Invasiveness Ranking System for Non-Native Plants of Alaska

Rubus discolor Weihe & NeesRanking SummaryEcoregion known or expected to occur inSouth CoastalInterior BorealArctic AlpineYesNoNoPotential Max. ScoreEcological Impact 40 38Biological Characteristics and Dispersal 25 18Amplitude and Distribution 25 12Feasibility of Control 10 9Relative Maximum 77Climatic ComparisonCollected inAlaska regions?CLIMEXsimilarity?South Coastal Yes –Interior Boreal No NoArctic Alpine No NoRubus discolor has been collected in Sitka (AKEPIC 2004). Theclimatic similarity between Fairbanks and Nome and nativeand introduced locations of the species is low (CLIMEX 1999,USDA, ARS 2005). Additionally, one of the requirements forseeds germination is warm stratification at 68 ° to 86 °F for 90-days (Hoshovsky 2000); these conditions rarely occur in interiorboreal and arctic alpine ecogeographic regions of Alaska (WRCC2001). Thus establishment of Rubus discolor in interior borealand arctic alpine ecogeographic regions is unlikely. Himalayanblackberry is known from the south coastal ecogeographic regionof Alaska. (Additionally, the introduced range of Himalayanblackberry includes Thredbo, Australia [Australia’s VirtualHerbarium 2005], which has 53% of climatic similarity withJuneau.)Ecological ImpactScoreImpact on Ecosystem Processes (0–10) 8Himalayan blackberry is a pioneer plant that colonizes intertidalzones in California and prevents establishment of native plants(Hoshovsky 2000, Tirmenstein 1989). Dense thickets ofHimalayan blackberry are considered a fire hazard (Hoshovsky1989, Hoshovsky 2000). Grasslands, meadows, and savannasare lost after Himalayan blackberry has invaded in the PacificNorthwest (M.L. Carlson pers. obs.).Impact on Natural Community Structure (0–10) 10Himalayan blackberry forms impenetrable thickets of pricklystems, eliminating all layers below. Density of canes can reach of525 canes per square meter. Mature thickets have large amountsof litter and standing dead canes (Hoshovsky 2000, Tirmenstein1989).Impact on Natural Community Composition (0–10) 10This species forms a dense canopy, shading out native vegetationand reducing plant species diversity (Hoshovsky 2000,Tirmenstein 1989).Impact on Higher Trophic Levels (0–10) 10Himalayan blackberry can hybridizes with a number of otherRubus species. It provides food and cover for many wildlifespecies. Fruits are eaten by numerous species of birds. A largediversity of mammals feed on the berries, stems, and leaves(Tirmenstein 1989). Dense thickets can hinder large mammalmovement (Hoshovsky 2000).Total for Ecological Impact 38/40common names: Himalayan blackberryBiological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 3Himalayan blackberry reproduces by seed and aggressivevegetative growth (rooting at cane apices, suckering of roots, andfrom root and shoot fragments). Up to 7,000–13,000 seeds can beproduced per square meter (Hoshovsky 2000, Richardson 1975).Long-distance dispersal (0–3) 3The seeds are readily dispersed by mammals and birds. Passingthrough digestive tracts scarifies seeds and may enhancegermination (Brunner et al. 1975, Tirmenstein 1989). It can alsobe spread long distances by streams and rivers (Hoshovsky 2000).Spread by humans (0–3) 2Himalayan blackberry is widely cultivated; it has escaped andbecome established (Hitchcock and Cronquist 1961).Allelopathic (0–2) 0There is no record concerning allelopathy.Competitive Ability (0–3) 3Himalayan blackberry is a very strong competitor. Thickets growquickly and produce a dense canopy that shades and limits thegrowth of other plants (Hoshovsky 2000).Thicket-forming/Smothering growth form (0–2) 2Himalayan blackberry forms very large impenetrable thickets(Hoshovsky 2000, Tirmenstein 1989).Germination requirements (0–3) 0Seedlings require open habitats or eroded soils for establishment(Hoshovsky 2000). Seedlings are intolerant of shading and areeasily surpassed by the rapidly growing vegetative daughter plants(Hoshovsky 2000).Other invasive species in the genus (0–3) 3Rubus argutus Link, R. ellipticus Sm., R. glaucus Benth., andR. niveus Thunb. are considered invasive species in Hawaii (Plansof Hawaii 2003).Aquatic, wetland or riparian species (0–3) 2Himalayan blackberry is common in wastelands, pastures, andclearcuts. It grows along roadsides, creek gullies, river flats, andfence lines. It is common in riparian areas, where it withstandsperiodic inundation by fresh or brackish water (Ertter 1993,Hoshovsky 2000).Total for Biological Characteristics and Dispersal 18/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Himalayan blackberry is widely cultivated. It was probablyintroduced to North America in 1885 as a cultivated crop(Hoshovsky 2000, Tirmenstein 1989).Known level of impact in natural areas (0–6) 1Himalayan blackberry is known to impact riparian woodlandsand intertidal zones of central California (Hoshovsky 2000,Tirmenstein 1989). This species invades pastures and forestplantations in Victoria, Australia (Amor 1973). It can becomedominant in clearcut coniferous forests in the Pacific Northwest(M.L. Carlson pers. obs.)Role of anthropogenic and natural disturbance in0establishment (0–5)Himalayan blackberry colonizes disturbed areas. The seedlingsrequire open habitats or eroded soils for establishment(Hoshovsky 2000). Seeds from the seed bank can germinate inlarge numbers after disturbance (Tirmenstein 1989).B-113