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| Rattail sixweeks grass on Auwahi, Maui, Hawaii. Photo courtesy Forest & Kimm Starr (USGS). |
Vulpia myuros (L.) C. Gmel. var. hirsuta (Hackrel) Asch. & Graebner
Vulpia myuros (L.) C. Gmel. var. myuros
Older taxonomic treatments describe V. megalura Nutt. and V. myuros as distinct species, with V. megalura native in North America and V. myuros nonnative [108,159,160]; however, more recent systematics classify the 2 entities as synonyms for a single, nonnative species [92,140]. This review follows the taxonomy of recent systematists in treating the 2 entities as synonyms.
The Vulpia genus is distinguished by annual life form and cleistogamous breeding habit, while Festuca is perennial and chasmogamous [48,140]. Not all systematists support the separation of these closely aligned genera [72,146,168,208,212].
SYNONYMS:In western North America, rattail sixweeks grass occurs from Alaska south to southern Mexico and east to Nevada and Arizona. It is occasional in the central United States and common in the East [46]. Based on early vegetation surveys, rattail sixweeks grass was probably first introduced in California before the 1800s [92,147] and was well established across the West by the 1890s. It is sometimes identified as a native annual (for example, [87,107,147,167]) in literature written before synonymy of V. myuros and V. megalura was widely accepted (see Taxonomy). Grass Manual on the Web provides a distributional map of rattail sixweeks grass in the United States and Canada.
The following biogeographic classification systems are a guide to where rattail sixweeks grass may occur. Except for the West Coast, precise distribution information is limited. Because rattail sixweeks grass so widespread, it is difficult to exclude many ecosystems as potential habitats for rattail sixweeks grass plants or populations; therefore, these lists are partially speculative.
ECOSYSTEMS [66]:| AL | AK | AZ | AR | CA | CT | DE | FL | GA | HI |
| ID | IL | IN | KS | KY | LA | ME | MD | MA | MI |
| MS | MO | MT | NV | NH | NJ | NM | NY | NC | OH |
| OK | OR | PA | RI | SC | TN | TX | UT | VA | WA |
| WV | WI | DC |
| BC | ON | YK |
Most lowland valleys of Oregon have a large component of annual grasses. Rattail sixweeks grass is common in the Willamette Valley, where nonnative annual grasses often predominate [63]. Rattail sixweeks grass is a component of mixed-species, nonnative annual grassland of Rouge Valley that was probably once dominated by bluebunch wheatgrass (Pseudoroegneria spicata) and Idaho fescue (Festuca idahoensis) [99]. A medusahead (Taeniatherum caput-medusae)-ripgut brome -rattail sixweeks grass community type has been identified near Pendleton [25].
Native grasslands: Nearly all relict grasslands of the West Coast states contain a component of nonnative annuals. Savelle [182] found rattail sixweeks grass was an understory dominant in a remnant purple needlegrass (Nassella pulchra) community of northern California. For a history of the type conversion from historic California prairie to annual grassland, see [36,116]. Rattail sixweeks grass is invasive on edges of California's vernal pools, which were historically surrounded by California prairie [18]. Vernal pools support a unique and highly endangered flora. Over three-fourths of relict vernal pool plant communities were historically composed of endemic California annuals, which Thorne [201] called "vernal pool ephemerals". Vernal pools are reduced 90% to 95% from historic numbers [5].
Western hardwoods: The same perennials that historically dominated California and Oregon's native prairies once dominated the groundlayer vegetation of native deciduous woodlands. As with the prairies, native groundlayer vegetation of these hardwood ecosystems has been largely replaced by nonnative annuals [75]. Rattail sixweeks grass is an important to dominant groundlayer component in western hardwood communities of the West Coast states. It is typically more common in oak (Quercus spp.) woodland understories than in adjacent chaparral [50]. Keeley [121] describes rattail sixweeks grass as an herbaceous groundlayer dominant or codominant in blue oak (Quercus douglasii) woodlands. Rattail sixweeks grass is also a component of the vegetation in several western hardwoods communities not listed in vegetation classifications above. Thomas [198] names rattail sixweeks grass as an herbaceous dominant in valley oak (Q. lobata) savanna of Santa Monica Mountains National Recreation Area, California. Rattail sixweeks grass also dominates or associates in Nuttall's scrub oak (Q. dumosa) [23] and interior live oak (Q. wislizenii) woodlands (personal observation by [101]) of California. It is a common to dominant groundlayer component in California woodlands dominated by nonnative bluegum eucalyptus (Eucalyptus globulus) [51].
Western shrublands: Rattail sixweeks grass is present to dominant in many western shrubland communities. It is often present in wedgeleaf ceanothus (Ceanothus cuneatus) communities in montane chaparral [68], and is noted in beach wormwood-California goldenbush (Artemisia pycnocephala-Ericameria ericoides) dunelands on the Monterey Peninsula of California [148]. In Mojave Desert communities of California and Nevada, rattail sixweeks grass associates in California broomsage (Lepidiospartum squamatum) riparian scrub and Joshua tree (Yucca brevifolia) communities [29].
In northwestern Oregon, rattail sixweeks grass was noted in a bigleaf maple/creeping snowberry (Acer macrophyllum/Symphoricarpos mollis) association surrounded by bare rock cliffs or talus; in a bigleaf maple/western sword fern (Polystichum munitum) association on xeric, logged sites; and on skid trails within a red huckleberry/salal (Vaccinium parvifolium/Gaultheria shallon) association [11].
Other: Information on rattail sixweeks grass associations outside of California and Oregon was scant as of 2006. Although described as common in the East, rattail sixweeks grass is usually noted on developed sites [46], not wildlands. A survey of Water Island, New York, vegetation showed rattail sixweeks grass was rare in mesic bayberry (Myrica spp.) thickets on stabilized dunes [55]. Rattail sixweeks grass was also noted as a component of freshwater tidal wetlands or adjacent uplands of the Delaware River, New Jersey (relative soil moisture where rattail sixweeks grass was found was not given) [136]. Rattail sixweeks grass is listed as a component of old fields surrounded by oak-pine (Quercus-Pinus spp.) forest on the Chickamauga Battlefield National Military Park of Georgia [175]. It is present in ecosystems of the Southwest [200], but its plant associations are largely undocumented there.
As of 2006, only California grassland vegetation typings described rattail sixweeks grass as a plant community dominant. Typings describing communities where rattail sixweeks grass is dominant include:
purple needlegrass-rattail sixweeks grass association on the Coast Ranges of west-central California [3]
purple needlegrass-rattail sixweeks grass association on the Hastings Natural Reserve [174]
wild oat (Avena fatua)-soft chess-rattail sixweeks grass communities in the ghost town of Tesla in Napa County, and on Mt Diablo [45]
soft chess-rattail sixweeks grass-San Diego tarweed (Hemizonia paniculata) communities at moist upper edges of vernal pools [97]
brome sixweeks grass (Vulpia bromoides)-rattail sixweeks grass-nit grass (Gastridium ventricosum) in the Central Valley [87]
mixed nonnative grasslands (often wild oat-soft chess-rattail sixweeks grass) of the Sacramento, San Joaquin, and Salinas valleys and the Los Angeles Basin [96]
tufted hairgrass (Deschampsia cespitosa)-rattail sixweeks grass-blue wildrye (Elymus glaucus)-California oatgrass (Danthonia californica) grassland on the central coast [190]
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| © Richard Old, Burke Museum of Natural History and Culture. |
Rattail sixweeks grass is a nonnative annual of ascending to erect growth form. Culms are 3 to 18 inches (8-46 cm) tall, growing solitary or in small tufts [46,52,70,92,168,180,212]. Plants on productive sites may exceed 18 inches in height, while plants on poor sites may top out at 1 to 2 inches (2.5-5.1 cm) [187]. Leaves are cauline, growing up to 6 inches (15 cm) long. Fruits are caryopses measuring 3.5 to 4.5 mm in length. Rattail sixweeks grass is distinguished by a narrow, many-flowered panicle with long awns (the "rattail"). The panicle is 1 to 10 inches (3-25 cm) long and bears 3 to 8 flowers. Spikelets are 5 to 11.5 mm long. Lemmas have 4.5- to 25-mm-long awns [46,52,70,92,168,180,212]. As the genus common name implies, sixweeks grasses (Vulpia spp.) are short lived [158,192].
