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Photo ©Larry Allain, USDA, NRCS
The currently accepted scientific name of blue grama is Bouteloua gracilis (Willd. ex Kunth) Lag. ex Griffiths (Poaceae) [118,124,129,130,160,167,184,210,213,241,365].
FEDERAL LEGAL STATUS:
No special status
Though it is widespread and globally secure , blue grama is vulnerable to extinction in some localized areas. In Idaho, blue grama is classified a state priority plant with imperiled status. This designation is based on species' rarity or because some factors demonstrably make it vulnerable to extinction. The Bureau of Land Management lists blue grama as "sensitive" in Idaho, either due to a declining population or its' occurrence in localized or unique habitats [197,332].
In Missouri, blue grama is ranked "critically imperiled" due to extreme rarity or vulnerability to extirpation from the state .
On the sagebrush steppe, blue grama occurs with big sagebrush (Artemisia tridentata), western wheatgrass (Pascopyrum smithii), threadleaf sedge (Carex filifolia), prairie Junegrass, Sandberg bluegrass (Poa secunda), green needlegrass (Nassella viridula), and needle-and-thread grass (Hesperostipa comata) [37,41]. In big sagebrush communities, blue grama occurs with big sagebrush, gray horsebrush (Tetradymia canescens), and green rabbitbrush (Chrysothamnus viscidiflorus). Common grass species in these communities include crested wheatgrass (Agropyron cristatum), cheatgrass (Bromus tectorum), prairie Junegrass, and bottlebrush squirreltail (Elymus elymoides) .
In salt-desert shrub communities, blue grama associated shrub species include shadscale (Atriplex confertifolia), Gardner's saltbush (Atriplex gardneri), mat saltbush (Atriplex corrugata), fourwing saltbush (Atriplex canescens), black greasewood (Sarcobatus vermiculatus), winterfat (Krascheninnikovia lanata), and spiny hopsage (Grayia spinosa). Associated grass species include Indian ricegrass (Achnatherum hymenoides), bottlebrush squirreltail, Sandberg bluegrass, galleta (Pleuraphis jamesii), alkali sacaton (Sporobolus airoides), and sand dropseed [47,143].
In the evergreen oak woodlands of the southwest, blue grama occurs in the understory with muhlys (Muhlenbergia spp.), plains lovegrass (Eragrostis intermedia), sideoats grama (Bouteloua curtipendula), hairy grama (B. hirsuta), little bluestem (Schizachyrium scoparium), and cane bluestem (Bothriochloa barbinodis) .
In ponderosa pine (Pinus ponderosa) communities, blue grama occurs with Colorado pinyon (P. edulis), Gambel oak (Quercus gambelii), alligator juniper (Juniperus deppeana), common juniper (J. communis), Saskatoon serviceberry (Amelanchier alnifolia), greenleaf manzanita (Arctostaphylos patula), black sagebrush (A. nova), big sagebrush, Fendler's ceanothus (Ceanothus fendleri), curlleaf mountain-mahogany (Cercocarpus ledifolius), true mountain-mahogany (C. montanus), snowberry (Symphoricarpos spp.), ninebark (Physocarpus spp.), and antelope bitterbrush (Purshia tridentata) [13,57,96,121,145]. Associated grass species include pinegrass (Calamagrostis rubescens), elk sedge (Carex geyeri), Idaho fescue (Festuca idahoensis), bluebunch wheatgrass (Pseudoroegneria spicata), purple threeawn (Aristida purpurea), prairie Junegrass, galleta, mountain muhly (Muhlenbergia montana), Kentucky bluegrass (Poa pratensis), mutton grass (Poa fendleriana), needle-and-thread grass, and bottlebrush squirreltail [13,13,28,35,57,96,118,121,228].
In pinyon-juniper communities, blue grama commonly occurs with Colorado pinyon, singleleaf pinyon (P. monophylla), alligator juniper, Utah juniper (J. osteosperma), oneseed juniper (J. monosperma), Gambel oak, Saskatoon serviceberry, black sagebrush, big sagebrush, fourwing saltbush, true mountain-mahogany, Stansbury cliffrose (Purshia mexicana var. stansburiana), green rabbitbrush, antelope bitterbrush, green ephedra (Ephedra viridis), red barberry (Mahonia haematocarpa), broom snakeweed (Gutierrezia sarothrae), and turpentine bush (Ericameria laricifolia). Associated grass species include western wheatgrass, poverty threeawn (Aristida divaricata), sideoats grama, black grama (B. eriopoda), prairie Junegrass, crested wheatgrass, muhlys, dropseeds (Sporobolus spp.), galleta, mutton grass, cheatgrass, fringed brome (Bromus ciliatus), California brome (B. carinatus), bottlebrush squirreltail, Indian ricegrass, needle-and-thread grass, New Mexico feathergrass (Hesperostipa neomexicana), Sandberg bluegrass, and purple threeawn [29,46,67,78,118,120,182,228,330].
Grassland associations: Blue grama is an important component of the shortgrass prairie [22,33,91,118,184], co-dominating with buffalo grass and occurring with hairy grama, purple threeawn, Sandberg bluegrass, threadleaf sedge, and little bluestem [3,7,22,33,91,94,230].
In the central and northern Great Plains mixed prairies, blue grama occurs with prairie sandreed (Calamovilfa longifolia), western wheatgrass, bluebunch wheatgrass, buffalograss, prairie Junegrass, needle-and-thread grass, hairy grama, green needlegrass, Sandberg bluegrass, and needleleaf sedge (Carex duriuscula) [1,2,3,10,31,33,112,264]. Shrubs occurring in these systems include fringed sagebrush (Artemisia frigida), big sagebrush, rubber rabbitbrush (C. nauseosus), and plains prickly-pear (Opuntia polyacantha) [1,3,10,31,112,264].
