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Overview

Brief Summary

Pinaceae -- Pine family

    Joseph E. Means

    Mountain hemlock (Tsuga mertensiana) is usually found on cold,  snowy subalpine sites where it grows slowly, sometimes attaining more than  800 years in age. Arborescent individuals that have narrowly conical  crowns until old age (300 to 400 years) and shrubby krummholz on cold,  windy sites near timberline add beauty to mountain landscapes. Taylor and  Taylor (76) thoroughly describe its form. Uses of its moderately strong,  light-colored wood include small-dimension lumber and pulp.

  • 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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Joseph E. Means

Source: Silvics of North America

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Distribution

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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© NatureServe

Source: NatureServe

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Mountain hemlock occurs along the crest of the Sierra Nevada; the Coast
Ranges and Cascade Range in Oregon; the Cascade Range and Olympic
Mountains in Washington; the northern Rocky Mountains in Idaho and
western Montana; the Insular, Coast, and Columbia mountains in British
Columbia; and in southeast and south-central Alaska [4,8,32,46]. In
California it is also locally abundant in the Klamath Mountains. The
extreme southern limit of mountain hemlock is near Silliman Lake in
Tulare County, California [32].
  • 32. Griffin, James R.; Critchfield, William B. 1972. The distribution of forest trees in California. Res. Pap. PSW-82. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 118 p. [1041]
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 46. 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]
  • 8. Atzet, Tom; Wheeler, David; Riegel, Gregg; [and others]. 1984. The mountain hemlock and Shasta red fir series of the Siskiyou Region of southwest Oregon. FIR Report. 6(1): 4-7. [9486]

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Regional Distribution in the Western United States

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

1 Northern Pacific Border
2 Cascade Mountains
4 Sierra Mountains
8 Northern Rocky Mountains

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Occurrence in North America

AK CA ID MT OR WA AB BC

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Mountain hemlock grows from Sequoia National Park in California (lat. 36°  38' N.) (62) to Cook Inlet in Alaska (lat. 61° 25' N.) (83). It grows  along the crest of the Sierra Nevada in California (31); the Cascade Range  in Oregon; the Cascade Range and Olympic Mountains in Washington; the  northern Rocky Mountains in Idaho and western Montana; the Insular, Coast,  and Columbia Mountains in British Columbia; and in southeast and  south-central Alaska.

     
- The native range of mountain 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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Joseph E. Means

Source: Silvics of North America

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Physical Description

Morphology

Description

Trees to 40m; trunk to 1.5m diam.; crown conic. Bark charcoal gray to reddish brown, scaly and deeply fissured. Twigs yellow-brown, glabrous to densely pubescent. Buds oblong, 3--4mm. Leaves 10--25(--30)mm, mostly spreading in all directions from twigs, curved toward twig apex, thickened centrally along midline, somewhat rounded or 4-angled in cross section, both surfaces glaucous, with ±inconspicuous stomatal bands; margins entire. Seed cones oblong-cylindric, 3--6 ´ 1.5--3cm; scales broadly fan-shaped, 8--l5 ´ 8--15mm, apex rounded to pointed. 2 n =24.
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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

Source: Missouri Botanical Garden

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Description

More info for the terms: shrub, tree

Mountain hemlock is a native, slow-growing, coniferous, evergreen tree
usually 75 to 100 feet (23-30 m) tall and 2.5 to 3.5 feet (0.8-1 m) in
diameter [59]. However, it takes on a variety of growth forms to adapt
to subalpine conditions. Below 4,000 feet (1219 m) in the Coast Ranges,
it grows in dense stands reaching diameters of 3 to 4 feet (0.8-0.9 m)
and heights up to 150 feet (46 m) [4]. On exposed ridges at high
elevations, it often grows as a low-spreading shrub or small tree
[38,4].

In the open, mountain hemlock develops a strongly tapered trunk bearing
slender branches almost to the ground; the branches usually droop and
often have ascending tips. The outline of the crown is narrowly conical
beneath a slender drooping leader. Crowns of old trees are often bent
or twisted. In dense stands, the crown covers only the upper half or
less of the tree, and the trunk below develops with a more gradual
taper, and becomes virtually clear of branches [38]. The twigs are
mostly short and slender. The needles are crowded on all sides of short
twigs and curved upward [4].

The bark is thick and deeply furrowed into scaly plates on old trees
[44,72]. The bark is early broken and rough on young trees [59]. The
root system is shallow and widespreading [38,49,59].
  • 38. Hosie, R. C. 1969. Native trees of Canada. 7th ed. Ottawa, ON: Canadian Forestry Service, Department of Fisheries and Forestry. 380 p. [3375]
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 44. Lackschewitz, Klaus. 1991. Vascular plants of west-central Montana--identification guidebook. Gen. Tech. Rep. INT-227. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 648 p. [13798]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 59. Preston, Richard J., Jr. 1948. North American trees. Ames, IA: The Iowa State College Press. 371 p. [1913]
  • 72. Weetman, G.; Vyse, A. 1990. Natural regeneration. In: Lavender, D. P.; Parish, R.; Johnson, C. M.; [and others], eds. Regenerating British Columbia's forests. Vancouver, BC: University of British Columbia Press: 118-129. [10711]

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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 entire (use magnification), Leaf apex obtuse, Leaves < 5 cm long, Leaves < 10 cm long, Leaves not blue-green, Needle-like leaves flat, Needle-like leaves somewhat rounded, 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, 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 mertensiana Bongard, Mém. Acad. Imp. Sci. St. Pétersbourg, Sér. 6., Sci. Math. 2: 163. 1832; Abies hookeriana A.Murray bis; A. pattoniana A.Murray bis; Hesperopeuce mertensiana (Bongard) Rydberg; H. pattoniana (A.Murray bis) Lemmon; Picea (Tsuga) hookeriana (A.Murray bis) Bertrand; Pinus hookeriana (A.Murray bis) McNab; Pinus pattoniana (A.Murray bis) Parlatore; Tsuga crassifolia Flous; T. hookeriana (A.Murray bis) Carrière; T. pattoniana var. hookeriana (A.Murray bis) Lemmon; ´Tsuga-Picea hookeriana (A.Murray bis) M.Van Campo-Duplan and Gaussen.
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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

Source: Missouri Botanical Garden

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Tsuga mertensiana is a subalpine species, occurring from near sea level in Alaska to 1,500 m a.s.l. along the coast; in the Cascade Range between 1,200 m and 2,100 m a.s.l., and in the Sierra Nevada (subsp. grandicona) between 1,800 m and 3,350 m a.s.l. It grows on a variety of non-calcareous acidic soils, sometimes on peat, more commonly on mor humus (pH 3.1-3.9). Subsp. mertensiana is restricted to a climatic zone with high precipitation, in British Columbia between 2,000 mm and 4,000 mm per year, with long, snowy winters and short, cool summers. Subsp. grandicona grows in a much drier climate, but there primarily on high, N-facing slopes. The species is a major component of the Mountain Hemlock-Subalpine Fir forest, occurring in pure stands or mixed with Abies lasiocarpa, locally also with A. amabilis, Picea glauca, P. sitchensis, P. engelmannii (Rocky Mts.), Pinus spp., Tsuga heterophylla, Xanthocyparis nootkatensis, Juniperus occidentalis, and Betula papyrifera.

Systems
  • Terrestrial
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© International Union for Conservation of Nature and Natural Resources

Source: IUCN

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Habitat characteristics

More info for the terms: marsh, organic soils, series

Mountain hemlock is commonly found on cold, snowy subalpine or boreal
sites where it grows slowly, sometimes reaching more than 800 years of
age. Though pure stands are less common than mixed stands, extensive
pure stands of mountain hemlock do occur in Alaska and in the central
high Cascades of Oregon [49]. In the Siskiyous, mountain hemlock is
generally confined to cool, north-facing, cirquelike topography. It
does not form extensive stands like those in the Cascades because
suitable habitat is found only on the highest peaks. In the Siskiyous,
the lower limit of mountain hemlock is governed by high temperatures and
competition with Shasta red fir (Abies magnifica shastensis) [8].
Mountain hemlock in western Montana is generally confined to the moist,
upper slopes of the Bitterroot Mountains [33].

Elevational range: The elevational range of mountain hemlock has been
recorded as follows [8,49]:

Alaska - 0 to 3,500 feet (0-1,067 m)
southern British Columbia - 1,000 to 3,000 feet (300-900 m)
northern Washington - 4,200 to 5,600 feet (1,300-1,700 m)
Rocky Mountains - 5,100 to 6,900 (1,550-2,100 m)
southern Oregon - 5,200 to 7,500 (1,600- 2,300 m)
Siskiyous - 4,000 to 7,000 (1,220 - 2,134 m)
northern Sierra Nevada - 7,900 to 10,000 (2,400-3,050 m)
southern Sierra Nevada - 9,050 to 10,000 (2,750-3,500 m)

Climate: Mountain hemlock generally occurs on sites with mild to cold
winters; short, warm to cool growing seasons; and moderate to high
precipitation [49]. Average annual snowfall ranges from about 32 to 50
feet (10-15 m) [4].

Soils: Mountain hemlock grows on soils derived from a wide variety of
parent materials, however, it is rare and stunted on soils derived from
calcareous parent materials in the Selkirk Mountains of British
Columbia. It is found on organic soils in the northern portion of its
range more often than in the southern portion. In Alaska it is found on
organic soils bordering muskegs where it may be a major stand component.
Best development of mountain hemlock is on loose, coarse-textured,
well-drained soils with adequate moisture [49]. In British Columbia
best growth is on thick, very acidic organic matter and decayed wood.
In the Siskiyous, soils in the mountain hemlock series are loam to silt
loam and average 40 inches (100 cm) in depth [7]. Adequate soil
moisture appears to be especially important in California and Montana.
Soils are typically acidic with a pH ranging from 3.4 to 5.0 [49]. In
the Coastal Mountains, mountain hemlock can grow on the rockiest soils,
even including recent lava flows, if moisture is adequate [4]. The
nutritional requirements of mountain hemlock are low [41].

