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Overview

Brief Summary

Pinaceae -- Pine family

    R. M. Godman and Kenneth Lancaster

    Eastern hemlock (Tsuga canadensis), also called Canada hemlock  or hemlock spruce, is a slow-growing long-lived tree which unlike many  trees grows well in shade. It may take 250 to 300 years to reach maturity  and may live for 800 years or more. A tree measuring 193 cm (76 in) in  d.b.h. and 53.3 m (175 ft) tall is among the largest recorded. Hemlock  bark was once the source of tannin for the leather industry; now the wood  is important to the pulp and paper industry. Many species of wildlife  benefit from the excellent habitat that a dense stand of hemlock provides.  This tree also ranks high for ornamental planting.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Comprehensive Description

Description

General: Pine family (Pinaceae). Native trees to 30 meters tall, with a broadly conic crown, the branches often drooping at the ends and “feathery;” twigs yellow-brown, densely pubescent. Bark brownish, scaly and fissured. Needles evergreen, flat, mostly appearing 2-ranked, (5-)15-20(-25) mm long, narrowed to a petiole-like base and set on peg-like projections, the lower surface waxy, with 2 broad, conspicuous stomatal bands (like pale lines), the upper surface shiny-green to yellow-green, the margins minutely toothed, especially toward apex. Seed cones ovoid, 1.5-2.5 cm long, borne near the branch tips, hanging. The common name pertains to its distribution in eastern North America.

Variation within the species: various studies have recorded physiological and morphological variation within the species, but no major discontinuities have been found to suggest that named entities should be recognized.

The geographic distribution of eastern hemlock completely overlaps that of Carolina hemlock (Tsuga caroliniana), which differs in its high elevation habitats, leaves mostly spreading all directions from the twigs, and more elongate seed cones.

Distribution: Eastern hemlock is a species of the northeastern and Appalachian regions of North America: from New Brunswick and Nova Scotia to southern Quebec and Ontario, south to northern Georgia and Alabama, west in the lake states to Minnesota with outliers in southern Michigan, western Ohio, and southern Indiana. Many disjunct populations, probably glacial relicts, occur east of the Appalachians in the middle Atlantic states. For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

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USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Comments

It's a pity that no remnant populations of this aristocratic tree have been found in Illinois. The widely scattered populations that exist along the fringes of this tree's range may be useful in preventing this tree's extinction from such invasive pests as the Hemlock Woolly Adelgid. It is to be hoped that an effective biocontrol for this insect will be found in the not too distant future. Eastern Hemlock is closely related to Tsuga caroliniana (Carolina Hemlock), which has a much smaller range in the Appalachian mountains. Compared to Eastern Hemlock, this latter species has slightly longer seed cones (1-1½" in length) and its needle-like leaves are less strongly divided into 2 opposite ranks. The foliage of Eastern Hemlock bears a surprising resemblance to the foliage of cultivated Taxus spp. (Yews), which can become small shrubby trees if they are not pruned. However, Yews have smaller seed cones that are red and berry-like in appearance, while Eastern Hemlock and other conifers in the Pine family have larger cones with woody scales.
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© John Hilty

Source: Illinois Wildflowers

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Description

This tree usually has a single trunk up to 5' across and a conical crown up to120' tall. The leafy lateral branches have a tendency to arrange themselves in horizontal layers. Trunk bark is gray or gray-brown, consisting of broad flat plates and shallow longitudinal furrows. Branch bark is gray, smooth, and sometimes irregularly fissured, while young twigs are hairy and yellowish to reddish brown. The needle-like evergreen leaves are arranged primarily in 2 opposite ranks on the lateral sides of twigs; some appressed leaves develop along the upper side of each twig. Individual leaves are ½-¾" long, linear in shape, and flattened; they have short petioles (less than 1/8" long) and blunt tips. The upper leaf surface is medium to dark green and glabrous, while the lower is whitish green or whitish blue-green and glabrous. Along the lower surface of each leaf, there are 2 white lines that run parallel to each other. Eastern Hemlock is monoecious, producing both pollen cones and seed cones on the same tree. Pollen cones occur near the tips of leafy twigs, while seed cones occur at the tips of such twigs. Each pollen cone has a yellow globoid head about 1/8" across that consists of several globular packets of pollen; the pollen head has a light green stalk at its base that becomes longer with age (up to 1/3" in length). At the time when cross-pollination occurs, the scaly seed cones are 1/3" in length, ovoid in shape, and green. The cones are wind-pollinated during the spring. Shortly afterwards, the pollen cones wither away, while the seed cones continue their development. At maturity, the seed cones are ½-1" in length and ovoid to ovoid-globoid in shape, becoming brown from thin woody scales. At the base of each scale, there is a pair of seeds with elongated membranous wings. The released seeds can be blown about by the wind. The spreading root system is shallow to moderately deep. This tree reproduces by reseeding itself. Cultivation
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© John Hilty

Source: Illinois Wildflowers

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Alternative names

Canada hemlock, hemlock spruce

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USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Distribution

Global Range: Ontario to Nova Scotia south to Maryland and eastern Minnesota, and along the Appalachian mountains to Georgia and Alabama (Fernald 1950, Kartesz 1999).

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Range and Habitat in Illinois

At the present time, Eastern Hemlock is not known to occur in Illinois (see Distribution Map) outside of cultivation, although native populations exist in natural areas of Indiana, Wisconsin, and Missouri. However, it is possible that this tree could turn up in a wooded ravine or other natural area that has been overlooked. Eastern Hemlock is more common in the Appalachian mountains, New England, and parts of southeastern Canada. Using information from other states, habitats include rocky bluffs, wooded hillsides (especially those facing north or east), and rocky ravines. The underlying bedrock of these habitats is acidic (e.g., sandstone or granite). Because of its attractive evergreen foliage, Eastern Hemlock is often cultivated as a landscape tree. Faunal Associations
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© John Hilty

Source: Illinois Wildflowers

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

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Occurrence in North America

     AL  CT  DE  GA  IN  KY  ME  MD  MA  MI
     MN  NH  NJ  NY  NC  OH  PA  RI  SC  TN
     VT  VA  WV  WI  NB  NS  ON  PE  PQ

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In the United States, eastern hemlock occurs throughout New England, the
mid-Atlantic states, and the Lake States, and extends south in the
Appalachian Mountains to northern Georgia and Alabama and west from the
mountains into Indiana, western Ohio, and western Kentucky.  At its
northern limit, eastern hemlock ranges along the southern border of
Canada from southern Ontario to Cape Breton Island, Nova Scotia [20,35].
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 35.  Little, Elbert L., Jr. 1979. Checklist of United States trees (native        and naturalized). Agric. Handb. 541. Washington, DC: U.S. Department of        Agriculture, Forest Service. 375 p.  [2952]

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The northern limit of eastern hemlock extends from outliers in  northeastern Minnesota and the western one-third of Wisconsin eastward  through northern Michigan, south-central Ontario, extreme southern Quebec,  through New Brunswick, and all of Nova Scotia. Within the United States  the species is found throughout New England, New York, Pennsylvania, and  the middle Atlantic States, extending westward from central New Jersey to  the Appalachian Mountains, then southward into northern Georgia and  Alabama. Outliers also appear in extreme southern Michigan and western  Ohio, with scattered islands in southern Indiana and east of the  Appalachians in the middle Atlantic States.

    The range completely overlaps that of Carolina hemlock (Tsuga  caroliniana), a closely related species limited to the slopes of the  Appalachians from Virginia and West Virginia into Georgia.

    Commercial volumes of eastern hemlock have been greatly reduced by  harvesting. In Michigan, for example, sawtimber volume decreased 69  percent and growing stock volume decreased 71 percent between 1935 and  1955 (10). Both the type area and volume are continuing to decline because  of harvesting and failure to regenerate, particularly in the western  portion of the range. The remaining sawtimber is concentrated in the  Northeast and the Lake States (5).

     
- The native range of eastern hemlock.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Adaptation

Eastern hemlock grows from about sea level to 1500 meters. In the more southern parts of its range, eastern hemlock occurs only where there is drainage of cool, moist air -- on moist rocky ridges, valleys and ravines, hillsides, and lakeshores. In the northern hardwood forest, it is found on a greater variety of sites, including low rolling hills and glacial ridges. Eastern hemlock most commonly grows in mixed stands with species such as white pine, northern red oak, sugar maple, American beech, yellow birch, and white ash.

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USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Physical Description

Morphology

Description

Trees to 30m; trunk to 1.5m diam.; crown broadly conic. Bark brownish, scaly and fissured. Twigs yellow-brown, densely pubescent. Buds ovoid, 1.5--2.5mm. Leaves (5--)15--20(--25)mm, mostly appearing 2-ranked, flattened; abaxial surface glaucous, with 2 broad, conspicuous stomatal bands, adaxial surface shiny green (yellow-green); margins minutely dentate, especially toward apex. Seed cones ovoid, 1.5--2.5 ´ 1--1.5cm; scales ovate to cuneate, 8--12 ´ 7--10mm, apex ± round, often projected outward. 2 n =24.
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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

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Description

Eastern hemlock is a native, evergreen conifer with heavily foliaged and
upsweeping branches.  At maturity, it is commonly 60 to 70 feet (18-21
m) tall and 24 to 48 inches (61-122 cm) in d.b.h.  One of the largest
eastern hemlock recorded was 175 feet (53 m) tall and 76 inches (193 cm)
in d.b.h.  It reaches ages in excess of 800 years.  Eastern hemlock
roots are shallow and widespreading [20,26].
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 26.  Hosie, R. C. 1969. Native trees of Canada. 7th ed. Ottawa, ON: Canadian        Forestry Service, Department of Fisheries and Forestry. 380 p.  [3375]

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Physical Description

Tree, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds not resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins finely serrulate (use magnification or slide your finger along the leaf), Leaf apex obtuse, Leaf apex mucronulate, Leaves < 5 cm long, Leaves < 10 cm long, Leaves yellow-green above, Leaves not blue-green, Needle-like leaves flat, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaf habit drooping, Needle-like leaves per fascicle mostly 1, Needle-like leaf sheath early deciduous, Needle-like leaf sheath persistent, Twigs pubescent, Twigs densely pubescent, Twigs not viscid, Twigs with peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones < 5 cm long, Bracts of seed cone included, Seeds brown, Seeds winged, Seeds unequally winged, Seed wings prominent, Seed wings equal to or broader than body.
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Stephen C. Meyers

Source: USDA NRCS PLANTS Database

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Diagnostic Description

Synonym

Pinus canadensis Linnaeus, Sp. Pl. ed. 2, 2: 1471. 1763
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Tsuga canadensis occurs from near sea level (Nova Scotia) to 600 m in N Michigan, in the southern Appalachians between 600 and 1,500 m a.s.l. The soils are of glacial, fluvio glacial, alluvial, or colluvial origin, podzolic and usually highly acidic (pH 3-4). The climate is cool and humid, with annual precipitation between 700 and 1,500 mm. T. canadensis grows locally pure, but is usually mixed with other conifers and broad leaved trees: Pinus strobus, P. resinosa, Abies balsamea, Picea rubens, P. glauca, Larix laricina, Betula spp., Acer saccharum, Quercus rubra, Fraxinus americana, F. nigra, Fagus grandifolia, Populus spp., and other species. It is very shade tolerant and allows very little vegetation to develop under its own canopy.

