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Tsuga canadensis

tsuga canadensis, tsuga canadensis pendula
Tsuga canadensis, also known as eastern hemlock,2 eastern hemlock-spruce3 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 Pennsylvania4

Contents

  • 1 Description
  • 2 Wood
  • 3 Distribution and habitat
    • 31 Climate
  • 4 Hemlock woolly adelgid
  • 5 Paleoecology
  • 6 Exceptional trees
  • 7 Cultivation
    • 71 Cultivars
  • 8 See also
  • 9 References
  • 10 External links

Descriptionedit

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 old5 The tree generally reaches heights of about 31 meters 102 feet,4 but exceptional trees have been recorded up to 53 meters 174 feet6 The diameter of the trunk at breast height is often 15 meters 4 feet 11 inches, but again, outstanding trees have been recorded up to 175 meters 5 feet 9 inches7 The trunk is usually straight and monopodial, but very rarely is forked8 The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age4 The twigs are a yellow-brown in colour with darker red-brown pulvini, and are densely pubescent The buds are ovoid in shape and are very small, measuring only 15 to 25 mm 1⁄16 to 3⁄32 in in length These are usually not resinous, but may be slightly so48

The leaves are typically 15 to 20 mm 9⁄16 to 13⁄16 in in length, but may be as short as 5 mm 3⁄16 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 colour The leaf margins are very slightly toothed, especially near the apex The seed cones are ovoid in shape and typically measure 15 to 25 cm 5⁄8 to 1 in in length and 1 to 15 cm 3⁄8 to 5⁄8 in in width The scales are ovate to cuneate in shape and measure 8 to 12 mm 5⁄16 to 1⁄2 in in length by 7 to 10 mm 1⁄4 to 3⁄8 in in width The apex is more or less rounded and is often projected outward Twenty-four diploid chromosomes are present within the trees' DNA48

Woodedit

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 manufacturing9

Distribution and habitatedit

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,8 but is found primarily at elevations of 600–1,800 metres 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 Alabama410 Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota811 In Canada, it is present in Ontario and all provinces to the east except Newfoundland and Labrador In the USA, it is found in all states east of and including Minnesota, Wisconsin, Indiana, Kentucky, Tennessee and Alabama, but excluding Florida4 Its range completely overlaps that of the closely related Tsuga caroliniana12

It is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture4

Climateedit

Eastern hemlock is generally confined to areas with cool and humid climates 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 °F12

Hemlock boughs in the autumn, shedding older foliage

Hemlock woolly adelgidedit

Shoot infested with hemlock woolly adelgid

The species is currently threatened by the hemlock woolly adelgid Adelges tsugae, a sap-sucking bug accidentally introduced from East Asia to the United States in 1924, and first found in the native range of eastern hemlock in the late 1960s13 The adelgid has spread very rapidly in southern parts of the range once becoming established, while its expansion northward is much slowercitation 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 yearscitation 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 It is through Tsuga Search that hemlocks have been found with trunk volumes of up to 448 m³ within the Park,14 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 least concern 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 range15

A 2009 study conducted by scientists with the US 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 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"16

Closeup of bark

In a 2009 case study, entomologists from the US 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 there are enough trees 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 detected17

Paleoecologyedit

The mid-Holocene decline of hemlock populations is a much-studied phenomenon18 From its foundation in the early Holocene c 16,000 BP in what is now the southeastern US, T canadensis expanded rapidly and successfully into its potential range19 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 populations1820 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 treesedit

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 528 metres 173 ft 3 in tall, though this tree is now dead from hemlock woolly adelgid; the tallest now surviving, the "Noland Mountain tree", is 518 metres 169 ft 11 in tall14 Altogether, ENTS has confirmed four trees to heights of 51 metres 167 ft or more by climb and tape drop In the Northeast, the tallest accurately measured tree is 44 metres 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 metres 128 ft In New England, ENTS has measured hemlocks to 42 metres 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 metres 115 ft Diameters of mature hemlocks range from 075–18 metres 2 ft 6 in–5 ft 11 in, with trees over 16 metres 5 ft 3 in diameter being very rare In New England, the maximum diameter is 14 metres 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 448 m³,14 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

Cultivationedit

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 treatable21 Its tendency to shed needles rapidly after being cut down renders it unsuitable as a Christmas tree

It was introduced to British gardens in 173622 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 there2223 In Germany, it is the most frequently seen hemlock in cultivation, and is also used in forestry24

Cultivarsedit

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:2125

  • 'Beehive' – a very small dwarf shrub typically growing to 1 m high and 15 m wide, resembling a spreading beehive in form
  • 'Bennett' – a dwarf shrub reaching 1 m high and 15 m 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 as an alternative to the prostrate junipers, it slowly grows to only 30 cm tall with a 13 m spread, with the central stems eventually becoming visible It also prefers partial shade
  • 'Gentsch White' – a dwarf shrub growing to 13 m 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 1 m high and 15 m wide, showing a small concavity in the centre, it is an alternative to the bird's nest spruce Picea abies 'Nidiformis' This cultivar has gained the Royal Horticultural Society's Award of Garden Merit26
  • 'Pendula' – an upright weeping form whose height is dependent on how long it is staked, but is typically seen 06–15 m tall with a 15 m spread
  • 'Sargentii' – a popular large weeping shrub that grows to 3 m tall with a wide spread up to 6 m, it features numerous pendulous branches and is most effectively employed near water, in rock gardens or on embankments

