Invasiveness Ranking System for Non-Native Plants of Alaska

Rumex acetosella L.Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 12Biological Characteristics and Dispersal 25 16Amplitude and Distribution 25 16Feasibility of Control 10 7Relative Maximum 51Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine Yes –Rumex acetosella is documented in all ecogeographic regions ofAlaska (Hultén 1968, Welsh 1974, AKEPIC 2005, UAM 2004).Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 3Sheep sorrel may impede the colonization of the post-fire areas bynative species. Sheep sorrel is documented as one of the commoncolonizer of burned areas (Hall 1955, Fonda 1974, Weaver et al.1990).Impact on Natural Community Structure (0–10) 3Sheep sorrel has been observed establishing in existing layerof vegetation and increasing the density of the layer in AlaskaNational Parks and remote areas of the Chugach National Forest(M.L. Carlson pers. obs., I. Lapina pers. obs.).Impact on Natural Community Composition (0–10) 3Sheep sorrel is reported to form dense stands and displace nativegrasses and forbs in California (Cal-IPC 2005). However, thisweed does not appear to cause a significant reduction in nativespecies population size in Alaska.Impact on Higher Trophic Levels (0–10) 3Sheep sorrel contains oxalic acid, which can be poisonous tolivestock; it is possible that it could be toxic to wildlife species(Cal-IPC 2005). Sheep sorrel is grazed by mule deer (Kruger andDonart 1974, Nixon et al. 1970). The seeds are rich source of foodfor birds (Schmidt 1936, Swenson 1985, Wilson et al. 1999).Total for Ecological Impact 12/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Sheep sorrel reproduces by seeds and from creeping roots andrhizomes (Kiltz 1930). Seed production per plant can varyfrom 250 to 1,622 seeds per season (Stevens 1932, Escarre andThompson 1991) with estimated seed production up to 2,700 perm².Long-distance dispersal (0–3) 2The seeds are large and lack adaptation for long-distancedispersal. However, seeds can be dispersed by wind, water, andants (Houssard and Escarre 1991).Spread by humans (0–3) 3The seeds of sheep sorrel can be transported on vehicles tires,agricultural equipment, with nursery stock or contaminatedseeds, and hay (Gooch 1963). Seeds remain viable after passingthrough digestive tract of domestic birds and animals (Dorph-Peterson 1925, Evershed and Warburton 1918).common names: sheep sorrelAllelopathic (0–2) 0Sheep sorrel is not known to be allelopathic.Competitive Ability (0–3) 1Sheep sorrel is fairly competitive on nitrogen poor soils.Competition from other species on good soils may reduce itsabundance and contain its spread (Putwain and Harper 1970).In Alaska parks units it persists only in areas where competitionfrom other plants is reduced (Densmore et al. 2001).Thicket-forming/Smothering growth form (0–2) 1Seep sorrel sometimes forms dense colonies by shoots fromroots and rhizomes on human-disturbed grounds. In Europe itcommonly forms monocultures on post-fire sites. Dense stands innative communities have not been observed in Alaska (I. Lapinapers. obs., M.L. Carlson pers. obs.).Germination requirements (0–3) 0Sheep sorrel requires open soil for germination (Putwain etal. 1968). No establishment of sheep sorrel in a closed swardof vegetation was recorded in a study by Putwain et al. (1968).The number of seedlings emerged from buried seeds increasedsubstantially on sites with open soil and removed vegetation inanother experiment (Putwain and Harper 1970).Other invasive species in the genus (0–3) 3Rumex crispus L. is declared a noxious weed in Iowa (USDA,NRCS 2006).Aquatic, wetland or riparian species (0–3) 3Sheep sorrel can be found in variety of habitats including riverbars, beaches (Fonda 974, Pojar and MacKinnon 1994), and freshwater and brine marshes (Fiedler and Leidy 1987).Total for Biological Characteristics and Dispersal 16/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 2Sheep sorrel is a weed of fields, gardens, and pastures (Douglasand MacKinnon 1999, Welsh 1974).Known level of impact in natural areas (0–6) 1Sheep sorrel is known to have moderate impact on plantcommunities and higher trophic levels in California wildlands(Cal-IPC 2005). Sheep sorrel is found in areas disturbed in thelast 10 years in Rocky Mountain National Park, Colorado, whereit may inhibit the establishment of native species (Rutledge andMcLendon 1996). Its impact on plant communities of KenaiFjords National Park and Sitka National Historical Park in Alaskais considered to be low (Densmore et al. 2001).Role of anthropogenic and natural disturbance inestablishment (0–5)Sheep sorrel rapidly colonizes clearcuts, burned, and flooddisturbedsites (Hall 1955, Fonda 1974, Weaver et al. 1990).Animal disturbances such as mole hills or cattle tracks canbe sufficient for establishment of sheep sorrel in naturalcommunities (Putwain et al. 1968).Current global distribution (0–5) 5Sheep sorrel is a forb of European origin. Today it has naturalizedthroughout temperate North America; it is introduced into SouthAmerica, Africa, and Hawaii (Hultén 1968).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)Sheep sorrel is found in nearly all American states. It is declared anoxious weed in Connecticut and Iowa (USDA, NRCS 2006).Total for Ecological Amplitude and Distribution 16/2535B-110