Plant Assessment Form

Fallopia japonica

Synonyms: Polygonum cuspidatum; Reynoutria japonica, Fallopia baldschuanica

Common Names: Japanese knotweed; Mexican bamboo

Evaluated on: 4/21/05

List committee review date:

Re-evaluation date:

Evaluator(s)

Elizabeth Brusati, project manager
California Invasive Plant Council
1442A Walnut St. #462, Berkeley, CA 94709
510-843-3902
edbrusati@cal-ipc.org

No list committee members listed

General Comments

Removed second scientific name, Polygonum cuspidatum, and added it to the synonym line 3/28/17. Ramona Robison

Table 2. Criteria, Section, and Overall Scores

Overall Score? Moderate
Alert Status? Alert
Documentation? 3 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes B Other Published Material
Impact?
Four-part score BABU Total Score
B
1.2 ?Impact on plant community A. Severe Reviewed Scientific Publication
1.3 ?Impact on higher trophic levels B. Moderate Other Published Material
1.4 ?Impact on genetic integrity U. Unknown
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Other Published Material
Invasiveness?
Total Points
15 Total Score B
2.2 ?Local rate of spread with no management A. Increases rapidly Observational
2.3 ?Recent trend in total area infested within state B. Increasing less rapidly Other Published Material
2.4 ?Innate reproductive potential
(see Worksheet A)
B. Moderate Other Published Material
2.5 ?Potential for human-caused dispersal D. Does not occur Other Published Material
2.6 ? Potential for natural long-distance dispersal A. Frequent Other Published Material
2.7 ?Other regions invaded A. Invades 3 or more ecological types Other Published Material
3.1 ?Ecological amplitude/Range
(see Worksheet C)
D. Narrow Other Published Material
Distribution?
Total Score D
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Other Published Material

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".

Section 1: Impact
Question 1.1 Impact on abiotic ecosystem processes? B Other Published Material
Identify ecosystem processes impacted:

Decreases water flow, increases erosion (1). However, impacts not severe (2). Thickets can clog small water ways. Creates bank erosion problems and is considered a flood control hazard.


Sources of information:

1. Anonymous. 2005. Invasive Knotweeds. King County (Washington) Noxious Weed Control Program Weed Alert. King County Department of Natural Resources and Parks, Water and Land Resources Division, Noxious Weed Control Program. Available: http://dnr.metrokc.gov/weeds
2. John Randall, The Nature Conservancy, pers. obs.


Question 1.2 Impact on plant community composition,
structure, and interactions?
A Reviewed Scientific Publication
Identify type of impact or alteration:

Creates dense colonies that exclude other vegetation (1). Preliminary data indicates that knotweeds reduce the quantity of native leaf litter inputs into streams (3). Early emergence and height of knotweeds (4m) allows them to shade out other species and prevent revegetation (2).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Seiger, L. 1991. Element Stewardship Abstract for Polygonum cuspidatum. The Nature Conservancy, Arlington, VA. Accessed on-line at www.tncweeds.ucdavis.edu
3. Lauren Urgenson, graduate student, University of Washington, pers. comm. E-mail 2/28/05


Question 1.3 Impact on higher trophic levels? B Other Published Material
Identify type of impact or alteration:

Decreases value of riparian habitat for fish and wildlife (1). Knotweed litter has a higher carbon-to-ratio than native plants along streams, giving it less nutritional value for aquatic insects than alder, willow, or cottonwood (2). If it blocks streams, fish passage will be inhibited.


Sources of information:

1. Anonymous 2005
3. Lauren Urgenson, graduate student, University of Washington, pers. comm. E-mail 2/28/05


Question 1.4 Impact on genetic integrity? U

There are numerous native and introduced Polygonum species in California (1). Most reproduction is vegetative so it is unlikely that it hybridizes with native species, but this is unknown.


Sources of information:

1. Hickman, J. C. (ed.) 1993. The Jepson Manual, Higher Plants of California. University of California Press. Berkeley, CA
2. Tu, M., and J. Randall. 2003. 2003 Cal-IPC Red Alert! Proceedings of the California Invasive Plant Council Symposium 2003. Available: www.cal-ipc.org


Section 2: Invasiveness
Question 2.1 Role of anthropogenic and natural disturbance
in establishment?
A Observational
Describe role of disturbance:

Inhabits riparian areas, forest edges, and other disturbed moist places (1). Does not appear to be a threat in undisturbed forests (2).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Seiger 1991


Question 2.2 Local rate of spread with no management? A Observational
Describe rate of spread:

Rhizomes spread very quickly. Sounds like an A but need better documentation for this.


