Source: California Invasive Plant Council


URL of this page: http://www.cal-ipc.org/site/paf/295
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Cal-IPC Plant Assessment Form

For use with "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands"
by the California Invasive Plant Council and the Southwest Vegetation Management Association

Table 1. Species and Evaluator Information

Species name
(Latin binomial):
The official Latin binomial name for this species. Specify only one name here. Additional species names may go into the Synonyms field.

Centaurea virgata var. squarrosa

Synonyms:
Additional Latin binomial names for this species. Separate multiple names with a ; character. Please avoid narrative descriptions, and list only the binomial names.
Centaurea squarrosa Willd. is an illegally applied name according to the rules of the International Code of Botanical Nomenclature (Saint Louis Code) since the name Centaurea squarrosa Roth was previously applied to a different species. Centaurea virgata Lam. var. squarrosa (Willd.) Boiss. is a synonym of Centaurea squarrosa Willd. Some taxonomists are using the name C. triumfetti All. for diffuse knapweed. Some flora use C. virgata Lam. ssp. squarrosa (Willd.) Gugler, but the taxon was given variety ranking first.
Common names:
Common names for this species. Separate multiple names with a ; character.
squarrose knapweed
Evaluation date:
The date(s) when this species PAF was filled out, modified, or reviewed. This is free-form text, so it may include multiple dates or other notes.
September 15, 2004
Evaluator #1 Carri Pirosko
California Department of Food and Agriculture, Noxious Weed Program
20235 Charlanne Drive, Redding, CA 96002
(530) 545-9119
cpirosko@cdfa.ca.gov
List committee members: Joe DiTomaso, John Randall, Carla Bossard
Committee review date: 3/11/05
List date:
Re-evaluation date(s):
General comments
on this assessment:
Enter any additional notes about this assessment, such as factors affecting the reliability or completeness of the answers, likely affects of impacts, or research which is not specific to California but is still relevant in the evaluation of this species.

Table 2. Criteria, Section, and Overall Scores

Overall Score

Plant scoring matrix
Based on letter scores from Sections 1 through 3 below

ImpactInvasivenessDistribution
AA BAnyHighNo Alert
AC DAnyModerateAlert
BA BA BModerateNo Alert
BA BC DModerateAlert
BC DAnyLimitedNo Alert
CAA BModerateNo Alert
CAC DLimitedNo Alert
CBAModerateNo Alert
CBB DLimitedNo Alert
CCAnyLimitedNo Alert
DAnyAnyNot ListedNo Alert

Moderate

Alert Status

Plant scoring matrix
Based on letter scores from Sections 1 through 3 below

ImpactInvasivenessDistributionAlert
AA or BC or DAlert
BA or BC or DAlert

No Alert

Documentation

The total documentation score is the average
of Documentation scores given in Table 2.

Reviewed Scientific Publication4 points
Other Published Material3 points
Observational2 points
Anecdotal1 points
Unknown or No Information0 points

3.5 out of 5

Score Documentation
1.1 Impact on abiotic ecosystem processes
Consider the impact on the natural range and variation of abiotic ecosystem processes and system-wide parameters in ways that significantly diminish the ability of native species to survive and reproduce. Alterations that determine the types of communities that can exist in a given area are of greatest concern. Examples of abiotic processes include:
- fire occurrence, frequency, and intensity;
- geomorphological changes such as erosion and sedimentation rates;
- hydrological regimes, including soil water table;
- nutrient and mineral dynamics, including salinity, alkalinity, and pH;
- light availability (e.g. when an aquatic invader covers an entire water body that would otherwise be open).

Select the one letter below that best describes this species’ most severe impact on an abiotic ecosystem process:
A. Severe, possibly irreversible, alteration or disruption of an ecosystem process.
B. Moderate alteration of an ecosystem process.
C. Minor alteration of an ecosystem process.
D. Negligible perceived impact on an ecosystem process.
U. Unknown.
B. Moderate Reviewed Scientific Publication
Impact
Section 1 Scoring Matrix
Q 1.1Q 1.2Q 1.3Q 1.4Score
AAAnyAnyA
ABA,BAnyA
ABC,D,UAnyB
AC,D,UAnyAnyB
BAAAnyA
BABAA
BAB,CB-D,UB
BAC,D,UAA
BAC,D,UB-D,UB
BBAAA
BC,D,UAAB
BB-DAB-D,UB
BB-DB-D,UAnyB
BD,UC,D,UA-BB
BD,UC,D,UC,D,UC
C-D,UAAAnyA
CBAAnyB
CA,BB-D,UAnyB
CC,D,UAnyAnyC
DA,BBAnyB
DA,BC,D,UAnyC
DCAnyAnyC
DD,UAnyAnyD
UAB,CAnyB
UB,CA,BAnyB
UB,CC,D,UAnyC
UUAnyAnyU


Four-part score
BBBD

Total Score
B
1.2 Impact on plant community
Consider the cumulative ecological impact of this species to the plant communities it invades. Give more weight to changes in plant composition, structure, and interactions that involve rare or keystone species or rare community types. Examples of severe impacts include:
- formation of stands dominated (>75% cover) by the species;
- occlusion (>75% cover) of a native canopy, including a water surface, that eliminates or degrades layers below;
- significant reduction or extirpation of populations of one or more native species.

