Invasiveness Ranking System for Non-Native Plants of Alaska

Impact on Higher Trophic Levels (0–10) 5This species is highly palatable and nutritious for all types oflivestock and most wild ruminants (Carey 1995). It is highlydesirable to moose (M. Shephard pers. com., J. Snyder pers.com.). It hybridizes with other ryegrass species (Beddows1973, Wilken 1993, Rutledge and McLendon 1996). Gopherpopulations increase in areas seeded with Italian ryegrass,possibly because of increased cover (Carey 1995). A number ofanimal herbivores and parasites have been recorded for Italianryegrass (Beddows 1973).Total for Ecological Impact 14/40Biological Characteristics and Dispersal ScoreMode of Reproduction (0–3) 1Italian ryegrass regenerates entirely by seed (Beddows 1973,Royer and Dickinson 1999). In two seasons in Californiafecundity ranged from 6.5 to 15 seeds per plant (Gulmon 1979).Long-distance dispersal (0–3) 1Seeds are relatively heavy and compact, and dispersal is limited(Beddows 1973, Rutledge and McLendon 1996).Spread by humans (0–3) 2Ryegrass is often used for soil stabilization, a rotation crop, range,pasture, hay, and turf. Many cultivars have been developed(Carey 1995, USDA 2002). Italian ryegrass is a problematic weedin cereal crops and grass seed crops (Carey 1995).Allelopathic (0–2) 2Ryegrass releases some allelopathic chemicals that reduce thegrowth of other species (McKell et al. 1963).Competitive Ability (0–3) 1Italian ryegrass competes well with native species (Carey 1995,McKell et al. 1969). However, it is highly shade intolerant andis quickly replaced if overtopped by tall herbaceous or shrubbyvegetation.Thicket-forming/Smothering growth form (0–2) 0Some varieties of ryegrass form dense stands (Facelli et al. 1987),but it generally does not form thickets.Germination requirements (0–3) 0Italian ryegrass is a shade intolerant species. Seedling survivalwas poor under the oak canopy in experiments in California(Maranon and Bartolome 1993).Other invasive species in the genus (0–3) 3Lolium perenne ssp. perenne L., Lolium persicum Boiss. & Hohen.,and L. temulentum L. (Hultén 1968, USDA 2002).Aquatic, wetland or riparian species (0–3) 0Italian ryegrass is cultivated in pastures, hayfields, and lawns. Itescapes from cultivation and becomes naturalized on disturbedsites such as waste places and roadsides (Royer and Dickinson1999).Total for Biological Characteristics and Dispersal 10/25Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 4Ryegrass is widely planted as an agricultural crop and for lawns inNorth America. Numerous cultivars have been developed (Carey1995, USDA 2002).Known level of impact in natural areas (0–6) 1Italian ryegrass causes a reduction of plant diversity inCalifornia’s chaparral (Zedler et al. 1983). It does not appear toinvade intact communities.Role of anthropogenic and natural disturbance in0establishment (0–5)Italian ryegrass readily colonizes disturbed areas and adjacentborder habitats (Beddows 1973).Current global distribution (0–5) 5Italian ryegrass is native to Central and Southern Europe,Northwest Africa and Southwest Asia. It now occurs in nearlyall states of the United States. It has been introduced into SouthAmerica, New Zealand, Tasmania, and Central and SouthernAfrica (Beddows 1973, Hultén 1968, USDA 2002).Extent of the species U.S. range and/or occurrence offormal state or provincial listing (0–5)Italian ryegrass now occurs in nearly all of the United States(USDA 2002). This species is not considered noxious in NorthAmerica (Invaders Database System 2003).Total for Ecological Amplitude and Distribution 15/25Feasibility of ControlScoreSeed banks (0–3) 0The seed bank for ryegrass is limited and transient (Thompsonand Grime 1979). Percent germination rapidly dropped off after 4years for stored seeds (Beddows 1973, Rutledge and McLendon1996).Vegetative regeneration (0–3) 0Italian ryegrass does not spread by vegetative means (Beddows1973, USDA 2002).Level of effort required (0–4) 2In crops herbicides have been used to control established plantsand prevent seed production, but this species is gaining resistanceto several herbicides (Carey 1995). In Alaska, this species doesnot appear to persist in sites where it was planted.Total for Feasibility of Control 2/10Total score for 4 sections 41/100§5B-69