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Overview

Brief Summary

Pinaceae -- Pine family

    E. C. Packee

    Western hemlock (Tsuga heterophylla), also called Pacific  hemlock and west coast hemlock, thrives in humid areas of the Pacific  coast and northern Rocky Mountains. Its potential for management as an  efficient producer of fiber has long been recognized. It is an important  browse species for deer and elk. Western hemlock provides an important  part of the esthetic background for eight national parks-four each in the  United States and Canada. It is a pioneer on many sites, yet it is  commonly the climax dominant. Although western hemlock grows like a weed,  its versatility and potential for management make it the "Cinderella  of the Northwest."

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E. C. Packee

Source: Silvics of North America

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Comprehensive Description

Description

General: Western hemlock (Tsuga heterophylla) is a large evergreen tree growing from ninety to two-hundred feet high. The needles are short stalked, flat, finely toothed, irregularly spare, and of unequal length (five to twenty millimeters long). The seed cones are ovoid, short-stalked, brown, with many thin papery scales, stalkless, and hanging down at the end of the twigs. The bark is smooth when young, reddish-brown, becoming darker, and deeply furrowed with flat-topped scaly ridges (Farrar 1995).

Distribution: Western hemlock is native in northwestern California, Oregon, Washington, British Columbia, Alaska, Idaho, and Montana (McMinn & Maino 1963). In California, western hemlock occurs near the coast in scattered localities from Del Norte County southward to the vicinity of Elk Creek, Mendocino County (Ibid.). In Oregon and Washington, it inhibits the Coast Ranges and Olympic Mountains, extending eastward to the Cascades (Ibid.). For current distribution, please consult the PLANT Profile page for this species on the PLANTS Web site.

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USDA NRCS National Plant Data Center

Source: USDA NRCS PLANTS Database

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Alternative names

West coast hemlock, pacific hemlock, coast hemlock

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USDA NRCS National Plant Data Center

Source: USDA NRCS PLANTS Database

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Distribution

Western hemlock occurs in the Coast Ranges from Sonoma County California
to the Kenai Peninsula in Alaska. Inland it occurs along the western
and upper eastern slopes of the Cascade Range in Oregon and Washington
and west of the Continental Divide in the northern Rocky Mountains of
Montana and Idaho, north to Prince George, British Columbia
[10,56,57,78].

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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
5 Columbia Plateau
8 Northern Rocky Mountains

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Occurrence in North America

AK CA ID MT OR WA AB BC

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Western hemlock is an important commercial tree species of the Pacific  coast and northern Rocky Mountains. Along the Pacific coast, its range  extends north along the Coast Ranges from central California to the Kenai  Peninsula in Alaska, a distance of 3200 km (2,000 mi) (11,18,33). It is  the dominant species in British Columbia and Alaska along the Coast  Mountains and on the coastal islands.

    Inland it grows along the western and upper eastern slopes of the  Cascade Range in Oregon and Washington and the west side of the  Continental Divide of the northern Rocky Mountains in Montana and Idaho  north to Prince George, BC (7,18,26).

     
- The native range of western hemlock.

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E. C. Packee

Source: Silvics of North America

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Adaptation

Western hemlock occurs on a variety of soil types. This species is well adapted to grow on humus and decaying wood, and is also found on mineral soil (Pojar & MacKinnon 1994). This species is very shade tolerant and thrives in full sun and regenerates well under a closed canopy. Western hemlock grows in pure stands or mixed at lower levels with Douglas-fir, silver and grand firs, giant arborvitae, redwood, and hardwood and at higher elevations with noble fir, Alaska cedar, mountain hemlock, western, white, and lodgepole pines (Preston 1989).

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USDA NRCS National Plant Data Center

Source: USDA NRCS PLANTS Database

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Physical Description

Morphology

Description

Trees to 50m; trunk to 2m diam.; crown narrowly conic. Bark gray-brown, scaly and moderately fissured. Twigs yellow-brown, finely pubescent. Buds ovoid, gray-brown, 2.5--3.5mm. Leaves (5--)10--20(--30)mm, mostly appearing 2-ranked, flattened; abaxial surface glaucous with 2 broad, conspicuous stomatal bands, adaxial surface shiny green (yellow-green); margins minutely dentate. Seed cones ovoid, (1--)1.5--2.5(--3) ´ 1--2.5cm; scales ovate, 8--15 ´ 6--10mm, apex round to pointed. 2 n =24.
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Description

More info for the term: tree

Western hemlock is a large, native, evergreen tree. At maturity it is
generally 100 to 150 feet (30-46 m) tall and 2 to 4 feet (0.6-1.2 m) in
trunk diameter [72]. On best sites, old-growth trees reach diameters
greater than 3.3 feet (1 m); maximum diameter is about 9 feet (3 m).
Heights of 160 to 200 feet (49-61 m) are not uncommon; maximum
height has been reported as 259 feet (79 m) [57].

Western hemlock has a long slender trunk often becoming fluted when
large and has a short, narrow crown of horizontal or slightly drooping
branches. The needles are short-stalked and 0.25 to 0.87 inch (6-22 mm)
long, flat and rounded at the tip. The twigs are slender [72]. The
bark is thin (1 to 1.5 inches [0.39-0.59 cm]) even on large trees; young
bark is scaly and on old trunks it is hard with furrows separating wide
flat ridges [60]. Western hemlock is shallow rooted and does not
develop a taproot. The roots, especially the fine roots, are commonly
most abundant near the surface and are easily damaged by harvesting
equipment and fire. Maximum ages are typically over 400 years but less
than 500 years. The maximum age recorded is in excess of 700 years
[57].

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Physical Description

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

Source: USDA NRCS PLANTS Database

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Diagnostic Description

Synonym

Abies heterophylla Rafinesque, Atlantic J. 1: 119. 1832
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Ecology

Habitat

Central and Southern Cascades Forests Habitat

The Oregon slender salamander is endemic to the Central and Southern Cascades forests ecoregion. The Central and Southern Cascades forests span several physiographic provinces in Washington and Oregon, including the southern Cascades, the Western Cascades, and the High Cascades, all within the USA. This ecoregion extends from Snoqualmie Pass in Washington to slightly north of the California border. The region is characterized by accordant ridge crests separated by steep, deeply dissected valleys, strongly influenced by historic and recent volcanic events (e.g. Mount Saint Helens).

This ecoregion contains one of the highest levels of endemic amphibians (five of eleven ecoregion endemics are amphibians) of any ecoregion within its major habitat type. The threatened Northern spotted owl has been used as an indicator species in environmental impact assessments, since its range overlaps with 39 listed or proposed species (ten of which are late-seral associates) and 1116 total species associated with late-seral forests. Late-seral forests in general are of national and global importance because they provide some of the last refugia for dependent species, and perform vital ecological services, including sequestration of carbon, cleansing of atmospheric pollutants, and maintenance of hydrological regimes.

There are a number ofl amphibian taxa present in the Central and Southern Cascades ecoregion; the totality of these amphibian taxa are: the Rough-skinned newt (Taricha granulosa);  the endemic and Vulnerable Shasta salamander (Hydromantes shastae);  the endemic and Vulnerable Oregon slender salamander (Batrachoseps wrighti); the Endangered Dunn's salamander (Bolitoglossa dunni); the Northwestern salamander (Ambystoma gracile); the Near Threatened western toad (Anaxyrus boreas); the Vulnerable Oregon spotted frog (Rana pretiosa); the Near Threatened Cascades frog (Rana cascadae); Coastal tailed frog (Ascaphus truei); Near Threatened Larch Mountain salamander (Plethodon larselli); California newt (Taricha torosa); Pacific giant salamander (Dicamptodon ensatus); Cope's giant salamander (Dicamptodon copei); Monterey ensatina (Ensatina eschscholtzii); the Near Threatened Foothill yellow-legged frog (Rana boylii); Northern Red-legged frog (Rana aurora); Pacific chorus frog (Pseudacris regilla); Van Dyke's salamander (Plethodon vandykei), an endemic of the State of Washington, USA; Long-toed salamander (Ambystoma macrodactylum); and the Olympic torrent salamander (Rhyacotriton olympicus).

There are a moderate number of reptilian species present in the ecoregion, namely in total they are: Western pond turtle (Emys marmorata); Western fence lizard (Sceloporus occidentalis); Sharp-tailed snake (Contia tenuis); Ringed-neck snake (Diadophis punctatus); Rubber boa (Charina bottae); California mountain kingsnake (Lampropeltis zonata); Yellow-bellied racer (Coluber constrictor); Western rattlesnake (Crotalus viridis); Western gopher snake (Pituophis catenifer); Common garter snake (Thanophis sirtalis); Northwestern garter snake (Thamnophis ordinoides); Western skink (Megascops kennicottii); Southern alligator lizard (Elgaria multicarinata); and the  Northern alligator lizard (Elgaria coerulea).

There is a considerable number of avifauna within the Central and Southern Cascades ecoregion; representative species being: Flammulated owl (Otus flammeolus); Western screech owl (Megascops kennicottii); White-tailed ptarmigan (Picoides albolarvatus); and White-headed woodpecker (Picoides albolarvatus).

There are a large number of mammalian taxa in the ecoregion, including: Bobcat (Lynx rufus); Wolverine (Gulo gulo); California ground squirrel (Spermophilus beecheyi); Yellow-bellied marmot (Marmota flaviventris); Ermine (Mustela erminea); Fog shrew (Sorex sonomae), an endemic mammal to the far western USA; Hoary marmot (Marmota caligata); Mountain beaver (Aplodontia rufa); and the Near Threatened red tree vole (Arborimus longicaudus); Yellow pine chipmunk (Tamias amoenus); and the American water shrew (Sorex palustris).

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Puget Lowland Forests Habitat

Cope's giant salamander is found in the Puget lowland forests along with several other western North America ecoregions. The Puget lowland forests occupy a north-south topographic depression between the Olympic Peninsula and western slopes of the Cascade Mountains, extending from north of the Canadian border to the lower Columbia River along the Oregon border. The portion of this forest ecoregion within British Columbia includes the Fraser Valley lowlands, the coastal lowlands locally known as the Sunshine Coast and several of the Gulf Islands. This ecoregion is within the Nearctic Realm and classified as part of the Temperate Coniferous Forests biome.

The Puget lowland forests have a Mediterranean-like climate, with warm, dry summers, and mild wet winters. The mean annual temperature is 9°C, the mean summer temperature is 15°C, and the mean winter temperature is 3.5°C. Annual precipitation averages 800 to 900 millimeters (mm) but may be as great as 1530 mm. Only a small percentage of this precipitation falls as snow. However, annual rainfall  on the San Juan Islands can be as low as 460 mm, due to rain-shadow effects caused by the Olympic Mountains. This local rain shadow effect results in some of the driest sites encountered in the region. Varied topography on these hilly islands results in a diverse assemblage of plant communities arranged along orographically defiined moisture gradients. Open grasslands with widely scattered trees dominate the exposed southern aspects of the islands, while moister dense forests occur on northern sheltered slopes characterized by Western red cedar (Thuja plicata), Grand fir (Abies grandis), and Sword fern (Polystichum munitum) communities.

