Invasiveness Ranking System for Non-Native Plants of Alaska

Hieracium aurantiacum L. andcommon names: orange hawkweedH. caespitosum Dumort. meadow hawkweedRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 29Biological Characteristics and Dispersal 25 23Amplitude and Distribution 25 19Feasibility of Control 10 8Relative Maximum 79Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine No YesHieracium aurantiacum has been collected in the south coastal[Juneau (Hultén 1968) and Kodiak (Spencer pers. com.)] andinterior boreal [Willow (Lapina 2003)] ecoregions in Alaska.Hieracium caespitosum has been collected in Juneau and Valdez(AKEPIC 2005, M. Shephard pers. com.). Using the CLIMEXmatching program, climatic similarity between Nome and areaswhere Hieracium aurantiacum is documented is moderatelyhigh. Range of the species includes Anchorage (Alaska), Vaasa(Finland), and Saint Petersburg (Russia) (Hultén 1968), whichhas a 61%, 54%, and 53% climatic match with Nome, respectively.These suggest that establishment of orange hawkweed in arcticalpine ecogeographic region may be possible. Range of Hieraciumcaespitosum includes Kirov and Kazan, Russia (Gubanov et al.1995), which has a 66%, and 58% climatic match with Nome, and60% and 59% climatic match with Fairbanks respectively. Thusestablishment of meadow hawkweed in interior boreal and arcticalpine ecogeographic regions may be possible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 7Orange and meadow hawkweed likely reduce soil moisture andnutrient availability (J. Snyder pers. com.).Impact on Natural Community Structure (0–10) 7Extensive stolons form dense mats of hawkweed plants creatinga new layer, and excluding other forbs and grasses (Callihan andMiller 1999, Prather et al. 2003, Rinella and Sheley 2002).Impact on Natural Community Composition (0–10) 8Orange and meadow hawkweed eliminate other vegetation byforming dense, monospecific stands (Callihan and Miller 1999,Prather et al. 2003, Rinella and Sheley 2002). Effects of this taxonare likely restricted to low herbaceous species (M. Carlson).Orange hawkweed reduces the population of native species inforbs–fern meadows in Kodiak (P. Spencer pers. com.).Impact on Higher Trophic Levels (0–10) 7Orange and meadow hawkweed are unpalatable and reduces theforage value of grasslands for grazing animals. It hybridizes freelywith native and non-native hawkweeds (Callihan and Miller1999, Noxious Weed Control Program 2004, Prather et al. 2003,Rinella and Sheley 2002). Orange hawkweed is also a host fornematode species (Townshend and Davidson 1962).Total for Ecological Impact 29/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Each rosette of hawkweed is capable of producing between 600and 45,000 tiny seeds. In addition to reproducing by seeds, thesehawkweeds are capable of spreading by rhizomes, stolons, andadventitious root buds (Callihan and Miller 1999, Prather et al.2003, Rinella ans Sheley 2002).Long-distance dispersal (0–3) 3The seeds are spread by wind and animals (Callihan and Miller1999, Rinella and Sheley 2002). Seeds are tiny and plumed.Spread by humans (0–3) 3The seeds are easily carried by vehicles, animals, and clothing.Orange hawkweed has escaped from flower gardens (NoxiousWeed Control Program 2004, Rinella and Sheley 2002).Allelopathic (0–2) 2These species are described as allelopathic (Murphy and Aarssen1995, Noxious Weed Control Program 2003).Competitive Ability (0–3) 3Orange and meadow hawkweeds outcompete many nativespecies by forming dense, monospecific stands (Prather et al.2003, Rinella and Sheley 2002).Thicket-forming/Smothering growth form (0–2) 2Orange and meadow hawkweeds form dense, monospecificstands. However, leaves are primarily basal and do not shadegrasses and most other forbs (Callihan and Miller 1999, Rinellaand Sheley 2002).Germination requirements (0–3) 2These hawkweed species can germinate in vegetated areas, butgermination is best in full sun (Rinella and Sheley 2002).Other invasive species in the genus (0–3) 3Hieracium umbellatum L., H. pilosella L., H. piloselloides Vill, andH. floribundum Wimmer & Grab. are listed as noxious weedsin U.S. (Invaders Database System 2002, Royer and Dickinson1999, USDA, NRCS 2002).Aquatic, wetland or riparian species (0–3) 2Orange and meadow hawkweeds generally inhabit roadsides,gravel pits, pastures, and moist grasslands (Callihan and Miller1999, Prather et al. 2003). In Alaska, orange hawkweed has beenobserved invading wetlands and boreal white spruce–birchforests (M. Shephard pers. obs., M. Carlson pers. obs.).Total for Biological Characteristics and Dispersal 23/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Orange hawkweed was first introduced into United States for useas an herbal remedy and garden ornamental. It is currently beingplanted as an ornamental in Girdwood and the Susitna Valley(I. Lapina pers. obs.).Known level of impact in natural areas (0–6) 4Orange and meadow hawkweeds invade permanent meadows,grasslands, rangelands, and pastures in Montana andWashington. It is a major environmental weed in montane areasin Canada and New Zealand (Noxious Weed Control Board2004, Prather 2003, Rinella and Sheley 2002). Orange hawkweedinvades forb–fern meadows in Kodiak (P. Spencer pers. com.).B-47