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The few studies that report alpine sweetvetch abundance on burned and unburned sites suggest that
abundance is typically lower on burned than unburned sites and increases with increased time since fire.
Additional fire studies are needed to determine how fire season and/or fire severity affect alpine
sweetvetch recovery on burned sites.
Alpine sweetvetch was not present on a 3-year-old burned site in black spruce forests north of Tulita,
Northwest Territories. The site burned in a high-severity crown fire that killed most trees. Alpine
sweetvetch frequency was 6.7% on a similar unburned site. Researchers noted species composition and cover
differences between burned and unburned sites, making it impossible to attribute alpine sweetvetch
frequency differences entirely to effects of the fire [51].
On subalpine and alpine sites burned in a prescribed fire on the eastern Rocky Mountain slopes of
Banff National Park, Alberta, alpine sweetvetch was present but with low cover. Time since fire did not
seem to affect alpine sweetvetch cover. Alpine sweetvetch cover averaged less than 0.55% on 3- and
8-year-old willow-bog birch, 7-year-old Engelmann spruce/feather moss (Picea engelmannii/Holocomium
spp.), 7-year-old lodgepole pine (Pinus contorta)/russet buffaloberry, and 8-year-old
kinnikinnick/boreal wildrye (Arctostaphylos uva-ursi/Leymus innovatus) stands. Fires were not
described [57].
Alpine sweetvetch cover and frequency were lower on logged and burned than on unburned white
spruce/thinleaf alder/mountain-fern moss (H. splendens) sites on Willow Island in the Tanana River
near Fairbanks. Alpine sweetvetch cover and frequency, respectively, were 2.1% and 22% on unburned and 0.1%
and 5% on logged and burned sites. Slash fires burned when conditions were "fairly dry" and
consumed almost all available fuels. Researchers found that soil temperatures at 4-inch (10 cm) and at
8-inch (20 cm) depths were significantly (P<0.01 and P<0.05, respectively) higher on
treated (burned, logged, or burned and logged) than untreated sites. For information on alpine sweetvetch
recovery on clearcut and shelterwood logged sites, see Logging [23].
In Engelmann spruce-dominated forests in the subalpine zone of Alberta's Rocky Mountains, alpine
sweetvetch importance values were lower on 10-year-old and 59-year-old burned than on unburned sites.
Mortality occurred in a majority of overstory in the burned area studied. Alpine sweetvetch prominence
values (the product of mean percent cover and the square root of percent
frequency) were 9.7 and 9.3 on 10-year-old and 59-year-old burned sites, respectively. Prominence values were 18.9 and 14.5 on unburned
sites near the 10-year-old and 59-year-old burned sites, respectively [4].
When burned and logged sites were compared in upland boreal forests of the Tanana and Yukon river
drainages in central Alaska, researchers found alpine sweetvetch only on burned sites. Stands were white
spruce-dominated before the disturbances and after the disturbances were a mix of quaking aspen, paper birch,
and white spruce. Sites were burned or logged 2 to 18 years before the study. Researchers suggested that
reduced organic layer thickness on burned sites may have created conditions more conducive to early-seral
species dominance. Canopy closure was >75% in 2-to 18-year-old logged stands and 32% in 2-to 18-year-old
burned stands [55].
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [1,8,17,27,28]).
Aboveground description: Alpine sweetvetch is an herbaceous, perennial legume. It produces numerous clumped stems from a branching caudex. Stems are erect and measure 8 to 30 inches (20-70 cm) tall [1,8,28,39,60]. Leaves are longer than they are wide, pinnately compound, and have an alternate arrangement. Leaves contain 9 to 31 leaflets that are 0.4 to 1 inch (10-35 mm) long and 5 to 10 mm wide [1,8,17,28,40]. Alpine sweetvetch produces showy flowers that are densely organized in a long raceme. Flowers can be 9 to 18 mm long and are often deflexed and spreading [1,18,39]. Alpine sweetvetch produces flat, indehiscent, pod fruits that are constricted between the seeds. There are typically 2 to 5 but sometimes as many as 9 constricted joints/pod and just one seed/joint. Pods can be 5 to 7 mm long and 3 to 5.5 mm wide [18,28,35,60]. Seeds are smooth and measure 3.5 to 4 mm long and 2 to 2.5 mm wide [28]. Two hundred seeds weigh approximately 1 gram [12].
