Invasiveness Ranking System for Non-Native Plants of Alaska

Trifolium pratense L.Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 16Biological Characteristics and Dispersal 25 12Amplitude and Distribution 25 16Feasibility of Control 10 7Relative Maximum 53Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal Yes –Arctic Alpine No YesTrifolium pratense is documented in the south coastal and interiorboreal ecogeographic regions of Alaska (Hultén 1968, Welsh1974, AKEPIC 2005, UAM 2004). The CLIMEX matchingprogram indicates the climatic similarity between the arcticalpine ecogeographic region of Alaska and areas of native rangeof Trifolium pratense are moderately high. The range of red cloverincludes Røros and Dombås, Norway (Markenschlager 1934,Lid and Lid 1994), which have a 76% and 63% climatic matchwith Nome. Thus establishment of red clover in the arctic alpineecogeographic region is likely.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 5Red clover increases soil nitrogen levels by fixing atmosphericnitrogen (USDA, NRCS 2006). The alteration of soil conditionsmay delay establishment of native species (Rutledge andMcLendon 1996) and facilitate colonization by other exotic plantspecies.Impact on Natural Community Structure (0–10) 3Red clover is capable of creating very dense stands (Gettle et al.1996a). It produces a large biomass (Gettle et al. 1996b, Hofmannand Isselstein 2004), which influences the structure of the layer.Density of up to 632 stems per m² was recorded in field study(Gettle et al. 1996a).Impact on Natural Community Composition (0–10) 3Red clover reduces the number of individuals of native species inthe community (Gettle et al. 1996a). Density of grasses decreasedas density of established red clover increased in switchgrasscommunities (Gettle et al. 1996a).Impact on Higher Trophic Levels (0–10) 5Moose and mule deer graze on red clover in California. Theleaves of red clover are also eaten by beaver, woodchuck, muskrat,meadow mice, and sharp-tailed grouse. Seeds are eaten by crow,horned lark, and ruffed and sharp-tailed grouse. Red clover isvisited by bumblebees and sometimes by introduced honeybees(Graham 1941).Total for Ecological Impact 16/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 1Red clover reproduces by seeds. It can produce moderate amountof seeds (11–1,000) (Densomore et al. 2001).common names: red cloverLong-distance dispersal (0–3)USeeds of red clover are large and do not have a specific adaptationfor long-distance dispersal.Spread by humans (0–3) 2Red clover escaped cultivation (Rutledge and McLendon 1996,Welsh 1974). The seeds of red clover are commercially available.It has been planted for trials in Alaska (Panciera et al. 1990,Sparrow et al. 1993).Allelopathic (0–2) 0Red clover is not allelopathic (USDA, NRCS 2006).Competitive Ability (0–3) 3Red clover is capable of outcompeting exotic and native grasses(Gettle et al. 1996a, Hofmann and Isselstein 2004). Red cloverhas the ability to fix nitrogen (USDA, NRCS 2006). The highestablishment success of red clover seedlings in existing swardswas obtained in field experiments (see Gettle et al. 1996a).Resources of the large seeds apparently allow seedlings to surviveperiods of establishment in deep shade of existing vegetation(Hofmann and Isselstein 2004). Once red clover has establishedit competes with neighboring grasses (Gettle et al. 1996a).Thicket-forming/Smothering growth form (0–2) 0In seeded fields red clover can reach a density of 632 plants perm² (Gettle et al. 1996a). Red clover has not been observed at highdensities in noncultivated sites in Alaska (I. Lapina pers. obs.).Germination requirements (0–3) 3Red clover can germinate and establish in existing swards(Gettle et al. 1996b, Hofmann and Isselstein 2004); however,mechanical disturbances that provide gaps in existing vegetationcreate favorable conditions for the establishment of red clover(Hofmann and Isselstein 2004).Other invasive species in the genus (0–3) 3Trifolium arvense L., T. campestre Schreb., T. incarnatum L., andT. repens L. (USDA, NRCS 2006).Aquatic, wetland or riparian species (0–3) 0Red clover is often planted as a forage crop, it escapes andestablishes on roadsides, clearcuts, lawns, gardens, and meadows(Rutledge and McLendon 1996, Welsh 1974).Total for Biological Characteristics and Dispersal 12/23Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Red clover is widely planted as a component of pasture and foragemixes. It is recommended for soil improvement. Several varietieshave been developed (USDA, NRCS 2006). It was first cultivatedin northern Europe around 1650 (Merkenschlager 1934).Known level of impact in natural areas (0–6) 1Red clover does not appear to have a perceivable impact onhabitats within Rocky Mountain National Park (Rutledge andMcLendon 1996).Role of anthropogenic and natural disturbance in3establishment (0–5)If seeded, red clover can successfully establish in pastures(Gettle et al. 1996a, b). Soil disturbances, cutting or grazingof competitive vegetation increases the rate of establishment(Guretzky et al. 2004, Hofmann and Isselstein 2004). It hasbeen found in sites disturbed in the last 11–50 years in RockyMountain National Park (Rutledge and McLendon 1996). Itis found in Wrangell–St. Elias National Park in sites disturbedwithin the last 10 years (Densmore et al. 2001).B-133