Examples of impacts usually less than severe include:
- reduction in propagule dispersal, seedling recruitment, or survivorship of native species;
- creation of a new structural layer, including substantial thatch or litter, without elimination or replacement of a pre-existing layer;
- change in density or depth of a structural layer;
- change in horizontal distribution patterns or fragmentation of a native community;
- creation of a vector or intermediate host of pests or pathogens that infect native plant species.

Select the one letter below that best describes this species’ impact on community composition, structure and interactions:
A. Severe alteration of plant community composition, structure, or interactions.
B. Moderate alteration of plant community composition.
C. Minor alteration of community composition.
D. Negligible impact known; causes no perceivable change in community composition, structure, or interactions.
U. Unknown.
B. Moderate Other Published Material
1.3 Impact on higher trophic levels
Consider the cumulative impact of this species on the animals, fungi, microbes, and other organisms in the communities that it invades. Although a non-native species may provide resources for one or a few native species (e.g. by providing food, nesting sites, etc.), the ranking should be based on the species’ net impact on all native species. Give more weight to changes in composition and interactions involving rare or keystone species or rare community types.
Examples of severe impacts include:
- extirpation or endangerment of an existing native species or population;
- elimination or significant reduction in native species’ nesting or foraging sites, cover, or other critical resources (i.e., native species habitat), including migratory corridors.

Examples of impacts that are usually less than severe include:
- minor reduction in nesting or foraging sites, cover, etc. for native animals;
- minor reduction in habitat connectivity or migratory corridors;
- interference with native pollinators;
- injurious components, such as awns or spines that damage the mouth and gut of native wildlife species, or production of anti-digestive or acutely toxic chemical that can poison native wildlife species.

Select the one letter below that best describes this species’ impact on community composition and interactions:
A. Severe alteration of higher trophic populations, communities, or interactions.
B. Moderate alteration of higher trophic level populations, communities, or interactions.
C. Minor alteration of higher trophic level populations, communities or interactions.
D. Negligible impact; causes no perceivable change in higher trophic level populations, communities, or interactions.
E. Unknown.
B. Moderate Reviewed Scientific Publication
1.4 Impact on genetic integrity
Consider whether the species can hybridize with and influence the proportion of individuals with non-native genes within populations of native species. Mechanisms and possible outcomes include:
- production of fertile or sterile hybrids that can outcompete the native species;
- production of sterile hybrids that lower the reproductive output of the native species.

Select the one letter below that best describes this species’ impact on genetic integrity:
A. Severe (high proportion of individuals).
B. Moderate (medium proportion of individuals).
C. Minor (low proportion of individuals).
D. No known hybridization.
U. Unknown.
D. None Observational
2.1 Role of anthropogenic and natural disturbance in establishment
Assess this species’ dependence on disturbance—both human and natural—for establishment in wildlands. Examples of anthropogenic disturbances include:
- grazing, browsing, and rooting by domestic livestock and feral animals;
- altered fire regimes, including fire suppression;
- cultivation;
- silvicultural practices;
- altered hydrology due to dams, diversions, irrigation, etc.;
- roads and trails;
- construction;
- nutrient loading from fertilizers, runoff, etc.

Examples of natural disturbance include:
- wildfire;
- floods;
- landslides;
- windthrow;
- native animal activities such as burrowing, grazing, or browsing.

Select the first letter in the sequence below that describes the ability of this species to invade wildlands:
A. Severe invasive potential—this species can establish independent of any known natural or anthropogenic disturbance.
B. Moderate invasive potential—this species may occasionally establish in undisturbed areas but can readily establish in areas with natural disturbances.
C. Low invasive potential—this species requires anthropogenic disturbance to establish.
D. No perceptible invasive potential—this species does not establish in wildlands (though it may persist from former cultivation).
U. Unknown.
B. Moderate Reviewed Scientific Publication
Invasiveness
Section 2 Scoring Matrix
Total pointsScore
17-21A
11-16B
5-10C
0-4D
More than two U’sU


Total Points
14

Total Score
B
2.2 Local rate of spread with no management
Assess this species’ rate of spread in existing localized infestations where the proportion of available habitat invaded is still small when no management measures are implemented.

Select the one letter below that best describes the rate of spread:
A. Increases rapidly (doubling in <10 years)
B. Increases, but less rapidly
C. Stable
D. Declining
U. Unknown
B. Increases less rapidly Observational
2.3 Recent trend in total area infested within state
Assess the overall trend in the total area infested by this species statewide. Include current management efforts in this assessment and note them.

