Invasiveness Ranking System for Non-Native Plants of Alaska

Polygonum cuspidatum Sieb. & Zucc. Common name: Japanese knotweed,(Fallopia japonica (Houtt.) R. Decr.)Japanese bambooPolygonum sachalinense F. Schmidt ex Maxim.giant knotweed(Fallopia sachalinensis (F. Schmidt ex Maxim.) R. Decr.)Polygonum ×bohemicumBohemian knotweed( J. Chrtek & Chrtkovß [cuspidatum × sachalinense]) Zika & Jacobson(Fallopia ×bohemica (Chrtek & Chrtková) J.P. Bailey)Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesNoPotential Max. ScoreEcological Impact 40 33Biological Characteristics and Dispersal 25 21Amplitude and Distribution 25 23Feasibility of Control 7 7Relative Maximum 87Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine No NoJapanese knotweed has been collected from Sitka, Anchorage,Juneau, and Port Alexander (Densmore et al. 2001, UAM 2003).Using the CLIMEX matching program, climatic similaritybetween Nome and areas where the species is documented ismodest. It does occur in gardens within Anchorage (UAM 2003),which has 61% climatic match with Nome. However, this speciesranges only as far north as Nova Scotia and Newfoundland inCanada and is restricted to regions of high precipitation in theUK (Seiger 1991). In northern Europe it is restricted to areas withgreater than 120 frost-free days (Beerling et al. 1994). Nome has80 frost-free days. This information suggests that establishmentin the arctic alpine ecoregion of Alaska is unlikely andestablishment in the interior boreal region may only be possibleunder garden conditions.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 7Japanese knotweed increases the risk of soil erosion followingremoval of stands. The dead stems and leaf litter decompose veryslowly and form a deep organic layer which prevents native seedsfrom germinating, altering the natural succession of native plantspecies (Japanese Knotweed Alliance 2004, Seiger 1991). Duringdormancy, dried stalks can create a fire hazard (Ahrens 1975).Impact on Natural Community Structure (0–10) 10Japanese knotweed forms an extremely dense mid-canopy layeras a single-species stand, and eliminates plants below by shadingout native vegetation (Seiger 1991, Beerling et al. 1994, MaineNatural Areas Program 2004).Impact on Natural Community Composition (0–10) 9Japanese knotweed prevents native seeds from germinating, andhinders the natural succession of native herbs, shrubs, and trees.It reduces species diversity (Seiger 1991, Beerling et al. 1994).Impact on Higher Trophic Levels (0–10) 7Japanese knotweed clogs waterways and lowers the quality ofhabitat for wildlife and fish. It reduces the food supply for juvenilesalmon in the spring (Seiger 1991). It reduces the diversity ofphytophagous insects (Beerling & Dawah 1993). Hybridizes withthe introduced Polygonum sachalinense.Total for Ecological Impact 33/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Reproduction is primarily vegetative [rhizomes and stemtissue] (Japanese Knotweed Alliance 2004). Plants can produceabundant seed. But a large proportion is nonviable when fertilemale plants are rare or absent (Conolly 1977). Densmore etal. (2001) observed, however, that the P. cuspidatum in SitkaNational Historical Park appears to have established from seed.Long-distance dispersal (0–3) 2The fragments of plants are easily washed downstream wherethey can resprout. There are also documented occurrences ofspread across sea water (Beerling et al. 1994). Fruits maintaina winged perianth and have an abscission zone on the pediclesuggesting adaptation for wind dispersal (Beerling et al. 1994).Spread by humans (0–3) 3Japanese knotweed has been planted as an ornamental insoutheast Alaska and in Anchorage and escapes from gardens.Transportation of soil containing rhizome fragments is likely tooccur frequently (Seiger 1991, Densmore et al. 2001).Allelopathic (0–2) 0Unknown. No records of allelopathy were found. Biochemicalstudies indicate it possesses antibacterial and antifungialproperties, but no mention of allelopathic effects (Beerling et al.1994)Competitive Ability (0–3) 3Japanese knotweed effectively competes for light by emergingearly in the spring and using its extensive rhizomatous reservesto quickly attain a height of 2–3 meters (Densmore et al. 2001,Seiger 1991).Thicket-forming/Smothering growth form (0–2) 2It forms very dense thickets that are generally taller (4–9 feet)than the surrounding herbaceous and shrubby vegetation(Densmore et al. 2001, Seiger 1991, Whitson et al. 2000).Germination requirements (0–3) 2Japanese knotweed can germinate in vegetated areas. Theseeds require chilling to break dormancy (Beerling et al. 1994,Densmore et al. 2001).B-103