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Photo by David C. Powell, USDA Forest Service
AUTHORSHIP AND CITATION:
Meyer, Rachelle 2009. Festuca thurberi. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us /database/feis/plants/graminoid/festhu/all.html .
NRCS PLANT CODE :
The scientific name of Thurber's fescue is Festuca thurberi Vasey (Poaceae) .
FEDERAL LEGAL STATUS:
Information on state- and province-level protection status of plants in the United States and Canada is available at NatureServe.
Photo by David C Powell, USDA Forest Service
Thurber's fescue occurs in New Mexico, Utah, Colorado, and a small portion of southern Wyoming [10,21,38,103,113]. Some floras include Arizona in Thurber's fescue range [51,64,113], and Thurber's fescue was dominant on a site in northeastern Arizona . Grass Manual on the Web provides a distributional map of Thurber's fescue, although no locations from Arizona are included.
The occurrence of Thurber's fescue in South Carolina documented on the Plants Database is based
on specimens collected from a wool combing mill during the late 1950s and early 1960s
(personal communication ). It is uncertain if Thurber's fescue has persisted on this
site, since it was not detected during a preliminary survey of the area in 2004
(personal communication ).
HABITAT TYPES AND PLANT COMMUNITIES:
Thurber's fescue is a major component of an extensive mosaic of grassland communities interspersed within open forests [16,69]. Open parks, dry meadows, open slopes, and broad, rounded ridgetops dominated by Thurber's fescue [10,39,104,113] are often intermixed with forests where Thurber's fescue is an understory indicator [16,69,77]. These forests or woodlands include those dominated by quaking aspen (Populus tremuloides) [9,16,40,46,54,74,75,80,111], Rocky Mountain bristlecone pine (Pinus aristata) [24,54,61,69,96], or Engelmann spruce (Picea engelmannii) [9,23]. Mountain big sagebrush (Artemisia tridentata subsp. vaseyana)-Thurber's fescue shrublands also occur in forest openings and areas adjacent to upland forests [100,111]. Thurber's fescue occurs as an understory indicator in shrublands dominated by silver sagebrush (Artemisia cana) on alluvial floodplains in Colorado [9,32,100]. Baker  includes mountain snowberry (Symphoricarpos oreophilus)-Thurber's fescue shrubland in a preliminary classification of the vegetation of Colorado. Herbaceous species associated with Thurber's fescue in several woodland, shrubland and herbaceous communities include Idaho fescue [41,53,102], Arizona fescue (F. arizonica) [1,25,70], elk sedge (Carex geyeri) [41,46,54,68], and aspen peavine (Lathyrus lanszwertii var. arizonicus) [41,54,60,68,80,100].
Thurber's fescue occurs at lesser frequencies and coverages in several other woodlands, shrublands, and herbaceous communities. It occurs in forests and woodlands dominated by subalpine fir (Abies lasiocarpa) [2,24,54], blue spruce (P. pungens) [2,24,31,54,96], Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) [2,54], limber pine (Pinus flexilis) , or interior ponderosa pine (Pinus ponderosa var. scopulorum) [16,33,39,107]. It has been documented in shrubland communities including common juniper-hairy false goldenaster (Juniperus communis var. montana-Heterotheca villosa), common juniper-gooseberry currant (Ribes montigenum) , and mountain brush . Herbaceous types where Thurber's fescue occurs without dominating include Idaho fescue/sticky purple geranium (Festuca idahoensis/Geranium viscosissimum var. incisum), Porter's licorice-root (Ligusticum porteri)/American vetch (Vicia americana)-aspen peavine , Parry oatgrass (Danthonia parryi)-Idaho fescue , and herbaceous communities in lower elevations of the alpine zone [18,84,87].
Classifications that include Thurber's fescue as a dominant in grassland, shrubland, and/or forest communities and the state in which they occur are listed in the following table.
|Plant communities where Thurber's fescue is a dominant species|
|Arizona fescue-Thurber's fescue||Colorado [9,53]|
|Thurber's fescue-Arizona fescue-mixed forb association||New Mexico |
|Thurber's fescue subalpine meadow||New Mexico [8,70]
|Thurber's fescue-mixed forb association||New Mexico |
|Thurber's fescue-Idaho fescue||Colorado [41,53,111]|
|Idaho fescue-Thurber's fescue||Colorado |
|Thurber's fescue/American vetch-aspen peavine||Colorado [41,53,111]|
|Thurber's fescue-Parry oatgrass||Colorado|
|Thurber's fescue-alpine oreoxis (Oreoxis alpina subsp. puberulenta)||Colorado|
|Thurber's fescue-bush oceanspray (Holodiscus dumosus)||Colorado |
|Silver sagebrush/Thurber's fescue||Colorado [9,32,100,111]|
|Thurber's fescue-silver sagebrush||Colorado |
|Mountain big sagebrush/Thurber's fescue||Colorado [9,32,100]|
|Big sagebrush/Thurber's fescue||Colorado [41,111].|
|Big sagebrush-Thurber's fescue||Colorado |
|Mountain snowberry/Thurber's fescue||Colorado |
|Thurber's fescue-mountain snowberry||Colorado|
|Shrubby cinquefoil (Dasiphora floribunda)-Thurber's fescue||Colorado |
|Quaking aspen/Thurber's fescue||Colorado [9,40,46,47,54,80,111]
|Quaking aspen/mountain snowberry/Thurber's fescue||Utah [13,74,75]|
|Quaking aspen/Thurber's fescue/elk sedge||Colorado |
|Engelmann spruce/Thurber's fescue||New Mexico
|Engelmann spruce/Rocky Mountain bristlecone pine/Thurber's fescue||Colorado |
|Rocky Mountain bristlecone pine/Thurber's fescue||Colorado [24,47,54,61,82]
New Mexico [24,61,96]
|Douglas fir-limber pine/Thurber's fescue||New Mexico|
|Douglas fir-Rocky Mountain bristlecone pine/Thurber's fescue||New Mexico |
Thurber's fescue is a densely tufted [10,21,48,113], cool-season , perennial [21,36,38,64,113] bunchgrass [48,98,104]. Its culms are 15.8 to 47 inches (40-120 cm) tall [10,21,64,113] and stout [76,104,113]. According to a flora of the Intermountain West, Thurber's fescue "tufts" are 12 to 18 inches (30-45 cm) tall . A Wyoming  and 2 Colorado floras [38,39] state that Thurber's fescue leaves are typically less than 2 mm wide and 2 to 8 inches (6-20 cm) long. A key to New Mexico Festuca includes Thurber's fescue plant heights up to 59 inches (150 cm) and describes leaf blades as 10 to 18 inches (25-45 cm) long . Leaves are mostly basal  and are generally involute [21,36,64,76,113]. Thurber's fescue has elongated ligules, often 2 to 6 mm long [36,38,39,64], and occasionally up to 9 mm long [4,10,21,113]. Sheaths [4,10,21,113] and flower stalks  are persistent. Flowers are arranged in a panicle that is 3.2 to 6.7 inches (8-17 cm) long [4,21,113]. Spikelets are 0.3 to 0.6 inch (0.8 to 1.4 cm) long and have 3 to 6 flowers [10,21,113]. Awns on lemmas are minute [4,21,113] or absent [4,64,104,113].
