Northern Prairie Wildlife Research Center
The potential lethal hazard of fire for large mammals depends on a combination of variables. Fire can be and often is a disaster for animals dwelling in forests or other places where fires are infrequent. But mammals living in environments exposed to frequent fires, as in grasslands, survive because of their adaptations (Handley 1969).
Plains Indians extensively burned the prairies to attract the roaming herds of bison (Higgins 1986a). But Europeans brought with them an ingrained fear of fire. They suppressed fire without any awareness of its part in the maintenance of grassland communities. Reduction of fire in a fire-evolved system promotes the development of advanced successional stages which may not provide the optimum ecological conditions for large mammals adapted to fire (Gruell 1983).
Since fire is a natural part of the environment for many animals, Komarek (1969) hypothesized that these animals lack an innate fear of fire and that some sensing mechanism and behavior patterns certainly must give warning in sufficient time for large mammals to move out of danger. His observation of large mammals showed their relative disregard of fire.
Ivey and Causey (1984) reached a similar conclusion in a study of radio-tagged white-tailed deer (Odocoileus virginianus). Immediate and short-term responses of deer during burning activities showed deer to use streambeds and other moist sites as refuges from fire. Deer were observed feeding to within 65 ft (20 m) of approaching fire with no apparent alarm. At no time were deer observed running in response to fire.
Ivey and Causey (1984) also reported that burning up to 70% of a home range did not cause deer to change their home range.
Natural fires in grasslands usually burn cool near the ground, then progress in a discontinuous front, leaving a mosaic pattern of burned and unburned areas (Handley 1969). This allows large mammals to avoid fire and leaves shelter and mature food sources near burned areas.
Grass and forb eating species that do not exhibit strong requirements for abundant escape cover, such as pronghorn antelope, bison (Bison bison), and bighorn sheep (Ovis canadensis), are favorably influenced by the increase in the grass component of habitats after fire. We could expect that fires would also have a favorable influence on wintering elk (Cervus elaphus), which are primarily grass foragers in these ecosystems.
In deep snow country, where trees provide critical snow interception and thermal cover, optimum habitat may not be reached for 30 years or more after fire. During early stages of regrowth, diversity apparently improved through development of woody plants on grassland sites. Increased cover seems to have benefited mule deer (Odocoileus hemionus) and elk in marginal habitats previously lacking in cover.
But the absence of fire for 50 years or more, with subsequent conifer encroachment, canopy closure, and deterioration of herbs and shrubs, has resulted in deterioration of big game habitat. Loovas (1976) reported that fire suppression in the Black Hills of South Dakota resulted in thickening of pine stands and decreases in secondary stages of plant succession important to mule and white-tailed deer.
Small burns of variable intensity can improve deer habitat by creating temporary openings, improving shrub growth, and generally creating more diversity by changing the age class structure of vegetation (Wallmo 1981).
Prescribed fire has largely replaced herbicides in control and reduction of big sagebrush and stimulation of herbaceous plants (Gruell 1983). Such conversion has enhanced elk spring and winter ranges. Prescribed burning has also improved spring ranges used by mule deer. Some prescribed burns have short-term negative effects on mule deer habitat by removing big sagebrush, an important winter forage.
Bison in Wind Cave National Park in South Dakota showed a strong affinity for prescribed burn areas (Forde et al 1984). They fed within the confines of the Red Valley burn in 1981 and 1982 and moved to another area burned by wildfire in 1983. Their continued grazing may be important in delaying the normal progression of plant succession in the Red Valley.
Fire may affect the short- and long-term seasonal use of habitat by altering the distribution and movements of large mammals. Historically, it appears mule deer were largely confined to breaks and rough terrain where shrubs were protected from fires. White-tailed deer frequented riparian bottomlands that were less susceptible to frequent fire.
In Minnesota, Irwin (1975) showed white-tailed deer preferred the periphery and unburned forest in winter and spring and the burn area in summer and fall following a spring burn. Moose (Alces alces) selected the periphery of the burn in winter and open parts of the burn from May to September 2 years after the fire.
Observations prior to a May 1965 fire on the Nebraska National Forest indicated white-tailed deer utilized the unburned plantation areas over 80% of the time. Few deer were seen in the burned plantation area. Whitetails in the Sand Hills of Nebraska are essentially inhabitants of the tree-shrub community. Their use of the burned area was about 8% in 1965, and declined to about 5% the following year (Wolfe 1973).
Mule deer, in comparison, showed a very substantial response to the burned area. They are normally considered a deer of the prairie baseline. Observations in 1964 showed that mule deer utilized the prairie only slightly more than evergreen plantations (53% vs. 48%). After the 1965 fire, mule deer made about equal use of the burned and unburned plantation areas. During the same period, numbers of mule deer observed in the prairie declined substantially. By 1966, only about 28% of the mule deer observed were using the burned plantations.
