Western Hemlock

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

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.

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.

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

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

western hemlock
Pacific hemlock
west coast hemlock

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].

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 for the terms: fire intensity, fire interval, fire regime, forest, frequency, habitat type, lichen, mean fire interval, mesic, 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].

FIRE REGIMES :
Find fire regime information for the plant communities in which this
species may occur by entering the species name in the FEIS home page under
"Find FIRE REGIMES".

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 Review.

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More info for the term: phanerophyte

Phanerophyte

More info for the terms: density, fern, herb, 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 productivity 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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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 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 plant community types (as classified by Küchler 1964):

More info for the term: forest

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

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]. Postfire 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: climax, cover, forest, seed, 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].

More info for the terms: association, climax, codominant, cover, cover type, forest, 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].

More info for the term: tree

Tree

More info for the terms: competition, forest, natural, seed, seed tree, 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].

AK CA ID MT OR WA AB BC

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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More info for the terms: cone, phenology, seed, 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].

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 terms: root crown, secondary colonizer

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

More info for the terms: cone, duff, epigeal, layering, litter, natural, root collar, seed, stratification, 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
sufficient 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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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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More info for the terms: climax, forest, succession

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 term: natural

The 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].

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].

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].

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).

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).

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.

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.

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.

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.

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.

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 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.

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).

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.

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 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.

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."

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.

Tsuga heterophylla, the western hemlock or western hemlock-spruce, 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. The Latin species name means 'variable leaves'.