Introductory
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



ABBREVIATION : 
BOUBARB

SYNONYMS : 
   Bouteloua barbata


SCS PLANT CODE : 
   BOBA2


COMMON NAMES : 
   sixweeks grama
   six-weeks grama
   six weeks grama


TAXONOMY : 
Numerous floras list sixweeks grama as a distinct species, Bouteloua
barbata Lag. [3,10,14,15].  However, a taxonomic revision of the genus
Bouteloua by Gould [9] treats sixweeks grama as a variety of Bouteloua
barbata.  Under Gould's treatment, the previously distinct species
Bouteloua barbata Lag., B. rothrockii Vasey, and B. sonorae Griffiths
are considered to be three varieties of a single species.  Gould's
treatment is presented below:

  Bouteloua barbata Lag. Varied. Ci.

    var. barbata (sixweeks grama)

    var. sonorae (Griffiths) Gould, comb. Nov. (Sonoran grama)

    var. rothrockii (Vasey) Gould, comb. Nov. (Rothrock grama) 

This paper follows Gould's taxonomic treatment.  Discussion is limited
to sixweeks grama.  

It is interesting to note that sixweeks grama is a short-lived annual,
while the other two varieties are perennial.


LIFE FORM : 
Graminoid

FEDERAL LEGAL STATUS : 
No special status

OTHER STATUS : 
NO-ENTRY


COMPILED BY AND DATE : 
Ronald Uchytil/November 1990


LAST REVISED BY AND DATE : 
NO-ENTRY


AUTHORSHIP AND CITATION : 
Uchytil, Ronald J. 1990. Bouteloua barbata var. barbata. In: Remainder of Citation

DISTRIBUTION AND OCCURRENCE
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



GENERAL DISTRIBUTION : 
Sixweeks grama is distributed from southern California, Nevada, Utah,
and Colorado south through Mexico [3].  In southern New Mexico and
Arizona, sixweeks grama and Rothrock grama (B. barbata var. rothrockii)
grow together and are difficult to distinguish [9].


ECOSYSTEMS : 
   FRES30  Desert shrub
   FRES32  Texas savanna
   FRES33  Southwestern shrubsteppe
   FRES35  Pinyon - juniper
   FRES38  Plains grasslands
   FRES40  Desert grasslands


STATES : 
     AZ  CA  CO  NV  NM  TX  UT  MEXICO


ADMINISTRATIVE UNITS : 
     ARCH  BIBE  CACA  CHCU  CORO  DEVA
     FOBO  GLCA  GUMO  JOTR  LAME  MOCA
     ORPI  PEFO  SAGU


BLM PHYSIOGRAPHIC REGIONS : 
    7  Lower Basin and Range
   12  Colorado Plateau
   13  Rocky Mountain Piedmont
   14  Great Plains


KUCHLER PLANT ASSOCIATIONS : 
   K023  Juniper - pinyon woodland
   K031  Oak - juniper woodland
   K041  Creosotebush
   K042  Creosotebush - bursage
   K043  Paloverde - cactus shrub
   K044  Creosotebush - tarbush
   K046  Desert: vegetation largely lacking
   K054  Grama - tobosa prairie
   K058  Grama - tobosa shrubsteppe
   K059  Trans-Pecos shrub savanna
   K060  Mesquite savanna
   K084  Cross Timbers
   K085  Mesquite - buffalograss
   K086  Juniper - oak savanna


SAF COVER TYPES : 
    66  Ash juniper - redberry (Pinchot) juniper
    68  Mesquite
   239  Pinyon - juniper


SRM (RANGELAND) COVER TYPES : 
NO-ENTRY


HABITAT TYPES AND PLANT COMMUNITIES : 
Sixweeks grama has not been listed as a dominant in vegetation
classification schemes.

VALUE AND USE
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



WOOD PRODUCTS VALUE : 
NO-ENTRY


IMPORTANCE TO LIVESTOCK AND WILDLIFE : 
Sixweeks grama is poor livestock forage.  Plants are small and produce
little forage, are green for only a short time, are nutritionally
deficient after maturity, and the roots often pull up when grazed
[11,26].  Its abundance and, therefore, availability to livestock is
irregular from year to year.

The seeds of grama grasses (Bouteloua spp.) are eaten by numerous
species of song birds and small mammals [19].  Rabbits and wild
ungulates eat grama grasses [19].  The banner-tailed kangaroo rat,
Merriam's kangaroo rat, and white-throated woodrat store sixweeks grama
seeds in their dens [20].


PALATABILITY : 
Sixweeks grama is of low palatability to livestock.


