Vulpia microstachys

Small sixweeks grass is native, occurring from southern British Columbia and Montana south to New Mexico and Baja California Norte. It also occurs on the Pacific slope of South America [22,57,105,114].

Distributions of the varieties overlap considerably. Eastwood small sixweeks grass occurs from central Washington south to northern Baja California and western Arizona [67]. Desert small sixweeks grass is distributed from Washington east to western Montana and south to northern Baja California, western Nevada, and southern New Mexico [104,114]. Confusing small sixweeks grass is the least common variety, occurring from south-central Washington to southern California. Pacific small sixweeks grass occurs from Washington east to western Montana and south to Baja California Sur [65,104]. Plants database provides a distributional map of small sixweeks grass and its infrataxa.

The following biogeographic classification systems are a guide to where small sixweeks grass may occur. Except for the West Coast, precise distribution information for small sixweeks grass is limited, and small sixweeks grass may occur in ecosystems and plant communities that are not listed below.

(key to state/province abbreviations)
UNITED STATES AZ CA CO ID MT NV NM OR UT WA
CANADA BC
MEXICO B.C.N. B.C.S.

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This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):

BLM PHYSIOGRAPHIC REGIONS [9]:

1 Northern Pacific Border

2 Cascade Mountains

3 Southern Pacific Border

4 Sierra Mountains

5 Columbia Plateau

6 Upper Basin and Range

7 Lower Basin and Range

8 Northern Rocky Mountains

12 Colorado Plateau

Festuca microstachys Nutt.:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Vulpia microstachys (Nutt.) Munro:
Canada (North America)
Mexico (Mesoamerica)
Peru (South America)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

More info for the term: caryopsis

This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for species identification are available (e.g., [42,67,111]). Lonard and Gould [67] provide a detailed key for identifying infrataxa.

Small sixweeks grass is an annual. Culms are 5.9 to 30 inches (15-75 cm) long and spreading, growing solitary or in small tufts. The inflorescence is a narrow, 0.8- to 9-inch-long (2-24 cm), many-flowered panicle. Spikelets are 5.5 to 10 mm long. Lemmas are 4 to 9.5 mm long, and awned. Awns are relatively long (3.5-20 mm) . The fruit is a caryopsis, ranging from 3.5 to 6 mm in length [22,42,56,67,111].

Annuals, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems erect or ascending, Stems geniculate, decumbent, or lax, sometimes rooting at nodes, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves she athing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath hairy, hispid or prickly, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Ligule present, Ligule an unfringed eciliate membrane, Inflorescence terminal, Inflorescence an open panicle, openly paniculate, branches spreading, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence lax, widely spreading, branches drooping, pendulous, Inflorescence with 2-10 branches, Flowers bisexual, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 3-7 florets, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or betw een the florets, Spikelets secund, in rows on one side of rachis, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes distinctly unequal, Glumes shorter than adjacent lemma, Glumes equal to or longer than adjacent lemma, Glumes 1 nerved, Glumes 3 nerved, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma 5-7 nerved, Lemma body or surface hairy, Lemma apex acute or acuminate, Lemma distinctly awned, more than 2-3 mm, Lemma with 1 awn, Lemma awn less than 1 cm long, Lemma awn 1-2 cm long, Lemma awned from tip, Lemma awns straight or curved to base, Lemma margins thin, lying flat, Lemma straight, Palea present, well developed, Palea membranous, hyaline, Palea about equal to lemma, Palea 2 nerved or 2 keeled, Stamens 1, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

More info for the terms: cover, mesic, serpentine soils

Small sixweeks grass grows on mesic to dry sites that are often disturbed [22,42,67]. In Utah it is reported along roadsides and waterways [111]. In Nevada it occurs on open dry or rocky slopes [56]. In Baja California Norte, small sixweeks grass grows in sands on the dry sides of toeslopes [114].

Soils: Small sixweeks grass most commonly grows in loose, sandy soils [67], although it may also grow on clays [42,67]. In California small sixweeks grass prefers open sites, and is often found on thin or heavily compacted soils [95]. Small sixweeks grass tolerates low-nutrient soils [103]. Desert small sixweeks grass, for example, grows on serpentine or shale soils [42]. North of San Francisco, Pacific small sixweeks grass cover was positively correlated with a low soil calcium:magnesium ratio, which is characteristic of serpentine soils, although mean plant biomass was lower for Pacific small sixweeks grass growing on serpentine soils compared to plants on nonserpentine soils [53]. Pacific small sixweeks grass also grows on clay soils with favorable phosphorus and available water contents [89].

