Plant Assessment Form

Centaurea jacea ssp. pratensis

Synonyms: Centaurea debeauxii Gren. & Godr., Centaurea x pratensis; Centaurea jacea L. x Centaurea nigra L.

Common Names: meadow knapweed

Evaluated on: 5/3/05

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

Gina Skurka and Elizabeth Brusati
Cal-IPC
1442-A Walnut St. #462, Berkeley, CA 94709
510-843-3902
edbrusati@cal-ipc.org
Joseph DiTomaso
University of California-Davis
Dept. Plant Sci., Mail Stop 4, Davis, CA 95616
530-754-8715
jmditomaso@ucdavis.edu

List commitee members

Carla Bossard
John Randall
Carri Pirosko
Dan Gluesenkamp
Gina Skurka
Brianna Richardson

General Comments

No general comments for this species

Table 2. Criteria, Section, and Overall Scores

Overall Score? Moderate
Alert Status? Alert
Documentation? 2.5 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes C Other Published Material
Impact?
Four-part score CBCD Total Score
B
1.2 ?Impact on plant community B. Moderate Other Published Material
1.3 ?Impact on higher trophic levels C. Minor Other Published Material
1.4 ?Impact on genetic integrity D. None Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Other Published Material
Invasiveness?
Total Points
14 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 A. Increasing rapidly Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
B. Moderate Other Published Material
2.5 ?Potential for human-caused dispersal C. Low Other Published Material
2.6 ? Potential for natural long-distance dispersal C. Rare Other Published Material
2.7 ?Other regions invaded B. Invades 1 or 2 ecological types Observational
3.1 ?Ecological amplitude/Range
(see Worksheet C)
B. Moderate Other Published Material
Distribution?
Total Score C
3.2 ?Distribution/Peak frequency
(see Worksheet C)
D. Very low Observational

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? C Other Published Material
Identify ecosystem processes impacted:

Taproot with a wooly crown, plants grow 0.4 - 1 meter tall. Taproot may change soil water content.


Sources of information:

Meadow Knapweed. A Guide to Weeds in British Columbia. www.weedsbc.ca/weed_desc/meadow.html.


Question 1.2 Impact on plant community composition,
structure, and interactions?
B Other Published Material
Identify type of impact or alteration:

Can invade rangeland and pastures, causing reduction in carrying capacity. Forms dense stands. It can also result in reduced yields in hayfields. Meadow knapweed out competes grasses and other pasture species and is difficult to control due to its extensive root system. This level of infestation have not occurred in California and may require more nothern climates.


Sources of information:

Meadow Knapweed. A Guide to Weeds in British Columbia. www.weedsbc.ca/weed_desc/meadow.html.
Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05
Carri Pirosko, California Dept. of Food and Agriculture, pers. obs.


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

Low palatability to grazing animals. Reduce winter forage for Elk. Negligible impact; causes no perceivable change in higher trophic level populations, communities, or interactions.


Sources of information:

Meadow Knapweed. A Guide to Weeds in British Columbia. www.weedsbc.ca/weed_desc/meadow.html.
Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


Question 1.4 Impact on genetic integrity? D Other Published Material

Brown knapweed (C. jacea) and black knapweed (C. nigra) produce fully fertile hybrids (meadow knapweed) that appear to be weedier than either of the parents. May hybridize with YST. Not known to hybridize with native species.
No native Centaurea species.


Sources of information:

Roche, B.F. Jr. , C.T. Roche. Identification, Introduction, Distribution, Ecology, and Economics of Centaurea Species. Noxious Range Weeds. 1991. 274-291. Ed. James L.F. et al. Westview Press, Boulder, San Francisco, Oxford.
Hickman, J. C. (ed.) 1993. The Jepson Manual, Higher Plants of California. University of California Press. Berkeley, CA


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

Meadow knapweed inhabit disturbed places in the northwestern region and the San Francisco Bay region, to 500 m. Typically it grows on roadsides and disturbed areas, where it forms dense stands that hinder re-establishment of native species. Meadow knapweed does not need disturbance to establish new populations. One example is the only known infestation in Colorado that is not overgrazed and has a riparian area that has been described as "very healthy." The existing native plant community is quite diverse and the infestation is in all the different plant communities.