Thurber's fescue has numerous fibrous roots  and no rhizomes [10,38,109]. Langenheim  states that Thurber's fescue's "root system is extensive but shallowly placed". According to Hess and Wasser , Thurber's fescue roots are deeper than Idaho fescue roots. Roots of a 4-inch (10 cm) diameter Idaho fescue may extend 16 inches (40 cm) deep . Thurber's fescue plants are mycorrhizal, with individuals from a site in Gunnison County, Colorado having an average of 2.3 fungi species and an average of 80% of the root length infected .
As of 2009, little detailed information is available on ages or lifespan of Thurber's fescue. Four-inch wide Thurber's fescue tussocks on the White River Plateau in Colorado were less than 15 years old . Longevity of Thurber's fescue was rated as excellent by Monsen and others , who reviewed characteristics of grasses useful in reseeding rangelands. Several characteristics were categorized as "poor", "fair", "medium", "good", or "excellent". The ranking of other Thurber's fescue characteristics is referred to in other sections of this review.
Thurber's fescue growth begins in May  or early June  and continues through the summer [39,72,98]. Turner and Paulsen  state that Thurber's fescue grows new but chlorotic leaves under snowpack in the central Rocky Mountains. As temperatures warm Thurber's fescue growth accelerates . Monsen and others  ranked Thurber's fescue growth in spring as excellent, while summer and fall growth rates were ranked fair. In a Thurber's fescue-dominated grassland in southwestern Colorado, leaves were observed growing as late as mid-July .
Flowering may begin in June and continue into August [21,64,77,99],
and seed is dispersed in August and September [77,104]. Two seeds planted in
containers on a field site in southwestern Colorado in August germinated by October,
and several more germinated by mid-June . The effects of warming and drying
on Thurber's fescue phenology are discussed in the Climate section.
Pollination and breeding system: Thurber's fescue reproduces by seed [72,77,103]. Flowers of Festuca species are perfect [10,42]. Perennial grasses are typically cross-pollinated [35,42] by wind [35,106].
Seed production and dispersal: As of 2009, no quantitative information was available regarding Thurber's fescue seed production. Reported Thurber's fescue seed production has been described as "fair"  to "abundant" . Thurber's fescue seed production was ranked as fair by Monsen and others . Abundant seed production of Thurber's fescue in plots in southwestern Colorado may explain its success following experimental removal of vegetation with herbicide .
Variation in Thurber's fescue seed production may be explained by the influence of weather on flowering. In a Thurber's fescue-dominated grassland in southwestern Colorado, only 10% of Thurber's fescue flowered in a warm, dry year while flowering rates of 70% to 90% were observed in relatively cool, moist summers .
According to a review , Thurber's fescue seeds are dispersed by wind.
Seed banking: As of 2009, no information was available on Thurber's fescue seed banking or seed longevity.
Germination, seedling establishment, and plant growth: Thurber's fescue exhibits high germination rates in appropriate conditions [72,77]. In a greenhouse experiment Thurber's fescue had an average germination rate of 94%, and at the optimum temperature, 59 °F (15 °C), germination rate in a laboratory experiment was 98% after 35 days. Germination was generally lower at higher temperatures and declined with decreasing moisture. Germination rate at 0 MPa water potential ranged from 15% to 34%, while germination rate at -0.75 MPa water potential ranged from 11% to 19%. Thurber's fescue germination rate at -1.5 MPa averaged 0%. These results were consistent with the field portion of this study, which suggests Thurber's fescue germination occurs primarily in spring in southwestern Colorado (See Seasonal Development). In containers on the field site, 14% of Thurber's fescue seed germinated on litter and 12% germinated on bare soil .
Monsen and others  rank Thurber's fescue seedling vigor as good and growth rate as medium. Although comparatively low flowering rates resulted in few seedlings in some years during a southwestern Colorado study, in years with high flowering rates and seed production, Thurber's fescue seedlings were the most abundant of any of the perennial species studied. Successful seedling establishment and vigorous growth may explain the success of Thurber's fescue in experimental plots where vegetation was removed with herbicide .
Thurber's fescue has abundant roots  that may grow quickly. In planter boxes, Thurber's fescue roots grew over 8 inches (20 cm) in 70 days during summer .
Vegetative regeneration: Thurber's fescue bunches enlarge [59,77,104] and may recover from damage by tillering . Langenheim  observed rapid expansion of bunches by tillering on a site in Colorado. Five years following herbicide application that killed all but 1 or 2 shoots, Thurber's fescue had tuft diameters nearly as large as before the treatment. Paulsen  concludes that Thurber's fescue "recovery by tiller development surpassed all other grasses."
Thurber's fescue generally occurs at high elevations. It occupies many topographic conditions and typically occurs in loamy soil. The climate at sites where Thurber's fescue dominates the understory is cool and often relatively dry.