There are only a small number of amphibian taxa in the Puget lowland forests, namely: Cope's giant salamander (Dicamptodon copei); Monterey ensatina (Ensatina eschscholtzii); Long-toed salamander (Ambystoma macrodactylum); Western redback salamander (Plethodon vehiculum); Northwestern salamander (Ambystoma gracile); Pacific chorus frog (Pseudacris regilla); Coastal giant salamander (Dicamptodon tenebrosus); Rough-skin newt (Taricha granulosa);  the Vulnerable Spotted frog (Rana pretiosa); Tailed frog (Ascopus truei); and Northern red-legged frog (Rana aurora).

Likewise there are a small number of reptilian taxa within the ecoregion: Common garter snake (Thamnophis sirtalis); Western terrestrial garter snake (Thamnophis sirtalis); Northern alligator lizard (Elgaria coerulea); Western fence lizard (Sceloporus occidentalis); Northwestern garter snake (Thamnophis ordinoides); Sharp-tailed snake (Contia tenuis); Yellow-bellied racer (Coluber constrictor); and Western pond turtle (Clemmys marmorata).

There are numberous mammalian taxa present in the Puget lowland forests. A small sample of these are:Creeping vole (Microtus oregoni), Raccoon (Procyon lotor), Southern sea otter (Enhydra lutris), Mink (Mustela vison), Coyote (Canis latrans), Black-tailed deer (Odocoileus hemionus), Pallid bat (Antrozous pallidus), and Harbour seal (Phoca vitulina).

A rich assortment of bird species present in this ecoregion, including the Near Threatened Spotted owl (Strix occidentalis), Turkey vulture (Cathartes aura), Bald eagle (Haliaeetus leucocephalus), Blue grouse (Dendragapus obscurus), as well as a gamut of seabirds, numerous shorebirds and waterfowl.

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Habitat and Ecology

Habitat and Ecology
Tsuga heterophylla occurs from sea level to 600 m a.s.l. along the Pacific coast, in the Rocky Mountains it reaches to 1,800 m. It grows on a variety of soils with an acid organic top layer (pH 3.5-5). The climate is cool maritime along the coast, cold montane in the interior, the annual precipitation varies between (500-)900-3,800 mm, decreasing towards the interior. Dry summers limit its range in the Rocky Mountains. It is highly sympatric with Picea sitchensis in most of the range. It is extremely shade tolerant, but has a shorter life span than Pseudotsuga menziesii or Picea sitchensis. Close along the coast it may form occasionally pure stands, but more commonly it is an important constituent of the (maritime) mesothermal coniferous forest. On the Olympic Peninsula of Washington it reaches maximum size, together with other giant conifers. Its tolerance to shade allows it to grow up under the canopy of other trees, but a thick moss layer usually prevents the light seeds from reaching the soil. Instead, seeds germinate massively on fallen trees ('nurse logs'), from where a few saplings are able to send roots down into the soil; as a result T. heterophylla often stands in rows ('collonades') long after the nurse log has rotten away.

Systems
  • Terrestrial
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Central Pacific Coastal Forests Habitat

This taxon is found in the Central Pacific Coastal Forests ecoregion, as one of its North American ecoregions of occurrence. These mixed conifer rainforests stretch from stretch from southern Oregon in the USA to the northern tip of Vancouver Island, Canada. These forests are among the most productive in the world, characterized by large trees, substantial woody debris, luxuriant growths of mosses and lichens, and abundant ferns and herbs on the forest floor. The major forest complex consists of Douglas-fir (Pseudotsuga menziesii) and Western hemlock (Tsuga heterophylla), encompassing seral forests dominated by Douglas-fir and massive old-growth forests of Douglas-fir, Western hemlock, Western red cedar (Thuja plicata), and other species. These forests occur from sea level up to elevations of 700-1000 meters in the Coast Range and Olympic Mountains. Such forests occupy a gamut of environments with variable composition and structure and includes such other species as Grand fir (Abies grandis), Sitka spruce (Picea sitchensis), and Western white pine (Pinus monticola).

Characteristic mammalian fauna include Elk (Cervus elaphus), Black-tailed Deer (Odocoileus hemionus), Coyote (Canis latrans), Black Bear (Ursus americanus), Mink (Mustela vison), and Raccoon (Procyon lotor).

The following anuran species occur in the Central Pacific coastal forests: Coastal tailed frog (Ascaphus truei); Oregon spotted frog (Rana pretiosa VU); Northern red-legged frog (Rana pretiosa); Pacific chorus frog (Pseudacris regilla); Cascade frog (Rana cascadae NT), generally restricted to the Cascade Range from northern Washington to the California border; Foothill yellow-legged frog (Rana boylii) and the Western toad (Anaxyrus boreas NT).  A newt found in the ecoregion is the Rough skinned newt (Taricha granulosa).

Salamanders within the ecoregion are: Del Norte salamander (Plethodon elongatus NT);  Van Dyke's salamander (Plethodon vandykei); Western redback salamander (Plethodon vehiculum); Northwestern salamander (Ambystoma gracile);  Olympic torrent salamander (Rhyacotriton olympicus VU), whose preferred habitat is along richly leafed stream edges; Long-toed salamander (Ambystoma macrodactylum), whose adults are always subterranean except during the breeding season; Dunn's salamander (Plethodon dunni), usually found in seeps and stream splash zones; Clouded salamander (Aneides ferreus NT), an aggressive insectivore; Monterey ensatina (Ensatina eschscholtzii), usually found in thermally insulated micro-habitats such as under logs and rocks; Pacific giant salamander (Dicamptodon tenebrosus), found in damp, dense forests near streams; and Cope's giant salamander (Dicamptodon copei), usually found in rapidly flowing waters on the Olympic Peninsula and Cascade Range.

There are a small number of reptilian taxa that are observed within this forested ecoregion, including: Pacific pond turtle (Emys marmorata); Common garter snake (Thamnophis sirtalis), an adaptable snake most often found near water; Northern alligator lizard (Elgaria coerulea); and the Western fence lizard.

Numerous avian species are found in the ecoregion, both resident and migratory. Example taxa occurring here are the Belted kingfisher (Megaceryle alcyon); Wild turkey (Meleagris gallopavo); and the White-headed woodpecker (Picoides albolarvatus) and the Trumpeter swan (Cygnus buccinator), the largest of the North American waterfowl.

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Habitat characteristics

More info for the terms: density, shrub, vine

Western hemlock thrives in humid areas of the Pacific Coast and northern
Rocky Mountains. Growth is best in mild, humid climates where frequent
fog and precipitation occur during the growing season. The best stands
occur in the humid coastal regions. In subhumid regions with relatively
dry growing seasons, western hemlock is confined primarily to northerly
aspects, moist stream bottoms, or seepage sites [10,57,59]. In Alaska,
western hemlock attains its largest size on moist flats and low slopes
[72].

Precipitation and temperature: In the coastal range, western hemlock
occurs on sites with a mean annual precipitation of less than 15 inches
(380 mm) in Alaska to at least 262 inches (6,650 mm) in British
Columbia. In the Rocky Mountains it occurs on sites with mean annual
precipitation ranging from 22 inches (560 mm) to at least 68 inches
(1,730 mm). Mean annual temperatures where western hemlock commonly
occurs range from 32.5 to 52.3 degrees Fahrenheit (0.3-11.3 deg C) on
the coast and 36 to 46.8 degrees Fahrenheit (2.2-8.2 deg C) in the Rocky
Mountains. The frost-free period within the coastal range of western
hemlock averages less than 100 to more than 280 days. In the Rocky
Mountains the frost-free period is 100 to 150 days [57].

Elevation: The elevational range of western hemlock is from sea level
to 7,000 feet (2,130 m). On the coast, western hemlock develops best
between sea level and 2,000 feet (610 m); in the Rocky Mountains, it
develops best between 1,600 and 4,200 feet (490-1,280 m) [57].

Soils: Western hemlock grows on soils derived from all bedrock types
(except serpentines) within its range [57]. It grows well on
sedimentary, metamorphic, and igneous materials. Western hemlock is
found on most soil textures. Height growth, however, decreases with an
increase in clay content or soil bulk density. This is attributed to
inadequate soil aeration or the inability of roots to penetrate compact
soils. Western hemlock does not do well on sites where the water table
is less than 6 inches (15 cm) below the soil surface. The pH under
stands containing western hemlock ranges from less than 3.0 to nearly
6.0 in the organic horizons. The pH in the surface mineral horizons
ranges from 4.0 to 6.3 and that of the C horizons from 4.8 to 6.2. The
optimum range of pH for seedlings is 4.5 to 5.0. Western hemlock is
highly productive on soils with a high range of available nutrients.
The produtivity of western hemlock increases as soil nitrogen increases
[57].

In the Coast Range, western hemlock is commonly associated with the
following shrub species: vine maple (Acer circinatum), dwarf
Oregongrape (Mahonia nervosa), Pacific rhododendron (Rhododendron
macrophyllum), stink currant (Ribes bracteosum), salmonberry, trailing
blackberry (R. ursinus), Pacific red elder (Sambucus callicarpa),
Alaska blueberry (Vaccinium alaskaense), big huckleberry (V.
membranaceum), oval-leaf huckleberry (V. ovalifolium), evergreen
huckleberry (V. ovatum), and red huckleberry (V. parvifolium)
[12,31,32,57].

In the Rocky Mountains, western hemlock is commonly associated with the
following shrub species: Oregon grape (Mahonia repens), russet
buffaloberry (Shepherdia canadensis), birchleaf spirea (Spiraea
betulifolia), dwarf blueberry (Vaccinium caespitosum), globe huckleberry
(V. globulare), and grouse whortleberry (V. scoparium) [55,57,59,69,73].

Common shrub associates of both coastal and Rocky Mountain regions are
as follows: Sitka alder (Alnus sinuata), snowbush ceanothus (Ceonothus
velutinus), oceanspray (Holodiscus discolor), rustyleaf mensziesia
(Menziesia ferruginea), devilsclub, Pacific ninebark (Physocarpus
capitatus), prickly currant (Ribes lacustre), thimbleberry, and common
snowberry (Symphoricarpos albus) [57].

Common herb associates with western hemlock include maidenhair fern
(Adiantum pedatum), ladyfern (Athyrium filix-femina), deerfern (Blechnum
spicant), mountain woodfern (Dryopteris austriaca), oakfern
(Gymnocarpium dryopteris), swordfern (Polystichum munitum), bracken fern
(Pteridium aquilinum), vanillaleaf (Achlys triphylla), wild ginger
(Asarum caudatum), princes-pine (Chimaphila umbellata), queenscup
beadlily (Clintonia unifora), cleavers bedstraw (Galium aparine),
sweetscented bedstraw (G. triflorum), twinflower (Linnaea borealis),
one-sided pyrola (Pyrola secunda), feather solomonplume (Smilacina
racemosa), white trillium (Trillium ovatum), roundleaf violet (Viola
orbiculata), and beargrass (Xerophyllum tenax) [55,57,59,69,73].

