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SPECIES:  Sorbus sitchensis
Western mountain-ash in Alpine Lakes Wilderness, Washington. Wikimedia Commons image by Walter Siegmund.


SPECIES: Sorbus sitchensis
AUTHORSHIP AND CITATION: Matthews, Robin F. 1993. Sorbus sitchensis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. Updates: On 2 February 2018, the common name of this species was changed in FEIS from Sitka mountain-ash to western mountain-ash. The plant and map images were also added.
ABBREVIATION: SORSIT SYNONYMS: NO-ENTRY SCS PLANT CODE: SOSI COMMON NAMES: western mountain-ash Pacific mountain-ash Sitka mountain-ash TAXONOMY: The scientific name of western mountain-ash is Sorbus sitchensis M. Roemer [16,18,24,39]. Varieties are [16,20,37]: Sorbus sitchensis M. Roem. var. grayi (Wenzig) C.L. Hitchc., western mountain-ash Sorbus sitchensis M. Roem. var. sitchensis, Sitka mountain-ash Western mountain-ash hybridizes with Greene's mountain-ash (S. scopulina) [39]. LIFE FORM: Tree, Shrub FEDERAL LEGAL STATUS: No special status OTHER STATUS: NO-ENTRY


SPECIES: Sorbus sitchensis
GENERAL DISTRIBUTION: Western mountain-ash is distributed from Alaska south along the Pacific Coast and through the Cascade Range to northern California and east to northern Idaho and northwestern Montana [16,24,39].
Distribution of western mountain-ash. 1976 USDA, Forest Service map digitized by Thompson and others [40].
   FRES20  Douglas-fir
   FRES22  Western white pine
   FRES23  Fir - spruce
   FRES24  Hemlock - Sitka spruce
   FRES25  Larch

     AK  CA  ID  MT  OR  WA  BC

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

   K001  Spruce - cedar - hemlock forest
   K002  Cedar - hemlock - Douglas-fir forest
   K003  Silver fir - Douglas-fir forest
   K004  Fir - hemlock forest
   K007  Red fir forest
   K012  Douglas-fir forest
   K013  Cedar - hemlock - pine forest
   K014  Grand fir - Douglas-fir forest
   K015  Western spruce - fir forest

   205  Mountain hemlock
   206  Engelmann spruce - subalpine fir
   207  Red fir
   210  Interior Douglas-fir
   211  White fir
   212  Western larch
   213  Grand fir
   215  Western white pine
   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




SPECIES: Sorbus sitchensis
WOOD PRODUCTS VALUE: Western mountain-ash has light-weight, fine-textured wood [39]. It has no commercial value [17]. IMPORTANCE TO LIVESTOCK AND WILDLIFE: Western mountain-ash berries remain on the trees until late winter, making them available as winter forage. They are important in the diet of many upland gamebirds, songbirds, and small mammals [14,26]. The twigs supply browse for deer and moose [14]. Roosevelt elk also utilize western mountain-ash in the summer months [19]. Black bear and grizzly bear eat the berries, leaves, and stems [21,27]. PALATABILITY: Western mountain-ash provides fair browse for sheep and fair to poor browse for cattle [38]. NUTRITIONAL VALUE: NO-ENTRY COVER VALUE: NO-ENTRY VALUE FOR REHABILITATION OF DISTURBED SITES: Western mountain-ash has been used for streambank rehabilitation in Oregon and Washington [25]. OTHER USES AND VALUES: Western mountain-ash is cultivated as an ornamental [17,26,39]. OTHER MANAGEMENT CONSIDERATIONS: Foliar glyphosate and broadcast 2,4-D applications caused severe injury to western mountain-ash in field experiments [28]. Western mountain-ash may produce allelopathic substances that inhibit Douglas-fir (Pseudotsuga menziesii) seedlings [30].


