Purple Threeawn

purple threeawn
red threeawn
wiregrass
democrat grass

More info for the term: cover

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

More info for the terms: culm, warm-season

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].

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]

More info for the terms: cover, fire regime, prescribed fire, seed

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".

More info on this topic.

More info for the term: hemicryptophyte

Hemicryptophyte

More info for the terms: grassland, xeric

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]

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

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

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

More info for the term: shrub

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

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

More info for the terms: forest, shrub, woodland

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

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

More info for the terms: association, grassland, shrub, shrubland, woodland

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

More info for the terms: cover, litter, prescribed fire

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.

More info for the term: seed

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].

More info for the terms: association, cactus, grassland

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].

More info for the term: graminoid

Graminoid

More info for the terms: cover, grassland

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].

More info for the term: fresh

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

AZ AR CA CO IA ID KS MN MT NE
NV NM ND OK OR SD TX UT WA WY
AB BC MEXICO

More info for the terms: grassland, seed

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 ----

More info on this topic.

More info for the term: fruit

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].

More info for the terms: cover, forb, forbs, fuel, grassland, prescribed fire, shrub, succession, wildfire

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

More info for the terms: ground residual colonizer, secondary colonizer

Caudex, growing points in soil
Ground residual colonizer (on-site, initial community)
Initial-offsite colonizer (off-site, initial community)
Secondary colonizer - on-site seed

More info for the terms: seed, stratification

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].

More info on this topic.

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

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

More info on this topic.

More info for the terms: climax, habitat type

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].

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]

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.

Perennials, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems erect or ascending, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stems branching above base or distally at nodes, Stem internodes solid or spongy, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly basal, b elow middle of stem, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath hairy, hispid or prickly, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Ligule present, Ligule a fringe of hairs, Inflorescence terminal, Inflorescence a contracted panicle, narrowly paniculate, branches appressed or ascending, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence lax, widely spreading, branches drooping, pendulous, Inflorescence with 2-10 branches, Flowers bisexual, Spikelets pedicellate, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisex ual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes equal to or longer than adjacent lemma, Glumes 1 nerved, Lemma coriaceous, firmer or thicker in texture than the glumes, Lemma 3 nerved, Lemma glabrous, Lemma apex acute or acuminate, Lemma distinctly awned, more than 2-3 mm, Lemma with 3 awns, Lemma awns about equal in length, Lemma awn 2-4 cm long or longer, Lemma awned from tip, Lemma awn once geniculate, bent once, Lemma margins inrolled, tightly covering palea and caryopsis, Lemma straight, Callus or base of lemma evidently hairy, Callus hairs shorter than lemma, Palea present, well developed, Palea membranous, hyaline, Palea shorter than lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinall y grooved, hilum long-linear.

Spikelets showing the characteristic three awns apiece

Aristida purpurea is a species of grass native to North America which is known by the common name purple three-awn.