Index of Species Information

SPECIES:  Aristida purpurea

Purple threeawn growing in Wyoming cobble. Cheatgrass is growing behind. Photo by Matt Lavin.


SPECIES: Aristida purpurea
AUTHORSHIP AND CITATION : Howard, Janet L., 1997. Aristida purpurea. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: []. Revisions: Photo added on 19 August 2014. ABBREVIATION : ARIPUR SYNONYMS : Aristida fendleriana Steud. [23,24] Aristida longiseta Steud. [23,24,37] Aristida purpurea var. robusta (Merrill) A. Holg. & N. Holg. = Aristida purpurea var. longiseta (Steud.) Vasey [22,32] Aristida purpurea var. glauca (Nees) A. Holg. & N. Holg. [22] = Aristida purpurea var. nealleyi (Vasey) Allred [32] Aristida wrightii Nash [23,24,33] = Aristida purpurea var. wrightii (Nash) Allred [26,32] SCS PLANT CODE : ARPU9 ARPUL ARPUN ARPUP5 ARPUP6 ARPUW COMMON NAMES : purple threeawn red threeawn wiregrass democrat grass TAXONOMY : The currently accepted scientific name of purple threeawn is Aristida purpurea Nutt. [26, 32,60,61]. Varieties are as follows: Aristida. purpurea var. longiseta (Steud.) Vasey, Fendler or red threeawn Aristida purpurea var. nealleyi (Vasey) Allred, blue threeawn Aristida purpurea var. parishii (A.S. Hitchc.) Allred, Parish's threeawn [22,32] Aristida purpurea var. purpurea Nutt., purple threeawn (typical variety) [22,26,32] Aristida purpurea var. wrightii (Nash) Allred, Wright's threeawn [22,32] The typical variety of purple threeawn is referred to several times in this report. It is preceded by its scientific name in parentheses when it is discussed in this Species Review. "Purple threeawn" refers to the species as a whole. LIFE FORM : Graminoid FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Aristida purpurea
GENERAL DISTRIBUTION : Purple threeawn is distributed from Iowa and Minnesota west to British Columbia and south to California, Texas, and northern Mexico [8,15,26,27]. Distribution of varieties is: Fendler threeawn - northern Mexico, southern California and Texas north to British Columbia and east to the Dakotas [8,26] blue threeawn - southern California east to southern Utah and Oklahoma and south to northern Mexico Parish's threeawn - southern California and southern Nevada south to Baja California purple threeawn - southern California east to Arkansas and south to (A. purpurea northern Mexico var. purpurea) Wright's threeawn - southern California east to Oklahoma and south to northern Mexico [26] ECOSYSTEMS : FRES15 Oak-hickory FRES20 Douglas-fir FRES21 Ponderosa pine FRES28 Western hardwoods FRES29 Sagebrush FRES30 Desert shrub FRES33 Southwestern shrubsteppe FRES34 Chaparral-mountain shrub FRES35 Pinyon-juniper FRES36 Mountain grasslands FRES38 Plains grasslands FRES39 Prairie FRES40 Desert grasslands STATES : AZ AR CA CO IA ID KS MN MT NE NV NM ND OK OR SD TX UT WA WY AB BC MEXICO BLM PHYSIOGRAPHIC REGIONS : 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 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : K005 Mixed conifer forest K009 Pine-cypress forest K010 Ponderosa shrub forest K011 Western ponderosa forest K012 Douglas-fir forest K013 Cedar-hemlock-pine forest K016 Eastern ponderosa forest K017 Black Hills pine forest K018 Pine-Douglas-fir forest K019 Arizona pine forest K022 Great Basin pine forest K023 Juniper-pinyon woodland K024 Juniper steppe woodland K026 Oregon oakwoods K027 Mesquite bosque K028 Mosaic of K002 and K026 K029 California mixed evergreen forest K031 Oak-juniper woodlands K032 Transition between K031 and K037 K033 Chaparral K034 Montane chaparral K035 Coastal sagebrush K037 Mountain-mahogany-oak scrub K038 Great Basin sagebrush K039 Blackbrush K040 Saltbush-greasewood K041 Creosotebush K043 Paloverde-cactus shrub K044 Creosotebush-tarbush K050 Fescue-wheatgrass K053 Grama-galleta steppe K054 Grama-tobosa prairie K055 Sagebrush steppe K056 