In the southern Great Plains, blue grama occurs with curly mesquite (Hilaria belangeri), galleta, New Mexico feathergrass, sideoats grama, tobosa (Pleuraphis mutica), vine-mesquite (Panicum obtusum), purple threeawn, Indian ricegrass, prairie Junegrass, buffalograss, plains lovegrass, and Texas tussockgrass (Nasella leucotrica) [63,69,144]. Woody plants occurring in these communities include honey mesquite (Prosopis glandulosa) and lotebush (Ziziphus obtusifolia) .
In the semi-desert grasslands of the Southwest, blue grama occurs with hairy grama, sideoats grama, black grama, bush muhly (Muhlenbergia porteri), threeawn (Aristida spp.), buffalograss, plains lovegrass, little bluestem, sand dropseed, bottlebrush squirreltail, curly mesquite, galleta, western wheatgrass, Indian ricegrass, New Mexico feathergrass, and needle-and-thread grass [17,70,122,146,270]. Shrubs occurring in these communities include shrub live oak (Quercus turbinella), mountain-mahogany (Cercocarpos spp.), skunkbush sumac (Rhus trilobata), and desert ceanothus (Ceanothus greggii) .
Classifications describing plant communities in which blue grama occurs as a dominant species are as follows:
New Mexico [12,13,13,121,145,148,149,182,217,228,257,337]
North Dakota [239,251,376]
In forest communities, blue grama occurs as a co-dominant with ponderosa pine [12,13,35,121,145,148,173,228,267,337], oneseed juniper , alligator juniper [35,182,217,337], Utah juniper [35,228], oneseed juniper [149,228,337], singleleaf pinyon [35,337], and Colorado pinyon [149,182,217,228,337].
In shrub communities, blue grama occurs as a co-dominant with sand sagebrush (Artemisia filifolia) , fourwing saltbush , rubber rabbitbrush , Parry's rabbitbrush (Ericameria parryi) , winterfat , and big sagebrush [148,149,183,341].
In grassland communities, blue grama occurs as a co-dominant with buffalo grass [233,340], needle-and-thread grass [227,233,239,264,382], prairie Junegrass , little bluestem, plains muhly (Muhlenbergia cuspidata) , bluebunch wheatgrass , western wheatgrass [149,149,183,239], alkali sacaton , saltgrass (Distichlis spicata) , galleta , Kentucky bluegrass , threadleaf sedge [233,239], and sun sedge (Carex heliophila) .
Blue grama patches may form ring patterns as blue grama develops a crown that is "pedastalled" on roots that extend 0.4 to 0.8 inch (1- 2 cm) above the soil. These roots are exposed to parasites and disease, resulting in loss of plant vigor and death of older plants at the center of patches .
Plant height at maturity ranges from 6 to 12 inches (15-30 cm) [131,193,240,274]. Blue grama leaves are flat and taper to a point , growing 1 to 10 inches (2.5-25 cm) long [7,47,188,261,349] and less than 1/8 inch (3 mm) wide [47,112,118,160,161,171,180,188,349], and persistent . Blue grama is solid-stemmed , and the flowering stems generally grow 7 to 18 inches (17-46 cm) tall [112,161,188,240,241,349]. Each inflorescence usually has 2 branches or spikes that extend at sharp angles from the main stem and are ascending to spreading and curved at maturity [47,124,188,349]. Blue grama has 20 to 90 spikelets per spike [112,164,180,241].
Blue grama fibrous root systems [30,107,274,356] are dense  and shallow [34,56,91,356]. Reports on rhizome formation are conflicting, with some authors reporting rhizome formation [116,137,164,167,180,265] and others disputing that information . Also unknown is whether or not stoloniferous ecotypes of blue grama exist as have been found in hairy grama, sideoats grama, and slender grama (Bouteloua repens) . White  found that in a greenhouse study, stolon development in blue grama is not controlled by day length, temperature, or shade except as they affect growth. Most blue grama plants in this study developed stolons if water, fertilizer, and light were adequate for sustained growth. Blue grama roots are usually less than 0.04 inches (1 mm) in diameter and often diminish to 0.008 inches (0.2 mm) with increasing depth . Roots of individual blue grama plants generally extend 12 to18 inches (30-46 cm) from the edge of the plant and 3 to 6 feet (0.9-1.8 m) deep [100,111,112,116,147,357]. Blue grama roots may penetrate deeper soil layers , and the maximum rooting depth of blue grama is approximately 6.5 feet (2 m) [82,110,116]. The density of blue grama root systems is attributed to abundance of branching; laterals are produced as frequently as 4.3 per inch (1.8 per cm) of main root in the upper 6 inches (15 cm) of soil. These laterals are up to 1 inch (2.5 cm) in length and branch to the 3rd order . The greatest branching of blue grama roots occurs in the top 18 inches (46 cm) of soil . Horizontal roots radiate in all directions from the base of blue grama stems, growing within 1.2 inches (3 cm) of the soil surface for up to 16 inches (40 cm). Lateral spreading of roots is more pronounced in mixed prairie vegetation than in the true prairie [112,356] and on more arid sites . Because the majority of blue grama roots are in the upper soil layers [100,111,235,358], it can respond rapidly to small amounts of rainfall [100,128]. In less xeric situations, the surface roots develop at a deeper level or follow an oblique course. Deeply penetrating roots usually descend obliquely or vertically from their origin .
Blue grama is a C4 plant with high water use efficiency [14,16,108]. Water use efficiency is greater under warm climatic conditions and may decrease with increasing water availability .
The Flora of the Great Plains provides a morphological description and identification key for blue grama .
RAUNKIAER  LIFE FORM:
Blue grama is readily established from seed [261,274,349], but depends more on vegetative reproduction [237,261,274].