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Key Plant Community Associations

More info for the terms: association, climax, codominant, cover, natural

Western hemlock commonly occurs as a dominant or codominant on low- to
mid-elevation moist sites. In northern Idaho, plant communities
dominated by western hemlock occupy the moist, moderate temperature
sites within the maritime-influenced climatic zone of the northern Rocky
Mountains. Here, western hemlock can be found as the climax dominant
from 2,500 to 5,500 feet (760-1,680 m) and can dominate sites of all
exposures and landforms except wet bottomlands where it is replaced or
codominant with western redcedar (Thuja plicata) [19]. In the Gifford
Pinchot National Forest of Washington, the western-hemlock-dominated
zone includes the lower elevation moist forests of the western Cascades
[68]. In Mount Rainier National Park, Washington, the western
hemlock/devil's club (Oplopanax horridus) community occupies wet
benches, terraces, and lower slopes at low elevations [32]. The western
hemlock riparian dominance type in Montana described by Hansen and
others [39] is an infrequent cover type restricted to northwestern
Montana on toe-slope seepages, moist benches, and wet bottoms adjacent
to streams. Published classifications identifying western hemlock as a
dominant or codominant are as follows:

Classification and management of riparian and wetland sites in northwest
Montana [14].
Classification of montane forest community types in the Cedar River
drainage of western Washington, U.S.A. [54].
The forest communities of Mount Rainier National Park [32].
Forest habitat types of Montana [59].
Forest habitat types of northern Idaho: A second approximation [19].
Forest types of the North Cascades National Park Service complex [5].
Forest vegetation of eastern Washington and northern Idaho [21].
A guide to the interior cedar-hemlock zone, northwestern transitional
subzone (ICHg), in the Prince Rupert Forest Region, British
Columbia [36].
Natural vegetation of Oregon and Washington [31].
Plant association and management guide [41].
Plant association and management guide for the western hemlock zone.
Gifford Pinchot National Forest [68].
Plant association and management guide for the western hemlock zone: Mt.
Hood National Forest [37].
Plant association and management guide. Willamette National Forest [42].
A preliminary classification of forest communities in the central
portion of the western Cascades in Oregon [25].
Preliminary forest plant association management guide. Ketchikan area,
Tongass National Forest [23].
Preliminary forest plant associations of the Stikine area Tongass
National Forest [70].
Preliminary plant associations of the Siskiyou Mountain province [12].
Preliminary plant associations of the southern Oregon Cascade Mountain
Province [11].
Reference material Daubenmire habitat types [69].
Riparian dominance types of Montana [39].
A study of the vegetation of southeastern Washington and adjacent Idaho
[73].
Vegetation mapping and community description of a small western cascade
watershed [40].
Vegetation of the Abbott Creek Research Natural Area, Oregon [53].

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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):

FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES22 Western white pine
FRES23 Fir - spruce
FRES24 Hemlock - Sitka spruce
FRES25 Larch
FRES26 Lodgepole pine
FRES27 Redwood
FRES28 Western hardwoods

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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):

202 White spruce - paper birch
205 Mountain hemlock
206 Engelmann spruce - subalpine fir
210 Interior Douglas-fir
212 Western larch
213 Grand fir
215 Western white pine
218 Lodgepole pine
221 Red alder
222 Black cottonwood - willow
223 Sitka spruce
224 Western hemlock
225 Western hemlock - Sitka spruce
226 Coastal true fir - hemlock
227 Western redcedar - western hemlock
228 Western redcedar
229 Pacific Douglas-fir
230 Douglas-fir - western hemlock
231 Port-Orford-cedar
232 Redwood

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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
K005 Mixed conifer forest
K006 Redwood forest
K008 Lodgepole pine - subalpine forest
K012 Douglas-fir forest
K013 Cedar - hemlock - pine forest
K014 Grand fir - Douglas-fir forest
K015 Western spruce - fir forest

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Soils and Topography

Western hemlock grows on soils derived from all bedrock types (except  possibly serpentines) within its range. It grows well on sedimentary  (argillites, shales, sandstones, limestones), metamorphic (gneisses,  marbles, quartzites, schists), and igneous (andesites, basalts, diorites,  gabbros, granites) materials. Under appropriate climatic conditions, it  thrives on all major landforms-colluvial, eolian, fluvial, lacustrine,  marine, morainal, residual, rock, and organic.

    Western hemlock grows on a variety of soils and is a characteristic  species on soils of 6 of the 10 soil orders: Alfisols, Entisols,  Histosols, Inceptisols, Spodosols, and Ultisols; and on many great groups,  including: Fragiboralfs, Fragiudalfs, Hapludalfs; Fluvaquents,  Udifluvents, Quartzipsamments; Borofolists, Cryolfolists; Cryandepts,  Dystrandepts, Vitrandepts, Cryaquepts, Haplaquepts, Dystrochrepts,  Cryumbrepts, Haplumbrepts; Fragiaquods, Placohumods, Cryorthods,   Fragiorthods, Haplorthods; and Haplohumults. It is found on most soil  textural classes. Height growth, however, decreases with increasing clay  content or soil bulk density. This is attributed to inadequate soil  aeration (35) or the inability of roots to penetrate compact soils.

    Western hemlock thrives on soils with perudic and udic soil moisture  regimes. If, however, internal soil drainage is restricted within 1 m (3.3  ft) of the soil surface, height growth decreases (35). Western hemlock is  poorly suited to sites where the water table is less than 15 cm (6 in)  below the soil surface (22). Although capable of existing on soils with  moisture regimes tending toward ustic or xeric, it grows poorly;  frequently, tops die back in years of drought.

    The soil organic horizon under mature stands ranges from less than 7 to  more than 57 cm (2.8 to 22.5 in); the average depth increases from 11.4 cm  (4.5 in) on soils with good drainage to 43.2 cm (17.0 in) on poorly  drained soils (15). Commonly, the majority of roots, especially fine  roots, are concentrated just below the organic horizon. The importance of  the organic horizon as a continual supply of available nutrients for  western hemlock cannot be overstated. In coastal British Columbia,  earthworms are common in the organic horizons, even where the pH is less  than 4; earthworms may play an important role in making nutrients  available for root uptake. On many soils of Oregon and Washington,  however, rooting depths exceed 1 m (3.3 ft).

    Soil reaction (pH) under stands containing western hemlock ranges from  less than 3.0 to nearly 6.0 in the organic horizons. The pH in the surface  mineral horizons ranges from 4.0 to 6.3 and that of the C horizon from 4.8  to 6.2 (21). Optimum range of pH for seedlings is 4.5 to 5.0.

    Western hemlock is highly productive on soils with a broad range of  available nutrients. Evidence from various locations on the Pacific coast  suggests that the productivity of western hemlock increases as soil  nitrogen increases (15,21). There is no evidence that seedlings prefer  ammonium over nitrate ions (32). Phosphorus may be limiting on some sites  as suggested by data from Oregon showing a strong relation between site  index and soil phosphorus (21). Although the requirement of western  hemlock for cations is unclear, rooting habit and field data suggest that  it requires or tolerates considerable amounts of calcium.

    The range in elevation at which western hemlock grows is broad, from sea  level to 2130 m (7,000 ft); its distribution varies by latitude and  mountain range. On the coast, western hemlock develops best between sea  level and 610 m (2,000 ft); in the Rocky Mountains, between 490 and 1280 m  (1,600 and 4,200 ft) (26).

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E. C. Packee

Source: Silvics of North America

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Climate

Western hemlock thrives in a mild, humid climate where frequent fog and  precipitation occur during the growing season. Best stands are in the  humid and superhumid coastal regions. In subhumid regions with relatively  dry growing seasons, western hemlock is confined primarily to northerly  aspects, moist stream bottoms, or seepage sites.

    Within the coastal range of western hemlock, mean annual total  precipitation ranges from less than 380 mm (15 in) in Alaska to at least  6650 mm (262 in) in British Columbia. The range in the Rocky Mountains is  560 mm (22 in) to at least 1730 mm (68 in) (25).

    Mean annual temperatures range from 0.3° to 11.3° C (32.5°  to 52.3° F) on the coast and 2.2° to 8.2° C (36.0° to  46.8° F) in the Rocky Mountains. Observed mean July temperatures lie  between 11.3° and 19.7° C (52.3° and 67.5° F)  along the coast and 14.4° and 20.6° C (58.0° and 69.0°  F) in the interior. Mean January temperatures reported for the two areas  range from -10.9° to 8.5° C (12.4° to 47.3° F) and  -11.1° to -2.4° C (12.0° to 27.6° F), respectively.  Recorded absolute maximum temperature for the coast is 40.6° C (105.0°  F) and for the Rocky Mountains, 42.2° C (108.0° F). Absolute  minimum temperatures tolerated by western hemlock are -38.9° C (-38.0°  F) for the coast and -47.8° C (-54.0° F) for the interior.

    The frost-free period within the coastal range of western hemlock  averages less than 100 to more than 280 days (25). In the Rocky Mountains,  the frost-free period is 100 to 150 days (20).

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E. C. Packee

Source: Silvics of North America

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Habitat & Distribution

Coastal to midmontane forests; 0--1500m; Alta., B.C.; Alaska, Calif., Idaho, Mont., Oreg., Wash.
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© Missouri Botanical Garden, 4344 Shaw Boulevard, St. Louis, MO, 63110 USA

Source: Missouri Botanical Garden

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Dispersal

Establishment

Propagation from Seed: Seed is best sown in a cold frame in the autumn or late winter. Dormancy is variable with some seed lots requiring cold stratification (Dirr & Heuser 1987). Stratification accelerates and improves total germination and, unless seeds are known not to require pretreatment, cold stratification at 41ºF from three weeks to three months is recommended (Ibid.). Young seedlings should be placed in individual pots, once they are large enough to handle, and allowed to grow in a cold frame. During early summer the following year, out plant seedlings to their permanent locations.

Public Domain

USDA NRCS National Plant Data Center

Source: USDA NRCS PLANTS Database

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Associations

Foodplant / pathogen
Armillaria mellea s.l. infects and damages Tsuga heterophylla

Foodplant / saprobe
fruitbody of Mycena capillaripes is saprobic on dead, decayed needle of litter of Tsuga heterophylla

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Associated Forest Cover

Western hemlock is either a major or a minor component in at least 20  forest cover types of the Society of American Foresters (6).

        Pacific 
Coast  Rocky Mountains      202 White Spruce-Paper Birch  x        205 Mountain Hemlock  x  x      206 Engelmann Spruce-Subalpine Fir    x      210 Interior Douglas-Fir    x      212 Western Larch    x      213 Grand Fir    x      215 Western White Pine    x      218 Lodgepole Pine  x  x      221 Red Alder  x        222 Black Cottonwood-Willow  x        223 Sitka Spruce  x        224 Western Hemlock  x  x      225 Western Hemlock-Sitka Spruce  x        226 Coastal True Fir-Hemlock  x        227 Western Redcedar-Western Hemlock  x  x      228 Western Redcedar  x        229 Pacific Douglas-Fir  x        230 Douglas-Fir-Western Hemlock  x  x      231 Port Orford-Cedar  x        232 Redwood  x          The forest cover types may be either seral or climax.

