Invasiveness Ranking System for Non-Native Plants of Alaska

Feasibility of ControlScoreSeed banks (0–3) 3The majority of seeds germinate in the first 4 years, but someviable seeds remain in the soil for more than 6 years (Chepil1948).Vegetative regeneration (0–3) 0Common pepperweed has no ability to resprout (Densmore et al.2001).Level of effort required (0–4) 1Common pepperweed can be easily control by hand pulling orherbicide applications. Due to the large, long lived seed bank,several treatments may be necessary (Densmore et al. 2001).Total for Feasibility of Control 4/10Total score for 4 sections 22/88§Lepidium latifolium L. common names: perennial pepperweed, tall whitetopRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineNoYesYesPotential Max. ScoreEcological Impact 40 28Biological Characteristics and Dispersal 22 17Amplitude and Distribution 25 16Feasibility of Control 7 6Relative Maximum 71Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal No NoInterior Boreal No YesArctic Alpine No YesLepidium latifolium has not been documented in Alaska (Hultén1968, Welsh 1974, AKEPIC 2004, UAM 2004). The native rangeof Lepidium latifolium includes southwestern Russia and westernSiberia (Gubanov et al 2003). The CLIMEX matching programshows that climatic similarity between Alaska and areas wherethe species is documented is high. Kazan, Penza, and Gorkiy,Russia have 72%, 68%, and 67% similarity with Anchorage, and59%, 53%, and 53% with Fairbanks, respectively. Nome has 58%,56%, and 57% climatic similarity with Kazan, Penza, and Gorkiy,respectively. Climatic similarity between Juneau and areas wherethe species is documented is low. This suggests that establishmentof perennial pepperweed may be possible in the interior borealand arctic alpine ecogeographic region of Alaska.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 7Perennial pepperweed may retard natural succession onpreviously disturbed areas. The roots of this species fragmenteasily, allowing soil erosion to occur more frequently in infestedareas (Renz 2000). This plant also takes salt ions from deep in thesoil profile, and transports them near the soil surface, drasticallyincreasing soil salinity (Blank and Young 2002, Blank and Young2004).Impact on Natural Community Structure (0–10) 7Perennial pepperweed creates a large monospecific layer anddisplaces native plants (Corliss 1993, Renz 2000).Impact on Natural Community Composition (0–10) 7Perennial pepperweed can displace native plant and animalspecies. It particularly interferes with regeneration of riparianplant species such as willows and cottonwoods (Young et al.1995). Stands of perennial pepperweed increase soil salinity;this favors halophytes and reduces other species, therebyshifting plant composition and diversity (Renz 2000). Perennialpepperweed creates a litter layer that prevents the emergence andestablishment of annual native plants (Renz 2000).Impact on Higher Trophic Levels (0–10) 7Perennial pepperweed degrades nesting and foraging sites forwaterfowl by outcompeting grasses. It also prevents willow andcottonwood regeneration, altering riparian species’ habitats(Howald 2000).Total for Ecological Impact 28/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Perennial pepperweed reproduces by seed or vegetatively froman intact root system or from pieces of the underground stems.The plant is capable of producing thousands of seeds annually(Howald 2000, Renz 2000).Long-distance dispersal (0–3) 2The seeds have no adaptations for long-distance dispersal;however, they are capable of being transported by wind, water,and possibly by waterfowl (Howald 2000). Root fragments canbe transported in streams and establish new populations (Renz2000).Spread by humans (0–3) 2It was likely introduced to North America as a contaminant ofsugar beet seed. Recent infestations in California are due to seedor plant fragments contaminating rice straw bales (Howald 2000).Allelopathic (0–2) 0Allelopathic potential has not been recorded.Competitive Ability (0–3) 3Infestations of perennial pepperweed are extremely competitiveand very few plant species can establish within these stands(Renz 2000). Extensive creeping root system enhances thecompetitiveness of perennial pepperweed for water and nutrients.Allocation of carbohydrate reserves to below ground organs isimportant for rapid shoot development in the spring (Renz 2000).Thicket-forming/Smothering growth form (0–2) 1Perennial pepperweed creates large monospecific stands that cangrow to over 3 feet in height (Corliss 1993, Douglas et al. 1998,Renz 2000, Whitson et al. 2000).B-62