RAUNKIAER [169] LIFE FORM:Breeding system/pollination: Rattail sixweeks grass is cleistogamous [140,212].
Seed production is not well documented, and anecdotal evidence conflicting, for rattail sixweeks grass. In California, Sampson and others [180] reported that rattail sixweeks grass had large, viable seed crops even in years of poor growth. However, others found low rattail sixweeks grass seed production in some years [24]. Further studies are needed to quantify rattail sixweeks grass seed production under various environmental conditions.
Seed dispersal: Rattail sixweeks grass seed usually falls near the parent plant or is dispersed by wind [47]. Most invasive mediterranean annual grasses have seed appendages that aid in long-distance dispersal. With its long awns, rattail sixweeks grass seed can easily catch on objects and travel long distances. The long seed awns easily catch on hairs or feathers [209]. Animals or water may disperse seed long distances [116].
Seed banking: Rattail sixweeks grass forms a soil seed bank [16,24,53,95,142,194,199]. Soil-stored seed is abundant enough to maintain populations in years of low seed production [24]. Field studies on longevity of banked rattail sixweeks grass seed are lacking; however, Buhler and Hoffman [35] found rattail sixweeks grass seed that was dry-stored for 2 years, sown in outside flats, and watered showed 72% germination 9 days after sowing. This suggests a viable seed bank in at least the short term. Extremely high precipitation may reduce rattail sixweeks grass's seed bank. Studies on the Sierra Foothill Range Field Station above Sacramento Valley, California, showed lower germination of rattail sixweeks grass recovered from litter in a very wet year (1973-1974, 8% germination) compared to litter-stored seed recovered in a dry year (1975-1976, 18% germination) [221].
Germination: Rattail sixweeks grass seed germinates over a range of environmental conditions. Germination rates are generally high. In a laboratory experiment comparing germination of nonnative and native California coastal grasses, rattail sixweeks grass and ripgut brome showed best germination rates of 9 grass species [170]. Rattail sixweeks grass seed apparently does not require scarification [194], but stratification enhances germination (review by [35]). High summer temperatures [133] and water imbibition break seed dormancy. Seeds require a fall rain of at least 0.5 inch (1.3 cm) to germinate [19].
Young and others [222] characterize rattail sixweeks grass's temperature requirements for germination as "highly variable". Length of stratification and diurnal light cycle also affect germination. Laboratory investigations found rattail sixweeks grass seeds generally needed daytime temperatures of 50 °F (10 °C) or above, and nighttime temperatures of 36 °F (2 °C) or above, to germinate. Constant or widely fluctuating diurnal temperatures inhibited germination [222]. Optimal temperature for germination was 72 °F (22 °C), with more seeds germinating in light than in dark treatments (review by [17]). In a greenhouse study, germination of rattail sixweeks grass seeds collected in June was 2% for fresh seed; 58% after a month's stratification; and 98% for seeds stratified 2 or 4 months. Optimal temperatures for germination were 54 °F to 73 °F (12-23 °C) in darkness and 54 °F to 88 °F (12-31 °C) in the light. Emergence was better for seeds planted 0 to 0.8 inch (1 cm) deep compared to seeds planted 2 inches (5 cm) deep (review by [35]). Another greenhouse experiment demonstrated faster germination in light than in dark, but after 5 days percent germination was nearly equal at around 83%. Temperature range for rattail sixweeks grass germination was 48 °F to 88 °F (9-31 °C) [16].
In southern Australia, rattail sixweeks grass establishes in common wheat (Triticum aestivum) fields in all seasons [53]. Period of rattail sixweeks grass establishment is probably more restricted in North America, but still extended in the mediterranean region. Rattail sixweeks grass showed a relatively long germination period at the Hopland Field Station of northwestern California, germinating throughout fall [16]. A greenhouse study also showed a long germination period, and the need for stratification, for rattail sixweeks grass seed. For seed collected in June of 1952 and 1953 at Davis, California, percent germination for 1952 and 1953 seed, respectively, was 2% and 0% on 18 June; 98% and 78% on 25 August; and 98% for both years on 13 October [132].
Light favors germination, so seeds may germinate better in litter than buried in soil with similar moisture conditions. In laboratory studies, total germination of well-watered rattail sixweeks grass seed was higher for seeds under lights than for seeds kept in dark (review by [17]). Deeply buried seed may fail to germinate unless soil disturbance brings seed closer to the soil surface. A greenhouse study showed substantially better germination of rattail sixweeks grass and brome sixweeks grass seed buried at depths of 0 to 0.4 inch (1 cm) compared to seed buried at depths of 0.4 to 0.8 inch (1-2 cm). Pooled germinant density of the sixweeks grasses was 744 germinants/m² and 93 germinants/m², respectively, at the 2 depths. The seed was from a Yolo County, California, coastal grassland [142]. In another greenhouse study, rattail sixweeks grass emergents buried 0 or 0.4 inch (1 cm) below ground had significantly (P<0.05) more biomass (8.5 mg) than emergents buried 2 inches (5 cm) below ground (3 mg). Biomass accumulation (used as a surrogate for growth) over a 4-month period was linear [53].
Fire effects on germination: It is unclear whether heat or charate affect rattail sixweeks grass germination. See Discussion and Qualification of Plant Response for further details.
Seedling establishment/growth: Rattail sixweeks grass cover varies greatly from year to year, depending upon precipitation received during the growing season [180,196]. In a pasture on the San Joaquin Experimental Range, rattail sixweeks grass's percentage of total species composition varied from 9.3% to 16.9% over a 3-year study period [196]. The beginning of the 1936 to 1938 study period, when rattail sixweeks grass coverage was lowest, coincided with severe drought. Rattail sixweeks grass grows rapidly with favorable temperatures and soil moisture. In the outside flats experiment above(see Buhler and Hoffman's [35] study in Seed banking), rattail sixweeks grass showed 62% seedling emergence. Five-day-old seedlings showed a mean height of 0.39 inch (0.99 cm) [35].
Seedling mortality rate can be high. On the San Joaquin Experimental Range, Biswell and Graham [24] found a mean of 20,875 rattail sixweeks grass seedlings/ft²over a 3-year period. On the densest plot the seedlings were "as thick as they could grow". The researchers estimated that about half the plants died before maturity, and one-half to three-fourths of live plants were stunted. A mean of 4,727 rattail sixweeks grass plants survived through spring [24].
Asexual regeneration: Because it is an annual, rattail sixweeks grass cannot sprout from the root crown after it produces seed. It dies. However, sixweeks grasses (Vulpia spp.) may die back to and sprout from the root crown when wet weather follows a short-term dry period during the growing season [105].
SITE CHARACTERISTICS:Soils: Rattail sixweeks grass tolerates a wide moisture regime but is most often found on dry soils. It is reported from dry sites in Baja California [217], on disturbed sandy or clayey soils in Texas [52], and on mesas in Arizona [200]. Rattail sixweeks grass is most frequent on poorly developed, dry, sandy soils in California [3,92,210] but grows on loamy and clayey soils as well [141]. Aspect may vary: in chamise (Adenostoma fasciculatum) chaparral in the Santa Monica Mountains, rattail sixweeks grass was common on both north- and south-facing slopes [77]. Vulpia myuros var. hirsuta and V. m. var. myuros are common on foothills and washes. Vulpia myuros var. myuros also occurs on California foothills and washes; additionally, it grows in annual grasslands, vernally moist chaparral, and poorly drained areas near vernal pools [82,92]. Rattail sixweeks grass occurs on moist to dry soils in Utah [212] and in seeps and on wet soils in Nevada [111].
Soil pH varies from acidic to alkaline on rattail sixweeks grass sites [82,90]. Rattail sixweeks grass grows on soils of low fertility [161] and on compacted soils [180]. It may tolerate very harsh conditions on some sites. It grows on serpentine soils [103]. Heeraman [90] found that rattail sixweeks grass was one of very few species growing on sulfur mine spoils near Clear Lake, California: It was the only plant on some plots. Soils were extremely acidic (pH <4.5) and contained high levels of arsenic and mercury [90].
