Stipa tenuissima Risk Assessment

Common names: Mexican feathergrass

Stipa tenuissima -- California

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Evaluation Summary
Summary: 
General Evaluation Information
Date of Evaluation: 
July 2, 2015
Evaluation Time (hrs): 
4 Hours
Evaluation Status: 
Completed
Plant Information
Plant Material: 
If the plant is a cultivar, and if the cultivar's behavior differs from its parent's (behavior), explain how: 
Regional Information
Region Name: 
Climate Matching Map
These maps were built using a toolkit created in collaboration between GreenInfo Network, PlantRight, Cal-IPC, and Agricultural Sustainability Institute at UC Davis.
Climate Matching Maps PDF: 
Invasive History and Climate Matching
1. Has the species (or cultivar or variety, if applicable; applies to subsequent "species" questions) become naturalized where it is not native?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima It is known to have naturalised in California, New Zealand and South Africa. In 2004, S. tenuissima was found naturalised in northern New South Wales, Australia – a mere eight years between its initial sale and naturalisation (High Risk Weeds in the Sydney & Blue Mountains region). Note, Jepson Manual for California only lists this as a waif (Jepson).
Reference(s): 
2. Is the species (or cultivar or variety) noted as being naturalized in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
S. tenuissima is known to have naturalised in California, New Zealand and South Africa. In 2004, S. tenuissima was found naturalised in northern New South Wales, Australia – a mere eight years between its initial sale and naturalisation (High Risk Weeds in the Sydney & Blue Mountains region). High climate overlap with California (Cal-IPC).
Reference(s): 
3. Is the species (or cultivar or variety) noted as being invasive in the U.S. or world?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
High
Answer / Justification: 
S. tenuissima has been noted as invasive in Australia, New Zealand, and the United States (High Risk Weeds in the Sydney & Blue Mountains region).
Reference(s): 
4. Is the species (or cultivar or variety) noted as being invasive in the US or world in a similar climate?
Yes or No: 
Yes
Points: 
3
Confidence Level: 
Very High
Answer / Justification: 
S. tenuissima is a drought-tolerant grass that is noted as invasive in New Zealand and Australia (Nassella tenuissima (grass)), and occurs in similar climates and regions in California, including agricultural areas, natural forests, rangelands and grasslands, riparian zones, ruderal and disturbed areas, and scrub and shrublands (High Risk Weeds in the Sydney & Blue Mountains region). High climate overlap with California (Cal-IPC).
Reference(s): 
5. Are other species of the same genus (or closely related genera) invasive in a similar climate?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
Several Stipa/Nassella species have demonstrated invasive behavior in a variety of other countries with similar climates across the range of California. More specifically: Stipa trichotoma (= Nassella trichotoma), Stipa neesiana (= Nassella neesiana) and Stipa tenuissima (= Nassella tenuissima) (Poaceae – common names: serrated tussock, Chilean needle grass and Mexican feather grass, respectively) are perennial grasses in the same genus. All three species have been voluntary introduced into the EPPO (European and Mediterranean Plant Protection Organization) region for ornamental purposes, where their distribution is still limited. Because these plants have demonstrated invasive behavior in different continents and are of limited distribution in the EPPO region, they can be considered as potential emerging invaders in areas in Europe and the Mediterranean, parts of which have climatic conditions that overlap with parts of California (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima). Nassella tenuissima is closely related to N. trichotoma, a serious pasture and environmental weed in temperate Australia, and looks so similar, especially when not flowering, that it could be mistaken in the field for N. trichotoma (Nassella tenuissima). Nassella neesiana is a congener that has naturalised sporadically in the UK, France, Italy and Spain, and more widely in Australia and New Zealand, where it has become a serious grassland weed. Many regions in these countries have similar climates as parts of California (The potential global distribution of the invasive weed Nassella neesiana under current and future climates). Nassella trichotoma is a a drought-tolerant, wind- and human-dispersed grass that has invaded pastures in Australia, Europe, New Zealand, and South Africa (Climate Change and the Potential Global Distribution of Serrated Tussock (Nassella trichotoma)). Closely related, invasive congeners in Australia include N. trichotoma (Nees) Hack. Ex Archav. (serrated tussock) and N. neesiana (Trin. & Rupr.) Bark. (Chilean needle grass), N. hyalina (Nees) Barkworth (cane needle grass), N. leucotricha (Trin. & Rupr.) (Texas needle grass) and N. charruana (Arech.) Bark. (lobed needle grass). The genus Nassella contains 98 species, of which 90 can be found in South America (Pest plant risk assessment: Mexican feather grass: Nassella tenuissima).
Reference(s): 
6. Is the species (or cultivar or variety) found predominately in a climate matching the region of concern?
Yes or No: 
Yes
Points: 
2
Confidence Level: 
Very High
Answer / Justification: 