Plant associates: In mixed stands, mountain hemlock usually coexists
with subalpine fir (Abies lasiocarpa), Pacific silver fir, or
Alaska-cedar (Chamaecyparis nootkatensis). In Montana, subalpine fir
and Engelmann spruce (Picea engelmannii) are nearly constant associates
of mountain hemlock [33]. Common understory associates with mountain
hemlock are as follows: beargrass, big huckleberry, grouse
whortleberry, rustyleaf menziesia (Menziesia ferruginea), Cascades
azalea (Rhododendron albiflorum), Alaska huckleberry (V. alaskaense),
ovalleaf huckleberry (V. ovalifolium), long-stoloned sedge (Carex inops
ssp. inops), mertens cassiope (Cassiope mertensiana), copperbush,
mountain heather, deer cabbage, marsh marigold (Caltha biflora), and
skunk cabbage (Lysichitum americanium) [1,19,33,68].
  • 1. Agee, James K.; Kertis, Jane. 1987. Forest types of the North Cascades National Park Service Complex. Canadian Journal of Botany. 65: 1520-1530. [6327]
  • 19. DeMeo, Thomas. 1989. Preliminary forest plant association management guide: Ketchikan Area, Tongass National Forest. [Portland, OR]: [U.S. Department of Agriculture, Forest Service]. 164 p. [19017]
  • 33. Habeck, James R. 1967. Mountain hemlock communities in western Montana. Northwest Science. 41(4): 169-177. [7258]
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 41. Krajina, V. J.; Klinka, K.; Worrall, J. 1982. Distribution and ecological characteristics of trees and shrubs of British Columbia. Vancouver, BC: University of British Columbia, Department of Botany and Faculty of Forestry. 131 p. [6728]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 68. U.S. Department of Agriculture, Forest Service, Alaska Region. [n.d.]. Preliminary forest plant associations of the Stikine Area, Tongass National Forest. R10-TP-72. Portland, OR. 126 p. [19016]
  • 7. Atzet, Thomas; Wheeler, David L. 1982. Historical and ecological perspectives on fire activity in the Klamath Geological Province of the Rogue River and Siskiyou National Forests. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 16 p. [6252]
  • 8. Atzet, Tom; Wheeler, David; Riegel, Gregg; [and others]. 1984. The mountain hemlock and Shasta red fir series of the Siskiyou Region of southwest Oregon. FIR Report. 6(1): 4-7. [9486]

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Key Plant Community Associations

More info for the terms: association, codominant, cover

Mountain hemlock commonly occurs as a dominant or codominant in
high-elevation alpine or subalpine forests. In western Washington and
Oregon, the mountain hemlock zone is the highest forested zone [32].
Mountain hemlock is often codominant with Pacific silver fir (Abies
amabilis) [1,21]. One of the most widespread mountain hemlock
communities is the mountain hemlock-Pacific silver fir/big huckleberry
(Vaccinium membranaceum) type found in British Columbia and the Oregon
and Washington Cascades. In the Rocky Mountains, the mountain
hemlock/beargrass (Xerophyllum tenax) habitat type is generally found on
south slopes and is characterized by a high cover of beargrass with big
huckleberry and grouse whortleberry (V. scoparium) as common associates.
A similar Pacific silver fir-mountain hemlock/beargrass association is
found in Oregon [49]. Published classifications identifying mountain
hemlock as a dominant or codominant are as follows:

Forest types of the North Cascades National Park Service complex [1].
Preliminary plant associations of the Southern Oregon Cascade Mountain
Province [5].
Preliminary plant associations of the Siskiyou Mountain Province [6].
Plant association and management guide for the Pacific silver fir zone [12].
Forest habitat types of northern Idaho: A second approximation [15].
Classification of montane forest community types in the Cedar River
drainage of western Washington, U.S.A. [18].
Preliminary forest plant association management guide. Ketchikan area,
Tongass National Forest [19].
Subalpine plant communities of the western North Cascades, Washington [21].
Alpine and high subalpine plant communities of the North Cascades Range,
Washington and British Columbia [22].
Fire ecology of western Montana forest habitat types [25].
Forest vegetation of the montane and subalpine zones, Olympic Mountains,
Washington [27].
Natural vegetation of Oregon and Washington [29].
The forest communities of Mount Rainier National Park [30].
Plant associations of south Chiloquin and Klamath ranger districts--
Winema National forest [37].
Vegetation and environment in old growth forests of northern southeast
Alaska: a plant association classification [48].
Forest habitat types of Montana [57].
Preliminary classification of forest vegetation of the Kenai Peninsula,
Alaska [61].
Preliminary forest plant associations of the Stikine area, Tongass
National Forest [68].
  • 1. Agee, James K.; Kertis, Jane. 1987. Forest types of the North Cascades National Park Service Complex. Canadian Journal of Botany. 65: 1520-1530. [6327]
  • 12. Brockway, Dale G.; Topik, Christopher; Hemstrom, Miles A.; Emmingham, William H. 1985. Plant association and management guide for the Pacific silver fir zone: Gifford Pinchot National Forest. R6-Ecol-130a. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 122 p. [525]
  • 15. Cooper, Stephen V.; Neiman, Kenneth E.; Roberts, David W. 1991. (Rev.) Forest habitat types of northern Idaho: a second approximation. Gen. Tech. Rep. INT-236. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 143 p. [14792]
  • 18. del Moral, Roger; Long, James N. 1977. Classification of montane forest community types in the Cedar River drainage of western Washington, U.S.A. Canadian Journal of Forest Research. 7: 217-225. [8778]
  • 19. DeMeo, Thomas. 1989. Preliminary forest plant association management guide: Ketchikan Area, Tongass National Forest. [Portland, OR]: [U.S. Department of Agriculture, Forest Service]. 164 p. [19017]
  • 21. Douglas, George W. 1972. Subalpine plant communities of the western North Cascades, Washington. Arctic and Alpine Research. 4(2): 147-166. [9960]
  • 22. Douglas, George W.; Bliss, L. C. 1977. Alpine and high subalpine plant communities of the North Cascades Range, Washington and British Columbia. Ecological Monographs. 47: 113-150. [9487]
  • 25. Fischer, William C.; Bradley, Anne F. 1987. Fire ecology of western Montana forest habitat types. Gen. Tech. Rep. INT-223. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 95 p. [633]
  • 27. Fonda, R. W.; Bliss, L. C. 1969. Forest vegetation of the montane and subalpine zones, Olympic Mountains, Washington. Ecological Monographs. 39(3): 271-301. [12909]
  • 29. Franklin, Jerry F.; Dyrness, C. T. 1973. Natural vegetation of Oregon and Washington. Gen. Tech. Rep. PNW-8. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 417 p. [961]
  • 30. Franklin, Jerry F.; Moir, William H.; Hemstrom, Miles A.; [and others]. 1988. The forest communities of Mount Rainier National Park. Scientific Monograph Series No 19. Washington, DC: U.S. Department of the Interior, National Park Service. 194 p. [12392]
  • 32. Griffin, James R.; Critchfield, William B. 1972. The distribution of forest trees in California. Res. Pap. PSW-82. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment Station. 118 p. [1041]
  • 37. Hopkins, William E. 1979. Plant associations of south Chiloquin and Klamath Ranger Districts--Winema National Forest. R6-Ecol-79-005. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 96 p. [7339]
  • 48. Martin, Jon Randall. 1989. Vegetation and environment in old growth forests of northern southeast, Alaska: a plant association classification. Tempe, AZ: Arizona State University. 221 p. Thesis. [18760]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 5. Atzet, Thomas; McCrimmon, Lisa A. 1990. Preliminary plant associations of the southern Oregon Cascade Mountain Province. Grants Pass, OR: U.S. Department of Agriculture, Forest Service, Siskiyou National Forest. 330 p. [12977]
  • 57. Pfister, Robert D.; Kovalchik, Bernard L.; Arno, Stephen F.; Presby, Richard C. 1977. Forest habitat types of Montana. Gen. Tech. Rep. INT-34. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 174 p. [1878]
  • 6. Atzet, Thomas; Wheeler, David L. 1984. Preliminary plant associations of the Siskiyou Mountain Province. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 278 p. [9351]
  • 61. Reynolds, Keith M. 1990. Preliminary classification of forest vegetation of the Kenai Penninsula, Alaska. Res. Pap. PNW-RP-424. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 67 p. [14581]
  • 68. U.S. Department of Agriculture, Forest Service, Alaska Region. [n.d.]. Preliminary forest plant associations of the Stikine Area, Tongass National Forest. R10-TP-72. Portland, OR. 126 p. [19016]

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Habitat: Ecosystem

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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):

FRES11 Spruce - fir
FRES22 Western white pine
FRES23 Fir - spruce
FRES24 Hemlock - Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES44 Alpine

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Habitat: Cover Types

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

205 Mountain hemlock
206 Engelmann spruce - subalpine fir
207 Red fir
208 Whitebark pine
210 Interior Douglas-fir
212 Western larch
215 Western white pine
218 Lodgepole pine
256 California mixed subalpine

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Habitat: Plant Associations

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

K001 Spruce - cedar - hemlock forest
K002 Cedar - hemlock - Douglas-fir forest
K003 Silver fir - Douglas-fir forest
K004 Fir - hemlock forest
K008 Lodgepole pine - subalpine forest
K013 Cedar - hemlock - pine forest

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Soils and Topography

Over its range, mountain hemlock grows on soils derived from a wide  variety of parent materials, including those of volcanic, sedimentary,  metamorphic, and glacial origin. It is, however, relatively rare and  stunted on soils derived from calcareous parent materials in the Selkirk  Mountains of British Columbia (11). Mountain hemlock was not found on  calcareous parent materials in the Rocky Mountains of the United States,  but edaphic factors influencing its distribution in that area are not  clear (12,63).

    Mountain hemlock is reported on organic soils (Histosols) in the  northern portion of its range (9,82) more often than in the southern  portion (62,64). In Alaska it is found down to sea level on noncommercial  forest land on organic soils bordering muskegs where it may be a major  stand component (35). A stunted or prostrate form is often found on these  muskegs. It also grows below its usual altitudinal range in British  Columbia on poorly drained sites where other species offer little  competition (11).