Aspect: Eastwood small sixweeks grass was most common on southeast-facing slopes (21% frequency) and least important on northeast-facing slopes (3% frequency) on annual grasslands of the Jasper Ridge Biological Preserve in San Mateo County, California. It only occurred on serpentine soils [70].

Elevation: Small sixweeks grass is documented at the following elevations:

Area Elevation Arizona low to mid-elevations [57] California sea level to 4,900 feet (0-1,500 m) [42,95] Nevada 3,600-6,200 feet (1,200-1,900 m) [56] Utah <6,000 feet (1,830 m) [111]

More info for the terms: cover, density, relict, serpentine soils

Small sixweeks grass is most important in California's annual grassland
communities and palouse prairies of the Pacific Northwest. Small sixweeks grass occurs in California riparian scrub vegetation
of the Transverse Ranges. Dominant riparian scrub species include mulefat
(Baccharis salicifolia), Nevada broomsage (Lepidospartum latisquamum),
and/or narrowleaf willow (Salix exigua).
Small sixweeks grass also occurs in riparian California broomsage (L. squamatum)
and/or Nevada broomsage scrub of southeastern California and Nevada [12].

California grasslands:
Small sixweeks grass is common to dominant in California's valleys and low foothills
[41]. On the San Joaquin Experimental Range near Fresno, it
was tallied as the 2nd most common grass over a 5-year period, comprising 9% to
17% cover [95].

It was also important in California's pristine valley grasslands. Small
sixweeks grass was probably abundant in California prairie in favorable years.
Historically, relative proportion of small sixweeks grass and other native
annual grasses was probably greatest on dry sites [40]. Grasslands on serpentine soils
are among the few remnants of California prairie,
because nonnative annual grasses cannot compete with serpentine-adapted native
annual grasses on serpentine sites [47]. Pacific small sixweeks grass is
typically the dominant grass on serpentine soils [74].
Pacific small sixweeks grass is also noted on relict purple needlegrass (Nassella
pulchra) communities [89]. Holland [45] lists Eastwood and Pacific small
sixweeks grasses as dominant with serpentine reedgrass (Calamagrostis
ophitidis) on serpentine bunchgrasslands of the Coast Ranges, Sierra Nevada,
and Transverse Ranges.
Palouse prairie:
In 1913, Weaver [110] recorded Pacific
small sixweeks grass as the dominant annual of bluebunch wheatgrass
(Pseudoroegneria spicata) steppe in southeastern
Washington and adjacent Idaho. It occurred between bunchgrass interspaces at an
average density of 150 plants/m², and also occurred
in rimrock communities on upper slopes [110].

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the terms: cover, shrub

SRM (RANGELAND) COVER TYPES [98]:

101 Bluebunch wheatgrass

102 Idaho fescue

104 Antelope bitterbrush-bluebunch wheatgrass

105 Antelope bitterbrush-Idaho fescue

106 Bluegrass scabland

107 Western juniper/big sagebrush/bluebunch wheatgrass

109 Ponderosa pine shrubland

110 Ponderosa pine-grassland

201 Blue oak woodland

202 Coast live oak woodland

203 Riparian woodland

204 North coastal shrub

205 Coastal sage shrub

206 Chamise chaparral

207 Scrub oak mixed chaparral

208 Ceanothus mixed chaparral

209 Montane shrubland

210 Bitterbrush

211 Creosote bush scrub

212 Blackbush

214 Coastal prairie

215 Valley grassland

302 Bluebunch wheatgrass-Sandberg bluegrass

304 Idaho fescue-bluebunch wheatgrass

314 Big sagebrush-bluebunch wheatgrass

315 Big sagebrush-Idaho fescue

317 Bitterbrush-bluebunch wheatgrass

318 Bitterbrush-Idaho fescue

319 Bitterbrush-rough fescue

320 Black sagebrush-bluebunch wheatgrass

321 Black sagebrush-Idaho fescue

322 Curlleaf mountain-mahogany-bluebunch wheatgrass

324 Threetip sagebrush-Idaho fescue

401 Basin big sagebrush

402 Mountain big sagebrush

403 Wyoming big sagebrush

404 Threetip sagebrush

405 Black sagebrush

412 Juniper-pinyon woodland

414 Salt desert shrub

415 Curlleaf mountain-mahogany

416 True mountain-mahogany

422 Riparian

501 Saltbush-greasewood

504 Juniper-pinyon pine woodland

505 Grama-tobosa shrub

506 Creosotebush-bursage

509 Transition between oak-juniper woodland and mahogany-oak association

607 Wheatgrass-needlegrass

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This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):