Belowground description: Alpine sweetvetch produces branching rhizomes and taproots. Aboveground shoots are often connected below ground [44]. Taproots are woody, long, and thick [28,39,40]. Mature plants may have roots with multiple branches that are several feet long and "as thick as a carrot" [35].
Alpine sweetvetch is a circumpolar species [1]. In North America, it is widely distributed throughout Alaska and Canada, and occurs in the northern part of the contiguous United States. It occurs in Glacier County in Montana, Albany and Weston counties in Wyoming, southwestern South Dakota, the upper peninsula of Michigan, Aroostook County in northern Maine, Orleans and Lamoilee counties in northern Vermont, Coos County in New Hampshire, and Warren County, Massachusetts [8,18,28,58,60,65,69]. A map of the states occupied by alpine sweetvetch is available through Plants Database.
The distribution of Hedysarum alpinum var. alpinum is not well described. Gillett and others [26] indicate that it occurs in Canada's Nunavut and Northwest Territories, and Thilenius [62] describes it on Alaska's Copper River Delta. This may not describe the entire range occupied by H. alpinum var. alpinum.
Fire adaptations: As of this writing (2007), no study describes alpine sweetvetch's POSTFIRE REGENERATION STRATEGY or fire adaptations. Vegetative regeneration from the caudex or rhizomes and/or on- or off-site seed germination and seedling establishment are possible.
FIRE REGIMES: Fires occur at 50- to 500-year intervals in northern boreal, alpine, and subalpine vegetation that provides alpine sweetvetch habitat.
Floodplain habitats: Descriptions of fire occurrence on alpine sweetvetch floodplain habitats vary widely. Researchers suggest that the youngest geomorphic surfaces along Riley Creek in the central Alaskan Range, which are disturbed annually by flooding, ice scouring, and sediment erosion and deposition, are "probably affected only rarely by fire" [49]. Fire is also considered rare on the Mackenzie River Delta where alpine sweetvetch occurs in white spruce forests [53]. However, in the taiga of interior Alaska, fire is common in black spruce forests. On the older river terraces, black spruce stands over 200 years old are rare in most of the taiga, and in some areas, stand-replacing fires occur at 50- to 100-year intervals [66]. In southwestern Yukon, charcoal in loess silts dates back 12,000 years. Charcoal deposits were partly attributed to the South Tutchone people who burned stream and lake banks to thaw the ground for alpine sweetvetch root harvests. Frequency of this type of burning was not reported (others cited in [34]).
Tundra habitats: A review of fire in northern ecosystems states that moderate-severity surface fires in tundra vegetation, which typically kill aboveground vegetation but not belowground structures, can occur at intervals as short as 100 years. However, longer fire-return intervals are likely due to cold, humid summers and patchy fuel distribution in tundra habitats [22].
Spruce and seral boreal forest habitats: Fires are not uncommon in northern boreal forests and alpine habitats, and fire is often more frequent in the western than eastern boreal forests in the United States and Canada [22]. On the east slopes of Banff National Park, fire is important to the maintenance of open and seral habitats within the climax spruce/mountain-fern moss-Schreber's big red stem moss (Pleurozium schreberi) community. Open seral habitats are used by grizzly bears to dig alpine sweetvetch roots. Alpine sweetvetch was most often dug in willow (greyleaf willow and Farr's willow (Salix farriae)) and willow-bog birch (Betula glandulosa) shrubfields. Using fire scars and stand age structure data, researchers calculated a mean fire-return interval of 15 years for the time period between 1580 and 1936 in the 148 km² study area. The longest fire-return interval was 45 years, and no fires had occurred in the last 49 years. Most fires were stand replacing. Ninety-two percent of digging sites burned in a fire 56 years before the study [31].
The average fire-return intervals for alpine, subalpine, and montane vegetation in Manitoba's Kluane National Park ranged from 133 years in the southern, wet, maritime climatic region to 234 years in the northern, dry, cold, continental climatic region. Montane habitats were predominantly white spruce forests, but some quaking aspen and balsam poplar occurred in areas recently disturbed by fire, flooding, or heavy snow. Subalpine vegetation was dominated by tall willow shrubs with scattered white spruce. Alpine communities were willow-birch (Betula spp.)/heath (Ericaceae)-krummholz shrub and tundra communities. Fires occurred from May to September. There were no lightning fires from 1963 to 1981, but Park records indicate lightning fires are likely every 20 to 50 years [34].
