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Effects of Fire in the Northern Great Plains

Effects of Fire on Shrubs


Fire commonly is used in rangelands to remove shrubs of low forage value (Stoddart et al 1975).

Burning increases range browse availability mainly by reducing shrub crown heights, by the addition of new browse plants through seed germination, and by increasing palatability associated with young growth (Vallentine 1971; Mathews 1984).

However, burns on wildlife range in any one year should be limited in size, since browsers are often unable to fully utilize all of the new sprouts on large continuous burns (Vallentine 1971). The amount of woody plants may actually increase.

Control of wildfire, Bailey (1976) said, resulted in an unprecedented increase in woody plants on grassland, to the advantage of big game populations. Conversely, brush encroachment has always decreased the carrying capacity of rangeland for cattle. There is a need for more controlled burns to maintain grasslands and shrublands (Bailey 1976).

After fall burning there is no regrowth of winter browse for wildlife. Spring burns usually increase sprouting after 4 to 8 weeks, but fall burns promote a taller regrowth the following year. In both spring and fall burns, shrubs are reduced in height and twig diameter, making regrowth more available for animal use (Leege and Hickey 1971). In general shrubs contain higher crude protein percentages in fall and winter and lower percentages in spring and summer than do grasses and forbs. The leaves of shrubs contain a higher percentage of crude protein than stems, and the tips of stems contain a higher protein level than the thicker mid and butt sections (Dietz 1972).

Most prescribed fires do not consume living woody material larger than 1/2 inch (1.2 cm) in diameter. Consequently, the proportion of smaller fuels is important in determining the character and behavior of a fire in a shrub stand. Living fuels usually contain large amounts of moisture and hence do not burn well. Burning dead fuels can provide the heat necessary to dry the living fuel to a point where it will ignite and add to the total energy release from a fire (Nord and Countryman 1972).

Plant age, soil moisture at time of burn, intensity of fire, season of burn, health of the plants, and frequency of droughts all play a part in how fire affects shrubs in the long run. To maintain a healthy shrub community, it is best to burn when the plants you wish to preserve are dormant and soil moisture is good (Wright 1972). Very probably, much of the true prairie would have evolved or would have succeeded into shrub or forest land if fire had been excluded.

Recurring fires generally favor grasses and herbaceous species over woody plants and shrubs (Vogl 1974). Most fire-adapted or fire-tolerant woody species cannot sustain large populations in grasslands subject to intense fires on a frequent basis (Glover 1972). Food is translocated in most deciduous woody plants prior to the seasonal dormancy period (White 1983), but they do not die back at the end of their growing season as most grasses and forbs do. Regardless of whether the plant is actively growing or dormant, fire will damage living tissue (Vogl 1974; White 1983).

Many woody plants sprout or "sucker" from meristematic buds on underground stems or roots (Anderson and Bailey 1980; Wright and Bailey 1982). The season and frequency of fire can determine the net change, if any, in density and stand of sprouting species. If fire occurs before active growth has begun, increased density from sucker development may result (Anderson and Bailey 1980).

Bitterbrush (Purshia tridentata) is a desirable shrub but may not be compatible with fire.

Clark et al (1982) stated that bitterbrush survival after burning in Oregon has been variable. In eastern Idaho, bitterbrush sprouted inversely with burn intensity; in California sprouting was variable, with 5 to 25% sprouting after a fire. In north and central Utah, limited sprouting occurred after wildfires; but in the steppes of Washington and in the western Great Basin, wildfire always killed bitterbrush.

Spring burns are the least detrimental to bitterbrush if soils are wet during or just after a burn (Vallentine 1971; Wright 1972).

Reports on poison ivy (Toxicodendron rybergii) are mixed. Fires produce a definite and long-lasting increase in poison ivy, according to Wright (1972). However, Bock and Bock (1984) reported that poison ivy was unaffected by fire.

Smoke from burning poison ivy contains resins that can severely irritate lungs.

Western wild rose (Rosa woodsii) is fire tolerant and is considered a desirable forage species which takes 2 to 3 years to recover completely from a fire (Monsen and Davis 1985). Leege and Hickey (1971) and Bock and Bock (1984) reported that wild rose plants sprouted after a burn and remained at the same densities as at pre-burn. Wright and Bailey (1982) reported that Rosa woodsii is enhanced by fire.

Raspberry (Rubus spp) increases after a fire, especially hot burns (Wright 1972; Wright and Bailey 1982).

Choke cherry, serviceberry (Amelanchier alnifolia), and snowberry sprout vigorously following fire (Miller 1963; Wright et al 1979; Pelton 1953; Wright and Bailey 1982).

However, prairie wild rose (Rosa arkansana) and western snowberry did not change appreciably after a fire in east-central North Dakota, and fire may reduce the abundance and vigor of silverberry (Kirsch and Kruse 1973; Wright and Bailey 1980).

