Plant Assessment Form

Centaurea stoebe ssp. micranthos

Synonyms: Centaurea maculosa; Centaurea biebersteinii, Centaurea stoebe ssp. stoebe and ssp. maculosa

Common Names: spotted knapweed

Evaluated on: 1/21/05

List committee review date: 08/07/2005

Re-evaluation date:

Evaluator(s)

Gina Skurka
Cal-IPC
530-400-8992
gmskurka@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

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

Table 2. Criteria, Section, and Overall Scores

Overall Score? High
Alert Status? No Alert
Documentation? 3.5 out of 5
Score Documentation
1.1 ?Impact on abiotic ecosystem processes B Reviewed Scientific Publication
Impact?
Four-part score BAAD Total Score
A
1.2 ?Impact on plant community A. Severe Reviewed Scientific Publication
1.3 ?Impact on higher trophic levels A. Severe Reviewed Scientific Publication
1.4 ?Impact on genetic integrity D. None Other Published Material
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Reviewed Scientific Publication
Invasiveness?
Total Points
16 Total Score B
2.2 ?Local rate of spread with no management A. Increases rapidly Other Published Material
2.3 ?Recent trend in total area infested within state B. Increasing less rapidly Observational
2.4 ?Innate reproductive potential
(see Worksheet A)
A. High Reviewed Scientific Publication
2.5 ?Potential for human-caused dispersal B. Moderate Reviewed Scientific Publication
2.6 ? Potential for natural long-distance dispersal B. Occasional Reviewed Scientific Publication
2.7 ?Other regions invaded B. Invades 1 or 2 ecological types Other Published Material
3.1 ?Ecological amplitude/Range
(see Worksheet C)
A. Widespread Other Published Material
Distribution?
Total Score B
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? B Reviewed Scientific Publication
Identify ecosystem processes impacted:

Stout elongated taproot may decrease soil moisture. Knapweed infestation can increase surface run-off and sedimentation. They are poor protectors of soil and water resources and they pose a wildfire threat. Success could be attributed to greater use, or more efficient use, of available soil nitrogen. Soil N often limits growth on semi-arid grasslands. Greater or more efficient use of soil N by spotted knapweed may inhibit establishment, survival, or reproduction of native grassess, if this occurred, but it doesn't. Also, Centaurea's success as an invasive species in North america cannot be attributed to greater use of soil water or greater water-use efficiency than native grasses. Knapweed infestation on bunchgrass rangeland is detrimental to water and soil resources. Lacy 1989 determined that surface water runoff and stream sediment yield were 56 and 192% higher, respectively, for spotted knapweed-dominated sites compared to bunchgrass-dominated sites. Bareground and water infiltration rates were greater on sites with unclipped bunchgrass than on those with spotted knapweed. Moderate alteration of ecosystem processes by decreasing soil moisture and facilitating erosion.


Sources of information:

Hoffman, Kerns. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants. Pgs 44-47. 1997.
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.
Blicker, P.S., B.E. Olson, and R.Engel. 2002. Traits of the invasive Centaurea maculosa and two native grasses: effect of N supply. Plant and Soil V. 247(2) P. 261-269.
Blicker, P.S., B.E. Olson, and J.M. Wraith. Water use and water-use efficiency of the invasive Centaurea maculosa and three native grasses. Plant and Soil. v. 254(2) p. 371-381.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


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

Spotted knapweed often attains high densities on sunny wild lands, even those undisturbed by human or livestock activitiy. Knapweed thends to dominate sites at the expense of community diversity or forage production. C. maculosa reduces the productivity of desirable forage plants and floristic diversity. It has the ability to invade mature native bunchgrass communities. Decreased bluebunch wheatgrass yield was correlated with increased production of spotted knapweed. Bluebunch wheatgrass-rough fescue production was reduced by 88% by knapweed invasion. Moderate alteration of plant community composition by reduction in survivorship of native grasses


Sources of information:

Hoffman, Kerns. Wisconsin Manual of Control Recommendations for Ecologically Invasive PLants. Pgs. 44-47. 1997.
Blicker, P.S., B.E. Olson, and R.Engel. 2002. Traits of the invasive Centaurea maculosa and two native grasses: effect of N supply. Plant and Soil V. 247(2) P. 261-269.
Lacey, J.R., P. Husby, and G. Handl, Observations on Spotted and Diffuse Knapweed Invasion into Ungrazed Bunchgrass Communities in Western Montana. Rangelands 12 (1). 1990. 30-32.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


Question 1.3 Impact on higher trophic levels? A Reviewed Scientific Publication
Identify type of impact or alteration:

Knapweeds are grazed by dear and sheep. These plants also provide nectar and pollen for domestic bees. Domestic animals and wildlife such as elk rely on range grasses and herbs for up to 80% of diet. Knapweed encroachment can destroy the forage base and would result in a significant decline in deer and elk numbers. Detrimental to range resource values because they have low platability to livestock and wildlife. Spotted knapweed reduces livestock forage and negatively impacts wildlife. Elk use was reduced by 98% on spotted knapweed-dominated range compared to bunchgrass-dominated sites. Spoon 1983 predicted a loss of 220 elk annually in Montana because of spotted knapweed infestations on winter range.


Sources of information:

Knapweed: Its Cost to British Columbia. Pamphlet from Province of British Columbia, Ministry of Agriculture, Fisheries and Food.
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.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


Question 1.4 Impact on genetic integrity? D Other Published Material

none No native Centaurea species in California.


Sources of information:

Hickman, J. (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 Other Published Material
Describe role of disturbance:

Spotted knapweed has invaded relatively undisturbed native plant communities and natural areas as well as heavily disturbed sites. Moderate invasive potential - this species may occasionally establish in undistrubed areas but can readily establish in areas with natural disturbances.


