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Alpine milkvetch has widespread circumpolar distribution in the arctic and subarctic regions .
Astragalus a. var. alpinus is found across North America, from Alaska to Newfoundland south to Nevada, New Mexico, and South Dakota. It occurs rarely in Minnesota and Wisconsin [2,6,14,15,16,19,21,23,24,26,31,53,54]. Astragalus a. var. alpinus is also found in Eurasia [24,31,54].Astragalus a. var. brunetianus is found only in Quebec and Newfoundland south to Nova Scotia and Maine. It historically occurred in Vermont and New Hampshire as well [23,42] but has been extirpated . Plants Database provides a distributional map of alpine milkvetch and its infrataxa.
Alpine milkvetch is a native, perennial forb with a matted growth habit [2,6,7,19,21,23,24,31,39,54].
The following botanical characteristics describe A. a. var. alpinus; comprehensive descriptions of A. a. var. brunetianus were not found in the literature available as of 2007. Alpine milkvetch has an initial taproot , with stems arising singly or a few together from a subterranean caudex  and from slender, widely creeping and adventitiously rooting subterranean rhizomes [2,6,19,26]. Aerial stems are decumbent to ascending and reach 0.5 to 12 inches (1-30 cm) long [2,6,26,31,54]. Alpine milkvetch's ovate leaves are 1 to 6 inches (3-15 cm) long, with 5 to 26 leaflets 4 to 20 mm long and 2 to 10 mm wide [2,26,31,54]. Alpine milkvetch has a spreading, raceme inflorescence with 5 to 30 flowers that are 9 to12 mm long [26,54]. Seeds are borne in pendulous pods 7 to 17 mm long and 2.5 to 4 mm wide [2,6,26,31,54].The nitrogen-fixing root nodules of alpine milkvetch [34,39] are 4 to 5 mm long . Alpine milkvetch is able to fix nitrogen at soil temperatures down to 32 oF (0 oC), with maximum nitrogen fixation occurring at soil temperatures from 59 to 77 oF (15-25 oC) . Treu and others  found no mycorrhizae associated with alpine milkvetch.
Alpine milkvetch is insect pollinated . The light seeds are dispersed by wind and water [7,12] and may stay afloat for 3 to 13 days .
Site Characteristics: Astragalus a. var. alpinus is generally an alpine to subalpine plant , found from sea level to 6,600 feet (2,000 m) in Alaska and 11,200 feet (3,400 m) in the Intermountain West [2,21,24,31,54]. Alpine milkvetch is commonly found near alpine lakes and creeks [6,7,11,19,20,40,41,53], in cool, moist woodlands and mountain meadows [2,6,21,24,26,31,53,54], and on harsh arctic sites including tundra and sites exposed to wind and cold [26,40,41]. It is frequently found on excessively drained soils , for example, scree slopes , river alluvium , and gravel bars . Parent materials are commonly calcareous [1,38] or siliceous .
Astragalus a. var. brunetianus is primarily a wetland plant  and is commonly found on limy river beaches .
Successional Status: Alpine milkvetch is an early seral colonizer [5,7,13]. It may be an important pioneer species on mechanically disturbed areas (e.g., old roads, abandoned gravel pads) in arctic tundra [4,13,25,32]. Alpine milkvetch is also a pioneer on bare areas caused by frost heaving in arctic heath (Ericaceae) communities, though it is not found in climax heath vegetation. It is confined to disturbed sites in protected areas that eventually develop rich heath communities. Alpine milkvetch does, however, persist in fully developed tundra vegetation. It frequently grows in windswept areas, but there is no disturbance requirement for alpine milkvetch to establish in tundra. These observations suggest that alpine milkvetch is limited in its competitive ability with other established plants (heath), but is less limited in its ability to persist under exposure to rigorous climate conditions (tundra) . Another study also found that grass planted to revegetate disturbed areas of tundra did not affect the establishment of alpine milkvetch, though establishment of other early seral species was impeded by the planted grass . Uresk and Severson  found that in ponderosa pine (Pinus ponderosa) forest of the Black Hills, alpine milkvetch growth was greater at low tree densities than at high densities; however, no alpine milkvetch was present in clearcuts. Similarly, a study of lodgepole pine (P. contorta) forest succession in Yellowstone National Park, Wyoming, found alpine milkvetch was characteristic of intermediate-aged stands but was not present where the forest canopy had closed .
Seasonal Development: Alpine milkvetch flowers from late May to early August [31,46] and produces seed from August to early September .
Importance to Wildlife and Livestock: Caribou , arctic hares , and greater snow geese  graze alpine milkvetch. Grizzly bears forage underground parts of alpine milkvetch . Some members of the Astragalus genus are poisonous to domestic livestock (e.g., lesser rushy milkvetch (A. convallarius), woolly locoweed (A. mollissimus)) , though alpine milkvetch has not been specifically identified as one of these species.
Value for Rehabilitation of Disturbed Sites: Because it is leguminous, alpine milkvetch may be useful in restoring nitrogen to disturbed sites. However, little is known about alpine milkvetch's response to disturbance .
Alpine milkvetch seed may require scarification. A study of seed bank samples from Yellowstone National Park found alpine milkvetch germinants present after the seeds were exposed to 212 oF (100 oC) for 1 hour. Germinants were not present in the control, the 122 oF (50 oC) treatment, or the 302 oF (150 oC) treatment . The temperature required to kill 50% of alpine milkvetch seeds in a sample exceeds 248 oF (120 oC) . Laboratory tests in another study found alpine milkvetch germination may be enhanced by mechanical scarification .
Transplanting alpine milkvetch may be moderately successful. In a British Columbia study, transplant survivorship of alpine milkvetch was 57% to 73% on unamended coal mine soils. In general, plants did not flower or set seed until the second or third year after transplanting. Survival of alpine milkvetch decreased rapidly during the first 2 years and then gradually leveled off. Mortality was attributed to seedling drought stress, frost damage, and wildlife foraging .
Fire Information: There is some evidence that alpine milkvetch may be an early seral species on burned sites. A study conducted in Grand Teton National Park, Wyoming, found alpine milkvetch was an important postfire species in severely burned areas of Engelmann spruce-subalpine fir-lodgepole pine (Picea engelmannii-Abies lasiocarpa-Pinus contorta) forest where all trees were killed and aboveground portions of understory vegetation were consumed. Alpine milkvetch remained on these sites for at least 17 years after the fire, increasing to 25% cover in the first 8 postfire years and then decreasing to 10% cover over the next 8 years. Alpine milkvetch was not present on similar, unburned sites . Doyle and others  described alpine milkvetch as a "transient" or "opportunistic" early successional species In Grand Teton National Park. It is not found in mature forest but generally appeared in the first postfire year in severely burned stands. It presumably developed from seeds and/or rhizomes already in the soil at the time of the fire, though the study did not conclusively demonstrate the presence of a seed bank or rhizome propagules.
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 :
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