In a review of fire in northern ecosystems, researchers suggest that fires occur at 35- to 200-year intervals in northern aspen and aspen-birch woodlands. Mixed and stand-replacing fires are possible in spring, late summer, and fall when fuels are flammable. Balsam-fir (Abies balsamifera) forests in high precipitation areas of eastern Canada and the northeastern United States burn on average every 150 to 300 years. Both crown and severe surface fires are possible following drought conditions. Black spruce forests burn at 50- to 100-year intervals in northwestern Canada and Alaska, and the interval increases to 500 years in southeastern Labrador and 480 years in western Newfoundland. Fires in black spruce forests are often large due to continuous fuels. In boreal white spruce forests, crown or severe surface fires are possible every 150 to 300 years. In Kluane National Park, Yukon, dry cool white spruce/quaking aspen forests have an average fire-return interval of 113 to 238 years [22].
The following table provides fire regime information on vegetation communities in which alpine sweetvetch may occur. 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 regime information on vegetation communities in which alpine sweetvetch may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [47]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the .pdf file linked from each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model. Northern Rockies Northern Great Plains Great Lakes Northeast Northern Rockies Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics Percent of fires Mean intervalGravel and sandbars along streambanks and lake shores are important alpine sweetvetch habitat; however, it also occurs on rock slopes, open hillsides, in meadows, prairies, deciduous woodlands, and spruce (Picea spp.) forests throughout its range [18,19,28,35,39].
Climate: Alpine sweetvetch primarily occurs in boreal or northern temperate climates [27]. In Alaska, a range of climatic conditions is tolerated by alpine sweetvetch. In northern Alaska near Umiat, alpine sweetvetch occurs in low arctic, graminoid-moss habitats where January and July temperatures average 10.9 °F (-11.7 °C) and 53.1 °F (11.7 °C), respectively. Annual precipitation near Umiat averages 4.7 inches (119 mm) [6]. In the east-central part of the state near Eagle, the climate is continental, and January and July temperatures average -9 °F (-23 °C) and 59 °F (15 °C), respectively. Average annual precipitation near Eagle is 12 inches (308 mm) [70]. In southeastern Alaska's Copper River Delta, the climate is marine to continental. The growing season averages 109 days from late May to mid-September. Day lengths during the growing season average 18 hours and 45 minutes. Growing seasons are cool, cloudy, wet, and windy. In August 1981, the area received 28 inches (711 mm) of rain in 48 hours [62].
Elevation: While minimum and maximum elevational tolerances are not described for alpine sweetvetch, it is described from the following elevations: 8,100 to 8,200 feet (2,470-2,500 m) in Wyoming; 5,000 feet (1,500 m) in Montana [16]; 1,720 to 2,330 feet (525-710 m) in the upper Yukon Valley, interior Alaska [24], and 3,900 to 5,400 feet (1,190-1,646 m) in the Kluane Lake area of Yukon, Canada [44].
Soils: Alpine sweetvetch often occurs on moist to dry calcareous soils [21,27,58,69]. Temporary flooding is tolerated [53]. Researchers characterized alpine sweetvetch as a calciphilic legume in high subarctic and low arctic parts of northwestern Canada, where alpine sweetvetch occupied sites with calcareous, fine-textured loams [64]. Alpine sweetvetch was considered a xerophyte by Mann and Plug [49] studying in the taiga of the central Alaskan range and by Rowe [56] studying in western Manitoba. In western Manitoba, alpine sweetvetch preferred dry forests and occurred in open white spruce-quaking aspen stands on excessively drained till on the Duck Mountain Forest Reserve. Alpine sweetvetch site preference was evaluated by assessing abundance and "vigor" [56].
In white spruce forests of the Mackenzie River Delta in the Northwest Territories, alpine sweetvetch occupies sites that are rarely flooded. Sediment deposition ranges from 0 to 2 cm, and depth to permafrost is 8 to 30 inches (20-70 cm). Soils are Static or Organic Cryosols, well to poor draining, with a pH range of 4.5 to 8.4. Soil temperatures range from 40 to 50 °F (5-10 °C) at 0- to 4-inch (10 cm) depths and 39 to 40 °F (2-5 °C) at 4- to 8-inch (10-20 cm) depths. July soil moisture content ranges from 12% to 60% [53].
Alpine sweetvetch is important in the diets of many northern large mammals. Black bears, grizzly bears, moose, Dall's sheep, and caribou utilize alpine sweetvetch and alpine sweetvetch habitats.
