Invasiveness Ranking System for Non-Native Plants of Alaska

Centaurea biebersteinii DCRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesNoPotential Max. ScoreEcological Impact 40 34Biological Characteristics and Dispersal 25 22Amplitude and Distribution 25 21Feasibility of Control 10 9Relative Maximum 86Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine No NoSpotted knapweed has been recorded in Skagway, Valdez, andPrince of Wales Island (south coastal) and along Turnagain Arm(interior boreal) (AKEPIC 2004, J. Snyder pers. com.). UsingCLIMEX matching program, climatic similarity between Nomeand areas where the species is documented is very low. Thissuggests that establishment in arctic and alpine Alaska may be notpossible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 8Erosion of topsoil has been shown to increase after spottedknapweed invasions. Surface runoff had approximately threetimes more sediments in Centaurea biebersteinii dominated sitescompared with adjacent native bunchgrass sites (Rice et al. 1997).Impact on Natural Community Structure (0–10) 7Spotted knapweed is capable of forming dense stands in naturalcommunities, reducing native plant diversity.Impact on Natural Community Composition (0–10) 9Spotted knapweed reduces native plant population size, decreasesplant diversity, reduces forage quality, and habitats.Impact on Higher Trophic Levels (0–10) 10This species may likely affect spawning habitats by increasingsurface runoff and sedimentation (UAF). Winter-ranging elk mayavoid foraging in habitats dominated by Centaurea biebersteinii(Rice et al. 1997). Knapweeds are allelopathic, inhibiting theestablishment and growth of surrounding vegetation (Whitson etal. 2000).Total for Ecological Impact 34/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Spotted knapweed reproduces only by seed. However, lateralroot sprouting is possible (Carpinelli 2003, Mauer et al.1987). Average plants produce about 1,000 seeds (Lym andZollinger 1992, Mauer et al. 1987, Wisconsin DNR 2004), butlarge individuals may produce over 20,000 seeds (Royer andDickinson 1999).Long-distance dispersal (0–3) 2Seeds lack pappus; however, dispersal by wind as well astransportation by rodents and livestock has been reported(Mauer et al. 1987).common names: spotted knapweedSpread by humans (0–3) 3Humans are the primary factor for spotted knapweed movement.Seeds are dispersed by vehicles, heavy machinery, and evenlight aircraft. It also is widely dispersed as a contaminant in hay,commercial seed, and floral arrangements (Lym and Zollinger1992, Mauer et al. 1987).Allelopathic (0–2) 2Knapweeds are allelopathic, inhibiting the growth ofsurrounding plants (Lym and Zollinger 1992, Royer andDickinson 1999, Whitson et al. 2000).Competitive Ability (0–3) 3Knapweed is able to outcompete neighboring plants formoisture and nutrients due to its early spring growth (Royer andDickinson 1999).Thicket-forming/Smothering growth form (0–2) 2Spotted knapweed often forms dense stand up to 6 feet tall(Royer and Dickinson 1999).Germination requirements (0–3) 3Spotted knapweed seeds germinate over a wide range of soilconditions and temperatures regimes (Schirman 1981).Other invasive species in the genus (0–3) 3Centaurea cyanus L., C. diffusa Lam., C. iberica Trev. Ex Spreng.,C. pratensis Thuill., C. solstitialis L., and C. virgata Lam.var. squarrosa (Willd.) Boiss (Whitson et al. 2000).Aquatic, wetland or riparian species (0–3) 1It typically invades along highways, waterways, railroad ways,pipelines, grasslands, and open forests (Lym and Zollinger 1992,Rice et al. 1997). Spotted knapweed establishes primarily innonwetland or riparian sites, however, it can invade streambanksand nearby meadows (Snyder and Shephard 2004).Total for Biological Characteristics and Dispersal 22/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Spotted knapweed generally is not a problem in cultivated fields.However, it is one of the most problematic weeds in rangelandsand pastures (Royer and Dickinson 1999, Whitson et al. 2000).Known level of impact in natural areas (0–6) 6Spotted knapweed invades nearly undisturbed grasslands andopen forests in Montana, Idaho, Colorado, Massachusetts, NorthDakota, and Wisconsin (K. Boggs pers. com., Lym and Zollinger1992, Rice et al. 1997, Wisconsin DNR 2004). It is widespread inwildland in British Columbia (Canada) (MAFF 2004).Role of anthropogenic and natural disturbance inestablishment (0–5)Anthropogenic disturbances such as overgrazing and mechanicalsoil disturbance accelerate its invasion in natural areas. Bothbiotic and abiotic soil disturbances (e.g., frost heave, smallmammal burrowing, and trampling and grazing by nativeungulates) can facilitate Centaurea biebersteinii invasion (Tyserand Kye 1988). Once a stand is established, it may invaderelatively undisturbed adjacent areas (Mauer et al. 1987).Current global distribution (0–5) 3Spotted knapweed is native to Central and Southeastern Europe.Now it occurs also in Northern Europe, North America, Asia, andAustralia (Weeds Australia 1998).3B-17