IMMEDIATE FIRE EFFECT ON PLANT:

Idaho fescue grows in a dense, fine-leaved tuft. Fires tend to burn within the accumulated fine leaves at the base of the plant and may produce temperatures sufficient to kill some of the root crown [2]. Mature Idaho fescue plants are commonly reported to be severely damaged by fire in all seasons [35,52,253,309]. Initial mortality may be high (in excess of 75%) on severe burns, but usually varies from 20 to 50% [15]. Idaho fescue is commonly reported to be more sensitive to fire than bluebunch wheatgrass [27,61,62,145,309]; however Robberecht and Defosse [231], using special instrumentation to control the intensity and duration of fire treatment for individual plants, suggested the latter was more sensitive. They observed culm and biomass reduction with moderate fire severity in bluebunch wheatgrass, whereas a high fire severity was required for this reduction in Idaho fescue. Also, given the same fire severity treatment, postfire culm production was initiated earlier and more rapidly in Idaho fescue [231]. 

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

Fire effects vary with condition and size of the plant, season and severity of fire, and ecological conditions. Rapid burns leave little damage to root crowns, and new tillers are produced with onset of fall moisture [145]. This was the case with small bunches of Idaho fescue when a "hot" June wildfire caused incomplete burning of the root crowns on a western Montana grassland [9]. After decades of fire exclusion and/or the absence of grazing, the thicker duff layer and dense, dry crowns burn longer, so heat penetrates deeper and may kill the plants [10]. The dense culms may provide enough fuel to burn for hours after the fire has passed, reaching temperatures as high as 1000 degrees Fahrenheit (538 ^oC), thus killing or seriously injuring the plant regardless of the intensity of the fire [309]. Bunting [44] also points out that Idaho fescue is sometimes rooted in the litter under western juniper (Juniperus occidentalis) which will, of course, burn. 

PLANT RESPONSE TO FIRE:

Most studies show that fire initially reduces frequency [48,162,243] and basal area [16,243] of Idaho fescue. Recovery to prefire levels may require more than 25 years if density is severely reduced [15], as was observed by Harniss and Murray [125] in Idaho, where return to prefire cover took over 30 years after summer prescribed burning in a big sagebrush/Idaho fescue range. Effects of most fires are not, however, so extreme, and show a wide range of responses. Idaho fescue plants burned in Nevada in the spring of 1973 still showed signs of damage in 1976, but they were recovering [16]. Idaho fescue frequency was not significantly (p<0.05) different between burn and control plots 2 and 4 years after prescribed burning on a mountain big sagebrush/Idaho fescue site in Idaho [175]. On a lodgepole pine site in Idaho, Idaho fescue plants had regained vigor by the 3^rd year and showed improved vigor by the 5^th year [222]. Idaho fescue resprouted after spring prescribed burns in central Oregon, and within 3 months more than 80% of Idaho fescue plants had vigorous growth, with greater production in burned areas than in adjacent unburned areas [1]. Forage biomass of burned Idaho fescue grassland had surpassed that of unburned grassland following fires in Yellowstone National Park in both grazed (by elk and some bison) and ungrazed portions, 2 years after burning [248]. 

Idaho fescue on burned areas may have more protein than those on unburned areas [16]. Singer and Harter [248] found that digestibility of Idaho fescue was enhanced (for 1 year) on grazed but not on ungrazed sites following the 1988 fires in Yellowstone National Park. Dry matter digestibility was higher in Idaho fescue plants the 1^st year following burning in Yellowstone, and both digestibility and percent protein were higher the 2^nd year [212]. Similarly, crude protein in Idaho fescue increased from 0.6 to 2.6% after spring burning in Douglas-fir and limber pine in central Montana [156]. 

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Plant response varies with fire severity, season of burn, ecological condition at the time of the burn, and management activities before and after burning [2]. Vigor of surviving Idaho fescue plants is reduced by high severity fires because the root crown's budding zone is confined to a relatively small area at or above the surface of the ground where it may be exposed to higher temperatures for prolonged periods [62]. Spring prescribed burns in a Nevada big sagebrush/grassland were classified as "hot" and "cool" fires, and cool fires resulted in only a small decrease in Idaho fescue cover, while hot burns resulted in a significant (p<0.05) decrease that recovered to prefire levels in 3 years [162]. 

Idaho fescue is sensitive to severe burns in late summer and early fall in eastern Oregon [146]. Such fires favor succession to forbs in Idaho fescue plant associations [2]. Both number of plants and basal crown area were severely reduced in Idaho fescue following an August wildfire on northern California perennial range and remained reduced 5 years later [66]. A hot June wildfire in a Montana grassland reduced biomass and cover of Idaho fescue. The damaged clumps failed to produce much autumn growth, so Idaho fescue cover remained low in the following spring in favor of forb species. Idaho fescue recovered completely (98% of unburned cover) 3 years after the fire [9]. Spring and late fall burns on sites with good soil moisture and favorable Idaho fescue root reserves are thought to injure plants less [16,309,314]. Britton and others [37] observed greater plant damage with late August than mid-October burning; however, they also found that plants watered immediately before or after burning had the greatest basal area reduction and produced the least re-growth. They explained that with increasing water content, thermal conductivity increases, and therefore the potential for the heat pulse to reach the grass' meristematic tissue faster and remain at lethal temperatures longer exists when soils are wet. 

