Invasiveness Ranking System for Non-Native Plants of Alaska

Polygonum aviculare L. common names: prostrate knotweed, yard knotweedRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 7Biological Characteristics and Dispersal 25 15Amplitude and Distribution 25 16Feasibility of Control 10 7Relative Maximum 45Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine Yes –Polygonum aviculare has been documented in all ecogeographicregions of Alaska (Hultén 1968, UAM 2004, AKEPIC 2005).Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 1Although toxins from the roots and leaves of prostrate knotweedmay prevent native species establishment (Alsaadawi and Rice1982a, Klott and Boyce 1982), in Alaska this species is alwaysassociated with anthropogenic disturbances (M. Carlson pers.obs., J. Conn pers. obs.), and likely does not have a significantimpact on natural ecosystem processes.Impact on Natural Community Structure (0–10) 0Prostrate knotweed is capable of colonizing disturbed groundand changing the density of the layer (I. Lapina pers. obs.).No impact on the natural community structure has beendocumented.Impact on Natural Community Composition (0–10) 1Prostrate knotweed has not been observed in undisturbedareas in Alaska (Densmore et al. 2000, I. Lapina pers. obs.).It is unlikely that measurable impacts on native communitycomposition occur due to its presence.Impact on Higher Trophic Levels (0–10) 5Prostrate knotweed is a food and habitat for many bird and smallmammal species (Firbank and Smart 2002, Watson et al. 2003).Sixty-one species of insects have been observed feeding onprostrate knotweed (Marshall et al. 2003). Flowers are frequentlyvisited by insects, particularly by bees and flies. Prostrateknotweed is a host for number of fungi, viruses, and nematodespecies (Townshend and Davidson 1962).Total for Ecological Impact 7/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Prostrate knotweed reproduces by seed (Costea and Tardif2005). A single plant may produce from 125–200 to 6,400achenes (Stevens 1932).Long-distance dispersal (0–3) 3The achenes can be dispersed by birds and animals afteringestion. The seeds float and can be dispersed by irrigationwater, rain, streams, and watercourses (Costea and Tardif 2005).Spread by humans (0–3) 3The seeds can be easily carried on footwear, motor vehicles,or farm machinery. Seeds can also contaminate harvestedcrops, seeds, topsoil, and horticultural stock (Hill et al. 1999,Hodkinson and Thompson 1997). Some seeds are not damagedafter passing through digestive tracts of domestic animals andbirds (Costea and Tardif 2005).Allelopathic (0–2) 2Several chemical compounds from living plants and residues inthe soil inhibit seed germination and seedling growth of most testspecies in experiments (Alsaadawi and Rice 1882a, Alsaadawiand Rice 1882b, Klott and Boyce 1982). Some of the allelopathicsubstances have an inhibitory role over some test strains of thenitrogen-fixing bacteria Rhizobium and Azotobacter (Alsaadawiand Rice 1982, Alsaadawi et al 1983).Competitive Ability (0–3) 1Prostrate knotweed is more competitive than many other weedspecies (Alsaadawi and Rice 1982a, Alsaadawi and Rice 1982b).This species possesses extreme endurance and adaptability,multiple possibilities of seed dispersal, a persistent seed bank,high genetic polymorphism, and has allelopathic properties.Prostrate knotweed inhibits germination and growth ofChenopodium album, Polygonum persicaria, Stellaria media, andsome other weeds (Alsaadawi and Rice 1982a, Alsaadawi andRice 1982b).Thicket-forming/Smothering growth form (0–2) 0Prostrate knotweed does not possess a climbing or smotheringgrowth habit (Welsh 1974, Whitson et al. 2000).Germination requirements (0–3) 0Prostrate knotweed requires open soil and disturbance togerminate (Densmore et al. 2000).Other invasive species in the genus (0–3) 3Polygonum cuspidatum Sieb. & Zucc., P. perfoliatum L.,P. polystachyum Wallich ex Meisn., and P. sachalinense F. Schmidtex Maxim. are declared noxious in a number of American states(USDA, NRSC 2006). Also Polygonum arenastrum Jord. exBoreau, P. caespitosum Blume, P. convolvulus L., P. orientale L.,P. persicaria L., and P. lapathifolium L. are listed as a weeds in thePLANTS Database (USDA, NRSC 2006). A number of nativeto North America Polygonum species have a weedy habit and arelisted as noxious weeds in some of the American states. Althoughsome of the latest taxonomic treatments considers these speciesas members of three different genus: Polygonum, Fallopia, andPersicaria (FNA 1993+), they are closely related taxa and can beconsidered as congeneric weeds.Aquatic, wetland or riparian species (0–3) 0Prostrate knotweed is one of the most common weeds alongroadsides, sidewalks and paved areas. It also occurs in gardensand cultivated fields (Alex and Switzer 1976, Welsh 1974).Total for Biological Characteristics and Dispersal 15/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Prostrate knotweed is a weed of roadsides and waste areas. It alsooccurs in gardens and cultivated fields (Alex and Switzer 1976).Known level of impact in natural areas (0–6) 0Prostrate knotweed is a plant of disturbed areas. No records onthe ecological impact of prostrate knotweed in natural areas werefound.B-100