Invasiveness Ranking System for Non-Native Plants of Alaska

Germination requirements (0–3)UThe seeds rapidly germinate in laboratory conditions, but fewseedlings are observed in the field. Reasons for this are unknown.Population is mostly maintained by vegetative growth from rootsegments (Renz 2000).Other invasive species in the genus (0–3) 3Lepidium campestre (L.) Ait.f., L. densiflorum Schrad.,L. perfoliatum L., and L. ruderale L. (Royer and Dickinson 1999,USDA 2002).Aquatic, wetland or riparian species (0–3) 3This species can invade a wide range of habitats including riparianareas, wetlands, marshes, estuaries, irrigation channels, and floodplains, as well as meadows, crop fields, roadsides, and rangelands(Renz 2000).Total for Biological Characteristics and Dispersal 17/22Ecological Amplitude and Distribution ScoreHighly domesticated or a weed of agriculture (0–4) 2Perennial pepperweed is primarily a weed of rangeland, pastures,and hay meadows. It can occasionally invade croplands (Whitsonet al. 2000).Known level of impact in natural areas (0–6) 1Perennial pepperweed invades brackish to saline wetlands andnative hay meadows throughout California. It is well establishedin marshes of the San Francisco Bay (Howald 2000).Role of anthropogenic and natural disturbance in5establishment (0–5)Perennial pepperweed can established on disturbed areas andmay disperse into minimally managed or undisturbed habitats.This plant is known to establish in areas with no natural oranthropogenic disturbances (Howald 2000).Current global distribution (0–5) 3Perennial pepperweed is native to Southeastern Europe andSouthwestern Asia. It is naturalized throughout Europe, NorthAmerica, and Australia (Renz 2000).Extent of the species U.S. range and/or occurrence of5formal state or provincial listing (0–5)Perennial pepperweed is found in all western states. It is reportedfrom three Canadian provinces. Lepidium latifolium is declareda noxious weed in 13 American states, including Alaska (AlaskaAdministrative Code 1987, Invaders Database System 2003,USDA 2002).Total for Ecological Amplitude and Distribution 16/25Feasibility of ControlScoreSeed banks (0–3)USeeds lack a hard coat and do not seem to be capable of survivinglong periods in the soil, thus seed viability is likely to be short(Renz 2000), but seed longevity remains unknown.Vegetative regeneration (0–3) 2Perennial roots can remain dormant in the soil for several years.New plants readily grow from pieces of rootstock less than 1-inchlong (Wotring et al. 1997 cited in Howald 2000).Level of effort required (0–4) 4Once established, perennial pepperweed can be very difficult toremove. Mechanical methods are unlikely to control perennialpepperweed because new plants quickly regenerate from piecesof rootstock. Chemical methods have been used successfully;however, most effective herbicides cannot be applied near orover water. No biological control agents have been introducedto control perennial pepperweed due to several importantcultivated crops within this family (canola, mustard, cabbage,and kale), and several threatened and endangered native speciesof Lepidium in the United States. Old stems and litter take severalyears to degrade, and it may be necessary to remove the litter,which prevents germination and establishment of desirable plantspecies. If soil salinities are dramatically increased, an intensivesoil remediation program may be necessary before native speciescan reestablish. Areas must be monitored since it can recover fromdormant root fragments (Howald 2000, Renz 2000).Total for Feasibility of Control 6/7Total score for 4 sections 67/93§B-63