Systems
  • Terrestrial
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Range and Habitat in Illinois

At the present time, Eastern Hemlock is not known to occur in Illinois (see Distribution Map) outside of cultivation, although native populations exist in natural areas of Indiana, Wisconsin, and Missouri. However, it is possible that this tree could turn up in a wooded ravine or other natural area that has been overlooked. Eastern Hemlock is more common in the Appalachian mountains, New England, and parts of southeastern Canada. Using information from other states, habitats include rocky bluffs, wooded hillsides (especially those facing north or east), and rocky ravines. The underlying bedrock of these habitats is acidic (e.g., sandstone or granite). Because of its attractive evergreen foliage, Eastern Hemlock is often cultivated as a landscape tree. Faunal Associations
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Source: Illinois Wildflowers

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Comments: Mostly hilly or rocky woods (Fernald, 1950); in southern portion of range, frequently in moist, shaded ravines, or other sheltered microhabitats.

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Habitat characteristics

More info for the terms: shrub, swamp, tree

At its western and southern limits, eastern hemlock is confined to moist
cool valleys, moist flats, northern and eastern slopes, coves, benches,
and ravines.  In the northern part of its range, it tolerates drier and
warmer sites.  Eastern hemlock also occurs at swamp borders provided
peat and muck soils are shallow [14,20,40,65].

Favorable eastern hemlock sites are moist to very moist with good
drainage.  Eastern hemlock grows in a wide variety of acidic soils;
textures include sandy loams, loamy sands, and silty loams with gravel
of glacial origin in the upper profile [14,20].

While generally considered a moisture-demanding species, eastern hemlock
grows on dry sites protected from fire, such as rocky ledges [22].  Two
types of eastern hemlock have been described:  one grows in mesophytic
habitats and one on subxeric slopes [30].  The types cannot be termed
ecotypes, however, because of incomplete habitat differentiation.
Eastern hemlock growing on "subxeric" slopes may actually be receiving
moisture from seeps [51].

In the northeastern United States, eastern hemlock grows at elevations
ranging from sea level to 2,400 feet (730 m).  In the southern
Appalachian Mountains it grows from 2,000 to 5,000 feet (610-1,520 m).
In the Allegheny Plateau region of New York, Pennsylvania, and Ohio, it
grows from 1,000 to 3,000 feet (300-910 m) [13,20,34].

Understory associates are scarce because of acidic infertile humus, low
light, and cool conditions [14,34].  Shrub and small tree associates
that occur in canopy gaps include sweet birch (Betula lenta), striped
maple (Acer pensylvanicum), mountain maple (A. spicatum), hobblebush
(Viburnum alnifolium), mapleleaf viburnum (V.  acerifolium), mountain
winterberry (Ilex montana), rhododendron (Rhododendron spp.),
mountain-laurel (Kalmia latifolia), and witch hazel (Hamamelis
virginiana).  Herbs can include Canada mayflower (Maianthemum
canadense), star flower (Trientalis borealis), common woodsorrel (Oxalis
montana), and goldthread (Coptis groenlandica).  Other associated
species include clubmosses (Lycopodium spp.), bracken (Pteridium
aquilinum), woodfern (Dryopteris spp.), and sedges (Carex spp.).  Common
mosses include Dicranium spp. and Polytrichum spp. [14,20,32,45,65].
  • 13.  Duncan, Wilbur H.; Duncan, Marion B. 1988. Trees of the southeastern        United States. Athens, GA: The University of Georgia Press. 322 p.        [12764]
  • 14.  Eyre, F. H., ed. 1980. Forest cover types of the United States and        Canada. Washington, DC: Society of American Foresters. 148 p.  [905]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 22.  Hemond, Harold F.; Niering, William A.; Goodwin, Richard H. 1983. Two        decades of vegetation change in the Connecticut Arboretum Natural Area.        Bulletin of the Torrey Botanical Club. 110(2): 184-194.  [9045]
  • 30.  Kessell, S. R. 1978. Adaptations and dimorphism in eastern hemlock,        Tsuga canadensis (L.)Carr. American Naturalist. 113(3): 333-350.        [20410]
  • 32.  Kotar, John; Kovach, Joseph A.; Locey, Craig T. 1988. Field guide to        forest habitat types of northern Wisconsin. Madison, WI: University of        Wisconsin, Department of Forestry; Wisconsin Department of Natural        Resources. 217 p.  [11510]
  • 34.  Kudish, Michael. 1992. Adirondack upland flora: an ecological        perspective. Saranac, NY: The Chauncy Press. 320 p.  [19376]
  • 40.  Martin, William H. 1992. Characteristics of old-growth mesophytic        forests. Natural Areas Journal. 12(3): 127-135.  [19371]
  • 45.  Nelson, John B. 1986. The natural communities of South Carolina.        Columbia, SC: South Carolina Wildlife & Marine Resources Department. 54        p.  [15578]
  • 51.  Rogers, R. S. 1978. Forests dominated by hemlock (Tsuga canadensis):        distribution as related to site and postsettlement history. Canadian        Journal of Botany. 56: 843-854.  [20408]
  • 65.  Eriksson, Gosta; Jonsson, Alena; Dormling, Ingegerd; [and others]

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Key Plant Community Associations

More info for the terms: codominant, natural

Eastern hemlock occurs as a dominant or codominant in coniferous and
mixed-hardwood forests.  It is often the only conifer present in mixed
mesophytic forests of the eastern United States [40].

Publications listing eastern hemlock as codominant or dominant are as
follows:

The natural forests of Maryland: an explanation of the vegetation map
   of Maryland [7]
A multivariate analysis of forest communities in the western Great Smoky
   Mountains National Park [9]
The vegetation of Wisconsin [10]
The principal plant associations of the Saint Lawrence Valley [11]
Field guide: forest habitat types of northern Wisconsin [32]
A classification of the deciduous forest of eastern North America [42]
The natural communities of South Carolina [45]
Forest associations in the Harvard Forest [55]
Vegetation of the Great Smoky Mountains [65]
 
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 11.  Dansereau, Pierre. 1959. The principal plant associations of the Saint        Lawrence Valley. No. 75. Montreal, Canada: Contrib. Inst. Bot. Univ.        Montreal. 147 p.  [8925]
  • 32.  Kotar, John; Kovach, Joseph A.; Locey, Craig T. 1988. Field guide to        forest habitat types of northern Wisconsin. Madison, WI: University of        Wisconsin, Department of Forestry; Wisconsin Department of Natural        Resources. 217 p.  [11510]
  • 40.  Martin, William H. 1992. Characteristics of old-growth mesophytic        forests. Natural Areas Journal. 12(3): 127-135.  [19371]
  • 42.  Monk, Carl D.; Imm, Donald W.; Potter, Robert L.; Parker, Geoffrey G.        1989. A classification of the deciduous forest of eastern North America.        Vegetatio. 80: 167-181.  [9297]
  • 45.  Nelson, John B. 1986. The natural communities of South Carolina.        Columbia, SC: South Carolina Wildlife & Marine Resources Department. 54        p.  [15578]
  • 55.  Spurr, Stephen H. 1956. Forest associations in the Harvard Forest.        Ecological Monographs. 26(3): 245-262.  [7451]
  • 65.  Eriksson, Gosta; Jonsson, Alena; Dormling, Ingegerd; [and others]
  • 7.  Brush, Grace S.; Lenk, Cecilia; Smith, Joanne. 1980. The natural forests        of Maryland: an explanation of the vegetation map of Maryland.        Ecological Monographs. 50(1): 77-92.  [19035]
  • 9.  Callaway, Ragan M.; Clebsch, Edward E. C.; White, Peter S. 1987. A        multivariate analysis of forest communities in the western Great Smoky        Mountains National Park. American Midland Naturalist. 118(1): 107-120.        [15604]

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Habitat: Cover Types

More info on this topic.

This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

     5  Balsam fir
    17  Pin cherry
    18  Paper birch
    19  Gray birch - red maple
    20  White pine - northern red oak - red maple
    21  Eastern white pine
    22  White pine - hemlock
    23  Eastern hemlock
    24  Hemlock - yellow birch
    25  Sugar maple - beech - yellow birch
    26  Sugar maple - basswood
    27  Sugar maple
    28  Black cherry - maple
    30  Red spruce - yellow birch
    31  Red spruce - sugar maple - beech
    32  Red spruce
    33  Red spruce - balsam fir
    34  Red spruce - Fraser fir
    35  Paper birch - red spruce - balsam fir
    37  Northern white-cedar
    39  Black ash - American elm - red maple
    44  Chestnut oak
    52  White oak - black oak - northern red oak
    53  White oak
    57  Yellow-poplar
    58  Yellow-poplar - eastern hemlock
    59  Yellow-poplar - white oak - northern red oak
    60  Beech - sugar maple
    97  Atlantic white-cedar
   108  Red maple

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Habitat: Plant Associations

More info on this topic.

This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

   K093  Great Lakes spruce - fir forest
   K094  Conifer bog
   K095  Great Lakes pine forest
   K096  Northeastern spruce - fir forest
   K097  Southeastern spruce - fir forest
   K103  Mixed mesophytic forest
   K104  Appalachian oak forest
   K106  Northern hardwoods
   K107  Northern hardwoods - fir forest
   K108  Northern hardwoods - spruce forest

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Habitat: Ecosystem

More info on this topic.