Idaho fescue is tolerant of late-season burning [2,3,308], but again, results are varied. Armour and others [10] saw recovery to preburn levels of Idaho fescue in 3 years after fall prescribed burning in Douglas-fir/ninebark (Physocarpus malvaceus) habitat type in Idaho. Britton and Clark [40] compared early May, mid-June, and mid-October burns in eastern Oregon and found highest mortality in early May (30%), and no mortality in mid-June or mid-October. Corresponding basal area reductions were 48% in May, 52% in June, and 34% in October [40]. A comparison of spring and fall burning in Idaho fescue grassland in Oregon showed no difference for season of burn [277]. A significant (p<0.05) decrease in Idaho fescue cover occurred in both seasons, although frequency was not reduced, and Idaho fescue remained the dominant prairie species [277]. Conversely, Shwecke and Hann [243] observed 25% kill of Idaho fescue after a spring burn, compared with 40% kill after a fall burn, in a Douglas-fir and big sagebrush/grass mosaic in western Montana. There was a similar decrease in basal crown sizes for both burns, but the canopy cover of surviving fescue (Festuca spp.) plants almost doubled compared to prefire canopy cover. Sagebrush sites became dominated by fescues 1 year after fire in both cases [243]. Another comparison of spring and fall burning found that fall burning killed 20% of the Idaho fescue population and reduced basal area by 23% the 1^st year. Spring burning resulted in no significant change in basal area and only 3.5% mortality. Plants recovered to 90% of their preburn size by the 2^nd year after the fall burn [238]. Idaho fescue is sensitive to burning in any season in areas where it is at the margins of its ecological range [27,62,309]. 

Fire in water-limited environments generally reduces the productivity of grasses during the 1st postfire growing season [27,74,231,307], and in many cases reduces productivity of Idaho fescue for several years to come [125]. Defosse and Robberecht [84] used a special device to apply similar fire severity levels inside the meristematic root crown region to several Idaho fescue and bluebunch wheatgrass plants and followed the treatment with different levels of competition simulated by removing varying amounts of aboveground biomass of neighboring potential competitors. Idaho fescue did show meristematic damage after the fire, but no mortality was observed. Regrowth occurred within 15 days - more rapidly than bluebunch wheatgrass. Subsequent competition reduced root production and restricted aboveground productivity by 115% in Idaho fescue, and by 70% for bluebunch wheatgrass. These results suggest that survival and productivity following fires is related to subsequent soil water availability. A species with roots concentrated in upper soil layers (e.g., Idaho fescue) will experience a decline of water availability when compared with a deeper rooted species (e.g., bluebunch wheatgrass), thus affecting subsequent growth [84]. This may help explain why many studies show that Idaho fescue is more severely damaged by fire than bluebunch wheatgrass [2]. 

Conrad and Poulton [62] observed that Idaho fescue basal diameter reduction was less after fire in grazed conditions (27%) than in ungrazed conditions (40%). Idaho fescue basal area was reduced equally by burning and clipping (an average of 48%) in May and June in eastern Oregon [39]. Other treatment-date combinations (late summer and fall) did not significantly (p<0.05) reduce basal area, suggesting that it is less susceptible to late-season defoliation than reported previously. 

Recovery of Idaho fescue frequency is also a function of seed production and germination after a fire. Sapsis [238] found higher numbers of vegetative culms in burned plants compared with unburned plants. Seed production of Idaho fescue plants subjected to fall prescribed burning in the sagebrush/grassland region in Idaho and Oregon was not different from seed production on unburned controls in postfire years 1 and 3, but was greater on a 5-year-old burn [217]. Both severe and lower-severity fire treatments reduce emergence of Idaho fescue from seed [57]. Warg [294] cites a study in which seeds of Idaho fescue are exposed to temperatures of 80, 100, 125, and 150 ^oC for periods of 5, 15, 30, and 60 minutes. Germination was good for seeds exposed to 80, 100 and 125 ^oC for 5 minutes, but did not occur beyond that temperature or time period. Clark and others [59] studied the effects of fire on seed banks and found the LD 50 for most seeds was between 70 to 85 ^oC. 

FIRE MANAGEMENT CONSIDERATIONS:

Fire suppression coupled with grazing pressure has changed the structure of Idaho fescue communities, often by increasing cover of woody species [2,12]. Prescribed burning can be an effective management tool for all types of Idaho fescue communities. Early spring burning is preferred in some cases e.g., [163,243], late season burning in others (e.g., [3,40,238,308]). Beardall and Sylvester [16] recommend burning of big sagebrush/grasslands before or just after the plants have broken dormancy, when root reserves remain high, to improve survival of perennial species. Johnson and Simon [146] suggest that cool, light burns in late winter or early spring, when plant moisture levels are high, help protect root crowns from damage. Similarly, Wright [307] suggests conducting burns when preferred plants are dormant, and includes that it is better to burn during wet years and never during extended dry periods, so as to not magnify drought stress on plants. 

Bunting and others [45] concluded that postfire plant mortality and productivity might be related to the length of time grazing is excluded during postfire regeneration period. Early spring fire alone resulted in low mortality, and early season defoliation (simulated grazing) after fire resulted in 50 % mortality for Idaho fescue. Detrimental effects were lessened when defoliation was delayed by 1 growing season after fire [45]. In a big sagebrush/grassland in Idaho burned once in September of 1933, again in August of 1936, and subsequently "conservatively" grazed after 1 full year of protection, Blaisdell [27] observed no significant differences in total grass production on any severity of burn 15 years after burning. Idaho fescue was, however, significantly reduced, achieving prefire levels within 12 years after a light-severity burn, and at only 77 and 53% of prefire levels 12 years after a moderate and heavy burn, respectively. All other grasses had recovered beyond prefire levels by postfire year [27]. 

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Related categories for SPECIES: Festuca idahoensis | Idaho Fescue

• Introductory
• Distribution and Occurrence
• Value and Use
• Botanical and Ecological Characteristics
• Fire Ecology
• Fire Effects
• References
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