the last two to three years. Attempts to save representative examples on both public and private lands are on-going. A project named "Tsuga Search", funded by the
Great Smoky Mountains National Park Great Smoky Mountains National Park is an American national park in the southeastern United States, with parts in North Carolina and Tennessee. The park straddles the ridgeline of the Great Smoky Mountains, part of the Blue Ridge Mountains, whi ...
, is being conducted to save the largest and tallest remaining eastern hemlocks in the Park. Through Tsuga Search, hemlocks have been found with trunk volumes up to 44.8 m³ within the park, making it the largest eastern evergreen conifer, eclipsing in volume both eastern white pine (''Pinus strobus'') and
loblolly pine ''Pinus taeda'', commonly known as loblolly pine, is one of several pines native to the Southeastern United States, from East Texas to Florida, and north to southern New Jersey. The wood industry classifies the species as a southern yellow pine. ...
(''Pinus taeda''). The tree is currently listed as a
near threatened A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...
species in the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
, but this is based largely on its wide distribution and because the adelgid populations have not reached the northern areas of its range. A 2009 study conducted by scientists with the
U.S. Forest Service The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency in ...
Southern Research Station suggests the hemlock woolly adelgid is killing hemlock trees faster than expected in the southern Appalachians, and rapidly altering the
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and Earth's atmosphere, atmosphere of the Earth. Carbon is the main component of biological compounds as well as ...
of these forests. According to ''
Science Daily ''Science Daily'' is an American website launched in 1995 that aggregates press releases and publishes lightly edited press releases (a practice called churnalism) about science, similar to Phys.org and EurekAlert!. The site was founded by mar ...
'', the pest could kill most of the region's hemlock trees within the next decade. According to the study, researchers found "hemlock woolly adelgid infestation is rapidly impacting the carbon cycle in emlocktree stands," and "adelgid-infested hemlock trees in the South are declining much faster than the reported 9-year decline of some infested hemlock trees in the Northeast."Hemlock Trees Dying Rapidly, Affecting Forest Carbon Cycle
/ref> In a 2009 case study,
entomologists Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...
from the U.S. Forest Service,
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
, and the
University of Massachusetts-Amherst The University of Massachusetts Amherst (UMass Amherst, UMass) is a public research university in Amherst, Massachusetts and the sole public land-grant university in Commonwealth of Massachusetts. Founded in 1863 as an agricultural college, i ...
released 900 '' Laricobius nigrinus'' beetles into a stand of adelgid-infested hemlocks near
Lansing, New York Lansing () is a town in Tompkins County, New York, United States. The population was 11,691 at the 2020 census. The town is named after John Lansing. People from Lansing were early settlers of Lansing, Michigan, and named it after their hometo ...
. ''L. nigrinus'', which is native to the Pacific Northwest, naturally preys on the hemlock wooly adelgid. The particular site near Lansing was chosen because its hemlocks are only lightly infested with the woolly adelgid, and enough trees are found to sustain a long-term study. The site will be left untreated with pesticides for 10 years to study how well the ''L. nigrinus'' beetles become established; if the experiment proves successful, researchers expect the population will take two to three years to build to levels where they can be readily detected.Predator Beetle to Battle Hemlock Pest
/ref>


Ecology

The tree can be found living in association with many forest mushrooms, such as ''
Ramaria flavosaponaria ''Ramaria flavosaponaria'' is a species of coral fungus in the family Gomphaceae. It is found in the mountains of eastern North America from Georgia and Tennessee to Nova Scotia. Names The specific epithet is from the ('yellow') and ('soapy ...
''.


Paleoecology

The mid-
Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...
decline of hemlock populations is a much-studied phenomenon. From its foundation in the early Holocene (around 16,000 BP) in what is now the southeastern US, ''T. canadensis'' expanded rapidly and successfully into its potential range. However,
palynological Palynology is the "study of dust" (from grc-gre, παλύνω, palynō, "strew, sprinkle" and ''-logy'') or of "particles that are strewn". A classic palynologist analyses particulate samples collected from the air, from water, or from deposit ...
analyses show the hemlock population experienced a pronounced decline approximately 5,500 BP that lasted for about 1,000 years. Continued research points to other, though less dramatic, dips in Holocene hemlock populations. Pathogens, insects, and climatic change, and a combination of these, have all been proposed to explain these anomalies. The eastern hemlock increased again after the major decline, but did not recover its former place as a dominant species.


Exceptional trees

Due to its being a long-lived tree, several very large or otherwise impressive trees exist along the east coast of North America. One organization, the Eastern Native Tree Society (ENTS), has been particularly active in discovering and measuring these trees. In the southern Appalachians, many individuals reach tall, and one tree has been measured in the Great Smoky Mountains National Park to tall, though this tree is now dead from hemlock woolly adelgids; the tallest now surviving, the "Noland Mountain tree", is tall. Altogether, ENTS has confirmed four trees to heights of or more by climb and tape drop. In the Northeast, the tallest accurately measured tree is . This tree, named the Seneca hemlock, grows in Cook Forest State Park, PA. Above 43°N latitude, the maximum height of the species is less, under . In New England, ENTS has measured hemlocks to , although trees above are extremely rare in New England. By 44°N, the maximum height is probably not more than . Diameters of mature hemlocks range from , with trees over in diameter being very rare. In New England, the maximum diameter is . Trunk volume is the third dimension to receive attention by ENTS. Many eastern hemlocks have been modeled to over trunk volume, and the largest has been calculated to be , making it the largest natural evergreen conifer in the eastern United States. The center of maximum size development for the species is the southern Appalachians, especially the Great Smoky Mountains.


