Tsuga canadensis

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Tsuga canadensis
Tsuga canadensis morton.jpg
Large specimens at Morton Arboretum
Status TNC G4.svg
Apparently Secure  (NatureServe) [2]
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
(unranked): Gymnosperms
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Pinaceae
Genus: Tsuga
T. canadensis
Binomial name
Tsuga canadensis
Tsuga canadensis range map 1.png
Natural range
Tsuga canadensis range map 4.png
Closeup view of range

Tsuga canadensis, also known as eastern hemlock, [3] eastern hemlock-spruce, [4] or Canadian hemlock, and in the French-speaking regions of Canada as pruche du Canada, is a coniferous tree native to eastern North America. It is the state tree of Pennsylvania. [5] Eastern hemlocks are widespread throughout much of the Great Lakes region, the Appalachian Mountains, the Northeastern United States, and Maritime Canada. They have been introduced in the United Kingdom 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, 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.

Eastern hemlocks are long lived trees, with many examples living for more than 500 years. They can grow to heights of more than 100 feet (30 m), and are tolerant of shade, moist soil, and slopes. Hemlock wood is used in construction, and for railroad ties. Historically its bark was an important source of tannin for the leather tanning industry. [6] 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.


A line drawing of the leaves and cones from Britton and Brown's 1913 Illustrated flora of the northern states and Canada Tsuga canadensis drawing.png
A line drawing of the leaves and cones from Britton and Brown's 1913 Illustrated flora of the northern states and Canada

The eastern hemlock grows well in shade and is very long lived, with the oldest recorded specimen, found in Tionesta, Pennsylvania, being at least 554 years old. [7] The tree generally reaches heights of about 31 m (102 ft), [5] but exceptional trees have been recorded up to 53 m (174 ft). [8] The diameter of the trunk at breast height is often 1.5 m (4 ft 11 in), but again, outstanding trees have been recorded up to 1.75 m (5 ft 9 in). [9] The trunk is usually straight and monopodial, but very rarely is forked. [10] The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age. [5] The twigs are a yellow-brown in color with darker red-brown pulvini, and are densely pubescent. The buds are ovoid in shape and are very small, measuring only 1.5 to 2.5 mm (0 to 18 in) in length. These are usually not resinous, but may be slightly so. [5] [10]

The leaves are typically 15 to 20 mm (0.59 to 0.79 in) in length, but may be as short as 5 mm (0.20 in) or as long as 25 mm (1 in). They are flattened and are typically distichous, or two-ranked. The bottom of the leaf is glaucous with two broad and clearly visible stomatal 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 are ovoid in shape and typically measure 1.5 to 2.5 cm (58 to 1 in) in length and 1.0 to 1.5 cm (38 to 58 in) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (38 to 12 in) in length by 7.0 to 10 mm (14 to 38 in) in width. The apex is more or less rounded and is often projected outward. Twenty-four diploid chromosomes are present within the trees' DNA. [5] [10]


The wood is soft, coarse-grained, and light buff in color. Air-dried, a cubic foot weighs 28 lbs. 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. [11]

Distribution and habitat

Stand of eastern hemlock and eastern white pine in Tiadaghton State Forest, Pennsylvania, note the hemlocks' deeply fissured bark Stand of Eastern Hemlock and White Pine in Tiadaghton State Forest, Pennsylvania.jpg
Stand of eastern hemlock and eastern white pine in Tiadaghton State Forest, Pennsylvania, note the hemlocks' deeply fissured bark

T. canadensis occurs at sea level in the north of its distribution, [10] but is found primarily at elevations of 600–1,800 m (2,000–5,900 ft). It ranges from northeastern Minnesota eastward through southern Quebec and into Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. [5] [12] Disjunct populations occur in the Piedmont region, northern Alabama, western Ohio and into Indiana, as well as western Wisconsin and eastern Minnesota. [10] [13] In Canada, it is present in Ontario and all provinces to the east except Newfoundland and Labrador. [5] Its range completely overlaps that of the closely related Tsuga caroliniana . [14]

