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Wildlife, Animals, and Plants
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FIRE EFFECTS
SPECIES: Pseudoroegneria spicata
| Bluebunch Wheatgrass
Burning bluebunch wheatgrass may remove most of the aboveground biomass but does not usually result in plant mortality [205,209]. Bluebunch wheatgrass is generally favored by burning [4]. The buds of bluebunch wheatgrass are well protected from fire by the foliage of the plant [3] or are underground [71,72]. Burning stimulates flowering and seed setting [3,191,209]. However, season of burning affects mortality. Britton and others [49] saw 40% mortality in May-burned plants in Oregon, while June-burned plants suffered only 10% mortality, and no October-burned plants died [49].
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The effect of fire on bunchgrasses relates to culm density, culm-leaf morphology, and the size of the plant [205]. Bluebunch wheatgrass has coarse stems and little leafy material, and therefore the tops burn quickly and little heat is transferred downward into the meristem tissue located near or in the soil [233,234]. Most authors classify the plant as undamaged by fire [162].
Timing of the burn is an important factor in determining the effects of fire on bluebunch wheatgrass [118,209,234]. Bluebunch wheatgrass probably suffers the least amount of damage if burned while dormant [175], and the most if burned while actively growing, prior to dormancy [234]. Most authors conclude that fall burning generally causes less damage to the plants than spring burning and stimulates productivity of bluebunch wheatgrass following the fire [50,209]. November and March burning in British Columbia reduced tiller production in bluebunch wheatgrass the following spring. Meristem tissue was elevated in March and therefore more susceptible to higher temperatures [230]. However, Cook and others [75] recommend spring burning to increase bluebunch wheatgrass productivity.
Range and others [202] evaluated the effects of prescribed burns on bluebunch wheatgrass in Nevada. The burns occurred in late August, when the plants were dormant. Their study sample was small, but the plants that died appeared to suffer from 2 factors. One, the dead plants were in areas of deep litter or surrounding brush, both of which increase the duration and temperature of the flame. Two, increased litter may increase the moisture of the plants themselves, increasing heat conductivity inside the plant. The authors also mentioned lack of postfire precipitation as a possible factor in bluebunch mortality.
Recovery of bluebunch wheatgrass following fire is rapid to very rapid, usually 1 to 3 years [55] or 3 to 5 years [219]. However, the plants may be damaged and recover more slowly if burned in a dry year [46,233]. One of the most important factors affecting the ability of bluebunch wheatgrass to recover from fire is the availability of soil moisture following the burn, regardless of season [205].
Postfire productivity varies considerably. While few studies clearly show a permanent negative effect of fire on the survival and productivity of the plant, the degree to which bluebunch wheatgrass responds positively to fire is disputed [57,62,66,67,72,75,86,118,127,148,162,168,176,177,180,189,193,194,205]. Most studies suggest a 1st year decrease in productivity following fire [198,209,221,226,228,232,235], followed by increased productivity in the following years. In Wyoming, bluebunch wheatgrass production averaged 3.9 times higher on 4 3-year-old burned sites than on controls. Differences were significant (P<0.05) on 2 of the sites, but only after the 2nd post-burn year [75]. In central Oregon, late September burns significantly increased mean basal area of bluebunch wheatgrass, while late May burns slightly decreased basal area [209].
Other factors that may affect bluebunch wheatgrass productivity following fire include habitat type, aspect, and climate. In the Missouri River Breaks area of central Montana, bluebunch wheatgrass canopy in a north-facing Douglas-fir/Rocky Mountain juniper association was reduced for several years, in part due to mortality, but 12 years after the burn it was the dominant grass species on the site, with up to 53% canopy coverage, compared to the unburned site with 4% [102]. Burning was less severe, with less fuel, on a nearby ponderosa pine/bluebunch wheatgrass site, and the bluebunch wheatgrass responded quite differently. Coverage was reduced the 1st year following burning, but by the 3rd year following the burn, bluebunch wheatgrass and western wheatgrass (Pascopyrum smithii) had already reached 52% coverage on the site.
In western juniper woodlands in the Owyhee Mountains of southwestern Idaho, bluebunch wheatgrass can suffer high mortality in stands with dense tree overstories. Fire intensity of prescribed fires often must be high in order to get these low-fuel stands to burn, and if there is sparse understory bluebunch wheatgrass, there may not be sufficient survival to regenerate a stand [53].
The primary effect of fire on bluebunch wheatgrass in northeastern Oregon was on plant size (basal area), not on plant density [72].
Antos and others [14] evaluated the effects of a human-caused fire on a fescue (Festuca spp.)-dominated grassland in western Montana. Rough fescue (F. scabrella) dominates the site, with Idaho fescue and bluebunch wheatgrass. The site averages around 13 inches (340 mm) of precipitation, mostly in winter, and spans from 3,200 to 5,100 feet (975-1570 m). The authors estimate the presettlement fire frequency to be slightly longer than 6 years. The fire burned 121 acres (49 ha) in June, 1977, a very dry (55% of average precipitation) year. Almost all aboveground biomass was charred or consumed, and many bunchgrasses burned below the surface.
Due to the mosaic nature of the burn, the researchers were able to do burned/unburned comparisons. The following chart details the effects of the burn on the average percent cover of bluebunch wheatgrass on the study plots [14]:
Autumn 1977 Spring 1978 Summer 1978
Unburned Burned Unburned Burned Unburned Burned
5.2 4.1 3.1 4.8 3.9 5.5
These values reflect no significant difference between burned and unburned stands. The authors found the buds 0.39 inch (1 cm) below the soil surface, apparently deep enough to avoid damage, since vigorous resprouting occurred. The authors concluded that the timing of the fire in June, when bluebunch wheatgrass was dormant at the onset of the summer drought, allowed the plant to be unaffected by fire. They also concluded that this site may be most resistant to change in response to fire with a fire frequency of from 5-10 years.