See alsoedit

  • Tsuga caroliniana
  • Tsuga

Referencesedit

  1. ^ "Tsuga canadensis" NatureServe Explorer NatureServe Retrieved 2007-07-05 
  2. ^ "Tsuga canadensis" Natural Resources Conservation Service PLANTS Database USDA Retrieved 12 December 2015 
  3. ^ "BSBI List 2007" Botanical Society of Britain and Ireland Archived from the original xls on 2015-02-25 Retrieved 2014-10-17 
  4. ^ a b c d e f g h Taylor, Ronald J "Tsuga canadensis" Flora of North America FNA Missouri Botanical Garden – via eFlorasorg 
  5. ^ Gove, JH; Fairweather, SE 1988, "Tree-ring analysis of a 500-year old hemlock in central Pennsylvania", US Forest Service General Technical Report NC-120, 1, pp 483–489 
  6. ^ Blozan, Will February 16, 2007, The Usis Hemlock Climb, retrieved 2007-06-08 
  7. ^ Blozan, Will December 18, 2006, The Laurel Branch Leviathan Climb, retrieved 2007-06-08 
  8. ^ a b c d e Farjon, A 1990 Pinaceae Drawings and Descriptions of the Genera Koeltz Scientific Books ISBN 3-87429-298-3
  9. ^ Collingwood, CH and Warren D Brush Revised and Edited by Devereux Butcher 1974 Knowing Your Trees American Forestry Association Washington, District of Columbia 374 pp "EASTERN HEMLOCK", pp 88-89
  10. ^ South, David B 2016 "Eastern hemlock found in Macon County, Alabama" 
  11. ^ Thompson, Robert S; Anderson, Katherine H; Bartlein, Patrick J 1999, "Tsuga canadensis", Atlas of Relations Between Climatic Parameters and Distributions of Important Trees and Shrubs in North America PDF, US Geological Survey, retrieved 2007-07-05 
  12. ^ a b Godman, R M; Lancaster, Kenneth 1990 "Tsuga canadensis" In Burns, Russell M; Honkala, Barbara H Conifers Silvics of North America Washington, DC: United States Forest Service USFS, United States Department of Agriculture USDA 1 Retrieved 2007-07-05 – via Northeastern Area State and Private Forestry wwwnafsfedus 
  13. ^ McClure, M S 1987, "Biology and control of hemlock woolly adelgid" PDF, Bulletin of the Connecticut Agricultural Experiment Station, 851: 1–9, retrieved October 24, 2011 
  14. ^ a b c Gymnosperm Database: Tsuga canadensis
  15. ^ Conifer Specialist Group 1998 "Tsuga canadensis" IUCN Red List of Threatened Species Version 2006 International Union for Conservation of Nature Retrieved 12 May 2006 
  16. ^ Hemlock Trees Dying Rapidly, Affecting Forest Carbon Cycle
  17. ^ Predator Beetle to Battle Hemlock Pest
  18. ^ a b Oswald, W W; Foster, D R 8 August 2011 "Middle-Holocene dynamics of Tsuga canadensis eastern hemlock in northern New England, USA" PDF The Holocene 22 1: 71–78 doi:101177/0959683611409774 Retrieved 6 March 2013 
  19. ^ Delcourt, Hazel R; Delcourt, Paul A 1991 Quaternary Ecology: a Paleoecological Perspective 1st ed London: Chapman and Hall pp 43–44 ISBN 0-412-29790-6 
  20. ^ Zhao, Yan; Yu, Zicheng; Zhao, Cheng 23 April 2010 "Hemlock Tsuga canadensis declines at 9800 and 5300 cal yr BP caused by Holocene climatic shifts in northeastern North America" The Holocene 20 6: 877–886 doi:101177/0959683610365932 Retrieved 6 March 2013 
  21. ^ a b "Tsuga canadensis" UConn Plant Database University of Connecticut Retrieved 19 August 2013 
  22. ^ a b Mitchell, A F 1974 A Field Guide to the Trees of Britain and Northern Europe Collins ISBN 0-00-212035-6
  23. ^ Mitchell, A F 1972 Conifers in the British Isles Forestry Commission Booklet 33
  24. ^ in German Schmeil, O, Fitschen, J, & Seybold, S 2006 Flora von Deutschland 93 Auflage, p 424 Quelle & Meyer Verlag, Wiebelsheim ISBN 3-494-01413-2
  25. ^ Welch, H, & Haddow, G 1993 The World Checklist of Conifers Landsman's ISBN 0-900513-09-8
  26. ^ "Tsuga canadensis 'Jeddeloh' AGM" Royal Horticultural Society Retrieved 14 February 2013 

External linksedit

  • Trees portal
  • Pennsylvania portal
  • Media related to Tsuga canadensis at Wikimedia Commons
  • Data related to Tsuga canadensis at Wikispecies
  • Tsuga canadensis images at bioimagesvanderbiltedu
  • Eastern Native Tree Society's Tsuga Search Project

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