Elevation: Thurber's fescue occurs from montane to alpine habitats [10,84,87,88] from 6,500 to 12,500 feet (2,000-3,700 m). It is an understory dominant in communities from 8,000 to 12,500 feet (2,440-3,800 m). Quaking aspen/Thurber's fescue communities in Utah  and silver sagebrush/Thurber's fescue communities in Colorado occurred at 8,000 feet (2,440 m) . In contrast, Rocky Mountain bristlecone pine/Thurber's fescue communities in northern Colorado occurred up to 12,300 feet (3,600 m) , and Thurber's fescue meadows may occur up to 12,500 feet (3,800 m) in New Mexico  and Colorado .
|Thurber's fescue elevation ranges by state|
|New Mexico||9,000-12,500 [4,8]|
Despite some overlap, Thurber's fescue generally dominates at higher elevations than Arizona fescue and at lower elevations than sheep fescue (Festuca ovina) . Arizona fescue is replaced by Thurber's fescue in the upper elevations of the pine zone . A review of New Mexico vegetation states that sheep fescue generally dominates at higher elevations than Thurber's fescue , although Thurber's fescue dominated the vegetation at higher elevations than any other fescue community on a site in northern New Mexico 
Topography: Thurber's fescue occurs on sites with variable topographic positions, shapes, slopes, and aspects. Thurber's fescue grows on alluvial floodplains [32,100], slopes [10,23,47,51,61,64,96], and mountain tops . Topography on sites with Thurber's fescue may be gently rolling, convex , or concave [40,46,74]. Concave slopes with suitable snow accumulation may support aspen-Thurber's fescue communities [40,46]. Mountain big sagebrush-Thurber's fescue communities are commonly found on concave terrain at lower elevations and flat to convex slopes at higher elevations [41,111].
Slope: Reported steepness of Thurber's fescue occupied slopes ranges from flat to very steep. Thurber's fescue-Idaho fescue habitat occurs on gentle slopes from 4% to 16% in the White River-Arapaho National Forest area of Colorado . In Middle Park, Colorado, Thurber's fescue/American vetch-aspen peavine occurs on 3% to 54% slopes . Rocky Mountain bristlecone pine-Thurber's fescue  also occurs on slopes over 50%. Mountain big sagebrush/Thurber's fescue and quaking aspen/Thurber's fescue habitat was observed on sites with slopes up to 72% in the White River-Arapaho National Forest area of Colorado . Langenheim  suggests that dense Thurber's fescue cover on slopes over 30% stabilizes areas that might otherwise lack cover. See Other Uses for more information on the ability of Thurber's fescue to prevent erosion and protect watersheds.
Aspect: Thurber's fescue is found on all aspects in a variety of habitat types. Quaking aspen/Thurber's fescue communities occur on all aspects [46,80], although they may be less common on north-facing slopes [47,80,111]. Mountain big sagebrush/Thurber's fescue communities [40,100,111] and Rocky Mountain bristlecone pine/Thurber's fescue communities  also occur on all aspects. Thurber's fescue-Idaho fescue [41,111] and silver sagebrush-Thurber's fescue  communities occur on most aspects but are rare on southern slopes.
Thurber's fescue-dominated herbaceous communities occur predominantly on south-facing slopes [3,8,17,41,59,86,88,111]. This trend is more pronounced at higher elevations, such as above 11,500 feet in Colorado . At lower elevations Thurber's fescue-dominated herbaceous communities occur on more aspects, although generally not on northern slopes [60,70]. Low soil moisture in Thurber's fescue meadows in northwestern Colorado  and a lack of spruce or fir germination in Thurber's fescue meadows in south-central New Mexico  suggest Thurber's fescue dominates in these locations because it is more tolerant of soils dried by wind and solar radiation than are conifer seedlings and other high elevation species. See Climate for more information on the conditions appropriate for Thurber's fescue. For information on mechanisms for Thurber's fescue grassland dominance or decline, see Factors influencing meadow persistence.
Soil: Thurber's fescue generally occurs on deep loams with pH ranging from acidic to slightly alkaline. Thurber's fescue occurs on soils derived from many parent materials [40,46] including granite, volcanic materials , sandstone, limestone , and shale [60,111]. In western Colorado, Thurber's fescue is commonly associated with glacial till . Soils in Thurber's fescue grasslands are generally moderately  to well drained [41,111]. See Factors influencing meadow persistence for a discussion of the influence of soil characteristics on conifer establishment in Thurber's fescue grasslands.
Depth: Many Thurber's fescue habitat types occur on deep soils, including Thurber's fescue-Idaho fescue, Thurber's fescue/American vetch-quaking aspen peavine [41,111], Thurber's fescue high elevation grassland [59,102], mountain big sagebrush/Thurber's fescue [41,100,111], and silver sagebrush/Thurber's fescue communities . However, Rocky Mountain bristlecone pine/Thurber's fescue community occurred on a site in northern Colorado with "very shallow" soil . Soil depth on a Rocky Mountain bristlecone pine/Thurber's fescue community in Gunnison National Forest, Colorado was from 12 to 24 inches (30-62 cm). Soil depth in a quaking aspen/Thurber's fescue community in this area was about 11 inches (28 cm) . Quaking aspen/Thurber's fescue habitat types may occur on moderately deep soil [46,111].
Soil texture: Thurber's fescue commonly occurs in loams. It has been documented in sandy loam in Utah , New Mexico , and quaking aspen/Thurber's fescue habitat in Colorado [40,54,111]. Thurber's fescue occurred on loams in Thurber's fescue-Idaho fescue, Thurber's fescue/American vetch-aspen peavine, mountain sagebrush/Thurber's fescue , quaking aspen/Thurber's fescue [40,41], and Rocky Mountain bristlecone pine/Thurber's fescue  communities of Colorado. Thurber's fescue grasslands occur on clay loams in some regions of western Colorado [68,102]. According to a 1937 Forest Service publication, Thurber's fescue can grow in clay loam but prefers sandy loam .
Thurber's fescue occurs in soils with variable percentages of gravel and/or cobble, including sites with high percentages of coarse fragments. Quaking aspen/Thurber's fescue communities in central Colorado occurred in gravelly and cobbly soils [40,41] with proportion of coarse fragments ranging from 4% to 55% . In northern Colorado, a quaking aspen/Thurber's fescue community occurred on a site with 4% to 15% coarse fragments, and a Rocky Mountain bristlecone pine/Thurber's fescue community occurred on a site with a "high" percentage of coarse fragments . Big sagebrush/Thurber's fescue vegetation in Colorado occurred on gravelly and cobbly soils . Several floras note Thurber's fescue's occurrence on "rocky" slopes [10,38,51,64].