Elevation: As of 2006, published data for rattail sixweeks grass's elevational range were lacking except in the West. There, rattail sixweeks grass was reported from the following elevations:
| State | Elevation |
| California | < 7,000 feet (2,000 m) [92] |
| Nevada | 4,000-6,000 feet (1,000-2,000 m) [111] |
| New Mexico | 4,000-6,000 feet [146] |
| Utah | < 6,000 feet (1,830 m) [212] |
| Baja California Norte | < 5,600 feet (1,700 m) [217] |
Light shade may favor rattail sixweeks grass on some sites. On the Jasper Ridge Biological Preserve in the Santa Cruz Mountains of California, rattail sixweeks grass was one of the most common herbs beneath coyote bush (Baccharis pilularis) on sites where coyote bush was invading open grassland. Five to 6 years after coyote bush invasion, rattail sixweeks grass and scarlet pimpernel (Anagallis arvensis, a nonnative forb) were the only herbs still abundant under coyote bush [94]. Similarly, rattail sixweeks grass showed a "slightly significant" canopy × site interaction (P=0.22) in blue oak woodlands across California, with rattail sixweeks grass more prevalent beneath blue oak canopies than in the open [149].
Disturbance favors rattail sixweeks grass [11,36]. East of the West Coast states, rattail sixweeks grass is most prevalent on disturbed sites. It is mostly reported from disturbed sites in the Intermountain West [46] and the Southeast, occurring on roadsides, fields, and "waste places" [168,220].
Although it is not confined to disturbed sites, rattail sixweeks grass occupies some of the most highly disturbed sites on the West Coast. It was present on xeric rock mound tops on the banks of the Merced River of California. Rocks were piled when the river was dredged for gold from 1910 to 1950, and postdredge vegetation surveys were conducted in the early 1980s [216]. Rattail sixweeks grass also grows on toxic mine spoils (see discussion of Heeraman's [90] sulfur mine spoils study in Soils). Rattail sixweeks grass was a component of "highly disturbed" logging sites in bigleaf maple/western sword fern and red huckleberry/salal communities of northwestern Oregon [11].
Disturbances that expose bare ground favor rattail sixweeks grass establishment. A survey of construction, landfill, and tilled sites in southern California found rattail sixweeks grass was abundant to dominant on such severely disturbed soils [193]. It was also dominant on California foothills fuel break and fireline sites where construction exposed bare soil (see Fire suppression) [152].
Rattail sixweeks grass may be a facultative wetland species on disturbed sites; for example, it dominated hog wallows in California's Central Valley [3]. Rattail sixweeks grass was a facultative wetland species near the southern edge of the San Francisco Bay, growing on an upland horse pasture and on moist, drained lowland soils. It did not occur on tidally flooded sites [109].
Rattail sixweeks grass was noted in primary succession following the 1980 eruption of Mount St Helens. It was first recorded in 1981 on ungulate exclosure study plots, where it established from wind-blown seed. It was noted outside exclosures in surveys conducted 3, 9, 14, and 20 years after eruption [47].
Fire: Rattail sixweeks grass is common on early seral burns [11,50,62,77,194]. For example, it established during postfire year 1 on a burned site in mixed chaparral of Shasta County, California [179] and was common 1 to 4 years after a chaparral wildfire on the Stunt Ranch Santa Monica Mountains Reserve [77]. See Plant Response to Fire for further information on rattail sixweeks grass occurrence in early postfire succession.
Rangeland: Rattail sixweeks grass tends to increase when rangeland conditions deteriorate [11,36]. Boyd [29] characterizes it as one of the annual "dense invaders" of California oakwoods (Quercus spp.) subject to intense gazing.
SEASONAL DEVELOPMENT:| Area | Flowers | Germinates |
| California | March-June [160] | early-late Oct. (at Hopland Field Station) [16] |
| Carolinas | May-June [168] | .... |
| Florida | spring [220] | .... |
| Nevada | May-June [111] | .... |
| New Mexico | May-July [146] | .... |
| Texas | April-May [52] | .... |
| Intermountain Region | April-July [46] | .... |
| Baja California | March-June [217] | .... |
Fire regimes: Rattail sixweeks grass is most important in grasslands, open-canopy forests, woodlands, and shrublands (see Distribution and Occurrence) that are maintained by frequent fire. It is well adapted to short-return-interval grassland fires, which are characterized by flashy fuels and rapid fire fronts that burn through quickly and cause little soil heating and damage to seed [120,199]. Rattail sixweeks grass shows good coverage after fire in open forests, woodlands, and shrublands. Fire is important in retaining open structure in most of the communities where rattail sixweeks grass is common. Frequent fire in annual and mountain grasslands maintains the grasses by preventing invasion of woody plants [166,176,190,218]. Western oak (Quercus spp.) woodlands and ponderosa pine (Pinus ponderosa) forests are maintained by frequent understory fire [7,209]. Fire plays a more variable ecological role in shrublands where rattail sixweeks grass occurs. Some of the shrublands (e.g., chamise and other chaparral types) depend on moderate-interval (30-100 years), stand-replacing fire [166]; others are adapted to mixed-severity fires (e.g., big sagebrush) [9,38,154,181]; and most desert shrubland types (such as creosotebush (Larrea tridentata)) are poorly adapted to fire [32]. In California and Oregon, relative species composition is unknown for historical plant communities that rattail sixweeks grass and other nonnative annual grasses now dominate (for example, see [36,116]). For California and Oregon's annual grasslands and oak woodlands, it is therefore impossible to assess how fuel loading has changed from presettlement times or how presence of rattail sixweeks grass and other nonnative annuals may alter historic fire regimes in those communities. Rattail sixweeks grass's most serious ecological impact in California and Oregon may be its potential to increase relative nonnative:native species cover after fire, especially where rattail sixweeks grass is seeded in for postfire rehabilitation (see Fire Management Considerations). Descriptions of fire regimes of communities where rattail sixweeks grass is important follow.
Annual grasslands experience frequent fires. Keeley [123] attributes the resilience of annual grasses to "copious seed production and high seed survival under low-intensity fires". Annual grasslands originated following severe disturbances, and can be maintained by frequent fire [36,116,123,211]. Because they are dominated by nonnative annuals, annual grasslands have no "natural" fire regime. There are no data and few historic records of presettlement fire-return intervals in pristine California prairie. Probable mean fire intervals (estimates of fire intervals that are derived from historical or very limited physical evidence) for California prairie are frequent: approximately every 1 to 2 years. Probable mean fire intervals for annual grasslands are every 20 to 30 years [190]. Christensen [41] estimated a mean fire-return interval of 10 years on sites where rattail sixweeks grass is dominant.
Oak woodlands of California and Oregon historically experienced frequent surface fires, with fire-return intervals ranging from 1 to 30 years [74]. Understory vegetation was composed of either perennial bunchgrasses and annual herbs or a combination of herbaceous vegetation and chaparral shrubs. Fires were most severe in oak communities with shrub understories [144]. Urbanization and fire exclusion have greatly increased fire-return intervals. For example, probable mean fire interval in coast live oak woodlands of the Monterey Bay Peninsula of California has increased from 1 to 2 years in pre-Columbian times to 225 years since 1929 [74]. In prescribed fire and wildland use fire programs, rattail sixweeks grass and other annual grasses can carry understory fire at fire-return intervals similar to historic intervals (see the discussion of Agee and Biswell's study in Fuel enhancement).
Chaparral: Historic fire-return intervals in chamise and mixed-chaparral range from 10 to 90 years [166,194]. Intervals between fires were longer in communities dominated by nonsprouting shrubs, such as bigberry manzanita (Arctostaphylos glauca), than in communities dominated by sprouting shrubs such as chamise [126].
Coastal sage scrub chaparral: Documentation of historic fire-return intervals in coastal sage scrub is sparse. Current fire-return intervals vary widely. Total area burned strongly correlates with precipitation during the previous winter, with heaviest burning occurring after wet years. Fire is rare following drought [155]. Vogl [207] estimated an average fire-return interval of 20 years for lightning-ignited fire in chaparral adjacent to coastal sage scrub. Fire severity is generally higher in coastal sage scrub than in other chaparral types due to higher litter loading and the higher percentage of terpenes in coastal sage scrub vegetation [73,143]. For a California sagebrush-eastern Mojave buckwheat (Artemisia californica-Eriogonum fasciculatum) community on the Cleveland National Forest, California, fire records show that stand-replacing fire occurs at approximate 28-year intervals [215].
