Invasiveness Ranking System for Non-Native Plants of Alaska

Germination requirements (0–3) 0Seedlings are rare and only established in disturbed areas,including molehills (Turkington et al. 1979). Soil temperaturesof at least 50 °F are required for germination (Royer andDickinson 1999). The seeds do not germinate until the seed coatis sufficiently broken down (by decay or abrasion) to admit water(Densmore et al. 2001).Other invasive species in the genus (0–3) 3Trifolium angustifolium L., T. arvense L., T. aureum L., T. campestreSchreb., T. dubium Sibth., T. hirtum All., T. hybridum L.,T. incarnatum L., T. pratense L., and T. subterraneum L.Aquatic, wetland or riparian species (0–3) 1White clover is a serious weed of lawns, roadsides, and disturbedareas (Hultén 1968; Royer and Dickinson 1999).Total for Biological Characteristics and Dispersal 15/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4White clover was common as a forage crop in Canada (Royerand Dickinson 1999) It has been widely planted for lawns andrevegetation on roadsides and other disturbed areas in Alaska(Densmore et al. 2001).Known level of impact in natural areas (0–6) 1White clover invades prairies in Wisconsin (WDNR 2004).Role of anthropogenic and natural disturbance inestablishment (0–5)In Alaska white clover is found in sites disturbed in recent yearsand readily invades open habitats (Densmore et al. 2001). Itis relatively shade intolerant (USDA 2002). Frequent, intensegrazing encourages growth of white clover (Rutledge andMcLendon 1996).0Current global distribution (0–5) 5White clover is native to Europe and Asia. It has been introducedto North and southern Africa, North and South America, NewZealand, Australia, Tasmania, and India (Hultén 1968). It is oftenfound north of the Arctic Circle (Royer and Dickinson 1999).Extent of the species U.S. range and/or occurrence of4formal state or provincial listing (0–5)White clover occurs in nearly all states of the United States. It islisted as a weed in Kentucky (USDA 2002).Total for Ecological Amplitude and Distribution 14/25Feasibility of ControlScoreSeed banks (0–3) 3Seeds of white clover remain viable in the soil over 30 years(Rutledge and McLendon 1996).Vegetative regeneration (0–3) 2Grazing promotes resprouting of white clover (Rutledge andMcLendon 1996).Level of effort required (0–4) 3It is virtually impossible to eradicate white clover from invadedsites (Densmore et al. 2001). Herbicides can be used to controlwhite clover (Rutledge and McLendon 1996).Total for Feasibility of Control 8/10Total score for 4 sections 59/100§Tripleurospermum perforata(Merat) M. LainzRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 13Biological Characteristics and Dispersal 23 13Amplitude and Distribution 25 15Feasibility of Control 10 6Relative Maximum 48Climatic ComparisonCollected inAlaska regions?common names: scentless false mayweed,scentless chamomileCLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine Yes –Scentless false mayweed has been collected in the south coastal,interior boreal, and arctic alpine ecogeographic regions of Alaska(AKEPIC 2004, UAM 2004).Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 3Scentless false mayweed reduces soil moisture and nutrientsfor other species. It likely causes retardation of successionalestablishment of native species (NAPPO 2003).B-135Impact on Natural Community Structure (0–10) 3Dense stands of scentless false mayweed in prairies have beenreported (CWMA 2000, NAPPO 2003, Parchoma 2004). Thisplant has not been observed in dense stands in Alaska, but it doesincrease the density of the early successional herbaceous layer(I. Lapina pers. obs.).Impact on Natural Community Composition (0–10) 3Spring-emergent seedlings can form very dense stands, reducingthe growth of seedlings of other species (NAPPO 2003).Impact on Higher Trophic Levels (0–10) 4Scentless false mayweed is unpalatable to animals and can formdense stands in pastures and hayfields, thus altering the quantityof foraging sites (CWMA 2000, Parchoma 2004). The flowersattract bees and flies (Harris and McClay 2003) and may alter thepollination ecology of native communities.Total for Ecological Impact 13/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Scentless false mayweed reproduces entirely by copious amountsof seed. A single plant can produce up to a million seeds, withdense stands capable of producing 1,800,000 seeds per squaremeter (Harris and McClay 2003, Juras et al. 2004, NAPPO 2003,Parchoma 2004).