Select the one letter below that best describes the current trend:
A. Increasing rapidly (doubling in total range statewide in <10 years)
B. Increasing, but less rapidly
C. Stable
D. Declining
U. Unknown
B. Increasing less rapidly Other Published Material
2.4 Innate reproductive potential
(see Worksheet A)
Assess the innate reproductive potential of this species. Worksheet A is provided for computing the score.
A. High Reviewed Scientific Publication
2.5 Potential for human-caused dispersal
Assess whether this species is currently spread—or has high potential to be spread—by direct or indirect human activity. Such activity may enable the species to overcome natural barriers to dispersal that would not be crossed otherwise, or it may simply increase the natural dispersal of the species. Possible mechanisms for dispersal include:
- commercial sales for use in agriculture, ornamental horticulture, or aquariums;
- use as forage, erosion control, or revegetation;
- presence as a contaminant (seeds or propagules) in bulk seed, hay, feed, soil, packing materials, etc.;
- spread along transportation corridors such as highways, railroads, trails, or canals;
- transport on boats or boat trailers.

Select the one letter below that best describes human-caused dispersal and spread:
A. High—there are numerous opportunities for dispersal to new areas.
B. Moderate—human dispersal occurs, but not at a high level.
C. Low—human dispersal is infrequent or inefficient.
D. Does not occur.
U. Unknown.
B. Moderate Reviewed Scientific Publication
2.6 Potential for natural long-distance dispersal
We have chosen 1 km as the threshold of "long-distance." Assess whether this species is frequently spread, or has high potential to be spread, by animals or abiotic mechanisms that can move seed, roots, stems, or other propagules this far. The following are examples of such natural long-distance dispersal mechanisms:
- the species’ fruit or seed is commonly consumed by birds or other animals that travel long distances;
- the species’ fruits or seeds are sticky or burred and cling to feathers or hair of animals;
- the species has buoyant fruits, seeds, or other propagules that are dispersed by flowing water;
- the species has light propagules that promote long-distance wind dispersal;
- The species, or parts of it, can detach and disperse seeds as they are blown long distances (e.g., tumbleweed).

Select the one letter below that best describes natural long-distance dispersal and spread:
A. Frequent long-distance dispersal by animals or abiotic mechanisms.
B. Occasional long-distance dispersal by animals or abiotic mechanisms.
C. Rare dispersal more than 1 km by animals or abiotic mechanisms.
D. No dispersal of more than 1 km by animals or abiotic mechanisms.
U. Unknown.
B. Occasional Reviewed Scientific Publication
2.7 Other regions invaded
Assess whether this species has invaded ecological types in other states or countries outside its native range that are analogous to ecological types not yet invaded in your state (see Worksheets B, C, and D for California, Arizona, and Nevada, respectively, in Part IV for lists of ecological types). This information is useful in predicting the likelihood of further spread within your state.

Select the one letter below that best describes the species' invasiveness in other states or countries, outside its native range.
A. This species has invaded 3 or more ecological types elsewhere that exist in your state and are as yet not invaded by this species (e.g. it has invaded Mediterranean grasslands, savanna, and maquis in southern Europe, which are analogous to California grasslands, savanna, and chaparral, respectively).
B. Invades 1 or 2 ecological types that exist but are not yet invaded in your state.
C. Invades elsewhere but only in ecological types that it has already invaded in the state.
D. Not known as an escape anywhere else.
U. Unknown.
C. Already invaded Reviewed Scientific Publication
3.1 Ecological amplitude/Range
(see Worksheet C)
Refer to Worksheet C and select the one letter below that indicates the number of different ecological types that this species invades.
A. Widespread—the species invades at least three major types or at least six minor types.
B. Moderate—the species invades two major types or five minor types.
C. Limited—the species invades only one major type and two to four minor types.
D. Narrow—the species invades only one minor type.
U. Unknown.
A. Widespread Reviewed Scientific Publication
Distribution
Section 3 Scoring Matrix
Q 3.1Q 3.2Score
AA, BA
AC,D,UB
BAA
BB,CB
BDC
CA,BB
CC,DC
DAB
DB,CC
DDD
A,BUC
C,DUD
UUU


Total Score
B
3.2 Distribution/Peak frequency
(see Worksheet C)
To assess distribution, record the letter that corresponds to the highest percent infested score entered in Worksheet C for any ecological type.
C. Low Reviewed Scientific Publication

Table 3. Documentation

Scores are explained in the "Criteria for Categorizing Invasive Non-Native Plants that Threaten Wildlands".
Short citations may be used in this table. List full citations at end of this table.

Section 1: Impact

Reviewed Scientific Publication B Question 1.1 Impact on abiotic ecosystem processes
Consider the impact on the natural range and variation of abiotic ecosystem processes and system-wide parameters in ways that significantly diminish the ability of native species to survive and reproduce. Alterations that determine the types of communities that can exist in a given area are of greatest concern. Examples of abiotic processes include:
- fire occurrence, frequency, and intensity;
- geomorphological changes such as erosion and sedimentation rates;
- hydrological regimes, including soil water table;
- nutrient and mineral dynamics, including salinity, alkalinity, and pH;
- light availability (e.g. when an aquatic invader covers an entire water body that would otherwise be open).