Bears: Black bears consume the aboveground portions of alpine sweetvetch, and roots are consumed by grizzly bears. Grizzly and black bear scat collected from Glacier National Park, the Flathead National Forest, and Waterton Lakes National Park showed that sweetvetch (Hedysarum spp.) was consumed with the greatest frequency (17%) and volume (13%) in early October to mid-November [42]. In more northern areas, alpine sweetvetch is utilized throughout the growing season [30,38].
In the Rocky Mountain foothills of Kananaskis Country, Alberta, researchers analyzed scat to determine the seasonal frequency of alpine sweetvetch and white sweetvetch (H. sulphurescens) in black bear diets. The frequency of herbaceous sweetvetch vegetation was greatest in early summer (41% in 1984, 38% in 1985). In early spring, the frequency of sweetvetch was 33% in 1984 and 25% in 1985. In late summer the frequency was 6% in 1984 and 21% in 1985. Frequency of sweetvetch ranged from zero to 8% in the fall. Scat sample sizes ranged from a low of 4 in the fall of 1984 to a high of 34 in the late summer of 1984. Researchers indicated that black bears do not have the claw length or musculature to easily dig sweetvetch roots as grizzlies do [38].
Alpine sweetvetch roots are a primary food for grizzly bears in the Front Ranges of Banff National Park [29], and the entireleaf mountain-avens-alpine sweetvetch-red fescue community on the Savage River floodplain in western Alaska is utilized by grizzly bears for alpine sweetvetch root digging (personal communication in [33]). Hamer [30] studied the foods and habitats of grizzly bears for 4 years in a 250 km² study area in Banff National Park using fecal analysis, feeding site examinations, direct observations, and radio tracking. Alpine sweetvetch roots were eaten primarily in the early and late parts of the growing season when nutrient content was high and other green forage and fruits were unavailable. Use of alpine sweetvetch decreased as spring progressed, and roots were rarely dug when alpine sweetvetch was in flower and crude protein levels were lowest. In late July and early August, alpine sweetvetch roots reentered the grizzly bear diet in 3 of 4 years. Nearly all alpine sweetvetch roots were dug in mesic to subhygric greyleaf willow-Farr's willow-bog birch/boreal wildrye communities. Digging sites were more common at lower elevations in May than in June, and researchers suggested that grizzlies may prefer alpine sweetvetch in its early phenological stage [30].
Large ungulates: American bison, Dall's sheep, caribou, and moose feed on alpine sweetvetch. Based on field observations, feeding and pasture tests, and examinations of stomach contents, sweetvetch is considered a key component of American buffalo and Dall's sheep diets in Alaska [52]. In southwestern Yukon, alpine sweetvetch flowers are important Dall's sheep forage items on alpine summer range [37]. Eightpetal mountain-avens-Bellardi bog sedge-alpine sweetvetch communities on mountain slopes along the Toglat River in McKinley National Park are "preferred" Dall's sheep winter grazing habitat (personal communication in [33]). In south-central Alaska, alpine sweetvetch is common in alpine sites, is considered highly palatable, and is an important source of summer caribou nutrition [59]. Entireleaf mountain-avens-alpine sweetvetch-red fescue vegetation on the Savage River floodplain in western Alaska is considered important moose grazing habitat (personal communication in [33]).
Small mammals and birds: Alpine sweetvetch habitats are utilized as nesting habitat for many bird species and voles, which are common in alpine sweetvetch habitats, and provide a food source for short-tailed weasels and other birds. The alpine sweetvetch-Bering's tufted hairgrass community type on the Copper River Delta is important Canada goose nesting habitat. Ducks, gulls, short-eared owls, arctic terns, savannah sparrows, and short-billed dowitchers also nested in this habitat. Voles used the alpine sweetvetch-Bering's tufted hairgrass community type extensively and grazed alpine sweetvetch. High vole populations provided prey for short-tailed weasels, short-eared owls, and northern harriers [11].
Palatability/nutritional value: The nutritional content of 2-year-old alpine sweetvetch plants grown from seed collected in west-central Saskatchewan is provided by Bassendowski and others [3]. In the early flowering stage (16 June-5 July) plants were harvested and the chemical makeup and digestibility determined. Alpine sweetvetch protein and fiber levels were similar, tanin contents greater, and digestibility lower than those of alfalfa [3]. Other nutritional information is provided in Bears.