High climate overlap with California (Cal-IPC). S. tenuissima is found in the following regions (in addition to California, where it is already introduced), whose climates match those in California: EPPO region: France (including Corse), Italy. Africa: South Africa. North America: USA (New Mexico (native), Texas (native)). South America (native): Argentina, Chile. Oceania: Australia (New South Wales, Victoria), New Zealand. Note: in Australia, S. tenuissima is regulated in Queensland, New South Wales, Southern Australia, Victoria and Western Australia. It is predicted that S. tenuissima may be more invasive than S. trichotoma because of its ability to adapt to a wide range of climates (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima).
Reference(s): 
Impact on Native Plants and Animals
7. Does this plant displace native plants and dominate (overtop or smother) the plant community in areas where it has established?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
In general, S. tenuissima forms pure, dense, monotypic stands that prevent native plants from thriving or establishing. S. tenuissima forms pure stands in low-growing plant communities, especially in harsh sites, and prevents the seedlings of native species establishing (Nassella Tussock). It has the ability to form dense stands and thrive in arid environments, and increases fire hazards (Nassella tenuissima). S. tenuissima has been shown to be invasive in fire-driven or littoral ecosystems and habitats, which has precipitated concern in South Africa that it could threaten native grassland habitats. It forms long-lived, pure colonies, producing masses of highly viable, long-lived, well dispersed seed (Grasses as invasive alien plants in South Africa : working for water).
Reference(s): 
8. Is the plant noted as promoting fire and/or changing fire regimes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima creates a fire hazard in urban areas (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima). Fire enhances seeding of S. tenuissima (Nassella tenuissima). S. tenuissima is tolerant to fire (Nassella Tussock).
Reference(s): 
9. Is the plant a health risk to humans or animals/fish? Has the species been noted as impacting grazing systems?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima (commonly known as Mexican feather grass) can be a weed in its native range at sites under high disturbance, such as that caused by overgrazing. It forms indigestible balls in the stomach of stock and, if they are forced to graze the infected pasture, and they may lose weight and die as S. tenuissima has a high fiber content and a low nutritive value. It is an extremely vigorous, invasive plant, which crowds out desirable pasture species, reducing stock carrying capacity. It is a species of low nutritional value, with a high fiber content which some animals do not consume, thus reducing the carrying capacity; its abundance indicates degradation of the pasture (Nassella tenuissima (grass)).
Reference(s): 
10. Does the plant produce impenetrable thickets, blocking or slowing movement of animals, livestock, or humans?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima forms dense, monotypic stands of 2 foot tall plants that may block or hinder passage. It is an extremely vigorous plant, which crowds out pasture species as well as native grasses in coastal areas (Nassella / Stipa tenuissima; Nassella tenuissima). It grows in a dense fountain-like clump with slender, wiry culms 1-2 ft (0.3-0.6 m) tall (Nassella tenuissima Plant Profile). It is a densely caespitose perennial with very numerous, often sterile, intravaginal innovations and wiry roots, with tussocks to 70 cm tall (Nassella tenuissima (Gramineae) recorded from Australia, a potential new weed related to Serrated Tussock). It is long-lived and forms pure colonies, producing masses of highly viable, long-lived, well dispersed seed, and prevents the seedlings of native species establishing (Nassella Tussock).
Reference(s): 
Reproductive Strategies
11. Does this species (or cultivar or variety) reproduce and spread vegetatively?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
S. tenuissima reproduces by seed only (Mexican feather grass (Nassella tenuissima)).
Reference(s): 
12. If naturally detached fragments from this plant are capable of producing new plants, is this a common method of reproduction for the plant?
Yes or No: 
No
Points: 
0
Confidence Level: 
High
Answer / Justification: 
S. tenuissima reproduces by seed only, and fragments do not produce new plants (Mexican feather grass (Nassella tenuissima)).
Reference(s): 
13. Does the species (or cultivar or variety) commonly produce viable seed?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima reproduces by seed only (Mexican feather grass (Nassella tenuissima)).
Reference(s): 
14. Does this plant produce copious viable seeds each year (> 1000)?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Very High
Answer / Justification: 
While exact quantitative data on seed production was not found, at least several thousand seeds can be produced annually by one plant. Mexican feather grass reproduces from seeds. While there are no data on seed production for S. tenuissima from this source, closely related species, such as Chilean needle grass, can produce more than 20,000 seeds per square meter (Mexican feather grass (Nassella tenuissima)). N. tenuissima produces many thousands of seeds annually (Weeds of the future? : threats to Australia's grazing industries by garden plants : final report).
15. Is there significant germination (>25%) of seeds the next growing season, with no requirement of an infrequent environmental condition for seeds to germinate (i.e. fire) or long dormancy period?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
Medium
Answer / Justification: 