Select the one letter below that best describes this species’ most severe impact on an abiotic ecosystem process:
A. Severe, possibly irreversible, alteration or disruption of an ecosystem process.
B. Moderate alteration of an ecosystem process.
C. Minor alteration of an ecosystem process.
D. Negligible perceived impact on an ecosystem process.
U. Unknown.
Identify ecosystem processes impacted:
light availability is impacted in dense stands of squarrose knapweed- this is the only plant in stands that reach monotypic levels It is suspected that available water in the rangeland profile is severely reduced by dense stands of squarrose knapweed, based on findings with yellow starthistle in similar rangeland settings. The success of Centaurea species in dominating grasslands is explained by their ability to compete successfully for the new limiting resource or resources (K.D. LeJeune et al.) Wildfires create the ideal conditions for rapid expansion. Squarrose knapweed's fire and drought tolerance, excellent seed dispersal, and rapid response to soil resources released by fire nearly guarantee spread into burned closed-canopy juniper sites with little understory.

Sources of information:
C. Pirosko, personal observation. LeJeune, Katherine D., Seastedt, Timothy R. 2001. Centaurea species: The forb that won the west. Conservation Biology. 15(6). December: 1568-1574. Sheley and Petroff. Biology and Management of Noxious Rangeland Weeds.

Other Published Material B Question 1.2 Impact on plant community composition,
structure, and interactions
Consider the cumulative ecological impact of this species to the plant communities it invades. Give more weight to changes in plant composition, structure, and interactions that involve rare or keystone species or rare community types. Examples of severe impacts include:
- formation of stands dominated (>75% cover) by the species;
- occlusion (>75% cover) of a native canopy, including a water surface, that eliminates or degrades layers below;
- significant reduction or extirpation of populations of one or more native species.

Examples of impacts usually less than severe include:
- reduction in propagule dispersal, seedling recruitment, or survivorship of native species;
- creation of a new structural layer, including substantial thatch or litter, without elimination or replacement of a pre-existing layer;
- change in density or depth of a structural layer;
- change in horizontal distribution patterns or fragmentation of a native community;
- creation of a vector or intermediate host of pests or pathogens that infect native plant species.

Select the one letter below that best describes this species’ impact on community composition, structure and interactions:
A. Severe alteration of plant community composition, structure, or interactions.
B. Moderate alteration of plant community composition.
C. Minor alteration of community composition.
D. Negligible impact known; causes no perceivable change in community composition, structure, or interactions.
U. Unknown.
Identify type of impact or alteration:
Formation of dense stands dominate >75% cover by squarrose knapweed, with remaining cover being bare ground. Dense stands build up over time and alter plant community structure and composition. May have allelopathic properties, as other knapweeds (spotted and Russian) do allowing other vegetation to be excluded.

Sources of information:
J. DiTomaso and E. Healy, Weeds of California and Other Western States, as yet unpublished. C. Pirosko personal observation.

Reviewed Scientific Publication B Question 1.3 Impact on higher trophic levels
Consider the cumulative impact of this species on the animals, fungi, microbes, and other organisms in the communities that it invades. Although a non-native species may provide resources for one or a few native species (e.g. by providing food, nesting sites, etc.), the ranking should be based on the species’ net impact on all native species. Give more weight to changes in composition and interactions involving rare or keystone species or rare community types.
Examples of severe impacts include:
- extirpation or endangerment of an existing native species or population;
- elimination or significant reduction in native species’ nesting or foraging sites, cover, or other critical resources (i.e., native species habitat), including migratory corridors.

Examples of impacts that are usually less than severe include:
- minor reduction in nesting or foraging sites, cover, etc. for native animals;
- minor reduction in habitat connectivity or migratory corridors;
- interference with native pollinators;
- injurious components, such as awns or spines that damage the mouth and gut of native wildlife species, or production of anti-digestive or acutely toxic chemical that can poison native wildlife species.

Select the one letter below that best describes this species’ impact on community composition and interactions:
A. Severe alteration of higher trophic populations, communities, or interactions.
B. Moderate alteration of higher trophic level populations, communities, or interactions.
C. Minor alteration of higher trophic level populations, communities or interactions.
D. Negligible impact; causes no perceivable change in higher trophic level populations, communities, or interactions.
E. Unknown.
Identify type of impact or alteration:
Dense stands impact bird and wildlife, as well as range animal use of the system. Highly competative, dense stands can exclude desirable vegetation and wildlife in natural areas

Sources of information:
J. DiTomaso and E. Healy, Weeds of California, as yet unpublished. Sheley, R. L, and J. K. Petroff. 1999. Biology and Management of Noxious Rangeland Weeds. Oregon State University Press, Corvallis, OR

Observational D Question 1.4 Impact on genetic integrity
Consider whether the species can hybridize with and influence the proportion of individuals with non-native genes within populations of native species. Mechanisms and possible outcomes include:
- production of fertile or sterile hybrids that can outcompete the native species;
- production of sterile hybrids that lower the reproductive output of the native species.