NUTRITIONAL VALUE : 
Sixweeks grama is fairly nutritious when green [26], but its nutritional
value drops rapidly after maturity, and plants become "practically
worthless" [5].  Data from a winter nutritional analysis of sixweeks
grama are presented below [22]:

                              (% of dry weight)
date         protein   ether   acid det.  ash   calcium   phosphorus
                      extract    fiber

February       5.1      1.4      51.3     6.2     .30        .05
March          6.3      1.5      53.2     1.7     .63        .05


COVER VALUE : 
Because of its small stature, sixweeks grama presumably provides cover
for only small wildlife species.


VALUE FOR REHABILITATION OF DISTURBED SITES : 
NO-ENTRY


OTHER USES AND VALUES : 
NO-ENTRY


MANAGEMENT CONSIDERATIONS : 
Sixweeks grama is highly resistant to grazing and is classified as an
invader [26].  Rangelands with an abundance of annual grasses, including
sixweeks grama, are only productive for a couple of months following
summer rains, and can be heavily stocked at this time before the grasses
deteriorate [5].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



GENERAL BOTANICAL CHARACTERISTICS : 
Sixweeks grama is a small, native, warm-season, annual bunchgrass which
grows up to about 1 foot (0.3 m) in height [26].  The slender, hollow,
tufted culms are usually prostrate but sometimes somewhat erect [3].
Plants are generally light green when growing, but cure to a straw color
[11].  Leaves are 0.4 to 2.4 inch (1-6 cm) long and 0.04 to 0.06 inch
(1-1.5 mm) wide and occur sparingly along the culms [10,21].  The
inflorescence consists of three to seven persistent, comblike spikes per
culm.  The spikes are smaller than those of perennial gramas.  Each is
0.4 to 0.8 inch (1-2 cm) long [3,24].

Robust, erect sixweeks grama plants are sometimes mistaken for Rothrock
grama, a closely related short-lived perennial.  In general, sixweeks
grama has shorter awns and the stems are more branched [3,15].  Several
floras allow proper identification [3,10,15,21].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Therophyte
   Burned or Clipped State:  Therophyte


REGENERATION PROCESSES : 
Sixweeks grama is a summer annual.  Seeds stored in the soil germinate
after summer rains; plants grow quickly and set seed in the fall before
they die.  In Joshua Tree National Monument at elevations below 1,000
feet (304 m), sixweeks grama grew and produced seeds within 4 weeks of
germination, but above 1,000 feet (304 m) plants took 6 weeks to
complete their life cycle [28].

Germination:  For germination to occur under natural conditions, two
requirements must be met:  (1) a single large rainfall of 0.6 to 1 inch
(1.5-2.5 cm) [17,28] and (2) warm daytime and nighttime soil
temperatures, which normally occur only during the summer or fall
[13,29].  Generally a heavy rainfall which saturates the soil
surrounding sixweeks grama seeds is needed for germination.  However,
following light rains, seeds sometimes germinate along washes or in
depressions [28].  In laboratory experiments, sixweeks grama exhibited
good germination under a temperature regime of warm days (80 degrees F
[27 C] for 8 hours) and warm nights (78 degrees F [26 C] for 16 hours)
but poor germination under a temperature regime of warm days (80 degrees
F [27 C]) and cool nights (55 degrees F [13 C]) [29].  Another study
showed that large numbers of sixweeks grama seeds germinated when
daytime soil temperatures were 86 degrees F (30 C), small to moderate
numbers germinated when daytime soil temperatures were between 62 and 72
degrees F (17 and 23 C), and no seeds germinated when daytime soil
temperatures were 50 degrees F (10 C) [13].

Seed dormancy:  Information concerning the length of time seeds will
remain viable is lacking.  However, considering that numerous authors
have observed that germination of sixweeks grama occurs only during
infrequent years at particular locations [6,7,13], seeds must remain
viable for a number of years.


SITE CHARACTERISTICS : 
Sixweeks grama occupies dry to moist sites [27].  In desert areas, it is
found on open, rocky or sandy slopes, gravelly flats, bajadas, and
disturbed areas with bare soil [3,11,21].  It also occupies washes and
intermittent water courses.  Sixweeks grama is most often found in
desert shrub, semidesert grassland and pinyon-juniper vegetation types
[6,21,25].  Its density is extremely variable from year to year because
of its dependence on summertime precipitation for germination.  On the
Jornada Expermintal Range in New Mexico, sixweeks grama is found in
grasslands dominated by black grama (Bouteloua eriopoda), tobosa grass
(Hilaria mutica), and burrograss (Scleropogon brevifolius) [6].  In
desert areas it is often associated with other summer annuals which
germinate at the same time.  Common associates in the Mojave Desert
include prickly pears (Opuntia spp.) and numerous summer annuals such as
needle grama (Bouteloua aristidoides), cinchweed fetidmarigold (Pectis
papposa), pigweed (Amaranthus fimbriatus), euphorbia (Euphorbia
micromera), and spiderling (Boerhaavia spicata) [24,29].

