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Vulpia microstachys

• INTRODUCTORY
• DISTRIBUTION AND OCCURRENCE
• BOTANICAL AND ECOLOGICAL CHARACTERISTICS
• FIRE ECOLOGY
• FIRE EFFECTS
• MANAGEMENT CONSIDERATIONS
• REFERENCES

INTRODUCTORY

AUTHORSHIP AND CITATION FEIS ABBREVIATION NRCS PLANT CODE COMMON NAMES TAXONOMY SYNONYMS LIFE FORM FEDERAL LEGAL STATUS OTHER STATUS
	Vulpia microstachys-Parvisedum pumilum-Lasthenia californica association. Photo courtesy of Julie Evans, California Native Plant Society.

• Vulpia microstachys (Nutt.) Benth. var. ciliata (Beal) Lonard & Gould [67], Eastwood small sixweeks grass

• Vulpia microstachys (Nutt.) Benth. var. confusa (Piper) Lonard & Gould [67,68], confusing small sixweeks grass

• Vulpia microstachys (Nutt.) Benth. var. microstachys [22,67,68], desert small sixweeks grass

• Vulpia microstachys (Nutt.) Benth. var. pauciflora (Beal) Lonard & Gould [22,42,55,67], Pacific small sixweeks grass

The genus Vulpia is distinguished by annual life form and cleistogamous breeding habit, while Festuca is perennial and chasmogamous [67]. Not all systematists support the separation of these closely aligned genera [33,84,109,111].

DISTRIBUTION AND OCCURRENCE

• GENERAL DISTRIBUTION
• ECOSYSTEMS
• STATES/PROVINCES
• BLM PHYSIOGRAPHIC REGIONS
• KUCHLER PLANT ASSOCIATIONS
• SAF COVER TYPES
• SRM (RANGELAND) COVER TYPES
• HABITAT TYPES AND PLANT COMMUNITIES

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.

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.

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

GENERAL BOTANICAL CHARACTERISTICS RAUNKIAER LIFE FORM REGENERATION PROCESSES SITE CHARACTERISTICS SUCCESSIONAL STATUS SEASONAL DEVELOPMENT
	© 2004 Carol W. Witham

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].

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 ²F (70 ²C) 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].

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:

FIRE ECOLOGY

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

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 (mean=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. 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".

FIRE EFFECTS

• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

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 ²>F (46-49 ²C) temperatures [63], while most Pacific small sixweeks grass seed exposed to temperatures of 160 ²F (70 ²C) for only 5 minutes remained viable. Germination of unscarified Pacific small sixweeks grass seed dropped as follows [101]:

In another laboratory study, Sweeney [101] tested Pacific small sixweeks grass's maximum heat tolerance at 320 ²F (160 ²C). 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].

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

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]:

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]:

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].

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.

MANAGEMENT CONSIDERATIONS

• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES
• OTHER MANAGEMENT CONSIDERATIONS

Palatability/nutritional value: Sampson and others [95] rate palatability of green small sixweeks grass as good for cattle and horses and fair for domestic sheep. Initially nutritious, nutritional value drops quickly as plants senesce [95].

Cover value: Vulpia species provide poor cover for small mammals and birds [26].

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].

Vulpia microstachys: REFERENCES

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