Lowe et al (1978) studied long-term use of habitats by deer and elk after fire, finding deer summer-fall use declined the first year following fire but increased to levels approaching 2.5 times the control through the rest of the 20-year evaluation period. Deer winter-spring use also declined immediately following fire, returned to the control level for several years, and then increased to levels exceeding 20 times that of the control.
Deer winter-spring values reflected the relatively high use in the latter years of the evaluation period. Low winter-spring deer use on all areas except the 20-year-old burn indicated an annual shift to winter range as the summer range became increasingly less suitable.
The 20-year old burn was used more as winter range because it was relatively open and provided easy movement along the edge to and from nearby lower elevations.
Elk summer-fall use declined after fire, then increased to levels nearly three times the level of the control before dropping back at the end of the 20-year period. Elk winter-spring use was higher than the control throughout the entire evaluation period, with the highest recorded post-fire use 7 years after fire.
The relatively low elk summer fall use 20 years after fire was due to unpredictable shifts in elk population centers, or to the fact that sheep used the 20-year-old burn for a few weeks in late spring and early summer. Elk remained on summer range as long as forage was available or the weather was tolerable. Higher grass production on the burned areas was sufficient to sustain at least seven times the elk use of the control during winter.
The size of a burn will affect habitat use. Klebenow and Beall (1978) found deer ranged 0.25 mile (0.4 km) into a burn, but forage use was concentrated at the edge within a 274-yd (250 m) range inside and outside of the burn.
On recent burns in a grass-forb succession stage, deer did not penetrate the burns (Klebenow and Beall 1978). Most deer sign was concentrated within 109 yd (100 m) or less of the burn edge in unburned woodland. On older burns (over 24 years) in a shrub dominated stage of succession, more deer pellet groups were found within the burn area away from the edge than within 55 yd (50 m) of the edge. Steep and broken topography substituted for tree cover in the older burns.
Fire may provide a reproductive advantage for adapted species. Efficient use of a variety of several habitats suggests evolutionary adaptation to fire through genetic diversity.
Exclusion of fire through suppression programs tends to compress genetic diversity and reduce the ability of populations to respond to dramatic environmental changes (Martinka 1976).
Current habitat relationships of wintering elk reflect both adaptability and responsiveness to the spectrum of vegetation change associated with a fire program, particularly at an intermediate stage in post-fire faunal succession. Wintering elk populations responded to fire by expanding population levels, but at a rate less than biological potential. Expansions correlated directly with improving forage conditions. Mule deer population levels seemed favored by extensive shrub fields of early post-fire successional stages (Martinka 1976).
Fire stimulated the production of browse, which resulted in an increase in deer populations (Bendell 1974). An area opened by burning produced heavier deer. Does had a higher frequency of ovulation and more fawns at heel, and they wintered in better condition (Bendell 1974).
The increased nutritional quality of burned grasslands provides good summer range capable of carrying deer in good condition through the breeding season, a necessary requirement for maximum herd productivity. White-tailed deer on poor range showed ovulation rates 67% of those attained by deer on good range (Julander et al 1961).
A comparison of wildlife production on burned and unburned grassland on the Woodworth Study Area of North Dakota (Kirsch and Kruse 1973) found no white-tailed deer fawns on an unburned 124-acre (50 ha) plot, compared to four fawns each during the second growing season on burned plots of 135 and 121 acres (55 ha and 49 ha).
Vogl and Beck (1970) determined the summer density of white-tailed deer on a burned area 8 years after a major fire to be 2.4 times greater than on the unburned control area.
Ten years after fire, if there is no further burning, tree crowns close in, reduce browse supply, and result in a lowered carrying capacity and a deer population too large to be supported by the reduced food supply (Leopold et al 1947).
Fires, in general, increase the diversity of wildlife species as well as the population densities on most vegetation types, with some exceptions. An increased abundance of one species may reduce the number of other large mammals through interspecific competition (Bendell 1974). Mule deer, moose, and bighorn sheep abundance in Banff and Jasper national parks, Canada, declined after fires which encouraged grassland and shrubland habitat favorable to elk. The elk outcompeted the other species for food and shelter.
Drew et al (1985) found prescribed spring burning in central Alberta reduced but did not eliminate the number of winter tick (Dermacentor albicuptus) larvae available in autumn.