The elevational range for sixweeks grama in several western states is
presented below:

        elevational range                   state            authority

from 1,000 to 5,500 feet (305-1,676 m)       AZ                [15]
below 3,200 feet (975 m)                Rincon Mtns., AZ       [2]
below 5,000 feet (1,524 m)                  s CA               [21]
below 7,000 feet (2,134 m)                   NM                [5]
from 2,800 to 6,000 feet (850-1,820 m)       UT                [27]


SUCCESSIONAL STATUS : 
Sixweeks grama is an early seral species.  It often occupies disturbed
areas with much bare ground or areas where other vegetation is scarce
[2,7,11].  


SEASONAL DEVELOPMENT : 
Sixweeks grama grows only during the summer or fall.  Following rains of
sufficient quantity to induce germination, plants grow rapidly, set seed
within about 6 weeks, and then die [17,28].  The phenological
development of sixweeks grama in southern New Mexico is presented below
[17]:

    phenological event       timing of event

    seeds germinate          late-August to early-September
    flowering                September
    seeds mature             late-September to early-October
    seeds dispersed          late October

The time of flowering for sixweeks grama in several areas is presented
below:

    time of flowering        location                   authority
 
    June-October         s CA                             [21]
    July-October         AZ                               [15]
    August-October       Kelso Dunes, s CA                [25]
    July-September       Desert Experimental Range, UT    [7]

FIRE ECOLOGY
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



FIRE ECOLOGY OR ADAPTATIONS : 
Sixweeks grama often occupies desert sites where vegetation is too
scarce to carry fire [12].  However, in some years rainfall is
sufficient in deserts to produce an abundance of summer annuals which
can easily carry fire.  Sixweeks grama also occurs in semidesert
grasslands dominated by black grama, tobosa grass, or other perennial
grasses of the Southwest.  These grasslands readily carry fire.

Sixweeks grama seeds appear to be long-lived, and large numbers may be
stored in the soil [28,29].  The relatively low temperatures produced by
grassland fires probably do not harm sixweeks grama seeds [16].
Following fire, surviving seeds remain dormant until germination
requirements are met.


POSTFIRE REGENERATION STRATEGY : 
   ground-stored residual colonizer; seed on-site in soil

FIRE EFFECTS
SPECIES: Bouteloua barbata var. barbata | Sixweeks Grama 



IMMEDIATE FIRE EFFECT ON PLANT : 
Plants actively growing when consumed by fire are killed.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Because seeds survive burning, fire has little effect on sixweeks grama.
When favorable conditions for germination occur (warm temperatures and
moist soil), surviving seeds germinate.  Thus precipitation during the
summer following burning largely determines the response of summer
annuals in the Southwest [30].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
NO-ENTRY

References for species: Bouteloua barbata var. barbata

1. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]

2. Bowers, Janice E.; McLaughlin, Steven P. 1987. Flora and vegetation of the Rincon Mountains, Pima County, Arizona. Desert Plants. 8(2): 50-94. [495]

3. Cronquist, Arthur; Holmgren, Arthur H.; Holmgren, Noel H.; [and others]. 1977. Intermountain flora: Vascular plants of the Intermountain West, U.S.A. Vol. 6. The Monocotyledons. New York: Columbia University Press. 584 p. [719]

4. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; [and others]. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]

5. Gay, Charles W., Jr.; Dwyer, Don D. 1965. New Mexico range plants. Circular 374. Las Cruces, NM: New Mexico State University, Cooperative Extension Service. 85 p. [4039]

6. Gibbens, Robert P.; Beck, Reldon F. 1988. Changes in grass basal area and forb densities over a 64-year period on grassland types of the Jornada Experimental Range. Journal of Range Management. 41(3): 186-192. [5227]

7. Goodrich, Sherel. 1986. Vascular plants of the Desert Experimental Range, Millard County, Utah. Gen. Tech. Rep. INT-209. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 72 p. [1033]

8. Gould, Frank W. 1978. Common Texas grasses. College Station, TX: Texas A&M University Press. 267 p. [5035]

9. Gould, Frank W. 1979. The genus Bouteloua (Poaceae). Annals of the Missouri Botanical Garden. 66: 348-416. [5758]

10. Great Plains Flora Association. 1986. Flora of the Great Plains. Lawrence, KS: University Press of Kansas. 1392 p. [1603]