Sagebrush/bunchgrass: Prior to the 1890s, only a few grass species likely occupied a prominent position in early postfire sagebrush communities of the Great Basin. In southern Idaho, native sixweeks grass (Vulpia octoflora) and small sixweeks grass were among the most important of these early postfire annuals. Generally, native Vulpias would increase for a few years, then be suppressed by recovering bunchgrasses such as bluebunch wheatgrass, bottlebrush squirreltail, and Idaho fescue, and by shrubs such as basin big sagebrush (Artemisia tridentata ssp. tridentata) and rabbitbrush (Chrysothamnus spp.). Today, rattail sixweeks grass establishes in early postfire succession along with its conspecifics [167].
Historic fire-return intervals in sagebrush ecosystems were variable, ranging from around 20 to 100 years. Most fires were mixed-severity and of small extent, although more widespread fires occurred on some sites [100,218,219]. Cheatgrass and medusahead, nonnative annual grasses, have altered fire regimes and successional patterns in some sagebrush communities. Fine fuel loads from dry cheatgrass and/or medusahead can support fire-return intervals as short as 3 to 6 years [167,214]. There is no evidence to date (2006) that rattail sixweeks grass is fueling an annual grass/fire cycle.
Fuels: Because it is an annual, rattail sixweeks grass productivity varies greatly from year to year. It may contribute little biomass on some sites or in some years [64,106,161]. Rattail sixweeks grass sometimes forms dense stands that become flashy fine fuels when stands dry and then burn in the summer or fall fire season [1,125]. Holland [98] found that together, soft chess, longbeak stork's-bill (Erodium botrys), and ripgut brome produced 84% of understory fine fuels in blue oak/annual grass woodland and annual grassland on the San Joaquin Experimental Range. Total mean understory production was approximately 240 g/m², with rattail sixweeks grass contributing about 6.3g/m². Rattail sixweeks grass produced more aboveground biomass in open annual grassland than in blue oak woodland [98]. Total fuel biomass for plant communities with rattail sixweeks grass varies considerably with geographic location, plant community composition and structure, and local climate. Frost and others [64] found large differences in understory production in California oak (Quercus spp.) woodlands with rattail sixweeks grass. In areas receiving <20 inches (50 cm) mean annual precipitation, oaks had either no effect on or enhanced productivity of understory vegetation including rattail sixweeks grass. In areas receiving >20 inches of annual precipitation, dense oak canopies suppressed understory productivity [64]. Heady and others [86] found annual productivity of annual grassland at the Hopland Field Station, where rattail sixweeks grass is common, ranged from 106 g/m² to 562 g/m² in a 19-year period.
The following table provides fire-return intervals for plant communities and ecosystems where rattail sixweeks grass is important. For further information, see the FEIS review of the dominant species listed below. This list may not be inclusive of all plant communities in which rattail sixweeks grass occurs. Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". .
| Community or Ecosystem | Dominant Species | Fire Return Interval Range (years) |
| silver fir-Douglas-fir | Abies amabilis-Pseudotsuga menziesii var. menziesii | >200 [7] |
| California chaparral | Adenostoma and/or Arctostaphylos spp. | <35 to <100 |
| sagebrush steppe | Artemisia tridentata/Pseudoroegneria spicata | 20-70 [166] |
| basin big sagebrush | Artemisia tridentata var. tridentata | 12-43 [181] |
| mountain big sagebrush | Artemisia tridentata var. vaseyana | 15-40 [8,38,154] |
| coastal sagebrush | Artemisia californica | <35 to <100 |
| saltbush-greasewood | Atriplex confertifolia-Sarcobatus vermiculatus | <35 to <100 |
| desert grasslands | Bouteloua eriopoda and/or Pleuraphis mutica | 5-100 [166] |
| cheatgrass | Bromus tectorum | <10 [167,214] |
| California montane chaparral | Ceanothus and/or Arctostaphylos spp. | 50-100 |
| paloverde-cactus shrub | Parkinsonia microphylla/Opuntia spp. | <35 to <100 [166] |
| curlleaf mountain-mahogany* | Cercocarpus ledifolius | 13-1,000 [9,183] |
| mountain-mahogany-Gambel oak scrub | Cercocarpus ledifolius-Quercus gambelii | <35 to <100 |
| blackbrush | Coleogyne ramosissima | <35 to <100 |
| California steppe | Festuca-Danthonia spp. | <35 |
| western juniper | Juniperus occidentalis | 20-70 |
| Rocky Mountain juniper | Juniperus scopulorum | <35 |
| creosotebush | Larrea tridentata | <35 to <100 [166] |
| pine-cypress forest | Pinus-Cupressus spp. | <35 to 200 [7] |
| pinyon-juniper | Pinus-Juniperus spp. | <35 [166] |
| Mexican pinyon | Pinus cembroides | 20-70 [156,195] |
| Jeffrey pine | Pinus jeffreyi | 5-30 |
| Pacific ponderosa pine* | Pinus ponderosa var. ponderosa | 1-47 [7] |
| interior ponderosa pine* | Pinus ponderosa var. scopulorum | 2-30 [7,12,134] |
| loblolly pine | Pinus taeda | 3-8 |
| loblolly-shortleaf pine | Pinus taeda-P. echinata | 10 to <35 [209] |
| mountain grasslands | Pseudoroegneria spicata | 3-40 (x = 10) [6,7] |
| coastal Douglas-fir* | Pseudotsuga menziesii var. menziesii | 40-240 [7,157,172] |
| California mixed evergreen | Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus menziesii | <35 |
| California oakwoods | Quercus spp. | <35 [7] |
| coast live oak | Quercus agrifolia | 2-75 [74] |
| canyon live oak | Quercus chrysolepis | <35 to 200 [7] |
| blue oak-foothills pine | Quercus douglasii-P. sabiniana | <35 |
| Oregon white oak | Quercus garryana | <35 [7] |
| California black oak | Quercus kelloggii | 5-30 [166] |
| interior live oak | Quercus wislizenii | <35 [7] |
| redwood | Sequoia sempervirens | 5-200 [7,60] |
| western redcedar-western hemlock | Thuja plicata-Tsuga heterophylla | >200 [7] |
| California annual grasslands | Vulpia myuros | x = 10 [41] |
Fire in any season may reduce rattail sixweeks grass's seed bank [49]. Sixweeks grass (Vulpia spp.) seeds in litter or lying on the soil surface are most vulnerable to fire kill [104,122]. Most surface fires do not harm sixweeks grass seeds that are buried in soil [86,162]; however, shallowly buried rattail sixweeks grass seeds can die if ground fire heats soil to lethal temperatures. A laboratory test showed heating soils to approximately 155 °F (68.3 °C) killed buried rattail sixweeks grass seed. Heat exposure time was brief, but not quantified in the research article [133]. In another laboratory experiment, most rattail sixweeks grass seed exposed to temperatures of 160 °F (70 °C) for 5 minutes remained viable. Germination of rattail sixweeks grass seed exposed to 5 minutes of heat dropped as follows [194]:
| Control (room temperature) |
50 °C | 60 °C | 70 °C | 80 °C | |
| germination (%) | 100 | 100 | 95 | 65 | 0 |
In a survey of 90 coastal sage chaparral and chaparral sites in southern California that burned in the fall of 1993, rattail sixweeks grass was an important component of early postfire vegetation on many sites. The survey began in spring 1994 and continued through 5 postfire growing seasons. Rattail sixweeks grass was present on two-thirds or more of the burns. Rattail sixweeks grass had been seeded in on some of the coastal sage sites. Where seeded, it generally dominated for 2 postfire years and was then replaced by shortpod mustard (Hirschfeldia incana), annual wild oats (Avena spp.), and annual bromes (Bromus spp.). Mean pooled density of rattail sixweeks grass and brome sixweeks grass on 33 of the burns was 5,791,800 plants/ha (SE=1,506,800) on coastal sage chaparral and 6,066,600/plants ha (SE=1,246,500) on chaparral. For nonnative species, relative dominance of the 2 sixweeks grasses was second only to soft chess across burned sites [124].