Select the one letter below that best describes this species’ impact on genetic integrity:
A. Severe (high proportion of individuals).
B. Moderate (medium proportion of individuals).
C. Minor (low proportion of individuals).
D. No known hybridization.
U. Unknown.
Identify impacts:
No information found as to impacts within populations of native species. Suspected that crossing does occur with other non-native knapweeds- as specimens are found with characteristics of squarrose, spotted, and diffuse knapweeds.

Sources of information:
C. Pirosko, personal observation.

Section 2: Invasiveness

Reviewed Scientific Publication B Question 2.1 Role of anthropogenic and natural disturbance
in establishment
Assess this species’ dependence on disturbance—both human and natural—for establishment in wildlands. Examples of anthropogenic disturbances include:
- grazing, browsing, and rooting by domestic livestock and feral animals;
- altered fire regimes, including fire suppression;
- cultivation;
- silvicultural practices;
- altered hydrology due to dams, diversions, irrigation, etc.;
- roads and trails;
- construction;
- nutrient loading from fertilizers, runoff, etc.

Examples of natural disturbance include:
- wildfire;
- floods;
- landslides;
- windthrow;
- native animal activities such as burrowing, grazing, or browsing.

Select the first letter in the sequence below that describes the ability of this species to invade wildlands:
A. Severe invasive potential—this species can establish independent of any known natural or anthropogenic disturbance.
B. Moderate invasive potential—this species may occasionally establish in undisturbed areas but can readily establish in areas with natural disturbances.
C. Low invasive potential—this species requires anthropogenic disturbance to establish.
D. No perceptible invasive potential—this species does not establish in wildlands (though it may persist from former cultivation).
U. Unknown.
Describe role of disturbance:
Largely invades disturbed sites. Largely dependant on human disturbances such as: over grazing, logging/replanting activities, roadside maintenance/scraping, roads and trails. Dispersal by vehicles and trains appears increasingly important, judging by the expansion of squarrose knapweed along roads, railroads, and off-road vehicles. Often grows on degraded rangeland soils and is more adaptable to drought and cold temperatures than other knapweeds.

Sources of information:
J. DiTomaso and E. Healy, Weeds of California, as yet unpublished. Sheley and Petroff. Biology and Management of Noxious Rangeland Weeds.

Observational B Question 2.2 Local rate of spread with no management
Assess this species’ rate of spread in existing localized infestations where the proportion of available habitat invaded is still small when no management measures are implemented.

Select the one letter below that best describes the rate of spread:
A. Increases rapidly (doubling in <10 years)
B. Increases, but less rapidly
C. Stable
D. Declining
U. Unknown
Describe rate of spread:
Rate of spread is slow and steady within sites- gradually expands at the edges of the populations over time. Spread in the Big Valley area of Lassen County is the best documentation of spread. Since 1950 when the plant was first officially documented (infestation likely had been there since 1930-40's), the infestation has slowly crept along roadways, from ranch to ranch on equipment and sheep. So that today extensions of the original infestation spread up into the forest behind the Kramer Ranch in Big Valley, up into Lookout, Modoc County, and down all the way into Pittville area to the southeast of Big Valley.

Sources of information:
personal observation, C. Pirosko California Department of Food and Agriculture. Internal Document (typed document from 1973, author unknown), California Department of Food and Agriculture, Integrated Pest Control Branch, Noxious Weed Program, Redding Field Office.

Other Published Material B Question 2.3 Recent trend in total area infested within state
Assess the overall trend in the total area infested by this species statewide. Include current management efforts in this assessment and note them.

Select the one letter below that best describes the current trend:
A. Increasing rapidly (doubling in total range statewide in <10 years)
B. Increasing, but less rapidly
C. Stable
D. Declining
U. Unknown
Describe trend:
Not widely distributed throughout the State. Primarily has been isolated to the Great Basin area in northeastern California. Rate of spread is slow and steady. Spread in the Big Valley area of Lassen County is the best documentation of spread. Since 1950 when the plant was first officially documented (infestation likely had been there since 1930-40's), the infestation has slowly crept along roadways, from ranch to ranch on equipment and sheep. So that today extensions of the original infestation spread up into the forest behind the Kramer Ranch in Big Valley, up into Lookout, Modoc County, and down all the way into Pittville area to the southeast of Big Valley.

Sources of information:
personal observation, C. Pirosko California Department of Food and Agriculture. Internal Document (typed document from 1973, author unknown), California Department of Food and Agriculture, Integrated Pest Control Branch, Noxious Weed Program, Redding Field Office.

