Invasiveness Ranking System for Non-Native Plants of Alaska

Hypericum perforatum L.Ranking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesYesYesPotential Max. ScoreEcological Impact 40 11Biological Characteristics and Dispersal 25 15Amplitude and Distribution 25 18Feasibility of Control 10 8Relative Maximum 52Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South CoastalYesInterior BorealYesArctic AlpineNoHypericum perforatum has been recorded from Anchorage,Sitka, Ketchikan, and Baranof Island (AKEPIC 2004). Climaticsimilarity is high between Nome (arctic alpine ecoregion) andareas where the species is documented. Native range of thespecies includes Ust’Tsil’ma, Ust’Shchugor, and Zlatoust, Russia(Gubanov et al. 2003, USDA, ARS 2004), which has a 78%, 73%and 71% climatic match with Nome and 66%, 67%, and 64%with Fairbanks, respectively. The species has been recordedfrom Anchorage which has a 61% climatic match with Nome.Thus establishment of Hypericum perforatum in arctic alpine andinterior boreal ecoregions may be possible.Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 3Common St. Johnswort depletes soil moisture. It is likely todelay the establishment of native species in disturbed sites. Inlate summer, the dry stalks of St. Johnswort may constitute a firehazard to forests and rangelands (Sampson and Parker 1930).Impact on Natural Community Structure (0–10) 3Common St. Johnswort is capable of forming dense stands ingrasslands and pastures (Powell et al. 1994, Tisdale et al. 1959,White et al. 1993).Impact on Natural Community Composition (0–10) 3Common St. Johnswort is capable of displacing native speciesand modifying native plant community composition (Rutledgeand McLendon 1996).Impact on Higher Trophic Levels (0–10) 2The plant contains a toxin that causes severe dermatitis inlight-haired livestock when they are exposed to strong sunlight(Powell et al. 1994, Rutledge and McLendon 1996, Whitson et al.2000). Hybrids of H. perforatum and H. maculatum are commonin Europe where both species occur (Campbell and Delfosse1984, Lid and Lid 1994).Total for Ecological Impact 11/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Common St. Johnswort reproduces by seed and short runners.The root system spreads horizontally and forms new buds(Rutledge and McLendon 1996). According to Davey (1919)plants are capable of producing up to 15,000 seeds. Seedproduction during a 2-year study in Idaho averaged 23,350 seedsper plant (Tisdale et al. 1959).common names: St. JohnswortLong-distance dispersal (0–3) 3Water and animals are likely the main factors of seed dispersal(Rutledge and McLendon 1996, Parsons 1957). Seeds have noadaptation to wind dispersal; however, a few tests conducted inIdaho indicate that seeds can be dispersed by wind up to 30 feetfrom the nearest plant (Tisdale et al. 1959). A gelatinous coat ofthe seed facilitates long-distance dispersal by sticking to objectsor animals (Sampson and Parker 1930 cited in Crompton et al.1988).Spread by humans (0–3) 3Common St. Johnswort was introduced to new areas forornamental and medicinal purposes (Parsons 1957). It has beencultivated on farms in Eastern European countries (Gubanovet al. 2003). Seeds may contaminate commercial crop seed(USDA, ARS 2005). Seeds also can be distributed over largeareas, adhering to wheels of vehicles, or contaminating hay or soil(Parsons 1957).Allelopathic (0–2) 0Allelopathy has never been reported for common St. Johnswort,there is likely no allelopathy potential for this plant.Competitive Ability (0–3) 1Seedlings of common St. Johnswort are very small, growslowly, and are extremely susceptible to competition from otherpasture plants. Once the new seedlings pass their first year andare established, they are able to outcompete and displace theirneighbors (Cambell 1985). Tisdale and others (1959) found thatperennial pasture grasses are more competitive plants comparedto common St. Johnswort. The root system of seedlingscommonly attains a depth of about 1 foot during its first growingseason. Mature plants have an extensive root system whichextends 4–5 feet in depth and about 3 feet laterally. The deeproot system is capable of supporting the plant when soil water hasbeen depleted (Tisdale et al. 1959).Thicket-forming/Smothering growth form (0–2) 1Common St. Johnswort forms a dense spreading canopy over3 feet tall and may overtop other pasture forbs and grasses(Crompton et al. 1988).Germination requirements (0–3) 0Seeds require bare soil, sunlight, and/or heavy rain forgermination (Tisdale et al. 1959). Germination is generallyinhibited by high levels of litter (Rutledge and McLendon 1996).Other invasive species in the genus (0–3) 3Hypericum androsaemum is a very important weed in Australia(Parsons 1957).Aquatic, wetland or riparian species (0–3) 1Common St. Johnswort is commonly found along roadsides andon other disturbed areas. It also invades rangelands, pastures,and meadows (Guide to weeds in British Columbia 2002, Powellet al. 1994). It is known to invade large areas on riverbanks innortheastern Australia (Parsons 1957).Total for Biological Characteristics and Dispersal 15/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Although common St. Johnswort is not domesticated, it has beencultivated on farms in Eastern European countries for medicinalpurposes (Gubanov et al. 2003)B-55