Tsuga heterophylla

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."

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.

West coast hemlock, pacific hemlock, coast hemlock

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].

More info on this topic.

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

AK CA ID MT OR WA AB BC

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.

Tsuga heterophylla (Raf.) Sarg.:
Canada (North America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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).

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.

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].

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.

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

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].

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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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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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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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

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).

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).

Coastal to midmontane forests; 0--1500m; Alta., B.C.; Alaska, Calif., Idaho, Mont., Oreg., Wash.

Systems

• Terrestrial

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.

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

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).

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.

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].

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].

More info for the terms: root crown, secondary colonizer

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

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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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].

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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More info for the term: phanerophyte

Phanerophyte

More info for the term: tree

Tree

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.

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).

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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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].

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.

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.

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.

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.

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.

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.

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

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

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

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.

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].

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.”

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.).

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.

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.