    Tree associates specific to the coast include Pacific silver fir (Abies  amabilis), noble fir (A. procera), bigleaf maple (Acer  macrophyllum), red alder (Alnus rubra), giant chinkapin (Castanopsis  chrysophylla), Port-Orford-cedar (Chamaecyparis lawsoniana), Alaska-cedar  (C. nootkatensis), incense-cedar (Libocedrus decurrens), tanoak  (Lithocarpus densiflorus), Sitka spruce (Picea sitchensis),  sugar pine (Pinus lambertiana), redwood (Sequoia  sempervirens), and California laurel (Umbellularia californica).  Associates occurring in both the Pacific coast and Rocky Mountain  portions of its range include grand fir (Abies grandis), subalpine  fir (A. lasiocarpa), paper birch (Betula papyrifera), western  larch (Larix occidentalis), Engelmann spruce (Picea  engelmannii), white spruce (P. glauca), lodgepole pine (Pinus  contorta), western white. pine (P. monticola), ponderosa pine  (P. ponderosa), black cottonwood (Populus trichocarpa), Douglas-fir  (Pseudotsuga menziesii), Pacific yew (Taxus brevifolia), western  redcedar (Thuja plicata), and mountain hemlock (Tsuga  mertensiana).

    Western hemlock is a component of the redwood forests on the coasts of  northern California and adjacent Oregon. In Oregon and western Washington,  it is a major constituent of the Picea sitchensis, Tsuga heterophylla,  and Abies amabilis Zones and is less important in the Tsuga  mertensiana and Mixed-Conifer Zones (7). In British Columbia, it is a  major element of the Tsuga heterophylla-Picea sitchensis, Tsuga  heterophylla-Abies amabilis, Tsuga heterophylla, Abies amabilis-Tsuga  heterophylla, and Abies amabilis-Tsuga mertensiana Vegetation  Zones; it is confined to a distinct understory portion or to moist sites  in the Pseudotsuga menziesii-Tsuga heterophylla and Pseudotsuga  menziesii Zones (25). In the Rocky Mountains, it is present in  the Thuja plicata and Tsuga heterophylla Vegetation Zones  and the lower portion of the Abies lasiocarpa Zone (26).

    Various persons have described the plant associations and biogeocoenoses  in which western hemlock is found; more than 75 are listed for the west  coast and more than 30 for the Rocky Mountains (25). Little effort  has been made to correlate the communities with one another.

    Because of its broad range, western hemlock has a substantial number of  understory associates. In its Pacific coast range, common shrub species  include the following (starred species are also common associates in the  Rocky Mountains): vine maple (Acer circinatum), Sitka alder* (Alnus  sinuata), Oregongrape (Berberis nervosa), snowbrush ceanothus*  (Ceanothus velutinus), salal (Gaultheria shallon), oceanspray*  (Holodiscus discolor), rustyleaf menziesia* (Menziesia  ferruginea), devilsclub* (Oplopanax horridus), Oregon boxwood*  (Pachistima myrsinites), Pacific ninebark* (Physocarpus  capitatus), Pacific rhododendron (Rhododendron macrophyllum), stink  currant (Ribes bracteosum), prickly currant* (R. lacustre),  thimbleberry* (Rubus parviflorus), salmonberry (R.  spectabilis), trailing blackberry (R. ursinus), Pacific red  elder (Sambucus callicarpa), common snowberry* (Symphoricarpos  albus), Alaska blueberry (Vaccinium alaskaense), big  huckleberry (V. membranaceum), ovalleaf huckleberry (V.  ovalifolium), evergreen huckleberry (V. ovatum), and red  huckleberry (V. parvifolium). The following are other common  associates in the Rocky Mountains: creeping western barberry (Berberis  repens), russet buffaloberry (Shepherdia canadensis), birchleaf  spirea (Spiraea betulifolia), dwarf blueberry (Vaccinium  caespitosum), globe huckleberry (V. globulare), and grouse  whortleberry (V. scoparium).

    Common herbaceous species include the ferns: maidenhair fern (Adiantum  pedatum), ladyfern (Athyrium filix-femina), deerfern (Blechnum  spicant), mountain woodfern (Dryopteris austriaca), oakfern  (Gymnocarpium dryopteris), swordfern (Polystichum munitum),  and bracken (Pteridium aquilinum). Herb associates include  vanillaleaf (Achlys triphylla), wild ginger (Asarum caudatum),  princes-pine (Chimaphila umbellata), little princes-pine (C.  menziesii), queenscup (Clintonia uniflora), cleavers bedstraw  (Galium aparine), sweetscented bedstraw (G. triflorum), twinflower  (Linnaea borealis), Oregon oxalis (Oxalis oregana), one-sided  pyrola (Pyrola secunda), feather solomonplume (Smilacina  racemosa), starry solomonplume (S. stellata), trefoil  foamflower (Tiarella trifoliata), coolwort foamflower (T.  unifoliata), white trillium (Trillium ovatum), roundleaf  violet (Viola orbiculata), evergreen violet (V. sempervirens),  and common beargrass (Xerophyllum tenax).

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Diseases and Parasites

Damaging Agents

Many agents adversely affect the growth,  health, and quality of western hemlock trees and stands.

    Because of its thin bark and shallow roots, western hemlock is highly  susceptible to fire. Even light ground fires are damaging. Prescribed  burning is an effective means of eliminating western hemlock advance  regeneration from a site.

    Because of its shallow roots, pole-size and larger stands of western  hemlock are subject to severe windthrow. Thousands of hectares of young  stands dominated by coastal western hemlock have originated after such  blowdown.

    Western hemlock suffers frost damage in the Rocky Mountains, especially  along the eastern edge of its range where frost-killed tops are reported  (20,26). Snowbreak occurs locally; it appears to be most common east of  the Cascade and Coast Mountains, and especially in the Rocky Mountains. On  droughty sites, top dieback is common; in some exceptionally dry years,  entire stands of hemlock saplings die. Suddenly exposed saplings may  suffer sunscald. Excessive amounts of soil moisture drastically reduce  growth.

    Western hemlock is one of the species most sensitive to damage by sulfur  dioxide (16). Spring applications of the iso-octyl esters of 2,4-D and  2,4,5-T in diesel oil can kill leader growth of the last 3 years.

    Severe fluting of western hemlock boles is common in southeast Alaska,  much less common on Vancouver Island, and relatively uncommon in  Washington and Oregon. There appears to be a clinal gradient from north to  south; the causal factor is not known.

    No foliage diseases are known to cause serious problems for western  hemlock.

    Dwarf mistletoe (Arceuthobium tsugense) is a serious parasite  along the Pacific coast from California nearly to Glacier Bay, AK; its  presence on western hemlock in the Rocky Mountain States is unconfirmed.  It increases mortality, reduces growth, lowers fiber quality, and provides  an entryway for decay fungi. Uninfected to lightly infected trees may have  a greater growth in volume (40 percent) and height (84 percent) than  severely infected trees; in mature stands, volume losses as high as 4.2 m³/ha  (60 ft³/acre) per year have been reported (29). Dwarf mistletoe in  western hemlock is easy to control; success is nearly 100 percent if  methods of sanitation are good.

    Armillaria mellea, Heterobasidion annosum, Phaeolus schweinitzii,  Laetiporus sulphureus, Inonotus tomentosus, Poria subacida, and Phellinus  weiri are the major root and butt pathogens of western hemlock. Armillaria  mellea occurs widely, seldom kills trees directly, and is not a major  source of cull.

    Heterobasidion annosum, the most serious root pathogen of  western hemlock, can limit the alternatives available for intensive  management (3). The incidence of infected trees in unthinned western  hemlock stands ranges from 0 to more than 50 percent. In some thinned  stands, every tree is infected. Heterobasidion annosum spores  colonize freshly cut stumps and wounds; the spreading mycelium infects  roots and spreads to adjacent trees through root grafts. Treating stumps  and wounds with chemicals can reduce the rate of infection.

    Phellinus weiri is a common root pathogen where Douglas-fir is  or was a major component of the stand. In the Rocky Mountains, a similar  relationship may exist with western redcedar. Phellinus weiri rapidly  extends up into the bole of western hemlock. The first log is frequently  hollow; only the sapwood remains. The only practical controls for P.  weiri are pulling out the stumps and roots or growing resistant  species.

    High risk bole pathogens include Echinodontium tinctorium,  Heterobasidion annosum, and Phellinus weiri. Echinodontium  tinctorium causes extensive decay in overmature stands in the Rocky  Mountains. It is less destructive in immature stands, although it is found  in trees 41 to 80 years old; 46 percent of the trees in this age group in  stands studied were infected. Echinodontium tinctorium is of  little consequence on the coast. Heterobasidion annosum spreads  from the roots into the bole of otherwise vigorous trees. On Vancouver  Island, an average of 24 percent (range 0.1 to 70 percent) of the volume  of the first 5-m (16-ft) log can be lost to H. annosum (24).

    Rhizina undulata, a root rot, is a serious pathogen on both  natural and planted seedlings on sites that have been burned. It can kill  mature trees that are within 8 m (25 ft) of the perimeter of a slash burn  (3).

    Sirococcus strobilinus, the sirococcus shoot blight, causes  dieback of the tip and lateral branches and kills some trees in Alaska;  the potential for damage is not known (27).

    Of the important insects attacking western hemlock, only three do not  attack the foliage. A seed chalcid (Megastigmus tsugae) attacks  cones and seeds; the larva feeds inside the seed. This insect normally is  not plentiful and is of little consequence to seed production (14). A  weevil (Steremnius carinatus) causes severe damage in coastal  British Columbia by girdling seedlings at the ground line. In the Rocky  Mountains, the western larch borer (Tetropium velutinum) attacks  trees that are weakened by drought, defoliated by insects, or scorched by  fire; occasionally it kills trees (9).

    Since 1917, there have been only 10 years in which an outbreak of the  western blackheaded budworm (Acleris gloverana) did not cause  visible defoliation somewhere in western hemlock forests (28). Extensive  outbreaks occur regularly in southeast Alaska, on the coast of British  Columbia, in Washington on the south coast of the Olympic Peninsula and in  the Cascade Range, and in the Rocky Mountains. In 1972, nearly 166 000 ha  (410,000 acres) were defoliated on Vancouver Island alone. Damage by the  larvae is usually limited to loss of foliage and related growth reduction  and top kill. Mortality is normally restricted to small stands with  extremely high populations of budworms.

    The western hemlock looper (Lambdina fiscellaria lugubrosa) has  caused more mortality of western hemlock than have other insect pests.  Outbreaks last 2 to 3 years on any one site and are less frequent than  those of the budworm. The greatest number of outbreaks occurs on the south  coast of British Columbia; the western hemlock looper is less prevalent  farther north. Heavy attacks have been recorded for Washington and Oregon  since 1889. The insect is less destructive in the interior forests.  Although mortality is greatest in old growth, vigorous 80- to 100-year-old  stands are severely damaged.

    Two other loopers, the greenstriped forest looper (Melanolophia  imitata) and the saddleback looper (Ectropis crepuscularia), cause  top kill and some mortality. The phantom hemlock looper (Nepytia  phantasmaria) in the coastal forest and the filament bearer (Nematocampa  filamentaria) play minor roles, usually in association with the  western hemlock looper (28).