Rattail sixweeks grass is most prevalent in early postfire succession on burned sites [11,50,62,77,164,189,194]. Sampson and others [180] described recent chaparral burns as prime rattail sixweeks grass habitat, and Florence [62] characterized rattail sixweeks grass as an early seral "fire-follower" in Pinnacles National Monument, California. Several vegetation surveys demonstrate rattail sixweeks grass abundance in early postfire succession. In a survey of postfire succession in 28 burns in Santa Barbara County, California, rattail sixweeks grass was common 1 to 5 years after wildfires on maritime coast live oak and maritime chamise chaparral sites. Mean frequency of rattail sixweeks grass was similar on coast live oak and chaparral sites (11.5% and 11.0%, respectively) [50]. A survey of chamise chaparral burns in the San Bernardino and San Gabriel mountains of southern California showed mean density of rattail sixweeks grass was highest in postfire years 4 through 7, peaking in postfire year 5 [102]. In a similar survey of California chaparral burns, Sweeney [194] reported rattail sixweeks grass was "common on 1-year-old burns, becoming increasingly abundant on 2-, 3-, and 4-year-old burns". Rattail sixweeks grass density after one of these wildfires, in chamise chaparral near Highland Springs, California, was [194]:
|
Density (rattail sixweeks grass plants/28 m²) |
|||
| Postfire year 1 | Postfire year 2 | Postfire year 3 | Postfire year 4 |
| 20 | 24 | 417 | 737 |
In a blue oak savanna in Sequoia National Park, rattail sixweeks grass gained biomass after 3 successive spring fires compared to its prefire biomass. For detailed information on this study, see the Research Paper by Parsons and Stohlgren [213].
Rattail sixweeks grass has persisted after repeated burning. An eastern Mojave buckwheat-California sagebrush costal sage community in the Santa Monica Mountains of California experienced wildfire on 1978 June 18, and a portion of the site reburned in June 1979. The site was a southeast-facing, xeric slope where, fortuitously, vegetation sampling had been conducted in 1977. Prefire (1977) vegetation sampling showed 0% mean coverage of rattail sixweeks grass. Postfire (spring 1980) sampling showed 25.3% mean rattail sixweeks grass cover. The fire had relatively long burnout times (2-minute exposure to 9 kcal/sec/m²; reaction intensity of the fire was modeled at 120 kcal/sec/m² [213].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:Precipitation in the growing season is critical for establishment of rattail sixweeks grass and other annuals (see Germination); yet postfire weather data are often omitted from studies on postfire responses of annuals. Prescribed burning on nonnative annual grasslands of Santa Cruz Island, California, showed that postfire weather in the growing season was a greater factor in early postfire response of native and nonnative herbs, including rattail sixweeks grass, than either aspect or elevation. Three fires were conducted in from 1993 to 1995 in 3 contiguous areas, with an adjacent control. Prefire dominants included rattail sixweeks grass, slender oat (Avena barbata), wild oat (A. fatua), soft chess, red brome, and Italian ryegrass (Lolium multiflorum). Postfire vegetation surveys revealed that all study plots (3 burns and a control) were dominated by nonnative annual grasses. Cover of nonnative annual grasses was pooled, so data are not available for rattail sixweeks grass's individual response to fire. Cover of nonnative annual grasses peaked in postfire year 2, a wet year. The authors concluded that in the wet year, extensive annual grass cover probably retarded germination of native herbs. Mean percent coverage of annual grasses was significantly lower (P<0.05) on burned plots compared to unburned plots for all 3 postfire years. By postfire year 3, topography was the most important factor affecting postfire recovery (P<0.05) [127].
Postfire studies show that although fire generally increases rattail sixweeks grass cover in the short term, fire sometimes reduces or has no apparent effect on population density of rattail sixweeks grass. Presumably, postfire cover is greatly affected by relative density of rattail sixweeks grass in the prefire seed bank and by postfire weather in the growing season. To date (2006), however, prefire seed bank studies and fire studies that include weather data are few. The following studies illustrate how fire may increase, have no effect on, or reduce rattail sixweeks grass.
Hansen [82] found an increase in rattail sixweeks grass after prescribed burning on 2 Nature Conservancy Preserves (Pixley Vernal Pools and Creighton) in northern California's Tulare Lake Basin. Repeated burning was especially favorable for rattail sixweeks grass. Both Preserves are dominated by annual grasses: Pixley Vernal Pools Preserve is a dwarf barley-Mediterranean barley (Hordeum depressum-H. marinum ssp. gussonianum)-soft chess community and Creighton Preserve is a soft chess-leporinum barley (H. murinum ssp. leporinum)-red brome community. Dwarf barley is native; the other dominant annual grasses are nonnative. In prefire sampling in March 1981, rattail sixweeks grass was the fifth most common species on Pixley Vernal Pools sites and was less common on Creighton sites (relative frequency not given). Pre- and postfire vegetation was sampled in March on all plots. Burning was conducted from August to October in 1980, 1981, and 1983 at Pixley Vernal Pools Preserve and from August to October in 1982, 1983, and 1984 at Creighton Preserve. Treatments were a control, a single burn, a double repeat burn, and a triple repeat burn. Fire increased rattail sixweeks grass coverage on both sites in nearly every sample year: No other annual grass responded so favorably to the fires. In contrast to all other annual grasses, rattail sixweeks grass was most abundant on thrice-burned plots. Mean composition of rattail sixweeks grass was [82]:
| Cover (%) | ||||
| Control | Single burn | Double burn | Triple burn | |
| Pixley Vernal Pools | ||||
| 1981 | 14% | 13% | .... | .... |
| 1982 | 5% | 33% | 30% | .... |
| 1983 | 5% | 43% | 55% | .... |
| 1984 | 1% | 4% | 28% | 39% |
| 1985 | 4% | 9% | 39% | 50% |
| Creighton | ||||
| 1982 | 4% | 4% | .... | .... |
| 1983 | 3% | 36% | 31% | .... |
| 1984 | trace | 5% | 25% | 45% |
| 1985 | 5% | 12% | 20% | 57% |
For further information on this study, see Hansen's [82] thesis: The effect of fire and fire frequency on grassland species composition in California's Tulare Basin.pdf.
Other California and Oregon studies found a neutral to negative effect of fire on rattail sixweeks grass. Following prescribed burning of chamise chaparral on Mt Hamilton, California, Dunne and others [56] called rattail sixweeks grass a "non-fire follower", meaning that it was present after burning but did not increase. On pile-and-burn clearcuts in coast Douglas-fir (Pseudotsuga menziesii var. menziesii) sites on the Siuslaw National Forest, Oregon, rattail sixweeks grass was not present on burned plots at postfire years 1 and 2. It showed mean frequencies of 7.7% and 8.3%, respectively, on adjacent unburned plots at postfire years 1 and 2 [44].
Another study showed a decrease in rattail sixweeks grass after summer fire, with prescribed burning significantly reducing yield of rattail sixweeks grass and other annuals on annual rangeland. On the Coast Ranges near Berkeley, California, a cattle rangeland was burned under prescription in July 1947. Postfire growth was not measured on grazed plots. Postfire response of Vulpia myuros var. hirsuta in exclosures was [91]:
| Postfire date | Months after fire | Mean height (inches) | |||
| Exclosure 1 | Exclosure 2 | ||||
| burned | unburned | burned | unburned | ||
| 1947 Dec. 1 | 5 | 1.5 | 3.0 | 2.0 | 2.5 |
| 1948 Feb. 20 | 19 | 3.1 | 5.1 | 2.4 | 3.6 |
| 1948 May 1 | 22 | 14.7 | 13.8 | 12.0 | .... |
The Research Project Summary Changes in grassland vegetation following fire in northern Idaho provides information on prescribed fire and postfire response of many plant species including rattail sixweeks grass.
For information on native grassland restoration and rattail sixweeks grass response after prescribed fires, see Restoration.