    Best development of mountain hemlock is on loose, coarse-textured,  well-drained soils with adequate moisture (9,11,62), and in British  Columbia (9), on thick and very acidic organic matter and decayed wood.  Adequate soil moisture appears to be especially important in California  (11,62) and Montana (33)- portions of its range where summer drought is  most pronounced. Mature soils typically found under mountain hemlock  stands in Alaska, British Columbia, and Washington are Cryaquods and  Cryorthods of the order Spodosols. These soils typically have a 13- to  28-cm (5- to 11-in) forest floor with a root mor or mycelial root mor  humus layer in British Columbia (9), and a 5- to 10-cm (2- to 4-in) forest  floor with a mor or duff mull humus layer in the Washington Cascades (20).  In the central and southern Oregon Cascades and in northeastern Washington  and northern Idaho, mature soils are generally weakly developed  Haplorthods with densely matted felty mor humus layers 2 to 5 cm (1 to 2  in) thick (12,20,90). Mountain hemlock also commonly grows on immature  soils (Entisols and Inceptisols). For example, it grows on Andepts (soils  derived from volcanic ash) in the Cascade Range in Oregon (38,42). Forest  floors and mineral soil surfaces of pumice and ash soils supporting  mountain hemlock in Oregon show moderate resistance to wetting when dry  (42).

    Stands dominated by mountain hemlock typically have very acidic forest  floors (pH 3.4 to 5.0, rarely 6.0) and mineral soils (pH 4.2 to 6.2) with  low base saturation (9 to 18, rarely 37 percent) in British Columbia (9),  Washington, Oregon (77,90), and northern Idaho (12). Mountain hemlock  accumulates aluminum in its foliage and fine roots, so it may increase the  acidity and speed up podzolization of these soils (85). Total nitrogen in  the forest floor (0.4 to 1.13 percent) and mineral soil (0.05 to 0.4  percent) in British Columbia (9), Washington, and Oregon (51,77,90) are  comparable to those of other coniferous forests in the region. Levels of  available nitrogen in an old-growth stand in Oregon, as indexed by 7-day  anaerobic 40° C (104° F) incubations, are extremely low in the  mineral soil (1.7 to -2.3 µg N/g) and 100 times higher but still low  in the forest floor (45 to 225 µg N/g) relative to levels for lower  elevation stands in Oregon and Washington (51). A study of forests on an  altitudinal gradient in western Oregon indicates that, as for available  nitrogen, a high proportion of soil calcium (98 percent), organic matter  (50 percent), and total nitrogen (34 percent) is in the forest floor  relative to most lower elevation forest types (77). Because of this,  nutrients in the forest floor are very important to the productivity of  these forests. These edaphic differences are caused by slower (measured)  decomposition rates caused in large part by lower temperatures and, on  some sites, by the youth and infertility of the volcanic ash parent  material.

    Mountain hemlock will grow on most landforms, but individuals typically  develop best in mixed stands of the forest subzone on sheltered slopes or  in draws. From southern British Columbia south, the tree grows better on  northerly exposures (11). The preference for relatively moist, cool sites  evidently becomes a necessity as the climate becomes more continental in  western Montana (33) and more mediterranean in the central Sierra Nevada  (62) at these extremes of its range. In these locations, mountain hemlock  typically grows in isolated populations in north-facing glens and cirque  basins where snow collects and may remain well into summer.

    Limited data on stomatal behavior from Carson Pass, CA, indicate that  mountain hemlock is adapted to sites with long-lasting snowpacks. In the  spring, mountain hemlocks emerging through 2 to 4 m (7 to 13 ft) of snow  were transpiring and, presumably, photosynthesizing (73), whereas nearby  whitebark pines (Pinus albicaulis) did not transpire until the  soil beneath them was free of snow. Water uptake by seedlings in a  greenhouse decreases to near zero at soil water potential of about -2 MPa  (versus about -3 MPa for Douglas-fir) because of greater uptake resistance  (5). Such decreases suggest that mountain hemlock is less well adapted to  droughty sites or sites with high evaporative demand.

  • 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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Joseph E. Means

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Climate

Areas occupied by mountain hemlock generally have a cool to cold  maritime climate that includes mild to cold winters, a short, warm to cool  growing season and moderate to high precipitation (table 1). Annual and  summer precipitation and the proportion of precipitation as snow show  notable latitudinal climatic trends in the range of mountain hemlock  (table 1). Latitudinal trends in mean temperatures are not evident.

    Table 1- Climatological data from 14 weather stations  within the range of mountain hemlock            Temperature  Precipitation                Location and number of stations   
Annual   
January 
  July   
Annual  June to August  Portion¹ as snowfall              °C  mm  mm  pct      Alaska², 3  4  -7  13  1681  346  14      British Columbia, 4  3  -3  11  3021  361  29      Washington, 2  4  -3  12  2728  270  51      Northern Idaho, 1  3  -7  15  971  124  65      Oregon, 1  4  -4  13  1643  99  81      California, 3  3  -4  13  1048  51  88        °F  in  in  pct      Alaska² (80)  39  20  56    62  13  14      British Columbia (9,45)  38  26  52  104  14  29      Washington (20)  39  27  53  107  11  51      Northern Idaho (79)  37  19  59    38    5  65      Oregon (20)  39  25  56    65    4  81      California (64,77)  38  24  56    39    2  88      ¹Estimated  snowfall by assuming 10 cm (4 in) of snow is equivalent to 1 cm (0.4 in)  of rain, for all locations but those in British Columbia. 
²Stations in Alaska are near sea level. Mountain hemlock grows  at higher elevations where temperature and precipitation levels are  likely to vary from those recorded.        The high snowfall results in snowpacks with maximum depths that range  from 245 cm (96 in) in Idaho to 380 cm (150 in) in British Columbia (9). A  snowpack may cover the ground for long periods (7 to 10 months in  southwestern British Columbia) (9). The relatively short growing season  (frost-free period) ranges from 95 to 148 days in southwestern British  Columbia (9,45) and from 49 to 63 days in the central Sierra Nevada (64).

    Climatic extremes include a temperature range of -29° to 38° C  (-20° to 100° F) (11), annual snowfall in excess of 2200 cm (866  in) (66), snowpack up to 750 cm (295 in) (20), and persistence of the  snowpack until August or September (9,66). Because there are few weather  stations in the range of mountain hemlock, reported extremes are probably  often exceeded.

    Mountain hemlock grows in an altitudinal band 300 to 1000 m (1,000 to  3,300 ft) wide that increases in altitude from north to south:

        Altitude        m  ft      Alaska (83)        0 to  1067           0  to 3,500      Northern British Columbia (46)      300 to 900    1,000 to 3,000      Southern British Columbia (46)    900 to 1800    3,000 to 5,900      Northern Washington (20)  1300 to 1700    4,200 to 5,600      Rocky Mountains (12,33,63)  1550 to 2100    5,100 to 6,900      Southern Oregon (42)  1600 to 2300    5,200 to 7,500      Northern Sierra Nevada (64)  2400 to 3050  7,900 to 10,000      Southern Sierra Nevada (62)  2750 to 3050  9,050 to 10,000        The presence of mountain hemlock in the Rocky Mountains is closely  correlated with the eastward penetration of moist maritime air masses  (33). On the east side of the Coast Mountains in British Columbia,  mountain hemlock is limited to relatively moist sites where snow  accumulates early in the fall (46). Krajina (46) proposes that mountain  hemlock does not grow on sites with later, thinner snowpacks because it  cannot tolerate the frozen soils there.

    Throughout most of the range of mountain hemlock local climate  differentiates two types of subalpine mountain hemlock forest. A parkland  subzone of single trees and small tree clumps (average canopy cover  less than 25 percent) extends from treeline or near treeline to the lower  forest subzone of relatively continuous forest cover (canopy cover  more than 25 percent) (2,9,21,82). Most climatic data (table 1) are from  the forest subzone. Detailed microclimatic data (9) and data extrapolated  upslope from the weather stations (45) in southwestern British Columbia  indicate that the parkland subzone has shorter frost-free and snow-free  periods and that maximum snowpack, range of summer temperatures, and  actual evapotranspiration are greater than in the forest subzone. Mountain  hemlock also grows above treeline in the alpine environment as prostrate  krummholz (elfinwood) throughout most of its range (10,20,35).

    If climate warms as hypothesized for western North America (24),  existing mountain hemlock forests will probably increase in productivity;  upper and lower boundaries of the mountain hemlock zone, within which new  mountain hemlock forests become established after disturbance, will  increase in elevation; and the zone will decrease in area. Near Mount  Baker, Washington, ring width of mountain hemlock increases with  increasing monthly temperatures in the preceding 12 months, decreasing  winter precipitation (37), and decreasing spring snow depth, down to about  1 m (3.3 ft) (27). This implies productivity should increase with  predicted temperature increases. Graumlich and others (28) estimated that  productivity increased 60 percent in the last century in four  high-elevation stands in Washington, three of which contained 48 to 96  percent mountain hemlock. They related this increase most strongly to the  increase in growing-season temperature during this period (about 1.5°  C or 2.7° F). Thus, further increases in temperature may cause  further increases in productivity.

    Based on the current elevational distribution of major forest zones in  the Oregon Cascades and a mean temperature lapse rate of 4.4° C/100 m  (2.4° F/1,000 ft), Franklin and others (24) have hypothesized the  effects of two warmer climates. If mean annual temperature increases 2.5°  C (4.5° F), the mountain hemlock zone in Oregon may be shifted  upwards 570 m (1,900 ft) and decrease in area from 9 to 2 percent; an  increase of 5.0° C (9° F) may move it upwards 1140 m (3,700  ft)-above all but the tallest peaks-so it is effectively eliminated.

  • 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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Joseph E. Means

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Habitat & Distribution

Coastal and montane forests to alpine slopes (where it occurs in krummholz form); 0--2400m; B.C.; Alaska, Calif., Idaho, Mont., Nev., Oreg., Wash.
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Associations

Associated Forest Cover

The mountain hemlock zone includes the upper Canadian and most of the  Hudsonian Life Zones (11) and includes all of the forest cover type  Mountain Hemlock (Society of American Foresters, Type 205) (16). Mountain  hemlock is a major component of Coastal True Fir-Hemlock (Type 226),  California Mixed Subalpine (Type 256) and (in the Cascade Range) Whitebark  Pine (Type 208). Mountain hemlock is a minor associate in 12 other  coniferous types: Engelmann Spruce-Subalpine Fir (Type 206), Red Fir (Type  207), Interior Douglas-Fir (Type 210), Western Larch (Type 212), Western  White Pine (Type 215), Lodgepole Pine (Type 218), Sitka Spruce (Type 223),  Western Hemlock (Type 224), Western Hemlock-Sitka Spruce (Type 225),  Western Redcedar-Western Hemlock (Type 227), Western Redcedar (Type 228),  and Port-Orford-Cedar (Type 231).