It is found primarily on rocky ridges, ravines, and hillsides with relatively high levels of moisture. [5]


Eastern hemlock is generally confined to areas with highland climates, with cool and humid conditions. Precipitation in the areas where it grows is typically 740 mm (29 in) to more than 1,270 mm (50 in) 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 1,520 mm (60 in). In the north of its range, the temperatures in January average −12 °C (10 °F), while in July they average only 16 °C (61 °F). 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 6 °C (43 °F). [14]

Hemlock boughs in the autumn, shedding older foliage Hemlock's deciduous nature.jpg
Hemlock boughs in the autumn, shedding older foliage

Hemlock woolly adelgid

Shoot infested with hemlock woolly adelgid Tsuga canadensis adelges.jpg
Shoot infested with hemlock woolly adelgid

The species is currently threatened by the hemlock woolly adelgid (Adelges tsugae), a sap-sucking bug introduced from East Asia to the United States in 1924, and first found in the native range of eastern hemlock in the late 1960s. [15] The adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slower.[ citation needed ] 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.[ citation needed ] 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, 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, [16] making it the largest eastern evergreen conifer, eclipsing in volume both eastern white pine (Pinus strobus) and loblolly pine (Pinus taeda). The tree is currently listed as a near threatened species in the IUCN Red List, but this is based largely on its wide distribution and because the adelgid populations have not reached the northern areas of its range. [1]

A 2009 study conducted by scientists with the U.S. Forest Service 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 of these forests. According to Science Daily , the pest could kill most of the region's hemlock trees within the next decade.[ needs update ] According to the study, researchers found "hemlock woolly adelgid infestation is rapidly impacting the carbon cycle in [hemlock] tree 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." [17]

Closeup of bark TsugaCanadensisBark.jpg
Closeup of bark

In a 2009 case study, entomologists from the U.S. Forest Service, Cornell University, and the University of Massachusetts-Amherst released 900 Laricobius nigrinus beetles into a stand of adelgid-infested hemlocks near Lansing, New York. 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. [18]


The tree can be found living in association with many forest mushrooms, such as Ramaria flavosaponaria . [19]


The mid-Holocene decline of hemlock populations is a much-studied phenomenon. [20] 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. [21] However, palynological 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. [20] [22] 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 45 metres (148 ft) tall, and one tree has been measured in the Great Smoky Mountains National Park to 52.8 m (173 ft 3 in) tall, though this tree is now dead from hemlock woolly adelgids; the tallest now surviving, the "Noland Mountain tree", is 51.8 m (169 ft 11 in) tall. [16] Altogether, ENTS has confirmed four trees to heights of 51 m (167 ft) or more by climb and tape drop. In the Northeast, the tallest accurately measured tree is 44 m (144 ft). 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 39 m (128 ft). In New England, ENTS has measured hemlocks to 42 m (138 ft), although trees above 39 m are extremely rare in New England. By 44°N, the maximum height is probably not more than 35 m (115 ft). Diameters of mature hemlocks range from 0.75–1.8 m (2 ft 6 in – 5 ft 11 in), with trees over 1.6 m (5 ft 3 in) in diameter being very rare. In New England, the maximum diameter is 1.4 m (4 ft 7 in).

Trunk volume is the third dimension to receive attention by ENTS. Many eastern hemlocks have been modeled to over 30 m³ trunk volume, and the largest has been calculated to be 44.8 m³, [16] 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.


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. 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. [23] Its tendency to shed needles rapidly after being cut down renders it unsuitable as a Christmas tree.