More info for the term: cover

SAF COVER TYPES [27]:

210 Interior Douglas-fir

213 Grand fir

214 Coastal prairie

215 Valley grassland

221 Red alder

229 Pacific Douglas-fir

230 Douglas-fir-western hemlock

233 Oregon white oak

234 Douglas-fir-tanoak-Pacific madrone

235 Cottonwood-willow

237 Interior ponderosa pine

238 Western juniper

239 Pinyon-juniper

243 Sierra Nevada mixed conifer

244 Pacific ponderosa pine-Douglas-fir

245 Pacific ponderosa pine

246 California black oak

249 Canyon live oak

250 Blue oak-foothills pine

255 California coast live oak

256 California mixed subalpine

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

More info for the term: shrub

KUCHLER [62] PLANT ASSOCIATIONS:

K002 Cedar-hemlock-Douglas-fir forest

K003 Silver fir-Douglas-fir forest

K005 Mixed conifer forest

K009 Pine-cypress forest

K010 Ponderosa shrub forest

K011 Western ponderosa forest

K012 Douglas-fir forest

K014 Grand fir-Douglas-fir forest

K018 Pine-Douglas-fir forest

K020 Spruce-fir-Douglas-fir forest

K023 Juniper-pinyon woodland

K024 Juniper steppe woodland

K025 Alder-ash forest

K026 Oregon oakwoods

K028 Mosaic of K002 and K026

K029 California mixed evergreen forest

K030 California oakwoods

K031 Oak-juniper woodland

K032 Transition between K031 and K037

K033 Chaparral

K034 Montane chaparral

K035 Coastal sagebrush

K036 Mosaic of K030 and K035

K037 Mountain-mahogany-oak scrub

K038 Great Basin sagebrush

K039 Blackbrush

K040 Saltbush-greasewood

K041 Creosote bush

K042 Creosote bush-bur sage

K047 Fescue-oatgrass

K048 California steppe

K050 Fescue-wheatgrass

K051 Wheatgrass-bluegrass

K055 Sagebrush steppe

K058 Grama-tobosa shrubsteppe

K063 Foothills prairie

K064 Grama-needlegrass-wheatgrass

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

ECOSYSTEMS [30]:

FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES28 Western hardwoods

FRES29 Sagebrush

FRES30 Desert shrub

FRES34 Chaparral-mountain shrub

FRES35 Pinyon-juniper

FRES36 Mountain grasslands

FRES38 Plains grasslands

FRES40 Desert grasslands

FRES42 Annual grasslands

More info for the terms: cover, frequency

Prescribed and wildfires are most likely to benefit or have no effect on small sixweeks grass coverage and frequency. Typically a minor grass favored by disturbance and varying in cover from year to year, small sixweeks grass is well adapted to establish in most early postfire environments. Widespread fire that burns into the soil, killing seed, can reduce small sixweeks grass's ability to recover from fire. Nonnative annual grasses, which outcompete sixweeks grass (see Invasives), can also negatively impact postfire coverage and frequency of small sixweeks grass. A postfire reduction in sixweeks grass is likely if annual bromes, schismus, and/or lovegrasses are present before fire or represented in the seed bank.

Small sixweeks grass is sometimes used in seed mixes to reduce postfire erosion [38]. Its effectiveness in doing so has not been tested, although it is generally recommended for short-term erosion protection (see Value for Rehabilitation of Disturbed Sites).

More info for the terms: density, forb, frequency, wildfire

A July 1961 wildfire had little effect on Pacific small sixweeks grass near
Clarkston, Washington. The fire occurred in an old field succeeding to
rubber rabbitbrush (Chrysothamnus nauseosus)/cheatgrass and bluebunch wheatgrass-Sandberg bluegrass communities.
In the rubber rabbitbrush/cheatgrass community, Pacific small sixweeks grass was not present on burned plots
and had had approximately 1% coverage on adjacent unburned plots.
Mean percent coverage of Pacific small sixweeks grass on burned and adjacent
unburned plots in the bluebunch wheatgrass-Sandberg bluegrass community was [23]:

 Postfire year 2Postfire year 4Postfire year 12BurnedCover (%)1trace1Frequency (%)58255UnburnedCover (%)0trace1Frequency (%)01825
Fall and spring prescribed burning in east-central Oregon had no significant
effect on small sixweeks grass density or frequency in postfire year 1 or 2 [96]. See the Research Project Summary of this work for more information on fire effects
on small sixweeks grass and 60 additional grass, forb, and woody plant species.