Wheatgrass-needlegrass shrubsteppe K057 Galleta-three-awn shrubsteppe K058 Grama-tobosa shrubsteppe K059 Trans-Pecos shrub savanna K063 Foothills prairie K064 Grama-needlegrass-wheatgrass K065 Grama-buffalograss K066 Wheatgrass-needlegrass K067 Wheatgrass-bluestem-needlegrass K068 Wheatgrass-grama-buffalograss K069 Bluestem-grama prairie K070 Sandsage-bluestem prairie K074 Bluestem prairie K076 Blackland prairie K077 Bluestem-sacahuista prairie K081 Oak savanna K084 Cross Timbers K085 Mesquite-buffalograss SAF COVER TYPES : 40 Post oak-blackjack oak 68 Mesquite 210 Interior Douglas-fir 220 Rocky Mountain juniper 229 Pacific Douglas-fir 230 Douglas-fir-western hemlock 233 Oregon white oak 234 Douglas-fir-tanoak-Pacific madrone 236 Bur oak 237 Interior ponderosa pine 238 Western juniper 239 Pinyon-juniper 240 Arizona cypress 241 Western live oak 242 Mesquite 243 Sierra Nevada mixed conifer 244 Pacific ponderosa pine-Douglas-fir 245 Pacific ponderosa pine 246 California black oak 247 Jeffrey pine 249 Canyon live oak 250 Blue oak-foothills pine 255 California coast live oak SRM (RANGELAND) COVER TYPES : 101 Bluebunch wheatgrass 102 Idaho fescue 103 Green 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 204 North coastal shrub 205 Coastal sage shrub 206 Chamise chaparral 207 Scrub oak mixed chaparral 209 Montane shrubland 210 Bitterbrush 211 Creosotebush scrub 212 Blackbush 301 Bluebunch wheatgrass-blue grama 302 Bluebunch wheatgrass-Sandberg bluegrass 304 Idaho fescue-bluebunch wheatgrass 305 Idaho fescue-Richardson needlegrass 306 Idaho fescue-slender wheatgrass 307 Idaho fescue-threadleaf sedge 309 Idaho fescue-western wheatgrass 310 Needle-and-thread-blue grama 311 Rough fescue-bluebunch wheatgrass 312 Rough fescue-Idaho fescue 314 Big sagebrush-bluebunch wheatgrass 315 Big sagebrush-Idaho fescue 316 Big sagebrush-rough fescue 317 Bitterbrush-bluebunch wheatgrass 318 Bitterbrush-Idaho fescue 319 Bitterbrush-rough fescue 322 Curlleaf mountain-mahogany-bluebunch wheatgrass 323 Shrubby cinquefoil-rough fescue 401 Basin big sagebrush 402 Mountain big sagebrush 403 Wyoming big sagebrush 407 Stiff sagebrush 408 Other sagebrush types 412 Juniper-pinyon woodland 413 Gambel oak 414 Salt desert shrub 415 Curlleaf mountain-mahogany 416 True mountain-mahogany 501 Saltbush-greasewood 502 Grama-galleta 503 Arizona chaparral 504 Juniper-pinyon pine woodland 505 Grama-tobosa shrub 506 Creosotebush-bursage 507 Palo verde-cactus 508 Creosotebush-tarbush 509 Transition between oak-juniper woodland and mahogany-oak association 601 Bluestem prairie 602 Bluestem-prairie sandreed 603 Prairie sandreed-needlegrass 604 Bluestem-grama prairie 605 Sandsage prairie 606 Wheatgrass-bluestem-needlegrass 607 Wheatgrass-needlegrass 608 Wheatgrass-grama-needlegrass 609 Wheatgrass-grama 610 Wheatgrass 611 Blue grama-buffalograss 612 Sagebrush-grass 613 Fescue grassland 614 Crested wheatgrass 615 Wheatgrass-saltgrass-grama 702 Black grama-alkali sacaton 703 Black grama-sideoats grama 704 Blue grama-western wheatgrass 705 Blue grama-galleta 706 Blue grama-sideoats grama 707 Blue grama-sideoats grama-black grama 708 Bluestem-dropseed 709 Bluestem-grama 710 Bluestem prairie 711 Bluestem-sacahuista prairie 713 Grama-muhly-threeawn 714 Grama-bluestem 715 Grama-buffalograss 716 Grama-feathergrass 718 Mesquite-grama 720 Sand bluestem-little bluestem (dunes) 721 Sand bluestem-little bluestem (plains) 722 Sand sagebrush-mixed prairie 724 Sideoats grama-New Mexico feathergrass-winterfat 727 Mesquite-buffalograss 731 Cross timbers-Oklahoma 732 Cross timbers-Texas (little bluestem-post oak) 733 Juniper-oak 735 Sideoats grama-sumac-juniper HABITAT TYPES AND PLANT COMMUNITIES : Publications describing plant communities in which purple threeawn is dominant are: Steppe vegetation of Washington [9] Plant associations of the Wallowa-Snake Province [31] The palouse grassland association in northern Utah [49] Canyon grasslands and associated shrublands of West-central Idaho and adjacent areas [51] Listings of common plant associates of purple threeawn follow. Southern Idaho: Associates in Fendler threeawn/Sandberg bluegrass (Poa secunda) communities include cheatgrass (Bromus tectorum), Japanese brome (B. japonicus), Kentucky bluegrass (P. pratensis), and common yarrow (Achillea millefolium) [51]. Eastern Colorado: Common plant associates in Fendler threeawn/blue grama-buffalograss (Bouteloua gracilis-Buchloe dactyloides) communities include sand scurfpea (Psoralidium lanceolatum), slimflower scurfpea (P. tenuiflorum), and plains pricklypear cactus (Opuntia polyacantha) [39]. Southern Arizona: Fendler threeawn associates in desert grassland of the Huachuca Mountains include gramas (Grama spp.), crinkle-awn (Trachypogon secundus), Arizona threeawn (Aristida arizonica), purple muhly (Muhlenbergia rigida), and Texas timothy (Lycurus phleoides) [57]. North-central Texas: Associates of Wright's and purple threeawn (A. purpurea var. purpurea) in a redberry juniper (Juniperus pinchotii)-mixed grassland community of northeastern King County, Texas, include fragrant sumac (Rhus aromatica), littleleaf sumac (R. microphylla), algerita (Mahonia trifoliolata), sideoats grama (Bouteloua curtipendula), little bluestem (Schizachyrium scoparium), silver beardgrass (Bothriochloa laguroides), and tall dropseed (Sporobolus asper var. asper) [47].


SPECIES: Aristida purpurea
IMPORTANCE TO LIVESTOCK AND WILDLIFE : Livestock: In most regions, forage value of purple threeawn is only poor to fair [11,40,56]. The long awns irritate and cause abscesses in the mouths and nostrils of grazing animals. Livestock generally avoid purple threeawn for most of the year when other forage is available. In areas where purple threeawn is abundant, livestock may make moderate use of it in spring before awns develop and in fall and winter after seed shatter [56]. In some areas of the southern Great Plains, cattle prefer purple threeawn in winter because it is one of few plants that remain green all season [15]. Small mammals: In a Colorado study, purple threeawn was one of a variety of grass species grazed by white-tailed jackrabbit [12]. Black-tailed prairie dog graze purple threeawn lightly [18] but do not prefer it [7,15]. Purple threeawn is often one of the few grasses remaining in areas severely disturbed by prairie dogs [15]. PALATABILITY : Purple threeawn is generally unpalatable due to its spike-like awns, which can injure grazing animals. It may be grazed to some extent before seedheads are produced and after seed shatter [15,25]. Livestock may graze new purple threeawn growth after fire [15]. Dyksterhuis [13] reported that on post oak-blackjack oak (Quercus stellata-Q. marilandica)/buffalograss communities in the Cross Timbers region of Texas, cattle grazed purple threeawn only in December and January. However, cattle on desert grassland of the Jornada Experimental Range, New Mexico, grazed Fendler threeawn in all months of the year except January and February [42]. Wildlife: Bison on blue grama-buffalograss prairie in northeastern Colorado commonly grazed Fendler threeawn in March and August. In June, Fendler threeawn was a preferred grass [44]. The degree of use shown by livestock and wildlife species for purple threeawn is rated as follows [11]: CO MT ND UT WY Cattle poor poor/fair ---- fair poor/fair Sheep poor poor/fair ---- fair fair Horses poor poor ---- fair poor/fair Pronghorn ---- ---- poor fair ---- Elk ---- fair ---- poor ---- Mule deer ---- fair poor poor ---- White-tailed deer ---- fair poor ---- ---- Small mammals ---- ---- ---- fair ---- Small nongame birds ---- ---- ---- fair ---- Upland game birds ---- ---- ---- fair ---- Waterfowl ---- ---- ---- poor ---- NUTRITIONAL VALUE : Purple threeawn is rated poor to fair in energy content and poor in protein value [11]. Percent digestible protein of fresh purple threeawn (Aristida purpurea var. purpurea) and Fendler's threeawn collected at several locations throughout the western United States was as follows [41]: ______________________________________________________________________ | Cattle Goats Horses Rabbits Sheep | | ------ ----- ------ ------- ------| |purple threeawn 3.7 2.9 3.3 3.9 3.3 | |Fendler threeawn 2.7 1.8 2.3 3.0 2.2 | |____________________________________________________________________| Nutritional content of Fendler threeawn collected in on the Jornada Experimental Range, New Mexico, was [42]: ___________________________________________________________________________ | Dry Matter Composition (%) | |_________________________________________________________________________| | Ether A-D A-D | |Stage of Maturity Month Protein extract fiber lignin ash Ca | |_________________________________________________________________________| |early leaf April 8.2 1.1 48.7 6.5 14.0 0.56| |mature May --- 2.4 53.7 6.4 12.8 ----| |mature June-July 7.0 1.1 53.1 6.6 8.0 0.26| |mature Aug.-Sept. 10.4 2.8 42.4 5.5 8.8 0.49| |overripe Oct. 6.9 2.1 48.0 6.5 15.4 0.51| |dormant Nov. 5.0 1.4 53.7 7.6 10.6 0.36| |dormant Dec. 3.7 1.4 53.1 7.0 12.4 0.48| |_________________________________________________________________________| A-D = acid-detergent Nutritional content of Wright's threeawn from the Edwards Plateau of Texas was as follows [29]: _____________________________________________________________________________ | | |_______________Composition (%)_____________| | |Collection Date|Water Ash Cell wall P Protein DOM| |_______________|_______________|___________________________________________| |leaves 4/13/73 32 11 71 0.08 7 36| |old and new growth 5/24/73 35 9 74 0.08 7 42| |leaves and stems 6/28/73 45 6 77 0.10 8 48| |total 7/27/73 42 7 74 0.09 7 46| |leaves 8/30/73 23 7 74 0.05 5 39| |leaves and stems 10/03/73 38 5 79 0.07 6 43| |___________________________________________________________________________| P = phosphorus; DOM = digestible organic matter COVER VALUE : The value of purple threeawn cover for wildlife was been rated as follows [9]: CO ND UT Pronghorn ---- fair poor Elk ---- ---- poor Mule deer ---- fair poor White-tailed deer ---- poor ---- Small mammals poor ---- fair Small nongame birds poor ---- fair Upland game birds poor ---- fair Waterfowl ---- ---- poor VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : NO-ENTRY OTHER MANAGEMENT CONSIDERATIONS : Purple threeawn tends to increase with grazing. In east-central Texas, mean (+/- SE) purple threeawn percent cover on long-term protected sites (39 years of cattle exclusion) and long-term grazed sites (30 years of continuous heavy cattle grazing) was as follows [2]: ______________________________________ |Long-term protected|Long-term grazed| |___________________|________________| | 0 (+/- 0.0) | 17 (+/- 1.6) | |___________________|________________| Threeawns (Aristida spp.) may remain important constituents of some rangelands even after grazing is stopped or reduced. On grama (Bouteloua spp.) grassland on dry mesas of the Santa Rita Experimental Range, southern Arizona, cover of blue threeawn and spidergrass (A. ternipes var. hamulosa) on sites ungrazed for 25 years was about half that of blue threeawn and spidergrass cover on sites in various stages of grazing recovery. Grama spp. cover was 36 percent on sites protected for 25 years, and threeawn cover was 14 percent. Canfield [4] suggested that on dry mesas of Arizona, a grama-threeawn mixture may be indicative of rangeland in good condition. Awns of purple threeawn often catch in the fleece or hair of livestock, causing injury and lowering the value of the fleece or hide [50,56].


