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(Redirected from Canadian Hemlock)
'''Tsuga canadensis''', also known as 'Eastern' 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 ranges from northeastern Minnesota eastward through southern Quebec to Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Scattered outlier populations occur in several areas east and west of the Appalachians. It grows well in shade and is very long lived with the oldest recorded specimen being at least 554 years old. The species is currently under serious threat of extinction across much of its range due to a sap-sucking insect, the hemlock woolly adelgid, which was introduced from Asia and is capable of killing large trees within one to two years. Before its introduction, the eastern hemlock was a dominant component of Appalachian forests. It is the state tree of Pennsylvania.
The eastern hemlock generally reaches heights of about 30 metres (100 feet), but exceptional trees have been recorded up to 53 metres (173 feet). The diameter of the trunk at breast height is often 1.5 metres (5 feet), but again, outstanding trees have been recorded up to 1.75 meters (6 feet). The crown is broadly conic, while the browinsh bark is scaly and deeply fissured, especially with age. The twigs are a yellow-brown in colour and are densely pubescent. The buds are ovoid in shape and are very small, measuring only 1.5 to 2.5 mm (0.05 to 0.1 inches) in length.
The leaves are typically 15 to 20 mm (0.6 to 0.9 inches) in length, but may be a short as 5 mm (0.2 inches) or as long as 25 mm (1 inch). They are flattened and are typically distichous, or two-ranked. The abaxial surface of the leaf, or underside, is glaucous with 2 broad and clearly visible stomatal bands, while the adaxial surface, i.e. the upper-side, is a shiny green to yellow-green in colour. The leaf margins are very slightly dentate, or toothed, especially near the apex. The seed cones are ovoid in shape and typically measure 1.5 to 2.5 cm (0.6 to 1 inch) in length and 1 to 1.5 cm (0.4 to 0.6 inches) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (0.3 to 0.5 inches) in length by 7 to 10 mm (0.3 to 0.4 inches) in width. The apex is more or less rounded and is often projected outward. 24 diploid chromosomes are present within the tree's DNA.
''T. canadensis'' is found primarily at elevations of 600 to 1800 metres from northeastern Minnesota eastward through southern Quebec and into Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota. In Canada it is present in all provinces east from and including Ontario, but discludng Newfoundland. In the USA it is found in all states east of and including Minnesota, Wisconsin, Indiana, Kentucky, Tennessee and Alabama, but discluding Florida. Its range completely overlaps that of the closely related ''Tsuga caroliniana''.
''T. canadensis'' is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.
The tree is generally confined to areas with cool and humid climates. Precipitation in the areas where it grows is typically between 740 mm (29 inches) to more than 1270 mm (50 inches) per year. The lower number is more typical of northern forests that receive heavy snowfall, and 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 there greatest heights, annual rainfall often exceeds 1520 mm (60 inches). In the north of its range the temperatures in January average -12° C (10° Fahrenheit), while in July they average only 16° C (60° F). In these areas less than 80 are without frost. In contrast to this, the southern end of the range experiences up to 200 days without frost and January temperatures as high as 6° C (42° F). Tsuga canadensis, Eastern Hemlock
The future of the eastern hemlocks is currently under threat due to the hemlock woolly adelgid (''Adelges tsugae''), a sap-sucking bug accidentally introduced from East Asia to the United States in 1924. The Adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slower. Virtually all of the hemlocks in the southern Appalachian mountains have seen infestations of the insect within the last 5 to 7 years, with thousands of acres of stands dying within the last 2 to 3 years. Attempts to save representative examples on both public and private lands are on-going. At exceptionally important 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. It is through Tsuga Search that Hemlocks have been modeled to nearly 1,700 cubic feet of trunk volume within the Park, making the Eastern Hemlock the largest eastern evergreen conifer, eclipsing in volume the White Pine and Loblolly Pine. The tree is currently listed as a least concern species in the IUCN Red List, but this is based largely on its wide distribution and the fact that the adelgid populations have not reached the northern areas of its range.[1]
Due to ''Tsuga canadensis'' being a particularly long lived tree, several very large or otherwise impressive trees exist up and down the east coast of North America. One organisation, the Eastern Native Tree Society, has been particularly active in discovering and measuring these trees. In the southern Appalachians many individuals reach to 150 feet in height and one tree has been measured in the Great Smoky Mountains National Park to 173.1 feet by an actual climb and tape drop, performed by the Eastern Native Tree Society (ENTS). Altogether, ENTS has confirmed 4 Hemlocks to heights of 170 feet or more by climb and tape drop. In the Northeast, the tallest accurately measured tree is 145.4 feet. This tree, named the Seneca Hemlock, grows in Cook Forest State Park, PA. Above 43 degrees north latitude, the maximum height of the species trails off to under 130 feet. In New England, ENTS has measured Hemlocks to 138 feet, although trees above 130 feet are extremely rare in New England. By 44 degrees, maximum heights of the Eastern Hemlock is probably not more than 115 feet.