FIRE MANAGEMENT CONSIDERATIONS:Fuel enhancement: 'Zorro' rattail sixweeks grass (see Other Uses for information on this cultivar) can be used to enhance fuels prior to prescribed burning; however, managers may not want to introduce rattail sixweeks grass and soft chess where they do not already grow or are uncommon. 'Zorro' rattail sixweeks grass was seeded in for fuel enhancement at Sugarloaf Ridge State Park, California, where fire was prescribed to control yellow starthistle (Centaurea solstitialis). The seeded-in area was a severely eroded gully where yellow starthistle cover was nearly 100%, and yellow starthistle did not provide enough fine fuels to carry a fire. 'Zorro' rattail sixweeks grass and 'Blando' soft chess (also nonnative) were broadcast seeded into the gully early December. A backing fire was set downslope against the wind in July to coincide with yellow starthistle's dough stage and maximize yellow starthistle seed kill. Fire behavior and weather were [85]:
| Flame length | Temperature | Relative humidity | Windspeed |
| 2-6.5 feet | 60 °F | 54% | 2-5 mph |
'Zorro' rattail sixweeks grass and 'Blando' soft chess provided sufficient fine fuels to carry the fire, and nearly all yellow starthistle plants died. This fire was 1 of 3 annual burns set for yellow starthistle management [85]. For further information on this study, see the Fire Case Study Sugarloaf Ridge State Park Prescribed Burns.
'Zorro' rattail sixweeks grass and 'Blando' soft chess were also planted for fuels enhancement in November and December 1994 on Mt Tamalpais in the North Coast Ranges of California. Common barley (Hordeum vulgare) was previously planted but failed to establish densely enough to provide an even fuelbed. The management goal was to use prescribed fire to reduce nonnative French broom (Genista monspessulana) and increase coverage of native coyote bush. By spring 1995, 'Zorro' rattail sixweeks grass had 21% mean cover, and 'Blando' soft chess had 26% mean cover. Prescribed burning was conducted in late July 1995. Areas seeded to 'Zorro' rattail sixweeks grass and 'Blando' soft chess carried fire, while sites previously seeded to common barley generally had patchy burns that died out. Most French broom plants were killed in areas where fire carried, while others were top-killed and sprouted later. Nearly 100% of coyote bush and nonnative sweet fennel (Foeniculum vulgare) sprouted after the fire [27,28]. Postfire coverages of rattail sixweeks grass and soft chess were not provided in the study.
Rattail sixweeks grass can carry fire on some sites where it is already established. In Pinnacles National Monument, blue oak-foothills pine/annual grassland communities are burned under prescription in winter, fall, or early spring to reduce encroachment of chaparral shrubs and encourage oak regeneration. Rattail sixweeks grass is the most abundant annual grass in blue oak woodlands within the Monument. Upslope strip burning is conducted in winter and early spring. Broadcast burning is done in early May after rattail sixweeks grass and other grasses are dry, and in late October or November after fall rains start. Rattail sixweeks grass and other annual grasses are the main fuels that carry prescribed and wildland use fires in the blue oak woodland-foothills pine woodlands of Pinnacles National Monument [1].
Rehabilitation: Rattail sixweeks grass is sometimes used for short-term erosion control after fire [21]. 'Zorro' rattail sixweeks grass is often included in seed mixes with Italian ryegrass and/or soft chess [28,85,114]. Labeled as foxtail fescue (Vulpia megalura), rattail sixweeks grass is sometimes included in so-called "native" seed mixes [125] (see Taxonomy regarding nonnativity of V. megalura).
Postfire seeding is controversial [114,125]. Seeded-in nonnatives in general and rattail sixweeks grass in particular do not always decline after seeding treatments, may interfere with postfire establishment of native plant species, and do not always reduce erosion [42,114,125]. Expert opinion leans against postfire seeding of rattail sixweeks grass and other nonnative species. Conard and others [42] concluded that too few studies have been conducted on the effects of postfire seeding to predict its effectiveness. They studied the ability of seeded grasses to reduce erosion in California chaparral, applying a seed mix with both native and nonnative herbs (including rattail sixweeks grass and Italian ryegrass) to 3 chaparral burns in the Transverse Ranges of California. They found that seeding-in slightly reduced erosion on some sites but not on northern aspects. Native shrub cover was insignificantly reduced by seeding, and nonnative herbaceous cover reduced natural regeneration of native herbaceous species. The authors raised concerns over the effects of such seedings on the native flora [42].
Keeley and others [125] do not recommend postfire seedings of nonnatives. For 'Zorro' rattail sixweeks grass, they state it "can locally dominate and form dense fine fuels that would be subject to flash fires" [125]. Keeley [120] further states that 'Zorro' rattail sixweeks grass "may establish and become invasive in some plant communities, although it does not persist in chaparral". He investigated postfire seeding effects on the flora of the San Gabriel Mountains, where 'Zorro' rattail sixweeks grass and Italian ryegrass were seeded in after the 1993 Kinneloa Fire. The seeding resulted in a dense stand of nonnative grasses that interfered with postfire establishment of native flora [118]. 'Zorro' rattail sixweeks was common after it was seeded in 2 years after a wildfire in a desert saltbush (Atriplex polycarpa)/red brome community [163].
Rattail sixweeks grass and other seeded-in annuals sometimes fail to establish, so the objective of soil stabilization is not met. Given California's often low precipitation in early postfire environments, establishment of either seeded-in or seed banked species is often sparse in postfire year 1, when seeded-in species are meant to provide emergency cover. Keeley [119] states that after postfire year 1, native species provide more stable cover compared to seeded-in species.
Keeley [119] monitored the short-term effectiveness of seeded-in grass mixes on reducing erosion on burned California foothills. In the fall of 1993, 2 large wildfires (the Old Topanga and Green Meadow fires) burned on opposite sides on the Santa Monica Mountains. Both sites were approximately half coastal sage chaparral and half chamise chaparral, and both had similar cover of nonnative annuals. The Old Topanga Burn was seeded in with a mix of nonnative herbs. Rattail sixweeks grass composed the majority of the mix (56%) by seed number, and was second greatest by seed biomass (26%). California brome was a minor component of the mix, but California brome is not native to the area. The Green Meadow Burn was left to revegetate naturally. Rainfall was 21% below normal the first 4 months after the fires. For plots sampled in March 1994, there was no significant difference (P<0.001) in establishment of either nonnative or native species between the Old Topanga and the Green Meadow burns. Rattail sixweeks grass, rose clover (Trifolium hirtum, a nonnative forb), and soft chess―which together comprised the majority of the seeded-in species―were more common on the Old Topanga Burn but did not provide high coverage on either of the burns. Pooled cover of the rattail sixweeks grass, rose clover, and soft chess ranged from 1% to 8% on Old Topanga Burn and Green Meadow Burn sites. California brome cover was limited to a few individuals on the Old Topanga Burn, and California brome was not present on the Green Meadow burn. Percentage cover of natural regeneration was 100 times greater on both burns compared to cover of seeded-in species. Keeley [119] concluded that "because seeded species never represented more than a minor fraction of the total plant cover", aerial seeding was not cost effective. Robichaud and others [173] review the effectiveness of postfire seedings and other Burned Area Emergency Rehabilitation watershed projects in California chaparral.
Restoration: Keeley [120] cautions that repeated early spring burning may eventually select for nonnative annuals over native annual species. At best, repeated spring burning does little to shift the native:nonnative species ratio. Greatest success for promoting native herbaceous species in annual grasslands has been in the southern portion California's annual grasslands. The southern annual grasslands are drier than annual grasslands to the north, and probably had a larger proportion of native annuals in presettlement times. Late spring burning has generally increased coverage of native annuals in the southern San Joaquin Valley [120]. A research note from a study in Cuyamaca Rancho State Park of eastern San Diego County, California, reported that "low-intensity" burning (mean fire temperature was ~200 °F (93 °C)) on 1980 April 4 reduced rattail sixweeks grass cover relative to native deergrass (Muhlenbergia rigens). Rattail sixweeks grass was a prefire dominant, and was in a "critical" growth period in April [130] (probably setting seed). Further quantitative data were not provided.