Acidity: Reported pH on Thurber's fescue sites ranges from 5.5 to 7.7. The following table displays soil pH values reported for several Thurber's fescue communities.
|Soil pH of Thurber's fescue communities|
|Thurber's fescue meadow||New Mexico||5.5 |
|Thurber's fescue grassland||Gunnison county, Colorado||5.5 |
|Northwestern Colorado||5.8-5.9 |
|Thurber's fescue/American vetch-aspen peavine||Middle Park, Colorado||5.9-6.6|
|Thurber's fescue/Idaho fescue grassland||6.1-7.0|
|Silver sagebrush/Thurber's fescue||6.4-6.8|
|Mountain big sagebrush/Thurber's fescue||6.6-7.6 |
|Quaking aspen/Thurber's fescue||Central Colorado||6.0-6.6 |
|Western Colorado||6.0-7.4 |
|Gunnison National Forest, Colorado||6.7-6.9|
|Rocky Mountain bristlecone pine/Thurber's fescue||Gunnison National Forest, Colorado||7.7 |
Climate: Thurber's fescue occurs in cool, xeric to moist sites. In Thurber's fescue grasslands of Colorado, monthly mean temperature ranged from 14 to 57 °F (-10 to 14 °C). The frost-free season was 2 months long . Increased moisture may result in greater survival  and faster phenological development . For a discussion of the influence of relatively dry conditions on conifer establishment in grasslands see Factors influencing meadow persistence and the following sources: [29,68,70].
Moisture: Thurber's fescue occurs in xeric to moist communities. For example, Engelmann spruce/Thurber's fescue , Rocky Mountain bristlecone pine/Thurber's fescue [47,96], and Thurber's fescue grasslands  are commonly dry. Quaking aspen/Thurber's fescue communities are moderately dry  and have been described as some of the driest of the quaking aspen series [40,41]. In contrast, a Utah flora described Thurber's fescue occurring on "mesic to moist sites" , and Thurber's fescue was a major species on mesic sites in south-central Colorado . Thurber's fescue occurs with silver sagebrush, which is generally found in moist environments , and often occurs in floodplains near stream bottoms .
In Thurber's fescue grasslands of Colorado, average annual precipitation was 24 inches (61 cm) . According to a guide to important Utah range species, Thurber's fescue requires 18 to 30 inches (460-760 mm) of precipitation a year . Average June to August soil moisture content in a mosaic of Thurber's fescue grasslands and quaking aspen groves in north-central New Mexico was 9.6%. Thurber's fescue occurred in forest and grassland communities of this area with average June to August soil moisture content from 10.5% to 21.9% . Despite the potential for high snow accumulations in Thurber's fescue communities [8,100], rapid melting and run-off  may contribute to relatively xeric late winters and springs . However, evapotranspiration exceeded precipitation in a Thurber's fescue grassland in Colorado in only 1 month of a dry year (precipitation 2 standard deviations below the mean). In Arizona fescue and Idaho fescue grasslands, evapotranspiration exceeded precipitation in 2 or 3 months of the same dry year . Thurber's fescue flood tolerance was ranked as fair by Monsen and others .
Experiments suggest that increased moisture levels result in greater survival of Thurber's fescue seedlings . Thurber's fescue seedling survival in a greenhouse was 83% when watered nearly to saturation at a 7-inch (18 cm) depth every 2 weeks. With half as much water, seedling survival was 51%. Survival under the comparatively dry conditions was lower than that of Idaho fescue. In a second experiment 83% to 91% of Thurber's fescue seedlings in the high moisture treatment survived compared to 67% to 79% of Thurber's fescue seedlings in the low moisture treatment. Application of 0.5 inch (1 cm) of water to plots every 2 weeks had little impact on plant cover in southwestern Colorado .
Moisture levels may also influence flowering and timing of development. Thurber's fescue flowering increased in moist years in Colorado . In a subalpine meadow in Gunnison County, Colorado, Thurber's fescue flowered significantly (P=0.006) earlier in soil dried by a warming treatment than in the control. Warming treatments also tended to lengthen the period from the presence of bud to the presence of enlarged fruit .
Thurber's fescue occurs in early, mature, and climax communities. It has been described as an early successional pioneer species , "early seral", and "fairly sun-loving" . Thurber's fescue established quickly and vigorously on herbicide treated plots in southwestern Colorado . Thurber's fescue occurs in mature and climax communities dominated by quaking aspen and/or some conifers. Thurber's fescue is present in quaking aspen stands considered successional to conifers such as Engelmann spruce and limber pine , and in climax quaking aspen communities [59,80]. Its shade tolerance was ranked fair by Monsen and others , and it commonly occurred in deep shade in spruce-fir-aspen habitat in Utah .
Several researchers have concluded that Thurber's fescue grassland is a climax community [3,29,68,70]. Available evidence in the Jemez Mountains suggested that Thurber's fescue grasslands have been present on their current sites for several hundred years, possibly thousands . According to a review of subalpine and montane grassland in New Mexico, meadows with sharp boundaries may be climax communities . Thurber's fescue was associated with pioneer species such as twolobe larkspur (Delphinium nuttallianum), Nuttall's violet (Viola nuttallii), and oblongleaf bluebells (Mertensia oblongifolia) in early successional stages and American vetch and aspen peavine in late seral stages . However, expansion of quaking aspen stands by root suckers suggests that in some areas Thurber's fescue grasslands may succeed to quaking aspen communities [59,60].
Although the origins of Thurber's fescue grassland communities are uncertain, current information suggests that Thurber's fescue grasslands are unlikely to develop following stand-replacement fire in spruce-fir forests. Grasslands and shrublands did not develop following numerous stand-replacement fires in subalpine forests in southwestern Colorado. In all cases stands recovered to spruce-fir forest . Following fire in spruce-fir forests in New Mexico, clearings were dominated by gooseberry currant (Ribes montigenum) and Wolf's currant (Ribes wolfii), which did not occur in Thurber's fescue grasslands . Langenheim  hypothesized that a "burned grassland community" in Gunnison county, Colorado, with an average Thurber's fescue cover of 7.1% originated following stand-replacement fires in spruce-fir forests. Details regarding the fires that cleared these areas are not provided, except that the most recent fire in the area occurred about 60 years before the study .
Factors influencing meadow persistence: Persistence of grasslands and succession to forests are influenced by complex interactions of several factors including aridity, disturbance history, and fire [3,7,14,55,66,67,68,108,115].