    The hemlock sawfly (Neodiprion tsugae) occurs over most of the  range of western hemlock. Its outbreaks often occur in conjunction with  outbreaks of the western blackheaded budworm. The larvae primarily feed on  old needles; hence, they tend to reduce growth rather than cause mortality  (9). The hemlock sawfly is considered the second most destructive insect  in Alaska (13).

    Black bear girdle pole-size trees and larger saplings or damage the bark  at the base of the trees, especially on the Olympic Peninsula of  Washington. Roosevelt elk and black-tailed deer browse western hemlock in  coastal Oregon, Washington, and British Columbia. The snowshoe hare and  the brush rabbit damage hemlock seedlings, principally by clipping off the  main stem; clipping of laterals rarely affects survival of seedlings (5).  Mountain beaver clip the stems and lateral branches of seedlings and  girdle the base of saplings along the coast south of the Fraser River in  British Columbia to northern California. Four years after thinning,  evidence of girdling and removal of bark was present on 40 percent of the  trees (5). Mortality results from both kinds of damage.

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General Ecology

Plant Response to Fire

More info for the terms: competition, natural

Burning may or may not benefit natural regeneration of western hemlock.
The response of seedlings to burning varies according to aspect, slope,
latitude, climate, etc. After broadcast burning in coastal hemlock
zones, more seedlings were found in burned areas than in unburned areas
due to elimination of brush competition and reduction of dense patches
of slash [76]. On Vancouver Island after the third growing season,
burned seedbeds had 58 percent more seedlings with better distribution
than unburned seedbeds [57]. However, on a site near Vancouver, British
Columbia, due to sunscald, all new germinants on burned humus were dead
by mid-July [76].

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Immediate Effect of Fire

More info for the term: crown fire

Western hemlock is commonly killed by fire. High-severity fires often
destroy all western hemlock [24]. After a severe crown fire at Olympic
Mountain, Washington, overstory western hemlock suffered 91 percent
mortality [4]. Even light ground fires are damaging because the shallow
roots are scorched [57]. Postburn mortality of western hemlock is
common due to fungal infection of fire wounds [29]. Most western hemlock
seedlings are killed by broadcast burning [27,64].

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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 intensity, fire interval, fire regime, frequency, lichen, mean fire interval, mesic, resistance, wildfire

Western hemlock has a low degree of fire resistance [20,58]. It has
thin bark, shallow roots, highly flammable foliage, and a low-branching
habit which make it very susceptible to fire. Western hemlock tends to
form dense stands and its branches are often lichen covered, which
further increases its susceptibility to fire damage [15,29,57].

The frequency of fire in western hemlock stands tends to be low because
it commonly occupies cool mesic habitats which offer protection from all
but the most severe wildfire [22,64]. In western hemlock forests of the
Pacific Northwest, the fire regime is generally from 150 to 400 or more
years [58]. At Desolation Peak, Washington, western hemlock forest
types had a mean fire interval of 108 to 137 years [3]. In the western
hemlock/Pachistima habitat type described by Daubenmire and Daubenmire
[21], the mean fire interval is 50 to 150 years, and fire intensity in
these stands is quite variable [9]. In the Bitterroot Mountains,
western hemlock stands are more likely to be destroyed by
stand-replacing fires because they often occupy steep montane slopes
which favor more intense burning [8].

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Successional Status

More info on this topic.

More info for the terms: climax, succession

Obligate Climax Species

Western hemlock is very shade tolerant. Only Pacific yew (Taxus
brevifolia) and Pacific silver fir are considered to have equal or
greater tolerance of shade than western hemlock. Western hemlock is
generally considered a climax species either alone or in combination
with its shade-tolerant associates, but it can be found in all stages of
succession [57]. It is an aggressive pioneer because of its quick
growth in full overhead light and its ability to survive on a wide
variety of seedbed conditions [29,57]. It also invades seral stages of
forest succession after a forest canopy has formed [35]. If several
centuries pass without a major disturbance, a climax of
self-perpetuating, essentially pure western hemlock can result [10]. On
drier upland slopes in Glacier National Park, western hemlock often
achieves dominance over western redcedar. Western hemlock rarely
replaces western redcedar entirely [35]. In Idaho, western white pine
(Pinus monticola) stands are slowly replaced by a western
hemlock-western redcedar climax [52].

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Regeneration Processes

More info for the terms: epigeal, litter, natural, root collar, tree

Seed production and dissemination: Western hemlock is generally a good
cone and seed producer. Cones may form on open-grown trees that are
less than 20 years old, but good cone crops usually do not occur until
trees are between 25 and 30 years old. Individuals usually produce some
cones every year and heavy cone crops every 3 or 4 years. Each cone
contains 30 to 40 seeds. The number of viable seeds ranges from fewer
than 10 to approximately 20 per cone [18,56]. Seeds are light and
small, ranging from 189,000 to 508,000 cleaned seeds per pound, with an
average of 260,000 seeds per pound (371,000-900,000/kg, average 530,000
seeds/kg) [56,63].

Western hemlock seeds have large wings enabling them to be distributed
over long distances. In open, moderately windy areas, most seeds fall
within 1,968 feet (600 m) of the parent tree. Some seeds can travel as
far as 3,772 feet (1,150 m) under these conditions. In dense stands,
most seeds fall much closer to the base of the tree [56].

Germination: Germination is epigeal. Stratification for 3 to 4 weeks
at 33 to 39 degrees Fahrenheit (1-4 deg C) improves germination. The
optimum temperature for germination is 68 degrees Fahrenheit (20 deg C)
[57,63]. For each 9 degrees Fahrenheit (5 deg C) below the optimum, the
number of days required for germination is nearly doubled [63]. Given
sufficent time (6-9 months) and an absence of pathogens, western hemlock
will germinate at temperatures just above freezing. Western hemlock
seeds remain viable only into the first growing season after seedfall
[57]. Viability seems to vary between 36 and 55 percent with an average
of about 46 percent [76].

Western hemlock seed appears to germinate well and seedlings grow well
on almost all natural seedbeds whether rotten wood, undisturbed bed duff
and litter, or bare mineral soil. The principal requirement for
adequate development on any seedbed appears to be adequate moisture.
For drier situations, mineral soils appear to be best for hemlock
seedlings [76].

Seedling development: Most seedling mortality occurs in the first 2
years after germination [76]. Seedlings are very shade tolerant but are
sensitive to heat, cold, drought and wind [56]. In British Columbia,
the main cause of mortality appeared to be either drought or frost [76].
Initial growth is slow; 2-year-old seedlings are commonly less than 8
inches (20 cm) tall. Once established, seedlings in full light may have
an average growth rate of 24 inches (60 cm) or more annually [57]. In
inland regions, one study showed partial shade to be beneficial in
reducing mortality caused by high temperatures and drought. Once
seedlings are over 2 years old, survival appears to be very good [76].

Vegetative reproduction: Western hemlock will reproduce vegetatively by
layering or cuttings. Seedlings that die back to the soil surface
commonly sprout from buds near the root collar. Sprouting does not
occur from the roots or the base of larger saplings. Western hemlock
grafts readily. Growth of grafted material is better than that of
rooted material [57].

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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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Fire Management Considerations

Fire danger increases with the increasing volume of logging residue.
Logging old-growth stands or western hemlock can leave huge volumes of
residue compared with logging young stands, which leave little residue.
Burning cleans up the area and facilitates planting. Therefore burning
is often favored by land managers who intend to plant Douglas-fir to
obtain a mixture of Douglas-fir and western hemlock. The general trend
in western hemlock management, however, is away from broadcast burning
except where a huge accumulation of residues constitutes a fire hazard
[64].

Burning in western hemlock stands is a valuable treatment when seedlings
and saplings are infected with dwarf mistletoe and need to be destroyed.
Fire is helpful in rehabilitation of brushy areas; burning brush to
ground level facilitates planting and favors planted seedlings in
keeping ahead of the brush sprouts [64].

Fire spreads more slowly in western hemlock slash than in western
redcedar slash. Western hemlock slash drops its foliage. The slash of
western hemlock is less flammable when chipped [52]. Slash from western
hemlock/western redcedar/Alaska-cedar forests produce greater nutrient
losses to the atmosphere when the slash composition has a greater
proportion of Alaska-cedar and western redcedar. One can expect smaller
nutrient losses when western hemlock makes up the majority of the slash
[28]. For further details on burning of western hemlock slash refer to
the fire case study in the Alaska-cedar Fire Effects Information System
species writeup.

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Reaction to Competition

Western hemlock is rated to be very  tolerant of shade. Only Pacific yew and Pacific silver fir are considered  to have equal or greater tolerance of shade than western hemlock.

    Western hemlock responds well to release after a long period of  suppression. Advance regeneration 50 to 60 years old commonly develops  into a vigorous, physiologically young-growth stand after complete removal  of the overstory; however, poor response to release has been noted for  suppressed trees over 100 years old. Advance regeneration up to 1.4 m (4.5  ft) tall appears to respond better to release than taller individuals.  Because of its shade tolerance, it is an ideal species for management that  includes partial cutting; however, if it is present and the management  goal is for a less tolerant species, normal partial cutting practices are  not recommended.

    Under conditions of dense, even-aged stocking, early natural pruning  occurs, tree crowns are usually narrow, and stem development is good.  Given unrestricted growing space, the quality of western hemlock logs is  reduced because of poorly formed stems and persistent branches. Trees that  develop in an understory vary greatly in form and quality.

    The successional role of western hemlock is clear; it is a climax  species either alone or in combination with its shade-tolerant associates.  Climax or near-climax forest communities along the Pacific coast include  western hemlock, western hemlock-Pacific silver fir, western  hemlock-western redcedar, Pacific silver fir-western hemlock-Alaska-cedar,  and western hemlock-mountain hemlock. The longevity of some associates of  western hemlock makes it difficult to determine if some of these  near-climax communities will develop into pure western hemlock stands or  if western hemlock will ultimately be excluded.

    Climax or near-climax communities in the Rocky Mountains include western  hemlock, western hemlock-western redcedar, and occasionally subalpine  fir-western hemlock. In the last community, western hemlock plays a  distinctly minor role (26).

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Rooting Habit

Western hemlock is a shallow-rooted species; it  does not develop a taproot. The roots, especially the fine roots, are  commonly most abundant near the surface and are easily damaged by  harvesting equipment and fire.

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Life History and Behavior

Cyclicity

Phenology

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More info for the terms: phenology, tree

The reproductive cycle of western hemlock occurs over 15 to 16 months
from the time of cone initiation in early summer, until seeds are shed
in the fall of the following year. Fertilization and seed development
occur in the second year. Phenology varies between coastal and interior
regions [56,57,76]. Trees in the interior region or at higher
elevations begin development later in the spring and complete
development earlier in the fall than do trees growing in coastal and
low-elevation regions [56].

At low-elevation coastal British Columbia locations, pollination
commonly occurs in early to mid-April, whereas in the interior of
British Columbia, it may occur from May until mid-June. Records from
western Washington and Oregon show that pollination may occur from
mid-April until late May [56]. Fertilization occurs in coastal western
hemlock about mid-May. The time from pollination to seed release ranges
from 120 to 160 days in western hemlock. It can vary according to
weather and temperature during cone maturation. Dry, warm weather in
late summer may cause more rapid drying and earlier opening of cones
with consequently, earlier seed release. Wet, cool weather may delay
cone opening and seed release. Most seeds are shed in the fall when
cones first open [50,56,76]. Cones may close in wet weather and reopen
more fully with subsequent dry weather. As a result, seeds may be shed
throughout the winter or even during the next spring. Mature cones
often persist on the tree throughout the second year but contain few
viable seeds [56,57].

