Rare Species Guide

  Basis for Listing

Shepherdia canadensis (soapberry) is primarily a shrub of boreal and montaine regions, reaching Minnesota sporadically from the north. Although there are a few records of S. canadensis from forests near Lake Superior in the Duluth area (North Shore Highlands Subsection), most are from the northern border region (Border Lakes and Aspen Parklands Subsections). They range from Cook County in the east to Kittson County in the west. Extensive searches in the region have found far fewer occurrences of this species than expected. This is true even where apparently suitable habitat exists. It is not known which factors limit its occurrence in Minnesota; it could be that the climate here is only marginally suited for this species. Other factors could include soil conditions, availability of pollinators, and seed dispersal agents.  On the basis of the small number of known populations, and the small size of those populations, S. canadensis was listed as a special concern species in 2013.

  Description

Shepherdia canadensis is a striking shrub, with multiple upright or arching stems up to 3.2 m (10 ½ ft.) tall. The leaves are 4-7 cm (1.6-2.8 in.) long, 1.8-3.3 cm (0.70-1.3 in.) wide, simple, opposite on the stem, and rather stiff or rigid. They also have a distinctive blunt tip and entire margins. The upper surface is dark green; the lower surface is covered with dense silvery hairs and scattered brown scales. The young twigs and buds are covered with reflective reddish scales, and even the bright red fruits (considered unpalatable) have a few scales. There is a short spike, with 5-12 flowers, each 3-5 mm (0.12-0.20 in.) across. The flowers are unisexual, so each plant has either male flowers or female flowers but not both. The fruit is shiny red, berrylike, and 5-9 mm (0.20-0.35 in.) across.

  Habitat

In the northeastern counties, S. canadensis occurs in a coniferous forest landscape, usually in forests of Pinus spp. (pine) but also with hardwoods (fire-dependent forest), especially on steep rocky bluffs, rocky ledges, and outcrops . This is a fire-maintained landscape, though the interval between wildfires is relatively long, perhaps 100-150 years. Habitats in the northwestern counties are in an aspen parkland landscape, specifically in dry to mesic soil in open groves of Populus tremuloides (trembling aspen) that develop within a prairie matrix (fire-dependent woodland). In this region, the normal interval between wildfires is relatively short, possibly just 5-10 years (Smith 2008).

  Biology / Life History

Although S. canadensis is essentially a forest species, it does not do well in deep shade; it seems to thrive only under a thin canopy or along an exposed edge. Shepherdia canadensis has the unusual ability to produce nodules on its roots that can convert atmospheric nitrogen into nitrate, a form useful to plants (Rodriguez-Barrueco 1968). This would allow S. canadensis to have a competitive advantage in nitrogen-poor soils. Shepherdia canadensis is widely reported to prefer calcareous soils, though specifics are lacking.

The structure of the flowers indicates they are pollinated by insects, though no species of insect have actually been identified as pollinators. Since the flowers are unisexual, both male plants and female plants must be present within the foraging distance of the pollinator.

The fruit is eaten by a number of mammals and birds that spread the seeds in their droppings. The seeds are reported to germinate poorly and sporadically in horticultural trials (Thilenius et al. 1974).

  Conservation / Management

The widely dispersed nature of this species makes it difficult to prescribe uniform management recommendations. Most habitats where this species occurs are not suited to agriculture or typical types of urban development, yet logging or other types of forest management practices could be a concern. It is likely that management will need to be determined on a site-by-site basis, with an emphasis on maintaining the natural composition and structure of the vegetation of the site.

  Best Time to Search

Shepherdia canadensis is a distinctive species and can be identified anytime that mature leaves are present, which is typically from the first of June through the middle of September.

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Hamer, D. 1996. Buffaloberry [Shepherdia canadensis (L.) Nutt.] fruit production in fire-successional bear feeding sites. Journal of Range Management 49:520-529.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

Rodriguez-Barrueco, C. 1969. The occurrence of nitrogen-fixing root nodules on nonleguminous plants. Botanical Journal of the Linnean Society 62(1):77-84.

Smith, W. R. 2008. Trees and shrubs of Minnesota. University of Minnesota Press, Minneapolis. 703 pp.

Thilenius, J. F., K. E. Evans, and E. C. Garrett. 1974. Shepherdia Nutt. buffaloberry. Pages 771-773. in Schopmeyer, C.S., editor. Seeds of woody plants in the United States. USDA, Forest Service Agricultural Handbook 450, Washington, D.C.