11. Humphrey, Robert R. 1970. Arizona range grasses: Their description, forage value and management. Bulletin 298. Tucson, AZ: The University of Arizona, Agricultural Experiment Station. 159 p. [5567]

12. Humphrey, Robert R. 1974. Fire in the deserts and desert grassland of North America. In: Kozlowski, T. T.; Ahlgren, C. E., eds. Fire and ecosystems. New York: Academic Press: 365-400. [14952]

13. Juhren, Marcella; Went, F. W.; Phillips, Edwin. 1956. Ecology of desert plants. IV. Combined field and laboratory work on germination of annuals in the Joshua Tree National Monument, California. Ecology. 37(2): 318-330. [12975]

14. Kartesz, John T.; Kartesz, Rosemarie. 1980. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. Volume II: The biota of North America. Chapel Hill, NC: The University of North Carolina Press; in confederation with Anne H. Lindsey and C. Richie Bell, North Carolina Botanical Garden. 500 p. [6954]

15. Kearney, Thomas H.; Peebles, Robert H.; Howell, John Thomas; McClintock, Elizabeth. 1960. Arizona flora. 2d ed. Berkeley, CA: University of California Press. 1085 p. [6563]

16. Keeley, Jon E. 1981. Reproductive cycles and fire regimes. In: Mooney, H. A.; Bonnicksen, T. M.; Christensen, N. L.; [and others], technical coordinators. Fire regimes and ecosystem properties: Proceedings of the conference; 1978 December 11-15; Honolulu, HI. Gen. Tech. Rep. WO-26. Washington, DC: U.S. Department of Agriculture, Forest Service: 231-277. [4395]

17. Kemp, Paul R. 1983. Phenological patterns of Chihuahuan desert plants in relation to the timing of water availability. Journal of Ecology. 71: 427-436. [5054]

18. Lyon, L. Jack; Stickney, Peter F. 1976. Early vegetal succession following large northern Rocky Mountain wildfires. In: Proceedings, Tall Timbers fire ecology conference and Intermountain Fire Research Council fire and land management symposium; 1974 October 8-10; Missoula, MT. No. 14. Tallahassee, FL: Tall Timbers Research Station: 355-373. [1496]

19. Martin, Alexander C.; Zim, Herbert S.; Nelson, Arnold L. 1951. American wildlife and plants. New York: McGraw-Hill Book Company, Inc. 500 p. [4021]

20. Monson, Gale; Kessler, Wayne. 1940. Life history notes on the banner-tailed kangaroo rat, Merriam's kangaroo rat, and white-throated wood rat in Arizona and New Mexico. Journal of Wildlife Management. 4(1): 37-43. [12166]

21. Munz, Philip A. 1973. A California flora and supplement. Berkeley, CA: University of California Press. 1905 p. [6155]

22. Nelson, A. B.; Herbel, H. M.; Jackson, H. M. 1970. Chemical composition of forage species grazed by cattle on an arid New Mexico range. Bulletin 561. Las Cruces, NM: New Mexico State University, Agricultural Experiment Station. 33 p. [4034]

23. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

24. Sampson, Arthur W.; Chase, Agnes; Hedrick, Donald W. 1951. California grasslands and range forage grasses. Bull. 724. Berkeley, CA: University of California College of Agriculture, California Agricultural Experiment Station. 125 p. [2052]

25. Thorne, Robert F.; Prigge, Barry A.; Henrickson, James. 1981. A flora of the higher ranges and the Kelso Dunes of the eastern Mojave Desert in California. Aliso. 10(1): 71-186. [3767]

26. Van Dyne, George M. 1958. Ranges and range plants. Unpublished manuscript on file at: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 290 p. [7310]

27. Welsh, Stanley L.; Atwood, N. Duane; Goodrich, Sherel; Higgins, Larry C., eds. 1987. A Utah flora. The Great Basin Naturalist Memoir No. 9. Provo, UT: Brigham Young University. 894 p. [2944]

28. Went, F. W. 1948. Ecology of desert plants. I. Observations on germination in the Joshua Tree National Monument, California. Ecology. 29(3): 242-253. [12915]

29. Went, F. W. 1949. Ecology of desert plants. II. The effect of rain and temperature on germination and growth. Ecology. 30(1): 1-13. [12916]

30. Wright, Henry A. 1980. The role and use of fire in the semidesert grass-shrub type. Gen. Tech. Rep. INT-85. Odgden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Forest and Range Experimental Station. 24 p. [24972]

Related categories for Species: Bouteloua barbata var. barbata | Sixweeks Grama