Breeding system: No information
Pollination: No information
Seed production: Seed production of blue grama is generally low, but may be plentiful in favorable years [112,198,316]. Seed yields of 100 to 180 pounds per acre (112 kg/ha) have been obtained from natural stands . Amount of seed produced by blue grama depends on whether moisture is plentiful and temperatures are cool during the period of blossoming and seed formation [138,349]. Seed production may also be reduced by shading . In years of good growing conditions, blue grama may produce 2 or 3 seed crops . Presence of seed heads and seed head densities of blue grama may be increased by repeated annual burning [18,19].
Seed dispersal: Blue grama seed is dispersed by wind , insects , ingestion by large herbivores [272,282], and by adhesion to animal hides, fur, and feathers [231,329]. Wind disperses seed a few meters. In a seed dispersal study in Pennsylvania, Laughlin  found best seed dispersal occurred when blue grama fruits adhered to elk and bison fur. Since both ungulates are extirpated from large portions of their former range, long-distance seed dispersal of blue grama may be adversely affected. Fragmented populations are "trapped," with few opportunities for seed dispersal and population exchanges of genetic traits.
Seed banking: No information
Germination: In the tall grass prairie of Kansas and Nebraska, Blake  found that blue grama germination rates ranged between 3 and 31% over a 4-year period. In laboratory experiments, the highest rates of blue grama germination were achieved at day/night temperatures of 85/64.5 degrees Fahrenheit (29.5/18 oC), compared to 2 other treatments at 55.5/44.5 degrees Fahrenheit (13/7 oC) and 75/55.5 degrees Fahrenheit (24/13 oC), respectively. Jordan and Haferkamp  found the minimum germination temperature of blue grama to be approximately 51 degrees Fahrenheit (10.6 oC), while Knipe  achieved 94% germination at constant temperatures ranging from 60 to 100 degrees Fahrenheit (140-212 oC). Increases in the level of water stress generally cause a delay in the initiation and a decline in the rate of germination [52,221].
Seedling establishment/growth: Blue grama seedling establishment, survival, and growth are highest when isolated from neighboring adult plants. Adult blue grama plants effectively exploit water stored in the soil zone used by blue grama seedlings, increasing competition and decreasing seedling emergence and root development . Competition with other grasses may also reduce survival  and development  of blue grama seedlings. In field experiments at the Central Plains Experimental Range in northeast Colorado, Aguilera and Lauenroth  found the emergence of seedlings 20 days after seeding was 1 order of magnitude higher without neighboring adult plants than with neighbors (p<0.0001). Seedlings growing without the presence of active roots from neighboring adults had more leaves (p<0.0001) and were taller (p<0.0001) than seedlings growing with active roots present. At the end of the growing season, seedlings with neighbors excluded had more tillers and adventitious roots than seedlings with neighbors present (p<0.0001). A 2nd study further supports these conclusions, finding that establishment of blue grama seedlings was promoted by gap disturbances that involved removal of established adult blue grama plants . Increased opening size may also affect blue grama seedlings, resulting in higher emergence and greater survival rates . Blue grama seedlings develop rapidly; they may tiller when only 21 days old and flower at 2 months .
Consistent blue grama establishment requires average soil temperatures above 59 degrees Fahrenheit (15 oC), 2 properly spaced 2- to 4-day periods with a continuously moist soil surface (1 for emergence and 1 for adventitious root development), and a soil water potential of -0.3 bars in the 0 to 15 inch (0-40 cm) zone at the time of emergence . Blue grama seedlings have a single seminal root that is short-lived; therefore, seedling establishment requires development and extension of adventitious roots [66,268,355]. Ries and Svejcar  found that development of adventitious roots in the northern Great Plains occurred approximately 14 days after blue grama seedling emergence. Light is an important factor in the formation of adventitious roots. In laboratory experiments, blue grama seedlings only formed adventitious roots at the soil surface . Under usual range conditions, the development of adventitious roots is initiated in dry soil and seedling mortality may result [296,297].
Asexual regeneration: The principal means of blue grama reproduction is by tillering [112,237,261].SITE CHARACTERISTICS:
Climate: Blue grama generally requires 8 to 15 inches (203-381 mm) of annual precipitation , which occurs primarily in spring and summer months throughout its range [33,49,230,321]. The following table presents climate information for some of the areas in which blue grama occurs:
|Northern Great Plains||> 8 inches||-40 to 100 oF 120-160 frost-free days||[39,97,280]|
|mixed prairie||15 inches annually along northern and eastern boundaries, 9 inches along western and southern boundaries||January
1 to 23 oF
July average: 68 oF
|shortgrass steppe||12 to 22 inches||150-200 frost-free days|||
|Southern Great Plains||18 to 34 inches||7 to 100 oF||[43,70,97]|
|Great Basin||irregular, < 7 inches||100-150 frost-free days|||
|Southwestern U.S.||17 inches||January minimum: 29 oF July maximum: 90 oF|||
Site types: Blue grama grows both in low-lying areas and on uplands [34,38,77,92,131,188,280,291]. It is found on dry prairies and sandhills in the northeastern United States and in Canada . In the western United States, blue grama is found east of the Continental Divide on valley floors, alluvial benches and fans, drainages, mesas, toeslopes, and steeper slopes up to 35% [35,38,47,49,50,93,153,180,215,241,264].
Soils: Blue grama occupies a range of well-drained [187,236,355] soil types, from fine to coarse textured [34,50,74,92,107,112,121,131,145,188,298,299,315,355]. It grows on clay [30,65,77,114,164], silt , fine loams [1,47], loams [15,280,316], sandy loams [65,77,118], sand [15,47,89,112,316], and gravelly soils [47,112,118,164]. Soil texture may affect reproductive development of blue grama; density of culms produced per plant, height of culms, density of viable seeds, and number of viable seeds decrease with decreasing soil coarseness . Finer soil textures may result in shallower penetration of moisture, greater water loss from runoff, and a consequent increase in abundance of blue grama on mixed-prairie sites in Canada . In a study of grassland in North Dakota, blue grama occurred more frequently on more xeric sites where infiltration of water is less efficient .
