SPECIES: Achnatherum thurberianum
Archer, Amy J. 2000. Achnatherum thurberianum.
In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/plants/graminoid/achthu/all.html .
No special status
Thurber needlegrass occurs in eastern parts of Washington, Oregon, and California; and across northern Nevada to southern Idaho, southwestern Montana, and northeastern Wyoming .
FRES21 Ponderosa pine
FRES34 Chaparral-mountain shrub
FRES36 Mountain grasslands
FRES38 Plains grasslands
|Crude Protein||Calcium||Phosphorus||Crude Fiber||Crude Fat||Digestibility|
Thurber needlegrass provides protective cover to many small and medium-sized animals . In a southeast Oregon big sagebrush ecosystem, sage grouse use perennial bunchgrasses for cover, and the residual grass cover around the sage grouse nests has been found to be a major factor reducing nest depredation . A Wyoming big sagebrush/Thurber needlegrass cover type hosted pre-laying sage grouse hens in eastern Oregon .
The success of rehabilitation rests heavily on the amount of competition from the alien annual grass, cheatgrass , since it is a highly successful competitor with Thurber needlegrass seedlings [32,102]. Methods of manual seed planting were assessed and it was found that more Thurber needlegrass seedlings emerged in the standard and deep furrow seeding treatments than in broadcast treatments. Thurber needlegrass was found to have higher frequency in plowed soil than in unplowed soil .
Livestock grazing and fire have been recognized as potentially detrimental to the maintenance of perennial grasses such as Thurber needlegrass in sagebrush/grass communities [29,60,97]. This species increases under protection from livestock grazing . After 30 years of rest from grazing, a 20-acre (8 ha) tract of eroded sagebrush/grass range in northern Nevada increased its Thurber needlegrass population 7-fold ; however, Thurber needlegrass decreased when protected from grazing in a Wyoming big sagebrush/Thurber needlegrass community . In Nevada, basal area of Thurber needlegrass in a big sagebrush/Thurber needlegrass community type decreased under heavy grazing during the growing season .
A single defoliation, particularly during the boot state, can reduce subsequent herbage production and root mass and possibly lower the competitive ability of Thurber needlegrass . A grazing system which allows seed production, trampling of plant seed, and a non-use period may increase the establishment of new plants in interspaces .
Thurber needlegrass is a native, perennial, cool-season bunchgrass [63,81]. This species is densely tufted with erect culms 12 to 24 inches (30-60 cm) tall, and involute blades 4 to 10 inches (10-25 cm) long and 0.04 to 0.08 inch (1-2 mm) wide. The culms are narrow, erect, and few flowered . Inflorescence characteristics include 3- to 9-inch- (7-24 cm) long panicles and single-flowered spikelets with sharp calluses and awned lemmas . The crown typically acquires a circular appearance, as the plant dies from the center outward . Maximum reported rooting depth of Thurber needlegrass in Idaho is 24 inches (61 cm) .
Thurber needlegrass reproduces from seeds and tillers . However, regeneration is usually by seed on sites where the grass has been killed by fire . Reestablishment on burned sites may be relatively slow due to low germination and seedling vigor , and because seed production is usually "low" . Heavy seed production after fire has been reported in central Oregon [60,90]. Because the seed is undesirable to livestock, a large portion matures, allowing for fairly good reproduction rates  even in grazed areas. In a controlled environment study, Thurber needlegrass had a maximum germination rate of 25% and an optimum germination temperature of 59-77 degrees Fahrenheit (15-25oC) .In south central Idaho, a litter of twisted moss (Tortula ruralis), big sagebrush, and green rabbitbrush (Chrysothamnus viscidiflorus) retarded germination and early growth of Thurber needlegrass, but stimulated growth 4 weeks after germination .
Thurber needlegrass is commonly found in semiarid landscapes [1,52,56,57,58], and occurs on a variety of soil types [1,42,58], most of which are dry and coarse textured . This species is often found on arid hillsides [48,97], and is most prevalent on north and east slopes where there is more moisture and less variation in temperature [38,48,91].
