Index of Species Information
SPECIES: Tsuga heterophylla
Introductory
SPECIES: Tsuga heterophylla
AUTHORSHIP AND CITATION :
Tesky, Julie L. 1992. Tsuga heterophylla. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station,
Fire Sciences Laboratory (Producer). Available:
https://www.fs.usda.gov/database/feis/plants/tree/tsuhet/all.html [].
ABBREVIATION :
TSUHET
SYNONYMS :
NO-ENTRY
SCS PLANT CODE :
TSHE
COMMON NAMES :
western hemlock
Pacific hemlock
west coast hemlock
TAXONOMY :
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].
LIFE FORM :
Tree
FEDERAL LEGAL STATUS :
No special status
OTHER STATUS :
NO-ENTRY
DISTRIBUTION AND OCCURRENCE
SPECIES: Tsuga heterophylla
GENERAL DISTRIBUTION :
Western hemlock occurs in the Coast Ranges from Sonoma County California
to the Kenai Peninsula in Alaska. Inland it occurs along the western
and upper eastern slopes of the Cascade Range in Oregon and Washington
and west of the Continental Divide in the northern Rocky Mountains of
Montana and Idaho, north to Prince George, British Columbia
[10,56,57,78].
ECOSYSTEMS :
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
STATES :
AK CA ID MT OR WA AB BC
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
4 Sierra Mountains
5 Columbia Plateau
8 Northern Rocky Mountains
KUCHLER PLANT ASSOCIATIONS :
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
SAF COVER TYPES :
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
SRM (RANGELAND) COVER TYPES :
NO-ENTRY
HABITAT TYPES AND PLANT COMMUNITIES :
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].
MANAGEMENT CONSIDERATIONS
SPECIES: Tsuga heterophylla
WOOD PRODUCTS VALUE :
Western hemlock wood is recognized as an all-purpose raw material. It
is one of the best pulpwoods for paper and paper board products [57,72].
It is the principal source of alpha cellulose fiber used in the
manufacture of rayon, cellophane, and many plastics [10]. Other uses
are lumber for general construction, railway ties, mine timbers, and
marine piling. The wood is suited also for interior finish, boxes and
crates, kitchen cabinets, flooring, and ceiling, gutter stock, and
veneer for plywood [57,72].
IMPORTANCE TO LIVESTOCK AND WILDLIFE :
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].
PALATABILITY :
NO-ENTRY
NUTRITIONAL VALUE :
NO-ENTRY
COVER VALUE :
NO-ENTRY
VALUE FOR REHABILITATION OF DISTURBED SITES :
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].
OTHER USES AND VALUES :
Alaska Indians made coarse bread from the inner bark of western hemlock
[72]. Young western hemlock saplings can be sheared to make excellent
hedges. In Britain western hemlock is often planted as an ornamental
[46].
OTHER MANAGEMENT CONSIDERATIONS :
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].
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Tsuga heterophylla
GENERAL BOTANICAL CHARACTERISTICS :
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].
RAUNKIAER LIFE FORM :
Phanerophyte
REGENERATION PROCESSES :
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].
SITE CHARACTERISTICS :
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].
SUCCESSIONAL STATUS :
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].
SEASONAL DEVELOPMENT :
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].
FIRE ECOLOGY
SPECIES: Tsuga heterophylla
FIRE ECOLOGY OR ADAPTATIONS :
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".
POSTFIRE REGENERATION STRATEGY :
Tree without adventitious-bud root crown
Secondary colonizer - off-site seed
FIRE EFFECTS
SPECIES: Tsuga heterophylla
IMMEDIATE FIRE EFFECT ON PLANT :
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].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
NO-ENTRY
PLANT RESPONSE TO FIRE :
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].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
NO-ENTRY
FIRE MANAGEMENT CONSIDERATIONS :
Fire danger increases with the increasing volume of logging residue.
Logging old-growth stands or western hemlock can leave huge volumes of
residue compared with logging young stands, which leave little residue.
Burning cleans up the area and facilitates planting. Therefore burning
is often favored by land managers who intend to plant Douglas-fir to
obtain a mixture of Douglas-fir and western hemlock. The general trend
in western hemlock management, however, is away from broadcast burning
except where a huge accumulation of residues constitutes a fire hazard
[64].
Burning in western hemlock stands is a valuable treatment when seedlings
and saplings are infected with dwarf mistletoe and need to be destroyed.
Fire is helpful in rehabilitation of brushy areas; burning brush to
ground level facilitates planting and favors planted seedlings in
keeping ahead of the brush sprouts [64].
Fire spreads more slowly in western hemlock slash than in western
redcedar slash. Western hemlock slash drops its foliage. The slash of
western hemlock is less flammable when chipped [52]. Slash from western
hemlock/western redcedar/Alaska-cedar forests produce greater nutrient
losses to the atmosphere when the slash composition has a greater
proportion of Alaska-cedar and western redcedar. One can expect smaller
nutrient losses when western hemlock makes up the majority of the slash
[28]. For further details on burning of western hemlock slash, refer to
the Fire Case Study in the Alaska-cedar Fire Effects Information System
Species Review.
REFERENCES
SPECIES: Tsuga heterophylla
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