Tolerances: Blue grama is cold [355,359,365] and drought [16,34,71,74,87,94,261,266,274,315,365] tolerant. In laboratory tests, blue grama perennating structures (extravaginal crowns) survived 2 months of exposure of -31 degrees Fahrenheit (-35 oC) . Drought tolerance and adaptation to xeric conditions allow blue grama to occupy drier sites throughout its range [89,112,118,131,153,173,228,259,266,291,349]. Prolonged drought, however, results in decreased root numbers, spread, and depth of penetration in blue grama root systems . Blue grama has an opportunistic water use strategy, using water rapidly when available and becoming dormant under dry soil conditions [281,291]. Epstein and others  found that aboveground net primary production of blue grama generally increased in response to an increase in mean annual temperature, while production decreased in response to increasing mean annual precipitation. Blue grama production was highest with 8 to 12 inches (200-300 mm) of precipitation, and lowest at greater than 31 inches (800 mm) annual precipitation. In New Mexico, however, blue grama may be restricted to sites with higher soil moisture than adjacent areas [64,217]. Season of precipitation may be important to blue grama production; dry summers may cause tiller death and thinning of blue grama stands, while wet summers promote thickening of stands .
Blue grama is also tolerant of alkaline soils [188,315,316,334,349,355] and is rarely found on even weakly acid soils [315,334,355]. However, in a study in southeastern Arizona, blue grama was most abundant on acidic, relatively infertile, sandy clay loam soils . Blue grama has been reported as fair to moderately tolerant [172,315,334,355] and intolerant of salt, tending to have a shallow root system that avoids soil salinity [56,243]. Miyamoto  found that with applications of 50, 100, 150, and 200 milliequivalent (me)/liter of salt solution, blue grama germination began decreasing markedly at the highest concentration. Blue grama vegetative growth was also sensitive to salt solutions. In greenhouse experiments, Weiler  found that dry weight of blue grama was much lower when irrigated with saline solution than with tap water, and Weiler and Gould  found that heights of blue grama decreased with applications of increasing salt concentrations.
Blue grama is primarily a late seral to climax grass species [44,103,110,114,140,173,212,283,298,299,304,343], though it may appear infrequently in early seral vegetation as isolated clumps . When it occurs as an understory species, blue grama is found primarily in open forests [190,191,344]. Pieper  found that blue grama biomass increased substantially with reductions in pinyon-juniper canopy cover. Though not tolerant of shade [207,277,315,334,355], blue grama is not affected as much by canopy cover as it is by accumulations of tree litter, which may reduce blue grama production . Root competition from trees in forested areas may also reduce the growth of blue grama . In the tall grass prairie, blue grama forms a late-seral short grass stage with buffalo grass; these two species make up approximately half the cover during this seral stage .
Following disturbance, recolonization of blue grama is a relatively slow
process that differs depending on the spatial extent of the disturbed patch.
Disturbances smaller than an individual plant reduce blue grama cover by killing
tillers, and recolonization is primarily by tiller replacement from the damaged
plant. As patch size increases and entire blue grama plants are killed,
recolonization is through seedling establishment. As a result, these larger disturbances
not only reduce cover but also kill individual plants .
However, distance from a disturbed patch to areas bordering the disturbed
area may have a greater effect than size of the disturbance on recovery
time of blue grama . Coffin and others  found that
blue grama is likely to recolonize agricultural fields (large disturbances) in
shortgrass prairie systems within 50 years of abandonment, while also subject to
grazing. Establishment of blue grama may be slowed on continuously
disturbed areas because fewer pre-existing plants may survive over long periods
of disturbance . Recovery of blue grama on disturbed sites may be constrained by soil texture,
climatic factors, and seed production and availability [102,103], as well as by type and intensity of disturbance
. Recovery of blue grama is greatly favored by increased moisture
content and deeper soils .
Blue grama is a warm season grass species [28,47,55,107,131]. Growth of blue grama begins late in the season [94,112,349], depending on soil temperature  and how much moisture is available [188,349]. In 1 study in the Northern Great Plains, blue grama growth did not begin until soil temperatures at 6-inch (15.2 cm) depths averaged 52 degrees Fahrenheit (11 oC) . Growth may cease during long droughts, but begins again upon return of favorable moisture and temperature conditions [7,94,113,118,161,177,188,207,261,349,365]. In a field study in northern Colorado, blue grama demonstrated a rapid response to a simulated 0.2-inch (5 mm) rainfall event following a period of water stress . The severity of the drought, however, may determine the ability of blue grama to recover. New blue grama root growth in response to increased moisture availability depends on duration of the soil water increase. Blue grama responds to a small rainfall event following a period of drought by increasing the water uptake of surviving roots. However, after a large rainfall event, water absorption is the result of uptake by both surviving and new roots . Blue grama can effectively mobilize, utilize, and replenish total nonstructural carbohydrates during short periods of favorable growing conditions, contributing to both its drought tolerance and rapid regrowth capability .
Growth of blue grama generally begins from mid-April [161,240] to June [315,319] and continues into October , reaching maturation in 2 months [76,112,240,261,315]. Tillering occurs in early June in the central Great Plains . Greatest increases in blue grama leaf area generally occur in June , and maximum leaf heights may be reached as early as mid-June  or late July . Blue grama flowers from July to August, with seeds ripening and dispersing from August to October [123,240].
