Invasiveness Ranking System for Non-Native Plants of Alaska

Impact on Higher Trophic Levels (0–10) 10Leafy spurge is unpalatable and often toxic to herbivores suchas deer, elk, and antelope. Infestations of leafy spurge reducethe availably of forage for these species (Kreps 2000, Mastersand Kappler 2002). Most North American insects avoid leafyspurge. Alteration of grassland vegetation structure by leafyspurge may degrade nesting habitat of breeding birds. In a NorthDakota study, densities, breeding, nest-site selection, and nestsuccess of Savanna sparrow was lower on sites infested by leafyspurge (Scheiman et al. 2003).The milky sap contained in leafyspurge tissue may cause severe skin rashes in humans (Royer andDickinson 1999). Bees, flies, ants, and mosquitoes feed on thenectar of leafy spurge flowers (Messersmith et al. 1985, Fowler1983, Selleck et al. 1962). Over 60 species of insects have beenrecorded visiting leafy spurge flowers (Butterfield et al. 1999).Decomposing plant tissues release allelopathic chemicals thatsuppress the growth of other plant species (Steenhagen andZimdahl 1979, Royer and Dickinson 1999).Total for Ecological Impact 31/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Leafy spurge can spread by seed, rhizome, or root fragment.Root buds can regenerate new shoots if the stems are destroyed.Each stem of leafy spurge can produce up to 250 seeds and denseinfestations can produce over 8,000 seeds per square meter(Royer and Dickinson 1999, Selleck et al. 1962).Long-distance dispersal (0–3) 3Fruits open explosively and can scatter seeds up to 15 feet fromthe parent plant. Long-distance dispersal by animals is alsosuspected (Best et al. 1980, Butterfield et al. 1996) and the seedscan float and geminate in water (Masters and Kappler 2002).Leafy spurge seeds contain fat and protein which make thema desirable food source for ants who act as dispersal agents(Remberton 1988).Spread by humans (0–3) 3It is likely that the first introduction of leafy spurge to NorthAmerica was in contaminated oats from Russia. Leafy spurgeis known to contaminate commercial seed, grain, and hay.Fragments of roots and rhizomes can be carried on roadmaintenance or farm equipment (Kreps 2000, Butterfield etal.1996, Dunn 1985, Selleck et al. 1962).Allelopathic (0–2) 2Decomposing plant tissues release allelopathic chemicalsthat inhibit the growth or development of other plant species(Butterfield et al. 1996, Royer and Dickinson 1999, Steenhagenand Zimdahl 1979). In greenhouse experiments the growth oftomato seedlings was inhibited 60% when leafy spurge litter waspresent in soil (Steenhagen and Zimdahl 1979). A reduction infrequency and density of quackgrass and common ragweed wasalso reported.Competitive Ability (0–3) 3Leafy spurge outcompetes native forbs and grasses (Mastersand Kappler 2002), and is alleopathic toward associated species(Steenhagen and Zindahl 1979). Leafy spurge has extensivevegetative reproduction, effective seed dispersal, high seedviability, and very rapid development of seedlings (Masters andKappler 2002). In a detailed study of Euphorbia esula growingwith smooth brome and crested wheatgrass neither species wassuccessful in competition with leafy spurge (Selleck at al. 1962).Thicket-forming/Smothering growth form (0–2) 1Leafy spurge is capable of creating dense monocultures. A densityof 200 shoots per square meter was recorded in Saskatchewan(Selleck et al. 1962). Stem densities of 1,000 per square yard arenot uncommon (Kreps 2000).Germination requirements (0–3) 2Leafy spurge requires anthropogenic or natural disturbances forgermination (Belcher and Wilson 1989, Selleck et al. 1962).Other invasive species in the genus (0–3) 3Euphorbia cyparissias, E. myrsinites, E. oblongata, E. serrata, andE. terracina have state noxious status in various American states(USDA 2002).Aquatic, wetland or riparian species (0–3) 1Although leafy spurge prefers dry sandy soils, it is able to establishin irrigated meadows and along riparian areas (Masters andKappler 2002). Leafy spurge is known from riverbanks in CentralEurope, Sweden, and Western Asia. In Saskatchewan infestationsoften follow drain channel contours (Selleck et al. 1962).Total for Biological Characteristics and Dispersal 21/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Leafy spurge is a successful weed in untilled fields (Kreps 2000).Known level of impact in natural areas (0–6) 6Leafy spurge has invaded prairies, pine savannas, and riparianareas in Minnesota, North and South Dakota, Idaho, Oregon,Colorado, and California (Kreps 2000, Dunn 1979). It is knownto invade native grassland in Ontario, Quebec, and Saskatchewan(Selleck et al. 1962). Leafy spurge is spreading rapidly into nativerangeland in Western Canada (Frankton and Mulligan 1970).Role of anthropogenic and natural disturbance inestablishment (0–5)Leafy spurge requires anthropogenic or natural disturbancesfor initial establishment. It has been found to spread in nativegrassland, presumably after establishment from seed in a gophermound (Selleck et al. 1962). Almost all (95%) of leafy spurgeinfestations are associated with anthropogenic disturbances suchas vehicle tracks, road construction, and fire lines (Belcher andWilson 1989).Current global distribution (0–5) 5Leafy spurge is native to Eurasia. It is presently found worldwide(including the boreal zone), except for Australia (Biesboer 1996,Butterfield et al. 1996).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)Leafy spurge has spread into 30 states and every Canadianprovince, except Newfoundland (Best et al. 1980, Butterfield etal. 1996, USDA 2002). All indications are that it will continue toexpand its range in Canada (White et al. 1993). Leafy spurge isa noxious weed in 22 American states and 6 Canadian provinces(Invaders Database System 2003, Royer and Dickinson 1999).Leafy spurge is a prohibited noxious weed in Alaska (AlaskaAdministrative Code 1987).Total for Ecological Amplitude and Distribution 23/2535B-37