Girths of mature Hemlocks range from 8 to 19 feet, with trees over 16 feet being very rare. In New England, 15 feet represents the maximum girth. The term girth is used as opposed to circumference, since trees are not truly circular in cross sectional area. Girth is also preferred to diameter (thickness), because girth is directly measured and does not assume circularity.
Trunk volume is the 3rd dimension to receive attention by ENTS. The Eastern Hemlock has been modeled to nearly 1,700 cubic feet by ENTS. This makes the hemlock the largest natural evergreen conifer in the eastern United States. This distinction previously was shared by the eastern white pine and the loblolly pine. But recent research by ENTS places the hemlock in the first position. Many eastern hemlocks have been modeled to over 1,000 cubic feet of trunk volume. The center of maximum size development for the species is the southern Appalachians and within that region, the Great Smoky Mountains.
''Tsuga canadensis'' has been a popular tree in cultivation for some time, shown by the fact that it has been used in British gardens since 1736. Trees of Britain & Northern Europe, , Alan, Mitchell, Harper Collins Publishers, , ISBN 0-00-219213-6 The tree is equally tolerant of full shade and full sun, making it a versatile tree. In addition, its very fine textured foliage that droops to the ground, its pyrimidal growth habit and its ability to withstand hard pruning make it a desirable ornamental. In cultivation it prefers sites that are slightly acidic to neutral with nutrient-rich soil that is moist but well-drained. 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. Other improper uses include employing it as windbreak tree, which causes dieback in winter winds, and use as a foundation shrub, as it will eventually become much too large unless it is pruned annually. It has several drawbacks, such as a fairly low tolerance for urban stress, intolerance for very wet or very dry soils, and it is susceptible to attack by the hemlock woolly adelgid discussed above, though this is treatable.
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 the western hemlock (''Tsuga heterophylla''). In Germany it is the most frequently seen hemlock in cultivation and is also used in forestry. Flora von Deutschland, 93. Auflage, , Otto, Schmeil, Quelle & Meyer Verlag, ,
Over 300 cultivars 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 3 feet in height and 5 feet in width and resembling a spreading beehive in form
★ ''Bennett'' - a dwarf shrub reaching 3 feet in height with a 5 foot spread 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 as an alternative to the prostrate junipers. It slowly grows to only one foot tall with a 4 foot spread with the central stems eventually becoming visible. It also prefers partial shade.
★ ''Gentsch White'' - a dwarf shrub growing to 4 feet 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 in order to keep it compact and create more tip growth.
★ ''Jeddeloh'' - a dwarf shrub reaching to 3 feet in height by 5 feet in width and showing a small concavity in the centre. It is an alternative to the bird's nest spruce (''Picea abies'' 'Nidiformis')
★ ''Pendula'' - an upright weeping form whose height is dependent on how long it is staked, but is typically seen at 2 to 5 feet with a 5 foot spread.
★ ''Sargentii'' - a popular large weeping shrub that grows to 10 feet in height with a wide spread up to 20 feet. It features numerous pendulous branches and is most effectively employed near water, in rock gardens or on embankments.
1.
★
★ Gymnosperm Database: ''Tsuga canadensis''
★ Flora of North America: ''Tsuga canadnsis'' RangeMap:
★ US Forest Service - Hemlock Woolly Adelgid website
★ ''Tsuga canadensis'' images at bioimages.vanderbilt.edu
★ Photo of cones
★ Eastern Native Tree Society's Tsuga Search Project
'''Tsuga canadensis''', also known as 'Eastern' 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 ranges from northeastern Minnesota eastward through southern Quebec to Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Scattered outlier populations occur in several areas east and west of the Appalachians. It grows well in shade and is very long lived with the oldest recorded specimen being at least 554 years old. The species is currently under serious threat of extinction across much of its range due to a sap-sucking insect, the hemlock woolly adelgid, which was introduced from Asia and is capable of killing large trees within one to two years. Before its introduction, the eastern hemlock was a dominant component of Appalachian forests. It is the state tree of Pennsylvania.