This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

   FRES10  White - red - jack pine
   FRES11  Spruce - fir
   FRES15  Oak - hickory
   FRES18  Maple - beech - birch
   FRES19  Aspen - birch

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Soils and Topography

The soil requirements for eastern hemlock are not exacting (35). They  are universally characterized as being moist to very moist but with good  drainage. In the Lake States the species grows on upland sandy loams,  loamy sands, and silt loams, often with an abundance of ground or coarse  rocky material throughout the upper profile deposited from glacial or  fluvial material. In Canada and the northeastern States the soils under  eastern hemlock tend to be shallow loams and silt loams, often over  granite, gneiss, and slate bedrock (Typic, Lithic, and Entic Haplorthods  of the order Spodosols). Typically, most soils are highly acid,  particularly in the upper horizons, but some are near neutral. The heavy,  slowly decomposing litter fosters podzolization or leaching as the stand  increases in age. On sites in which eastern white pine (Pinus strobusis a major component, the soils tend to be of a sandy texture, well  mixed with humus, moist, and well drained (Alfic Haplorthods). Scattered  patches of hemlock also occur on the finer glacial tills as well (Alfic  Fragiorthods), but in general these soils have less hemlock than the  coarser soils.

    Eastern hemlock grows from sea level to about 730 m (2,400 ft) in  elevation in the northeastern and northern portions of the range. Most  commonly it is found on benches, flats, and swamp borders, provided the  peat and muck soils are shallow (Aquic Haplorthods or Aerie Haplaquods).  On the Allegheny

    Plateau, especially in New York and Pennsylvania, most of the hemlock  grows between 300 and 910 m (1,000 and 3,000 ft) (35). In the southern  Appalachians the most frequent occurrences are at elevations of 610 to  1520 m (2,000 to 5,000 ft) and often are restricted to north and east  slopes, coves, or cool, moist valleys (35). Outliers tend to be severely  restricted by a combination of edaphic and climatic factors.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Climate

Eastern hemlock is generally restricted to regions with cool humid  climates. In the northern areas January temperatures average about -12°  C (10° F) and July temperatures about 16° C (60° F).  Precipitation ranges from less than 740 mm. (29 in) in heavy snowfall  areas of the north to more than 1270 mm (50 in) per year, about one-half  occurring as summer precipitation. In the more productive areas near the  Atlantic coast and southern Appalachians, January temperatures range as  high as 6° C (42° F) and annual precipitation exceeds 1520 mm  (60 in). The frost-free period is less than 80 days at the northern limits  and nearly 200 days in the eastern and southern portions of the range.

    Fully stocked stands of eastern hemlock tend to develop similar  microclimates because of their dense canopy, dense shading, deep duff  layer, and subsequent retention of moisture and uniformly low  temperatures. In the few stands in which understories do develop, the type  of vegetation tends to be similar to other forest types in the area  although fewer species become established (30).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Habitat & Distribution

Moist rocky ridges, ravines, and hillsides; 600--1800m; N.B., N.S., Ont., P.E.I., Que.; Ala., Conn., Del., Ga., Ind., Ky., Maine, Md., Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.
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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

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Dispersal

Establishment

Eastern hemlocks begin to produce cones at about age 15 in vigorous trees or much later in suppressed trees. There is a high frequency of cone crops and individual trees have a long duration of cone production (excellent cone production has been reported for trees more than 450 years old), but the viability of seed usually is low. Seeds are particularly easily damaged by drying. The best conditions for germination and seedling establishment are under a 70-80% crown cover on an exposed, partially decomposed layer. Otherwise, regeneration is restricted to rotten logs, stumps, and mounds that normally have warmer surfaces and better moister retention than the forest floor.

Eastern hemlock is the most shade tolerant of all tree species and individuals may remain in the understory in natural stands for 25-400 years. After a plant reaches 1-2 meters in height, the root system has reached a depth not radically afffected by surface drying, and release from overstory competition may greatly increase annual growth. In general, eastern hemlock is a slow-growing tree that may take 250 to 300 years to reach maturity and may live for 900 years or more.

Public Domain

USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Associations

Associated Forest Cover

Eastern hemlock is a major component of four forest cover types (9): In  the Northern Forest Region, White Pine-Hemlock (Society of American  Foresters Type 22), Eastern Hemlock (Type 23), and Hemlock-Yellow Birch  (Type 24); in the Central Forest Region, Yellow-Poplar-Eastern Hemlock  (Type 58). It is also a common associate in seven types of the Northern  Forest Region: White Pine-Northern Red Oak-Red Maple (Type 20), Eastern  White Pine (Type 21), Red Spruce-Yellow Birch (Type 30), Red Spruce-Sugar  Maple-Beech (Type 31), Red Spruce (Type 32), Red Spruce-Balsam Fir (Type  33), Red Spruce-Fraser Fir (Type 34). Eastern hemlock occurs in the  following 18 types but only as a minor species:

        5  Balsam Fir 
  17  Pin Cherry 
  18  Paper Birch 
  25  Sugar Maple-Beech-Yellow Birch 
  26  Sugar Maple-Basswood 
  27  Sugar Maple 
  28  Black Cherry-Maple 
  35  Paper Birch-Red Spruce-Balsam Fir 
  37  Northern White-Cedar 
  39  Black Ash-American Elm-Red Maple 
  44  Chestnut Oak 
  52  White Oak-Black Oak-Northern Red Oak 
  53  White Oak 
  57  Yellow-Poplar 
  59  Yellow-Poplar-White Oak-Northern Red Oak 
  60  Beech-Sugar Maple 
  97  Atlantic White-Cedar 
108  Red Maple

    Fully stocked stands of eastern hemlock form such a dense canopy that an  understory seldom is able to develop. When an understory does exist, the  most common herbs are false lily-of-the-valley (Mianthemum canadense),  starflower (Trientalis borealis), woodfern (Dryopteris  spp.), common woodsorrel (Oxalis montana), goldthread  (Coptis groenlandica), clubmoss (Lycopodium spp.),  and sedges (Carex spp.). Common mosses are Dicranum  and Polytrichum (30,39).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Diseases and Parasites

Damaging Agents

Seeds of eastern hemlock are sensitive to  damage from several molds, particularly Botrytis spp., that reduce  or delay germination (23). Some molds are borne internally while others  colonize the seeds during germination. In one study, the fungus Aureobasidum  pullulans was isolated from 73 percent of the seedcoats. In another  test this mold was isolated twice from the embryonic tissue and 13 times  from the seedcoat. Generally, molds are less injurious than desiccation  during the germination and seedling stages.

    The most damaging agents to young seedlings, other than desiccation, are  damping-off fungi and root rots (16). Pythium spp. and Rhizoctonia  spp. flourish in wet, poorly drained soils and in well-drained soils,  respectively, and are common on eastern hemlock. At least three root rots-  Cylindrocladium scoparium, Rhizina undulata (common on burn  areas), and Fusarium moniliforme- are common on eastern hemlock.  F. moniliforme has been isolated from embryonic tissue and  seedcoats as well as in the soil (16,23).

    Several diseases affect the needles and twigs of eastern hemlock. The  rust caused by Melampsora farlowii is one of the most damaging. It  causes shoot blight and curls and attacks the cone often resulting in cone  abortion. Three rusts caused by M. abietiscanadensis, Pucciniastrum  hydrangeae, and P. vaccinii spp. affect only the needles.  Single needle browning throughout the crown is caused by Fabrella  tsugae. Lower foliage in very wet and shady areas often has a grayish  mat appearance on both the needles and twigs caused by Rosellinia  herpotrichioides. Dimerosporium tsugae occasionally forms a black,  sooty growth on the needles.

    Living heartwood of eastern hemlock is attacked by Tyromyces  borealis, particularly in the northeast, leaving white flecks in the  wood. Pholiota adiposa is fairly common in the Lake States and  causes a cavity along the pith axis. Other rots are the trunk rot caused  by Haematostereum sanguinolentum; abrown, red ring rot  caused by Phellinus pini; and a red heart rot caused by P.  robustus. The red-varnish-topped fungus, Ganoderma tsugae, is  the most common decayer of stumps and old logs.

    Numerous fungi are associated with the root system but rarely develop  conks or kill trees. The most common are the shoestring fungus, Armillaria  mellea, and the velvet top fungi, Phaeolus schweinitzii, Tyromyces  balsameus, and Heterobasidion annosum. At least two mycorrhiza  are known to occur on the roots (16).

    Although at least 24 insects attack eastern hemlock, few are  economically important. The most important is the hemlock borer, Melanophila  fulvoguttata, which attacks weakened trees. Symptoms usually consist  of woodpecker-like holes in the bark, galleries filled with dark  excrement, and yellowing shoot tips (27). Spruce budworm, Choristoneura  fumiferana, defoliates and kills hemlock after defoliating all the  balsam fir in the stand.

    The hemlock looper, Lambdina fiscellaria fiscellaria, devours  part of the needle after which the remainder turns brown. In nurseries,  white grubs of the strawberry root weevil, Otiorhynchus ovatus, consume  the roots, and larvae of the black vine weevil, O. sulcatus, feed  on the needles (40). In the eastern States the hemlock scale, Abgrallaspis  ithacae, damages young shade trees, and the gypsy moth, Lymantria  dispar, kills understory trees.

    Numerous animals feed on eastern hemlock and often cause serious damage,  marked loss of vigor, or even death. White-tailed deer readily browse this  species although it has been ranked seventh in winter food preference. In  some regions, patches of regeneration have been eliminated following heavy  browsing in years when deer populations are high. Although deer have been  blamed for the absence of eastern hemlock in many localities, no  regeneration occurred under similar conditions in fenced areas; thus,  overstory-site-temperature requirements are presumably more critical  (2,6,8).

    Snowshoe hares and New England cottontails frequently browse eastern  hemlock. Mice, voles, squirrels, and other rodents also feed on seeds and  small seedlings both under natural stands and in nurseries (1). Porcupines  occasionally gnaw the bark on larger trees causing serious wounds and  top-kill (4). Sapsuckers have been associated with ring shake in some  areas (19,21).

    Small eastern hemlock trees are highly susceptible to wildfire but  prescribed burns are beneficial for securing natural regeneration. The  thick bark of older trees is resistant to light burns but saplings are  usually destroyed. Root injury often occurs from high intensity fires  because of heavy litter accumulation.

    Drought is probably the most serious damaging agent to eastern hemlock,  especially during the seedling stage. Winter drying caused by excessive  transpiration on warm, windy days has caused severe needle injury.

    In later stages of stand development, heavy cuttings predispose trees to  windthrow because of their shallow rooting habit. Older trees are  susceptible to radial stress cracks and ring shake, particularly in  partially cut stands (19). Eastern hemlock is sensitive to salt spray or  drift and sulfur fumes and is one of the species most often struck by  lightning (16,25).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

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© NatureServe

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General Ecology

Broad-scale Impacts of Plant Response to Fire

More info for the term: prescribed fire

The Research Project Summary Early postfire effects of a prescribed fire in the southern Appalachians of North Carolina provides information on prescribed fire and postfire response of plant community species, including eastern hemlock, that was not available when this species review was originally written.