Flowering of blue grama is dependent on geographic distribution, occurring earlier to later along both north/south and west/east gradients . In the northern Great Plains, blue grama flowering occurs primarily in July [81,112,161]; in the central Great Plains, flowering occurs from July through August [123,319]. In Montana, blue grama is finished flowering by mid-July . Blue grama flowers from July to October in New Mexico , Arizona  and Texas . Flowering of blue grama is also directly impacted by immediate moisture availability, and later flowering of a population may be due to later availability of moisture . Blue grama seeds usually mature in late summer [137,188,316,349] or fall [30,107,112], and seed heads ripen rapidly as they near maturity . Senescence occurs in late October or early November . Approximately 12% of overwintering blue grama shoots become reproductive .
Grassland fuels, generally fine fuels, burn readily. However, compact arrangement of stems in the "tufts" of bunchgrasses makes this portion of the plant difficult to ignite. Once ignited, they can smolder for long periods of time if enough material has accumulated. Plant density is a critical factor in a grassland's ability to propagate fire. Heat output is relatively low, so fairly continuous fuels are necessary for fire to spread .
Fire return intervals for plant communities and ecosystems in which blue grama occurs are summarized below. Find further 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)|
|Nebraska sandhills prairie||Andropogon gerardii var. paucipilus-Schizachyrium scoparium||< 10|
|bluestem-Sacahuista prairie||Andropogon littoralis-Spartina spartinae||< 10|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70 |
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||15-40 [26,75,253]|
|Wyoming big sagebrush||Artemisia tridentata var. wyomingensis||10-70 (40**) [354,383]|
|saltbush-greasewood||Atriplex confertifolia-Sarcobatus vermiculatus||< 35 to < 100|
|desert grasslands||Bouteloua eriopoda and/or Pleuraphis mutica||5-100|
|plains grasslands||Bouteloua spp.||< 35|
|blue grama-needle-and-thread grass-western wheatgrass||Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii||< 35|
|blue grama-buffalo grass||Bouteloua gracilis-Buchloe dactyloides||< 35|
|grama-galleta steppe||Bouteloua gracilis-Pleuraphis jamesii||< 35 to < 100|
|blue grama-tobosa prairie||Bouteloua gracilis-Pleuraphis mutica||< 35 to < 100 |
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1000 [27,312]|
|mountain-mahogany-Gambel oak scrub||Cercocarpus ledifolius-Quercus gambelii||< 35 to < 100|
|juniper-oak savanna||Juniperus ashei-Quercus virginiana||< 35|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||Juniperus scopulorum||< 35|
|Ceniza shrub||Larrea tridentata-Leucophyllum frutescens-Prosopis glandulosa||< 35|
|wheatgrass plains grasslands||Pascopyrum smithii||< 35|
|pinyon-juniper||Pinus-Juniperus spp.||< 35 |
|Mexican pinyon||Pinus cembroides||20-70 [258,339]|
|Colorado pinyon||Pinus edulis||10-49 |
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-30 [25,32,234]|
|galleta-threeawn shrubsteppe||Pleuraphis jamesii-Aristida purpurea||< 35 to < 100 |
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [25,170,249]|
|mesquite||Prosopis glandulosa||< 35 to < 100|
|mesquite-buffalo grass||Prosopis glandulosa-Buchloe dactyloides||< 35|
|Texas savanna||Prosopis glandulosa var. glandulosa||< 10 |
|mountain grasslands||Pseudoroegneria spicata||3-40 (10**) [24,25]|
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||< 35 to < 200|
|shinnery||Quercus mohriana||< 35|
|blackland prairie||Schizachyrium scoparium-Nassella leucotricha||< 10|
|Fayette prairie||Schizachyrium scoparium-Buchloe dactyloides||< 10|
|little bluestem-grama prairie||Schizachyrium scoparium-Bouteloua spp.||< 35 |
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Fire exclusion, and subsequent woody plant invasion, has resulted in blue grama decline. Combined effects of fire exclusion, agriculture, and other development has reduced blue grama populations by 48% (based upon herbarium records) in the Appalachians .
FIRE MANAGEMENT CONSIDERATIONS:
With normal precipitation, blue grama is not harmed by prescribed burning, but may decrease following burning for 2 to 3 years during drought years . On a semidesert grassland site in Arizona, blue grama declined significantly (p<0.001) during the 1st season following a prescribed burn; however, it recovered fully after 2 postfire years . This study was part of an extensive of body of research on fire effects in semidesert grassland, oak savanna, and Madrean oak woodlands of southeastern Arizona. See the Research Project Summary of this work for more information on burning conditions, fires, and fire effects on more than 100 species of plants, birds, small mammals, and grasshoppers.
Annual burning may favor blue grama. On aspen-parkland sites in central Alberta, blue grama occurred in at least 10% of the plots that had been repeatedly burned but did not occur in adjacent, unburned sites . Gibson and Towne  also found that blue grama occurred on sites that had been annually burned for several years in a Kansas tallgrass prairie, but it did not occur on adjacent unburned sites. In a study at the Konza Prairie Research Natural Area in Kansas, average cover of blue grama was comparatively higher on annually burned sites than on sites burned once every 4 years or unburned sites . On paired plots in North Dakota, however, blue grama frequency varied little between burned and unburned sites.