| Contents |
| Description |
| Distribution and habitat |
| Climate |
| Ecology |
| Exceptional trees |
| Cultivation |
| Cultivars |
| References |
| External links |
Description
The eastern hemlock generally reaches heights of about 30 metres (100 feet), but exceptional trees have been recorded up to 53 metres (173 feet). The diameter of the trunk at breast height is often 1.5 metres (5 feet), but again, outstanding trees have been recorded up to 1.75 meters (6 feet). The crown is broadly conic, while the browinsh bark is scaly and deeply fissured, especially with age. The twigs are a yellow-brown in colour and are densely pubescent. The buds are ovoid in shape and are very small, measuring only 1.5 to 2.5 mm (0.05 to 0.1 inches) in length.
A line drawing of the leaves and cones from Britton & Brown's 1913 ''Illustrated flora of the northern states and Canada''
The leaves are typically 15 to 20 mm (0.6 to 0.9 inches) in length, but may be a short as 5 mm (0.2 inches) or as long as 25 mm (1 inch). They are flattened and are typically distichous, or two-ranked. The abaxial surface of the leaf, or underside, is glaucous with 2 broad and clearly visible stomatal bands, while the adaxial surface, i.e. the upper-side, is a shiny green to yellow-green in colour. The leaf margins are very slightly dentate, or toothed, especially near the apex. The seed cones are ovoid in shape and typically measure 1.5 to 2.5 cm (0.6 to 1 inch) in length and 1 to 1.5 cm (0.4 to 0.6 inches) in width. The scales are ovate to cuneate in shape and measure 8 to 12 mm (0.3 to 0.5 inches) in length by 7 to 10 mm (0.3 to 0.4 inches) in width. The apex is more or less rounded and is often projected outward. 24 diploid chromosomes are present within the tree's DNA.
Distribution and habitat
''T. canadensis'' is found primarily at elevations of 600 to 1800 metres from northeastern Minnesota eastward through southern Quebec and into Nova Scotia, and south in the Appalachian Mountains to northern Georgia and Alabama. Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota. In Canada it is present in all provinces east from and including Ontario, but discludng Newfoundland. In the USA it is found in all states east of and including Minnesota, Wisconsin, Indiana, Kentucky, Tennessee and Alabama, but discluding Florida. Its range completely overlaps that of the closely related ''Tsuga caroliniana''.
''T. canadensis'' is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.
Climate
The tree is generally confined to areas with cool and humid climates. Precipitation in the areas where it grows is typically between 740 mm (29 inches) to more than 1270 mm (50 inches) per year. The lower number is more typical of northern forests that receive heavy snowfall, and 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 there greatest heights, annual rainfall often exceeds 1520 mm (60 inches). In the north of its range the temperatures in January average -12° C (10° Fahrenheit), while in July they average only 16° C (60° F). In these areas less than 80 are without frost. In contrast to this, the southern end of the range experiences up to 200 days without frost and January temperatures as high as 6° C (42° F). Tsuga canadensis, Eastern Hemlock
Ecology
The future of the eastern hemlocks is currently under threat due to the hemlock woolly adelgid (''Adelges tsugae''), a sap-sucking bug accidentally introduced from East Asia to the United States in 1924. The Adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slower. Virtually all of the hemlocks in the southern Appalachian mountains have seen infestations of the insect within the last 5 to 7 years, with thousands of acres of stands dying within the last 2 to 3 years. Attempts to save representative examples on both public and private lands are on-going. At exceptionally important 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. It is through Tsuga Search that Hemlocks have been modeled to nearly 1,700 cubic feet of trunk volume within the Park, making the Eastern Hemlock the largest eastern evergreen conifer, eclipsing in volume the White Pine and Loblolly Pine. The tree is currently listed as a least concern species in the IUCN Red List, but this is based largely on its wide distribution and the fact that the adelgid populations have not reached the northern areas of its range.[1]
Exceptional trees
Due to ''Tsuga canadensis'' being a particularly long lived tree, several very large or otherwise impressive trees exist up and down the east coast of North America. One organisation, the Eastern Native Tree Society, has been particularly active in discovering and measuring these trees. In the southern Appalachians many individuals reach to 150 feet in height and one tree has been measured in the Great Smoky Mountains National Park to 173.1 feet by an actual climb and tape drop, performed by the Eastern Native Tree Society (ENTS). Altogether, ENTS has confirmed 4 Hemlocks to heights of 170 feet or more by climb and tape drop. In the Northeast, the tallest accurately measured tree is 145.4 feet. This tree, named the Seneca Hemlock, grows in Cook Forest State Park, PA. Above 43 degrees north latitude, the maximum height of the species trails off to under 130 feet. In New England, ENTS has measured Hemlocks to 138 feet, although trees above 130 feet are extremely rare in New England. By 44 degrees, maximum heights of the Eastern Hemlock is probably not more than 115 feet.
