Astragalus alpinus var. alpinus
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Basis for Listing
Astragalus alpinus var. alpinus has a wide circumboreal distribution in America and Eurasia, extending south in alpine habitats to New Mexico. In Minnesota, this species is known from only one area in Lake County, where plants occur around portions of several nearby local ponds, all of which are within 1.3 km (0.8 mi.) of each other. Although the habitat does not appear to be immediately threatened, it is dependent on a very specific and sensitive hydrological system that could be inadvertently disrupted by a variety of human activities. Astragalus alpinus var. alpinus was listed as an endangered species in Minnesota in 1996.
Stems of A. alpinus var. alpinus are glabrous or nearly so, decumbent, up to 76 cm (30 in.) long, and scattered on a freely branching underground stem that sprouts at the nodes. There are usually 15-29 oblong to ovate leaflets. The nodding flowers have a purple keel and white wings. Pods are pendulous, the lower side is deeply marked with longitudinal grooves and the suture is intruded to form a partial partition. Several taxonomic varieties of A. alpinus var. alpinus have been described based on variations in pod characteristics. Variety alpinus is found in arctic regions and extends south into Ontario, South Dakota, Minnesota, Wisconsin, and throughout the Rocky Mountains. It has a densely pubescent pod with dark and light hairs (Gleason and Cronquist 1991).
In Minnesota, A. alpinus var. alpinus has been found on rocky, gravelly margins of shallow groundwater-fed ponds at a single site in Lake County. Herbaceous cover is typically sparse. This population of A. alpinus var. alpinus is associated with Amelanchier spp. (Juneberry), Carex cryptolepis (northeastern sedge), C. viridula (little green sedge), Deschampsia cespitosa (hair grass), Lysimachia ciliata (fringed loosestrife), Packera paupercula (balsam ragwort), and Vaccinium spp. (blueberry).
Biology / Life History
The pond habitat where this species occurs has a very complicated hydrology. The water level varies greatly, sometimes flooding the population. This condition is not a problem for A. alpinus var. alpinus because it is very well adapted to periodic spring flooding. In fact, it may require this natural flood cycle to maintain itself. Population size and even specific location within the site may vary from year to year. Sometimes there may be only a few, almost stunted clumps, while in other years the whole area may be covered with robust plants. The densest occurrences of the population are often in the more open and recently flooded beach habitat. Some plants may even be found in the open edge of the Pinus banksiana (jack pine) forest at the edge of the beach (U.S. Forest Service 2000). Peak flowering occurs primarily in late May through June. The fruiting period typically lasts longer, from August into autumn, but it can be affected by dry conditions or flooding (high water). Above ground portions of plants may be gone or greatly reduced in abundance by mid-summer.
Conservation / Management
Habitat alteration and the spread of non-native and invasive species such as Phalaris arundinacea (reed canary grass), Cirsium arvense (Canada thistle), and C. vulgare (bull thistle) pose a real threat to A. alpinus var. alpinus because of the small size of its only known population in Minnesota and the limited amount of suitable habitat. Astragalus alpinus var. alpinus is considered critically imperiled in both Minnesota and Wisconsin, so any reported threats must be taken very seriously. Activities such as road building, ATV and other off-road vehicle use which may cause rutting, recreational pursuits, chemical alteration of ponds (e.g., rotenone application), permanent changes in hydrology, or changes in forest cover constitute potential threats. Astragalus alpinus var. alpinus colonizes different areas of the habitat in different years. It apparently needs to be able to move around in a habitat larger than is actually occupied at any one time. Water level and unique hydrological processes may be crucial elements for this species' survival, but at this point, more information is needed (U.S. Forest Service 1999, 2000).
Conservation Efforts in Minnesota
The Minnesota population of A. alpinus var. alpinus is apparently visited every year or so by U.S. Forest Service personnel to estimate the size of the population and to note presence or absence of colonies (Brzeskiewicz 2003). The general area supporting A. alpinus var. alpinus has been identified as a Unique Biological Area (UBA) by the Superior National Forest, which means management emphasis will be on conserving or enhancing the area (U.S. Forest Service 2004). Minnesota Biological Survey staff visited the population in 2003, further clarifying the known distribution of A. alpinus var. alpinus. Additional survey, monitoring, and resource protection efforts are warranted for this species.
References and Additional Information
Barneby, R.C. 1964. Atlas of North American Astragalus. 2 Vols. New York Botanical Garden, Bronx, New York. 1188 pp.
Brzeskiewicz, M. 2003. Conservation Assessment for Alpine milkvetch (Astragalus alpinus). United States Department of Agriculture Forest Service, Eastern Region, Chequamegon-Nicolet National Forest, Park Falls, Wisconsin. 35 pp.
Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.
United States Department of Agriculture. Not dated. Condensed Sensitive Plant Species Abstracts. Nicollet and Chequamegon National Forests.
U.S. Forest Service. 1999. Population viability assessment in forest plan revision. Statement of purpose and reason. Draft species data records: Astragalus alpinus. United States Forest Service, Region 9.
U.S. Forest Service. 2000. Population viability assessment in forest plan revision. Questions for plant population viability assessment panel: Astragalus alpinus. United States Forest Service, Region 9, Duluth, Minnesota.
U.S. Forest Service. 2004. Superior National Forest Land and Resource Management Plan. Superior National Forest, Eastern Region, Milwaukee, Wisconsin.
Wisconsin Department of Natural Resources, Bureau of Endangered Resources. 1993. Guide to Wisconsin's Endangered and Threatened Plants. Wisconsin Department of Natural Resources PUBL-ER-067, Madison, Wisconsin. 128 pp.