Cover value: See Small mammals and birds section above. No additional information is available on this topic.
Alpine sweetvetch is common in pioneer communities along rivers and lakes throughout its range. It often
occurs in willow, birch, and alder (Salix, Betula, and Alnus spp.) thickets along
waterways and in boreal forests. Alpine sweetvetch is also described in grasslands with little bluestem
(Schizachyrium scoparium), Canada bluegrass (Poa compressa), and American dunegrass
(Leymus mollis). Literature suggests that alpine sweetvetch tolerates some shade, and it is described
in boreal forests dominated by black spruce (Picea mariana), white spruce (P. glauca), quaking
aspen (Populus tremuloides), and balsam poplar (P. balsamifera). Alpine sweetvetch is not often
dominant but is considered an indicator or dominant species in the following vegetation classifications.
Alaska:
alpine sweetvetch-Bering's tufted hairgrass (Deschampsia beringensis)
community type on foreshore and channel levees of the Copper River Delta [11,62,63]
alpine sweetvetch-variegated scouringrush (Equisetum variegatum)
community type on levees adjacent to Copper River Delta channels [11,63]
entireleaf mountain-avens (Dryas integrifolia)-alpine sweetvetch-red
fescue (Festuca rubra) communities on the Savage River floodplain in western Alaska
eightpetal mountain-avens-Bellardi bog sedge (D. octopetala-Kobresia
myosuroides)-alpine sweetvetch communities on mountain slopes along the Toglat River in McKinley
National Park [33]
Canada:
basic, mesic tundra, medium shrub/mountain-avens (Dryas spp.) forest
tundra physiognomic type in the Northwest Territories and Manitoba [64]
Early and present-day Alaskan natives utilized alpine sweetvetch as a food source. Roots and young stems are eaten raw, boiled, roasted, and fried [35,39,40]. Correct identification of alpine sweetvetch is important, as its relative, northern sweetvetch (Hedysarum boreale subsp. mackenziei), may have poisonous roots [35]. A study of native Alaskan subsistence-based economies revealed that alpine sweetvetch, referred to as wild potato, is harvested by Inupiat people of the Kaktovik village on Barter Island along the Beaufort sea coast. Alpine sweetvetch was an important source of fiber in their diets [25].
The Dena'ina of south-central Alaska dig alpine sweetvetch roots in the spring, fall, and winter if they run out of stored food. Alpine sweetvetch roots are the most important food of the Dena'ina after wild fruits. Roots are eaten in many ways. A beverage is made by frying alpine sweetvetch in grease and soaking it in water. Babies who reject their mother's milk suck on the chewed end of the root. Roots are stored in lard or oil in underground caches and used as trade items with other groups. If stored food runs out, the Dena'ina may harvest alpine sweetvetch in the winter. Alpine sweetvetch growing sites are recalled from memory or found by looking for mouse tracks. Fires are set and burn all day to thaw the ground for harvest [40].
Alpine sweetvetch regenerates sexually through seed production and germination [12] and spreads vegetatively through rhizome production and growth [44].
Pollination: Insect visitors are required for alpine sweetvetch flower pollination and seed set. In Fairbanks, Alaska, worker bumble bees (Bombus flavifrons) were the most abundant visitor, making up 46% of 2,458 observed flower visits [50]. Others indicate that honey bees are a primary visitor of alpine sweetvetch flowers [3]. Alpine sweetvetch flowers produce small amounts of nectar with sugar concentrations over 65% [44].
Breeding system: As with all species within the Fabaceae family, alpine sweetvetch produces perfect flowers [27]. Cross pollination is common, and self pollination is possible only between 2 different flowers on the same plant [44].
Seed production: The few studies that report alpine sweetvetch seed and flower production suggest high rates of full seed development and a potential for high seed production per plant. Approximately 94% to 97% of alpine sweetvetch seeds set in the field develop fully [12]. From a field site in southwestern Alberta, the average number of flowers/inflorescence produced by 26 alpine sweetvetch plants was 72.5 ± 25.6 (SD), and the number of inflorescences/plant was 7.6 ± 3.1 [68]. In the Kluane Lake area of Yukon, experimental pollinations produced 1.2 viable seeds/legume [44]. If all the flowers on all inflorescences counted in southwestern Alberta produced 1.2 seeds/fruit, as in the Kluane Lake Area, the number of seeds produced per plant would have been 661.