Dry climatic conditions may limit conifer establishment in Thurber's fescue grasslands, as can topography, and soil characteristics that contribute to low soil moisture. There is a general trend of increased conifer establishment coinciding with increased precipitation on dry sites [67,85,108], including areas of south-central New Mexico with Thurber's fescue [17,30]. The interaction of aspect with wind and snow cover affects snow accumulation and soil moisture and thus may influence the distribution of grasslands interspersed within conifer forests in the western United States , including northwestern Colorado . Exposure to direct sunlight and wind-mediated transfer of snow off open, south-facing slopes of the Jemez Mountains in New Mexico likely contributed to relatively xeric conditions in Thurber's fescue grasslands in late winter and spring. Although these conditions likely limited establishment of conifers, ponderosa pine and Douglas-fir were encroaching into these meadows . In northwestern Colorado, soil moisture in a Thurber's fescue grassland was at the permanent wilting point for several weeks of the growing season, a condition that could interfere with germination and seedling establishment of spruce and fir [3,68]. Dry conditions do not always reduce tree establishment, however. In meadows that are generally too moist and/or cool for trees, warm years  or lower snowpack associated with dry years can lead to longer growing seasons that increase tree establishment [67,85].
Large trees at the edges of or within grasslands can provide more mesic microhabitat conditions that enhance further tree establishment [17,29,67,115]. Moderate microclimates [17,67,115], nearby seed sources [3,115], and reduced competition from grasses  may contribute to increased recruitment in these areas. Meadows with evidence of conifer encroachment in southwestern Colorado were predominantly in small forest openings. It was suggested that the surrounding forest produced increased snow accumulation and shade, allowing further establishment of conifers from nearby seed sources .
Even where moisture conditions are favorable to trees, some disturbance may be required to reduce competition from grassland vegetation and/or create a seed bed favoring the establishment of woody species [11,69,70]. Grazing can provide such disturbances [25,28,67,108]. Although grazing may inhibit tree establishment through trampling or browsing [14,67,108], soil disturbance and decreased vigor of grassland vegetation can enhance tree seedling establishment following the elimination of grazing or reduction of its intensity [25,28,67,108]. Other disturbances can have similar results. For example, pocket gopher activity can disturb soil sufficiently to favor tree establishment .Lack of periodic fire in intermountain grasslands is likely a major cause of grassland succession to shrubland and woodland [7,55]. During wet periods, fire exclusion may result in greater rates of tree encroachment than would otherwise occur [20,67,108]. The lack of fire following reductions in fuels from grazing was suggested as a major cause of tree encroachment into mountain grasslands in New Mexico [3,96]. Allen  suggests that fire exclusion, combined with a history of heavy sheep grazing followed by light cattle grazing, has allowed ponderosa pine and Douglas-fir establishment in Thurber's fescue grasslands. The study found only weak support for microclimate factors driving conifer establishment . In meadows of this area above 8,860 feet (2,700 m), Coop and others  concluded that establishment of ponderosa pine, blue spruce, aspen, and other species, likely Douglas-fir, white fir, and Engelmann spruce, was due to the lack of fire. However, not all persistent grasslands have a history of frequent fire. Subalpine meadows in northwestern Colorado  and south-central New Mexico  showed few or no signs of recent or periodic fires. Tree encroachment has been observed in meadows near high elevation spruce-fir communities where fire intervals were historically long and in areas with little or no grazing history .
Immediate fire effect
on plant: As of 2009 there is no information in the literature on the immediate impact
of fire on Thurber's fescue plants or seeds. Reviews by Bradley and others [12,13] suggest Thurber's fescue
root crowns may survive fire. This and its potential for rapid tillering  suggest
that Thurber's fescue may only be top-killed by fire.
Postfire regeneration strategy :
Caudex or an herbaceous root crown, growing points in soil
Ground residual colonizer (on site, initial community)
Secondary colonizer (on- or off-site seed sources)
Fire adaptations and plant response to fire:
Fire adaptations: As of 2009, there is little information available regarding Thurber's fescue's fire adaptations. According to reviews, Thurber's fescue has a root crown that may survive fire. Seeds can be blown from off site and may colonize burned areas [12,13]. Because tillering has been observed in response to damage from herbicides , it is possible that tillering would allow Thurber's fescue to recover following fire.
Plant response to fire: As of 2009, detailed information regarding Thurber's fescue's response to fire is lacking. There are no studies with prefire and postfire Thurber's fescue cover data or comparisons to unburned controls. There are no data on the effect of fire severity, season, or frequency on Thurber's fescue. Most of the following information is based on postfire information or anecdotal observations or are generalizations based on the response of grasses in general. Most of the available evidence suggests that a single fire does not have long-term negative impacts on Thurber's fescue.
Thurber's fescue has been observed in recently burned areas. Thurber's fescue cover on 2 quaking aspen/Thurber's fescue sites that had burned in spring at "moderate" severity 4 years previously was 50% and 38%. On an adjacent site the fire was thought to have led to "a slight increase in Thurber's fescue density" . Thurber's fescue was present in a quaking aspen community in Colorado before and after a low-severity, fall prescribed fire. Whether it increased, declined, or was not impacted by the fire was not discussed . Thurber's fescue occurred at high elevations on burned and unburned sites in north-central New Mexico. Descriptions of the study area suggest that Thurber's fescue was more abundant on the unburned site. Differences in site characteristics such as elevation and plant community likely explain much of the difference in Thurber's fescue occurrence on the burned and unburned sites .
If Thurber's fescue is similar to many grasses occurring in ponderosa pine communities, recovery following fire may take up to 3 years . In a classification of quaking aspen communities in south-central Colorado, Thurber's fescue's regeneration time following fire was described as "moderate" and its resistance to fire as "low" .
Increased fire severity would likely result in greater mortality of Thurber's fescue and longer recovery time. A review notes that Thurber's fescue may suffer detrimental effects of fire in areas where accumulated litter results in "severe soil heating" . In a classification of quaking aspen communities in south-central Colorado, Powell  noted that if fire severity is carefully managed, quaking aspen/Thurber's fescue communities recover quickly and may be "rejuvenated" by fire.
