Mountain Hemlock

mountain hemlock
alpine hemlock
black hemlock
hemlock spruce

More info for the terms: shrub, tree

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

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

The bark is thick and deeply furrowed into scaly plates on old trees
[44,72]. The bark is early broken and rough on young trees [59]. The
root system is shallow and widespreading [38,49,59].

Mountain hemlock occurs along the crest of the Sierra Nevada; the Coast
Ranges and Cascade Range in Oregon; the Cascade Range and Olympic
Mountains in Washington; the northern Rocky Mountains in Idaho and
western Montana; the Insular, Coast, and Columbia mountains in British
Columbia; and in southeast and south-central Alaska [4,8,32,46]. In
California it is also locally abundant in the Klamath Mountains. The
extreme southern limit of mountain hemlock is near Silliman Lake in
Tulare County, California [32].

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

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

Mountain hemlock sites are typically moist with average precipitation
over 50 inches (127 cm), making fire occurrence low (400-800 years)
[7,11,34]. Fuel loading in these sites is often low [7]. In the
Pacific Northwest, the estimated prelogging fire regime in mountain
hemlock forest types is 611 years [11]. Fires in these cool wet forest
types generally occur as infrequent crown fires. When fires do occur in
mountain hemlock forests, they are often severe stand-replacing fires
[25].

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".

More info for the terms: natural, scarification

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

In northern Idaho, burning slash produced better stocking of mountain
hemlock natural regeneration compared to leaving slash untreated.
However, manual scarification generally produced better stocking than
did burning. In contrast, slash burning in Oregon increased the time it
took mountain hemlock to reach 60 percent stocking [24].

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More info for the term: phanerophyte

Phanerophyte

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

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

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

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

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

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

Plant associates: In mixed stands, mountain hemlock usually coexists
with subalpine fir (Abies lasiocarpa), Pacific silver fir, or
Alaska-cedar (Chamaecyparis nootkatensis). In Montana, subalpine fir
and Engelmann spruce (Picea engelmannii) are nearly constant associates
of mountain hemlock [33]. Common understory associates with mountain
hemlock are as follows: beargrass, big huckleberry, grouse
whortleberry, rustyleaf menziesia (Menziesia ferruginea), Cascades
azalea (Rhododendron albiflorum), Alaska huckleberry (V. alaskaense),
ovalleaf huckleberry (V. ovalifolium), long-stoloned sedge (Carex inops
ssp. inops), mertens cassiope (Cassiope mertensiana), copperbush,
mountain heather, deer cabbage, marsh marigold (Caltha biflora), and
skunk cabbage (Lysichitum americanium) [1,19,33,68].

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

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

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

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

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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
K008 Lodgepole pine - subalpine forest
K013 Cedar - hemlock - pine forest

Mountain hemlock is easily killed by fire [7,73,65]. The most common
method of killing is root charring and crown scorching [65]. In a
krummholz community of the North Cascades, Washington, all but one
mountain hemlock were killed by fire [73].

More info for the terms: cover, forbs

Mountain hemlock stands provide good hiding and thermal cover for many
wildlife species [8,45]. Sites dominated by mountain hemlock provide
important summer range for deer in Alaska and Vancouver Island because
of abundant nutrient-rich forbs available in the understory [19,49]. In
Montana, mountain hemlock habitat types provide summer range for mule
deer, elk, and bear [57]. Mountain hemlock seeds have been found in the
stomachs of crows and grouse [70].

More info for the terms: association, codominant, cover, forest, habitat type, natural

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

Forest types of the North Cascades National Park Service complex [1].
Preliminary plant associations of the Southern Oregon Cascade Mountain
Province [5].
Preliminary plant associations of the Siskiyou Mountain Province [6].
Plant association and management guide for the Pacific silver fir zone [12].
Forest habitat types of northern Idaho: A second approximation [15].
Classification of montane forest community types in the Cedar River
drainage of western Washington, U.S.A. [18].
Preliminary forest plant association management guide. Ketchikan area,
Tongass National Forest [19].
Subalpine plant communities of the western North Cascades, Washington [21].
Alpine and high subalpine plant communities of the North Cascades Range,
Washington and British Columbia [22].
Fire ecology of western Montana forest habitat types [25].
Forest vegetation of the montane and subalpine zones, Olympic Mountains,
Washington [27].
Natural vegetation of Oregon and Washington [29].
The forest communities of Mount Rainier National Park [30].
Plant associations of south Chiloquin and Klamath ranger districts--
Winema National forest [37].
Vegetation and environment in old growth forests of northern southeast
Alaska: a plant association classification [48].
Forest habitat types of Montana [57].
Preliminary classification of forest vegetation of the Kenai Peninsula,
Alaska [61].
Preliminary forest plant associations of the Stikine area, Tongass
National Forest [68].