Sources of information:

DiTomaso, J. M. E.A. Healy. Weeds of California and Other Western States. As yet unpublished.
Meadow Knapweed. A Guide to Weeds in British Columbia. www.weedsbc.ca/weed_desc/meadow.html.
Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


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

Existing populations are small but rapidly spreading. Has doubled in less than 10 years in Siskiyou and Del Norte Counties.


Sources of information:

Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


Question 2.3 Recent trend in total area infested within state? A Observational
Describe trend:

Currently, meadow knapweed has a limited distribution in California. Meadow knapweed presently occurs in a limited distribution in Siskiyou, Humboldt, and Del Norte Counties. Fewer than 10 known sites. All locations are relatively small, but the weed is spreading at an alarming rate. See Carri's report for current management efforts.


Sources of information:

Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


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

Meadow knapweed has sterile outer flowers. Primarily reproduce by seed and to some extent by short lateral shoots from the parent plants. Root and crown fragments resprout when disturbed by heavy equimpment or cultivation. Suspected to have upwards of 30 seeds per seedhead. 5 points


Sources of information:

DiTomaso, J.M., E.A Healy. Weeds of California and Other Western States. As yet unpublished (J. DiTomaso files, KND 8/10/04, hardcopy at Cal-IPC).
Roche, B.F. Jr. , C.T. Roche. Identification, Introduction, Distribution, Ecology, and Economics of Centaurea Species. Noxious Range Weeds. 1991. 274-291. Ed. James L.F. et al. Westview Press, Boulder, San Francisco, Oxford.
Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


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

Seeds carried by irrigation water systems and vehicles. All indications are that it will spread along road systems and thus increase potential to infest highly valued wildlands such as Botanical Areas and Wilderness Areas. Was used as forage. Present as contaminant in ship ballast. Transplanted into gardens. Infestation in Humboldt County resulted from an overturned hay truck. These methods of dispersal can occur but are not common.


Sources of information:

Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.
Roche, B.F. Jr. , C.T. Roche. Identification, Introduction, Distribution, Ecology, and Economics of Centaurea Species. Noxious Range Weeds. 1991. 274-291. Ed. James L.F. et al. Westview Press, Boulder, San Francisco, Oxford.


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

Seeds are carried in rivers, but generally grow in areas not adjacent to water so long distance dispersal by natural means in very uncommon.


Sources of information:

Roche, B.F. Jr. , C.T. Roche. Identification, Introduction, Distribution, Ecology, and Economics of Centaurea Species. Noxious Range Weeds. 1991. 274-291. Ed. James L.F. et al. Westview Press, Boulder, San Francisco, Oxford.


Question 2.7 Other regions invaded? B Observational
Identify other regions:

The earliest records of meadow knapweed in the Pacific Northwest are from Multnomah and Lane counties, Oregon, between 1910 and 1920. Occurs at elevations up to 6600 feet in the mountains of Central Europe. In Washington State, it grows in the more mesic meadow and pasture areas, usually in openings in forested areas or along drainages. Further, hybrids such as meadow knapweed can exhibit greater adaptability to new conditions, beyond that of either the brown or black parent stock. In several western states, meadow knapweed has been found growing in : irrigated meadows, along riparian areas, in dry sagebrush upland country, dry-land meadows, aspen stands, and under mixed conifer stands. Scoring as A because has a limited distribution in California but occurs in a number of habitats in the northwest.


Sources of information:

Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


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

Introduced from Europe in early 1900s, by 1960 meadow knapweed was well established in the valley between the Coast and Cascade Ranges from British Columbia to northern California. In the past 100 yrs, it has demonstrated a superior ability to move and occupy a yet undefined niche in the more mesic grasslands at lower and middle elevations.
Del Norte County, southern edge of Crescent City, gravel bars in Klamath National Forest, meadow in Siskiyou County.


Sources of information:

Roche, B.F. Jr. , C.T. Roche. Identification, Introduction, Distribution, Ecology, and Economics of Centaurea Species. Noxious Range Weeds. 1991. 274-291. Ed. James L.F. et al. Westview Press, Boulder, San Francisco, Oxford.


Question 3.2 Distribution/Peak frequency? D Observational
Describe distribution:

Very limited distribution in California so far.


Sources of information:

Meadow Knapweed. Proposal for listing as an A-rated Weed. Personal communication from Carri Pirosko, California Department of Food and Agriculture 5/5/05.


Worksheet A - Innate reproductive potential

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

Infested Jepson Regions

Click here for a map of Jepson regions