SPECIES: Sorbus sitchensis
GENERAL BOTANICAL CHARACTERISTICS: Western mountain-ash is a native, deciduous shrub 4 to 8 feet (1.2-2.4 m) tall, or a small tree up to 20 feet (4.5-6.0 m) tall and 6 inches (15 cm) d.b.h. On rocky alpine sites at higher elevations western mountain-ash is often only 1 to 2 feet (0.3-0.6 m) tall. Leaves are pinnately compound and are 4 to 8 inches (10-20 cm) long with 7 to 11 leaflets. Western mountain-ash bark is thin and smooth. Flowers are borne in terminal corymbs with 15 to 60 flowers per head. Fruits are small pommes [39]. RAUNKIAER LIFE FORM: Phanerophyte REGENERATION PROCESSES: Western mountain-ash mainly propagates by seed [32,38]. Mountain-ashes (Sorbus spp.) begin producing seed at about 15 years of age and usually produce a good seed crop every year. Seeds are mainly dispersed by birds. Seedlings are hardy and are not very susceptible to insects or disease, but may be injured by deer browsing [14]. Cooper [7] reports that American mountain-ash (S. americana), a closely related species, sprouts from the stump when top-killed. Propagation: Cleaned seeds have been stored for 2 to 8 years without loss of viability. Seeds sown in the spring require 60 or more days of previous stratification at 32 to 41 degrees Fahrenheit (0-5 deg C) in moist sand, moss, soil, or other medium. Unstratified seed should be sown in the fall or early winter. Germination is slower and not as successful if seeds are not removed from the berries before sowing [14]. SITE CHARACTERISTICS: Western mountain-ash occurs in dry to moist, well-drained sandy loam or other soils [38]. In southern and southeastern Alaska, western mountain-ash is an uncommon to rare forest tree, occurring from sea level to timberline along the coast [39]. In coastal British Columbia, western mountain-ash is an indicator of moderately dry to fresh, nitrogen-poor soils. It is common but scattered in British Columbia, where it is found in montane to subalpine, open-canopy coniferous forests. Its occurrence there increases with increasing precipitation and elevation [22]. In the Pacific Northwest, it occurs in mid- to upper-elevation coniferous forests and forest openings, and is particularly widespread from 3,000 to 5,000 feet (900-1,515 m) on the western slope of the Cascade Range [35]. Western mountain-ash is found at elevations from 3,400 to 6,700 feet (1,030-2,030 m) in Montana [9]. In the Bitterroot Mountains of west-central Montana, it is most often found in moist, deep soils along creeks or streams [24]. SUCCESSIONAL STATUS: Western mountain-ash is shade intolerant and persists in clearings [22]. It is present in many climax forests and plant associations [2,3,12,15,34,36]. Western mountain-ash may inhibit growth of other vegetation [8]. SEASONAL DEVELOPMENT: Western mountain-ash flowers from June to July. Fruits ripen from September to October and persist through late winter [14,39].


SPECIES: Sorbus sitchensis
FIRE ECOLOGY OR ADAPTATIONS: A closely related species, American mountain-ash, sprouts from the bole when top-killed by fire [7]. Western mountain-ash may have this ability as well, but western mountain-ash sprouting has not been documented in the literature. Some areas in which western mountain-ash occurs have long intervals between fires [2,29]. Cool, wet maritime forests may have fire return intervals of several hundred years or more [4]. POSTFIRE REGENERATION STRATEGY: Initial-offsite colonizer (off-site, initial community) Secondary colonizer - off-site seed


SPECIES: Sorbus sitchensis
IMMEDIATE FIRE EFFECT ON PLANT: Specific information on the immediate effect of fire on western mountain-ash is not available in the literature. Since it is a small tree with thin bark, it may survive light-severity fire but is probably killed by severe fire. Mature mountain-ashes (Sorbus spp.) have been eliminated by fires at various locations throughout the United States and Canada [6]. DISCUSSION AND QUALIFICATION OF FIRE EFFECT: NO-ENTRY PLANT RESPONSE TO FIRE: Western mountain-ash was absent from burned sites but present on adjacent unburned sites 29 years following fire in alpine heath and krummholz communities in Washington [10]. Mountain-ash (Sorbus spp.) sprouts and seedlings appeared in the first and second postfire years after spring and summer wildfires and spring prescribed fires in Minnesota [1]. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE: The Research Project Summary Revegetation in a subalpine fir forest after logging and fire in central British Columbia provides information on prescribed fire and postfire response of plant community species, including western mountain-ash, that was not available when this species review was originally written. FIRE MANAGEMENT CONSIDERATIONS: NO-ENTRY


SPECIES: Sorbus sitchensis
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