New clarification on this question means that it should be answered a "Yes". As seeds naturally germinate readily in the following growing season, and no evidence was found of strong dormancy mechanisms or unusual environmental conditions for germination, this defaults to a "Yes" answer. From mid spring to summer it germinates freely on well-drained soils where there is little competition from other vegetation (NSW Weedwise). Prior answer: We can infer that seeds will germinate almost any time after collection, but seed collection generally occurs many months after seed production. Thus, as seeds are produced in winter, but do not naturally germinate until warmer conditions in the heat (although they may be started indoors in artificially warm conditions), it is unlikely that seeds germinate within 2 months after they are produced under natural conditions. See details on germination and planting below: Collect seed in May - June when it is blonde and comes away easily. Use a comb or your fingers to rake seed off in such a way as not to damage the look of the plant. Seed Treatment: Can be started all year, but may grow faster in the heat (Nassella tenuissima from Lady Bird Johnson Wildflower Center). From mid-spring to summer it germinates freely on well-drained soils where there is little competition from other vegetation (Mexican feather grass (Nassella tenuissima)). In South America, seedlings of S. tenuissima emerge in autumn and early winter, prior to the winter rains. Flowering generally occurs from December to January (summer in the Southern Hemisphere) (Pest plant risk assessment: Mexican feather grass: Nassella tenuissima).
Reference(s): 
NSW Department of Primary Industries, Primary Industries Agriculture, New South Wales Department of Primary Industries (2014).  NSW Weedwise.
16. Does this plant produce viable seed within the first three years (for an herbaceous species) to five years (for a woody species) after germination?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima grows quickly and blooms the first year from seed (Nassella tenuissima).
Reference(s): 
17. Does this plant continuously produce seed for >3 months each year or does seed production occur more than once a year?
Yes or No: 
Points: 
0
Confidence Level: 
Low
Answer / Justification: 
It is unclear how long S. tenuissima will flower in California; conflicting reports from a variety of sources show generally short flowering periods, although one source (for plants in the UK) gives a four-month window for flowering. Information about persistence on the plant does not inform length of seed production. It seems unlikely, however, given the short flowering and seed production windows for most noted areas, that seed production occurs for > 3 months per year in California. In South America, seedlings of S. tenuissima emerge in autumn and early winter, prior to the winter rains. Flowering generally occurs from December to January (summer in the Southern Hemisphere) (Pest plant risk assessment: Mexican feather grass: Nassella tenuissima). In the Northern UK, flowers June to September (Stipa tenuissima - stipa ( syn. Stipa tenuifolia )). It blooms in late spring with a greenish flower cluster that persists well into fall as it ripens to golden brown (Nassella tenuissima Plant Profile).
Dispersal
18. Are the plant’s propagules frequently dispersed long distance (>100 m) by mammals or birds or via domestic animals?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
Seeds spread naturally by adherence to clothing and livestock (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima).
Reference(s): 
NSW Department of Primary Industries, Primary Industries Agriculture, New South Wales Department of Primary Industries (2014).  NSW Weedwise.
19. Are the plant’s propagules frequently dispersed long distance (>100 m) by wind or water?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima seeds are also dispersed by wind and water (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima; NSW Weedwise).
Reference(s): 
NSW Department of Primary Industries, Primary Industries Agriculture, New South Wales Department of Primary Industries (2014).  NSW Weedwise.
20. Are the plant’s propagules frequently dispersed via contaminated seed (agriculture or wildflower packets), equipment, vehicles, boats or clothing/shoes?
Yes or No: 
Yes
Points: 
1
Confidence Level: 
High
Answer / Justification: 
S. tenuissima seeds are dispersed by contaminated soil, attachment to human clothing and shoes, and via vehicles and equipment (NSW Weedwise). S. tenuissima seeds are also dispersed on farm machinery or as a contaminant of seeds and fodder (www.eppo.int -- Stipa trichotoma, Stipa neesiana and Stipa tenuissima). Personal observation is that this plant is distributed via horticulture, and seeds stick in clothing.
Reference(s): 
NSW Department of Primary Industries, Primary Industries Agriculture, New South Wales Department of Primary Industries (2014).  NSW Weedwise.
Evaluation Notes

Reviewed by Irina Irvine (Santa Monica Mtns Nat’l Recreation Area, irina_irvine@nps.gov) and Sarah Reichard, University of Washington (added by J Merryweather, PlantRight).

NSW Weedwise: http://weeds.dpi.nsw.gov.au/Weeds/Details/162

Jepson: http://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=11182

Total PRE Score

  • < 13 : accept (low risk of invasiveness)
  • 13 - 15 : evaluate further
  • > 15 : reject (high risk of invasiveness)

PRE Score: 
22
Number of questions answered: 
19
Screener Confidence (%): 
83.2
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Organization: 
Evaluation visibility: 
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