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Immediate Effect of Fire

More info for the terms: ground fire, presence

Low-severity fire readily kills seedlings and saplings of eastern
hemlock, and may also kill larger trees.  A low-severity ground fire in
a northern hardwoods community in south-central New York killed 93
percent of the eastern hemlock saplings.  Sixty percent of the mature
eastern hemlock died or were badly injured as a result of the fire [58].
The presence of fire scars indicates that larger trees have thick enough
bark to survive low-severity surface fires [18,36].
  • 18.  Frelich, Lee E.; Lorimer, Craig G. 1991. Natural disturbance regimes in        hemlock-hardwood forests of the upper Great Lakes region. Ecological        Monographs. 61(2): 145-164.  [15036]
  • 36.  Martin, S. Clark. 1980. Mesquite. In: Eyre, F. H., ed. Forest cover        types of the United States and Canada. Washington, DC: Society of        American Foresters: 118.  [9858]
  • 58.  Swan, Frederick R., Jr. 1970. Post-fire response of four plant        communities in south-central New York state. Ecology. 51(6): 1074-1082.        [3446]

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Post-fire Regeneration

More info for the terms: secondary colonizer, tree

   Tree without adventitious-bud root crown
   Secondary colonizer - off-site seed

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Fire Ecology

More info for the terms: litter, tree

Eastern hemlock is very susceptible to fire because of its thin bark,
shallow roots, low-branching habit, and heavy litter deposits [20,51].
It is possibly the most fire-sensitive mesophytic tree species in its
range [51].

Eastern hemlock usually escapes fire because it occurs in moist habitats
and is often associated with hardwoods which do not readily burn.  If a
fire starts in a cutover area, a windfall area, or an area with dead
standing timber, it may carry into a northern hardwoods forest if there
is strong wind [18].  In Michigan, the average return time for severe
crown fires in the hemlock-white pine-northern hardwoods type is
estimated to be about 1,400 years [63].  In northeastern Maine, the
average return interval for fire in spruce-fir forests in which eastern
hemlock is a minor component is about 800 years [37].

Vogl [61] considers eastern hemlock a fire-initiated species rather than
a fire-independent species because it benefits from fire-prepared
seedbeds.  However, suggestions that fire promotes regeneration of
eastern hemlock are not well documented.  Given the difficulties in
accurate age estimates because of heart rot, Rogers [51] suggests that
even-aged eastern hemlock forests that regenerated after fire may
actually be uneven-aged.
  • 18.  Frelich, Lee E.; Lorimer, Craig G. 1991. Natural disturbance regimes in        hemlock-hardwood forests of the upper Great Lakes region. Ecological        Monographs. 61(2): 145-164.  [15036]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 37.  Lorimer, Craig G. 1977. The presettlement forest and natural disturbance        cycle of northeastern Maine. Ecology. 58: 139-148.  [9711]
  • 51.  Rogers, R. S. 1978. Forests dominated by hemlock (Tsuga canadensis):        distribution as related to site and postsettlement history. Canadian        Journal of Botany. 56: 843-854.  [20408]
  • 61.  Vogl, Richard J. 1977. Fire: a destructive menace or a natural process?.        In: Cairns, J., Jr.; Dickson, K. L.; Herricks, E. E., eds. Recovery and        restoration of damaged ecosystems: Proceedings of the international        symposium; 1975 March 23-25; Blacksburg, VA. Charlottesvile, VA:        University Press of Virginia: 261-289.  [10055]
  • 63.  Whitney, Gordon G. 1986. Relation of Michigan's presettlement pine        forests to substrate and disturbance history. Ecology. 67(6): 1548-1559.        [8713]

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Successional Status

More info on this topic.

More info for the terms: climax, litter

Obligate Climax Species

Eastern hemlock is very shade tolerant [5].  Seedlings survive in as
little as 5 percent of full light [14].  Individuals are able to survive
several hundred years of suppression, and many show numerous growth
releases and suppressions [6].  Saplings less than 2 inches (5 cm) in
d.b.h. may be more than 100 years old [10].

Seedlings are able to establish under the canopy of mature individuals.
Eastern hemlock establishes under dense sugar maple canopies and can
replace that species [39].  Eastern hemlock uniquely modifies
semipermanent soil properties, such as acidity, which favors its
reproduction.  Opportunities to establish in a mature forest increase
over time as nurse logs and tip-up mounds accumulate [51].

The general desgination of eastern hemlock as a climax species has been
questioned [22,41].  In some old-growth eastern hemlock stands, the
smaller size classes of hemlock are being replaced by American beech
(Fagus grandifolia) and sugar maple [41].  Because of this lack of
regeneration, Hemond and others [22] suggest that eastern hemlock
requires disturbance to perpetuate itself.

In contrast, other authors suggest that disturbance is responsible for
the lack of regeneration in mature hemlock forests [3,6,51].
White-tailed deer populations have increased since presettlement times
because logging of virgin forests opened up habitat, predators declined,
and the deer were protected.  Deer often consume all eastern hemlock
seedlings and saplings in the winter.  Where deer populations are low,
eastern hemlock appears to be able to reproduce in its own shade and
become a component of a self-perpetuating homogenous climax forest [3].

Eastern hemlock requires partial shade for establishment and is a late
colonizer of disturbed sites [24].  In the Pisgah Forest in southwestern
New Hampshire, 80 percent of old-growth eastern hemlock established
within 37 years of disturbance.  Hardwoods grew rapidly into the canopy
while eastern hemlock grew slowly as shade-tolerant saplings.  Eastern
hemlock extended into the canopy following subsequent disturbance [23].

The understory population of eastern hemlock readily takes advantage of
canopy gaps.  Eastern hemlock increased in importance as American
chestnut (Castanea dentata) declined from chestnut blight [8].  It is
currently replacing American beech where that species is succumbing to
beech bark disease [53].  Eastern hemlock is not successful in
regenerating in canopy gaps in areas such as the New York Botanical
Forest, where the occasional light arson fire, trampling, and other
urban stresses kill seedlings.  In addition, the removal of fallen logs
in the forest decreases the amount of adequate substrate for germination
[52].

The slow invasion of oak-dominated sites by eastern hemlock appears to
be related to heavy leaf litter and the absence of favorable seedbed
conditions [22].
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 14.  Eyre, F. H., ed. 1980. Forest cover types of the United States and        Canada. Washington, DC: Society of American Foresters. 148 p.  [905]
  • 22.  Hemond, Harold F.; Niering, William A.; Goodwin, Richard H. 1983. Two        decades of vegetation change in the Connecticut Arboretum Natural Area.        Bulletin of the Torrey Botanical Club. 110(2): 184-194.  [9045]
  • 23.  Henry, J. D.; Swan, J. M. A. 1974. Reconstructing forest history from        live and dead plant material- an approach to the study of forest        succession in southwest New Hampshire. Ecology. 55: 772-783.  [8725]
  • 24.  Hibbs, D. E. 1983. Forty years of forest succession in central New        England. Ecology. 64(6): 1394-1401.  [9613]
  • 3.  Anderson, Roger C.; Loucks, Orie L. 1979. White-tail deer (Odocoileus        virginianus) influence on structure and composition of Tsuga canadensis        forests. Journal of Applied Ecology. 16: 855-861.  [20403]
  • 39.  Martin, N. D. 1959. An anaylsis of forest succession in Algonquin Park,        Ontario. Ecological Monographs. 29(3): 187-218.  [19930]
  • 41.  McIntosh, Robert P. 1972. Forests of the Catskill Mountains, New York.        Ecological Monographs. 42: 143-161.  [8857]
  • 5.  Baker, Frederick S. 1949. A revised tolerance table. Journal of        Forestry. 47: 179-181.  [20404]
  • 51.  Rogers, R. S. 1978. Forests dominated by hemlock (Tsuga canadensis):        distribution as related to site and postsettlement history. Canadian        Journal of Botany. 56: 843-854.  [20408]
  • 52.  Rudnicky, James L.; McDonnell, Mark J. 1989. Forty-eight years of canopy        change in a hardwood-hemlock forest in New York City. Bulletin of the        Torrey Botanical Club. 116(1): 52-64.  [12567]
  • 53.  Runkle, James R. 1990. Eight years change in an old Tsuga canadensis        woods affected by beech bark disease. Bulletin of the Torrey Botanical        Club. 117(4): 409-419.  [13759]
  • 6.  Brown, James H., Jr.; Castaneda, Cesar A.; Hindle, Robinson J. 1982.        Floristic relationships anddynamics of hemlock (Tsuga canadensis)        communities in Rhode Island. Bulletin of the Torrey Botanical Club.        109(3): 385-391.  [20407]
  • 8.  Busing, Richard T. 1989. A half century of change in a Great Smoky        Mountains cove forest. Bulletin of the Torrey Botanical Club. 116(3):        283-288.  [10901]

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Regeneration Processes

More info for the terms: cover, density, litter

Trees begin producing seed when they are 20 to 30 years old.  Eastern
hemlocks older than 450 years still produce large seed crops.  This
species bears cones every year, and large crops are frequent, usually
every 3 to 4 years.  The small winged seeds are dispersed by gravity and
wind; most fall within one-tree-height distance from the source [20,54].

The seeds are partially dormant and germinate best when stratified for
about 10 weeks at or slightly above freezing.  Germination occurs at a
range of temperatures; seeds from the northern portion of its range
germinate at lower temperatures than seeds from the southern portion
[20,54].  Seeds do not remain viable if they do not germinate the first
spring after seedfall [38].

Seeds germinate best on moist substrates, such as rotten wood, mineral
soil, mineral soil mixed with humus, well-decomposed litter, and moss
mats [14,62].  The number of seedlings established on rotten logs and
stumps increases as the wood decays and the moss cover increases.
Seedlings commonly establish on "tip-up mounds" formed by fallen trees
[10].  Seedlings grow slowly and cannot tolerate full sunlight until
fully established, usually when they are 3 to 5 feet (0.9-1.5 m) tall
[20].

Eastern hemlock regeneration appears to be periodic and is influenced by
fire, windthrow, drought, and stand conditions.  A young dense stand may
exclude regeneration for many years because of severe root competition
in the upper soil layers, dense low shade, and dry acidic litter
[27,56].  Hemlock regeneration is present in the understory of stands
with a parent overstory density of up to 140 square feet per acre (32 sq
m/ha) but is most abundant when eastern hemlock comprises 80 to 100
square feet per acre (18-23 sq m/ha) of the overstory [31].