SPECIES: Aristida purpurea
GENERAL BOTANICAL CHARACTERISTICS : Purple threeawn is a warm-season, native perennial bunchgrass [5,8,22,26]. It is a mid-grass, with 6- to 12-inch (15-30.5 cm) culms. Leaves primarily grow in basal tufts, but there are a few culm leaves. The inflorescence is a panicle. Florets have sharp-pointed lemmas with stiff, hairy calluses and three-parted awns. Awns are 1 to 5 inches (2.5-13 cm) long [15,25,56]. Roots are moderately deep. On widely scattered sites on short- and mixed-grass prairies from South Dakota to Kansas, Weaver [58] found that maximum depth of purple threeawn roots averaged 4 feet (1.2 m). Purple threeawn is highly competitive during droughts lasting only a few years [19,39]. It tends to decrease during periods of extended drought. In eastern Colorado during the drought of 1931-1937, Fendler threeawn nearly disappeared from the Fendler threeawn/blue grama-buffalograss communities it once dominated. It reestablished during the 1940's, a decade when regional precipitation was mostly above normal [39,59]. RAUNKIAER LIFE FORM : Hemicryptophyte REGENERATION PROCESSES : Purple threeawn regenerates by seed and by tillering [15,19]. Seed crops are usually plentiful [53]. With adequate summer and fall rainfall, plants in the Southwest may produce two seed crops: one in spring and one in fall [34,43]. Second seed crops are rare, however, because late-season rains are seldom abundant enough to support a second seed crop [34]. Upon seed shatter, the seed falls nears the parent plant or is dispersed by animals when the long seed awns catch on their hides [56]. The combination of divergent awns and a sharp-pointed callus promotes rapid penetration of seed into soil [15,16]. Purple threeawn apparently maintains a persistent seedbank [35]. Seed usually germinates in spring, but may germinate in fall in warm climates. There is no light requirement [14,15,30], but high temperatures are required for germination. In northern locales, temperatures high enough to stimulate purple threeawn germination generally occur only in spring on flats and low-elevation, south- and west-facing slopes [15]. In the laboratory, 3-month-old seed from southeastern Montana showed optimum germination at 69 degrees Fahrenheit (20 deg C). Older seed germinated best at 77 degrees Fahrenheit (25 deg C). Temperatures below 50 degrees Fahrenheit (10 deg C) and above 86 degrees Fahrenheit (30 deg C) inhibited germination. Neither stratification nor light had significant effects on germination [14]. Seed from southern Idaho showed 92 percent germination within 10 days with day/night temperatures of 109 and 43 degrees Fahrenheit (43 and 23 deg C). Germination was less than 5 percent after 30 days at room temperature. Seedlings rapidly grow deep roots. Greenhouse seedlings attained a primary root length of 19 inches (37 cm) in 30 days, then began developing secondary roots that grew downwards with little lateral development. Purple threeawn seedlings may not tolerate wet soils. Purple threeawn seedlings subjected to 1 week in saturated soil followed by 3 weeks in soil at field capacity showed no growth during the 4-week period. In contrast, bluebunch wheatgrass (Pseudoroegneria spicata) seedlings did not grow during saturation but grew well when soil moisture was at field capacity [15,16]. SITE CHARACTERISTICS : Purple threeawn is most common on coarse-grained, xeric soils [15,16]. In the Intermountain region, it often dominates grassland communities on gravelly or sandy soils [16,28]. Purple threeawn is also common on disturbed sites such as roadsides and railway rights-of-way [28]. In Colorado and the Southwest, purple threeawn is a relatively minor species generally confined to xeric sites. It is also described as a minor species in the Pacific Northwest, usually occurring on sandy and gravelly soils [16]. Although purple threeawn generally grows on rocky or sandy soils, it may occur on soils of other textures [28,31]. Tisdale [51] reported that in canyon grasslands of southern Idaho, the Fendler threeawn/Sandberg bluegrass community type occurred on sandy to silty loams that were deeper and lower in organic matter and pH than soils of surrounding sand dropseed (Sporobolus cryptandrus)/Sandberg bluegrass communities. Elevational ranges of purple threeawn in several states are as follows: Arizona - 1,000 to 5,000 feet (305-1525 m) [28] California - below 6,600 feet (2,000 m) [26] Colorado - a few specimens have been collected from 5,300 to 6,800 feet (1,615-2,070 m) [24]; actual elevational range may be greater Idaho - below 2,800 feet (853 m) [15] Utah - 2,700 to 7,655 feet (820-2,320 