Seed dispersal: Patterns and methods of alpine sweetvetch seed dispersal are largely unknown. Some suggest that erect stem structure is advantageous to seed dispersal [3]. Greater alpine sweetvetch colonization on gravel pads near rivers than on sites further away from rivers on Alaska's North Slope suggests that waterways may disperse seeds and/or pods [5]. Researchers attempting to grow alpine sweetvetch reported that removal of seeds from pods was difficult. Often seed ripening was uneven, and pods were fragmented once ripe [3].
Seed banking: Longevity of alpine sweetvetch seed in the soil was not reported as of the writing of this review (2007).
Germination: Kowalczyk [44] indicates that alpine sweetvetch seeds surviving the winter germinate readily in moist spring conditions in Kluane Lake [44], and controlled studies suggest that seed scarification and/or stratification can increase germination success [12,15]. In controlled experiments, researchers found that alpine sweetvetch germinated best after 60 days of cold stratification [15]. In experiments designed to test the future of alpine sweetvetch as a forage legume, researchers planted pods because of difficult seed removal. Germination from pods was difficult, but some germination and seedling establishment occurred [3]. Germination rates were 91% to 95% after moist seeds were stratified for 1 to 2 months at 37 to 43 °F (3-6 °C) and seed coats were artificially scarified. The germination procedure was not described [12].
Seedling establishment/growth: No information is available on this topic.
Vegetative regeneration: Rhizome growth allows alpine sweetvetch to spread vegetatively [44]. Sprouting from the caudex, rhizomes, or roots following top-killing disturbances other than winter-kill is likely but has not been described. Growth of alpine sweetvetch after being cut to 4 to 6 inches (10-15 cm) tall was slow, and some plants showed "very little" regrowth [3]. Dena'ina people of south-central Alaska, who harvest alpine sweetvetch, cut off and planted the thick end of alpine sweetvetch roots to encourage future harvests [40].
Alpine sweetvetch occurs in both early- and late-seral habitats. It is an important pioneer species on floodplains, shores and disturbed sites [5,21,66], but it is also described in climax forest types [20].
Shade tolerance: Alpine sweetvetch tolerates some shading. In upper Michigan, alpine sweetvetch habitats were partly shaded by a mixed paper birch (Betula papyrifera), white spruce, hemlock (Tsuga spp.), and cedar (Thuja spp.) overstory [9].
Primary succession: Alpine sweetvetch appears early in the successional development of rock and glaciated surfaces. In Glacier Bay, Alaska, level or depressed areas with crevices that collect soil are colonized by alpine sweetvetch [10]. From a chronosequence of the Muldrow Glacier in Alaska, alpine sweetvetch did not occur on the youngest surfaces (25-100 years old) dominated by pioneer and meadow species but was present with low cover and frequency on older surfaces (150-300 years old) dominated by low bog birch (B. glandulosa) [67].
Floodplain succession: Numerous studies highlight alpine sweetvetch as a pioneer species in floodplain succession. Alpine sweetvetch is one of the first persistent species on floodplains in Alaska's boreal forests [66]. Along Riley Creek in the central Alaskan Range, alpine sweetvetch is most common on the youngest geomorphic surface. Associated species include grayleaf willow (S. glauca), diamondleaf willow (S. pulchra), russet buffaloberry (Shepherdia canadensis), and mountain alder (Alnus viridis subsp. crispa) [49]. Along the Colville River, near Umiat, alpine sweetvetch establishes on bare floodplain gravel where sand and silt collect, and is also noted in the understory of more successionally advanced communities dominated by Alaska willow (Salix alaxensis) [7]. Findings were very similar on Firth River Valley floodplains in Alaska and Yukon where alpine sweetvetch occurs in pockets of silt and sand on bare gravel bars [21].
Disturbance succession: Alpine sweetvetch tolerates flooding, ice scouring, and sediment deposition along streambanks and shores [49,53] and often is an early colonizer of disturbed sites [5,13].
Following ice breakup flooding in white spruce forests on the Mackenzie River Delta, alpine sweetvetch cover increased [53]. Along Riley Creek in the central Alaskan Range, alpine sweetvetch occupies sites that are disturbed annually by flooding, ice scouring, and sediment erosion and deposition [49]. After an earthquake lifted the Copper River Delta 6.2 feet (1.9 m) above sea level, cover of alpine sweetvetch decreased by 44%. The researcher indicated that improved drainage and decreased tidal influence lead to decreased cover [11].