    Mountain hemlock usually grows in mixture with other trees, and it has  many associates, as is evident from the large number of forest types in  which it is found. Though pure stands are less common than mixed stands,  there are extensive pure stands of mountain hemlock in Alaska (11) and in  the central high Cascades of Oregon (20).

    One of the most widespread mountain hemlock communities is the mountain  hemlock-Pacific silver fir/big huckleberry (Tsuga mertensiana-Abies  amabilis/Vaccinium membranaceum) type found in British Columbia (9)  and the Oregon and Washington Cascades (1,20). In British Columbia, the  understory is dominated by deciduous ericaceous shrubs: Cascades azalea  (Rhododendron albiflorum), Alaska huckleberry (Vaccinium  alaskaense), rustyleaf menziesia (Menziesia ferruginea), ovalleaf  huckleberry (Vaccinium ovalifolium), and big huckleberry. Also  included are strawberryleaf blackberry (Rubus pedatus) and several  mosses. Silver fir and Alaska-cedar (Chamaecyparis nootkatensis) are  common tree associates in this community in coastal areas, and subalpine  fir (Abies lasiocarpa) and Engelmann spruce (Picea  engelmannii) are common associates in inland areas (9).

    In the Rocky Mountains, the mountain hemlock/beargrass (Xerophyllum  tenax) habitat type is generally found on south slopes and is  characterized by a high cover of beargrass with big huckleberry and grouse  whortleberry (Vaccinium scoparium) as common associates (12,63).  Subalpine fir and lodgepole pine (Pinus contorta) are common  arborescent associates. A similar Pacific silver fir-mountain  hemlock/beargrass association is found in Oregon (20).

    The extensive pure or nearly pure mountain hemlock forests in the high  Cascades of Oregon are primarily in the mountain hemlock/grouse  whortleberry community (38,42,48,72). Except for grouse whortleberry,  understory plant cover is generally low, long-stoloned sedge (Carex  pensylvanica) being the most commonly mentioned associate.

    Mountain hemlock forests in Crater Lake National Park were classified  with 89 percent accuracy using Landsat imagery (86), which offers hope for  broadscale mapping of this forest type.

  • 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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Joseph E. Means

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Diseases and Parasites

Damaging Agents

The most striking damage to mountain hemlock is  probably that caused by laminated root rot (Phellinus weiri) in  the high Cascades of central Oregon (49). This fungus spreads from centers  of infection along tree roots so that all trees are killed in circular  areas that expand radially. Mountain hemlock is the most susceptible tree  in these forests (18,49), and Phellinus moves faster (34 cm/yr;  13.3 in/yr) through nearly pure mountain hemlock (91 percent hemlock) than  through a more heterogeneous conifer (74 percent hemlock) stand (23 cm/yr;  9.1 in/yr) (49). Growth and coalescence of Phellinus pockets have  produced infected areas of more than 40 ha (100 acres). The low levels of  available nitrogen in the forest floor and mineral soil (51) stress  mountain hemlock, increasing its susceptibility to infection by Phellinusas indicated by a seedling growth chamber study (52).

    Seedlings of mountain hemlock and associated species recolonize  disease-killed areas immediately behind the advancing mortality front.  These seedlings are apparently not susceptible to reinfection by P.  weiri for 80 to 120 years (89). This may be due to greater vigor  caused by higher levels of available nitrogen (up to a 4-fold increase),  higher temperatures, and more growing-season moisture in this regrowth  zone (7,89).

    Other common fungal pests of mountain hemlock include several heart rots  (Heterobasidion annosum, Phellinus pini, Fomitopsis pinicola, and  Phaeolus schweinitzii) (11,72), of which Indian paint fungus (Echinodontium  tinctorum) is perhaps the most common and damaging (42). Several  needle diseases and a snow mold (Herpotrichia nigra) also attack  mountain hemlock but are not considered serious pests (11).

    The mountain hemlock race of hemlock dwarf mistletoe (Arceuthobium  tsugense) is a potentially damaging parasite that causes witches'  broom, reduction in vigor, and occasionally death (11,50). It is found  throughout most of the range of mountain hemlock, but reported infection  of mountain hemlock decreases from Washington north (36). Dwarf mistletoe  rarely infects mountain hemlock in Alaska, though western hemlock is often  infected. Several defoliating insects, bark beetles, and wood-boring  insects attack mountain hemlock but do not cause extensive damage (11).

    Before effective fire suppression, many mountain hemlock stands south of  Alaska probably succumbed to fire, as is indicated by the many young  stands (11,20). The species is considered susceptible to fire because it  often retains branches almost to the ground, grows in clusters, and, in  Oregon, often has well-developed forest floors that dry out in the summer  (72).

    Wind commonly destroys trees in the coastal strip of British Columbia  (45) and Alaska where fire is not important (35). As cutting is increased  in mountain hemlock forests, wind damage will probably become a more  common cause of mortality of this shallow-rooted species. Periodic snow  breakage may remove 2 to 6.5 percent of the foliage mass (29).

    After the eruption of Mount St. Helens and deposition of tephra on  foliage and soil (18 cm, 7 in), growth slowed but trees did not die (41).

  • 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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Joseph E. Means

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General Ecology

Fire Management Considerations

More info for the term: natural

Fire injury makes mountain hemlock very susceptible to insects and
disease [17,25]. Old-growth mountain hemlock stands 460 years or older
are very susceptible to stand-replacing fires [20].

In northern Idaho, burning slash produced better stocking of mountain
hemlock natural regeneration compared to leaving slash untreated.
However, manual scarification generally produced better stocking than
did burning. In contrast, slash burning in Oregon increased the time it
took mountain hemlock to reach 60 percent stocking [24].
  • 17. Davis, Kathleen M.; Clayton, Bruce D.; Fischer, William C. 1980. Fire ecology of Lolo National Forest habitat types. INT-79. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 77 p. [5296]
  • 20. Dickman, Alan; Cook, Stanton. 1989. Fire and fungus in a mountain hemlock forest. Canadian Journal of Botany. 67(7): 2005-2016. [13015]
  • 24. Feller, M. C. 1982. The ecological effects of slashburning with particular reference to British Columbia: a literature review. Victoria, BC: Ministry of Forests. 60 p. [10470]
  • 25. Fischer, William C.; Bradley, Anne F. 1987. Fire ecology of western Montana forest habitat types. Gen. Tech. Rep. INT-223. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 95 p. [633]

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Plant Response to Fire

More info for the terms: tree, wildfire

Mountain hemlock is generally slow to regenerate after fire [25,49].
Most burned areas in the mountain hemlock zone on the Olympic Peninsula
do not have adequate stocking for commercial forests even 55 to 88 years
after wildfire [49]. Tree establishment in burned areas is higher
during normal to wet growing seasons [2].
  • 2. Agee, James K.; Smith, Larry. 1984. Subalpine tree reestablishment after fire in the Olympic Mountains, Washington. Ecology. 65(3): 810-819. [6102]
  • 25. Fischer, William C.; Bradley, Anne F. 1987. Fire ecology of western Montana forest habitat types. Gen. Tech. Rep. INT-223. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 95 p. [633]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]

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Post-fire Regeneration

More info for the terms: root crown, secondary colonizer

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

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Fire Ecology

More info for the terms: fire occurrence, fire regime, fuel, fuel loading, resistance

Mountain hemlock is not well adapted to fire [25]. Fire resistance of
mountain hemlock has been rated as low [65]. Its relatively thick bark
provides some protection, but low-hanging branches, highly flammable
foliage, and a tendency to grow in dense groups make it very susceptible
to fire injury [25].

Mountain hemlock sites are typically moist with average precipitation
over 50 inches (127 cm), making fire occurrence low (400-800 years)
[7,11,34]. Fuel loading in these sites is often low [7]. In the
Pacific Northwest, the estimated prelogging fire regime in mountain
hemlock forest types is 611 years [11]. Fires in these cool wet forest
types generally occur as infrequent crown fires. When fires do occur in
mountain hemlock forests, they are often severe stand-replacing fires
[25].
  • 11. Booth, Douglas E. 1991. Estimating prelogging old-growth in the Pacific Northwest. Journal of Forestry. 89(10): 25-29. [16223]
  • 25. Fischer, William C.; Bradley, Anne F. 1987. Fire ecology of western Montana forest habitat types. Gen. Tech. Rep. INT-223. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 95 p. [633]
  • 34. Habeck, James R. 1985. Impact of fire suppression on forest succession and fuel accumulations in long-fire-interval wilderness habitat types. In: Lotan, James E.; Kilgore, Bruce M.; Fisher, William C.; Mutch, Robert W., technical coordinators. Proceedings-Symposium and Workshop on Wilderness Fire; 1983 November 15 - November 18; Missoula, MT. General Technical Report INT-182. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station: 110-118. [7358]
  • 65. Spalt, Karl W.; Reifsnyder, William E. 1962. Bark characteristics and fire resistance: a literature survey. Occas. Paper 193. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 19 p. In cooperation with: Yale University, School of Forestry. [266]
  • 7. Atzet, Thomas; Wheeler, David L. 1982. Historical and ecological perspectives on fire activity in the Klamath Geological Province of the Rogue River and Siskiyou National Forests. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 16 p. [6252]

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Successional Status

More info on this topic.