Eastern hemlock does not sprout and layers only rarely [20].
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 14.  Eyre, F. H., ed. 1980. Forest cover types of the United States and        Canada. Washington, DC: Society of American Foresters. 148 p.  [905]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 27.  Hough, A. F.; Forbes, R. D. 1943. The ecology and silvics of forests in        the high plateaus of Pennsylvania. Ecological Monographs. 13(3):        299-320.  [8723]
  • 31.  Kittredge, David B.; Ashton, P. Mark S. 1990. Natural regeneration        patterns in even-aged mixed stands in southern New England. Northern        Journal of Applied Forestry. 7: 163-168.  [13323]
  • 38.  Marquis, David A. 1975. Seed storage and germination under northern        hardwood forests. Canadian Journal of Forestry Resources. 5: 478-484.        [6684]
  • 54.  Ruth, Robert H. 1974. Tsuga (Endl.) Carr. hemlock. In: Schopmeyer, C.        S., ed. Seeds of woody plants in the United States. Agric. Handb. 450.        Washington, DC: U.S. Department of Agriculture, Forest Service: 819-827.        [7770]
  • 56.  Stearns, Forest. 1951. The composition of the sugar maple-hemlock-yellow        birch association in northern Wisconsin. Ecology. 32(2): 245-265.        [10588]
  • 62.  Wendel, G. W.; Della, Bianca, Lino; Russell, James; Lancaster, Kenneth        F. 1983. Eastern white pine including eastern hemlock. In: Burns,        Russell M., tech. comp. Silvicultural systems for the major forest types        of the United States. Agric. Handb. 445. Washington, DC: U.S. Department        of Agriculture, Forest Service: 131-134.  [20409]

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Growth Form (according to Raunkiær Life-form classification)

More info on this topic.

More info for the term: phanerophyte

  
   Phanerophyte

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Life Form

More info for the term: tree

Tree

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Plant Response to Fire

Eastern hemlock appears to invade burned sites over time.  In the Pisgah
Forest in southwestern New Hampshire, 80 percent of old-growth hemlock
germinated within the first 37 years after a major fire in 1665 [23].
  • 23.  Henry, J. D.; Swan, J. M. A. 1974. Reconstructing forest history from        live and dead plant material- an approach to the study of forest        succession in southwest New Hampshire. Ecology. 55: 772-783.  [8725]

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Reaction to Competition

Eastern hemlock is the most shade  tolerant of all tree species (3,15,35). It can survive with as little as 5  percent of full sunlight, but under severe suppression only partial growth  rings form and some may be missing entirely from the lower bole areas. In  one study, from 10 to 40 rings were missing for a 120-year period of  suppression. The tree is capable of withstanding suppression for as long  as 400 years.

    At all ages, however, eastern hemlock responds to release in both height  and diameter growth. Growth rates in excess of 6.4 cm (2.5 in) per decade  are possible following release either from side or overhead suppression.  Excessive release often results in reduced growth and mortality and has  been a contributing factor to partial uprooting or windthrow because of  shallow rooting. Trees originating on logs or stumps often develop stilted  root systems and also are susceptible to windthrow (19).

    Even-aged or uneven-aged (selection) management systems can be  successfully used to manage hemlock, but with certain limitations on the  selection system. In the Lake States, the selection system has not always  been successful and is not recommended for upland sites. In the East, the  selection system has been used successfully on a limited basis, but the  even-aged system is preferred and most frequently used.

    A 2- or 3-cut shelterwood system is the best even-aged method for  regenerating eastern hemlock. It is effective because it promotes seed  germination and early seedling development by reducing moisture stress.  However, the site must be properly scarified and all competing understory  hardwoods removed to develop satisfactory seedbed conditions before or  immediately after the first and sometimes the second cut.

    In mixed stands of hardwoods and hemlock, where the proportion of  hemlock is 15 percent or more, it is feasible to manage for hemlock, but  at various residual stocking levels. Hemlock does not require as much  growing space as hardwoods, so residual stocking is greater in stands  where hemlock predominates. For example, a stand of trees averaging 25 cm  (10 in) in diameter that contains 15 to 29 percent hemlock would be marked  to favor hemlock at a residual stocking of about 22 m² (95 ft²)  basal area of both hemlock and hardwoods. This same stand with 30 percent  or more hemlock would be managed to 29 m² (125 ft²) of basal  area. If less than 15 percent hemlock, the stand should be managed for the  hardwood type represented.

    Many fully stocked stands of eastern hemlock have basal areas in excess  of 69 m²/ha (300 ft²/acre). When thinning heavily stocked  stands- 46 m²/ha (200 ft²/acre)- no more than one-third of the  total basal area should be removed at one time. Excessive cutting results  in reduced growth and increased mortality and contributes to windthrow. In  addition, hardwood encroachment interferes with the successful  establishment of hemlock. Fully stocked stands with densities less than 46  m²/ha (200 ft²/acre) can be thinned to a minimum of 27 m²/ha  (120 m²/acre) without jeopardizing the residual stand (22).

    Acceptable standards for implementation of the uneven-aged system, based  on field experience, include a residual stocking of 30 m²/ha (130 ft²/acre)  in stands predominantly hemlock (50 percent or more); a stand structure  (diameter distribution) of 35 percent poles 13 to 25 cm (5 to 10 in)  d.b.h., and 65 percent sawtimber 30 cm (12 in) and larger. These  guidelines will ensure a balanced growth between poletimber and sawtimber  size classes. In addition, a continuous flow of ingrowth will occur and  regeneration is assured if proper care is given to seedbed requirements.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Rooting Habit

To a great extent, site conditions determine the  rooting habits of eastern hemlock. When the watertable is near the  surface, root systems are shallow. On better drained sites, deeper rooting  patterns may be observed.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Life History and Behavior

Cyclicity

Phenology

More info on this topic.

Eastern hemlock male strobili open and pollen is dispersed in late April
to early June, depending on locality.  This is usually 2 weeks after the
leaf buds open.  Fertilization is complete in about 6 weeks, and cones
reach full size in late August or early September.  The cones open in
mid-October, but seed dispersal may extend into the winter [20].  Cones
close in wet weather and open again in subsequent dry weather,
prolonging seed dispersal.  Germination occurs in the spring [10].
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]

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Reproduction

Vegetative Reproduction

None of the hemlocks sprout and only  rarely layer. Vegetative propagation by cuttings and grafting are limited  to ornamental production (35). Stem cuttings are easily rooted but auxin  treatments will enhance the response under greenhouse conditions. Natural  root grafts have been reported in northern Wisconsin.

    Most of the stock used in planting, both under forest conditions and as  ornamentals, is grown from seed. Nursery grown seedlings grow slowly; 3-0  stock ranges from 13 to 23 cm (5 to 9 in) tall. Survival and height growth  of planted hemlock, unlike natural regeneration, tend to be good both in  the open and under partial overstories. Trees in a study in the  Alleghenies grew significantly faster on north slopes under overstories of  intermediate densities.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Seedling Development

Despite the high frequency of cone crops  and the long duration of cone production by individual trees, the  viability of eastern hemlock seed is usually low. Germinative capacity  commonly is less than 25 percent (36). In one locality only 2.1  viable seeds were produced per cone, 2.2 were destroyed by insects, and  the remaining 8.0 seeds were empty (29).

    Eastern hemlock seed is partially dormant at maturity and must be  stratified about 10 weeks at or slightly above freezing temperatures for  best germination. Unstratified seed must be exposed to light to break the  partial dormancy. Under natural conditions the chilling requirements are  met during the winter and the spring germination seldom is delayed because  of seed dormancy (35). Germination is epigeal.

    The temperature requirements for germination of eastern hemlock are more  exacting than for other species in the genus. A constant temperature of 15°  C (59° F) is about optimum for germination. High germination  percentages usually occur at temperatures ranging from 7° to 18°  C (44° to 64° F), depending on the seed source (29,35). These  temperatures are nearly identical to those required for yellow birch (Betula  alleghaniensis), the most common associated species in the northern  region, and help to explain the association of two species differing so  much in tolerance. Achieving desirable temperatures for germination under  natural conditions is difficult because eastern hemlock seeds require from  45 to 60 days to reach their peak in germinative energy. Contrary to  common belief, the species requires a warm, moist site for stand  establishment rather than the cool, moist conditions that usually develop  as stands mature.

    Eastern hemlock seeds are easily damaged by drying. In one study 60  percent of the seeds were severely damaged after only 2 hours of drying,  and 80 percent died or did not recover after 6 hours of drying (35).  Drying of the seedling after germination caused heavy root mortality  that could not be overcome once moisture conditions improved.

    Natural stands of eastern hemlock nearly always contain a large  component of relatively even-aged trees but consistently have a stocking  of older age classes and larger diameter trees that provided shelter  during the regeneration period (17,33,35,39). Consequently, new  stands of eastern hemlock and yellow birch can be established under a high  density overstory (from 70 to 80 percent crown cover) using the  shelterwood regeneration system. The site must be prepared, however, by  thorough mixing of organic and mineral soil or by prescribed fire to  expose a partially decomposed layer (6,12,14,18,26,32,34, 35,38). Under  this system, optimum conditions are created for germination and seedling  establishment. Without these conditions most eastern hemlock regeneration  is restricted to rotten logs, stumps, and mounds that normally have warmer  surfaces and better moisture retention than the forest floor.

    The rigid overstory and seedbed requirements for successful natural  regeneration of eastern hemlock were evident in a direct seeding study in  northwestern Pennsylvania. "No hemlock germinated on prepared spots  in the open (hemlock rarely germinates and becomes established in open  areas) and only a few germinated under a light overstory because of the  moisture stress created under these conditions." Germination was  good, however, on prepared sites under a pole-size stand, especially on  north slopes (20).

    Under ideal growing conditions, seedlings of eastern hemlock develop  slowly. First-year seedlings may grow only 25 to 38 mm (1 to 1.5 in) in  height and the roots extend less than 13 mm (0.5 in) into the soil. These  conditions provide moisture in the upper soil horizon throughout the  growing season. "Because of their stable moisture requirements,  seedlings are very sensitive to high temperatures and drying of the  surface soil during the establishment period. Once the root system has  reached a soil depth not radically affected by surface drying, usually  after the second year, the seedlings grow more rapidly without  interference of overhead shade. Seedlings are fully established when they  are 0.9 to 1.5 m (3 to 5 ft) tall and at that time, can be released  completely from overhead competition without fear of mortality."