It was introduced to British gardens in 1736. [24] 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, but is considered inferior for this usage compared to Tsuga heterophylla (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. [24] [25] In Germany, it is the most frequently seen hemlock in cultivation, and is also used in forestry. [26]


The weeping shrub form T. canadensis 'Sargentii' Img tsuga canadensis sargentii 1891.jpg
The weeping shrub form T. canadensis 'Sargentii'

Over 300 cultivars have been selected for use, many of them being dwarf forms and shrubs. A partial list of popular cultivars includes: [23] [27]


American pioneers made tea from the tree's leafy twigs and used its branches as brooms. [30] 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. [31]

Related Research Articles

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The Appalachian Mountains, often called the Appalachians, 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 once reached elevations similar to those of the Alps and the Rocky Mountains before experiencing natural erosion. The Appalachian chain is a barrier to east–west travel, as it forms a series of alternating ridgelines and valleys oriented in opposition to most highways and railroads running east–west.

<i>Tsuga</i> Genus of conifers

Tsuga is a genus of conifers in the subfamily Abietoideae of Pinaceae, the pine family. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock. Unlike the latter, Tsuga species are not poisonous.

Great Smoky Mountains American mountain range along North Carolina/Tennessee border

The Great Smoky Mountains are a mountain range rising along the Tennessee–North Carolina border in the southeastern United States. They are a subrange of the Appalachian Mountains, and form part of the Blue Ridge Physiographic Province. The range is sometimes called the Smoky Mountains and the name is commonly shortened to the Smokies. The Great Smokies are best known as the home of the Great Smoky Mountains National Park, which protects most of the range. The park was established in 1934, and, with over 11 million visits per year, it is the most visited national park in the United States.

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<i>Tsuga heterophylla</i> Species of conifer

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 Sonoma County, California. The Latin species name means 'variable leaves'.

<i>Tsuga mertensiana</i> Species of tree found in western North America

Tsuga mertensiana, known as mountain hemlock, 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 Tulare County, California. Mertensiana refers to Karl Heinrich Mertens (1796–1830), a German botanist who collected the first specimens as a member of a Russian expedition in 1826–1829.

Foundation species

In ecology, the foundation species are species that have a strong role in structuring a community. A foundation species can occupy any trophic level in a food web. The term was coined by Paul K. Dayton in 1972, who applied it to certain members of marine invertebrate and algae communities. It was clear from studies in several locations that there were a small handful of species whose activities had a disproportionate effect on the rest of the marine community and they were therefore key to the resilience of the community. Dayton’s view was that focusing on foundation species would allow for a simplified approach to more rapidly understand how a community as a whole would react to disturbances, such as pollution, instead of attempting the extremely difficult task of tracking the responses of all community members simultaneously. The term has since been applied to range of organisms in ecosystems around the world, in both aquatic and terrestrial environments. Aaron Ellison et al. introduced the term to terrestrial ecology by applying the term foundation species to tree species that define and structure certain forest ecosystems through their influences on associated organisms and modulation of ecosystem processes.

Fraser fir Species of conifer

The Fraser fir is a species of fir native to the Appalachian Mountains of the Southeastern United States.

<i>Tsuga caroliniana</i> Species of conifer

Tsuga caroliniana, the Carolina hemlock, is a species of hemlock endemic to the United States.

Hemlock woolly adelgid Species of true bug

The hemlock woolly adelgid, or HWA, is an insect of the order Hemiptera native to East Asia. It feeds by sucking sap from hemlock and spruce trees. In its native range, HWA is not a serious pest because populations are managed by natural predators and parasitoids and by host resistance. In eastern North America it is a destructive pest that threatens the eastern hemlock and the Carolina hemlock. HWA is also found in western North America, where it has likely been present for thousands of years. In western North America, it primarily attacks western hemlock Tsuga heterophylla and has only caused minor damage due to natural predators and host resistance. Accidentally introduced to North America from Japan, HWA was first found in the eastern United States near Richmond, Virginia, in 1951. The pest is now found from northern Georgia to coastal Maine and southwestern Nova Scotia. As of 2015, 90% of the geographic range of eastern hemlock in North America has been affected by HWA.