Reviewed Scientific Publication A Question 2.4 Innate reproductive potential
Assess the innate reproductive potential of this species. Worksheet A is provided for computing the score.
Describe key reproductive characteristics:
Can reach reproductive maturity in less than one year (goes from rosette to seeding plant with one little wimpy flowering stalk). Number of seeds are 2-8 per seed head, certainly less than other knapweeds, however the number of squarrose knapeed seed heads per plant is large. Long-lived perennial with deep roots and stout crown; squarrose knapweed can endure drought at either temperature extreme, and does not depend on annual seed production nor frequent seedling success to maintain it populations. Forms multiple rosettes from a single taproot Resprouts very easily after mowed, chopped, cut at ground surface or even with some underground root material removed- must get all of the root to avoid resprouting.

Sources of information:
Sheley and Petroff. Biology and Management of Noxious Rangeland Weeds. C. Pirosko personal observation.

Reviewed Scientific Publication B Question 2.5 Potential for human-caused dispersal
Assess whether this species is currently spread—or has high potential to be spread—by direct or indirect human activity. Such activity may enable the species to overcome natural barriers to dispersal that would not be crossed otherwise, or it may simply increase the natural dispersal of the species. Possible mechanisms for dispersal include:
- commercial sales for use in agriculture, ornamental horticulture, or aquariums;
- use as forage, erosion control, or revegetation;
- presence as a contaminant (seeds or propagules) in bulk seed, hay, feed, soil, packing materials, etc.;
- spread along transportation corridors such as highways, railroads, trails, or canals;
- transport on boats or boat trailers.

Select the one letter below that best describes human-caused dispersal and spread:
A. High—there are numerous opportunities for dispersal to new areas.
B. Moderate—human dispersal occurs, but not at a high level.
C. Low—human dispersal is infrequent or inefficient.
D. Does not occur.
U. Unknown.
Identify dispersal mechanisms:
Primarily Human caused. Long distance dispersal is primarily through sheep. The recurved spines of squarrose knapweed are ideally suited to transport by sheep's wool. Historically, most of the movement of squarrose knapweed has been associated with sheep. No reference has been found regarding the initial introduction of squarrose knapweed into the western U.S., but it is possible that seed was carried in wool, either of sheep or wool products, yarn, blankets, or clothing. Often grows on degraded rangeland soils and is more adaptable to drought and cold temperatures than other knapweeds. Roadside equipment, scraping of road shoulders by CalTrans and County Road departments is also a mode of long distance dispersal along roadways.

Sources of information:
Bellue, M. K. 1952. Virgate Star Thistle, Centaurea virgata var. squarrosa (Willd.) Boiss. in California. Bulletin, California Dept. of Agriculture. Vol. 41(2): 61-63. J. DiTomaso and E. Healy, Weeds of California, as yet unpublished. C. Pirosko, personal observation.

Reviewed Scientific Publication B Question 2.6 Potential for natural long-distance dispersal
We have chosen 1 km as the threshold of "long-distance." Assess whether this species is frequently spread, or has high potential to be spread, by animals or abiotic mechanisms that can move seed, roots, stems, or other propagules this far. The following are examples of such natural long-distance dispersal mechanisms:
- the species’ fruit or seed is commonly consumed by birds or other animals that travel long distances;
- the species’ fruits or seeds are sticky or burred and cling to feathers or hair of animals;
- the species has buoyant fruits, seeds, or other propagules that are dispersed by flowing water;
- the species has light propagules that promote long-distance wind dispersal;
- The species, or parts of it, can detach and disperse seeds as they are blown long distances (e.g., tumbleweed).

Select the one letter below that best describes natural long-distance dispersal and spread:
A. Frequent long-distance dispersal by animals or abiotic mechanisms.
B. Occasional long-distance dispersal by animals or abiotic mechanisms.
C. Rare dispersal more than 1 km by animals or abiotic mechanisms.
D. No dispersal of more than 1 km by animals or abiotic mechanisms.
U. Unknown.
Identify dispersal mechanisms:
Primarily Human caused. The highly deciduous nature of the seed heads could lend itself to distribution through wind and water and/or through the fur of wildlife and birds.

Sources of information:
Bellue, M. K. 1952. Virgate Star Thistle, Centaurea virgata var. squarrosa (Willd.) Boiss. in California. Bulletin, California Dept. of Agriculture. Vol. 41(2): 61-63. C. Pirosko, personal observation.

Reviewed Scientific Publication C Question 2.7 Other regions invaded
Assess whether this species has invaded ecological types in other states or countries outside its native range that are analogous to ecological types not yet invaded in your state (see Worksheets B, C, and D for California, Arizona, and Nevada, respectively, in Part IV for lists of ecological types). This information is useful in predicting the likelihood of further spread within your state.