Prescribed burning alone or in combination with other treatments may be used to increase relative cover of native herbs over nonnative grasses including rattail sixweeks grass. On the Cuyamaca Rancho State Park, this strategy was successful on a mountain meadow site but not in chaparral. Biswell conducted prescribed burning in pointleaf manzanita chaparral and montane meadow communities in December 1977. Native smallflower melicgrass (Melica imperfecta) dominated the burned meadow site after fire; however, rattail sixweeks grass maintained high cover and relative dominance on burned chaparral compared to unburned chaparral sites [15,145]. Native grass and rattail sixweeks grass prevalence at postfire months 7 and 8 were [145]:
|
Cover and relative dominance of rattail sixweeks grass and native grasses |
||||
| Foliar cover (%) | Relative dominance (%) | |||
| Chaparral site | Burned | Unburned | Burned | Unburned |
| 1980 June 17 | ||||
| deergrass | 16.00 | 53.00 | 25.00 | 56.80 |
| rattail sixweeks grass | 22.00 | 13.30 | 34.38 | 14.30 |
| 1980 July 16 | ||||
| deergrass | 15.33 | 30.33 | 22.70 | 35.49 |
| rattail sixweeks grass | 20.33 | 4.33 | 30.19 | 5.05 |
| Meadow site | Burned | Unburned | Burned | Unburned |
| 1980 June 17 | .... | .... | .... | .... |
| 1980 July 16 | ||||
| smallflower melicgrass | 76.00 | trace | 92.70 | trace |
| rattail sixweeks grass | 5.00 | 51.00 | 6.10 | 94.44 |
For further information on this study, see the Research Project Summary Response of vegetation to prescribed burning in a Jeffrey pine-California black oak woodland and a deergrass meadow at Cuyamaca State Park, California.
Also on Cuyamaca Rancho State Park, Garcia and Lathrop [65] reported that early spring burning reduced relative cover of nonnative annual grasses, including rattail sixweeks grass, and increased relative cover of native purple needlegrass.
Prescribed fire in combination with hand-pulling reduces nonnative grasses. Gillespie and Allen [69] used prescribed fire and plant removal experiment was conducted on the Santa Rosa Plateau Ecological Reserve of California to promote roundleaf stork's-bill (Erodium macrophyllum), a rare native forb. Roundleaf stork's-bill initially had low establishment rates on burned, hand-pulled plots compared to unburned, hand-pulled plots; however, roundleaf stork's-bill coverage was slightly higher on burned, hand-pulled plots by March, and end-of-season roundleaf stork's-bill fruit production was 12 times greater on burned, hand-pulled plots vs. unburned, hand-pulled plots. Hand-pulled species included rattail sixweeks grass, red brome, soft chess, wild oats (Avena spp.), and cutleaf filaree (E. cicutarium, a nonnative forb) [69].
Fire suppression efforts that expose bare ground may increase rattail sixweeks grass abundance, particularly on bulldozer and other firelines. In a survey of fuel breaks across California, Merriam and others [152] found nonnative plant abundance was 200% greater on fuel breaks than on adjacent wildlands. Study plots were located on conifer forest, oak woodland, chaparral, and coastal sage chaparral types, with rattail sixweeks grass occurring on all but coastal sage plots. Overall, rattail sixweeks grass was the third most frequent nonnative species occupying fuel breaks, just behind cheatgrass and red brome in abundance. Rattail sixweeks grass and other nonnatives on fuelbreaks were invading adjacent wildlands. Nonnative plant cover decreased with increasing distance from fuel breaks. Nonnnative plant cover was greatest (28%) on fuel breaks constructed with bulldozers; however, hand-constructed fuel breaks had more nonnative plants than fuel breaks constructed with mechanical equipment other than bulldozers (for example, grapple skidders). With large blades designed to remove soil, bulldozers are likely to disrupt native seed banks and transport seeds of rattail sixweeks grass and other nonnatives between sites. Overall nonnative cover on fuel breaks increased (P<0.001) with fire frequency on sites experiencing 1 or 2 fires over the past 50 years compared to fuel breaks with no fire. There was a significant grazing x fire interaction (P<0.001), with nonnative cover greater on grazed, burned sites compared to ungrazed, burned sites. Fuel breaks with a minimum of bare soil and those where some canopy cover was retained had fewer nonnative herbs. The authors recommend using fuel break construction and maintenance methods that leave some residual overstory and minimize exposure of bare soil [152].Herbivores may graze new rattail sixweeks grass growth. For example, mule deer near Pendleton, Oregon, grazed a medusahead-ripgut brome-rattail sixweeks grass community heavily in spring [25]. However, Columbian black-tailed deer on Vancouver Island, British Columbia, did not graze rattail sixweeks grass anytime during its growing season even though it was abundant [43]. Roosevelt elk in northwestern California grazed rattail sixweeks grass lightly [84].
Some small grazing mammals utilize rattail sixweeks grass. It was among the "most commonly eaten" herbs selected by Beechey ground squirrels in Alameda County, California [57]. However, California vole population size was negatively correlated with dominance of rattail sixweeks grass (r² = -0.55, P<0.05) at the Hopland Field Station [67].
Little else was documented concerning animal use of rattail sixweeks grass as of 2006. Chukar from the Temblor Range of southwestern California graze rattail sixweeks grass as a minor portion of their spring diet [83]. Umbar skipper butterfly larvae grazed rattail sixweeks grass in the laboratory. Whether or not the larvae use rattail sixweeks grass in the field was unknown at the time of the study [13].
Palatability/nutritional value: Sampson and others [180] rate rattail sixweeks grass as seasonally good forage for cattle and horses and fair for domestic sheep. However, rattail sixweeks grass matures rapidly, and nutritional quality drops rapidly as plants dry [180]. Domestic ewes and lambs in Willamette Valley showed good weight gain on green rattail sixweeks grass-soft chess pastures when managed under rotational grazing so that the sheep were not eating dry forage [184].
Nutritional content of Vulpia myuros var. hirsuta on the San Joaquin Experimental Range was highest in winter and lowest in summer. Mean crude protein content ranged from 10.45% oven dry weight in December (early leaf stage) to 2.72% in June (plants dry and dispersing seeds). Mean crude fiber content ranged from 20.95% in December to 42.41% in June. Gordon and Sampson [71] provide further nutritional analyses of rattail sixweeks grass including ash, silica, calcium, and phosphorus content.
Cover value: Vulpia species provide poor cover for small mammals and birds [54].
OTHER USES:Rattail sixweeks grass may be useful in rehabilitation of toxic soils [185]. Seeded-in 'Zorro' rattail sixweeks grass took up mercury on mine spoils near Clear Lake, California. The mine spoils were so contaminated with mercury and arsenic that they supported no other vegetation. Rattail sixweeks grass also aided soil stability on the toxic site, reducing soil leaching and erosion on the relatively less contaminated sites that could potentially support perennials [89,90].
Rattail sixweeks grass may show better establishment than native species, and it is less costly when nonnative species control is not an issue. Reviewing revegetation studies of California annual rangelands, Kay and others [112] found restoration seedings using native perennial grasses usually produced low yields, and seed cost of native species was higher compared to nonnative annual seeds. They recommended use of 'Zorro' rattail sixweeks grass and other nonnative annual cultivars on severely disturbed sites that would be subject to erosion without immediate cover [112]. Rattail sixweeks grass is likely to invade some plant communities, though, so site selection is critical to preventing rattail sixweeks grass expansion. In reviews, Keeley [120,122] stated that 'Zorro' rattail sixweeks grass is short lived in chaparral but may readily colonize adjacent grassland or savanna communities.
'Zorro' rattail sixweeks grass may be a component of so-called "native" commercial seed mixtures [112,139]. Keeley [118] urges managers using native seed mixtures to research which species are native in their area, and to read labels of seed mixtures to ensure that the mixes are truly native.