    Eastern hemlock seedlings are subject to damping-off as well as root rot  fungi (23,35). The fungi may be present in the soil or within the seed  before it is dispersed. At least seven species of fungi are known to  attack the seed, and several other species cause damping-off. Treatment of  seeds with fungicides is frequently ineffective in controlling diseases  and also delays or reduces germination. The high incidence of seedling  disease combined with low seed viability suggest that supplemental seeding  would enhance natural seeding under most conditions.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Seed Production and Dissemination

Cones of eastern hemlock are  the smallest in the genus, from 13 to 19 mm (0.5 to 0.75 in) long; 35.2  liters (1 bushel) of cones weigh about 15.4 kg (34 lb), and yield from  0.64 to 0.68 kg (1.4 to 1.5 lb) of seed. The number of cleaned seeds  ranges from 56,250 to 163,290/kg (25,500 to 74,070/1b). Seeds from eastern  and southern areas are usually larger than those from northern and western  regions. The seeds of eastern hemlock are slightly larger than those of  western hemlock (Tsuga heterophylla) but are smaller than those of  either Carolina or mountain hemlock (T. mertensiana) (36). The  single seeds are about 1.6 mm (0.06 in) long with a slightly longer  terminal wing.

    Seeds ripen about the time the cones change from yellowish green to  purple brown. Dispersal of the seeds begins when the cones turn deeper  brown indicating a reduction in moisture content. Most seeds fall within  tree height because of the small wings. Additional distribution may occur  from drifting on crusted snow. Some seeds may remain in the cones through  the winter but usually they are sterile, having developed without an  embryo (35). In healthy, vigorous seeds, the embryo extends the  full length of the seed.

    Eastern hemlock is one of the most frequent cone producers among the  eastern conifers. Good or better cone crops occur 61 percent of the years,  based on 32 years of observation in Wisconsin (13,29,37). Successive  good or better cone crops did occur for one 5-year period and successive  poor cone crops for a maximum of only 2 years. Excellent cone production  has been reported for trees more than 450 years of age (35).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Flowering and Fruiting

Flowering in eastern hemlock is  monoecious with the flowers in separate clusters on the same branch.  Beginning about age 15, male strobili arise from short-stalked  light-yellow flower clusters in the axis of needles from the preceding  year; they are then surrounded by bud scales to form the male conelet. The  shorter ovulate flowers develop on the terminals of the previous year's  branchlets and develop into erect conelets. Two ovules occur on each of  the bracts. The time of flowering ranges from late April to early June,  depending on the locality and season.

    Pollen usually is dispersed by the wind beginning about 2 weeks after  leaf buds burst, when the bracts on the female conelet are partially open  (28,29,35). At the close of pollination receptivity, the conelets are in a  drooping position and the cone scales reclose. Fertilization is complete  in about 6 weeks. During this period the pollen is extremely sensitive to  drying, often the cause of seed failure (28). Cones reach full size in  late August to early September, about the same time as the winter buds  begin to form. Cones open fully in mid-October, and seed dispersal extends  into the winter. Opened cones may persist on the trees for slightly more  than 1 year.

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

Source: Silvics of North America

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Growth

Growth and Yield

Because early growth of eastern hemlock is so  slow, trees less than 2.5 cm (1 in) in d.b.h. may be as old as 100 years  and 5 to 8 cm (2 to 3 in) saplings may be 200 years old (34). Growth  during the pole stage also tends to be slow, mainly because of crowding  and overstory suppression. One 26 cm (10.3 in) tree in a dense stand, for  example, was 359 years old. Other trees of the same age in the dominant  portion of the stand ranged from 61 to 91 cm (24 to 36 in) in d.b.h.   Although many trees may be suppressed for as long as 200 years, they  retain good stem form and live crown ratios.

    Mature eastern hemlock trees attain relatively large diameters and  height as well as retaining excellent stem form. The record age is  reported to be 988 years, largest diameter 213 cm (84 in), and maximum  height 49 m (160 ft) (34). In typical stands, however, ages approaching  400 years, diameters of 89 to 102 cm (35 to 40 in), and heights in excess  of 30 m (100 ft) are most common (table 1). "Accurate site index  curves are not available for hemlock because most dominant trees have been  suppressed during their early years, a result of the species' rigid  overstory requirements for successful natural regeneration."

    Table 1- Average dimensions of dominant eastern hemlock  trees at selected locations            Southern Appalachians  Michigan  New York                  Age  D.b.h.  Height  D.b.h.  Height  D.b.h.  Height            yr  cm  m  cm  m  cm  m        40    23  16  14  13  11  12        60    33  22  24  19  19  18        80    43  26  33  23  27  22      100    52  30  41  26  35  26      120    62  33  49  28  43  28      140    71  35  57  29  52  30      160    81  37  65  30  61  31      180    91  38  -  -  70  -      200  100  39  -  -  78  -      yr  in  ft  in  ft  in  ft        40    9.0    53    5.7    42    4.4    39        60  13.1    71    9.4    62    7.4    58        80  16.9    86  12.8    76  10.5    73      100  20.6    98  16.1    85  13.8    84      120  24.3  107  19.4    91  17.1    91      140  28.0  114  22.6    96  20.4    97      160  31.9  120  25.7  100  23.9  102      180  35.7  125  -  -  27.4  -      200  39.5  129  -  -  30.9  -              Yields of eastern hemlock tend to be higher than in most forest types  except for white pine and red pine (Pinus resinosa). In New  England, hemlock stands have about twice the volume of oak stands at 80  years of age but only from 50 to 60 percent of the volume of white pine  stands at the same age (35). In northeastern Wisconsin on a typical loam  podzol, well stocked hemlock and yellow birch stands attain volumes of 154  m³/ha (11,000 fbm) by age 110. On heavier soils, hemlock stands with  a mixture of hardwoods reach volumes of 217 m³/ha (15,500 fbm) at 100  years. In pure, older stands gross volumes are reported in excess of 322 m³/ha  (23,000 fbm) in Wisconsin and more than 560 m³/ha (40,000 fbm) in New  England, but cull percent tends to increase rapidly in large diameter  trees (31,35).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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Molecular Biology and Genetics

Genetics

Seedlings grown from 30 seed sources throughout the range showed a  pattern of clinal variation in photoperiodic response. However, many  species change abruptly when isolated on the basis of physiographic  features (35).

    Comparison of an outlier source with one from Wisconsin indicated that  races of eastern hemlock differ in physiological and morphological  characteristics associated with locality (7). No further studies have been  reported on the genetics of eastern hemlock and no superior trees have  been selected.

    The primary effort in genetic research is propagation of variants for  ornamental purposes. At least 280 clones are recorded as being variants,  ranging from prostrate to weeping forms (11).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
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R. M. Godman

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Molecular Biology

Barcode data: Tsuga canadensis

The following is a representative barcode sequence, the centroid of all available sequences for this species.


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Statistics of barcoding coverage: Tsuga canadensis

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
NT
Near Threatened

Red List Criteria

Version
3.1

Year Assessed
2013

Assessor/s
Farjon, A.

Reviewer/s
Stritch, L. & Thomas, P.

Contributor/s

Justification
This very widespread and abundant species occurs in many forests and woods. In parts of its range, mainly the southwest, dieback that is caused by an invasive alien insect pest is spreading. This causes the flagging of this species as Near Threatened (close to qualifying under criterion A4ae). Whether this pest is moving the species closer to extinction in the near future is uncertain as there is past (prehistoric) evidence of great fluctuations of Tsuga canadensis that were possibly caused by pest outbreaks, from which it recovered.
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National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N4 - Apparently Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

Reasons: Hemlock is widespread and still abundant in the northern portion of its range, but being killed by the hemlock woolly adelgid, an exotic insect pest, especially in the southeastern portion of its range. It is still unclear whether the adelgid will spread throughout the entire range of eastern hemlock, but in 2002 the insect had established in about one-half of its range and as far north as New Hampshire (USFS 2002). Isolated infestations have been discovered and treated in Maine and Michigan (Onken 2001). Eastern Hemlock is widespread and abundant in Canada.

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Status

Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status and wetland indicator values.

Public Domain

USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Population

Population
Locally common. Much rarer in the southwestern part of its range. A significant decline is occurring in some parts of its range but this has not yet reached the thresholds for a threatened category.

Population Trend
Decreasing
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Global Short Term Trend: Decline of 30 to >90%

Comments: Being killed by an exotic insect pest (hemlock wooly adelgid) in large portions of its range, particularly in the mid-Atlantic area and central Appalachians. In 2002, the adelgid is documented to be established in about half of eastern hemlock's range. The adelgid is established from New Hampshire to South Carolina and as far west as West Virginia (USFS 2002).

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Threats

Major Threats
An introduced insect pest, the Hemlock Woolly Adelgid (Adelges tsugae) is causing substantial dieback in many areas, expanding from Virginia where it was apparently introduced in 1951 to the north and east. It has not yet reached the main area of occupancy around the Great Lakes. Moderating temperatures associated with climate change could allow the spread of this pest into areas where it has so far been prevented from infesting due to low winter temperatures.
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Comments: A serious threat appears to be the hemlock woolly adelgid, an insect that is believed to have originated in Asia. "During the last decade, it has become a major killer of Canadian and Carolina hemlocks in forests from Maine to Virginia" (Cohn, 1993). Once established the adelgid is a chronic problem and trees that are attacked can die in several years (Souto and Shields 1999). A related threat is "pre-emptive logging" which may be occurring well outside the insect's present range (Foster 1999).

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Management

Conservation Actions

Conservation Actions
This species is present in many protected areas. Control of the insect pest Adelges tsugae is the main priority and is being researched. Pest control in wild populations is difficult because of negative environmental effects of spraying from airplanes with insecticides.
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Management considerations

More info for the terms: cover, selection, series, tree

Multiple removal cuttings are the best method for regenerating eastern
hemlock.  Suddenly released seedlings often die, and a series of
removals releases hemlock more slowly [28].  On moist sites, a two-cut
shelterwood system leaving about 50 percent cover may be adequate.  On
drier sites, a three-cut system is appropriate, initially leaving 70 to
80 percent crown cover and 50 percent after the second cut [62].  If too
few residual trees are left, they may die when exposed, and they are
subject to windthrow [28].  Scarification of seedbeds and removal of
competing hardwoods may be necessary [20].  Eastern hemlock regeneration
must be at least sapling size when released if it is to compete
successfully with uncontrolled hardwoods [29].  Single tree selection is
also an effective method to harvest and regenerate eastern hemlock [62].