Specific examples of sites where Thurber needlegrass is prevalent follow:
|Southern ID||4400-4600 ft (1341-1402 m)||10 in (250 mm)|||
|Northern NV||5000-7300 ft (1524-2225 m)||11 in (280 mm)|||
|Central OR||2400 ft (732 m)||9.3 in (236 mm)|||
|Eastern OR||4300 ft (1311 m)||11.5 in (290 mm)|||
|Southeastern OR||4600-5200 ft (1402-1585 m)||11.5 in (290 mm)|||
|South-central WA||1200 ft (366 m)||10 in (250 mm)||[52,56]|
Thurber needlegrass is a climax species in many sagebrush/grassland, pinyon-juniper, and western juniper plant associations . Burning and other disturbances often favor annual species such as cheatgrass over perennial grasses such as Thurber needlegrass, so Thurber needlegrass is most common in mid-successional seres [48,73,90]. The increase of perennial species such as Thurber needlegrass may either be correlated to the attainment of the critical biomass necessary for seed production or to the increase in ground cover that provides a favorable microsite for seed germination and plant survival . A study of secondary succession in north-central Nevada found Wyoming big sagebrush was a principal increaser species in the overstory while Thurber needlegrass was a principal understory decreaser in late succession .
Thurber needlegrass begins annual growth in early spring [67,81], fruits from May to June [67,70], produces ripe seed mid to late July [67,81], and continues growth until October . A study in southern Idaho found Thurber needlegrass grew rapidly in the spring, then become largely dormant in summer. After autumn rains, this grass regrew for a longer period of time than most associated grasses [79,84].
The following data indicate the seasonal development of Thurber needlegrass near Silver Lake, Oregon :
|Mid-May||Early June||Late June||Early July||Mid-July||Mid-August|
|early boot||in head||early milk||late milk||late dough||mature seed|
Thurber needlegrass is classified as "moderately" resistant , but depending on the season of burn, phenology, and fire severity, this perennial bunchgrass is moderately to severely damaged by fire [10,31,62,87,97]. Aboveground vegetation of needlegrass is often consumed by fire . The distribution of fuels within the plant influences the severity and length of burn time. Fire in the many leafy vegetative culms can promote burning beneath the soil surface, producing subsurface charring . The abundant dead material which is sometimes present with Thurber needlegrass contributes to fire damage regardless of season . Postburn regeneration usually occurs by seed . Thurber needlegrass has also adapted to fire by regenerating by fire-enhanced flowering .
Fire regimes for plant communities in which Thurber needlegrass occurs are summarized below. Historic fire severities ranged from nonlethal understory fire in ponderosa pine (Pinus ponderosa) to stand-replacing fire in chaparral and sagebrush communities. 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".
|Community or Ecosystem||Dominant Species||Fire Return Interval Range in Years (mean)|
|Pacific ponderosa pine*||Pinus ponderosa var. ponderosa||1-47|
|interior ponderosa pine*||P. ponderosa var. scopulorum||2-10|
|Colorado pinyon||P. edulis||10-49|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 |
|coastal Douglas-fir*||Pseudotsuga menziesii var. menziesii||95-242 [61,66]|
|California chaparral||Adenostoma and/or Arctostaphylos spp.||20-40|
|California montane chaparral||Ceanothus and/or Arctostaphylos spp.||50-100 |
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|Wyoming big sagebrush||Artemisia tridentata ssp. wyomingensis||10-70 (40) [89,103]|
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1,350 [3,72]|
|mountain grasslands||Pseudoroegneria spicata||3-40 (10) |
Wright and others  concluded that Thurber needlegrass is probably the least fire-resistant needlegrass, largely due to its densely tufted stems [90,106]. Aboveground vegetation is often consumed by fire , and burning has been found to decrease this needlegrass' vegetative and reproductive vigor . The seasonal response to burning is important in determining the extent of damage by fire ; early-season burning is more damaging than late-season burning [10,35,86,87,90]. The smaller the basal diameter, the less the plants are damaged by fire [90,97,100,106]. The root crowns of this species often show sub-surface charring , but Thurber needlegrass often survives wildfire and continues growth when conditions are "favorable" .