Season of burning: Blue grama may respond differently based on the season of prescribed fire activities. Spring burning in the shortgrass prairie may result in a greater reduction in blue grama production than fall burning, though recovery usually occurs within 3 growing seasons. Height reductions in blue grama can also be expected during the initial growing season, with recovery likely after the 2nd growing season . In the mixed prairie, blue grama may be favored by early and mid-spring burning [181,218,222]. On a site in the northern mixed prairie of Saskatchewan, blue grama growth increased following a late spring prescribed burn . In the mixed prairie of North Dakota, both spring (May) and fall (October) fires increased blue grama production with spring burning resulting in the greater increase . In a Kansas study, blue grama was least abundant on unburned sites and most abundant on early spring-burned sites. On one site in particular, the unburned pasture averaged 4.5% plant composition blue grama, late-spring burning averaged 31%, mid-spring burning 40%, and early-spring burning 47% blue grama . In the 1st and 2nd growing seasons following a spring burn in Nebraska mixed prairie, blue grama experienced a significant increase (p<0.10) in basal cover on burned plots compared to unburned plots . On sites in South Dakota, blue grama increased from 4 to 11% cover in the 1st growing season following a spring prescribed burn and increased from 12 to 18% cover during the 2nd growing season . Following early spring prescribed burning in Texas, blue grama yield increased up to 400 pounds per acre (452 kg/ha) in the 1st growing season . In a Montana study, prescribed burning resulted in increased yields over unburned areas, though initial late spring growth was greater on unburned plots . Spring burning (April) of blue grama stimulated production by mid- or late June, while fall burning (October) stimulated production to a lesser degree [374,375].
In the Alberta blue grama steppe, however, dry matter production was reduced 50% (from prefire production) during the 1st season following a spring fire and reduced 15% during the 2nd season, with recovery complete the 3rd season. Fall burning resulted in a 30% decrease in production, with recovery complete by the 2nd postburn season . Whisenant and Uresk  also found that prescribed burning in April reduced blue grama growth during the initial growing season. In studies in South Dakota, spring (April) burning was found to reduce productivity of blue grama whereas response to fall (October) burning was variable; increasing production when precipitation was adequate and decreasing it when precipitation was low. Late June prescribed burning in New Mexico inhibited blue grama growth throughout the growing season, though at the end of the season in October, blue grama on control sites was not significantly greater in height than on burned sites. Blue grama biomass was also not significantly different between burn and control plots, demonstrating that blue grama can recover from burning during the course of the growing season relative to controls .
Plant response to prescribed fire: During the 1st growing season following a fall fire in Nebraska, blue grama on the burned site initially had greater phytomass than blue grama on the control site. By the end of the growing season, however, the unburned site had relatively greater phytomass than the burned site . Trlica  found that the root crown circumference of blue grama increased 10 to 15% following spring, summer, and fall prescribed fire treatments, with similar increases occurring in control treatments also. Seedstalk production of blue grama in this study experienced greater increases following the fall burns than the spring and summer burns, though all burn treatments resulted in greater seedstalk production than the control. According to Pieper and others , season of burning had no significant effect (p<0.05) on height of blue grama plants, nor did plant heights differ between burned and unburned plots. Burning combined with nitrogen fertilizer, however, significantly increased (p<0.05) blue grama seedstalk heights and densities over those on the control and burned-only plots. There was no significant difference in seedstalk height and density between burned and unburned plots.
Other management considerations: A 3- to 4-month rest from grazing is recommended after fire .
Blue grama also provides important forage for mule deer [72,224]. However, in a study on the prairie of north-central Montana, mule deer were not found to browse blue grama, instead favoring forbs and shrub species . Blue grama provides important winter forage for elk in Colorado , and provides good forage for pronghorns during all seasons in western Texas and in Kansas [73,273]. Blue grama is only lightly browsed by pronghorn in Utah and Colorado, with use occurring primarily in the spring [36,313]. Blue grama is important summer forage for bighorn sheep in Colorado . It is also an important forage for bison [260,276], and blue grama development plays a role in seasonal bison movements .
Scaled quail and some songbirds eat the seeds of blue grama . Small mammals also eat blue grama seeds and stems [110,186], providing an important food source for prairie dogs, pocket gophers, and black-tailed jackrabbits in the Great Plains [54,132,142,273,338,352]. Flower heads and seeds of blue grama are also consumed by grasshoppers, which can all but eliminate an annual seed crop [71,222].
Blue grama is highly palatable forage [65,192,193,365], and retains its palatability when mature or during dry periods . The following table presents livestock palatability ratings for blue grama :
When blue grama is green, the leaves are low in fiber and high in protein. It may retain up to 50% of its nutritive value when dormant , and retains approximately 5% protein when dormant . In Colorado, crude protein content of live blue grama averages 10% throughout the year, with the highest content (18%) occurring during early in the growing season and the lowest content (8%) occurring just prior to dormancy. Crude protein content does not respond to different grazing intensities (ungrazed, light, moderate, and heavy grazing) . Fudge and Fraps  found that protein content of blue grama ranged from 3.3 to 9.8% in Texas, fair to good for cattle forage. In Oklahoma, crude protein of blue grama may range from 4.4% to 17.0%, calcium may range from 0.17% to 0.48%, and phosphorus may range from 0.07% to 0.31% . The percent composition of air-dried blue grama in Arizona is presented below :
|water||ash||crude protein||crude fiber||fat||N-free extract|
Nutrient content of blue grama in an Oklahoma plains grassland is presented below. Data is presented in percent of oven-dry weight and represents means over 5 years :
|Ca||P||Protein||Fat||N-free extract||crude fiber||ash|
Average nutrient concentrations (with standard deviation) of blue grama in a Central Plains saltgrass meadow were as follows :
Nitrogen concentration of senescent blue grama foliage has been reported as approximately 1% of the dry weight . Calcium, phosphorus, crude protein, iron, manganese, and magnesium in blue grama decrease with maturity, though some of these declines may be halted or mitigated by periods of precipitation [289,331].
Nitrogen fertilization of blue grama rangeland may result in increased
digestibility of dry matter, crude protein, copper, crude fiber, and lignin in blue
grama [216,279]. However, nitrogen fertilized blue
grama may contain less calcium and aluminum than unfertilized blue grama .