The degree of tick control is dependent upon the habitat type being burned, weather conditions prior to the burn, and the fuel load on the burn site. The majority of ticks are found in the elevated foliage of shrubs in the spring. Hot, intense burning of the shrub layer during spring melt and leaf-out was the most effective in reducing the number of engorged female ticks. Autumn burns would reduce tick numbers in the larval stage, provided a slow, hot fire is maintained to ensure adequate burning of the duff layer. A decrease in the amount of winter forage available to ungulates would be a factor to consider in the use of autumn burning.
Seip and Bunnell (1985) found higher counts of lungworm larvae in feces from Stone's sheep (Ovis canadensis) that used alpine winter ranges in February than in feces from sheep using burned, subalpine range. In May, sheep on unburned range that had wintered on the alpine meadows had higher lungworm levels than sheep that had wintered on the burned, subalpine range.
Ordinarily, after large burns the food supply exceeds demand, and large areas away from suitable cover receive little browsing pressure. In areas of light browsing the brush will rapidly grow back into dense stands. Lotan and Brown (1985) found small burns may concentrate ungulates and inhibit regeneration in browse species such as aspen.
Fire affects plant communities primarily through the nutritional content, quantity, and availability of forage. Hobbs and Spowart (1984) tested the hypothesis that prescribed burning improves the nutritional quality of the diets of mule deer and mountain sheep.
Prescribed burning increased the protein concentration and in vitro digestible organic matter (IVDOM) in winter but not spring diets of mountain sheep and mule deer feeding in grassland and mountain shrub communities.
Effects of burning on diet crude protein persisted for 2 years in both communities. Treatment effects on diet IVDOM lasted for 2 years in the mountain shrub area but were absent during the second year in grassland, possibly due to the less intense nature of fire in grassland which allowed quicker return to preburn conditions.
Hobbs and Spowart (1984) concluded fire substantially improved the winter diets of mountain sheep and mule deer in grassland and mountain shrub communities but caused only small changes in the quality of individual forages. Inferences based on forage studies alone may severely underestimate improvements in ungulate nutrition following burning.
Burning of big sagebrush and bluebunch wheatgrass increases bighorn sheep forage and decreases mule deer forage. The sheep prefer the grass in winter while mule deer prefer the sage. Thus, sheep competition is reduced (Peek et al 1979).
Hobbs and Swift (1985) found fire reduced range supplies of dry matter, metabolizable energy, and nitrogen in forages consumed by mule deer, primarily because of the large decrease in the standing crop of shrubs following burning.
Range food supply for mountain sheep was less strongly affected. Metabolizable energy and nitrogen remained the same, while dry matter declined following burning. Estimates of carrying capacity reflected these differences. Unburned areas could support more deer than burned areas, but burning had no effect on carrying capacity of mountain sheep. Burns tended to have more forage with high nutrient concentrations but less forage overall. Unburned habitat is superior to burned areas for supporting high densities of mule deer on a relatively low plane of nutrition.
Burning becomes a productive treatment when management objectives specify supporting fewer animals at higher diet quality levels.
Burning reduced litter and standing dead herbage, which increased the amount of green forage ungulates could find and consume (Hobbs and Spowart 1984).
Understory production decreased the first post-burn year in the Jackson Hole area, then increased to levels well above those on the unburned sites in the second and third post-burn years. On one site, second-year production of willow-herb (Epilobium angustifolium), a species palatable to elk, was double that prior to burning (Lotan and Brown 1985).
Forbs, particularly annuals, were abundant 4 years following a burn. Up through 16 years there were significantly more forbs than in unburned sites. Only a 24-year-old burn had significantly more forbs, indicating this may be about as long a change could be expected.
Grasses appeared to respond later; 24-, 45- and 115-year old burns had the most grass basal area (Klebenow 1985). This would be beneficial for species such as elk.
Wydeven and Dahlgren (1983) found graminoids to be the major forage class eaten by elk in spring and summer. Forbs were the most important forage class consumed in fall and winter, along with some graminoids.
Controlled burning of aspen provides more browse for deer. Following a spring burn, aspen stem densities had increased from a few hundred per acre prior to the fire to greater than 25,000/A (10,000/ha) due to root sprouting. Prior to treatment, aspen was too tall for ungulates to reach. Two years after the burn a large supply of aspen was at a height that could be utilized (Gordon 1976). These burns appeared to inexpensively provide not only an increased food supply but also increased cover.
Fire can affect forage species utilized. Following a burn in Alberta, pronghorn antelope showed a higher use of spineless, burned cactus, a forage item usually sparsely consumed (Stelfox and Vriend 1977).
In summary, fire creates vegetative diversity and therefore enhances wildlife habitat. Optimum benefits occur where fire creates a mosaic pattern of burned and unburned vegetation which provides new growth of nutritional forages, seasonal habitats, and maintenance of vegetation in early stages of succession. Improved habitat and forage increases the carrying capacity of habitats for large mammals.