More info for the terms: cover, frequency, natural, presence, relative frequency, serpentine soils, wildfire

Small sixweeks grass establishes from soil-stored seed in early postfire plant communities. It is often common after fire [39]. Sampson and others [95] describe recent chaparral burns as "favorite habitat" for small sixweeks grass. In California, Sampson and Burcham [94] noted Pacific small sixweeks grass presence the 1st year after prescribed burning in chamise and mix-shrub chaparral communities in Mendocino and Shasta counties. In a survey on chamise and mixed-shrub chaparral communities of California, Sweeney [101] found small sixweeks grass was "common on 1-year-old burns, becoming increasingly abundant on 2-, 3-, and 4-year-old burns." It was also abundant on open, disturbed sites adjacent to burns [101].

Harrison and others [39] found a significant (p<0.01) soil-fire interaction for Pacific small sixweeks grass on the California Natural Reserve in northern California. Pacific small sixweeks grass frequency (%) was highest on burned serpentine soils [39]:

Soil type

Frequency

burned unburned nonserpentine 0.4% 0.5% serpentine 3.6% 3.1%

Daubenmire [23] found a July 1961 wildfire promoted Pacific small sixweeks grass near Clarkston, Washington. The fire occurred in an old field succeeding to a bluebunch wheatgrass-Sandberg bluegrass community. Percent cover of Pacific small sixweeks grass was low under all conditions, but relative frequency increased in early postfire years [23]:

  Postfire year 2 Postfire year 4 Postfire year 12 Burned sites Cover (%) 0 1 1 Frequency (%) 0 58 55 Unburned sites Cover (%) 0 trace 1 Frequency (%) 0 18 25

Often, fire may have only a slight positive effect to no effect on small sixweeks grass. Small sixweeks grass was present but uncommon on both burned and unburned sites 6 years after wildfire in a blackbrush community in southwestern Utah [15]. In a survey of maritime burns, Eastwood small sixweeks grass had 4% frequency on earl seral burns (postfire years 1-5) in maritime coast live oak in Santa Barbara County, California. It was not present on maritime chamise chaparral burns [25].

More info for the terms: charate, prescribed burn

Odion [80] found an insignificant (p>0.05) positive effect of heat on small sixweeks grass seedling emergence in laboratory tests. At Vandenburg Air Force Base, California, pre- and postfire soil samples were collected from a maritime chamise community that had not burned for at least 75 years (at Site 1) or 50 years (at Site 2). Prefire soil cores were collected in fall, and both study sites were burned under prescription soon after. Postfire soil samples were also collected [80]. Fire intensity was relatively high (see [81] for fire data). Laboratory treatments for prefire soil samples were a control, heat (100 °C for 7 min.), and heat with chamise charate. Seedling emergence was counted for pre- and postfire soils samples and in the field on prescribed burn plots. Mean number of germinants/m² emerging from soil samples and on burn plots was [80]:

Prefire soil samples    Control 0    Heat 8.8    Heat and charate Site 1 Site 2 4.4 44.4 Postfire soil samples 0 0 Field emergence on burn 0 0

It is likely that high fire intensities killed small sixweeks grass seed on the prescribed burn sites.

More info for the terms: charate, fresh, litter, root crown

Fire occurring when plants are mature kills small sixweeks grass [24]. Annual grasses may sprout from the root crown when fire occurs early in the growing season [49].