Blue grama is poor cover for upland game birds and waterfowl, and fair to poor cover for small mammals . Blue grama provides fair nesting cover and is important to some prairie songbirds . The blue grama/kleingrass (Panicum coloratum) cover type in the southern high plains of Texas provides high-quality nesting habitat for ring-necked pheasants, contributing to increased nest success, high nest density, and increased pheasant production . Blue grama and buffalo grass flats provide good nesting sites for mountain plovers in Montana, Wyoming, and Colorado , and important herbaceous cover for quail in Texas .
VALUE FOR REHABILITATION OF DISTURBED SITES:
Because of its wide adaptation, ease of establishment, and economic value, blue grama is used extensively for conservation purposes [106,199,349], rangeland seeding [15,65,178,200,247,284,334], and landscaping [55,195,315]. Blue grama is useful for reclamation [143,150,172,248,310,315] and for erosion control in arid and semiarid regions [58,315,334,349,365]. Blue grama growing on abandoned mine sites does not show any significant increase in metal uptake .
Excellent stands of blue grama have been achieved by broadcast or solid-drill seeding, with a seeding rate of 8 to 12 pounds per acre (9-13.5 kg/ha) [188,349], though others report that blue grama may be difficult to establish by seed . As a general rule, blue grama seeds should be used near their point of origin to achieve maximum planting success [188,349]. Planting depth of 0.25 to 0.5 inches (0.6-1.3 cm) is critical for successful establishment, and blue grama seedling emergence decreases with increased planting depth [74,85]. Redmann and Qi  found that blue grama seedling emergence was highest at a planting depth of 0.6 inches (1.5 cm), and emergence decreased to 0% when seeds were sown at 2.5 inches (6 cm). Increased planting depths may result in decreased shoot and root weights of emerging seedlings , while at shallower planting depths, the developing seedlings are most likely adversely affected by the rapid drying of the soil. However, heavier blue grama seeds may have greater emergence success from deeper planting depths than lighter seeds , which may allow them to take advantage of moisture for germination and emergence . Summer planting and a minimum of 13 inches (330 mm) of annual precipitation is recommended for successful blue grama establishment . Eddleman  also recommends planting blue grama seed after soil temperature has reached at least 50 degrees Fahrenheit (10 oC). With temperatures of 50 to 68 degrees Fahrenheit (10-20 oC), blue grama seeds germinated at rates of 85 to 91%. A blue grama germination rate of 88% was achieved with night/day temperatures of 60 to 70 degrees Fahrenheit (15-21 oC) and 86 to 95 degrees Fahrenheit (30-35 oC), respectively . Other research has found that more than 88% of blue grama seeds may germinate in about 2 days when subject to a range of alternating temperatures of 80 to 99 degrees Fahrenheit (27-37 oC) for 8 hours and 95 to 99 degrees Fahrenheit (35-37 oC) for 16 hours. Constant temperatures of 61, 81, and 99 degrees Fahrenheit (16, 27, and 37 oC) resulted in 100% germination in mean times of 6, 2.4, and 2 days, respectively. Moisture stress did not inhibit germination of blue grama until stress exceeded -10 bars .
If done early in the growing season, transplanting blue grama as sod may result in successful establishment. Sod should be 2 inches (5 cm) thick and wet before cutting; after transplanting, sod should be irrigated as soon as possible. In transplanting studies, 9-week-old blue grama plants were planted in the Sonoran Desert. Survival of blue grama averaged 80% after 2 months and declined to 21% after 32 months . Establishment depends mainly on new adventitious roots produced on recently developed tillers . Under controlled conditions, Briske and Wilson  found that temperature impacts blue grama root development, with the greatest number of roots initiated (per seedling) at 68 degrees Fahrenheit (20 oC) and the greatest root length and weight (per seedling) occurring at 86 degrees Fahrenheit (30 oC). The greatest shoot growth was also achieved at 86 degrees Fahrenheit (30 oC). Seed used in this experiment was taken from several locations in the Great Plains, and temperature treatments ranged from 41 to 95 degrees Fahrenheit (5-35 oC). Favorable soil moisture conditions also impact adventitious root development, so recommendations for good blue grama establishment include planting when 2 or more consecutive days of precipitation are likely or when temperatures are favorable for emergence and root growth even if consecutive "wet" days are unlikely.
OTHER MANAGEMENT CONSIDERATIONS:
Blue grama production may increase following overstory-removal treatments in pinyon-juniper communities [95,97]. Clary and Jameson  found that blue grama production increased from 31 kg/ha pretreatment to 350 kg/ha posttreatment. Blue grama may substantially retard growth of tree seedlings, reducing their size, branching, and vigor .
Blue grama provides year-long grazing, but rotational grazing is recommended to promote vigor and herbage production [274,347]. Blue grama cover and net primary productivity are higher under short-duration grazing strategies than continuous grazing strategies . Blue grama is generally tolerant of grazing [49,144,336,365], increasing under grazing pressure [20,43,44,62,87,187,209,219,225,293,318,322,328,345] and resisting trampling [219,238,336]. Blue grama withstands clipping or grazing more effectively when grazed after it has matured or when it is only slightly grazed during its growing period [261,347]. Blue grama possesses primarily culmless vegetative shoots in which the actively growing tissue is not elevated to within reach of grazing animals, so potential for rapid regrowth is preserved [21,62]. In one study, blue grama plants on grazed sites allocated a higher percentage of biomass and nitrogen to the roots, while those plants on ungrazed areas allocated a higher percentage to aboveground production, demonstrating a potential strategy for responding to grazing impacts .