Effective reproduction may be absent in areas with high deer populations
[3,10].  Regeneration in the Porcupine Mountains in Michigan has
declined over the last several decades because of white-tailed deer
browsing in the winter [17].  In the Allegheny National Forest in
Pennsylvania, the eastern hemlock-northern hardwoods forest type covered
83.4 percent of the land in 1800 and only 15.8 percent in 1986.
Extensive harvesting, fire, and overbrowsing are responsible for the
decline [64].

Numerous insects attack eastern hemlock, but only a few are of economic
importance cause sporadic or local mortality [62].  Mortality
usually occurs following complete defoliation by insects [43,62].

Eastern hemlock seedlings are sensitive to damping-off fungi, root rots,
and stem and needle rusts [20].

Eastern hemlock appears to be resistant to ozone [21].
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 17.  Frelich, Lee E.; Lorimer, Craig G. 1985. Current and predicted long-term        effects of deer browsing in hemlock forests in Michigan, USA. Biological        Conservation. 34: 99-120.  [14264]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 21.  Hacker, David; Renfro, James. 1992. Great Smoky Mountain plants studied        for ozone sensitivity. Park Science. 12(1): 6-7.  [17788]
  • 28.  Kelty, Matthew J. 1987. Shelterwood cutting as an even-aged reproduction        method. In: Nyland, Ralph D., editor. Managing northern hardwoods:        Proceedings of a silvicultural symposium; 1986 June 23-25; Syracuse, NY.        Faculty of Forestry Miscellaneous Publication No. 13 (ESF 87-002);        Society of American Foresters Publication No. 87-03. Syracuse, NY: State        University of New York, College of Environmental Science and Forestry:        128-142.  [10653]
  • 29.  Kelty, Matthew J. 1988. Sources of hardwood regeneration and factors        that influence these sources. In: Smith, H. Clay; Perkey, Arlyn W.;        Kidd, William E., Jr., eds. Guidelines for regenerating Appalachian        hardwood stands: Workshop proceedings; 1988 May 24-26; Morgantown, WV.        SAF Publ. 88-03. Morgantown, WV: West Virginia University Books: 17-30.        [13931]
  • 3.  Anderson, Roger C.; Loucks, Orie L. 1979. White-tail deer (Odocoileus        virginianus) influence on structure and composition of Tsuga canadensis        forests. Journal of Applied Ecology. 16: 855-861.  [20403]
  • 43.  Jones, Steven M. 1989. Application of landscape ecosystem classification        in identifying productive potential of pine-hardwood stands. In:        Waldrop, Thomas A., ed. Proceedings of pine-hardwood mixtures: a        symposium on management and ecology of the type; 1989 April 18-19;        Atlanta, GA. Gen. Tech. Rep. SE-58. Asheville, SC: U.S. Department of        Agriculture, Forest Service, Southeastern Forest Experiment Station:        64-69.  [10259]
  • 62.  Wendel, G. W.; Della, Bianca, Lino; Russell, James; Lancaster, Kenneth        F. 1983. Eastern white pine including eastern hemlock. In: Burns,        Russell M., tech. comp. Silvicultural systems for the major forest types        of the United States. Agric. Handb. 445. Washington, DC: U.S. Department        of Agriculture, Forest Service: 131-134.  [20409]
  • 64.  Whitney, G. G. 1990. The history and status of the hemlock-hardwood        forests of the Allegheny Plateau. Journal of Ecology. 78: 443-458.        [13277]

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Cultivars, improved and selected materials (and area of origin)

These plant materials are readily available from commercial sources. Contact your local Natural Resources Conservation Service (formerly Soil Conservation Service) office for more information. Look in the phone book under ”United States Government.” The Natural Resources Conservation Service will be listed under the subheading “Department of Agriculture.”

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Eastern hemlock generally does not tolerate nutrient-poor soils, wet soils or poorly drained sites, prolonged drought, prolonged heat, sun scorch, windy and exposed sites, aerial pollution, or winter salt spray. Drought is probably the most serious damaging agent to the species, especially during the seedling stage. Damping-off fungi and root rots also are seriously damaging to young plants. Containerized plants are best for transplanting – move into sites that are cool, well-drained, and wind-protected, in partial sun to partial shade. Good drainage is essential for transplant success -- the porosity of the soil should be improved with peat moss or sand, with the root ball elevated about 2" to 4" above the surrounding soil grade.

A shallow root system makes trees highly susceptible to wind-throw when exposed through timber cutting or planted in open sites. Plants should be staked for the first two or three years following transplant, to prevent wind-throw. Saplings and small trees are highly susceptible to damage from fire because of the thin bark, and root injury often occurs from high intensity fires because of heavy litter concentration.

The most severe insect pest is the Asian hemlock woolly adelgid, a phloem-feeding insect that causes branch dieback and tree decline. Trees typically die after several years of adelgid infestation.

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Relevance to Humans and Ecosystems

Benefits

Cover Value

More info for the term: cover

Eastern hemlock provides cover to ruffed grouse, wild turkey, fishers,
and other wildlife [4,20].  It provides excellent thermal protection and
snowfall interception for moose and white-tailed deer in the winter
[2,17].
  • 17.  Frelich, Lee E.; Lorimer, Craig G. 1985. Current and predicted long-term        effects of deer browsing in hemlock forests in Michigan, USA. Biological        Conservation. 34: 99-120.  [14264]
  • 2.  Allen, Arthur W.; Jordan, Peter A.; Terrell, James W. 1987. Habitat        suitability index models: moose, Lake Superior region. Biol. Rep. 82        (10.155). Washington, DC: U.S. Department of the Interior, Fish and        Wildlife Service. 47 p.  [11710]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 4.  Arthur, Stephen M.; Krohn, William B.; Gilbert, James R. 1989. Habitat        use and diet of fishers. Journal of Wildlife Management. 53(3): 680-688.        [8671]

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Palatability

More info for the term: hardwood

In the winter, eastern hemlock browse is moderately preferred by moose
and highly preferred by white-tailed deer [2,10].  In the summer,
white-tailed deer prefer hardwood sprouts and seedlings to eastern
hemlock [44].  The seeds of eastern hemlock are not as preferred by
white-footed mice, red-backed voles, and meadow voles as red pine (Pinus
resinosa) and white pine seeds [1].
  • 1.  Abbott, Herschel G. 1962. Tree seed preferences of mice and voles in the        Northeast. Journal of Forestry. 60: 97-99.  [20402]
  • 10.  Curtis, John T. 1959. The vegetation of Wisconsin. Madison, WI: The        University of Wisconsin Press. 657 p.  [7116]
  • 2.  Allen, Arthur W.; Jordan, Peter A.; Terrell, James W. 1987. Habitat        suitability index models: moose, Lake Superior region. Biol. Rep. 82        (10.155). Washington, DC: U.S. Department of the Interior, Fish and        Wildlife Service. 47 p.  [11710]
  • 44.  Moore, William H.; Johnson, Frank M. 1967. Nature of deer browsing on        hardwood seedlings and sprouts. Journal of Wildlife Management. 31(2):        351-353.  [16394]

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Importance to Livestock and Wildlife

Dense stands of eastern hemlock provide excellent wildlife habitat [20].
Cove forests in the southern Appalachian Mountains provide nesting
habitat for many species of birds.  The black-throated blue warbler,
black-throated green warbler, and blackburnian warbler are especially
abundant in virgin eastern hemlock cove forests [25].

Large eastern hemlocks can be climbed by small black bear cubs.  In
northeastern Minnesota, black bear mothers and cubs spent more than 95
percent of the time in April and May within 600 feet (183 m) of either
an eastern hemlock or an eastern white pine (Pinus strobus) larger than
20 inches (51 cm) in d.b.h. [50].

Eastern hemlock has high cavity value for wildlife [12].  Large hollow
trees are commonly used as dens by black bears [49].

The seeds are eaten by birds and mammals [13], and in the winter the
foliage is browsed by white-tailed deer, moose, and snowshoe hares
[2,59].
  • 12.  DeGraaf, Richard M; Shigo, Alex L. 1985. Managing cavity trees for        wildlife in the Northeast. Gen. Tech. Rep. NE-101. Broomall, PA: U.S.        Department of Agriculture, Forest Service, Northeastern Forest        Experiment Station. 21 p.  [13481]
  • 13.  Duncan, Wilbur H.; Duncan, Marion B. 1988. Trees of the southeastern        United States. Athens, GA: The University of Georgia Press. 322 p.        [12764]
  • 2.  Allen, Arthur W.; Jordan, Peter A.; Terrell, James W. 1987. Habitat        suitability index models: moose, Lake Superior region. Biol. Rep. 82        (10.155). Washington, DC: U.S. Department of the Interior, Fish and        Wildlife Service. 47 p.  [11710]
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 25.  Hooper, Robert G. 1978. Cove forests:  bird communities and management        options. In: DeGraaf, Richard M, technical coordinator. Proceedings of        the Workshop Management of Southern Forests for Nongame Birds; 1978        January 24 - January 26; Atlanta, GA. Gen. Tech. Rep. SE-14. Asheville,        NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest        Experiment Station: 90-97.  [17951]
  • 49.  Rogers, Lynn L.; Allen, Arthur W. 1987. Habitat suitability index        models: Black bear, upper Great Lakes region. Biol. Rep. 82 (10.144).        Washingtion D. C.: U.S. Department of the Interior, Fish and Wildlife        Service. 54 p.  [11711]
  • 50.  Rogers, Lynn L.; Wilker, Gregory A.; Scott, Sally S. 1990. Managing        natural populations of black bears in wilderness. In: Lime, David W.,        ed. Managing America's enduring wilderness resource: Proceedings of the        conference; 1989 September 11-17; Minneapolis, MN. St. Paul, MN:        University of Minnesota, Minnesota Extension Service; Minnesota        Agricultural Experiment Station: 363-366.  [15409]
  • 59.  Telfer, Edmund S. 1972. Browse selection by deer and hares. Journal of        Wildlife Management. 36(4): 1344-1349.  [12455]

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Wood Products Value

Eastern hemlock wood is of low value because of brittleness and abundant
knots [26].  It is used for pulp, light framing, sheathing, roofing,
subflooring, and boxes and crates [20].
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 26.  Hosie, R. C. 1969. Native trees of Canada. 7th ed. Ottawa, ON: Canadian        Forestry Service, Department of Fisheries and Forestry. 380 p.  [3375]

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Other uses and values

From 1880 to 1930, eastern hemlock was extensively harvested for its
bark which is a source of tannin [64]. 