Sources of information:

Hoffman, Kerns. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants. Pgs 44-47. 1997.
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.
Blicker, P.S., B.E. Olson, and R.Engel. 2002. Traits of the invasive Centaurea maculosa and two native grasses: effect of N supply. Plant and Soil V. 247(2) P. 261-269.


Question 2.2 Local rate of spread with no management? A Other Published Material
Describe rate of spread:

Has spread rapidly in most other western states.


Sources of information:

Duncan, C.L. and J.K. Clark (eds.). 2005. Invasive plants of range and wildlands and their environmental, ecological, and societal impacts. WSSA.


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

Through the efforts of CDFA, spotted knapweed populations have remained about stable over the past few years. Without these efforts it is very likely that the infestations would expand exponentially, as they have in so many other states.


Sources of information:

DiTomaso, observational.


Question 2.4 Innate reproductive potential? A Reviewed Scientific Publication
Describe key reproductive characteristics:

Reproduces solely by seed. Individual flower heads bloom from late June through August for 2-6 days each. The bracts reopen after about 20 days and scatter seeds. Plants average about 1,000 seeds per plant. Seeds are viable for seven years, and germinate throughout the growing season. Seed production was 1,000-fold that needed to maintain observed levels of infestation. Lives up to 9 years and is able to produce seeds each year. Seed production of spotted knapweed ranges from 5,000 to 40,000 seeds/m2, with more seeds produced during wet years. High. 7 points


Sources of information:

Hoffman, Kerns. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants. Pgs 44-47. 1997.
Schirman R. Seed Production and Spring Seedling Establishment of Diffuse and spotted Knapweed. Journal of Range Management 34(1). 1981. 45-47.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


Question 2.5 Potential for human-caused dispersal? B Reviewed Scientific Publication
Identify dispersal mechanisms:

People spread knapweed as it is easily caught up and transported great distances in the undercarriage and doors of recreational vehicles, trains, light aircraft landing at infested air strips, logging trucks and heavy machinery. It is also spread by florists who use knapweed in dried floral arrangements, movement of hay from knapweed infested to non-infested areas. Spotted knapweed flower heads also become attached to the undercarriages of vehicles, are transported long distances in mud, and commonly become attached to or drop into shoes. May also be transported in wood brought from Washington for log cabin kits. There are numerous opportunities for dispersal to new areas, but not as high as some other species.


Sources of information:

Knapweed: Its Cost to British Columbia. Pamphlet from Province of British Columbia, Ministry of Agriculture, Fisheries and Food.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


Question 2.6 Potential for natural long-distance dispersal? B Reviewed Scientific Publication
Identify dispersal mechanisms:

Spread by cattle, deer, and elk may pick up the weed and disperse it, and some bird species and small rodents eat knapweed seed. Soil disturbance provides an ideal seedbed for new knapweed infestation. Spotted knapweed plants do not break off at ground level, and populations are largely extended through peripheral enlargement of existing stands. Movement of stem by wind or passing animals can flick the loosely held achenes up to 1 m from the parent plant. Long distance transport occurs when achenes become attached to passing animals, or by rodents and birds. Long-distnace dispersal by animals or abiotic mechanisms can occur but is not the primarily means of dispersal.


Sources of information:

Knapweed: Its Cost to British Columbia. Pamphlet from Province of British Columbia, Ministry of Agriculture, Fisheries and Food.
Sheley, R.L., Jacobs, J.S., Carpinelli M.F., Distribution, Biology and of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa). Weed Technology 12: 353-362. 1998.


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

This plant was probably introduced in the late 1890s as a contaminant in alfalfa or hay seed from Europe and Asia. Spotted knapweed, a native of Europe, was collected on Vancouver Island, British Columbia, in 1905 and San Juan Island, Washington, in 1923. By the 1930s it was common in Montana and northern Idaho.


Sources of information:

Duncan, C.L. and J.K. Clark (eds.). 2005. Invasive plants of range and wildlands and their environmental, ecological, and societal impacts. WSSA.
Hoffman, Kerns. Wisconsin Manual of Control Recommendations for Ecologically Invasive Plants. Pgs 44-47. 1997.


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

Can occur in Great Basin grasslands, foothill prairie, riparian habitats, along gravel bars. Habitats based on review committee observations.


Sources of information:

Duncan, C.L. and J.K. Clark (eds.). 2005. Invasive plants of range and wildlands and their environmental, ecological, and societal impacts. Weed Science Society of America.
Carla Bossard, St. Mary's College; John Randall, The Nature Conservancy; Carri Pirosko, California Dept. of Food and Agriculture, pers. obs.


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

Not commonly encountered because of the efforts of CDFA


Sources of information:

DiTomaso, observational.


Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes
Dense infestations produce >1,000 viable seed per square meter Yes
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: 7
Total unknowns: 1
Total score: A?

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 scrubD, < 5%
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparral
Grasslands, Vernal Pools, Meadows, and other Herb Communitiescoastal prairie
valley and foothill grasslandD, < 5%
Great Basin grasslandD, < 5%
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 woodland
riparian scrub (incl.desert washes)
Woodlandcismontane woodlandD, < 5%
piñon and juniper woodland
Sonoran thorn woodland
Forestbroadleaved upland forest
North Coast coniferous forest
closed cone coniferous forest
lower montane coniferous forestD, < 5%
upper montane coniferous forest
subalpine coniferous forest
Alpine Habitatsalpine boulder and rock field
alpine dwarf scrub
Amplitude (breadth): A
Distribution (highest score): D

Infested Jepson Regions

Click here for a map of Jepson regions