Fire in any season may reduce the seed bank [24]. Small sixweeks grass seed in litter or lying on the soil surface is most vulnerable to fire kill [101,117]. Most surface fires probably do not harm small sixweeks grass seed that is buried in soil [40,80]. However, even buried seed can die when exposed to heat for long periods of time. In laboratory experiments, small sixweeks grass seed buried in moist soil died after a 1-hour exposure to 115 to 121 °F (46-49 °C) temperatures [63], while most Pacific small sixweeks grass seed exposed to temperatures of 160 °F (70 °C) for only 5 minutes remained viable. Germination of unscarified Pacific small sixweeks grass seed dropped as follows [101]:

  Control
(room temperature) 50 °C 60 °C 70 °C 80 °C germination (%) 100 100 95 65 0

In another laboratory study, Sweeney [101] tested Pacific small sixweeks grass's maximum heat tolerance at 320 °F (160 °C). In a pot experiment, he obtained 100% germination of fresh, untreated Pacific small sixweeks grass seeds buried at 0.25 inch (0.63 cm), while germination dropped to 68% after excelsior was burned on top of similarly treated seeds. Charate slightly lowered germination of Pacific small sixweeks grass seed from 100% to 95% [101].

More info for the terms: ground residual colonizer, initial off-site colonizer, secondary colonizer

POSTFIRE REGENERATION STRATEGY [99]:
Ground residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)

More info for the terms: fire frequency, fire interval, fire regime, fire severity, frequency, fuel, fuel continuity, litter, serpentine soils, severity, shrub, shrubs, stand-replacing fire, succession, tree

Fire adaptations: Small sixweeks grass establishes from soil-stored seed after fire [25]. No other means of postfire regeneration are documented, although establishment from off-site wind- or animal-dispersal seed is possible.

FIRE REGIMES: Fire is important in retaining open structure in some of the communities where small sixweeks grass is common, but fire was historically infrequent in other plant communities where it occurs. Frequent fire in palouse prairies and annual grasslands maintains the grasslands by preventing invasion of woody plants and reducing litter [82,90,100,115]. Fire plays a more variable ecological role in shrublands where sixweeks grass is important. Some of the shrublands (e.g., chamise (Adenostoma fasciculatum) and other chaparral types) depend on moderate-interval (30-100 years), stand-replacing fire [82]; others are adapted to mixed-severity fires (e.g., big sagebrush (Artemisia tridentata)) [3,21,71,96]; while some desert shrubland types such as creosotebush (Larrea tridentata) are poorly adapted to fire [17]. Descriptions of fire regimes of communities where small sixweeks grass is important follow.

Palouse prairie: Fire frequencies for bluebunch wheatgrass-dominated habitats vary considerably, depending on the associated species [7]. Most mean fire intervals are less than 30 years. Estimates for historical fire intervals in the Snake River Canyon of Idaho for bluebunch wheatgrass-Idaho fescue-Sandberg bluegrass (Festuca idahoensis-Poa secunda) communities are 10 to 25 years [51].

Annual grasslands: 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 today's annual grasslands are 20 to 30 years [100].

Sagebrush/bunchgrass: Prior to the 1890s, probably only a few grass species occurred in early postfire sagebrush (Artemisia spp.) communities of the Great Basin. Of these, small sixweeks grass and sixweeks grass (Vulpia octoflora) might have been most important. Generally, native Vulpias would increase for a few postfire years, then be suppressed by bunchgrasses such as bluebunch wheatgrass, bottlebrush squirreltail (Elymus elymoides), and Idaho fescue, and by shrubs such as basin big sagebrush (A. tridentata ssp. tridentata) and rabbitbrush (Chrysothamnus spp.) [83]. Historic fire return interval ranged from around 20 to 100 years [46,115,116]. Cheatgrass and medusahead (Taeniatherum caput-medusae), 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 [83].

Desert shrub: Small sixweeks grass is a common component of southwestern steppe communities. For example, it had 40% frequency in a vegetation survey in a creosotebush-white bursage (Ambrosia dumosa) community in the Mojave Desert [14]. Fire is infrequent in pristine creosotebush-white bursage, Joshua tree (Yucca brevifolia), and saguaro (Carnegiea gigantea) communities. Discontinuity of fine fuels in most years hinders the spread of fire, which was historically uncommon to rare [15,17,19,48,79]. In most years, pristine stand structure of these southwestern desert shrub communities is widely spaced woody plants, bare interspaces, and some perennial bunchgrasses [13,17,18,91]. During wet winters and springs, annuals such as sixweeks grass increase fuels loads. Biomass accumulations from native annuals following an exceptionally wet growing season may provide enough fine fuels to carry a fire in desert ecosystems that otherwise rarely burned [11,102].