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Reproduction

Vegetative Reproduction

Western hemlock can be propagated by  layering and from cuttings. Seedlings that die back to the soil surface  commonly sprout from buds near the root collar. Sprouting does not occur  from the roots or the base of larger saplings.

    Western hemlock grafts readily. Incompatibility between the scion and  rootstock does not appear to be a problem. Growth of grafted material is  better than that of rooted material.

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Seedling Development

Western hemlock seeds are not deeply  dormant; stratification for 3 to 4 weeks at 1° to 4° C (33°  to 39° F) improves germination and germination rate. The germination  rate is sensitive to temperature; optimum temperature appears to be 20°  C (68° F). For each 5° C (9° F) drop below the optimum, the  number of days required for germination is nearly doubled. Given  sufficient time (6 to 9 months) and an absence of pathogens, western  hemlock will germinate at temperatures just above freezing (4).  Germination is epigeal. Western hemlock seeds remain viable only into the  first growing season after seedfall.

    Provided adequate moisture is available, seed germination and germinant  survival are excellent on a wide range of materials. Seeds even germinate  within cones still attached to a tree. Western hemlock germinates on both  organic and mineral seedbeds; in Alaska, establishment and initial growth  are better on soils with a high amount of organic matter. Mineral soils  stripped of surface organic material commonly are poor seedbeds because  available nitrogen and mineral content is low.

    In Oregon and Washington, exposed organic materials commonly dry out in  the sun, resulting in the death of the seedling before its radicle can  penetrate to mineral soil and available moisture. In addition, high  temperatures, which may exceed 66° C (150° F) at the surface of  exposed organic matter, are lethal. Under such moisture and temperature  conditions, organic seedbeds are less hospitable for establishment of  seedlings than mineral seedbeds (27). Burning appears to encourage natural  regeneration on Vancouver Island; after the third growing season, burned  seedbeds had 58 percent more seedlings with better distribution than  unburned seedbeds (17).

    Decaying logs and rotten wood are often favorable seedbeds for western  hemlock. Decayed wood provides adequate nutrition for survival and growth  of seedlings (23). In brushy areas, seedlings commonly grow on rotten wood  where there is minimum competition for moisture and nutrients. Seedlings  established on such materials frequently survive in sufficient numbers to  form a fully stocked stand by sending roots into the soil around or  through a stump or log.

    Because western hemlock can thrive and regenerate on a diversity of  seedbeds, natural regeneration can be obtained through various  reproduction methods, ranging from single-tree selection to clearcutting.  Through careful harvesting of old-growth stands, advance regeneration  often results in adequately stocked to overstocked stands.

    Western hemlock is difficult to grow in outdoor nurseries.  Container-grown stock appears to result in higher quality seedlings, less  damage to roots, and better survival than does bare root stock.

    Initial growth is slow; 2-year-old seedlings are commonly less than 20  cm (8 in) tall. Once established, seedlings in full light may have an  average growth rate of 60 cm (24 in) or more annually.

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Seed Production and Dissemination

There are 56,760 to 83,715  cones per hectoliter (20,000 to 29,500/bu). Each cone contains 30 to 40  small seeds. Extraction and cleaning yields an average of 0.79 kg of seed  per hectoliter (0.61 lb/bu) of cones. There are 417,000 to over 1,120,000  with an average 573,000 seeds per kilogram (189,000 to 508,000/lb; average  260,000). Slightly less than one-half of the seeds extracted from the  cones are viable.

    In coastal Oregon, more than 19.8 million seeds per hectare (8  million/acre) were released during each of two good seed years from  100-year-old stands, or about 30.3 kg/ha (27 lb/acre). In 1951, a  hemlock-spruce stand in Alaska produced 96.4 kg/ha (86 lb/acre) of western  hemlock seed. In the Rocky Mountains, western hemlock consistently  produces more seed than its associates in the Tsuga heterophylla Zone.

    Cone scales of western hemlock open and close in response to dry and wet  atmospheric conditions. Under wet conditions, seed may be retained in the  cones until spring. Western hemlock seed falls at a rate of 80 cm (31 in)  per second (27). Released in a strong wind, it can be blown more than 1.6  km (1 mi). In a wind of 20 km (12.5 mi) per hour, seed released at a  height of 61 m (200 ft) traveled up to 1160 m (3,800 ft); most fell within  610 m (2,000 ft) of the point of release (19). Seedfall under a dense  canopy is 10 to 15 times greater than that within 122 m (400 ft) of the  edge of timber in an adjacent clearcut.

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Flowering and Fruiting

Western hemlock is monoecious; male and  female strobili develop from separate buds of the previous year. Female  strobili occupy terminal positions on lateral shoots, whereas the male  strobili cluster around the base of the needles (4). Flowering and  pollination begin from mid-April to late April in western Oregon and  continue into late May and June in coastal Alaska. The solitary, long (19  to 32 mm; 0.75 to 1.25 in), pendent cones mature 120 to 160 days after  pollination. Time of maturity of cones on the same branch is variable;  ripe cones change from green to golden brown. The cone-scale opening  mechanism does not appear to develop fully until late in the ripening  period. Seeds are usually fully ripe by mid-September to late September,  but cone scales do not open until late October. Empty cones often persist  on the tree for 2 or more years.

    Although flowering may begin on 10-year-old trees, regular cone  production usually begins when trees reach 25 to 30 years of age. Mature  trees are prolific producers of cones. Some cones are produced every year,  and heavy crops occur at average intervals of 3 to 4 years; however, for a  given location, the period between good crops may vary from 2 to 8 years  or more. For example, in Alaska, good seed crops occur on an average of 5  to 8 years.

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Growth

Growth and Yield

Western hemlock may form pure stands or be a  component of mixed stands. Young stands vary in stocking, but  understocking is infrequent. Natural 20-year-old stands can have 14,800 to  24,700 or more stems per hectare (6,000 to 10,000/acre). Stocking levels  of 1,480 to 1,790 stems per hectare (600 to 725/acre) at crown closure are  believed to provide the best yields if commercial thinnings are part of  the management regime (12). If thinnings are not planned, stocking levels  as low as 740 well-distributed trees per hectare (300/acre) can provide  maximum yields at rotation age (27).

    The response of western hemlock to nitrogen fertilizer is extremely  variable. It appears to vary by geographic location and stocking level.  For overstocked stands, a combination of precommercial thinning and  fertilizer often gives the best response.

    Comparative yield data from paired British plantations strongly suggest  that western hemlock commonly outproduces two of its most important  associates, Douglas-fir and Sitka spruce (1). Natural stands of western  hemlock along the Pacific coast attain appreciably higher yields than  Douglas-fir stands having the same site index (34); the weighted mean  annual increment of western hemlock for some common forest soils in  Washington is 33 to 101 percent more than the mean annual increment for  Douglas-fir (30). On the Olympic Peninsula, western hemlock out-produces  Douglas-fir by 25 to 40 percent. Similar relationships occur in south  coastal British Columbia (12). The higher mean annual increment of western  hemlock apparently is due to the ability of western hemlock stands to  support more trees per hectare; individual trees also have better form  than other species and hence better volume (at least 4 to 14 percent)  (34).

    Mixed stands of western hemlock and Sitka spruce are especially  productive. In the Picea sitchensis Zone of Oregon and Washington,  the mean annual increment of such stands frequently exceeds 42 m³/ha  (600 ft³/acre). At higher elevations and farther north, mixed stands  of western hemlock and Pacific silver fir are also highly productive.

    Yield data for natural stands are given in table 1. Volumes predicted  for normally stocked stands may actually underestimate potential yields by  20 to 50 percent. Data from British Columbia suggest greater yields can be  had if a high number of stems per hectare are maintained (12). Yields of  western hemlock on the best sites can exceed 1848 m³/ha (26,400 ft³/acre)  at 100 years of age.

    Table 1- Characteristics of fully stocked, 100-year-old  western hemlock stands in Oregon (OR), Washington (WA), British Columbia  (BC), and Alaska (AK) (adapted from 2)            Average site index at  base age 100 years¹              Item  61 m or 200 ft  52 m or 170 ft  43 m or 140 ft  34 m or 110 ft  26 m or 
85 ft            Avg. height, m                  OR/WA  58.8  49.7  40.8  31.7  -        BC  -  50.0  40.8  31.7  22.3        AK  -  -  38.4  29.3  20.7      Avg. d.b.h., cm                  OR/WA  58  54  49  42  -        BC/AK  -  44  40  31  22      Stocking², trees/ha                  OR/WA  299  339  400  526  -        BC/AK  -  482  573  865  1,384      Basal area², m²/ha                  OR/WA  83.3  81.7  79.0  75.3  -        BC/AK  -  75.5  73.0  67.5  59.9      Whole tree volume², ft³/acre                  OR/WA  1771  1498  1218  938  -        BC  -  1449  1228  938  612        AK  -  -  1158  868  560            Avg. height, ft                  OR/WA  192.0  163.1  133.9  104.0  -        BC  -  164.0  133.9  104.0  73.2        AK  -  -  126.0    96.1  67.9      Avg. d.b.h., in                  OR/WA  23.0  21.4  19.2  16.5  -        BC/AK  -  17.5  15.6  12.4  8.8      Stocking², trees/acre                  OR/WA  121  137  162  213  -        BC/AK  -  195  232  350  560      Basal area², ft²/acre                  OR/WA  362.9  355.9  344.1  328.0  -        BC/AK  -  328.9  318.0  294.0  261.0      Whole tree volume², ft³/acre                  OR/WA  25,295  21,394  17,406  13,405  -        BC  -  20,693  17,549  13,405  8,746        AK  -  -  16,549  12,405  8,003      ¹Site indices  range within 4.6 m (15 ft) of the averages. 
²Trees larger than 3.8 cm (1.5 in) in d.b.h.        Western hemlock forests are among the most productive forests in the  world. The biomass production of several western hemlock stands with a  site index (base 100 years) of 43 m (140 ft) was investigated at the  Cascade Head Experimental Forest near Lincoln City, OR. The biomass of  standing trees of a 26-year-old, nearly pure western hemlock stand was 229  331 kg/ha (204,614 lb/acre) and that of a 121-year-old stand with a spruce  component of 14 percent was 1 093 863 kg/ha (975,966 lb/acre). Net primary  productivity per year for these two stands was estimated to be 37 460 and  22 437 kg/ha (33,423 and 20,019 lb/acre). Net primary productivity appears  to peak at about 30 years, then declines rapidly for about 50 years.  Foliar biomass in the stands at Cascade Head averages 22 724 kg/ha (20,275  lb/acre) with a leaf area of 46.5 m²/m² (46.5 ft²/ft²)  (8, 10). By comparison, available data indicate much lower values for  highly productive Douglas-fir stands- 12 107 kg/ha and 21.4 m²/m²  (10,802 lb/acre and 21.4 ft²/ft² ), respectively.