Alpine sweetvetch colonized some gravel pads on Alaska's North Slope, and abundance was greater on sites near rivers than sites further away from rivers. Gravel pads of up to 5.9 feet (1.8 m) thick were created in camp areas, work sites, and road-building sites to prevent permafrost melting. Pads were abandoned almost 10 years before the study and were likely fertilized and seeded with nonnative grasses 1 to 2 years after abandonment. Soils were 42% rock (> 2mm in size), low in organic matter (1.8%), and low in clay and water content. Alpine sweetvetch cover and frequency averaged less than 0.1% and 4%, respectively, for all 16 gravel pads [5]. Alpine sweetvetch colonized 14% of 22 borrow pits near the abandoned CANOL pipeline corridor and 16% of 58 borrow pits along the Dempster Highway in northwestern Canada. Researchers reported increased alpine sweetvetch prominence on sites with the longest time since disturbance; however, disturbed tundra site conditions were variable and likely affected colonization [43].
Forest succession: Forested habitats are occupied by alpine sweetvetch throughout its range. Alpine sweetvetch occurred in 89- to 168-year-old white spruce-balsam fir stands and in 112- to 145-year-old black spruce stands throughout the North American taiga [45]. In the Alsek River region of southwestern Yukon, alpine sweetvetch constancy was 47% to 60% in the understory of the climax white spruce-grayleaf willow community type where stands were 130 to 160 years old. The tree canopy was typically open and the shrub layer dense [20]. On Eagle Bluff above the Yukon River in Eagle, Alaska, alpine sweetvetch was absent from steppe vegetation dominated by fringed sagebrush (Artemisia frigida) and bluebunch wheatgrass (Pseudoroegneria spicata) but was present in forests dominated by quaking aspen, balsam poplar, and white spruce. Steppe vegetation was predominantly treeless, warmer, drier, received more radiation, and had lower pH and organic matter than forests. Forests and steppe communities received 57% and 94% full sun, respectively. Tree cover averaged 79% in forest and 5% in steppe vegetation [70].
Logging: Alpine sweetvetch occurred on logged sites, but cover was lower in the first postlogging year on Willow Island in the Tanana River near Fairbanks, Alaska. Researchers compared clearcut logging, shelterwood logging, and combined clearcut logging and burning treatments. Alpine sweetvetch cover and frequency increased with increasing time since disturbance on all but the clearcut and burned sites. On 2-year-old clearcuts, alpine sweetvetch cover and frequency were greater than on unlogged sites. Researchers found that soil temperatures at 4-inch (10 cm) and at 8-inch (20 cm) depths were significantly (P<0.01 and P<0.05, respectively) higher on treated than untreated sites [23].
Cover and frequency (%) of alpine sweetvetch 1 and 2 years after clearcutting, shelterwood logging, and clearcutting and burning in 2 white spruce forest types white spruce/mountain alder-thinleaf alder (Alnus incana subsp. tenuifolia)/mountain cranberry (Vaccinium vitis-idaea)/mountain-fern moss (Hylocomium splendens) forest type Years since treatment no treatment 1 2 1 2 1 2 control clearcut shelterwoodAlpine sweetvetch often colonizes disturbed sites and is often used in restoration or rehabilitation projects. On gold mine sites within the Kantishna mining area of Denali National Park and Preserve, alpine sweetvetch was present with low cover (<1%). Placer gold mining involves the removal of riparian vegetation and topsoil and the excavation and processing of gravel from the active floodplain. Reclamation of the sites began in 1988. By 1992, streambanks were contoured and stabilized. Establishing vegetation was evaluated in 1993 [13].
Establishment of alpine sweetvetch was more successful on subsoil than gravel fill on disturbed sites in the subalpine zone of Denali National Park and Preserve. Direct seeding of scarified alpine sweetvetch seed was successful, and seedlings reached mature plant size in 2 years on subsoil. On gravel fill, alpine sweetvetch established but seedling growth was slow. Greenhouse-propagated seedlings planted on gravel fill had 90% survival 3 years after planting [15].
On disturbed subalpine sites in Denali National Park, alpine sweetvetch seedling survival ranged from 73% to 87%, and survival was greater on plots without topsoil added. Disturbed sites were described as unvegetated gravel fill with very little silt or clay. Seedlings were grown in the greenhouse and planted in July. Survival was evaluated after 1 growing season [14].