Historically, dry sixweeks grass and other native annuals rarely fueled fires in desert shrublands [17], but nonnative, invasive annual grasses including red brome (B. rubens) and schismus have increased fuel loads from historic levels. While native annual grasses mostly grow in the protective shade of shrubs, nonnative grasses also grow in shrub interspaces, increasing fuel continuity and fire frequency and severity on invaded sites. Ecological consequences are serious, as most southwestern desert plants are poorly adapted to frequent and/or stand-replacing fire [17,18]. Nonnative annual grasses outcompete small sixweeks grass on most desert shrub sites (see Invasives). For detailed information on fine fuel production of small sixweeks grass, red brome, schismus, and other Mojave Desert annuals, see the Research Project Summary Nonnative annual grass fuels and fire in California's Mojave Desert.

Chaparral: Historic fire return intervals in chamise and mixed-chaparral ranged from 10 to 90 years [82,101]. 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 [59].

Coastal sage scrub chaparral: Documentation of historic fire intervals in coastal sage scrub is lacking. 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 [72]. Vogl [108] estimated an average fire 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 seral chaparral due to higher litter loading and the higher percentage of terpenes in coastal sage scrub vegetation [34,69]. 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. Sixweeks grass is noted in early postfire succession in the community [113].

Fuels: Dry sixweeks grass is a "poor" fuel. Because it contributes little fine fuel biomass and crumbles rapidly upon drying, small sixweeks grass typically contributes little fine fuel biomass during the fire season [17,106]. During prescribed burning on the Mojave Desert, native annual vegetation including sixweeks grass was unable to sustain fire despite abundant growth after above-average winter rains [17].

Productivity on serpentine soils is generally low. Pacific small sixweeks grass biomass on California's serpentine annual grasslands, where Pacific small sixweeks grass is often dominant, averages around 280 g/m² [37,70]. Mean biomass of Pacific small sixweeks grass on serpentine annual grassland of the Jasper Ridge Biological Preserve was 4.4 g/m² over 4 years (s x   =1.7 g/m², range=1.8-8.6 g/m²) [44].

The following table provides fire return intervals for plant communities and ecosystems where small sixweeks grass is important. For further information, see the FEIS review of the dominant species listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years) silver fir-Douglas-fir Abies amabilis-Pseudotsuga menziesii var. menziesii >200 grand fir Abies grandis 35-200 [3] California chaparral Adenostoma and/or Arctostaphylos spp. <35 to <100 sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [82] basin big sagebrush Artemisia tridentata var. tridentata 12-43 [96] mountain big sagebrush Artemisia tridentata var. vaseyana 15-40 [4,21,71] Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40**) [107,117] 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 blue grama-tobosa prairie Bouteloua gracilis-Pleuraphis mutica 82] cheatgrass Bromus tectorum 83,112] California montane chaparral Ceanothus and/or Arctostaphylos spp. 50-100 [82] curlleaf mountain-mahogany* Cercocarpus ledifolius 13-1,000 [5,97] blackbrush Coleogyne ramosissima 82] California steppe Festuca-Danthonia spp. 82,100] western juniper Juniperus occidentalis 20-70 creosotebush Larrea tridentata <35 to <100 [82] wheatgrass plains grasslands Pascopyrum smithii <5-47+ [82,115] pine-cypress forest Pinus-Cupressus spp. <35 to 200 [3] pinyon-juniper Pinus-Juniperus spp. <35 [82] Colorado pinyon Pinus edulis 10-400+ [28,32,58,82] Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [3] interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [3,6,64] mountain grasslands Pseudoroegneria spicata 3-40 (x = 10) [2,3] coastal Douglas-fir* Pseudotsuga menziesii var. menziesii 40-240 [3,75,88] Pacific coast mixed evergreen Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus menziesii <35 California oakwoods Quercus spp. <35 [3] oak-juniper woodland (Southwest) Quercus-Juniperus spp. <35 to <200 [82] coast live oak Quercus agrifolia 2-75 [35] canyon live oak Quercus chrysolepis <35 to 200 blue oak-foothills pine Quercus douglasii-P. sabiniana <35 Oregon white oak Quercus garryana <35 [3] California black oak Quercus kelloggii 5-30 [82] western redcedar-western hemlock Thuja plicata-Tsuga heterophylla >200 [3] *fire return interval varies widely; trends in variation are noted in the species review

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More info for the terms: frequency, succession

Small sixweeks grass prefers open sites [56,57]. It may be found in early to late succession when the canopy remains open. For example, it grows on burns in early succession [24,113] (see Fire Effects and the coastal sage scrub section of Fire Ecology). Renner and Allred [86] classify small sixweeks grass as an invader in late-successional plains grasslands. It tends to increase with disturbance or when rangeland conditions deteriorate [20]. In old field succession on a bluebunch wheatgrass-Sandberg bluegrass (Poa secunda) community near Clarkston, Washington, Pacific sixweeks grass showed trace coverage and 2% to 8% frequency on young fields (1-12 years since tilling); 1% to 2% coverage and 20% to 70% frequency on old fields (39-52 years since tilling); and 1% coverage and 35% to 38% frequency on untilled sites [23].