Given rough fescue's (Festuca campestris) close relationship to Thurber's fescue and their similar morphology  and ecology, the 2 species may have similar responses to fire. Rough fescue is adapted to periodic fire, with recovery times generally ranging from 2 to 3 years. However, high-severity, growing-season fires could result in substantial rough fescue mortality. Larger rough fescue bunches may be more susceptible to mortality because dense, old culms may burn below the soil surface, producing more heat and damaging the perennating tissues. This is most likely to occur after long periods without fire, when fuel loads are high and there is greater occurrence of large clumps . For more details, see the FEIS review of rough fescue.
FUELS AND FIRE REGIMES:
Fuels: Thurber's fescue grasslands accumulate large amounts of fuel. In western Colorado, litter cover varied from 6,000 to 14,000 pounds per acre in dense Thurber's fescue communities and 5,000 to 11,000 pounds per acre in open Thurber's fescue communities . See Production for information on fuel loads in other Thurber's fescue communities. The litter layer in a Thurber's fescue grassland in New Mexico averaged 2.5 inches thick and was comprised primarily of Thurber's fescue leaves and culms. The thickest portions occurred at the base of grass clumps . Growth of Thurber's and Arizona fescues in a New Mexico grassland was described as a "thick mat" . In the ecotone between subalpine meadow and sagebrush steppe in Colorado, 82% to 86% of 5 grams of Thurber's fescue litter remained after 46 to 63 days under the organic layer, and 62% to 67% remained after about 365 days under the organic layer .
Fire regimes: Fires occur periodically in communities occupied or dominated by Thurber's fescue and commonly burn in surface fuels. In open Engelmann spruce and/or Rocky Mountain bristlecone pine woodlands where Thurber's fescue dominates the understory, low-severity surface fires are typical [23,24], although Rocky Mountain bristlecone pine ecosystems have variable fire regimes. Quaking aspen/Thurber's fescue communities tend to have low- to moderate-severity fires with low spread rates . Due to slow fuel accumulation, fire-return intervals in ponderosa pine communities in the central Rocky Mountains may be from 12 to 25 years. Thurber's fescue may occur at relatively high elevations in these communities . Estimates of fire-return intervals in Thurber's fescue grasslands in the Jemez Mountains before 1900 range from 4.9 to 15.1 years. These fires tended to occur in the spring and early summer . For information on the role of fire in maintaining grassland communities, see factors influencing meadow persistence. See the Fire Regime Table for further information on fire regimes of vegetation communities in which Thurber's fescue may occur. 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".
FIRE MANAGEMENT CONSIDERATIONS:
The scant information available and responses of similar species suggest that any negative impacts of low-severity fire on Thurber's fescue would be short-lived. Severe heating of soil from high fuel loads would likely cause greater mortality than fires that burn quickly without exessive soil heating. Historic fire-return intervals in New Mexico suggest that Thurber's fescue may tolerate fires at approximately 10-year intervals . There is evidence that, in at least some portions of its range, periodic fire prevents the conversion of Thurber's fescue grasslands into woodlands or forests [3,61,96,103].
IMPORTANCE TO WILDLIFE AND LIVESTOCK:
Thurber's fescue is a moderate value forage species for cattle and big game. It provides cover for small animals, and communities such as quaking aspen/Thurber's fescue can provide cover for big game.
Palatability and/or nutritional value: Thurber's fescue generally provides moderate value forage, although this varies with the species of grazer, season, and seral stage. Thurber's fescue provides the greatest forage value in late spring and early summer. It is most heavily used by cattle, horses, and elk. According to New Mexico habitat classifications, palatability of Thurber's fescue declines from moderate in early-seral stages of Rocky Mountain bristlecone pine/Thurber's fescue vegetation to low in late-seral stages [61,96]. Quaking aspen/Thurber's fescue communities over 60 years old have been reported to have greater forage value for cattle than younger quaking aspen/Thurber's fescue communities . Thurber's fescue production is high in many areas. Some Thurber's fescue habitats, such as Rocky Mountain bristlecone pine/Thurber's fescue, are of limited use for livestock grazing due to steep slopes and remote locations restricting access [23,54].
Livestock: Thurber's fescue is generally a "good" [39,74,76] or "valuable" [48,104] forage species for livestock. In western Colorado, 28% utilization of Thurber's fescue was observed after 78 days of cattle grazing in a Thurber's fescue grassland and 7% utilization observed after 79 days of grazing in a quaking aspen/Thurber's fescue community . In south-central Colorado, Thurber's fescue comprised 6% relative density of plant fragments in cattle fecal samples . Thurber's fescue was a desirable species and comprised 35.5% of the cover on rangeland in "good condition". Thurber's fescue cover was 13.2% on rangeland in "fair condition," and it did not occur on rangeland in "poor condition" .
Forage value of Thurber's fescue is consistently higher for cattle than for sheep [26,40,48,54,63,76,104,109]. Thurber's fescue is generally considered moderately palatable [40,54]. However, its rough leaves [48,103,104,109] are thought to reduce palatability for sheep [48,54,76,104,109]. Palatability of Thurber's fescue in Utah and Colorado has been rated as good for cattle and horses and fair for sheep . Reduced palatability is likely the reason that Thurber's fescue forage value for sheep ranges from poor  to fair . In south-central Colorado, Thurber's fescue comprised only 1% relative density of plant fragments in sheep fecal samples .
Wildlife: Thurber's fescue may be important to some wildlife species. In quaking aspen communities in Utah, Thurber's fescue frequency and cover were similar in areas grazed only by wildlife and areas grazed by both wildlife and livestock (See Grazing) . In south-central Colorado, Thurber's fescue comprised 14% relative density of plant fragments in elk fecal samples and 2% in mule deer fecal samples . The forage value of Thurber's fescue in Utah was rated as good for elk; fair for mule deer, upland game birds, small mammals, and small nongame birds; and poor for pronghorn and waterfowl . Mule deer in the Rocky Mountains use Thurber's fescue lightly in summer (Gilbert 1952 as cited in ) and use trace amounts in spring and fall (Wallmo and Gill 1973 as cited in ). Forage suitability of Thurber's fescue in south-central Colorado is moderate for elk and deer . Rocky Mountain bristlecone pine/Thurber's fescue communities may be important summer range for elk [24,54], and quaking aspen/Thurber's fescue is used by big game for food during fall and winter [40,54]. In meadows of southwestern Colorado, pika likely ate Thurber's fescue . In contrast, Thurber's fescue is not likely an important food for least chipmunk, golden-mantled ground squirrel , or pocket gophers [101,110].
