Invasiveness Ranking System for Non-Native Plants of Alaska

Heracleum mantegazzianumSommier & LevierRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 33Biological Characteristics and Dispersal 25 22Amplitude and Distribution 25 17Feasibility of Control 10 9Relative Maximum 81Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal No YesInterior Boreal No YesArctic Alpine No YesHeracleum mantegazzianum has not been documented in Alaska(Hultén 1968, Welsh 1974, AKEPIC 2004, UAM 2004). Usingthe CLIMEX matching program, climatic similarity betweenJuneau and areas where the species is documented is high.Introduced range of the species includes Eskdalemuir, UnitedKingdom (Tiley et al. 1996) and Kristiansund, Norway (Lid andLid 1994), which has a 63% and 53% climatic match with Juneau.Range of the species includes Røros and Dombås, Norway(Lid and Lid 1994), which has a 76% and 63% climatic matchwith Nome, and 55% and 53% climatic match with Fairbanksrespectively. Thus establishment of Heracleum mantegazzianumin south coastal, interior boreal, and arctic alpine ecogeographicregions may be possible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 8Giant hogweed results in a reduction of native species and anincrease in soil erosion along streambanks in winter (NoxiousWeed Control Program 2003, Tiley and Philp 1992, Wright1984). The availability of nutrients increases in areas infested bygiant hogweed due to the large amount of easily decomposedbiomass (Pysek and Pysek 1995).Impact on Natural Community Structure (0–10) 7Giant hogweed has the ability to dominate native communitieswith 50–100% cover (Pysek and Pysek 1995).Impact on Natural Community Composition (0–10) 8Giant hogweed replaces native vegetation (Noxious WeedControl Program 2003, Tiley and Philp 1992, Tiley et al. 1996,Wright 1984). In studies by Pysek and Pysek (1995), invadedvegetation was 40.5% less species-rich than surroundingvegetation. Eleven species, which were not present in noninvadedvegetation, were recruited in areas invaded by giant hogweed.These species are mainly other invasive plants (Alopecuruspratensis, Dactylis glomerata, Elymus repens, Cirsium arvense,Lupinus polyphyllus, and Tanacetum vulgare).common names: giant hogweedImpact on Higher Trophic Levels (0–10) 10The plant is a public health hazard, causing severe dermatitis.Similar injury has been reported in birds and animals. Theflowers of giant hogweed are insect-pollinated and it may alterlocal pollination ecology. This plant produces coumarins thathave antifungial and antimicrobial properties. Numerousphytophagous animals and parasites are recorded for gianthogweed (Noxious Weed Control Program 2003, Tiley et al.1996, Wright 1984). Hybrids between H. mantegazzianum andH. sphondylium occur where the two grow in the same location(Stewart and Grase 1984, Tiley and Philp 1992).Total for Ecological Impact 33/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Giant hogweed reproduces by numerous seeds, from 27,000 toover 50,000 seeds on a vigorous plant, (Pysek 1991, Tiley et al.1996, Noxious Weed Control Program 2003).Long-distance dispersal (0–3) 2The majority of seeds fall near the maternal plant. Wind dispersesseeds a short distance (Pysek and Prach 1993, Tiley et al. 1996,Wright 1984). Long-distance dispersal occurs naturally alongwatercourses. The fruits float in water for up to 3 days. Most seedsand seedlings were found within 10 m of the colony and few morethan 50 m away (Clegg and Grace 1974).Spread by humans (0–3) 3Giant hogweed has escaped from ornamental gardens andnaturalizes easily. Despite prohibition of giant hogweed, it issometimes misidentified and sold in nurseries. Dispersal alsoincludes the use of seed heads in flower arrangements and it isspread along right-of-ways (Noxious Weed Control Program2003, Tiley et al. 1996, Wright 1984).Allelopathic (0–2) 0There is no recorded allelopathy in this species. The large volumeof literature on invasiveness of this species and lack of its mentionsuggests it is not allelopathic.Competitive Ability (0–3) 3Giant hogweed is very competitive due to its quick early-seasongrowth, tolerance of shade, and very large leaf area (NoxiousWeed Control Program 2003, Pysek and Pysek 1995).Thicket-forming/Smothering growth form (0–2) 2Giant hogweed has the ability to shade out the surroundingvegetation due to its height and large leaves (Noxious WeedControl Program 2003, Pysek and Pysek 1995, Wright 1984).Germination requirements (0–3) 3Under field conditions germination and establishment is bestin open vegetation with adequate light and moisture. However,germination also occurs under vegetation (Tiley et al. 1996).Other invasive species in the genus (0–3) 3Heracleum sphondylium is another introduced species, but it is notlisted as an invasive (USDA 2002).B-44