    On the best sites, old-growth trees commonly reach diameters greater  than 100 cm (39.6 in); maximum diameter is about 275 cm (108 in). Heights  of 50 to 61 m (165 to 200 ft) are not uncommon; maximum height is reported  as 79 m (259 ft). Trees over 300 years old virtually cease height growth  (27). Maximum ages are typically over 400 but less than 500 years. The  maximum age recorded, in excess of 700 years, is from the Queen Charlotte  Islands (16). Several major associates (Douglas-fir, western redcedar,  Alaska-cedar) typically reach much greater ages.

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Nurse logs provide new habitat: western hemlock
 

Tall, wide trees in the forests of the Pacific Northwest serve as nurse logs to their seedlings after they fall, providing decades of water and nutrients as they slowly decay.

     
  "In the coniferous forests of the north-west coast of America, the trees - Sitka spruce, hemlock and Douglas fir - may grow over two hundred feet high and they cut out most of the light. There is enough, however, to sustain ferns and other shade-loving plants, and the soil is so rich that they form a dense ground-cover through which you wade waste high. But beneath them, on the surface of the soil, it is very dark indeed. Seedlings, even if they were able to germinate, would not be able to gather enough light for them to photosynthesise. How then, can the giant trees regenerate themselves?

"They do so with the aid of their own dead bodies. The girth of an adult tree is such that the upper side of a fallen trunk remains above the ferns. A seed from a neighbouring tree that lands on it can thus get sufficient light to germinate. Being perched there brings another advantage: the bark of the prostrate tree is very fibrous and holds moisture like a sponge to the young plant does not lack for water. As the seedling sprouts, it sends down roots. They grow over the flank of the log and down into the rich soil beneath. As they gain strength, these roots thicken. While they are doing so, fungi are feasting in the wood of the log. Slowly it rots and begins to crumble away providing more sustenance for the young trees. After several decades, the log has been reduced to mouldering fragments. But the young seedlings still hold their position high above the ferns for their roots have now become so thick, they support them like stilts." (Attenborough 1995:180)
  Learn more about this functional adaptation.
  • Attenborough, D. 1995. The Private Life of Plants: A Natural History of Plant Behavior. London: BBC Books. 320 p.
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Functional adaptation

Disturbances help maintain diversity: western hemlock-Sitka spruce forests
 

Western hemlock-Sitka spruce forests maintain diversity partly thanks to wind disturbance patterns.

   
  "The dynamics of British planted forests are compared with disturbance dynamics of analogous natural forests with particular reference to disturbance by strong winds. Western hemlock-Sitka spruce (Tsuga heterophylla-Picea sitchensis) forests in the Pacific North-west of North America and particularly South-east Alaska provide the most promising comparison. There are few reports on disturbance in these forests, but the regime includes both gap-phase and stand replacement dynamics due to wind. However, the landscape proportion and pattern of resulting structural types are not well defined…Two stand types have been identified in the hemlock-spruce forest types in the Pacific North-west: (1) even-aged stands following catastrophic blowdown; and (2) multi-aged stands resulting from gradual but non-catastrophic attrition (Deal et al., 1991). Sitka spruce can maintain a presence in forest communities in both situations (Taylor, 1990). It is not known what the proportion of the two stand types (fine grain and even-aged) is for any one region." (Quine et al. 1999:337, 347)
  Learn more about this functional adaptation.
  • Quine CP; Humphrey JW; Ferris R. 1999. Should the wind disturbance patterns observed in natural forests be mimicked in planted forests in the British uplands?. Forestry. 72(4): 337-358.
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Molecular Biology and Genetics

Genetics

A natural cross between western hemlock and mountain hemlock, Tsuga  x jeffreyi (Henry) Henry, has been reported from the Mount  Baker area in Washington. Analysis of polyphenolic pigment suggests that  chemical hybrids between western hemlock and mountain hemlock occur but  are rare. Intergeneric hybridization between western hemlock and spruce  has been discussed in the literature; although similarities exist between  the two genera, they do not suggest hybridization (31).

    Albino individuals or those similarly deficient in chlorophyll have been  observed in the wild.

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Molecular Biology

Barcode data: Tsuga heterophylla

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 heterophylla

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 1
Specimens with Barcodes: 1
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
Stritch, L. & Thomas, P.

Contributor/s

Justification
Tsuga heterophylla is a very widespread and extremely abundant species. It is probably increasing in forests where fires are suppressed and/or as a result of removal of large competitors through past logging of e.g. Douglas-fir. Consequently it is assessed as Least Concern.

History
  • 1998
    Lower Risk/least concern (LR/lc)
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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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Status

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

Public Domain

USDA NRCS National Plant Data Center

Source: USDA NRCS PLANTS Database

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Population

Population
The population is probably increasing in many areas.

Population Trend
Increasing
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Threats

Major Threats
This species is not threatened with extinction and is probably increasing.
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Management

Conservation Actions

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

More info for the terms: competition, selection, tree

Insects and disease: The major root and butt pathogens of western
hemolock are: Armillaria mellea, Heterobasidion annosum, Phaeolus
schweinitzii, Laetiporus sulphureus, Inenotus tomentosus, Poria
subacida, Phellinus weiri, and Indian paint fungus (Echinodontium
tinctorium) [30,57]. Western hemlock is severely damaged by Indian
paint fungus in the high Cascades; cull due to this rot may run as high
as 80 percent in old-growth stands [30]. Dwarf mistletoe (Arceuthobium
campylopodum) is a common parasite on western hemlock which causes
wide-spread growth loss and mortality in old-growth stands [62].

Important insects attacking western hemlock are a weevil (Steremnius
carinatus), western larch borer (Tetropium velutinum), western
blackheaded budworm (Acleris gloverana), western hemlock looper
(Lambdina fiscellaria lugubrosa), green striped forest looper
(Melanolophia imitata), saddleback looper (Ectropis crepuscularia), and
hemlock sawfly (Neodiprion tsugae). The western hemlock looper has
caused more mortality of western hemlock than any other insect pest.
Outbreaks can last 2 to 3 years on any one site. Although mortality is
greatest in old-growth western hemlock, vigorous 80- to 100-year-old
stands can also be severely damaged by this insect. The hemlock sawfly
is considered the second most destructive insect of western hemlock in
Alaska [57].

Other damaging agents: Pole-sized and larger stands of western hemlock
are subject to severe windthrow. Uprooting is increased in areas where
a high water table or impenetrable layer in the soil causes trees to be
shallow rooted [62]. Blowdown is a major problem in western hemlock
forests, and the need to leave windfirm borders is always present. If
only part of the stand will be removed, the leave trees need to be as
windfirm as possible [64].

Western hemlock suffers frost damage in the Rocky Mountains, especially
along the eastern edge of its range [57].

On droughty sites, top dieback is common; in exceptionally dry years,
entire stands of western hemlock saplings die [57]. Western hemlock
seedlings and saplings are susceptible to sunscald following exposure of
young stems by thinning. Sunscald lesions often become infected with
decay organisms [62].

Western hemlock is one of the conifers most sensitive to damage by
sulfur dioxide.

Spring applications of the iso-octyl esters of 2,4-D and 2,4,5-T in
diesel oil can kill up to 3 years of leader growth [57].

Fertilization: The response of western hemlock to nitrogen fertilizer
is extremely variable. For overstocked stands, a combination of
precommercial thinning and fertilizer often gives the best response
[57].

Silvicultural considerations: In terms of biomass production, western
hemlock forests are among the most productive forests in the world.
Natural stands of western hemlock along the Pacific Coast attain higher
yields than Douglas-fir stands having the same site index [57,64]. Pure
stands of western hemlock are so densely stocked that an acre of
100-year-old western hemlock forest can yield more timber (150,000 to
190,000 board feet on a good site) than a comparable stand of larger,
less dense Douglas-fir [10,64].

Western hemlock can be regenerated by most standard harvest methods. In
the past, clearcutting was the most common method used in western
hemlock stands [64,74]. As an aesthetically viable alternative to
clearcutting, shelterwood cutting has been proposed as a means of
controlling brush competition and favoring western hemlock seedlings
[77]. The shelterwood method has been used successfully in even-aged
stands. Observations suggest that cutting of uneven-aged stands by the
individual tree selection method will be successful in obtaining western
hemlock regeneration [38,64]. In the grand fir (Abies
grandis)-cedar-hemlock ecosystem, Graham and Smith [34] found that the
individual tree selection method of harvest promotes the regeneration
and growth of shade-tolerant species, such as western hemlock. The seed
tree method will work, but rarely is used in harvesting of western
hemlock stands because many seed trees blow down during wind storms
[64].

A common problem in regeneration of western hemlock is overtopping by
competing vegetation such as alder, thimbleberry (Rubus parviflorus),
and salmonberry (Ribes spectabilis). When exposed to full sunlight
after clearcutting, these brush species tend to form dense thickets and
exclude hemlock regeneration. These species can be controlled with
herbicides [64].

Western hemlock responds well to release after long periods of
suppression. Advance regeneration up to 4.5 feet (1.4 m) tall appears
to respond better to release than taller individuals. Poor response to
release has been noted for suppressed trees over 100 years old [57].

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

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

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Seedling transplant well when they are 8 to 36 inches tall. However, the best survival rate can be achieved if seedling are transplanted between 8 and 20 inches, this is usually when they are about five to eight years old (Huxley 1992). Transplanting larger seedlings will check badly and hardly put on any growth for several years. This slow growth predisposes the seedling to pest, poor root development and wind throws, and related damage. (Ibid.).

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Relevance to Humans and Ecosystems

Benefits

Value for rehabilitation of disturbed sites

More info for the term: natural

Western hemlock is suitable for planting on moist, nutrient very poor to
nutrient medium sites in pure or mixed species stands (mainly with
Pacific silver fir [Abies amabilis], Sitka spruce [Picea sitchensis],
alder [Alnus spp.], or western redcedar). Natural regeneration is
preferred over planted stock [44]. Western hemlock is difficult to grow
in outdoor nurseries. Container-grown stock appears to result in higher
quality seedlings with less damage to roots and better survival than
bareroot stock [57]. Methods for collecting, storing and planting
western hemlock seeds and seedlings have been detailed [63].

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Importance to Livestock and Wildlife

More info for the terms: cover, tree

Roosevelt elk and black-tailed deer browse western hemlock in coastal
Oregon, Washington, and British Columbia [57]. In the Oregon Cascades
deer mice consumed about 22 percent of the western hemlock seed fall.
This consumption occurred just before or during the germination process
[76]. Black bear girdle pole-size western hemlock and larger saplings
or damage the bark at the base of the trees. Snowshoe hare and rabbit
clip off the main stems of western hemlock seedlings. Mountain beaver
clip the stems and lateral branches of seedlings and girdle the base of
saplings [57].

Old-growth western hemlock stands provide hiding and thermal cover for
many wildlife species. In the southern Selkirk Mountains of northern
Idaho, northeastern Washington, and adjacent British Columbia, grizzly
bear have been known to use heavily timbered western hemlock forests
[48]. In the western Oregon Cascades, western hemlock provides habitat
for many species of small mammals, including the northern flying
squirrel and red tree vole [7,67]. In Washington and Oregon, the
northern spotted owl is often found in forests dominated by Douglas-fir
(Pseudotsuga menziesii) and western hemlock. The majority of barred
owls observed in British Columbia have occurred in the Columbia Forest
Biotic Area in which western hemlock and western redcedar are the major
climax species [6]. Western hemlock is used for nest trees by cavity
nesting bird species such as the yellow-bellied sapsucker and northern
three-toed woodpecker [51].