More info for the terms: climax, series

Obligate climax species

Mountain hemlock is shade tolerant [24,49,4]. It is considered a major
or minor climax species over most of its habitat; however, it is also a
pioneer on glacial morianes in British Columbia and Alaska. Mountain
hemlock is commonly the major climax species in the mountain hemlock
zone south of central Oregon where Pacific silver fir does not occur.
It often succeeds lodgepole pine (pinus contorta) when these species
pioneer on drier sites and tends to replace Engelman spruce [49].
Mountain hemlock is considered a coclimax species with subalpine fir
where they occur together [17,25]. In the subalpine fir series in the
Lolo National Forest, mountain hemlock and subalpine fir are the only
two trees capable of perpetuating themselves as climax dominants [33].
  • 17. Davis, Kathleen M.; Clayton, Bruce D.; Fischer, William C. 1980. Fire ecology of Lolo National Forest habitat types. INT-79. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 77 p. [5296]
  • 24. Feller, M. C. 1982. The ecological effects of slashburning with particular reference to British Columbia: a literature review. Victoria, BC: Ministry of Forests. 60 p. [10470]
  • 25. Fischer, William C.; Bradley, Anne F. 1987. Fire ecology of western Montana forest habitat types. Gen. Tech. Rep. INT-223. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 95 p. [633]
  • 33. Habeck, James R. 1967. Mountain hemlock communities in western Montana. Northwest Science. 41(4): 169-177. [7258]
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]

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Regeneration Processes

More info for the terms: epigeal, formation, layering, tree

Seed production and dissemination: Mountain hemlock begins producing
seed at about age 20. Mature trees 175 to 250 years old produce
moderate to very heavy cone crops at about 3-year intervals in Oregon
and Washington, but crops may be complete failures in other years [49].
Cones average about 70 to 100 seeds [28]. There are 102,000 to 207,000
seeds per pound [70]. On one study site located at Santiam Pass,
Oregon, the largest number of cones counted was 1,700 on a 20-inch (51
cm) mountain hemlock [28]. Over 1,000 cones per tree were counted on
many other trees during the 5 year study period. Seed production is
better during normal to wet growing seasons than during dry growing
seasons [49].

Mountain hemlock's winged seeds are dispersed primarily by wind.
Germination is epigeal and occurs on snow, or mineral or organic soil if
sufficient moisture is available [49]. Germination rates range from 47
to 75 percent [28,49]. Cold stratification of mature seeds shortens
incubation time and may substantially increase germination [62]. Heavy
seeds germinate more rapidly than seeds with low percent dry weight.
Along the eastern high Cascades in Oregon, seed viability of mountain
hemlock varied from 36 to 76 percent over a 2-year period [49].

Seedling development: Young seedlings grow best in partial shade and
early development is often slow. Seedlings are relatively drought
intolerant [2]. Increasing light intensity and day length increase
seedling height but delay or prevent terminal bud formation under
shelter. Healthy mountain hemlock saplings respond well to release, in
both diameter and height growth. Seedlings and small saplings of
mountain hemlock tolerate heavy snowpacks well [49].

Vegetative reproduction: Mountain hemlock reproduces vegetatively by
layering [49,73]. This is an effective means of regenerating at
timberline, since layered saplings are sheltered by the growth of the
parent tree and initially receive their nutrients through the
established root system of the old tree [4]. Layering is an important
method of reproduction on muskegs and krummholz areas in Alaska [49].
  • 2. Agee, James K.; Smith, Larry. 1984. Subalpine tree reestablishment after fire in the Olympic Mountains, Washington. Ecology. 65(3): 810-819. [6102]
  • 28. Franklin, J. F. 1968. Cone production by upper slope conifers. Research Paper PNW-60. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 21 . [12912]
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 62. 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]
  • 70. Van Dersal, William R. 1938. Native woody plants of the United States, their erosion-control and wildlife values. Washington, DC: U.S. Department of Agriculture. 362 p. [4240]
  • 73. Douglas, George W.; Ballard, T. M. 1971. Effects of fire on alpine plant communities in the North Cascades, Washington. Ecology. 52(6): 1058-1064. [6738]

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Growth Form (according to Raunkiær Life-form classification)

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More info for the term: phanerophyte

Phanerophyte

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Life Form

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Tree

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Immediate Effect of Fire

Mountain hemlock is easily killed by fire [7,73,65]. The most common
method of killing is root charring and crown scorching [65]. In a
krumholz community of the North Cascades, Washington, all but one
mountain hemlock were killed by fire [73].
  • 65. Spalt, Karl W.; Reifsnyder, William E. 1962. Bark characteristics and fire resistance: a literature survey. Occas. Paper 193. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 19 p. In cooperation with: Yale University, School of Forestry. [266]
  • 7. Atzet, Thomas; Wheeler, David L. 1982. Historical and ecological perspectives on fire activity in the Klamath Geological Province of the Rogue River and Siskiyou National Forests. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 16 p. [6252]
  • 73. Douglas, George W.; Ballard, T. M. 1971. Effects of fire on alpine plant communities in the North Cascades, Washington. Ecology. 52(6): 1058-1064. [6738]

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Reaction to Competition

Mountain hemlock is classed as tolerant  of shade and other forms of competition (10,48,55) and, based on  synecological studies, is more tolerant than all its associates except  Pacific silver fir (46), western hemlock, and Alaska-cedar.

    Mountain hemlock is considered a minor climax species on most of its  habitats; however, it pioneers on glacial moraines in British Columbia and  Alaska (11) where it is nevertheless considered indicative of the climax  forest (46); also see references in 19). Pacific silver fir is a major  climax species in many communities of the mountain hemlock forest subzone  in British Columbia (9) and Washington and northern Oregon (20).  Alaska-cedar, western redcedar (Thuja plicata), and western  hemlock (Tsuga heterophylla), however, are climax associates on  some sites. Mountain hemlock is more commonly the major climax species in  the mountain hemlock zone south of central Oregon where Pacific silver fir  does not occur.

    Mountain hemlock often succeeds lodgepole pine or subalpine fir when  these species pioneer on drier sites (20). It also tends to replace  Engelmann spruce when the two species occur together, possibly because  hemlock is better able to withstand the allelopathic effects of spruce  than are other associated species (76).

  • 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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Rooting Habit

Mountain hemlock is usually shallow rooted. In  British Columbia, roots are mainly confined to the forest floor (9,45).  This is not surprising because of the high proportion of soil nutrients in  the forest floors of these forests. Mountain hemlock will root  adventitiously when, for example, 10 to 20 cm (4 to 8 in) of volcanic  tephra is added to the soil surface (91).

    Two-thirds to three-quarters of the net primary productivity (NPP) is  allocated below ground, according to the available data on three stands  130 to 280 years old dominated by silver fir but with significant mountain  hemlock components (30,84). This high allocation below ground is probably  caused by the need to obtain sufficient nutrients in these infertile soils  (30). Mycorrhizae were found to be important sinks for carbon and  components of nutrient cycles in one stand (84).

  • 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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Life History and Behavior

Cyclicity

Phenology

More info on this topic.

Mountain hemlock has a 2-year reproductive cycle. Pollination occurs in
the spring or early summer of the second year [55]. Mountain hemlock
releases pollen in June in the Cascade Range in Oregon, from mid-June to
mid-July in British Columbia, and from mid-May to late June in Alaska
[49]. Fertilization occurs from about late July to early August in
British Columbia. Reproductive buds can easily be identified in the
late summer and fall. Cones ripen and open from late September to
November [49,56]. In the Bitterroot Mountains of Idaho cones ripen in
August [62]. In Montana cones open and release the wide-winged seeds in
September or October and then abscise [44].
  • 44. Lackschewitz, Klaus. 1991. Vascular plants of west-central Montana--identification guidebook. Gen. Tech. Rep. INT-227. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 648 p. [13798]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 55. Owens, John N. 1986. Cone and seed biology. In: Shearer, Raymond C., compiler. Proceedings--conifer tree seed in the Inland Mountain West symposium; 1985 August 5-6; Missoula, MT. Gen. Tech. Rep. INT-203. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 14-31. [12782]
  • 56. Owens, John N.; Molder, Marje. 1975. Sexual reproduction of mountain hemlock (Tsuga mertensiana). Canadian Journal of Botany. 53: 1811-1826. [19164]
  • 62. 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]

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Reproduction

Vegetative Reproduction

Layering is an important method of  reproduction on muskegs and krummholz in Alaska but is insignificant in  subalpine tree clumps in the north Cascades of Washington (48) and in  forested areas in general.

  • 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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Seedling Development

Mountain hemlock is easily transplanted  and propagated by seed and cuttings (76). Heavy seeds germinate more  rapidly (44). Germination, which is epigeal, occurs on snow, mineral soil,  or organic soil if sufficient moisture is available. Young seedlings grow  best in partial shade (11), and early development is often slow.  Increasing light intensity and day-length increase seedling height but  delay or prevent terminal-bud formation under shelter (4). Stem dissection  of trees on the east side of the Oregon Cascades shows that growth to  breast height in natural stands is slower on sites thought to have a  late-lying snowpack than on warmer sites.

    Mountain hemlock is generally slow to regenerate after disturbances such  as logging, site preparation, or wildfire. Most burned areas in the  mountain hemlock zone on the Olympic Peninsula do not have adequate  stocking for commercial forests (600 trees/ha 1,500/acre) even 55 to 88  years after wildfires (3). Reproduction is greater during normal-to-wet  growing seasons, than during dry growing seasons, and greater in areas  near live trees at the edge of fires and near trees that survive the fires  than in areas farther from seed sources. In the parkland subzone,  reproduction is limited to the margins of tree clumps (48,72), except when  successive years with earlier than normal snowmelt allow invasion of  subalpine meadows (3,23).

    Young stands 20 to 40 years old (some in burned areas) in southern  Oregon and northern California may be pure mountain hemlock and quite  dense (9,900 to 24,700 trees/ha, or 4,000 to 10,000/acre) (11).

    In Oregon, mountain hemlock forests typically regenerate slowly after  they are clearcut. In a study of 25 clearcuts, 5 to 11 years were required  to reach 60-percent stocking on 0.0012-ha (0.003-acre) subplots (56).  Establishment of seedlings during the first 2 years in an Oregon  shelterwood cut was very low because germinants were few at low residual  basal areas (less than 11.5 m²/ha or 50 ft²/acre) and all  seedlings died at all higher basal areas (69).

    The normally slow restocking process is retarded by slash treatment. On  the east side of the Cascade Range in Oregon, treated (generally piled and  burned) clearcuts had lower stocking (33 percent based on 0.0004-ha  (0.001-acre) subplots) than untreated clearcuts (57 percent) because of  destruction of advance regeneration and a 50-percent decrease in the  number of subplots stocked with natural, post-harvest reproduction (61).  These clearcuts ranged from 3 to 19 years old. Stocking of mountain  hemlock and its associates near Willamette Pass, OR, in 13-year-old strip  cuts with unburned slash was 95 percent (on subplots of 0.0012 ha or 0.003  acre), compared with 82 percent in units that had been burned. The  difference was due to advance regeneration of silver fir and mountain  hemlock in the unburned clearcuts. These studies indicate that stocking in  clearcuts in the mountain hemlock zone is typically made up of  post-harvest naturally seeded trees, such as mountain hemlock, Shasta red  fir (Abies magnifica var. shastensis), silver fir,  lodgepole pine, and western white pine (Pinus monticola); and  advance regeneration of mountain hemlock and Shasta red fir (56,67).  Planting has been relatively ineffective in speeding regeneration on these  cold, snowy sites compared with advance and post-harvest natural  regeneration that slowly provide adequate to abundant stocking.

