Invasiveness Ranking System for Non-Native Plants of Alaska

Aquatic, wetland or riparian species (0–3) 3White sweetclover has been observed invading thousand of acresalong river systems: Nenena, Stikine, and Matanuska (Conn2003, Shephard pers. com.). The tendency of seed to disperseby water indicates that herbaceous riverine communities can bealtered by invasion of M. alba. However, this taxon is intolerantof consistently wet, non-well drained substrates (Heffernan et al.2001)Total for Biological Characteristics and Dispersal 22/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4White sweetclover has been extensively used as a forage crop,soil builder, and a nectar source for honeybees (Turkington1978, Eckardt 1987). A cold tolerant variety has been bred and isestablishing in Alaskan parks (Densmore et al. 2001)Known level of impact in natural areas (0–6) 4White sweetclover has invaded sand dunes and gravel barsalong the Stikine River, Tongass National Forest (Stensvold2000, Spencer pers. obs.); and Nenena and Matanuska Riverin south-central (Conn 2003). It has invaded rivers systems inAlaska and aspen woodlands in Rocky Mountain National Park,Colorado (Rutledge and McLendon 1996). It has been found inmid-successional sites that were disturbed in the last 11–50 years(Pipestone National Monument, Minnesota Butterfield et al.1996).Role of anthropogenic and natural disturbance inestablishment (0–5)White sweetclover readily invades open areas. Natural or humancausedfires promote invasion by scarifying seeds and stimulatinggermination. The clearings in forested land are easily colonized byMelilotus. It resprouts readily when cut or grazed (Eckardt 1987,Wisconsin DNR 2003). Soil disturbance from road constructionis known to facilitate invasion of this species (Parker 1993).3Current global distribution (0–5) 5White sweetclover is native to the Mediterranean area throughCentral Europe to Tibet. It is introduced into South Africa, Northand South America, New Zealand, Australia, and Tasmania(Hultén 1968).Extent of the species U.S. range and/or occurrence of5formal state or provincial listing (0–5)White sweetclover is found in all 50 states and all but twoCanadian provinces. It is listed as “exotic pest” in Tennessee,“ecologically invasive” in Wisconsin, “weed” in Kentucky andQuebec, Canada (Royer and Dickinson 1999, USDA, NRCS2002).Total for Ecological Amplitude and Distribution 21/25Feasibility of ControlScoreSeed banks (0–3) 3Seeds of white sweetclover can remain viable in the soil for11–50 years and up to 81 years (Stoa 1933, Butterfield et al. 1996,J. Conn pers. com., Royer and Dickinson 1999, Rutledge andMcLendon 1991).Vegetative regeneration (0–3) 2White sweetclover resprouts readily when burn, cut, or grazed(Butterfield et al., 1996, Wisconsin DNR 2003). However,Densmore et al. (2001) reports that it does not resprout.Level of effort required (0–4) 4Management requires a long-term investment due to longseed viability and density patches. Plant can be managed usingmechanical and chemical control methods. Several treatmentsmay be necessary. Sites must be monitored. Remote sitesespecially difficult to control (J. Conn pers. com., Eckardt 1987).Total for Feasibility of Control 9/10Total score for 4 sections 81/100§B-81