Eastern hemlock is planted as an ornamental [20].
  • 20.  Godman, R. M.; Lancaster, Kenneth. 1990. Tsuga canadensis (L.) Carr.        eastern hemlock. In: Burns, Russell M.; Honkala, Barbara H., technical        coordinators. Silvics of North America. Volume 1. Conifers. Agric.        Handb. 654. Washington, DC: U.S. Department of Agriculture, Forest        Service: 604-612.  [13421]
  • 64.  Whitney, G. G. 1990. The history and status of the hemlock-hardwood        forests of the Allegheny Plateau. Journal of Ecology. 78: 443-458.        [13277]

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Special Uses

Lumber production from eastern hemlock reached its peak between 1890 and  1910. Primary uses were in light framing, sheathing, roofing, subflooring,  boxes, crates, and general millwork. Much of the present production is  used in pulping or newsprint and wrapping papers, but the demand for  hemlock lumber appears to be increasing again.

    Currently, eastern hemlock stands are considered essential for shelter  and bedding of white-tailed deer during the winter. In regions of marked  reductions in type area, many public agencies have restricted cutting  until reliable methods of regenerating the stand become operational (6).  The type also is considered important as cover for ruffed grouse, turkeys,  and many other animals.

    Eastern hemlock often is planted as an ornamental because of its  relative freedom from insects and disease, good foliage color, and  adaptability to shearing. Some effort is being made to plant the species  under forest conditions because it is so important to wildlife.

    Tannin from the bark of eastern hemlock formerly was extracted for use  in processing leather. Now synthetic and important products are used and a  once prosperous industry has been eliminated (19).

  • Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods.   Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965).   U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp.   http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm External link.
Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

R. M. Godman

Source: Silvics of North America

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Uses

Industry: Eastern hemlock was early valued for its bark, an important source of tannin for the leather industry. Trees were felled and stripped of their bark, which was then milled for tannin extraction. To simplify stripping the bark and turning the logs, trees were often felled into lakes. Many of these logs were much later extracted from northern lakes and milled.

The wood has been used for light framing, roofing, boxes and crates, and pulping, but it tends to be brittle and eastern hemlock is not presently important as a timber tree. Commercial stands have been greatly reduced by prior harvesting and lack of restocking.

Ethnobotanic: American Indians used the cambium as the base for breads and soups or mixed it with dried fruit and animal fat for pemmican. Natives and white settlers also made tea from hemlock leaves, which have a high vitamin C content.

Conservation: Eastern hemlock can be used as a specimen, screen, or group planting, and it can be sheared over time into a formal evergreen hedge, which is densely leafy all the way to the ground (due to its full shade tolerance), although as a hedge it must be repeatedly pruned to keep it in size. It has a naturally open growth habit – if bought with a dense canopy effect, it may have been repeatedly sheared at the nursery (or Christmas tree farm).

Numerous cultivars of eastern hemlock have been developed, including compact shrubs, dwarfs, form mutants (weeping, fastigiate, prostrate, etc.), color mutants (variegated), and graceful trees. The wild type apparently also is common in cultivation. Eastern hemlock stands are considered important as shelter and cover for white-tailed deer and other wildlife species, such as turkey, ruffed grouse, and others.

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USDA NRCS National Plant Data Center & the Biota of North America Program

Source: USDA NRCS PLANTS Database

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Wikipedia

Tsuga canadensis

Tsuga canadensis, also known as eastern hemlock 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.[2]

Description[edit]

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.[3] The tree generally reaches heights of about 31 meters (100 feet),[2] but exceptional trees have been recorded up to 53 metres (173 feet).[4] 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).[5] The trunk is usually straight and monopodial, but very rarely is forked.[6] The crown is broadly conic, while the brownish bark is scaly and deeply fissured, especially with age.[2] 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 1.5 to 2.5 mm (0.05 to 0.1 inches) in length. These are usually not resinous, but may be slightly so.[2][6]

The leaves are typically 15 to 20 mm (0.6 to 0.9 inches) in length, but may be as 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 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 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. Twenty-four diploid chromosomes are present within the trees' DNA.[2][6]

Wood[edit]

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.[7]

Distribution and habitat[edit]

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,[6] 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 Alabama.[2] Disjunct populations occur in the southeastern Piedmont, western Ohio and into Illinois, as well as eastern Minnesota.[6][8] 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 Florida.[2] Its range completely overlaps that of the closely related Tsuga caroliniana.[9]

It is found primarily on rocky ridges, ravines and hillsides with relatively high levels of moisture.[2]

Climate[edit]

Eastern hemlock is generally confined to areas with cool and humid climates. Precipitation in the areas where it grows is typically 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; 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 1520 mm (60 inches). In the north of its range, the temperatures in January average -12°C, while in July they average only 16°C. 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.[9]

Hemlock boughs in the autumn, shedding older foliage.

Hemlock woolly adelgid[edit]

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 1960s.[10] 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. It is through Tsuga Search that hemlocks have been found with trunk volumes of up to 44.8 m³ within the Park,[11] 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 range.[12]

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. 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."[13]

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 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 detected.[14]

Paleoecology[edit]

The mid-Holocene decline of hemlock populations is a much-studied phenomenon.[15] 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 range.[16] 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.[15][17] 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[edit]

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 metres (173 ft) tall, though this tree is now dead from hemlock woolly adelgid; the tallest now surviving, the "Noland Mountain tree", is 51.8 metres (170 ft) tall.[11] 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 0.75–1.8 metres (2 ft 6 in–5 ft 11 in), with trees over 1.6 metres (5 ft 3 in) diameter being very rare. In New England, the maximum diameter is 1.4 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 44.8 m³,[11] 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[edit]

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.[18] 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.[19] 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.[19][20] In Germany, it is the most frequently seen hemlock in cultivation, and is also used in forestry.[21]

Cultivars[edit]

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:[18][22]

  • 'Beehive' – a very small dwarf shrub typically growing to 1 m high and 1.5 m wide, resembling a spreading beehive in form
  • 'Bennett' – a dwarf shrub reaching 1 m high and 1.5 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 1.3 m spread, with the central stems eventually becoming visible. It also prefers partial shade.
  • 'Gentsch White' – a dwarf shrub growing to 1.3 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 1.5 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 Merit.[23]
  • 'Pendula' – an upright weeping form whose height is dependent on how long it is staked, but is typically seen 0.6–1.5 m tall with a 1.5 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.

References[edit]

  1. ^ "Tsuga canadensis". NatureServe Explorer. NatureServe. Retrieved 2007-07-05. 
  2. ^ a b c d e f g h Taylor, Ronald J. (1993), "Tsuga canadensis", in Flora of North America Editorial Committee (eds.), Flora of North America 2, Oxford University Press 
  3. ^ Gove, J.H.; Fairweather, S.E. (1988), "Tree-ring analysis of a 500-year old hemlock in central Pennsylvania", U.S. Forest Service General Technical Report NC-120 1, pp. 483–489 
  4. ^ Blozan, Will (February 16, 2007), The Usis Hemlock Climb, retrieved 2007-06-08 
  5. ^ Blozan, Will (December 18, 2006), The Laurel Branch Leviathan Climb, retrieved 2007-06-08 
  6. ^ a b c d e Farjon, A. (1990). Pinaceae. Drawings and Descriptions of the Genera. Koeltz Scientific Books ISBN 3-87429-298-3.
  7. ^ Collingwood, C.H. 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.)
  8. ^ 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, U.S. Geological Survey, retrieved 2007-07-05 
  9. ^ a b Godman and, R. M.; Lancaster, K. (December 1990). "Tsuga canadensis, Eastern Hemlock". Silvics of Forest Trees of the United States, Volume 1. United States Department of Forestry. Retrieved 2007-07-05. 
  10. ^ McClure, M. S. (1987), Biology and control of hemlock woolly adelgid, Bulletin of the Connecticut Agricultural Experiment Station 851: 1–9, retrieved October 24, 2011 
  11. ^ a b c Gymnosperm Database: Tsuga canadensis
  12. ^ Conifer Specialist Group (1998). Tsuga canadensis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
  13. ^ Hemlock Trees Dying Rapidly, Affecting Forest Carbon Cycle
  14. ^ Predator Beetle to Battle Hemlock Pest
  15. ^ a b Oswald, W. W.; Foster, D. R. (8 August 2011). "Middle-Holocene dynamics of Tsuga canadensis (eastern hemlock) in northern New England, USA". The Holocene 22 (1): 71–78. doi:10.1177/0959683611409774. Retrieved 6 March 2013. 
  16. ^ Delcourt, Hazel R.; Delcourt, Paul A. (1991). Quaternary Ecology: a Paleoecological Perspective (1st ed.). London: Chapman and Hall. pp. 43–44. ISBN 0412297906. 
  17. ^ 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:10.1177/0959683610365932. Retrieved 6 March 2013. 
  18. ^ a b "Tsuga canadensis". UConn Plant Database. University of Connecticut. Retrieved 19 August 2013. 
  19. ^ a b Mitchell, A. F. (1974). A Field Guide to the Trees of Britain and Northern Europe. Collins ISBN 0-00-212035-6
  20. ^ Mitchell, A. F. (1972). Conifers in the British Isles. Forestry Commission Booklet 33.
  21. ^ (German) Schmeil, O., Fitschen, J., & Seybold, S. (2006). Flora von Deutschland 93. Auflage, p. 424. Quelle & Meyer Verlag, Wiebelsheim. ISBN 3-494-01413-2.
  22. ^ Welch, H., & Haddow, G. (1993). The World Checklist of Conifers. Landsman's. ISBN 0-900513-09-8.
  23. ^ "Tsuga canadensis 'Jeddeloh' AGM". Royal Horticultural Society. Retrieved 14 February 2013. 
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Notes

Comments

Numerous cultivars of Tsuga canadensis have been developed, including compact shrubs, dwarfs, and graceful trees. Wood of the species tends to be brittle and inferior to that of the other North American hemlocks. 

 Eastern hemlock ( Tsuga canadensis ) is the state tree of Pennsylvania.

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Source: Missouri Botanical Garden

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Names and Taxonomy

Taxonomy

The currently accepted scientific name for eastern hemlock is Tsuga
canadensis (L.) Carr. [35]. Fernald [15] recognizes a dwarf form, T.
canadensis forma parvula Vict. and Rousseau, that grows in mats up to 3
feet (1 m) high in Quebec and New England.
  • 15.  Fernald, Merritt Lyndon. 1950. Gray's manual of botany. [Corrections        supplied by R. C. Rollins]
  • 35.  Little, Elbert L., Jr. 1979. Checklist of United States trees (native        and naturalized). Agric. Handb. 541. Washington, DC: U.S. Department of        Agriculture, Forest Service. 375 p.  [2952]

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Common Names

eastern hemlock
Canada hemlock
hemlock spruce

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