Invasiveness Ranking System for Non-Native Plants of Alaska

Sonchus arvensis L. common names: field sowthistle, moist sowthistle,[including ssp. arvensis and uliginosus (Bieb.) Nyman] perennial sowthistleRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesNoPotential Max. ScoreEcological Impact 40 22Biological Characteristics and Dispersal 25 21Amplitude and Distribution 25 21Feasibility of Control 10 9Relative Maximum 73Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine No NoSonchus arvensis has been collected in south coastal (Hyderand Hoonah) and interior boreal (Fairbanks, Anchorage, DeltaJunction, and Palmer) ecogeographic regions (AKEPIC 2004,UAM 2004). Climatic similarity between Nome and areas wherethe species is documented is relatively high. The introducedrange of the species includes Anchorage and Fairbanks (AKEPIC2004) that have a 61% and 56% climatic match with Nome,respectively using CLIMEX. However, winter temperaturesin Nome are too low for Sonchus arvensis according to theWashington Noxious Weed Control Board (2003). This suggeststhat establishment of this species in arctic alpine Alaska may notbe possible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 5Perennial sowthistle may modify or retard the successionalestablishment of native species (Butterfield et al. 1996). Thisspecies can form very thick, nearly monospecific stands alongthe upper beach strands in southeast Alaska and likely has amoderate influence on nutrient, moisture, and light availability(B. Krieckhaus and T. Heutte, pers. com.).Impact on Natural Community Structure (0–10) 7Perennial sowthistle has recently been observed at a numberof sites forming large stands in the upper beach strand and inestuaries in southeastern Alaska, where it forms a tall herbaceouslayer over the dominant grass, Elymus mollis, intertidal sedges,and other species (B. Krieckhaus and T. Heutte, pers. com.).Impact on Natural Community Composition (0–10) 7At high densities perennial sowthistle has drastically reducedwater resources (Zollinger and Kells 1993) and possiblydecreased the number of plants in communities. Such densitieshave been observed in natural communities in Alaska (B.Krieckhaus and T. Heutte, pers. com.). Perennial sowthistlereduced soil moisture by 33–47% in field experiments (Zollingerand Kells 1993).Impact on Higher Trophic Levels (0–10) 3Perennial sowthistle is host to a number of plant pests. This plantis acceptable forage for rabbits and other animals (Noxious WeedControl Board 2003).Total for Ecological Impact 22/30Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Perennial sowthistle reproduces by seeds and horizontalroots. Each plant can produce 4,000–13,000 seeds (Royer andDickinson 1999, Rutledge and McLendon 1996, Stevens 1957).Long-distance dispersal (0–3) 3Seeds of perennial sowthistle possess long hairs and are spread bythe wind (Royer and Dickinson 1999, Rutledge and McLendon1996). Seeds may also become attached to animals (Butterfield etal. 1996).Spread by humans (0–3) 3Seeds of perennial sowthistle can be transported by vehicles andfarm equipment. The seeds often contaminate commercial seedsand hay (Butterfield et al. 1996, Noxious Weed Control Board2003).Allelopathic (0–2) 2Perennial sowthistle inhibits seed germination of native species(Weeds BC 2004).Competitive Ability (0–3) 2Perennial sowthistle is competitive for soil and water (Zollingerand Kells 1993). It also is considered a vigorous competitor forremoving minerals from soil (Lemna and Messersmith 1990).Thicket-forming/Smothering growth form (0–2) 1Perennial sowthistle can grow 2–4 feet tall (Whitson et al. 2000).In Alaska it can form dense stands (Krieckhaus and Heutte, pers.com.).Germination requirements (0–3) 3Seedlings emerge and survival is best in areas with plant cover orlitter. Achenes require a continual water supply for germination.Seedlings emerged from less than 1-inch seeding depth havehigher rate of survival and establishment (Hakansson andWallgren 1972).Other invasive species in the genus (0–3) 3Sonchus asper (L.) Hill, and S. oleraceus L. (Whitson et al. 2000).Aquatic, wetland or riparian species (0–3) 1Perennial sowthistle is common in gardens, cultivated crops,roadsides, and fertile waste areas (Rutledge and McLendon 1996,Whitson et al. 2000). It may occur on disturbed sites of meadows,beaches, ditches, and river and lakeshores (Butterfield et al. 1996,Gubanov et al. 1995, Noxious Weed Control Board 2003).Total for Biological Characteristics and Dispersal 21/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Perennial sowthistle is a common weed of gardens and cultivatedfields (Gubanov et al. 1995, Rutledge and McLendon 1996,Whitson et al. 2000).Known level of impact in natural areas (0–6) 4Perennial sowthistle is ranked as an exotic plant with amoderate impact on natural communities in Pipestone NationalMonument in Minnesota. It is found in mid-succesional sitesthat have been disturbed in the last 11–50 years (Butterfield etal. 1996). It is found in the Rocky Mountain National Park ofColorado (Rutledge and McLendon 1996).B-120