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Other uses and values

Alaska Indians made coarse bread from the inner bark of western hemlock
[72]. Young western hemlock saplings can be sheared to make excellent
hedges. In Britain western hemlock is often planted as an ornamental
[46].

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Wood Products Value

Western hemlock wood is recognized as an all-purpose raw material. It
is one of the best pulpwoods for paper and paper board products [57,72].
It is the principal source of alpha cellulose fiber used in the
manufacture of rayon, cellophane, and many plastics [10]. Other uses
are lumber for general construction, railway ties, mine timbers, and
marine piling. The wood is suited also for interior finish, boxes and
crates, kitchen cabinets, flooring, and ceiling, gutter stock, and
veneer for plywood [57,72].

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Special Uses

The forest industry recognizes western hemlock as an all-purpose raw  material. It treats well and is used for pilings, poles, and railway ties.  Strength and nailing characteristics make it a preferred species for  construction lumber in North America and overseas. Better lumber grades  are used for appearance and remanufacture products. Western hemlock has  good-to-excellent pulping characteristics and is an important fiber source  for groundwood, thermomechanical, kraft, and sulfite pulps.

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E. C. Packee

Source: Silvics of North America

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Uses

Ethnobotanic: Western hemlock bark has high tannin content and was used as a tanning agent, pigment and cleansing solution (Pojar & MacKinnon 1994). Some Coast Salish people used a red dye made from hemlock bark to color mountain goat wool and basket materials and as a facial cosmetic and hair remover (Ibid.). The wood was heavy, durable, and fairly easy to carve. Implements such as children’s bows, spoons, combs, roasting pits, dip-net poles, and edges were carved from hemlock wood. The Mainland Comox threaded oolichan and herring boughs for drying, and used for drying, and used the boughs for lining steaming pits (Ibid.). Kwakwaka’wakw dancers wore headdresses, and head-bands of hemlock boughs, and young women lived in hemlock-bough huts for four days after their first menstruation (Ibid.).

Pitch obtained from crevices in the bark, has been chewed as a gum (Ibid.). Western hemlock leaves and shoot tips were used to make an herbal tea. The leaves and young shoots have been chewed as an emergency food to keep one alive when lost in the woods (Ibid.).

Medicinal: Western hemlock was commonly employed medicinally by several native North American Indian tribes who used it to treat a variety of complaints (Moerman 1998). Hemlock pitch was applied for a variety of purposes, including poultices or poultice coverings, linaments rubbed on the chest for colds and when mixed with deer tallow as a salve to prevent sunburn (Pojar & MacKinnon 1994). A decoction of the pounded bark has been used in the treatment of hemorrhages, diaphoretic, and diuretic (Moerman 1998). The powdered bark can be put in shoes for foot odor.

Landscaping & Wildlife: Tsuga heterophylla is occasionally planted as an ornamental tree in northern states and in Western Europe (Sargent 1961). Western hemlock stands provide cover and habitat for many wildlife species and small mammals. It is also used for nest trees by cavity nesting birds. This species is browsed by elk and deer. The seedlings are eaten by snowshoe hares and rabbits.

Agroforestry: Western hemlock is used in forested riparian buffers to help reduce stream bank erosion, protect aquatic environments, enhance wildlife, and increase biodiversity.

Economic: It is one of the best pulpwood for paper and paperboard products. The wood is used in house construction for external walls, structural support and is suited for interior finish, kitchen cabinets, flooring, and ceiling.

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Wikipedia

Tsuga heterophylla

Tsuga heterophylla, the western 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 Sonoma County, California.[2][3]

Habitat[edit]

Tsuga heterophylla is an integral component of Pacific Northwest forests west of the Coast Ranges, where it is a climax species. It is also an important timber tree throughout the region, along with many of its large coniferous associates.[4]

Description[edit]

Tsuga heterophylla is a large evergreen coniferous tree growing to 165–230 ft (50–70 m) tall, exceptionally 273.42 ft (83.33 m),[5] and with a trunk diameter of up to 9 ft (2.7 m). It is the largest species of hemlock, with the next largest (mountain hemlock T. mertensiana) reaching a maximum of 194 ft (59 m). The bark is brown, thin and furrowed. The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, becoming cylindric in older trees; old trees may have no branches in the lowest 100–130 ft (30–40 m). At all ages, it is readily distinguished by the pendulous branchlet tips. The shoots are very pale buff-brown, almost white, with pale pubescence about 1 mm long. The leaves are needle-like, 5–23 mm long and 1.5–2 mm broad, strongly flattened in cross-section, with a finely serrated margin and a bluntly acute apex. They are mid to dark green above; the underside has two distinctive white bands of stomata with only a narrow green midrib between the bands. They are arranged spirally on the shoots but are twisted at the base to lie in two ranks on either side of the shoot. The cones are small, pendulous, slender cylindrical, 14–30 mm long and 7–8 mm broad when closed, opening to 18–25 mm broad. They have 15–25 thin, flexible scales 7–13 mm long. The immature cones are green, maturing gray-brown 5–7 months after pollination. The seeds are brown, 2–3 mm long, with a slender, 7–9 mm long pale brown wing.[2][3]

Ecology[edit]

Tsuga heterophylla is closely associated with temperate rain forests, and most of its range is less than 100 km from the Pacific Ocean. There is however an inland population in the Columbia Mountains in southeast British Columbia, northern Idaho and western Montana. It mostly grows at low altitudes, from sea level to 600 m, but up to 1800 m in the interior part of its range in Idaho.[2][3]

It is a very shade-tolerant tree; among associated species in the Pacific Northwest, it is matched or exceeded in shade tolerance only by Pacific yew and Pacific silver fir.[4] Young plants typically grow up under the canopy of other conifers such as Sitka spruce or Douglas-fir, where they can persist for decades waiting to exploit a gap in the canopy. They eventually replace these conifers, which are relatively shade-intolerant, in climax forest. However, storms and wildfires will create larger openings in the forest where these other species can then regenerate.

Initial growth is slow; one-year-old seedlings are commonly only 3–5 cm tall, and two-year-old seedlings 10–20 cm tall. Once established, saplings in full light may have an average growth rate of 50–120 cm (rarely 140 cm) annually until they are 20–30 m tall, and in good conditions still 30–40 cm annually when 40–50 m tall. The tallest specimen, 82.83 m tall, is in Prairie Creek Redwoods State Park, California (USA). It is long-lived, with trees over 1200 years old known.[3]

Western hemlock forms ectomycorrhizal associations with some well-known edible fungi such as chanterelles (Cantharellus formosus, C. subalbidus, and Craterellus tubaeformis).[6][7]

Uses[edit]

Tsuga heterophylla, western hemlock, is the state tree of Washington.[8]

Cultivation[edit]

Young western hemlock

Western hemlock is cultivated as an ornamental tree in gardens in its native habitats and along the U.S. Pacific Coast, where its best reliability is seen in wetter regions. In relatively dry areas, as at Victoria, British Columbia, it is exacting about soil conditions. It needs a high level of organic matter (well-rotted wood from an old log or stump is best; animal manures may have too much nitrogen and salt), in a moist, acidic soil. It is also cultivated in temperate regions worldwide. It has gained the Royal Horticultural Society's Award of Garden Merit.[9]

Forestry[edit]

When planted well upon the banks along a river, western hemlock can help to reduce erosion.

Outside of its native range, western hemlock is of importance in forestry for timber and paper production, and as an ornamental tree in large gardens, in northwest Europe and southern New Zealand.

It has naturalised in some parts of Great Britain and New Zealand, not so extensively as to be considered an invasive species, but an introduced species tree.

T. heterophylla often grows on coarse woody debris such as nurse logs and cut stumps

Food[edit]

The edible cambium can be collected by scraping slabs of removed bark. The resulting shavings can be eaten immediately, or can be dried and pressed into cakes for preservation. The bark also serves as a source of tannin for tanning.

Tender new growth needles (leaves) can be chewed directly or made into a bitter tea, rich in vitamin C (similar to some other hemlock and pine species).

Western hemlock boughs are used to collect herring eggs during the spring spawn in southeast Alaska. The boughs provide an easily collectible surface for the eggs to attach to as well as providing a distinctive taste. This practice originates from traditional gathering methods used by Native Alaskans from southeast Alaska, specifically the Tlingit people.

References[edit]

  1. ^ Conifer Specialist Group (1998). Tsuga heterophylla. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
  2. ^ a b c Farjon, A. (1990). Pinaceae. Drawings and Descriptions of the Genera. Koeltz Scientific Books ISBN 3-87429-298-3.
  3. ^ a b c d Gymnosperm Database: Tsuga heterophylla
  4. ^ a b Packee, E.C. Tsuga heterophylla. Silvics of North America, Volume 1. U.S. Department of Agriculture, Forest Service, Washington, DC. 1990. Tsuga heterophylla
  5. ^ Tallest Hemlock, M. D. Vaden, Arborist: Tallest known Hemlock, Tsuga heterophylla
  6. ^ Dunham, Susie M.; O'Dell, Thomas E.; Molina, Randy (2006). "Forest stand age and the occurrence of chanterelle (Cantharellus) species in Oregon’s central Cascade Mountains" (PDF). Mycological Research 110: 1433–40. doi:10.1016/j.mycres.2006.09.007. 
  7. ^ Trappe, MJ (May–Jun 2004). "Habitat and host associations of Craterellus tubaeformis in northwestern Oregon". Mycologia 96 (3): 498–509. doi:10.2307/3762170. PMID 21148873. 
  8. ^ Washington State Government: State Symbols
  9. ^ "RHS Plant Selector - Tsuga heterophylla". Retrieved 7 June 2013. 
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Notes

Comments

Tsuga heterophylla is a dominant species over much of its broad distributional range. It has become the most important timber hemlock in North America. The wood is superior to that of other hemlocks for building purposes and it makes excellent pulp for paper production. 

 Tsuga × jeffreyi (Henry) Henry was described from southwestern British Columbia and western Washington as a hybrid between T . heterophylla and T . mertensiana . Hybridization is rare, if it occurs at all, and it is therefore of little consequence (R.J. Taylor 1972). At the upper elevational limits of its distribution and under stressful conditions, T . heterophylla tends to resemble T . mertensiana , e.g., leaves are less strictly 2-ranked and stomatal bands on the abaxial leaf surfaces are less conspicuous than at lower elevations.

Western hemlock ( Tsuga heterophylla ) is the state tree of Washington.

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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

More info for the term: natural

The currently accepted scientific name for western hemlock is Tsuga
heterophylla (Raf.) Sarg. [57,60]. There are no recognized subspecies,
varieties, or forms. A natural hybrid between western hemlock and
mountain hemlock (Tsuga mertensiana), Tsuga x jeffreyi (Henry) Henry,
has been reported [57].

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Common Names

western hemlock
Pacific hemlock
west coast hemlock

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