Select the one letter below that best describes the species' invasiveness in other states or countries, outside its native range.
A. This species has invaded 3 or more ecological types elsewhere that exist in your state and are as yet not invaded by this species (e.g. it has invaded Mediterranean grasslands, savanna, and maquis in southern Europe, which are analogous to California grasslands, savanna, and chaparral, respectively).
B. Invades 1 or 2 ecological types that exist but are not yet invaded in your state.
C. Invades elsewhere but only in ecological types that it has already invaded in the state.
D. Not known as an escape anywhere else.
U. Unknown.
Identify other regions:
Utah, Oregon, Washington, Nevada, Michigan Primarily invades range and pasture lands, as well as along roadsides. Often grows on degraded rangeland soils and is more adaptable to drought and cold temperatures than other knapweeds. Native to Eastern Europe, Southern Russia, and Western Asia--- The climate of these native ranges are very similar to that of the Great Basin found in northeastern California, Eastern Oregon, and parts of Utah. Squarrose knapweed is native to Bulgaria, Lebanon, Anti-Lebanon, Transcaucasia, northern Iraq, Iran, Afghanistan, and Turkestan. In the Flora of Turkey, the U.S. specimens key to subspecies squarrosa of Centaurea virgata, which is found mainly in Inner Anatolia; much of the plateau of Inner Anatolia lies between 2,500 and 3,300 feet elevation, falling to a large salt lake in the center. The climate in that region is harsh, characterized by erratic precipitation, temperature extremes, wind and devastating hail storms. Precipitation primarily falls as snow in the winter and spring; summers are dry with very low humidity; Winter temperatures are lower than Mediterranean climates and in summer temperatures soar during the day and drop drastically at night. (NOTE: A PERFECT DESCRIPTION OF BIG VALLY, LASSEN COUNTY, CA, USA as well!) Squarrose knapweed is a threat to similar ecological types already invaded; similar great basin-like habitat found in eastern portions of the state; Could still invade range and pasture lands south of Lassen County, into regions along the California/Nevada Border. STILL VAST OPPORTUNITY to keep spreading in areas already invaded, expansion of current distribution. PLUS lots of range/pasture in the GREAT BASIN is still susceptible to invasion which would have significant impacts on productivity of these lands. Squarrose knapweed simply hasn't been introduced in these suceptible areas- if given the opportunity, squarrose knapweed could do more damage to northeastern rangelands.

Sources of information:
Internal Document (typed document from 1973, author unknown), California Department of Food and Agriculture, Integrated Pest Control Branch, Noxious Weed Program, Redding Field Office. J. DiTomaso and E. Healy, Weeds of California, as yet unpublished. Sheley and Petroff. Biology and Management of Noxious Rangeland Weeds.

Section 3: Distribution

Reviewed Scientific Publication A Question 3.1 Ecological amplitude/Range
Refer to Worksheet C and select the one letter below that indicates the number of different ecological types that this species invades.
A. Widespread—the species invades at least three major types or at least six minor types.
B. Moderate—the species invades two major types or five minor types.
C. Limited—the species invades only one major type and two to four minor types.
D. Narrow—the species invades only one minor type.
U. Unknown.
Describe ecological amplitude, identifying date of source information and approximate date of introduction to the state, if known:
In northern California, squarrose knapweed grows on dry rocky sites of degraded juniper-shrub savanna with scattered western juniper and poderosa pine and chaparral-type understory (Sheley and Petroff) In the Great Basin and intermountain foothills, the sagebrush and juniper range types appear to be the most susceptible to invasion by squarrose knapweed. Often grows on degraded rangeland soils and is more adaptable to drought and cold temperatures than other knapweeds. First official record was in 1950; this species was collected at the Kramer Ranch in Big Valley, Lassen County by Loring White and identified by J.T. Howell of the Academy of Sciences, and subsequently identified by Dr. S.F. Blake of the USDA. Prior to 1910 there is no information about this ranch on which the sample was collected. After 1910 records indicate that the ranch was rented out as sheep pasture and under lease to neighboring rancher, James Summers. This site was then used as an overnight campground by sheepmen when they trailed their bands of sheep from the Sacramento Valley to higher ranges in the summer and returned them in the fall. In 1935 Mr. Summers reported to have commented on a weed taking over his leased pasture. About 1944 Mr. Rupert Lyons purchased the property and found a heavy infestation of the weed. Mr Lyons sold the land to Mr. O.E. Brown, whose son collected the specimen identified in 1950. Squarrose knapweed has largely Squarrose knapweed is a threat to similar ecological types already invaded; similar great basin-like habitat found in eastern portions of the state; Could still invade range and pasture lands south of Lassen County, into regions along the California/Nevada Border. STILL VAST OPPORTUNITY to keep spreading in areas already invaded, expansion of current distribution. PLUS lots of range/pasture in the GREAT BASIN is still susceptible to invasion which would have significant impacts on productivity of these lands. Squarrose knapweed simply hasn't been introduced in these suceptible areas- if given the opportunity, squarrose knapweed could do more damage to northeastern rangelands.

