Invasiveness Ranking System for Non-Native Plants of Alaska

Known level of impact in natural areas (0–6) 4Purple loosestrife displaced grass cover in aquatic communitiesin New York State (Thompson 1991). In wetlands in Wisconsin itforms monospecific stands that reduce biotic diversity (WDNR2003).Role of anthropogenic and natural disturbance in3establishment (0–5)Purple loosestrife flourishes in disturbed and degraded habitats,for example, wetlands that suffered from draining, naturaldrawdown, bulldozing, siltation, shore manipulation, cattletrampling, or dredging (Bender and Rendall 1987, WDNR2003). But it also can colonize undisturbed wetland (Bossard etal. 2000). J. Snyder (pers. com.) observed this plant establishingin a pond and stream system in Michigan with no perceiveddisturbances.Current global distribution (0–5) 5This species is distributed all over the world except in theextremely cold and arctic regions. Purple loosestrife is native toEurasia, extending from Great Britain across Western Europe intoCentral and Southern Europe along the Mediterranean Basin.Japan is the core of the species native range in Asia; populationsextend to Southeast Asia and India (Blossey 2002). It is presentin North Africa and North America. It also is found in southeasttemperate Australia (Bender and Rendall 1987).Extent of the species U.S. range and/or occurrence of5formal state or provincial listing (0–5)Purple loosestrife occurs in nearly all states of the United States(USDA 2002). It is a noxious weed in 25 states and 2 Canadianprovinces (Invaders Database System 2003).Total for Ecological Amplitude and Distribution 21/25Feasibility of ControlScoreSeed banks (0–3) 2Viability of seeds decreased from 99% to 80% after 2 years ofstorage in a natural body of water (Bender and Rendall 1987).Seeds under cold dry storage remain highly viable for at least3 years, but longevity under field conditions is unknown(DiTomaso and Healy 2003).Vegetative regeneration (0–3) 2Purple loosestrife can resprout from cut stems and regeneratefrom root fragments and pieces of the stem (Bender and Rendall1987, Heidorn 1991, Royer and Dickinson 1999).Level of effort required (0–4) 4Current methods for eradication of large, dense populations ofloosestrife are not totally effective. Mechanical control methodsare ineffective, and most herbicides are nonselective. Follow-uptreatments are recommended for 3 years after plants are removed(Bender and Rendall 1987). Biological controls have beendeveloped in North America (Swearing 2002).Total for Feasibility of Control 8/10Total score for 4 sections 84/100§Marticaria discoidea DC.Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 5Biological Characteristics and Dispersal 25 9Amplitude and Distribution 25 15Feasibility of Control 10 3Relative Maximum 32Climatic ComparisonCollected inAlaska regions?common names: disc mayweed, pineappleweedCLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine Yes –Marticaria discoidea has been collected in Fairbanks, Anchorage,Iditarod, Seward, Juneau, Kodiak, and Baird Inlet (Hultén 1968,University of Alaska Museum 2003, Welsh 1974). It also is knownfrom Denali National Park and Preserve, Kenai Fjords NationalPark, Katmai National Park and Preserve, and Wrangell–St. EliasNational Park and Preserve (Densmore 2001, Fubrish 2001), andin right-of-way of the Trans Alaska Pipeline (McKendrick 1987).Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 1Though pineappleweed is only found in highly disturbedenvironments (Densmore et al. 2001, Hultén 1968, Welsh 1974)it has potential to retard natural succession in sites after it hasestablished (J. Conn pers. com.).Impact on Natural Community Structure (0–10) 1Pineappleweed establishes in an existing layer and changes thedensity of the layer (M.L. Carlson pers. obs., I. Lapina pers. obs.).Impact on Natural Community Composition (0–10) 0None. Pineappleweed has not been observed in undisturbed areasin Alaska, no perceived impact on native populations has beendocumented (Densmore et al. 2001).Impact on Higher Trophic Levels (0–10) 3Pineappleweed may have possible minor alterations due to diseasetransference (Royer and Dickinson 1999).Total for Ecological Impact 5/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Pineappleweed reproduces by seeds only. A single plant is capableof producing as many as 850 seeds (Stevens 1932).Long-distance dispersal (0–3) 3The seeds are gelatinous when wet, and may be dispersed byrainwash (Rutledge and McLendon 1996).Spread by humans (0–3) 3The achenes disperse in mud attached to motor vehicles andcan contaminate topsoil (Baker 1974, Densmore et al. 2001,Hodkinson and Thompson 1997).B-74