    Healthy mountain hemlock saplings (mean d.b.h. 4.5 cm, 1.8 in) respond  well to release, in both diameter and height growth (68). Understory  saplings with crown ratios greater than 50 percent and growing fastest  before release will likely be the best crop trees (68).

    Regeneration of mountain hemlock varies in response to environmental  gradients. In six strip cuts at Willamette Pass, OR, it decreases from the  south (shaded) side to the north (unshaded) side. In the Cascade Range in  central Oregon, it decreases with increasing cover of grass and forbs  (67). Near Windigo Pass, OR, mountain hemlock makes up an increasing  proportion of tree regeneration as elevation and pumice depth increase  (56) and so becomes increasingly important for reforesting these harsher  sites. In Oregon, the proportion of mountain hemlock to other species in  clearcuts and burned areas typically is lower than that in surrounding  mature stands, whereas the proportion of lodgepole pine, western white  pine, and Shasta red fir reproduction is relatively higher.

    Seedlings and small saplings of mountain hemlock tolerate heavy  snowpacks well. Bent boles and branches spring erect after snowmelt.  Leader replacement by axial buds is less frequent than in other North  American hemlocks, and the drooping leaders take 3 or more years to become  erect (40).

  • 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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Seed Production and Dissemination

Three years of data from  British Columbia indicate that high temperatures in July the year before  cone production favor cone-bud initiation (14). Cones ripen and open from  late September to November (11,61). Wild mountain hemlock as young as 20  years may bear cones (11,65). A study of cone-bud initiation indicates it  may be possible to induce cone production at younger ages (58). Mature  trees 175 to 250 years old produce medium to very heavy cone crops at  about 3-year intervals in Oregon and Washington but crops may be complete  failures in other years (22). Mountain hemlock seeds are dispersed  primarily by wind. During a bumper mountain hemlock seed year in Oregon,  seedfall at the clearcut-forest boundary was very high (215,000 to  4,144,000/ha or 87,000 to 1,677,000/acre) and was greatest at the south  edge and least at the north edge of a gently sloping 12.5-ha (31-acre)  clearcut (21). Seedfall was correlated with stand basal area in this  study, as basal areas at the north and south edges were 34 and 94 m²/ha  (149 and 410 ft²/acre), respectively. Seedfall was much less 114 m  (375 ft) from the edge of the clearcut but was still quite heavy (40,000  to 230,000/ha or 16,000 to 93,000/acre). Sound seed in this study varied  from 36 to 76 percent over 2 years. Germination of mountain hemlock seed  ranges from 47 to 75 percent (66).

  • 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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Flowering and Fruiting

Mountain hemlock is monoecious. Pollen  release occurs in June in the Cascade Range in Oregon (11), from mid-June  to mid July in British Columbia (14,61), and from mid-May to late June in  Alaska. In a British Columbia study, mountain hemlock and subalpine fir  were the last of 10 species to release pollen (14). Daytime temperature  appeared to be the most important variable regulating release of pollen,  with more release (and by inference more pollination) on warm, dry days.  Both protogyny (53) and synchrony between pollen release and female cone  receptivity on individual trees have been observed in British Columbia.  Fertilization occurs from about late July to early August in British  Columbia (61). Reproductive buds can easily be identified in the late  summer and fall (15). Many female strobili indicate the potential for a  large cone crop next year. Mature cones are oblong, purple or brownish  purple, and are generally longer than the other species of Tsuga  (2 to 9 cm or 0.75 to 3.5 in) (53). Owens and Molder (60) have thoroughly  described the reproductive cycle of mountain 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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Growth

Growth and Yield

Mature trees range in height from 15 m (50 ft)  on poor sites to 46 m (150 ft) on the best sites. Depending on stocking,  diameters of old trees range from 30 cm (12 in) on poor sites to 150 cm  (60 in) on good sites. The record tree of the American Forestry  Association's list of big trees is 34.4 m (113 ft) tall and 224 cm (88 in)  in d.b.h. Mountain hemlocks 700 to 800 or more years old are reported in  British Columbia (9) and at Mount Rainier National Park, WA.

    Mountain hemlock grows slowly in height (fig. 1) and in diameter. Three  investigators found that stem-dissected trees in Oregon and southern  Washington without signs of impeded height growth were only 7 to 28 m (23  to 91 ft) tall at 100 years (39,43,54). Height growth of mountain hemlock  is initially slower than that of western hemlock but continues at a  moderate rate to greater age. As a result, use of western hemlock site  curves in old mountain hemlock stands leads to large overestimates of  growth and yield (39).

     
Figure 1- Height growth curves for two mountain hemlock 
communities on the east side of the Cascade range in central 
Oregon (adapted from
43). Mean site index (base age 100 
years) and form of height growth curve differ markedly be- 
tween communities.


    Site index (base age 100 years) and the form of the height growth curve  are different in different plant communities in the central Oregon  Cascades (fig. 1) (43). The mountain hemlock/smooth woodrush (Tsuga  mertensiana/Luzula hitchcockii) and mountain  hemlock/prince's-pine-pinemat manzanita (T. mertensiana/Chimaphila  umbellata-Arctostaphylos nevadensis) communities have ranges in site  index of 7 to 14 m (23 to 46 ft) and 13 to 19 m (43 to 62 ft),  respectively. In the Coast Mountains of British Columbia, site index (base  age 100 years) ranges from less than 6 m (20 ft) on xeric sites to 34 m  (110 ft) on the best sites (46).

    Mountain hemlock stands at least 200 years old can have high basal areas  and volumes; the highest values are in mixed species stands. In the  mountain hemlock zone in British Columbia, stands in which that species  makes up more than half the volume (59 to 79 percent) have volumes of 125  to 924 m³/ha (1,786 to 13,204 ft³/acre); volumes are much higher  (range 588 to 1348 m³/ha, 8,397 to 19,260 ft³/acre) in stands  where mountain hemlock makes up less than half the volume (9 to 36  percent) (9). These more productive mixed-species stands usually grow on  deeper soils irrigated by seepage and have a slightly longer average  snow-free period, whereas the communities in which mountain hemlock forms  a majority of the stocking occupy the poorer, colder sites.

    A similar pattern occurs in the Cascade Range in southern Oregon (42).  The mountain hemlock/grouse whortleberry community (nearly pure mountain  hemlock) produces an estimated 1.0 m³/ha (14 ft³/acre) per year,  and the Shasta red fir-mountain hemlock/pinemat manzanita/long-stoloned  sedge community produces an estimated 3.8 to 9.8 m³/ha (54 to 140 ft³/acre)  per year (42). The latter community tends to grow on warmer sites, and  most of the productivity is by Shasta red fir, not mountain hemlock. Basal  areas of both communities are high, 76 and 62 m²/ha (330 and 270 ft²/acre),  respectively. Mountain hemlock communities in the western Cascades of  Oregon and Washington commonly have a mixture of other tree species;  estimated productivity ranges from 3.8 to 7.6 m³/ha (54 to 108 ft³/acre)  per year (8,38). Volume tables are available for mountain hemlock for  Alaska (32) and the central Oregon Cascades (6). Volume growth, biomass,  and leaf area equations are also available (1,26,71,81,87).

    Leaf area index (all sides), like volume productivity, is lower in  nearly pure mountain hemlock forest (10 m²/m² or 10 ft²/ft²)  (25) than in mixed species forest (35 m²/m² or 35 ft²/ft²)  (88) in the Cascade Range.

  • 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

Mountain hemlock has several morphological characteristics that separate  it from most other species of Tsuga, including branchlets not all in one  plane; needles radially arranged, relatively thick, with stomata on both  surfaces; cones generally larger with more scales; and pollen with air  bladders. Because of these spruce-like characteristics, the genetic  background of mountain hemlock was under some question (11,13) until  recently. Mountain hemlock was proposed as a hybrid between western  hemlock and Sitka spruce (Picea sitchensis) by several French  taxonomists and assigned to the new genus Tsugo-Picea (see  references in 11,13). Recent studies of pollination mechanisms (59),  embryology (61), and leaf pigment chemistry (74), however, place the  species firmly in the genus Tsuga. These studies are consistent  with the proposal by Taylor (74) that Picea and Tsuga are  closely related genera, and mountain hemlock is more similar to Picea  than are other Tsuga species (59,74).

    Individuals morphologically intermediate between western hemlock and  mountain hemlock are occasionally found where the two species occupy the  same site. These populations have been given hybrid status (Tsuga x  jeffreyi (Henry) Henry) (11, 13,47). A study of leaf pigment chemistry  of 43 morphologically intermediate individuals collected from throughout  western Washington indicated, however, that only three (all from Corral  Pass near Mount Rainier) were chemically intermediate and so were  potentially of hybrid origin (74). Six leaf cuticle characteristics of  Tsuga x jeffreyi in Britain were similar to mountain  hemlock and dissimilar to western hemlock (70), also not supporting hybrid  status. The limited overlap in the timing of pollen release (14) and  failure of all known controlled pollinations to produce filled seeds (in  British Columbia (53) and in Oregon (cited in 74) support the conclusion  that true hybrids are probably much rarer than the morphological  intermediates on which hybrid status is based, if such hybrids occur at  all.

    A California form of mountain hemlock has been given specific status  (Tsuga crassifolia Flous) and is proposed as a hybrid between  Engelmann spruce and mountain hemlock (13). The hybrid swarms expected  from backcrosses with the parent taxa have not been observed (13),  however, and this specific status and phylogeny are not generally  recognized by taxonomists (17,47,57).

    All mountain hemlock in the Siskiyou Mountains from the  Oregon-California border south were recently given subspecific status as  Tsuga mertensiana (Bong.) Carr. ssp. grandicona Farjon, in  recognition of the generally larger cones of trees in this region (17,63).  This classification is less ambitious than the new species T.  crassifolia.

