Plant Assessment Form

Saccharum ravennae

Synonyms: Erianthus ravennae (L.) P.Beauv and subspecies.

Common Names: ravennagrass; hardy pampas grass; plume grass; canna di Ravenna

Evaluated on: 2/14/07

List committee review date: 16/04/2007

Re-evaluation date:

Evaluator(s)

Jeffrey Firestone - PhD Candidate
Weed Science Program, UCDavis
Plant Sciences Mailstop 4, UCD, Davis, California 95616
530-752-8284
firestone@ucdavis.edu

List commitee members

Joe Ditomaso
Peter Warner

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 B Observational
Impact?
Four-part score BBUD Total Score
B
1.2 ?Impact on plant community B. Moderate Observational
1.3 ?Impact on higher trophic levels U. Unknown Anecdotal
1.4 ?Impact on genetic integrity D. None Reviewed Scientific Publication
2.1 ?Role of anthropogenic and natural disturbance in establishment B. Moderate Other Published Material
Invasiveness?
Total Points
17 Total Score A
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 B. Moderate Other Published Material
2.6 ? Potential for natural long-distance dispersal A. Frequent Observational
2.7 ?Other regions invaded B. Invades 1 or 2 ecological types Other Published Material
3.1 ?Ecological amplitude/Range
(see Worksheet C)
C. Limited 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? B Observational
Identify ecosystem processes impacted:

Alters fire dynamics, accumulates sediment, interferes with sunlight penetration to soil surface, may alter soil moisture & nutrient content; may alter bank and streambed erosion; may encourage flooding. Ravennagrass produces plants that are, in crude morphology, much like jubatagrass. Ravennagrass can grow on more exposed soil than many other riparian species, and so can add significant biomass to swift streams. Riparian vegetation generally produces less dry, herbaceous biomass than these large, grassy plants, so the risk of fire can be inferred, much as with Cortaderia spp (Inferred by Firestone and by AZ Working Group's PAF). Excepting Arundo and Tamarisk, this is one of the largest and most conspiuous species in the upper Cache Creek, and thus provides lots of shade and biomass to those areas it infests. As a large plant with a vegetatively thick profile, it appears to accumulate sediment and, in the seasonally flooding Capay Valley, accumulate organic matter and thatch filtered from the streamflow (Personal Observations: Firestone 2007, elsewhere: Northam 2005). The addition of sediment and detritus, combined with the density of infestation and the ability to grow on mid-channel islets or outcrops, suggests that the process may be self perpetuating, and there may be risk of flooding or erosion due to increased stream blockage (Inferred by AZ Working Group on their PAF; see also McLaughlin Reserve drain).
While its apparent preference for bare soil lessens its impact on riparian vegetation, as most vegetation stays clear of exposed or scoured areas, it is not constrained to stream channels. As Ravennagrass is able to establish on stream banks, seeps or other moist areas outside of a streambed, it may be able to impact wetland or riparian vegetation establishment. Further, it could potentially encourage and protect against erosion -- the former when interfering with stream flow via biomass and accumulated sediment, the latter when growing on a bank or roadcut.
Soil moisture and nutrient content inferred by AZ-WIPWG, but apparently speculative.


Sources of information:

Observation of reviewer, and inference from impacts of Cortaderia spp.; Personal observations of Arizona pops by F. Northam (Weed Biology Consultant, Tempe, AZ; reported on AZ-WIPWG-PAF); Similar conclusions reached by AZ-WIPWG.


