Invasiveness Ranking System for Non-Native Plants of Alaska

Verbascum thapsus L.Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesNoPotential Max. ScoreEcological Impact 40 20Biological Characteristics and Dispersal 25 9Amplitude and Distribution 25 16Feasibility of Control 10 7Relative Maximum 52Climatic ComparisonCollected inAlaska regions?common names: common mullein, big taper,flannel mullein, flannel plant, great mullein,velvet dock, velvet plant, woolly mulleinCLIMEXsimilarity?South Coastal No YesInterior Boreal Yes –Arctic Alpine No NoVerbascum thapsus is grown in Anchorage for horticulturalpurposes. There have been reports of mullein growing alongthe Seward Highway west of Girdwood but this populationapparently has not persisted (M. Rasy pers. com., J. Riley pers.com.). Verbascum thapsus is known from southern Norway,including Bergen (Lid and Lid 1994), which has a 73%climatic match (CLIMEX 1999) with Juneau (south coastalecogeographic region). It is likely to be able to establish in thisregion. According to Lid and Lid (1994), however, this speciesis rare in the coastal region of Norway. Common mullein isdocumented from high elevations in the Nord-Trøndelagprovince in Norway; this area has high similarity of climate witharctic alpine areas in Alaska (Lid and Lid 1994, WRCC 2001).However, according to the Gross and Werner (1978), this speciesrequires a growing season at least 140 days. It is unlikely toestablish in the arctic alpine ecoregion.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 5Common mullein likely alters normal successional pathways.At high densities common mullein appears to prevent theestablishment of native herbs and grasses in burned or disturbedareas (Pitcairn 2000).Impact on Natural Community Structure (0–10) 5Common mullein is likely to create a new sparse herbaceous layer(Hoshovsky 2000).Impact on Natural Community Composition (0–10) 5Common mullein is not often a problematic weed of naturalareas; however, it can displace native species in sparsely vegetatedmeadows (Pitcairn 2000).Impact on Higher Trophic Levels (0–10) 5Grazing animals avoid eating mullein (Rutledge and McLendon1996). Its flowers are visited by a number of insects. Commonmullein is also a host for numerous diseases and insect pests.Hybridization is known within the genus (Gross and Werner1978).Total for Ecological Impact 20/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Common mullein reproduces solely by seed. Seed productioncan be 100,000–180,000 seeds per plant (Gross 1980, Gross andWerner 1982).Long-distance dispersal (0–3) 0Seeds are not adapted to long-distance dispersal. Movement ofthe stalk by wind or large animals can dispersed seeds as far as 11m (Gross and Werner 1978, Hoshovsky 1986).Spread by humans (0–3) 2Common mullein was introduced into North America as amedicinal herb. It is often grown as an ornamental (Hoshovsky1986, Gross and Werner 1978).Allelopathic (0–2) 0This species is not known to be allelopathic (Gross and Werner1978).Competitive Ability (0–3) 0Common mullein is easily outcompeted by native plants(Hoshovsky 1986, Pitcairn 2000).Thicket-forming/Smothering growth form (0–2) 1Common mullein has been observed at densities of 5.2 floweringplants/m2 in woodlands 2 years after timber harvest. Gross andWerner (1978) report densities of 1 plant/m2 and 0.17 plant/m2 inthe 3 and 12 years old fields respectively. The stout flowering stemin the second year of growth can be up to 6 feet tall (Whitson etal. 2000).Germination requirements (0–3) 0Common mullein requires bare soil for successful establishmentand growth. In experiments in Ohio and Michigan, 50%emergence of seedlings took 9 days on bare soil, but 30 days onvegetated plots. Seedling growth rates were 4–7 times faster onbare soils, producing 2,000 times more biomass within the sametime period (Gross 1984).Other invasive species in the genus (0–3) 3Verbascum blattaria L. is considered a noxious weed in Colorado(USDA 2002).Aquatic, wetland or riparian species (0–3) 0Common mullein is a weed of pastures, abandoned fields, androadsides (Gross and Werner 1978). It also is can be found inmeadows and river bottoms (Rutledge and McLendon 1996).Total for Biological Characteristics and Dispersal 9/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 2Common mullein is not a weed of agricultural crops, as it cannottolerate tilling (Gross and Werner 1978, Patcairn 2000). It isoften grown as an ornamental (Hoshovsky 1986, Gross andWerner 1978).Known level of impact in natural areas (0–6) 3Common mullein can invade undisturbed meadows, displacingnative herbs and grasses in California. It also is been observedestablishing in burns in the Sierra Nevada Mountains. Highdensities of rosettes prevent colonization by native species(Pitcairn 2000). Common mullein was reported as not being aproblem species in natural areas in Canada (White et al. 1993).Common mullein invades riverbanks in open coniferous forest atBritish Colombia and Idaho border (J. Snyder pers. com.).B-137