Index of Species Information

SPECIES:  Tsuga mertensiana

Introductory

SPECIES: Tsuga mertensiana
Mountain hemlock grove in Emigrant Wilderness Area, CA. Photo by Janet L. Fryer, USFS, Fire Sciences Laboratory.
AUTHORSHIP AND CITATION : 
Tesky, Julie L. 1992. Tsuga mertensiana.  In: Fire Effects Information System, [Online]. 
U.S. Department of Agriculture, Forest Service, 
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). 
Available: http://www.fs.fed.us/database/feis/ [].  


ABBREVIATION : TSUMER SYNONYMS : NO-ENTRY SCS PLANT CODE : TSME COMMON NAMES : mountain hemlock alpine hemlock black hemlock hemlock spruce TAXONOMY : 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]. LIFE FORM : Tree FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY

DISTRIBUTION AND OCCURRENCE

SPECIES: Tsuga mertensiana
GENERAL DISTRIBUTION : 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]. ECOSYSTEMS : FRES11 Spruce - fir FRES22 Western white pine FRES23 Fir - spruce FRES24 Hemlock - Sitka spruce FRES25 Larch FRES26 Lodgepole pine FRES44 Alpine STATES : AK CA ID MT OR WA AB BC BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 4 Sierra Mountains 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 K008 Lodgepole pine - subalpine forest K013 Cedar - hemlock - pine forest SAF COVER TYPES : 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 SRM (RANGELAND) COVER TYPES : NO-ENTRY HABITAT TYPES AND PLANT COMMUNITIES : 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].

MANAGEMENT CONSIDERATIONS

SPECIES: Tsuga mertensiana
WOOD PRODUCTS VALUE : 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]. IMPORTANCE TO LIVESTOCK AND WILDLIFE : 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]. PALATABILITY : NO-ENTRY NUTRITIONAL VALUE : NO-ENTRY COVER VALUE : NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES : 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]. OTHER USES AND VALUES : 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]. OTHER MANAGEMENT CONSIDERATIONS : 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].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Tsuga mertensiana
GENERAL BOTANICAL CHARACTERISTICS : 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]. RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : 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]. SITE CHARACTERISTICS : 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]. SUCCESSIONAL STATUS : 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]. SEASONAL DEVELOPMENT : 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].

FIRE ECOLOGY

SPECIES: Tsuga mertensiana
FIRE ECOLOGY OR ADAPTATIONS : 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]. POSTFIRE REGENERATION STRATEGY : Tree without adventitious-bud root crown Secondary colonizer - off-site seed

FIRE EFFECTS

SPECIES: Tsuga mertensiana
IMMEDIATE FIRE EFFECT ON PLANT : 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]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : 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]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : 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].

References for species: Tsuga mertensiana


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