Blue grama is often more prevalent on areas subject to grazing than on areas where grazing has been excluded [204,206,227,288,309,320,326]. Sims and others  found that blue grama production increased more in response to heavy grazing treatments than to light, moderate or control treatments. In North Dakota, relative basal cover of blue grama was significantly lower (p<0.05) on sites protected from grazing than on sites subject to grazing treatments . In a mixed grass community in southwestern North Dakota, cover of blue grama was lower in exclosures than in the adjacent grazed areas . The relative basal cover (%) of blue grama on grazed and ungrazed sites was as follows :
However, there was little difference herbage production on grazed versus ungrazed sites, due to significantly (p<0.0041) increased height of blue grama on the ungrazed site . On pinyon-juniper sites in Arizona over a 13-year period, blue grama decreased on grazed sites, though a greater decrease was observed with the exclusion of grazing . At the Central Plains Experiment Station, a study conducted over 2 years found that blue grama basal cover was greater on "heavily grazed" than on "lightly grazed" sites . In contrast, Smith  found that blue grama increased 8-fold on lightly grazed sites, 4-fold under moderate grazing, and only 1.25-fold under heavy grazing in Colorado.
Blue grama may decrease if subject to continued heavy grazing [20,94,205], especially when accompanied by dry conditions . Heavy grazing also encourages a sod-forming rather than bunchgrass growth habit in blue grama [179,193,194,208]. Heavy grazing can potentially reduce tillering and tiller weight, and decrease concentrations of total nonstructural carbohydrates in blue grama forage [292,305]. Large increases in the basal cover of blue grama in the mixed prairie combined with decreases in the cover of other species, like needle-and-thread grass, may indicate deterioration of range conditions [264,328]. Buwai and Trlica  found that repeated defoliation treatments reduced herbage yield and vigor of blue grama plants below that of undefoliated control plants. In general, basal cover (%) was less for heavily defoliated plants than for moderately defoliated plants, and all heavily defoliated plants had at least a 50% reduction in basal cover as compared with the undefoliated plants. Defoliation also reduced plant heights 40 to 80% below that of undefoliated control plants. In a Colorado study, frequency of blue grama plants increased with light, moderate, and heavy grazing levels while biomass decreased relative to ungrazed areas . In a New Mexico study, blue grama density was not significantly different between grazed and ungrazed sites. However, blue grama percent cover was substantially higher on ungrazed sites than on grazed sites following a severe drought . Clipping treatments to simulate grazing in New Mexico did not result in significant changes (relative to controls) in blue grama height or biomass at the end of the growing season, demonstrating the ability of blue grama to recover quickly . Trlica and others , however, found that blue grama required more than 26 months of rest to recover its vigor following repeated heavy defoliations.
Frequent grazing or clipping of blue grama may encourage top-growth; however, it may result in poor root growth [45,94,322]. However, Santos and Trlica  found that frequent clipping (2- and 4-week intervals) of blue grama resulted in reduced biomass of both crowns and root. Buwai and Trlica [79,80] found that repeated defoliation treatments did not impact root weight or carbohydrate reserves of blue grama. The authors suggest that blue grama's resistance to clipping or grazing may be related to its ability to maintain adequate root growth by transferring more assimilated carbohydrate to belowground root production , or to the ability of defoliated plants to remain in a semi-dormant stage throughout most of the growing season while unclipped plants use their stored carbohydrates for growth . Grazing may also impact the reproductive ability of blue grama; Coffin and Lauenroth  found that the average weight of reproductive structures was greater and more than twice as many viable seeds were produced per flowering culm on ungrazed than grazed locations.
Blue grama production generally responds positively to fertilizer inputs, including nitrogen, phosphorus, potassium, and zinc [134,294,370,371,379]. Blue grama production (kg/ha) was significantly greater (p < 0.05) with sludge application rates of 10, 20, and 40 tons per acre (22.5, 45, 90 Mg/ha) . During the 1st and 2nd growing seasons, yields ranged from 1.5 to 2.7 times greater in the treated plots than in the unamended plots. Sludge amendments also increased the nutritional value of blue grama, resulting in higher nitrogen, phosphorus, potassium, and crude protein tissue concentrations. However, Fresquez and others  found that while production increased with applications of 10, 20, and 40 tons per acre (22.5, 45, 90 Mg/ha), only the 40-ton (90 Mg/ha) treatment resulted in significantly increased production compared to the control plots. Trace metals in plant tissue did not increase significantly in either study [4,151]. In a New Mexico study, blue grama height was significantly increased (p<0.05) with the application of 40 pounds of nitrogen per acre (45 kg/ha) compared to the control. The 60 pounds per acre (67.5 kg/ha) application did not result in significantly greater heights than the 40-pound treatment, and the density of blue grama increased significantly (p<0.05) in response to each of the treatment levels . In a greenhouse experiment, root and shoot biomass of blue grama increased with addition of both nitrogen and phosphorus . In contrast, Smoliak  found that blue grama basal areas decreased following applications of nitrogen fertilizer and manure. Another study conducted in North Dakota found that blue grama exhibited a decreasing trend in basal cover with increasing nitrogen application rates . Nitrogen fertilization may also worsen the effects of drought on blue grama .
Chemically thinning dense blue grama stands may result in increased herbage and seed production . Blue grama is greatly reduced initially by applications of atrazine, sylvex, picloram, and 2,4-D [158,242]. However, within 5 years of picloram application, blue grama recovers vigorously, producing a large amount of foliage and many seed heads . Atrazine applications, however, may also have long-term negative effects on blue grama and soil processes . Germination of blue grama seeds may be suppressed by applications of picloram and triclopyr . Atrazine, picloram, and 2,4-D may be useful in encouraging the production or rapid establishment of blue grama based on their control of competing plants [59,158,166,201].
Mechanical treatments (e.g. ripping and furrowing) result in decreased blue grama production [169,361].
Prairie dog mound building in the Great Plains may result in a substantial decrease in the size of blue grama clumps and patches, with blue grama cover increasing as distance from prairie dog burrows increases. The prairie dog habit of scratching topsoil from the area around burrows breaks larger patches of blue grama into smaller clumps . Pocket-gopher disturbances also have a lower basal cover (%) of blue grama than surrounding areas .
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