A close-up photo of the eastern hemlock's bark
Girths of mature Hemlocks range from 8 to 19 feet, with trees over 16 feet being very rare. In New England, 15 feet represents the maximum girth. The term girth is used as opposed to circumference, since trees are not truly circular in cross sectional area. Girth is also preferred to diameter (thickness), because girth is directly measured and does not assume circularity.
Trunk volume is the 3rd dimension to receive attention by ENTS. The Eastern Hemlock has been modeled to nearly 1,700 cubic feet by ENTS. This makes the hemlock the largest natural evergreen conifer in the eastern United States. This distinction previously was shared by the eastern white pine and the loblolly pine. But recent research by ENTS places the hemlock in the first position. Many eastern hemlocks have been modeled to over 1,000 cubic feet of trunk volume. The center of maximum size development for the species is the southern Appalachians and within that region, the Great Smoky Mountains.
Cultivation
''Tsuga canadensis'' has been a popular tree in cultivation for some time, shown by the fact that it has been used in British gardens since 1736. Trees of Britain & Northern Europe, , Alan, Mitchell, Harper Collins Publishers, , ISBN 0-00-219213-6 The tree is equally tolerant of full shade and full sun, making it a versatile tree. In addition, its very fine textured foliage that droops to the ground, its pyrimidal growth habit and its ability to withstand hard pruning make it a desirable ornamental. In cultivation it prefers sites that are slightly acidic to neutral with nutrient-rich soil that is moist but well-drained. 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. Other improper uses include employing it as windbreak tree, which causes dieback in winter winds, and use as a foundation shrub, as it will eventually become much too large unless it is pruned annually. It has several drawbacks, such as a fairly low tolerance for urban stress, intolerance for very wet or very dry soils, and it is susceptible to attack by the hemlock woolly adelgid discussed above, though this is treatable.
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 the western hemlock (''Tsuga heterophylla''). In Germany it is the most frequently seen hemlock in cultivation and is also used in forestry. Flora von Deutschland, 93. Auflage, , Otto, Schmeil, Quelle & Meyer Verlag, ,
Cultivars
Over 300 cultivars 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 3 feet in height and 5 feet in width and resembling a spreading beehive in form
★ ''Bennett'' - a dwarf shrub reaching 3 feet in height with a 5 foot spread 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 as an alternative to the prostrate junipers. It slowly grows to only one foot tall with a 4 foot spread with the central stems eventually becoming visible. It also prefers partial shade.
The weeping shrub form ''T. canadensis'' 'Sargentii'
★ ''Gentsch White'' - a dwarf shrub growing to 4 feet 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 in order to keep it compact and create more tip growth.
★ ''Jeddeloh'' - a dwarf shrub reaching to 3 feet in height by 5 feet in width and showing a small concavity in the centre. It is an alternative to the bird's nest spruce (''Picea abies'' 'Nidiformis')
★ ''Pendula'' - an upright weeping form whose height is dependent on how long it is staked, but is typically seen at 2 to 5 feet with a 5 foot spread.
★ ''Sargentii'' - a popular large weeping shrub that grows to 10 feet in height with a wide spread up to 20 feet. It features numerous pendulous branches and is most effectively employed near water, in rock gardens or on embankments.
References
1.
External links
★
★ Gymnosperm Database: ''Tsuga canadensis''
★ Flora of North America: ''Tsuga canadnsis'' RangeMap:
★ US Forest Service - Hemlock Woolly Adelgid website
★ ''Tsuga canadensis'' images at bioimages.vanderbilt.edu
★ Photo of cones
★ Eastern Native Tree Society's Tsuga Search Project
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