Seasonality: Available evidence suggests that Thurber's fescue is most palatable and nutritious in spring and early summer. Monsen and others  ranked Thurber's fescue palatability as good in spring and medium in summer. Cattle are known to eat Thurber's fescue in late spring and early summer . Komarkova and others  state that palatability of Thurber's fescue to cattle is moderate and limited to the late spring or early summer. Thurber's fescue is not generally used following snowfall in autumn [39,48,104]. However, Arizona and Thurber's fescues comprised 27.1% relative density of the plant material in elk fecal samples from January to April in mountain grasslands of New Mexico . In Colorado, Thurber's fescue that was tested early in the growing season had adequate protein, energy, and vitamin A for livestock. Midway through the growing season, Thurber's fescue was deficient in protein but had adequate magnesium and calcium. Once mature, Thurber's fescue had inadequate nutrient levels for livestock . The table below shows that Thurber's fescue in a mountain grassland-quaking aspen range in Colorado also exhibited higher nutritional value early in the growing season .
|Nutritional content of Thurber's fescue at various phenological stages |
|Phenological stage||Crude Protein||Phosphorus||Calcium|
|Seed ripening and dispersal (August)||
|Regrowth and dormancy (September)||
Production: Thurber's fescue production is moderate to high and varies across sites. Thurber's fescue grasslands produce as much as 1,000 to 2,000 pounds of vegetation per acre per year . Dense Thurber's fescue grasslands in western Colorado produced an average of 2,460 pounds of vegetation annually with Thurber's fescue comprising 53% to 94% of the grass cover. An open Thurber's fescue community produced about 1,970 pounds/acre with Thurber's fescue comprising 47% to 79% of the total grass cover . In a mountain grassland in Colorado that produced an average of 1,456 pounds/acre, Thurber's fescue produced 119 pounds/acre . Total herbage production in silver sagebrush/Thurber's fescue in Utah was 1,713 pounds/acre . Although productivity of Rocky Mountain bristlecone pine/Thurber's fescue communities may be low , potential Thurber's fescue production in this community is moderate to high [47,54]. Monsen and others  classified Thurber's fescue as having medium forage production.
Potential Thurber's fescue forage production is high in quaking aspen/Thurber's fescue communities of Colorado [40,46,54]. When carefully managed, Thurber's fescue in quaking aspen stands can form a dense undergrowth up to 4 feet tall . Quaking aspen/Thurber's fescue communities commonly produce 500 to 1,000 pounds/acre . Thurber's fescue herbage production averaged 24 pounds/acre in quaking aspen communities in Colorado  and 74 pounds/acre in a mosaic of bunchgrass meadows, quaking aspen, and Engelmann spruce groves in west-central Colorado . Due to its abundance, Thurber's fescue has been considered one of the most valuable grasses for cattle in quaking aspen communities .
Cover value: In Utah, Thurber's fescue provides good cover for small mammals, small nongame birds, and upland game birds . The herbaceous growth in quaking aspen/Thurber's fescue communities in south-central Colorado provides high quality pocket gopher habitat . Thurber's fescue provides poor cover for elk, mule deer, pronghorn, and waterfowl .
The cover value of Thurber's fescue communities is variable. Use of woodlands and forests by big game for cover may be heavy in fall and winter . Livestock may also use woodlands with Thurber's fescue understories for cover . Johnson  rated quaking aspen/Thurber's fescue as having moderate potential for providing year-round big game habitat. In south-central Colorado, mesic quaking aspen/Thurber's fescue communities had canopy closures near 70% and provided much more thermal cover for big game than drier, more open stands . Quaking aspen/mountain snowberry/Thurber's fescue communities in Utah had "fairly good" wildlife value while quaking aspen/Thurber's fescue communities were considered of limited value to wildlife due to simple habitat structure . Rocky Mountain bristlecone pine/Thurber's fescue has high potential as big game summer habitat . Silver sagebrush communities including mountain silver sagebrush (Artemisia cana ssp. viscidula)/Thurber's fescue may provide good greater sage-grouse brood rearing habitat when located near appropriate nesting habitat. Mountain big sagebrush communities, including mountain big sagebrush/Thurber's fescue, provide good greater sage-grouse nesting and brood rearing habitat. Neither of these sagebrush types provides good winter habitat for greater sage-grouse .
VALUE FOR REHABILITATION OF DISTURBED SITES:
The usefulness of Thurber's fescue for rehabilitating disturbed sites is unclear. Planting Thurber's fescue to restore high elevation areas has been recommended [78,91]. Monsen and others  ranked ease of harvesting Thurber's fescue seed as medium and the ease of cleaning and seeding as good. However, Vallentine  noted that Thurber's fescue had not performed well in reseeding projects in Utah. Reviews rank the competitive ability of Thurber's fescue poor  to moderate .
Thurber's fescue provides watershed protection due its ability to stabilize soil and high infiltration rates associated with Thurber's fescue communities. Rocky Mountain bristlecone/Thurber's fescue  and quaking aspen/Thurber's fescue  communities are important for soil and watershed protection. Thurber's fescue promotes rapid infiltration and controlled runoff due to rapid root growth (see Plant growth) and abundant litter production (See Fuels) . Thurber's fescue may stabilize steep slopes that would otherwise be sparsely vegetated . However, Monsen and others  ranked Thurber's fescue as "medium" for soil stabilization. Dense Thurber's fescue communities in western Colorado had infiltration rates that averaged 4.7 inches/hour and a total erosion rate of 76 pounds/year. Open Thurber's fescue communities had a lower average infiltration rate and a higher erosion rate but still provided "satisfactory" watershed protection .
Thurber's fescue has been reported as highly resistant to trampling and highly tolerant of recreational use in south-central Colorado. It may also be somewhat tolerant of some herbicides  such as glyphosate .
OTHER MANAGEMENT CONSIDERATIONS: There is potential for conversion from quaking aspen/Thurber's fescue [40,46,54] or Rocky Mountain bristlecone pine/Thurber's fescue [61,96] to Thurber's fescue meadow following timber harvest.