More info for the terms: cover, density, litter, root crown

Because it is an annual, sixweeks grass regenerates only from seed [54,95]. Published information on small sixweeks grass's reproductive biology is scarce, particularly in regard to seed biology and germination. Further research is needed on regeneration requirements of small sixweeks grass.

Breeding system/pollination: Small sixweeks grass is largely cleistogamous. Gene flow within and among populations is minimal to nonexistent due to cleistogamous habit [54,68]; however, there are occasional chasmogamous plants [54].

Seed production: In a greenhouse study, small sixweeks grass grown in serpentine soil significantly (p=0.05) increased aboveground vegetative and seed biomass when fertilized with either N-P-K with calcium amendment or compost with calcium amendment [78]. Information on small sixweeks grass seed production in the field was not found.

Seed dispersal: Seed is dispersed primarily by wind [1]. The seed awns provide a mechanism for possible animal dispersal, although animal dispersal is not documented.

Seed banking: Small sixweeks grass maintains a seed bank [8,101]. On annual grassland at the Hopland Field Station, California, Vulpia species (V. microstachys, V. bromoides, and V. myuros) had a mean density of 1,227 seeds/dm² in 1974 and 438 seeds/dm² in 1975. Mean seed:germinant ratios were 10:1 and 6:1 in 1974 and 1975, respectively. Vulpia grasses were pooled due to difficulty of identifying species in the field [8]. On a serpentine site near Colusa, California, small sixweeks grass seed density averaged 400/m² [78].

Germination: Few studies to date (2006) address germination requirements of small sixweeks grass. It appears to require neither scarification nor stratification [101,103], although such treatments or processes may increase germination. Desert small sixweeks grass seed collected from the Intermountain region showed 85% mean germination [52]. Sweeney [101] obtained 92.2% mean germination (range=80%-100%) of unstratified, unscarified Pacific small sixweeks grass collected in California.

Small sixweeks grass seed tolerates moderate heat for short periods. In a heat tolerance test, 65% of unscarified Pacific small sixweeks grass seeds that sustained a maximum temperature of 160 °F (70°C) for 5 minutes remained germinable (see IMMEDIATE FIRE EFFECT ON PLANT for further information on this study) [101]. Plant Response to Fire also provides further information on fire effects on small sixweeks grass germination.

As an annual, small sixweeks grass cover may fluctuate from year to year [95], and sometimes no viable seed may germinate in a seemingly favorable germinating season. On the Hopland Field Station, small sixweeks grass and other Vulpia species showed "good" germination at the beginning of the fall growing season, but viable seed was still plentiful in the seed bank in spring [8].

Soil or litter cover may increase germination. In a greenhouse study, Pacific small sixweeks grass germination was improved by covering seed with either 0.3 or 0.5 inch (0.8 or 1.2 cm) of topsoil. Serpentine litter had no effect on germination. Gulmon [36] suggested that Pacific small sixweeks grass seeds benefit from the increased wetting time afforded by topsoil coverage. Pacific small sixweeks grass showed significantly (p=0.007) reduced cover on plots where mulch was removed compared to plots with intact mulch (9.98% and 25.95%, respectively) [60].

Seedling establishment/growth: As of 2006, little information was available on growth rates of small sixweeks grass. Although some small sixweeks grass ecotypes are adapted to serpentine soils, the low calcium levels characteristic of such soils may inhibit seedling root growth [78]. After seedlings at the Hopland Field Station had reached several weeks of age, they suffered little mortality through winter and spring [8].

Asexual regeneration: Because it is an annual, small sixweeks grass does not sprout from the root crown after it produces seed. It dies. However, Vulpia species may die back and sprout from the root crown when wet weather follows a short-term dry period within the growing season [49].

