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.

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.

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?

Facts: Makarick 2003; Speculation: Firestone

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).

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

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.

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

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).

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

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

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).

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