Thurber needlegrass vegetation and reproduction are decreased with burning [10,14,86,87]. On the Arid Lands Ecology Reserve in south-central Washington, 3 years of burn monitoring showed that the average length of the leaves, culms, and spikes of Thurber needlegrass were shortened each year the area was burned, and the basal area and phytomass production were reduced [86,87]. Basal area has also been reduced by fire in Oregon  and California . Stanton  found flowerstalk production was much reduced the year following a burn; however, the number of inflorescences may increase after fire disturbance . Tagged Thurber needlegrass showed 21% mortality in a BLM prescribed burn; of those surviving, 91% produced seedheads .
Fire-caused mortality of Thurber needlegrass varies by both plant size and season . A study in Idaho found the plants suffered high mortality from June fires, were extremely susceptible to damage from burning in July, but were relatively resistant to fire in August . An eastern Oregon study determined that mortality for this species was 50% in May, 70% in June, and 10% in November. The season of burn is important in determining the extent of damage to Thurber needlegrass, but bunch size determines the amount of fire damage to individual bunches . Presumably, when fuel volume is small, less heat is released immediately above the perennating buds ; therefore, smaller bunches are less likely to be damaged by fire [97,100]. In a wildfire with higher surface temperatures than in a controlled study, large Thurber needlegrass plants showed greater mortality and basal area reduction than experimentally burned plants ; however, soil heated from 482 to 1382 degrees Fahrenheit (250-750 oC) increased the emergence of Thurber needlegrass seedlings .
If not killed outright by fire, Thurber needlegrass generally recovers slowly . Living tissue often survives only at the periphery of the crown . Thurber needlegrass plants that survive fire may have reduced vigor for many years . Although recovery time is variable, preburn herbage levels have been nearly reached after 3 years of regrowth on some sites . Competitive perennial and annual grasses often inhibit the postburn re-establishment of Thurber needlegrass [14,32,102,105].
Evidence suggests that the short-term productivity of Thurber needlegrass is decreased following fire . However, on limited sites where Thurber needlegrass was only "mildly damaged" by fire, herbage production exceeded that of unburned plots within 3 years of burning ; this result was uncommon as regrowth is usually slow [12,87].
Regeneration of Thurber needlegrass is often dependent on competition from other species. Cheatgrass is a highly successful competitor with seedlings of Thurber needlegrass . Basal cover of bluebunch wheatgrass and Sandberg's bluegrass equaled or exceeded prefire levels at Lava Beds National Monument in California, at the expense of Thurber needlegrass and Idaho fescue .
Wildfires in the big sagebrush/grasslands of the Great Basin can be extremely detrimental or beneficial, depending on management goals and rehabilitation efforts. Destruction of degraded big sagebrush communities by wildfires presents an opportunity for improvement in the range condition by seeding with perennial grasses and browse species. However, this opportunity can be quickly lost because the weed control effects of a wildfire are temporary. Failure to rehabilitate burned areas quickly may risk further environmental degradation . The success of techniques for revegetation of degraded big sagebrush communities burned in wildfires often depends on the level of competition from cheatgrass . Evidence also suggests that when Thurber needlegrass is burned and then grazed, recovery can be impaired .
Data suggest that prescribed fires contribute to a substantial decrease in mature bunches of Thurber needlegrass; however, due to Thurber needlegrass' stable frequency levels and postfire seedling establishment, negative long-term effects are negligible . It is recommended that prescribed burning take place during the fall to minimize damage to dominant cool-season plants such as Thurber needlegrass .
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