Sources of information:
Internal Document (typed document from 1973, author unknown), California Department of Food and Agriculture, Integrated Pest Control Branch, Noxious Weed Program, Redding Field Office; C. Pirosko personal observation. J. DiTomaso and E. Healy, Weeds of California, as yet unpublished. Sheley and Petroff. Biology and Management of Noxious Rangeland Weeds.

Reviewed Scientific Publication C Question 3.2 Distribution/Peak frequency
To assess distribution, record the letter that corresponds to the highest percent infested score entered in Worksheet C for any ecological type.
Describe distribution:
Klamath Ranges (n Humboldt, c Siskiyou, ce Trinity cos.), Cascade Range (Shasta Co.), Modoc Plateau (Modoc, ne Lassen cos.), northern Sierra Nevada (nc Plumas Co., to 1400 m. Present distribution in California: Lassen, Modoc, Siskiyou, and Shasta Counties. The major infestation is in Big Valley, Lassen County. The Modoc infestation is in the area of Lookout and Lookout Junction- are really extensions of the Big Valley infestation. Also found in the Pittville Area, also an extension of the Big Valley infestation. In Shasta County squarrose knapweed has been found on several ranches. The largest infestations are at the Bidwell Ranch (between Fall River Mills and Cassel), Kane Ranch (Off highway 89, north of the town of Hat Creek), on USFS lands on Brush Mountain, on Pit River Tribe lands called "Charlie Bone" off Highway 89, again north of town of Hat Creek, in and around Burney High School, and the PGE Right of Way off Mountain View Road, past Burney High School. Squarrose knapweed is a common find along the roadways- 299, 89, and 44 in Shasta County. A large site known as "Hawkensville" in Siskiyou county was under containment for over 30 years, until the late 1990s with Weed Management Area funding the site was aggressively treated. This Siskiyou site has been significantly reduced, follow-up spot treatments are ongoing until it is eradicated. The above mentioned sites are the primary active sites in the state, isolated, single plant finds have been found in other counties throughout the state- these have been eradicated by California Department of Food and Agriculture, Noxious Weed Program. Areas similar to Great Basin are vulnerable to invasion (HOT summers, Snow in Winters); certainly there is room for lots more invasion in the northeastern counties, as well as Nevada/California boarder counties.

Sources of information:
Internal Document (typed document from 1973, author unknown), California Department of Food and Agriculture, Integrated Pest Control Branch, Noxious Weed Program, Redding Field Office. J. DiTomaso and E. Healy, Weeds of California, as yet unpublished.

Worksheet A - Innate reproductive potential

Reaches reproductive maturity in 2 years or less Yes, 1 points
Dense infestations produce >1,000 viable seed per square meter Yes, 2 points
Populations of this species produce seeds every year. Yes, 1 points
Seed production sustained over 3 or more months within a population annually Yes, 1 points
Seeds remain viable in soil for three or more years Yes, 2 points
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, 1 points
Total points: 8
Total unknowns: 1
Total score: A
Scoring Criteria for Worksheet A
A. High reproductive potential (6 or more points).
B. Moderate reproductive potential (4-5 points).
C. Low reproductive potential (3 points or less and less than 3 Unknowns).
U. Unknown (3 or fewer points and 3 or more Unknowns).
Note any related traits:
Return to Table 2

Worksheet B - Arizona Ecological Types is not included here


Worksheet C - California Ecological Types
 
(sensu Holland 1986)

Major Ecological Types Minor Ecological Types Code
A means >50% of type occurrences are invaded;
B means >20% to 50%;
C means >5% to 20%;
D means present but ≤5%;
U means unknown (unable to estimate percentage of occurrences invaded)
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 scrubC. 5% - 20%
chenopod scrub
montane dwarf scrub
Upper Sonoran subshrub scrub
chaparralD. < 5%
Grasslands, Vernal Pools, coastal prairie
Meadows, and other Herbvalley and foothill grassland
CommunitiesGreat Basin grasslandC. 5% - 20%
vernal pool
meadow and seep
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swamp
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)
Woodlandcismontane woodland
piñon and juniper woodlandD. < 5%
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)  
Distribution (highest score)  
Return to Table 2

Addendum J - Jepson Regions Infested
 
Click here for a map of Jepson regions

Infested Jepson Regions:
Check the boxes to indicate the Jepson floristic provinces in which this species is found.














Addendum L - External Links & Resources

Cal-IPC Plant Profile
The Cal-IPC Plant Profile for this species.
http://www.cal-ipc.org/ip/management/plant_profiles/Centaurea_virgata.php
Calflora Plant Profile:
The Calflora Plant Profile for this species.
http://www.calflora.org/cgi-bin/species_query.cgi?where-calrecnum=1854
CalWeedMapper:
Load CalWeedMapper with this species already selected.
http://calweedmapper.cal-ipc.org/maps/?species=62