Invasiveness Ranking System for Non-Native Plants of Alaska

Spread by humans (0–3) 3The Siberian peashrub is cultivated in the more temperateregions of Alaska and Yukon (Welsh 1974). It has escaped fromcultivation. It is currently sold in nurseries (Duke 1983, I. Lapinapers. obs., WDNR 2003).Allelopathic (0–2) 0There is no known allelopathic potential (USDA 2002).Competitive Ability (0–3) 3Siberian peashrub is reported to tolerate alkalinity, drought,cold, poor soils, and wind (Duke 1983). It also is a nitrogen-fixer(USDA 2002).Thicket-forming/Smothering growth form (0–2) 2Plants can grow up to 12 feet tall (Welsh 1974) and form dense,impenetrable thickets (I. Lapina pers. obs.).Germination requirements (0–3) 3Cold stratification required for germination. In horticulture,seeds need to be presoaked for about 24 hours in warm waterand can then be sown in a cold period in the spring. Germinationusually takes place within 2–3 weeks (Plants for a future 2002). Insouth-central Alaska, plants appear to be recruiting in moderatelydisturbed and partially native habitats (M.L. Carlson pers. obs.)Other invasive species in the genus (0–3) 0No other weedy Caragana species are present (USDA 2002).Aquatic, wetland or riparian species (0–3) 0This is a plant of roadsides and gardens (Montana Plant Life2004).Total for Biological Characteristics and Dispersal 14/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Siberian peashrub is cultivated as ornamental and food plant. It iswidely planted in the United States and Canada for windbreaks,hedges, and outdoor screening. Because of its nitrogen-fixingcapacity, it is valued as a soil-improving plant. In the Arctic itis a supplementary fodder for reindeer herds (Duke 1983). It iscurrently sold at nurseries. Cultivars have been developed (MSUExtension 1999, USDA 2002).Known level of impact in natural areas (0–6) 4Siberian peashrub is known as an invader of forests in Wisconsin(WDNR 2003). It also invades forests in interior boreal ecoregionof European part of Russia (I. Lapina pers. obs.).Role of anthropogenic and natural disturbance in4establishment (0–5)Siberian peashrub is generally restricted to road and trailsideedges on disturbed and imported soils. Nevertheless, it has beenfound establishing in forested areas with no perceivable human ornatural disturbances (I. Lapina pers. obs.).Current global distribution (0–5) 5Siberian peashrub is native to Siberia, Kazakhstan, Mongolia, andChina. It now extends over Europe and North America, includingarctic regions (Duke 1983, USDA, ARS 2004).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)Siberian peashrub is found throughout Canada and the northernAmerican states. This species is not considered noxious in NorthAmerica (Invaders Database System 2003, USDA 2002).Total for Ecological Amplitude and Distribution 21/25Feasibility of ControlScoreSeed banks (0–3)UUnknownVegetative regeneration (0–3) 2Siberian peashrub can resprout after cutting (USDA 2002).Level of effort required (0–4) 3Mechanical treatments can be used for control of Siberianpeashrub. However, it is not very efficient, because shrub willresprout vigorously after cutting. Combination of mechanical andchemical treatments may be more efficient (Heiligmann 2006).Total for Feasibility of Control 5/7Total score for 4 sections 64/97§4B-14