    Clausen (10) studied the mountain hemlock phenotypes of erect simple  stems and prostrate krummholz (elfinwood) over a gradient in elevation  (3050 to 3350 m; 10,000 to 11,000 ft) in the Sierra Nevada and described  them as genetic races. It has not been determined, however, whether these  growth forms have different genotypes or result solely from different  environments.

  • 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

Barcode data: Tsuga mertensiana

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 mertensiana

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 6
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2013

Assessor/s
Farjon, A.

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

Contributor/s

Justification
The vast range of this species and its minor importance as a timber tree ensures its status as Least Concern well into the future.
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National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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Population

Population
In several areas, e.g. in the Coast Mountains of British Columbia, the Olympic Mountains of Washington, and in Lassen Volcanic National Park (Cascades), this species is invading subalpine meadows and late-lying snow basins. In some areas this has been going on for 150 years or longer, in other areas it seems to have begun more recently. The warming climate is likely responsible.

Population Trend
Increasing
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Threats

Major Threats
No threats have been identified for this species.
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Management

Conservation Actions

Conservation Actions
This species occurs in several protected areas, among which are famous national parks.
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Management considerations

More info for the terms: natural, seed tree, series, tree

Insects and disease: Mountain hemlock is very susceptible to laminated
root rot (Phellinus weiri) [20,49]. In the high Cascades of central
Oregon mountain hemlock is the most susceptible tree. This fungus
spreads from centers of infection along tree roots so that all trees are
killed in circular areas that expand radially. Laminated root rot moves
faster through a nearly pure stand of mountain hemlock than through a
more heterogeneous conifer stand. Growth and coalescence of laminated
rot root pockets in mountain hemlock have produced infected areas of
more than 100 acres (40 ha). Seedlings are not susceptible to
reinfection by laminated root rot for 80 to 120 years. This may be due
to greater vigor caused by higher levels of available nitrogen, higher
temperatures, and more growing-season moisture in this regrowth zone
[49].

Other common fungal and parasite pests of mountain hemlock include
several heart rots, of which Indian paint fungus (Echinodontium
tinctorum) is the most common and damaging; several needle diseases;
snow mold (Herpotrichia nigra); and dwarf-mistletoe (Arceuthobium
tsugense) [49].

Mountain hemlock is an occasional host for the western spruce budworm
(Choristoneura occidentalis) [14].

Frost tolerance: Mountain hemlock is very frost tolerant [41].

Wind damage: Because mountain hemlock is shallow rooted it is very
susceptible to windthrow. In the coastal strip of British Columbia and
Alaska, wind commonly destroys mountain hemlock by uprooting it. As
cutting is increased in mountain hemlock forests, windthrow will
probably become a more common cause of mortality [49].

Silvicultural considerations: Many sites dominated by mountain hemlock
are particularly difficult to reforest following clearcutting. In the
Gifford Pinchot, Mount Hood, and Willamette national forests, field
observations showed that the mountain hemlock/big huckleberry/beargrass
and mountain hemlock/grouse whortleberry associations are particularly
difficult to reforest due to a short growing season in a harsh
environment. Artifical reforestation within 5 years following
clearcutting and burning on these sites may not be possible [35].

The deep, persistent snowpack; short, cool growing season; and poorly
developed soils make regeneration difficult and productivity low for the
mountain hemlock series of the Siskiyou region of southwestern Oregon.
When mountain hemlock stands are managed for timber production, the
following silvicultural considersations are important [8]:

(1) Advanced regeneration and subsequent natural regeneration may
provide the most reliable source for a new stand in 5 years. Protection
from damage during harvest is essential. Damaged regeneration is very
susceptible to rot.

(2) Natural regeneration after harvest establishes sooner in small
openings than large openings and is often most rapid on the shaded south
edges of clearcuts. Keeping clearcuts small to maximize these edge
effects will probably speed regeneration, but it may still be
unsatisfactory in 5 years. The shelterwood system can provide adequate
regeneration in 5 to 10 years.

(3) Planting has been ineffective on these cold, snowy sites. Timing is
critical for articifical regeneration. Plant soon after snow melts.

In British Columbia, the recommended silvicultural method for harvest of
old-growth mountain hemlock is clearcut followed by natural
regeneration. For young natural stands that have developed after fire
or second-growth stands that have developed after clearcutting, the
clearcut method with natural regeneration, seed tree method, or
shelterwood method is recommended [72].
  • 14. Carlson, Clinton E.; Fellin, David G.; Schmidt, Wyman C. 1983. The western spruce budworm in northern Rocky Mountain forests: a review of ecology, past insecticidal treatments and silvicultural practices. In: O'Loughlin, Jennifer; Pfister, Robert D., eds. Management of second-growth forests: The state of knowledge and research needs: Proceedings of a symposium; 1982 May 14; Missoula, MT. Missoula, MT: University of Montana, School of Forestry, Montana Forest and Conservation Experiment Station: 76-103. [7097]
  • 20. Dickman, Alan; Cook, Stanton. 1989. Fire and fungus in a mountain hemlock forest. Canadian Journal of Botany. 67(7): 2005-2016. [13015]
  • 35. Halverson, Nancy M.; Emmingham, William H. 1982. Reforestation in the Cascades Pacific silver fir zone: A survey of sites and management experiences on the Gifford Pinchot, Mt. Hood and Willamette National Forests. U.S. Department of Agriculture Forest Service R-6 Area Guide R6-ECOL-091-1982. Pacific Northwest Region, Portland, Oregon 37 p. [12491]
  • 41. Krajina, V. J.; Klinka, K.; Worrall, J. 1982. Distribution and ecological characteristics of trees and shrubs of British Columbia. Vancouver, BC: University of British Columbia, Department of Botany and Faculty of Forestry. 131 p. [6728]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 72. Weetman, G.; Vyse, A. 1990. Natural regeneration. In: Lavender, D. P.; Parish, R.; Johnson, C. M.; [and others], eds. Regenerating British Columbia's forests. Vancouver, BC: University of British Columbia Press: 118-129. [10711]
  • 8. Atzet, Tom; Wheeler, David; Riegel, Gregg; [and others]. 1984. The mountain hemlock and Shasta red fir series of the Siskiyou Region of southwest Oregon. FIR Report. 6(1): 4-7. [9486]

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Relevance to Humans and Ecosystems

Benefits

Value for rehabilitation of disturbed sites

More info for the terms: association, natural

Mountain hemlock is important for watershed protection [49]. The
mountain hemlock/blueberry (Vaccinium spp.)-copperbush (Cladothamnus
pyrolaeflorus)/deer cabbage (Fauria crista-galli) association in Alaska
captures runoff from snowmelt [19]. Planted stock of mountain hemlock
does not perform well. In high-elevation regeneration trials in the
Vancouver forest region, its performance was poor compared to that of
the other high-elevation species. Natural regeneration may perform
better [63].
  • 19. DeMeo, Thomas. 1989. Preliminary forest plant association management guide: Ketchikan Area, Tongass National Forest. [Portland, OR]: [U.S. Department of Agriculture, Forest Service]. 164 p. [19017]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 63. Scagel, Rob; Green, Bob; Von Hahn, Helmar; Evans, Richard. 1989. Exploratory high elevation regeneration trials in the Vancouver forest region: 10-year species performance of planted stock. FRDA Report 098. Victoria, BC: BC Ministry of Forests, Research Branch. 40 p. [1477]

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Importance to Livestock and Wildlife

More info for the terms: cover, forbs

Mountain hemlock stands provide good hiding and thermal cover for many
wildlife species [8,45]. Sites dominated by mountain hemlock provide
important summer range for deer in Alaska and Vancouver Island because
of abundant nutrient-rich forbs available in the understory [19,49]. In
Montana, mountain hemlock habitat types provide summer range for mule
deer, elk, and bear [57]. Mountain hemlock seeds have been found in the
stomachs of crows and grouse [70].
  • 19. DeMeo, Thomas. 1989. Preliminary forest plant association management guide: Ketchikan Area, Tongass National Forest. [Portland, OR]: [U.S. Department of Agriculture, Forest Service]. 164 p. [19017]
  • 45. Lanner, Ronald M. 1983. Trees of the Great Basin: A natural history. Reno, NV: University of Nevada Press. 215 p. [1401]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 57. Pfister, Robert D.; Kovalchik, Bernard L.; Arno, Stephen F.; Presby, Richard C. 1977. Forest habitat types of Montana. Gen. Tech. Rep. INT-34. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experiment Station. 174 p. [1878]
  • 70. Van Dersal, William R. 1938. Native woody plants of the United States, their erosion-control and wildlife values. Washington, DC: U.S. Department of Agriculture. 362 p. [4240]
  • 8. Atzet, Tom; Wheeler, David; Riegel, Gregg; [and others]. 1984. The mountain hemlock and Shasta red fir series of the Siskiyou Region of southwest Oregon. FIR Report. 6(1): 4-7. [9486]

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Other uses and values

Mountain hemlock is often used as an ornamental for landscaping in the
Pacific Northwest and throughout Great Britain [42,49,4]. Its dense,
compact foliage coupled with its slow growth make it ideal as a garden
evergreen [42]. Hemlock species (Tsuga spp.) played a supernatural role
as magical objects in the mythology of the Thompson and Lillooet
Interior Salish of British Columbia [66].
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 42. Kruckeberg, A. R. 1982. Gardening with native plants of the Pacific Northwest. Seattle: University of Washington Press. 252 p. [9980]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 66. Turner, Nancy J. 1988. Ethnobotany of coniferous trees in Thompson and Lillooet Interior Salish of British Columbia. Economic Botany. 42(2): 177-194. [4542]

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Wood Products Value

Mountain hemlock is largely inaccessible because of the high altitudes
at which it occurs and is unimportant as commercial timber [71]. It is,
however, harvested to a limited extent near its lower limits; the wood
is generally marketed with western hemlock [71,4]. The wood is
moderately strong and light colored and is most often used for
small-demension lumber and pulp [49]. The wood is also used for railway
ties, mine timbers, interior finish, crates, kitchen cabinets, and
flooring and ceilings [71]. Nearly pure stands of mountain hemlock on
Prince of Wales Island have been logged for pulp [71].
  • 4. Arno, Stephen F.; Hammerly, Ramona P. 1977. Northwest trees. Seattle, WA: The Mountaineers. 222 p. [4208]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]
  • 71. Viereck, Leslie A.; Little, Elbert L., Jr. 1972. Alaska trees and shrubs. Agric. Handb. 410. Washington, DC: U.S. Department of Agriculture, Forest Service. 265 p. [6884]

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Special Uses

Perhaps the most important use of mountain hemlock is for watershed  protection and the scenic beauty it adds to subalpine landscapes. It is  well adapted to produce attractive forest on the more extreme subalpine  sites. The Mount Jefferson and Three Sisters Wildernesses, heavily used  year-round recreation areas in Oregon, provide excellent examples. Stands  of this species are said to be well suited to the conservation of snow  (see references in 19). Its slow growth contributes to its attractive,  dense foliage and usually balanced form so that it is a desirable  ornamental, including the cultivars that make fine dwarf specimens or have  silvery foliage (76).