More info for the term: tree

Tree

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

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

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

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

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

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

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

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

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

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

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

In British Columbia, the recommended silvicultural method for harvest of
old-growth mountain hemlock is clearcut followed by natural
regeneration. For young natural stands that have developed after fire
or second-growth stands that have developed after clearcutting, the
clearcut method with natural regeneration, seed tree method, or
shelterwood method is recommended [72].

AK CA ID MT OR WA AB BC

Mountain hemlock is often used as an ornamental for landscaping in the
Pacific Northwest and throughout Great Britain [42,49,4]. Its dense,
compact foliage coupled with its slow growth make it ideal as a garden
evergreen [42]. Hemlock species (Tsuga spp.) played a supernatural role
as magical objects in the mythology of the Thompson and Lillooet
Interior Salish of British Columbia [66].

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Mountain hemlock has a 2-year reproductive cycle. Pollination occurs in
the spring or early summer of the second year [55]. Mountain hemlock
releases pollen in June in the Cascade Range in Oregon, from mid-June to
mid-July in British Columbia, and from mid-May to late June in Alaska
[49]. Fertilization occurs from about late July to early August in
British Columbia. Reproductive buds can easily be identified in the
late summer and fall. Cones ripen and open from late September to
November [49,56]. In the Bitterroot Mountains of Idaho cones ripen in
August [62]. In Montana cones open and release the wide-winged seeds in
September or October and then abscise [44].

More info for the terms: tree, wildfire

Mountain hemlock is generally slow to regenerate after fire [25,49].
Most burned areas in the mountain hemlock zone on the Olympic Peninsula
do not have adequate stocking for commercial forests even 55 to 88 years
after wildfire [49]. Tree establishment in burned areas is higher
during normal to wet growing seasons [2].

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, epigeal, formation, layering, seed, stratification, tree

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

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

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

Vegetative reproduction: Mountain hemlock reproduces vegetatively by
layering [49,73]. This is an effective means of regenerating at
timberline, since layered saplings are sheltered by the growth of the
parent tree and initially receive their nutrients through the
established root system of the old tree [4]. Layering is an important
method of reproduction on muskegs and krummholz areas in Alaska [49].

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

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

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More info for the terms: climax, forest, series

Mountain hemlock is shade tolerant [24,49,4]. It is considered a major
or minor climax species over most of its habitat; however, it is also a
pioneer on glacial moraines in British Columbia and Alaska. Mountain
hemlock is commonly the major climax species in the mountain hemlock
zone south of central Oregon where Pacific silver fir does not occur.
It often succeeds lodgepole pine (Pinus contorta) when these species
pioneer on drier sites and tends to replace Engelmann spruce [49].
Mountain hemlock is considered a coclimax species with subalpine fir
where they occur together [17,25]. In the subalpine fir series in the
Lolo National Forest, mountain hemlock and subalpine fir are the only
two trees capable of perpetuating themselves as climax dominants [33].

The currently accepted scientific name for mountain hemlock is Tsuga
mertensiana (Bong.) Carriere [38,46,49]. Mountain hemlock in the
Siskiyous from the Oregon-California border south were recently
classified as Tsuga mertensiana spp. grandicona Farjon, in recognition
of the generally larger cones of trees in this region [49]. All others
are classified as Tsuga mertensiana spp. mertensiana. There are no
recognized varieties or forms. Mountain hemlock will hybridize with
western hemlock (T. heterophylla) [46].

More info for the terms: association, forest, natural

Mountain hemlock is important for watershed protection [49]. The
mountain hemlock/blueberry (Vaccinium spp.)-copperbush (Cladothamnus
pyrolaeflorus)/deer cabbage (Fauria crista-galli) association in Alaska
captures runoff from snowmelt [19]. Planted stock of mountain hemlock
does not perform well. In high-elevation regeneration trials in the
Vancouver forest region, its performance was poor compared to that of
the other high-elevation species. Natural regeneration may perform
better [63].

Mountain hemlock is largely inaccessible because of the high altitudes
at which it occurs and is unimportant as commercial timber [71]. It is,
however, harvested to a limited extent near its lower limits; the wood
is generally marketed with western hemlock [71,4]. The wood is
moderately strong and light colored and is most often used for
small-dimension lumber and pulp [49]. The wood is also used for railway
ties, mine timbers, interior finish, crates, kitchen cabinets, and
flooring and ceilings [71]. Nearly pure stands of mountain hemlock on
Prince of Wales Island have been logged for pulp [71].