Invasiveness Ranking System for Non-Native Plants of Alaska

Alliaria petiolata (Bieb.) Cavara & GrandeRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesNoNoPotential Max. ScoreEcological Impact 30 24Biological Characteristics and Dispersal 25 16Amplitude and Distribution 25 16Feasibility of Control 10 7Relative Maximum 70Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal No NoArctic Alpine No NoGarlic mustard has been collected in south coastal region, indowntown Juneau, (AKEPIC, 2004). Using the CLIMEXmatching program, climatic similarity between Fairbanks andareas where the species is documented is very low. This is truefor Nome as well. However, this taxon has been collected fromStockholm, Sweden (Natur Historiska Riksmuseet Database,2004), which has a moderate climate match (57% similarity)with Anchorage, suggesting that establishment in south-centralAlaska may be possible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10)UNo information was found identifying impacts to ecosystemprocesses.Impact on Natural Community Structure (0–10) 10Garlic mustard dramatically displaces native grasses, herbs,and tree seedlings (Blossey 2003, Blossey et al. 2002, PlantConservation Alliance Alien Plant Working Group).Impact on Natural Community Composition (0–10) 7Garlic mustard can completely dominate and displace nativeplants in the rich herbaceous understory layer (Nuzzo 2000).Impact on Higher Trophic Levels (0–10) 7Garlic mustard appears to alter habitat suitability for native birds,mammals, and amphibians, and may affect populations of thesespecies. Phytotoxic chemicals produced by Alliaria petiolata mayinterfere with growth of native species (Nuzzo 2000).Total for Ecological Impact 24/30Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Plant produce an average of 136–295 seeds (Byers and Quinn1998), and up to 2,421 seeds under lab conditions (Nuzzo 2000).Maximum production per plant is estimated at 7,900 seeds on aplant with 12 stems (Nuzzo 2000).Long-distance dispersal (0–3) 2Seeds typically fall within a few meters of the plant. Winddispersal is limited, and seeds do not float well, although seedsreadily attach to moist surfaces. It may be dispersed by rodents,birds, and deer (Nuzzo 2000).common names: garlic mustardSpread by humans (0–3) 3Anthropogenic distribution appears to be the primary dispersalmechanism of Alliaria petiolata. Seeds are transported on boots,clothes, and hair, and by roadside mowing, automobiles, andtrains (Nuzzo 2000). The species has medicinal properties(McGuffin 1997). This plant is an ingredient in several ‘gourmet’recipes. At least one U.S. seed company (Canterbury Farms)offers Alliaria petiolata seeds for sale ($1.00/package) (Nuzzo2000).Allelopathic (0–2) 2Alliaria petiolata produces several phytotoxic chemicals that mayinterfere with native plant species. The roots contain sinigrin andglucotopaeolin (Nuzzo 2000).Competitive Ability (0–3) 3Garlic mustard outcompetes native herbaceous species for light,moisture, nutrient, and space (Rowe and Swearingen 2003).Experiments demonstrated that seedlings of chestnut and oakhad reduced growth when grown with Alliaria petiolata (Nuzzo2000).Thicket-forming/Smothering growth form (0–2) 0Grows from 1 to 4 feet tall (Nuzzo 2000, Wisconsin DNR 2004).Although aggressive, this taxon does not have a smotheringgrowth habitGermination requirements (0–3) 3Seeds can remain dormant for 20 months (Blossey 2003). Coldstratification is necessary for germination. Germinates well inintact woodland communities (Wisconsin DNR 2004). Cangerminate in both light and dark after dormancy is broken (Byers1988, Bloom et al. 1990). Exposed soil caused by deer tramplinghas been suggested to facilitate spread of the species (Blossey2003), but garlic mustard is capable of germinating in the absenceof exposed soil.Other invasive species in the genus (0–3) 0Alliaria petiolata is the only species of the genus Alliaria in NorthAmerica. (Blossey et al. 2002, USDA 2002).Aquatic, wetland or riparian species (0–3) 0Alliaria petiolata formerly considered a plant of flood plainsand moist woods has become common in drier and more openhabitats (Byers and Quinn 1987). It occurs in forest edges,hedgerows, shaded roadsides, and urban areas, and occasionallyin full sun (Nuzzo 2000).Total for Biological Characteristics and Dispersal 16/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 0Alliaria petiolata is a weed of natural areas (Blossey et al. 2002).Although used in cooking and medicines, this taxon in notdomesticated or associated with agriculture.Known level of impact in natural areas (0–6) 4Garlic mustard is common in low-quality forests in centralPennsylvania (Nuzzo 2000) and less frequent in isolatedwoodlots in central Indiana (Brothers and Springarn 1992). It israrely found under coniferous trees in the Midwest, but has beenreported from under seven species of coniferous trees in Ontario.Garlic mustard is most frequently recorded from moist, usuallyriverine, habitat and waste ground in Kansas and Oklahoma(Nuzzo 2000).B-2