m) [61] SUCCESSIONAL STATUS : Purple threeawn is seral on most sites but is a component of stable plant communities on some sites. It is one of the first grasses to establish on abandoned fields and other disturbed sites [25]. In creosotebush (Larrea tridentata) communities of southwestern Nevada, it was more common on disturbed sites than on undisturbed sites [20]. In eastern Washington, it invaded and dominated an abandoned roadway in a bluebunch wheatgrass-sand dropseed habitat type [31]. In northeastern Arizona, purple threeawn was one of the first grasses to colonize volcanic cinders [15]. In Intermountain grasslands and shortgrass prairie, purple threeawn is generally a minor component of undisturbed plant communities protected from livestock grazing [38]. Purple threeawn tends to increase with heavy grazing and may persist after livestock grazing has stopped [15,31]. Bluebunch wheatgrass-sand dropseed-purple threeawn communities of the Oregon-Idaho border are stable, covering expansive areas where grazing was historically heavy [31]. Purple threeawn sometimes dominates stable communities on undisturbed sites, however. Daubenmire [9] described a Fendler threeawn-Kentucky bluegrass community in eastern Washington as a possible "edaphic climax." In eastern Colorado, a stable Fendler threeawn/blue grama-buffalograss community develops on sandy loam soils within what is otherwise buffalograss-blue grama prairie on clay [39]. SEASONAL DEVELOPMENT : Purple threeawn generally grows in spring and early summer [25]. In southern Idaho, it began growth in late March and flowered in mid-June. Seeds reached milk-dough stage in mid-August and dehisced in September. Plants stayed green all summer and did not put on new growth with fall rains [15,16]. Similar development is reported in southeastern Montana [14] and on Colorado shortgrass steppe [10]. Fendler threeawn had two growth periods on the Chihuahuan Desert of southwestern New Mexico. It first began growth in mid-March, flowered in mid-April, and set mature fruit in May. A second period of growth occurred from mid-July through mid-September [34].


SPECIES: Aristida purpurea
FIRE ECOLOGY OR ADAPTATIONS : Purple threeawn is generally reduced by fire for several growing seasons. Wright and others [63] found that purple threeawn cover usually decreased after fire on the southern Great Plains. Purple threeawn cover was not greatly reduced by fire, however, when winter and spring precipitation was 40 percent or more above normal. Purple threeawn recovers from fire by tillering [15,52,62,63]. It probably also establishes from seed after fire. It is a seedbanking species [35] with seeds stored below ground, where they are insulated from heat damage by fire [63]. New seeds are probably added to the seedbank soon after fire, since seeds from off-site plants are readily dispersed by animals [56]. Also, fire may stimulate seed production in surviving plants. Trlica and Schuster [52] reported that Fendler threeawn subjected to prescribed fire produced a large seedcrop the second growing season after fire (see PLANT RESPONSE TO FIRE). FIRE REGIMES : 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". POSTFIRE REGENERATION STRATEGY : Caudex, growing points in soil Ground residual colonizer (on-site, initial community) Initial-offsite colonizer (off-site, initial community) Secondary colonizer - on-site seed


SPECIES: Aristida purpurea
IMMEDIATE FIRE EFFECT ON PLANT : Threeawns (Aristida spp.) are readily harmed by fire because their rootcrowns are close to or above the soil surface [63]. Purple threeawn cover is generally reduced by fire [52,62,63]. Purple threeawn produces relatively large, densely culmed, fine-leaved bunches. Since it is grazed very little, litter usually accumulates around bunches. Wright and Bailey [63] stated that bunchgrasses with this growth habit may continue to burn for 2 or 3 hours after fire has passed. Such prolonged burning transfers heat downward and damages roots. Basal cover may be greatly reduced or plants may be killed. Fire-induced mortality varies, however. Evans [15] reported that only a few purple threeawn were killed by spring prescribed fire in southern Idaho. Small purple threeawn bunches were killed by a second fire 2 years later. Large bunches were not killed by repeated burning but split into several small bunches. DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : Fire reduced blue threeawn in a desert mountain shrub community near Big Bend National Park, Texas. Wildfire burned the community in November, 1975. Prefire vegetation was dominated by sotol (Dasylirion leiophyllum), lechuguilla (Agave lechuguilla), blue threeawn, and sideoats grama (Bouteloua curtipendula). Precipitation was above average in postfire years 1 and 2. At postfire year 2, blue threeawn cover on burned plots averaged 0.42 percent while blue threeawn cover on adjacent unburned plots averaged 4.09 percent. Grasses and succulents had decreased at the expense of forbs and subshrubs. Forb and subshrub cover on burned plots was 650 percent greater than on unburned plots [3]. Wright's and purple threeawn (Aristida purpurea var. purpurea) were slightly to greatly reduced for at least two growing seasons following chaining and burning in a redberry juniper (Juniperus erythro- carpa)-mixed grassland community in King County, Texas. In 1979 or 1980, plots were chained, chained and broadcast burned in March, or left untreated (control). Fine fuel loads averaged 2,264 lbs/acre (2,573 kg/ha) in 1979 and 1,327 lbs/acre (1,508 kg/ha) in 1980. Weather conditions were: relative humidity 25 to 40 percent, temperature 68 to 78 degrees Fahrenheit (20-26 deg C), and winds 7.7 to 14.4 miles/hour (12-24 km/hr). Fire spread was "excellent" in both years, with nearly 100 percent coverage. Precipitation following the 1979 fire was above average; drought followed the 1980 fire. Combined yield of Wright's and purple threeawn was [47]: _________________________________________________________________________ | 1979 Treatments (wet year) | 1980 Treatments (dry year)| |___________________________________________|___________________________| | 1st growing 2nd growing | 1st growing 2nd growing| | season season | season season | |___________________________________________|___________________________| |control 63a 63a* | 57a 25b | |chained 92a 113a | 85a 37b | |chained & burned 47a 56a | 12a 6b | |_______________________________________________________________________| *Values within a treatment year identified by the same letter are not significantly different (p > 0.05). Prescribed fire on the Texas Technological College Research Farm near Amarillo had little effect on Fendler threeawn size but stimulated seedstalk production. Six plots were used. Two plots were burned in fall, 1965 (1 with and 1 against the wind); two plots were burned in spring, 1966 (1 with and 1 against the wind); one plot was burned summer, 1966 (with the wind); and one plot was not burned (control). There were no significant differences in soil moisture between plots at the time of the fall or spring fires. Basal diameters of Fendler threeawn plants decreased between 1966 and 1967 on plots burned 2 years in succession, but either maintained or increased in size on the unburned control plot and plots burned only once the previous year. Height and seedstalk production decreased between 1966 and 1967 regardless of treatment. Relative to the control plot, fire had little effect on seedstalk numbers the first growing season after fire. However, in the second growing season (1967), Fendler threeawn seedstalk numbers were greater on all burned plots compared to the control plot. Average seedstalk production and average maximum height of Fendler threeawn was [52]: Number of Fendler Threeawn Seedstalks |----------------------Treatment-------------------------| |Control Fall Fall Spring Spring Summer| Year | 1965 1965 & 66 1966 1966 & 67 1966 | _______________|________________________________________________________| 1965* | 115 135 107 55 115 127 | 1966 | 40 105 82 25 67 37 | 1967 | 39 45 55 43 48 55 | _______________|________________________________________________________| *before burning Height (cm) |----------------------Treatment-------------------------| |Control Fall Fall Spring Spring Summer| Year | 1965 1965 & 66 1966 1966 & 67 1966 | _______________|________________________________________________________| 1965* | 33 32 30 27 27 35 | 1966 | 25 23 20 20 20 20 | 1967 | 12 11 10 11 11 11 | _______________|________________________________________________________| *before burning Fendler threeawn was reduced following wildfire in a cheatgrass stand in north-central Utah. Vegetation had been sampled at the end of the 1955 growing season. The wildfire occurred in summer 1956. Precipitation in 1957 (the only year for which precipitation data are given) was near average. Fendler threeawn cover and importance percentages were as follows [6]: Year ---------------------------------------- 1955 1957 1958 1960 1961 ---------------------------------------- cover (%) 11.5 3.4 6.2 9.9 5.0 importance (%) 17.7 4.2 8.6 11.6 5.9 DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : NO-ENTRY


SPECIES: Aristida purpurea
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