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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
Question | Comments | Rating | Confidence |
Establishment | |||
Germination requirements? | “Seedling establishment appears to be enhanced by soil disturbance” (Tunison, 1985). Requires cold stratification for seed germination (NPDC, 2006). Requires natural seasonal low temperatures to germinate. | MH | MH |
Establishment requirements? | Moderately shade tolerant…[as] under a sparse canopy. It can be shaded out or severely suppressed by deep shade” (Tunison, 1985). | MH | MH |
How much disturbance is required? | “Able to invade and take over native ecosystems without any apparent disturbance” (Smith, 1985). | H | MH |
Growth/Competitive | |||
Life form? | Shrub (NPDC, 2006). | L | MH |
Allelopathic properties? | Not noted in Smith (1985), “none” (NPDC, 2006). | L | MH |
Tolerates herb pressure? | Low hedging tolerance by livestock or wildlife with medium palatability (NPDC, 2006). | ML | MH |
Normal growth rate? | Rapid (NPDC, 2006). | H | MH |
Stress tolerance to frost, drought, w/logg, sal. etc? | “Occurs in wet to mesic habitats…Resprouts quickly following fire (Smith, 1985). Recorded in boggy sites (Tunison, 1991). Tolerates temperatures as low as –25°C (NPDC, 2006). Medium drought tolerance. Not tolerant to salinity (NPDC, 2006). Highly resistant to frost, fire and waterlogging, some drought tolerance but susceptible to salinity. | H | MH |
Reproduction | |||
Reproductive system | Seed and vegetatively (NPDC, 2006) by root sprouting and aerial shoots forming roots with soil contact (Smith, 1985). | H | MH |
Number of propagules produced? | High fruit/seed abundance (NPDC), 2006). | H | MH |
Propagule longevity? | Unknown | M | L |
Reproductive period? | Lifespan is moderate (rather than long or short) relative to most other plants (NPDC, 2006) and forms dense clonal thickets (monocultures) (Tunison, 1991). | H | MH |
Time to reproductive maturity? | Floricanes develop in the second year (Tunison, 1991). | MH | MH |
Dispersal | |||
Number of mechanisms? | Frugivorous birds (Smith, 1985). | H | MH |
How far do they disperse? | Bird dispersal (Smith, 1985) makes it very likely that some propagules will disperse greater than 1 km. | H | MH |