Cultivation

''Tsuga canadensis'' has long been a popular tree in cultivation. The tree's preference for partial shade and tolerance of full shade allows it to be planted in areas where other conifers would not easily grow. In addition, its very fine-textured foliage that droops to the ground, its pyramidal growth habit, and its ability to withstand hard pruning make it a desirable
ornamental tree Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that i ...
. In cultivation, it prefers sites that are slightly acidic to neutral with nutrient-rich and moist but well-drained soil. It is most often used as a specimen, for a screen, or in small group plantings, though it can also be trained as a dense formal hedge. It should not be used on roadsides where salt is used in winter, as its foliage is sensitive to salt spray. It is also poorly adapted as a windbreak tree, as wind exposure causes dieback in winter. It has several drawbacks, such as a fairly low tolerance of urban stress, intolerance for very wet or very dry soils, and susceptibility to attack by the hemlock woolly adelgid, though this is treatable. Its tendency to shed needles rapidly after being cut down renders it unsuitable as a
Christmas tree A Christmas tree is a decorated tree, usually an evergreen conifer, such as a spruce, pine or fir, or an artificial tree of similar appearance, associated with the celebration of Christmas. The custom was further developed in early modern ...
. It was introduced to British gardens in 1736.Mitchell, A. F. (1974). ''A Field Guide to the Trees of Britain and Northern Europe''. Collins In the UK, it is encountered frequently in gardens both large and small, as well as some parks, and is most common in the eastern areas of the country. It is sometimes employed as a
hedge A hedge or hedgerow is a line of closely spaced shrubs and sometimes trees, planted and trained to form a barrier or to mark the boundary of an area, such as between neighbouring properties. Hedges that are used to separate a road from adjoin ...
, but is considered inferior for this usage compared to ''
Tsuga heterophylla ''Tsuga heterophylla'', the western hemlock or western hemlock-spruce, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonom ...
'' (western hemlock); it is not well adapted to the UK climate and as a consequence often has a poorly developed, forked and sinuous trunk there.Mitchell, A. F. (1972). ''Conifers in the British Isles''. Forestry Commission Booklet 33. In
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, it is the most frequently seen hemlock in cultivation, and is also used in
forestry Forestry is the science and craft of creating, managing, planting, using, conserving and repairing forests, woodlands, and associated resources for human and environmental benefits. Forestry is practiced in plantations and natural stands. Th ...
. Schmeil, O., Fitschen, J., & Seybold, S. (2006). ''Flora von Deutschland'' 93. Auflage, p. 424. Quelle & Meyer Verlag, Wiebelsheim. .


Cultivars

Over 300
cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
s have been selected for use, many of them being dwarf forms and shrubs. A partial list of popular cultivars includes: *'Beehive' – a very small dwarf shrub typically growing to high and 1.5 m wide, resembling a spreading beehive in form *'Bennett' – a dwarf shrub reaching high and wide, with upper branchlets that first ascend and then arch upper, this selection prefers partial shade. *'Cole's Prostrate' – a groundcover form that can also be used in
bonsai Bonsai ( ja, 盆栽, , tray planting, ) is the Japanese art of growing and training miniature trees in pots, developed from the traditional Chinese art form of ''penjing''. Unlike ''penjing'', which utilizes traditional techniques to produce ...
as an alternative to the prostrate
juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' () of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere, from the Arcti ...
s, it slowly grows to only tall with a spread, with the central stems eventually becoming visible. It also prefers partial shade. *'Gentsch White' – a dwarf shrub growing to tall with an equal spread and new spring growth that turns creamy-white in autumn through winter, creating a dramatic contrast with the dark green old growth, it is easily scorched by the sun and requires partial shade. It is recommend to feather shear annually to keep it compact and create more tip growth. *'Jeddeloh' – a dwarf shrub reaching to high and wide, showing a small concavity in the centre, it is an alternative to the bird's-nest spruce (''
Picea abies ''Picea abies'', the Norway spruce or European spruce, is a species of spruce native to Northern Europe, Northern, Central Europe, Central and Eastern Europe. It has branchlets that typically hang downwards, and the largest cones of any spruce, ...
'' 'Nidiformis'). This cultivar has gained the
Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr (Nort ...
's
Award of Garden Merit The Award of Garden Merit (AGM) is a long-established annual award for plants by the British Royal Horticultural Society (RHS). It is based on assessment of the plants' performance under UK growing conditions. History The Award of Garden Merit ...
. *'Pendula' – an upright weeping form whose height is dependent on how long it is staked, but is typically seen tall with a spread. It has also won the AGM. *'Sargentii' – a popular large weeping shrub that grows to tall with a wide spread up to , it features numerous pendulous branches and is most effectively employed near water, in rock gardens, or on embankments.


Uses

American pioneers made tea from the tree's leafy twigs and used its branches as brooms. Tea can be made from the needles. The inner bark, which is best in winter and coming into spring, can be eaten raw or boiled; it can also be used to make flour.


References


External links


''Tsuga canadensis'' images at bioimages.vanderbilt.edu
{{Authority control canadensis Hardwood forest plants Trees of the Eastern United States Trees of Eastern Canada Trees of the Great Lakes region (North America) Trees of the Northeastern United States Flora of the Appalachian Mountains Trees of the Southeastern United States Symbols of Pennsylvania Trees of humid continental climate Natural history of the Great Smoky Mountains Garden plants of North America Ornamental trees Plants described in 1763