Invasiveness Assessment - Japanese knotweed (Fallopia japonica) in Victoria (Nox)
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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. |
The following table provides information on the invasiveness of Japanese knotweed.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Japanese knotweed
Scientific name: Fallopia japonica
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | Propagation in response to seasonal factors – “Perennating buds form on the stock and woody rhizome between autumn and winter and emerge to give vertical shoots in the following spring”. | Beerling et al (1994) p. 959 | MH |
| Establishment requirements? | Study showed plant was ‘shade intolerant where the photon flux density was < 20% full daylight’. Beerling et al (1994) p. 959. Most commonly found in ‘open’ habitats. E.g. “In its native habitats in Japan, it occurs on hillsides and mountain slopes in open sunny sites…In North America…it is most common and vigorous in open moist sites and occurs along riverbanks, wetlands, roadsides and in a variety of disturbed areas”. (Haber 1999 p. 1). “Grows best in full sunshine, providing sufficient nutrients and water are available, is affected even by moderate shade”. Beerling et al (1994) p. 964 | Beerling et al (1994) Haber (1999) | ML |
| How much disturbance is required? | Establishes in minor disturbed ecosystems, (e.g. wetlands, riparian areas, on the fringe of, or in open woodland). | Beerling et al (1994) Haber (1999) | MH |
| Growth/Competitive | |||
| Life form? | A geophyte according to the Raunkiaer system. | Beerling et al (1994) | ML |
| Allelopathic properties? | No Allelopathic properties described. |  | L |
| Tolerates herb pressure? | “In Britain sheep, cattle, horses and donkeys graze the above ground shoots”. Beerling et al (1994) p. 976.so consumed, but assumed to recover quickly from rhizomes. Most commonly found in ‘open’ habitats. E.g. “In its native habitats in Japan, it occurs on hillsides and mountain slopes in open sunny sites…In North America…it is most common and vigorous in open moist sites and occurs along riverbanks, wetlands, roadsides and in a variety of disturbed areas”. (Haber 1999 p. 1). “Grows best in full sunshine, providing sufficient nutrients and water are available, is affected even by moderate shade”. Beerling et al (1994) p. 964. | Beerling et al (1994) p. 976 | MH |
| Normal growth rate? | “The vigorous growth potential of this sp. Is reflected in its ability to regenerate from rhizomes buried up to 1 m deep…young shoots grow as rapidly as 8 cm a day. The plant’s deep root system and spreading rhizomes provide a competitive advantage in acquiring water and nutrients compared with other less vigorous species”. (Haber 1999. P. 3). Also described as being – ‘fast growing’ (Haber 1999, p. 5). “Considered by Crawley (1987) to be one of the ‘top 20’ invasive aliens of Britain”. (Beerling et al (1994) p. 967). | | H |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of frost (moderate). “Plants are vulnerable to late spring and early autumn frost”. However, a study in Japan revealed that “by October seedlings survived only the – SC treatment, whereas by November seedlings survived temperatures of -15oC”. (Beerling et al 1994 p. 969). “Fire is also a poor control method and seems not to affect the viability of the underground rhizomes”. (Beerling et al 1994 p. 967). Also assumed to be tolerant of some water logging as commonly occurs in wetlands and riparian areas, riverbanks and flood plains. (Beerling et al 1994 : Haber 1994). | | MH |
| Reproduction | |||
| Reproductive system | “In its native habitats in Japan, there is high seed set but low seedling survival”. So in Australia (Victoria), seed set is also assumed unlikely. | Seiger & Merchant (1997) Haber (1999) | MH |
| Number of propagules produced? | Outside its native range in Japan, reproduction is limited almost exclusively to vegetative spread, due to the rarity of male plants with fertile pollen. | Haber (1999) p. 2 | L |
| Propagule longevity? | “No systematic study of the longevity of seed has been undertaken, but seed from a tetraploid F. x bohemica, stored at room temperature retained viability for 4 years”. | Beerling et al (1994) p. 974 | L |
| Reproductive period? | “The stand-forming habit of F. x bohemica, produces a dense summer canopy beneath which few other species can survive”. (Beerling et al 1994 p. 959). “Dense monocultures” observed (De Waal et al 1995 p. 203). | De Waal et al 1995 p. 203 | H |
| Time to reproductive maturity? | Following quote in qu. 1…”Woody stocks continue to increase in mass with age and also provide lateral creeping rhizomes within their first year “. (Beerling et al 1999, p. 959). “Effective reproduction appears to be entirely by means of the extensive and rapidly-growing rhizome system”. (Grime et al 1990 p. 285). These new rhizomes are propagules, capable of germination and establishing if fragmented. “Even rhizome fragments as small as 8 g (fresh weight), are capable of regenerating new plants”. | Beerling et al (1994) p. 959 | H |
| Dispersal | |||
| Number of mechanisms? | Vegetative fragments spread by water, wind, and earthmoving activities. | Beerling et al (1994) Brock & Wade (1992) | MH |
| How far do they disperse? | Road making activities dispersed fragments 200 m. Winds in coastal areas have carried fragments “a few hundred metres”. Many colonies along rivers are result of down stream dispersal of fragments. | Beerling et al (1994) p. 969 | MH |
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