Grazing: Conflicting evidence regarding Thurber's fescue's sensitivity to grazing makes generalizations difficult. It has been reported as "sensitive" [53,66], "tolerant" , and "resistant" to grazing . Increases [60,76], declines [46,102,115], and replacement of Thurber's fescue with other species [25,70,74,102] have been attributed to grazing. Although supporting data are lacking, it is often asserted that heavy grazing [25,102,103], especially by cattle [68,74,103] reduces Thurber's fescue, while sheep grazing increases it [18,68,74].
Thurber's fescue declined after grazing in southwestern Colorado , western Colorado [46,102], and New Mexico (review by ). In southwestern Colorado, bunchgrass density declined on 22 of 30 repeat photography sites. These declines, including "extensive" losses on 13 of the 22, were likely due to heavy grazing by cattle and sheep from the late 1800s to the mid-1900s. Thurber's fescue was one of the bunchgrasses that occurred in subalpine portions of the study area . It is often reported that heavy livestock grazing [25,102], presumably by cattle [70,74] may result in the replacement of Thurber's fescue with Kentucky bluegrass (Poa pratensis), especially in fine soils. Thurber's fescue may be replaced by Idaho fescue following livestock grazing in other areas , including those with coarse soils . In Utah, grazing primarily by mule deer and to a lesser extent by elk resulted in similar Thurber's fescue cover as grazing by both wildlife and livestock. Cattle were the primary livestock grazers in the study area. The table below shows this similarity as well as the greater frequency and cover of Thurber's fescue in areas with no grazing .
|Thurber's fescue frequency and cover on sites with varying levels of grazing exclusion |
|Site||Frequency||Canopy cover||Sample size|
|Wildlife and livestock||31||6.2||4|
Despite potential for declines, Thurber's fescue was classified as an "increaser" on all but dry sites in Utah , and its production increased following grazing in southwestern Colorado . In a habitat classification for Gunnison county, Colorado, Langenheim  speculated that dense growth of Thurber's fescue was at least partially due to overgrazing of grasslands in this area. In at least some cases, increases occurred after grazing by sheep [18,68,74].
Although recovery of Thurber's fescue can occur quickly on some sites, on others long-term conversion to other habitat types may occur. According to a review, recovery of Thurber's fescue grassland species composition following exclusion of grazing may be as fast as 2 to 4 years on sites at 10,000 to 11,000 feet (3,000-3,300 m) elevation in New Mexico . Total cover in a mountain grassland in New Mexico increased 87% during 25 years of grazing exclusion, while cover in livestock grazed plots increased 69%. On at least 1 of the plots where grazing was excluded, the increase was due mainly to greater cover of Thurber's fescue and Columbia needlegrass (Achnatherum nelsonii) . However, on some sites in New Mexico, nonnative Kentucky bluegrass may form "relatively stable" communities (review by ). Native species composition on these sites is unlikely to completely recover with grazing exclusion alone.
For a discussion on the effects of grazing on fire regimes and tree encroachment into Thurber's fescue grasslands, see Factors influencing meadow persistence.
Grazing capacity: Recommended grazing capacity of areas with an understory dominated by Thurber's fescue ranges from 2 to 6 acres/ animal unit month (AUM) depending on habitat and slope. A 1946 publication had different recommendations for various slopes in ponderosa pine-bunchgrass communities. Flat areas and slopes up to 20% had capacities of 2 to 3 acres/AUM, and 40% to 60% slopes had capacities of 4 to 6 acres/AUM . In a 1976 review, the average grazing capacity under continuous, season-long use in mountain grasslands was estimated at about 2.5 acres/AUM. Another guideline is that about 40% of annual growth of palatable grass may be grazed per season without detrimental effects on mountain grasslands in good condition . A 2004 article notes that Thurber's fescue's critical stubble hieght is 4.0 inches (10 cm). Excluding drought, heights below this threshold indicate overgrazing .
The following table provides fire regime information that may be relevant to Thurber's fescue habitats. 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".
|Fire regime information on vegetation communities in which Thurber's fescue may occur. This information is taken from the LANDFIRE Rapid Assessment Vegetation Models , which were developed by local experts using available literature, local data, and/or expert opinion. This table summarizes fire regime characteristics for each plant community listed. The PDF file linked from each plant community name describes the model and synthesizes the knowledge available on vegetation composition, structure, and dynamics in that community. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Montane and subalpine grasslands||Replacement||55%||18||10||100|
|Surface or low||45%||22|
|Montane and subalpine grasslands with shrubs or trees||Replacement||30%||70||10||100|
|Surface or low||70%||30|
|Mountain sagebrush (cool sage)||Replacement||75%||100|
|Ponderosa pine/grassland (Southwest)||Replacement||3%||300|
|Surface or low||97%||10|
|Bristlecone-limber pine (Southwest)||Replacement||67%||500|
|Surface or low||33%||>1,000|
|Ponderosa pine-Douglas-fir (southern Rockies)||Replacement||15%||460|
|Surface or low||43%||160|
|Southwest mixed conifer (warm, dry with aspen)||Replacement||7%||300|
|Surface or low||80%||25||2||70|
|Southwest mixed conifer (cool, moist with aspen)||Replacement||29%||200||80||200|
|Surface or low||36%||160||10|
|Aspen with spruce-fir||Replacement||38%||75||40||90|
|Surface or low||23%||125||30||250|
|Stable aspen without conifers||Replacement||81%||150||50||300|
|Surface or low||19%||650||600||>1,000|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Great Basin Grassland|
|Mountain meadow (mesic to dry)||Replacement||66%||31||15||45|
|Great Basin Shrubland|
|Mountain big sagebrush||Replacement||100%||48||15||100|
|Mountain big sagebrush with conifers||Replacement||100%||49||15||100|
|Mountain sagebrush (cool sage)||Replacement||75%||100|
|Mountain shrubland with trees||Replacement||22%||105||100||200|
|Great Basin Woodland|
|Surface or low||78%||13|
|Great Basin Forested|
|Aspen with conifer (low to midelevation)||Replacement||53%||61||20|
|Surface or low||23%||143||10|
|Aspen with conifer (high elevation)||Replacement||47%||76||40|
|Surface or low||35%||100||10|
|Aspen with spruce-fir||Replacement||38%||75||40||90|
|Surface or low||23%||125||30||250|
|Stable aspen without conifers||Replacement||81%||150||50||300|
|Surface or low||19%||650||600||>1,000|
Replacement: Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed: Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low: Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [37,57].
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