Clark and others [65] studied seedbank density on blue grama, bluebunch wheatgrass and Idaho fescue grasslands in Yellowstone National Park, Wyoming, and how the grasslands were affected by the 1988 fires. They concluded that fire in such grasslands reduces seedbank density approximately by half, but they did not specify the exact species effect.
In south-central Montana, an antelope bitterbrush-mountain big sagebrush (Artemisia tridentata ssp. vaseyana)-bluebunch wheatgrass community was burned and allowed to rest from grazing for 1 year following the burn. After 8 years, vegetation populations were measured. There was no significant difference in bluebunch wheatgrass between the burned and unburned plots [107].
On the Snake River Plain in Idaho, sagebrush steppe was burned to eradicate big sagebrush and to assess the effects of various eradication techniques on associated species. Three years after the burn, production of bluebunch wheatgrass on the burned plots was less than half that of the controls, leading the authors to call bluebunch wheatgrass "harmed by burning" [187]. However, for cattle management purposes, the authors still concluded that the eradication of big sagebrush made more grass available as forage, even if absolute numbers were lower following the burn.
Concannon [71] compared vegetation on several burned and adjacent unburned sites in southeastern Oregon. On 69% of the study area, bluebunch wheatgrass showed higher cover on burned than unburned sites, including 1 site with 5 times the cover of bluebunch following fire. On 25% of the study area, coverage of bluebunch wheatgrass decreased following fire. Two of the 4 decreaser sites were on 2- or 3-year-old burns, one on a heavily grazed area, and one on an area disturbed by rodents. Concannon concluded that protection from grazing throughout the 1st growing season, until seed maturity in the 2nd season following the fire would greatly increase bluebunch wheatgrass production and survival.
Some studies have looked at the flammability of bluebunch wheatgrass and the role it plays as a fine fuel. Estimates for the time to reach 63% of total moisture change for bluebunch wheatgrass is approximately 2.5 hours, both to absorb and desorb moisture. This value ranked bluebunch wheatgrass as the second fastest drying species in 1 study, behind cheatgrass [11].
Fire suppression and the invasion of exotic species have altered succession and fire regimes from presettlement communities. Exclusion of fire from western juniper/bunchgrass communities shifts dominance from grasses to western junipers in Oregon, since western junipers are usually killed by fire [3,4]. Frequent burning, either intentional or as a result of cheatgrass invasion, favors annual grass establishment over perennial grasses [197,224]. Tausch and others [220] studied the re-establishment of various perennial grasses in a Utah juniper-Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) habitat in Nevada. Cheatgrass outcompeted bluebunch wheatgrass on some sites, and the authors postulate that on harsh sites, cheatgrass may establish more readily following fire if the VAM-dependent perennial species, like bluebunch wheatgrass, are nitrogen deficient when the VAM are killed by fire.
Cook and others [75] postulate that prescribed burning in high elevation basin big sagebrush (A. t. ssp. tridentata) communities has a particularly strong positive effect on perennial grasses, including bluebunch wheatgrass. They argue that burning in lower elevation grasslands, areas with competitive annual herbs such as cheatgrass, and xeric areas does not produce the same positive results.
Plants that undergo fire and subsequent defoliation have significantly higher mortality and lower productivity and reproduction than plants exposed to fire alone [55,180,219].
Livestock often collect in recently burned range areas to eat the highly palatable regrowth of bluebunch wheatgrass, which can be particularly damaging to stand regeneration [71].
Burning has been found to improve the nutritional quality and palatability of bluebunch wheatgrass in some studies. Burned bluebunch wheatgrass may have higher protein content than unburned controls for 2 years following the burn [219]. In Wyoming, burning significantly increased the crude protein content of the bluebunch wheatgrass, from 8% in August on the control plots, to 11% on the burned plots [75]. However, in the Snake River Canyon of Idaho, no differences were found between burned and unburned plots following a prescribed burn [151].
November burning in big sagebrush and Douglas-fir communities in British Columbia raised the spring calcium, phosphorous and magnesium concentrations in leaves of bluebunch wheatgrass [231]. Hobbs and Spowart [138] looked at the nutritional quality of forage on burned and unburned grassland and mountain shrub sites in Colorado. They found that mountain sheep and mule deer preferred grass on burned sites in the winter. The authors concluded that the blackened earth maintained higher soil temperatures following the burn, enabling more fall green up, and therefore, more available forage. Other authors have also found fall burning to increase soil temperatures [230]. When soil is blackened following fire, it warms up more quickly in the spring, allowing plants to commence growth earlier [230]. The temperature increases have been recorded from 19 to 26° Fahrenheit (-7 to
-3 °C) and the effects last 2 seasons [179].
Burning ponderosa pine/bluebunch wheatgrass habitat types appeared to increase their use by mule deer during the winter [158]. However, in a study in the Selway-Bitterroot Wilderness, eastern Idaho, white-tailed deer avoided or under-utilized burned ponderosa pine/bluebunch wheatgrass and bluebunch wheatgrass/Kentucky bluegrass (Poa pratensis) sites during January through May [157].
In Yellowstone National Park, following the fires of 1988, Norland and others [188] studied the effects of fire on elk habitat. They concluded that protein content and digestible dry matter of bluebunch wheatgrass was significantly greater in the fall of 1989 on burned than unburned plots, and crude protein continued to be significantly higher in the fall of 1990. Digestible dry matter was higher in 1990 as well, but not significantly.
Bluebunch wheatgrass responds more favorably to fire than does Idaho fescue [3,4,72,211,219].
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SPECIES: Pseudoroegneria spicata
| Bluebunch Wheatgrass
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