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

Change in structure of riparian community; loss of habitat; possible plant community impacts via abiotic processes such as fire. Ravennagrass is still emerging as a problem, so many of the impacts are predictive rather than reporting on that which has occurred. Ravennagrass grows in riparian zones, of which California does not have enough to spare, yet has broad habitat tolerances within that range. Significant naturalization has been found in Imperial and Yolo counties, a wetland in the Chihuahan desert and the Grand Canyon, so a variety of native plants may be affected.
As mentioned in 1.1, ravennagrass provides a large vertical component to the riparian vegetation previously provided largely by cottonwood, tamarisk and arundo, and often not even by them. At least as observed in Cache Creek (Yolo) it adds significant vertical biomass. Additionally, in Cache and Canadian River, OK, it appears to also grow in vegetation-free areas in riverbed rocks or sandy washes above waterline, respectively, thus adding a horizontal component to the vegetation addition. In some areas, it has formed monocultures or near-dominance, severely limiting streamside, stream channel or non-stream moist vegetation sites (e.g. Cache Creek near Yolo County parks; McLaughlin Reserve). I have no particular reason to believe that ravennagrass will remove soil moisture, as was suggested by AZ-WIPWG, because it is not known to establish without fairly ample water. Experience in the Grand Canyon suggests ravennagrass is capable of altering plant communities along banks. Capable of growing under the canopy of other riparian plants and/or displacing natives. (Makarick 1999 & 2003). In Canadian River, OK, dense stands are infrequent, but appear to exclude other vegetation when present; more data forthcoming on this instance.


Sources of information:

Personal Observation - Firestone; Personal observations of Arizona pops by F. Northam (Weed Biology Consultant, Tempe, AZ; reported on AZ-WIPWG-PAF); Similar conclusions reached by AZ-WIPWG. Lori Makarick 1999, 2003; Oklahoma data, personal communication Lacy Jo Burgess, PhD candidate.


Question 1.3 Impact on higher trophic levels? U Anecdotal
Identify type of impact or alteration:

Unknown, although can produce dense thickets if uncontrolled, perhaps favoring animals of certain sizes only? Has leaf serrations less than pampas grass, but also significantly irritating silicaceous hairs that can make life difficult for recreational users or control personnel. Presumably could cause grazers to have similar irritation?


Sources of information:

Facts: Makarick 2003; Speculation: Firestone


Question 1.4 Impact on genetic integrity? D Reviewed Scientific Publication

No native or important cultivated Saccharum in CA


Sources of information:

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:

Strongly prefers disturbance, but lives in habitats where natural disturbance is frequent, sufficient. Ravennagrass appears to prefer bare soil or similar environments to establish. As its optimal habitats regularly provide such areas through natural erosion, it will spread without any human-induced disturbance. It has been observed on inaccessible cliffside seeps and marshy fields (McLaughlin Reserve, Yolo) where no human disturbance was possible. It can also "hide" inside larger vegetation patches, although it generally prefers sandy riverbanks (Makarick 2003). Will use human disturbance, where useful (e.g. Canal Banks - Hitchcock 1950; Irrigation ditches - Jepson Manual 1993). Grand Canyon side channels and Bitter Lake NWR, NM are both free from human disturbance, yet invaded (Stevens 1993; Pers. Comm. Ulibarri 2007).


Sources of information:

Personal Observations, Firestone 2007, Northam 2005; AZ-WIPWG and citations in box above.


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

Can easily double in <10 years when increasing. Many populations show no increase at all, however. Cache Creek watershed infestation doubling in <10 years. Tempe, Arizona has one that doubled in 3 years, but another has shown no change in 40 (Northam). Grand Canyon populations have had at least 16,000 individuals removed in the 18 years since first identified within the park, and is under active management (Makarick 2003). Stevens describes a 'population explosion' over ~6 years 1987-1992 (Stevens 1993). Apperars to be stable in certain other areas in AZ, and herbarium records in DAV go back many years without the species having come to the attention of Cal-IPC. OK population present for several decades, showing only slow expansion. Therefore, it appears as if there is some limit that, once surpassed, frees the species to expand explosively.


Sources of information:

AZ-WIPWG; Personal observation, Firestone, Tanya Meyer Yolo RCD; OK data, personal communication, Lacy Jo Burgess, PhD Candidate.


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

Hard to measure. Clear increase in county presence/absence, and probably in acreage given how uncommon previously. Hard to assess, as all populations are small and records exist of scattered individuals elsewhere in state in years past. Jepson 1993 reports only Imperial County, while Yolo and adjacent Napa have infestations in 2007. Cache Creek (Yolo) infestation increasing rapidly in area and density, but Imperial unknown to reviewer. Record of one in Sutter County from 1975, one in Fresno in 1918 and various in Imperial suggest that, by some measures, increase is limited.