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Appalachian–Blue Ridge forests Temperate broadleaf and mixed forests ecoregion of the United States

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<i>Coleotechnites apicitripunctella</i> Species of moth

The green hemlock needleminer, hemlock leaf miner or baldcypress webworm is a moth of the family Gelechiidae. It is found in the eastern parts of the United States, as well as eastern Canada.

Eastern forest–boreal transition Temperate broadleaf and mixed forest ecoregion in Canada and the United States

The eastern forest–boreal transition is a temperate broadleaf and mixed forests ecoregion of North America, mostly in eastern Canada. It is a transitional zone or region between the predominantly coniferous Boreal Forest and the mostly deciduous broadleaf forest region further south.

The olive darter is a species of freshwater ray-finned fish, a darter from the subfamily Etheostomatinae, part of the family Percidae, which also contains the perches, ruffes and pikeperches. It is native to Tennessee, Kentucky, North Carolina, and Georgia, in the United States. It is found in the headwaters of Tennessee River system and the middle reaches of the Cumberland River system, its ideal habitat being clear, cold water over rocky substrates. It grows to a length of about 5 in (13 cm) and is an insectivore, feeding mainly on insect larvae on the riverbed. The fish matures at age two and lives till about age four. Up to 1500 eggs are spawned which fall to the riverbed and get lodged among gravel. The olive darter is classified as a "vulnerable species", being affected by habitat destruction and siltation, often resulting from damming and impoundment of the rivers or the creation of weirs. It is also affected by the change in the forest riparian habitat resulting from the killing of trees by the hemlock woolly adelgid.

<i>Pseudotsuga menziesii <span style="font-style:normal;">var.</span> menziesii</i> Variety of conifer

Pseudotsuga menziesii var. menziesii, commonly known as Coast Douglas-fir, Pacific Douglas-fir, Oregon pine, or Douglas spruce, is an evergreen conifer native to western North America from west-central British Columbia, Canada southward to central California, United States. In Oregon and Washington its range is continuous from the Cascades crest west to the Pacific Coast Ranges and Pacific Ocean. In California, it is found in the Klamath and California Coast Ranges as far south as the Santa Lucia Mountains with a small stand as far south as the Purisima Hills, Santa Barbara County. In the Sierra Nevada it ranges as far south as the Yosemite region. It occurs from near sea level along the coast to 1,800 metres (5,900 ft) in the California Mountains. Further inland, coast Douglas-fir is replaced by Rocky Mountain or interior Douglas-fir. Interior Douglas-fir intergrades with coast Douglas-fir in the Cascades of northern Washington and southern British Columbia.

Forest disturbance by invasive insects and diseases in the United States

Species which are not native to a forest ecosystem can act as an agent of disturbance, changing forest dynamics as they invade and spread. Invasive insects and pathogens (diseases) are introduced to the United States through international trade, and spread through means of natural and human-dispersal. Invasive insects and pathogens are a serious threat to many forests in the United States and have decimated populations of several tree species, including American chestnut, American elm, eastern hemlock, whitebark pine, and the native ash species. The loss of these tree species is typically rapid with both short and long-term impacts to the forest ecosystem.

<i>Laricobius nigrinus</i> Species of beetle

Laricobius nigrinus is a species of tooth-necked fungus beetle in the family Derodontidae. It is native to western North America, and it is being studied as a biological control agent for the hemlock woolly adelgid. It was first released in 2003 and continues to be reared and released across the Northeast to control infestations.

Ecological regions of Quebec

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Rivière-du-Moulin Ecological Reserve

Rivière-du-Moulin Ecological Reserve is a strictly protected ecological reserve in the province of Quebec, Canada. It contains a stand of mature eastern hemlock trees, with some white pines, a combination that was once common in Quebec but has almost disappeared due to forestry and farming.


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