OTHER MANAGEMENT CONSIDERATIONS:Several experiments show that rattail sixweeks grass interferes with establishment and/or growth of rare native California herbs. At Miramar Mounds National Natural Landmark in San Diego, California, rattail sixweeks grass competes with the federally endangered forb San Diego mesamint (Pogogyne abramsii) [205] for water near vernal pools. In a removal study on vernal pool edges, aboveground biomass of San Diego mesamint plants grown with rattail sixweeks grass was significantly less than biomass of San Diego mesamint plants grown alone. Negative effect of rattail sixweeks grass on San Diego mesamint biomass was greatest in early winter (P=0.06, r² = 0.46) and late winter (P=0.07, r² = 0.44) compared to the end of the growing season in April (P=0.15, r² = 0.32) [18]. On the Lawrence Livermore National Laboratory Site of California, the federally endangered largeflowered fiddleneck (Amsinckia grandiflora) [205] showed significantly reduced (P>0.01) inflorescence production on soft brome-rattail sixweeks grass-dominated sites compared with treatment sites where nonnative species were removed. Predawn soil water potential was significantly lower (P>0.01) on soft chess-rattail sixweeks grass sites compared with sites where nonnative annuals were removed. Carlsen and others [39] suggested that water competition may be one of the mechanisms whereby rattail sixweeks grass interferes with native herbs. On the Santa Rosa Plateau Ecological Reserve, roundleaf stork's-bill showed increased cover on plots where nonnative annuals, including rattail sixweeks grass, were removed compared to unweeded plots [69].
Rattail sixweeks grass also interferes with establishment and growth of more common West Coast native and cultivated species [81]. In an old-field experiment in Yolo County, California, 'Zorro' rattail sixweeks grass was included in a grass seed mix that was otherwise free of nonnative grasses to assess 'Zorro' rattail sixweeks grass's impact on establishment and growth of the seeded-in native grasses. Native grasses in the mix included blue wildrye, meadow barley (Hordeum brachyantherum), California melic (Melica californica), nodding needlegrass (Nassella cernua), purple needlegrass, and Sandberg bluegrass (Poa secunda). The field was disked before treatments. Four treatment plots at 4 different rattail sixweeks grass seed densities were used; seed densities of the native species were kept constant and response data for the native grass species were pooled. The researchers found rattail sixweeks grass was "strongly plastic in growth response, producing similar amounts of above-ground biomass at all seedling densities". However, native species showed significantly increased seedling mortality (P=0.0017), reduced weight:height ratio or etiolation (P=0.008), and decreased aboveground biomass (P=0.002) with increasing rattail sixweeks grass seedling density. Several unplanted herb species also established in treatment plots. The unplanted species, designated as "weeds", included fringed redmaids (Calandrinia ciliata, a native annual forb), field bindweed (Convolvulus arvensis, a nonnative perennial forb), yellow starthistle (a nonnative perennial forb), wild oat (a nonnative annual grass), and toad rush (Juncus bufonius, a native annual graminoid). Like the planted grasses, the weeds showed similar responses of increased seedling mortality (P=0.0017), etiolation (P=0.008), and decreased aboveground biomass (P=0.002) with increasing rattail sixweeks grass seedling density. The researchers concluded that rattail sixweeks grass interfered with establishment and growth of other herbs, and that "including this exotic annual in native seed mixtures is counterproductive to restoration efforts" [34]. Rattail sixweeks grass also interferes with growth of cultivated tall fescue (Schedonorus arundinaceus, a nonnative grass) in pastures [40].
Little is known of rattail sixweeks grass's potential to invade ecosystems in nonmediterranean climates. Although rattail sixweeks grass is noted in southwestern deserts [30,33], there are no studies to date (2006) showing it is invasive there. Rattail sixweeks grass may compete poorly with red brome in the Southwest, where red brome is highly invasive. In a greenhouse competition study using seeds from Arizona's Sonoran Desert, Salo and others [178] found that red brome outcompeted rattail sixweeks grass and sixweeks grass (Vulpia octoflora) for nitrogen. When grown with red brome, red brome significantly (P<0.01) reduced biomass gain of the sixweeks grasses compared to biomass accumulations when the sixweeks grasses were grown alone [178]. In temperate coast Douglas-fir rain forest on the Olympic National Forest, Washington, rattail sixweeks grass occurs as a ruderal roadside species but does not invade forestland [88]. Changing climate patterns may increase rattail sixweeks grass's invasiveness in some areas where it was formerly not a problem.
Rattail sixweeks grass is sometimes described as allelopathic [150]. Rattail sixweeks grass extracts inhibited common wheat (Triticum aestivum) germination in the laboratory [4]. It is uncertain whether or not natural concentrations of rattail sixweeks grass leachate are allelopathic in the field. Agricultural experiments in the Carolinas showed peach (Prunus persica) seedlings had higher mortality rates when rattail sixweeks grass, soft chess, and hard fescue (Festuca brevipila) were planted for ground cover compared to nimblewill (Muhlenbergia schreneri) [153]. Further field and laboratory investigations are needed on possible allelopathy of rattail sixweeks grass.
Control: Eradication of extensive rattail sixweeks grass stands is not a reasonable goal in mediterranean regions of California and Oregon. The type conversion from California and Oregon prairies to annual grasslands is complete and irreversible [36,87,112,116]. Nearly one-fifth of California was once bunchgrass prairie, yet Barry [14] estimated that 0.1% of the original California prairie remained in 1972. The exotic annuals cannot be eradicated, or even controlled, at the landscape level [36,87,116]. At smaller scales, however, control may reduce the proportion of rattail sixweeks grass and other nonnative annuals relative to native perennial bunchgrasses and forbs. Rattail sixweeks grass and other nonnative annual grasses are usually controlled as a guild, so individual species responses to control methods are often not tested or recorded. With its short life span, there is usually only a short window of opportunity to enact control while rattail sixweeks grass is actively growing. Control of rattail sixweeks grass is especially complicated because it resembles native sixweeks grasses (Vulpia spp.). Sixweeks grasses can be difficult to distinguish in the field, and rattail sixweeks grass and native sixweeks grasses respond similarly to control treatments [103,104]. Rattail sixweeks grass control may not be advisable when it occurs in mixed stands where native annual grasses form an important part of the plant community. Little work has been conducted in controlling rattail sixweeks grass in wildland settings. Research and publication of rattail sixweeks grass control efforts are needed.
Tu and others [202] provide a comprehensive review of weed control methods that are applicable for use in natural areas. The information is also available online (Weed control methods handbook).
Preventing rattail sixweeks grass seed spread is the best way to slow or stop its invasion onto new sites. Using native seed mixes in rehabilitation projects [114,125] (see Rehabilitation), and thoroughly cleaning vehicles and equipment [203] (see Fire suppression), can reduce rattail sixweeks grass spread. Rattail sixweeks grass's long awns, which are adapted for long-distance dispersal [209], are likely to catch on machinery.
Integrated management is usually the most effective way to control invasive plants [223]. However, as of 2006 there were few studies on integrated control of rattail sixweeks grass. Gillespie and Allen [69] successfully used prescribed fire in combination with hand-pulling to reduce relative cover of rattail sixweeks grass and other nonnatives annuals compared to native herbaceous annuals. See details of their study in Restoration. Further studies are needed on integrated control of rattail sixweeks grass and other nonnative annuals.
On the Agate Desert Preserve of southwestern Oregon, integrated controls that manipulated soil nitrogen levels in combination with herbicide were less effective at controlling rattail sixweeks grass and other nonnatives annuals than a single herbicide application [102] (see Chemical control below).
Physical/mechanical: No information is available on this topic.
Fire: See Fire Management Considerations.
Biological: No information is available on this topic.
Chemical control of rattail sixweeks grass with herbicides is problematic because most herbicides used on rattail sixweeks grass are nonselective, killing nontarget herbs as well as rattail sixweeks grass and other nonnatives. On the Agate Desert Preserve, late fall application of glyphosate―timed after annual grass seedling emergence but before emergence of native bluebunch wheatgrass, Idaho fescue, and Lemmon's needlegrass (Achnatherum lemmonii) seedlings― gave good control of rattail sixweeks grass and other nonnatives and promoted native forbs. There was no significant difference (P>0.05) in native grass cover between sprayed and unsprayed plots. Herbicide treatment reduced nonnative grass cover by 80% relative to mulch or nitrogen-enriched mulch treatments (P<0.05) [102]. Besides glyphosate, rattail sixweeks grass can also be controlled with simazine [137,138]. Applications of either quazilofop, fluazifop-p-butyl, fluazifop-p-butyl and simazine, sulfometuron, glyphosate, sethoxydim, or oryzalin controlled rattail sixweeks grass in Australian pastures, with sulfmeturon giving best control [10]. See EPA's Pesticides website for current information on usage restrictions for simazine and other herbicides.
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