Sources of information:

Jepson Manual 1993; Jepson Interchange reference to herbaria; UCD Herbarium collection.


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

Reproduces through large quantities of sexually produced caryopses, dispersed by wind and probably water. Resprouts readily after damage. Perennial. Known to self-sow when grown for horticulture. Being a perennial with large quantities of seed, the plant can wait out unfavorable recruitment conditions, and capitalize on them when present. Known to resprout after damage, but unknown (and probably unlikely) to disperse via resprouting away from main rootball.


Sources of information:

Makarick 2003; AZ-WIPWG;


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

Sold as ornamental, including by non-standard nurseries (e.g. eBay). Also, possibility of some recreational transport with equipment due to small size of seeds. Sold frequently online as "Hardy Pampas Grass" for those who want Cortaderia but live in cooler climates. Unclear if this means its use will increase, or the disfavor of pampas grass will decrease Ravennagrass usage. Several state extension services (Ohio, NC, Michigan, Missouri, others) have product listings for this plant. Reccomended for water-wise gardening in some areas. Reccomended by Kemper Center at MoBotanic Garden - notes that it is not invasive but may self-seed under optimal conditions. Grand Canyon invasion caused by National Park Service planting, believing it to be a low-risk plant (Stevens 1993).


Sources of information:

http://www.slowtheflow.org/apps/show.asp?file_store_id=432
http://mobot.org/gardeninghelp/plantfinder/Plant.asp?code=A410


Question 2.6 Potential for natural long-distance dispersal? A Observational
Identify dispersal mechanisms:

Wind and Water Seeds are wind dispersed, with hairs to assist, although larger than Cortaderia. Since it prefers growing in wet areas and the hairs are likely to promote floating above surface tension, reason to suspect water dispersal is effective. In smooth flows of irrigation canals or Delta / Bypass, distances covered could be significant. AZ-WIPWG only rates wind, not water, and Northam indicates that it would take unusually strong winds to disperse > 1 km, although basis is unclear. How canyon winds might affect is unknown. Their rating is therefore lower on this qustion.


Sources of information:

F. Northam, personal observation for wind & AZ-WIPWG. Remainder, speculation of Firestone & DiTomaso.


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

Sources of information:

Observation by Firestone for McLaughlin & Cache Creek areas. JepsonExchange & CalFlora herbarium searches for other records. OK data from personal communication, Lacy Jo Burgess, PhD candidate. See reference list for published sources. Ulibarri = Larry Ulibarri, Asst Manager of Bitter Lake NWR. MSU Extnsn: http://web1.msue.msu.edu/imp/modzz/00000570.htmlext here


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

See question 2.7 for discussion of actual and potential amplitude. Known from "rivers, streams, canals" in Imperial and Yolo, although only at D frequency. Known from Imperial Marshes, presumably at D frequency, based upon Jepson as this area is unknown to reviewer.
Introduced to state pre-1918 (DAV herbarium). In hort. trade at least by 1921 (Pilkington 1921) and continuing today (eBay 2007).


Sources of information:

Jepson Manual for Imperial data. Yolo - Firestone et al, personal observation. Herbarium record from 1918 roadside, Fresno, UCD Herbarium;


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

See q 2.7. Only confirmed to date in very few locations and not many types. Opportunity for control? This weed is emerging only now, so there is minimal distribution, paired with rapid spread and increasing density in the few areas of emergence. Apparently, only two watersheds involved.


Sources of information:

See also q 2.7, 3.1's sources and rationale


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 Unknown
Viable seed produced with both self-pollination and cross-pollination No
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: 1
Total score: B?

Related traits:

Prolific, wind-dispersed (and presumably water dispersed) seed from a perennial.

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 scrubU, Unknown
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 poolU, Unknown
meadow and seepU, Unknown
alkali playa
pebble plain
Bog and Marshbog and fen
marsh and swampD, < 5%
Riparian and Bottomland habitatriparian forest
riparian woodland
riparian scrub (incl.desert washes)D, < 5%
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

  • Cascade Range
  • Great Valley
  • Northwest
  • Desert Province
  • Mojave Desert
  • Sonoran Desert