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More info for the term: therophyte

RAUNKIAER [85] LIFE FORM:
Therophyte

More info for the term: graminoid

Graminoid

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More info for the terms: cool-season, phenology

Small sixweeks grass is a cool-season species which, depending on geographic location, establishes in late fall or early spring, flowers in spring or early summer, then matures, sets seed, and dies by late spring or early summer. Germination usually coincides with the beginning of fall precipitation [8]. Phenology of small sixweeks grass across its distributional range is shown below.

Area Germinates Flowers Seeds mature Arizona ---- April-June [57] ---- California mid-Oct. [8] March-June [76,95] ---- Nevada ---- April-June [56] ---- Intermountain region ---- May-June [22] late July-late Sept. [52] Baja California Norte ---- May-July [114] ----

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Specimens with Barcodes: 5
Species With Barcodes: 1

Information on state-level protected status of plants in the United States is available at Plants Database.

Canada

Rounded National Status Rank: N4 - Apparently Secure

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: G5 - Secure

More info for the terms: cover, density, frequency, interference, natural, serpentine soils

Rangeland:
Moderate to heavy grazing may favor small sixweeks grass at the expense of more
palatable perennial grasses [95]. On a clearcut in
northeastern Oregon, small sixweeks grass was slightly more frequent on
cattle-grazed than on big game-grazed plots, showing 4%, 2%, and 3% frequency on
plots used by cattle, big game, and both, respectively [61]. It was also more
common on clipped plots at Carrizo Plain National Monument, California, showing
0.30% on clipped plots and 0.15% cover on ungrazed plots [60]. However,
Pacific small sixweeks grass on the California Natural Reserve
was more frequent on ungrazed than on grazed sites.
On cattle-grazed plots, frequency was 0.3% on nonserpentine soils and 2.1% on serpentine soils,
and 0.6% and 3.3% on ungrazed nonserpentine and serpentine soils,
respectively [39].

Pacific small sixweeks grass greatly increased in cover
following addition of nitrogen fertilizer
on serpentine annual grassland of the Jasper Ridge Biological Preserve,
dominating some fertilized plots to near exclusion of other
species. Density of Pacific small sixweeks grass averaged 290 plants/m²
on fertilized plots and 150 plants/m² on
unfertilized plots. Most annuals (native or not) declined with nitrogen
amendment to the serpentine soil [44].
Invasives:
Nonnative annual grasses can interfere with establishment and growth
of small sixweeks grass. Cheatgrass has relegated small sixweeks grass to
minor status on dry portions of the Columbia Plateau, where
small sixweeks grass was once abundant [66]. In a greenhouse experiment using small sixweeks grass, red
brome (a nonnative species), and pinnate tansymustard (Descurainia pinnata, a native species)
seed from the Mojave Desert, red
brome extracted soil water faster and had higher total plant nitrogen content
compared to small sixweeks grass and pinnate tansymustard. Red brome also showed higher
germination rates compared to small sixweeks grass and pinnate tansymustard,
although small sixweeks grass produced more total seed. A growth chamber study showed
biomass of small sixweeks grass was significantly (p<0.01) reduced when grown
with red brome in nitrogen-fertilized desert soil compared to small sixweeks
grass grown with red brome in unfertilized desert soil [93].
Pacific small sixweeks grass is adapted to low-nitrogen soils and can outcompete
nonnative annual grasses on low-nitrogen serpentine soils. Nonnative Italian ryegrass (Lolium
multiflorum) and soft chess (Bromus hordeaceus) are infrequent on
serpentine soils unless nitrogen is added [29]. In a survey of California annual
grasslands on 92 sites, Pacific small sixweeks grass frequency averaged 48.5% on serpentine sites
and 5.5% on nonserpentine soils. Frequency was not significantly affected by
distance from roads [31].
A field inventory and follow-up experiment in grasslands north of San Francisco
showed evidence of growth interference from nonnative annuals, and also showed
that Pacific small sixweeks grass shows ecotypic differences. Pacific small
sixweeks grass was most common (and dominant) on rocky serpentine slopes, intermediate on serpentine
meadows (which were dominated by native forbs), and least common on
nonserpentine grasslands (which were dominated by nonnative annual grasses). On
plots treated with herbicide and seeded with Pacific small sixweeks grass
collected from nonserpentine sites, total Pacific
small sixweeks grass
seedling emergence and survival was greatest on nonserpentine soils and lowest
on serpentine soils. However, Pacific small sixweeks grass seed from rocky
serpentine slopes showed best emergence and survival on
serpentine soils [53].