Sources of information:

Mandy Tu, The Nature Conservancy, Oregon. pers. comm. Phone interview 2/05


Question 2.3 Recent trend in total area infested within state? B Other Published Material
Describe trend:

Currently present in a limited area, but has the potential to spread widely (1, 2, 3).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Tu and Randall 2003
3. Tu, Mandy. Personal communication. The Nature Conservancy, Invasive Species Program. Portland, OR. www.tncweeds.ucdavis.edu


Question 2.4 Innate reproductive potential? B Other Published Material
Describe key reproductive characteristics:

Fast-growing perennial that can grow up to 4m tall in one year. Mostly vegetative reproduction through fast-growing rhizomes. Fragments can develop into new plants (1). Seed production thought not to be important in northwestern U.S. (2).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Tu, Mandy. Personal communication. The Nature Conservancy, Invasive Species Program. Portland, OR. www.tncweeds.ucdavis.edu


Question 2.5 Potential for human-caused dispersal? D Other Published Material
Identify dispersal mechanisms:

In Washington and Oregon, was originally introduced as a ornamental, but is no longer used for this purpose. Because it occurs along roadsides, rhizome fragments could be carried by vehicles. Other knotweeds are carried in fill dirt. Sometimes planted by basketweavers.


Sources of information:

Tu and Randall 2003
Seigel 1991
DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488
Carri Pirosko, California Dept. of Food and Agriculture, pers. obs.


Question 2.6 Potential for natural long-distance dispersal? A Other Published Material
Identify dispersal mechanisms:

Because knotweed occurs along riparian areas, rhizome fragments could be transported by water.


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.


Question 2.7 Other regions invaded? A Other Published Material
Identify other regions:

A serious problem in the northeastern U.S., northern midwest, and England. Recent invader rapidly becoming a problem in the Pacific Northwest (1). Currently invades habitats in Oregon and Washington that are present but not invaded in California (2). Could still move into wetlands, marshes, and forests, particularly riparian forest. In the NW, it is a widespread invasive in all of these sites. Not widely distributed in California. Large potential for spread.


Sources of information:

1. Tu and Randall 2003
2. Tu, Mandy. Personal communication. The Nature Conservancy, Invasive Species Program. Portland, OR. www.tncweeds.ucdavis.edu


Section 3: Distribution
Question 3.1 Ecological amplitude/Range? D Other Published Material

Recent invader that is currently uncommon. Inhabits disturbed moist sites, roadsides, riparian areas, and wetlands. Has not invaded wetlands in California yet. Can also inhabit upland sites where water tables are shallow or in areas where seasonal rainfall is adequate. Tolerates some dryness and shade. In San Francisco Bay region, northern Sierra Nevada, northern Central Valley, Northwestern region, especially southern North Coast Ranges, Cascade Range, to 1000m (1). In the northwest, also invades forest edges and cobble bars in streams. Can tolerate some shade (2).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Tu, Mandy. Personal communication. The Nature Conservancy, Invasive Species Program. Portland, OR. www.tncweeds.ucdavis.edu


Question 3.2 Distribution/Peak frequency? D Other Published Material
Describe distribution:

Uncommon in California so far (1, 2).


Sources of information:

1. DiTomaso and Healy. 2006. Weeds of California. UC DANR Publ. #3488.
2. Tu, Mandy. Personal communication. The Nature Conservancy, Invasive Species Program. Portland, OR. www.tncweeds.ucdavis.edu


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter No
Populations of this species produce seeds every year. No
Seed production sustained over 3 or more months within a population annually No
Seeds remain viable in soil for three or more years Unknown
Viable seed produced with both self-pollination and cross-pollination Unknown
Has quickly spreading vegetative structures (rhizomes, roots, etc.) that may root at nodes Yes
Fragments easily and fragments can become established elsewhere Yes
Resprouts readily when cut, grazed, or burned Yes
Total points: 5
Total unknowns: 2
Total score: B?

Related traits:

Worksheet B - Arizona Ecological Types is not included here

Worksheet C - California Ecological Types

(sensu Holland 1986)
Major Ecological Types Minor Ecological Types Code?
Marine Systemsmarine systems
Freshwater and Estuarine lakes, ponds, reservoirs
Aquatic Systemsrivers, streams, canals
estuaries
Dunescoastal
desert
interior
Scrub and Chaparralcoastal bluff scrub
coastal scrub
Sonoran desert scrub
Mojavean desert scrub (incl. Joshua tree woodland)
Great Basin scrub
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparral
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairie
valley and foothill grassland
Great Basin grassland
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forestD, < 5%
riparian woodlandD, < 5%
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forest
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): C
Distribution (highest score): D

Infested Jepson Regions

Click here for a map of Jepson regions