    Some mountain hemlock forest types are important deer summer range on  Vancouver Island (34). A shrubby plant association (Mountain  Hemlock-Copperbush) there provides abundant browse in old stands as well  as in early seral conditions, so harvesting does not significantly affect  food availability.

  • 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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Joseph E. Means

Source: Silvics of North America

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Wikipedia

Tsuga mertensiana

Tsuga mertensiana, known as mountain hemlock, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Tulare County, California.[2][3][4] Mertensiana refers to Franz Carl Mertens (1764-1831), German botanist [5]

Description[edit]

Tsuga mertensiana is a large evergreen coniferous tree growing to 20 to 40 metres (66 to 131 ft) tall, with exceptional specimens as tall as 59 m (194 ft) tall. They have a trunk diameter of up to 2 m (6 ft 7 in). The bark is thin and square-cracked or furrowed, and gray in color. The crown is a neat slender conic shape in young trees with a tilted or drooping lead shoot, becoming cylindric in older trees. At all ages, it is distinguished by the slightly pendulous branchlet tips. The shoots are orange-brown, with dense pubescence about 1 mm long. The leaves are needle-like, 7–25 mm long and 1–1.5 mm broad, soft, blunt-tipped, only slightly flattened in cross-section, pale glaucous blue-green above, and with two broad bands of bluish-white stomata below with only a narrow green midrib between the bands; they differ from those of any other species of hemlock in also having stomata on the upper surface, and are arranged spirally all around the shoot.

Foliage and cones of subsp. mertensiana

The cones are small, but much longer than those of any other species of hemlock, pendulous, cylindrical, 30–80 mm long and 8–10 mm broad when closed, opening to 12 to 35 mm broad, superficially somewhat like a small spruce cone. They have thin, flexible scales 8–18 mm long. The immature cones are dark purple (rarely green), maturing red-brown 5 to 7 months after pollination. The seeds are red-brown, 2–3 mm long, with a slender, 7–12 mm long pale pink-brown wing.[2][3][4]

Distribution[edit]

The Tsuga mertensiana range matches that of Tsuga heterophylla (western hemlock) fairly closely, likewise mostly less than 100 km from the Pacific Ocean apart from a similar inland population in the Rocky Mountains in southeast British Columbia, northern Idaho and western Montana. Their ranges, however, differ in California, where western hemlock is restricted to the Coast Ranges, while mountain hemlock is found in the Klamath Mountains and Sierra Nevada. Unlike western hemlock, it mostly grows at high altitudes except in the far north, from sea level to 1000 m in Alaska, 1600–2300 m in the Cascades in Oregon, and 2500–3050 m in the Sierra Nevada.[2][3][4]

Taxonomy[edit]

There are three taxa, two subspecies and a minor variety:[2][4]

  • Tsuga mertensiana subsp. mertensiana. Northern mountain hemlock. Central Oregon northwards. Cones smaller, 30–60 mm long, 12–25 mm broad when open, with 50 to 80 scales.
    • Tsuga mertensiana subsp. mertensiana var. mertensiana. Northern mountain hemlock. Leaves gray-green on both sides.
    • Tsuga mertensiana subsp. mertensiana var. jeffreyi (Henry) Schneider. Jeffrey's mountain hemlock. Mixed with var. mertensiana; rare. Leaves greener, less glaucous above, paler below; cones indistinguishable from the type. At one time it was thought to be a hybrid with western hemlock, but there is no verified evidence for this.
Foliage of subsp. grandicona
  • Tsuga mertensiana subsp. grandicona Farjon. California mountain hemlock; syn. T. hookeriana (A.Murray) Carrière, T. crassifolia Flous. Central Oregon southwards. Leaves very strongly glaucous. Cones larger, 45–80 mm long, 20–35 mm broad when open, with 40 to 60 scales.

Ecology[edit]

Mountain hemlock is usually found on cold, snowy subalpine sites where it grows slowly, sometimes attaining more than 800 years in age. Arborescent individuals that have narrowly conical crowns until old age (300 to 400 years) and shrubby krummholz on cold, windy sites near timberline add beauty to mountain landscapes. Areas occupied by mountain hemlock generally have a cool to cold maritime climate that includes mild to cold winters, a short, warm to cool growing season and moderate to high precipitation.[6]

Best development of mountain hemlock is on loose, coarse-textured, well-drained soils with adequate moisture, and in British Columbia, on thick and very acidic organic matter and decayed wood.[7] Adequate soil moisture appears to be especially important in California and Montana, where summer drought is most pronounced.[6][8]

Mountain hemlock will grow on most landforms, but individuals typically develop best in mixed stands of forest on sheltered slopes or in draws. From southern British Columbia south, the tree grows better on northerly exposures. The preference for relatively moist, cool sites evidently becomes a necessity as the climate becomes more continental in western Montana and more mediterranean in the central Sierra Nevada at these extremes of its range.[8] In these locations, mountain hemlock typically grows in isolated populations in north-facing glens and cirque basins where snow collects and may remain well into summer.[6]

Mountain hemlock is adapted to sites with long-lasting snowpacks. In the spring, mountain hemlocks emerging through 2 to 4 metres (7 to 13 ft) of snow were transpiring, whereas nearby whitebark pines did not transpire until the soil beneath them was free of snow.[6] Mountain hemlock is well adapted to cope with heavy snow and ice loads, with tough branches, and the drooping branchlets shedding snow readily.[4]

Mountain hemlock is tolerant of shade and other forms of competition. It is more tolerant than all its associates except Pacific silver fir, western hemlock, and Alaska cedar.[9] Mountain hemlock is considered a minor climax species on most of its habitats; however, it pioneers on glacial moraines in British Columbia and Alaska. Pacific silver fir is a major climax species in many communities of the mountain hemlock forest in British Columbia and Washington and northern Oregon.[7][9] Alaska cedar, western redcedar, and western hemlock are climax associates on some sites. Mountain hemlock is more commonly the major climax species in the mountain hemlock zone south of central Oregon where Pacific silver fir does not occur.[6]

Mountain hemlock often succeeds lodgepole pine or subalpine fir when these species pioneer on drier sites. It also tends to replace Engelmann spruce when the two species occur together, possibly because hemlock is better able to withstand the allelopathic effects of spruce than are other associated species.[6]

Cultivation[edit]

Outside of its native range, mountain hemlock is grown as an ornamental tree. It is planted as a specimen tree in native plant landscapes in California, and particularly in gardens in northern Great Britain and Scandinavia, where it is appreciated for its blue-green color and tolerance of severe weather. Cultivation is limited by the very slow growth of young plants and its susceptibility to urban air pollution.

Several cultivars have been selected, mainly for intensely glaucous foliage color including:

  • 'Blue Star'
  • 'Glauca'[10]

References[edit]

  1. ^ Conifer Specialist Group (1998). Tsuga mertensiana. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
  2. ^ a b c d Farjon, A. (1990). Pinaceae. Drawings and Descriptions of the Genera. Koeltz Scientific Books. ISBN 3-87429-298-3. 
  3. ^ a b c "Tsuga mertensiana". Flora of North America. 
  4. ^ a b c d e "Tsuga mertensiana". Gymnosperm Database. 
  5. ^ David Gledhill in The Names of Plants 3rd Edition, Cambridge University Press 2002
  6. ^ a b c d e f  This article incorporates public domain material from the United States Department of Agriculture document "Silvics Manual, Volume 1, Tsuga mertensiana" by Joseph E. Means.
  7. ^ a b Brooke, Robert C.; Peterson, E. G.; Krajina, V. J. (1970). "The subalpine mountain hemlock zone". In Krajina, V. J. Ecology of western North America 2. Vancouver: University of British Columbia Department of Botany. pp. 147–349. 
  8. ^ a b Habeck, James R. (1967). "Mountain hemlock communities in western Montana". Northwest Science 41 (4): 169–177. 
  9. ^ a b Krajina, V. J. (1969). "Ecology of forest trees in British Columbia". In Krajina, V. J. Ecology of western North America 2. Vancouver, BC: University of British Columbia, Department of Biology. pp. 1–147. 
  10. ^ Rushforth, K. (1987). Conifers. Helm ISBN 0-7470-2801-X.

Further reading[edit]

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Notes

Comments

The wood of Tsuga mertensiana is somewhat inferior to that of western hemlock both for building purposes and as pulp. This is a very handsome tree with its branches densely clothed with pale, spreading leaves and is adaptable to a wide variety of climatic conditions. 

 M.Van Campo-Duplan and H.Gaussen (1948) postulated that this taxon originated by hybridization between Picea and Tsuga . Although this is unlikely, some characteristics such as leaf arrangement and shape, phenolic chemistry, and pollen grain structure lend some support for this hypothesis.

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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

Source: Missouri Botanical Garden

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Names and Taxonomy

Taxonomy

The currently accepted scientific name for mountain hemlock is Tsuga
mertensiana (Bong.) Carriere [38,46,49]. Mountain hemlock in the
Siskiyous from the Oregon-California border south were recently
classified as Tsuga mertensiana spp. grandicona Farjon, in recognition
of the generally larger cones of trees in this region [49]. All others
are classified as Tsuga mertensiana spp. mertensiana. There are no
recognized varieties or forms. Mountain hemlock will hybridize with
western hemlock (T. heterophylla) [46].
  • 38. Hosie, R. C. 1969. Native trees of Canada. 7th ed. Ottawa, ON: Canadian Forestry Service, Department of Fisheries and Forestry. 380 p. [3375]
  • 46. 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]
  • 49. Means, Joseph E. 1990. Tsuga mertensiana (Bong.) Carr. mountain 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: 623-634. [13423]

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Common Names

mountain hemlock
alpine hemlock
black hemlock
hemlock spruce

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