Annual spring burning is often used to control shrub invasion of Canadian grasslands (Bailey 1976). However, frequency and stem densities of serviceberry and prairie wild rose increased on annually burned areas in Alberta (Anderson and Bailey 1980). Western snowberry and wild raspberry declined in frequency and stem densities on areas burned annually, but no shrubs were eliminated. Stem densities of western snowberry and wild raspberry increased two to five times after single-event fires.

Blackberry (Rubus spp) can be eliminated with 2 to 3 successive years of burning in late spring (Owensby and Launchbaugh 1976).

Two cool-season fires (spring and fall) consistently reduced densities of Ribes spp (Bock and Bock 1984). Peek et al (1979) observed western red currant (R. cereum) resprouting on burned sites.

Desirable shrubs such as serviceberry, snowbrush (Ceanothus velutinus), and true mountain mahogany (Cercocarpus montanus) are only temporarily set back by fire (Wright and Bailey 1982). In another paper, Wright (1972) reported that serviceberry was severely damaged by fire. Bock and Bock (1984) found that serviceberry was reduced after a fire but increased during post-burn. Stem densities of serviceberry were greater on burned areas in an Idaho ponderosa pine community (Merrill et al 1982).

Merrill et al (1982) also found that seedlings of redstem ceanothus (Ceanothus sanguineus) increased following fire in the first year and that stem densities increased until the fourth year. In the first post-burn growing season, total shrub biomass on the burned area was about 50% that of the unburned area. By the third growing season, total shrub biomass exceeded that of the unburned sites. By the fourth season it was 35% more than the unburned area.

Smooth sumac (Rhus glabra) is an aggressive sprouter following fire (Wright 1972; Owensby and Launchbaugh 1976). Bragg and Hulbert (1976) found smooth sumac to be a major invader on all Kansas prairie sites, but that the invasion was negligible when sites were regularly burned.

Leadplant (Amorpha canescens) is a desirable leguminous shrub that is a prominent sprouter following burns (Wright 1972; Bock and Bock 1984; Towne and Owensby 1984).

In Kansas, a major grassland invader is roughleaf dogwood (Cornus drummondii). Thick stands are reported on unburned plots (Towne and Owensby 1984); but with regular burns, encroachment is negligible (Bragg and Hulbert 1976). With successive burns for 2 or 3 years, dogwood can be substantially reduced (Owensby and Launchbaugh 1976).

Burning in ungrazed Kansas tallgrass prairie had different effects on woody species, but shrub composition in any treatment rarely exceeded 1% of the total vegetation (Towne and Owensby 1984). Plots burned in winter and early and midspring contained significantly higher amounts of woody plants than late spring burned or unburned plots.

White coralberry (Symphoricarpos albus), when regularly burned, had greater stem densities compared with unburned control areas (Merrill et al 1982). Leege and Hickey (1971) and Bragg and Hulbert (1976) reported that white coralberry was held in check by regular burning and that stem densities did not increase.

Owensby and Launchbaugh (1976) indicated that 2 to 3 years of burning in late spring will substantially reduce coralberry (S. orbiculatus).

Anderson and Bailey (1979) said annual burning restricted expansion of western snowberry (S. occidentalis) colonies into grasslands, whereas periodic burning enhanced the spread of this species. Western snowberry begins sprouting about 2 weeks after a burn and, by the end of 3 months, usually has a canopy cover greater than on control plots.

Johnson and Strang (1983) found that fire virtually eliminated gray rabbit brush (Chrysothamnus nauseosus). Cluff et al (1983) found that salt rabbit brush (C. n. var consimilis) resprouted in small areas following fire.

Broom snakeweek (Gutierrezia sarothrae) is severely damaged by fire (Wright 1972). Although it is easily killed by fire, it will reestablish itself with seedlings following wet winters and springs (Wright and Bailey 1980). Oswald and Covington (1983) found a preponderance of broom snakeweed on severely burned sites, suggesting that the species is fire tolerant.

Soapweed (Yucca glauca) can be adversely affected by fire, but in general most Yucca species are tolerant of fires and hold their own in various plant communities despite fire (Wright 1980).

Four-wing saltbush (Atriplex canescens) and winter fat (Ceratoides lanata) are desirable shrubs that resprout vigorously after fire (Wright and Bailey 1980). Greasewood (Sarcobatus vermiculatus), sometimes an undesirable species, is also known to resprout following a burn (Cluff et al 1983).

Big sagebrush (Artemisia tridentata) is fire sensitive and is usually controlled by burning (Harniss and Murray 1973; Young and Evans 1974; Peek et al 1979; Cluff et al 1983; Johnson and Strang 1983).

A Wyoming big sagebrush (A. t. var. wyomingensis) site showed little re-establishment after 15 years post-burn, whereas mountain big sagebrush (A. t. var vaseyana) began to increase 12 years after the burn (Peek et al 1979).

Owensby and Launchbaugh (1976) reported that spring burning to top-kill plants, in combination with moderate grazing to retard sprouts and seedlings, will drastically reduce the density of sand sagebrush (A. filifolia). They urged caution with sandy sites where thick brush occurs, because complete removal by fire and hoof action may open an area up to wind and water erosion.

Wright (1972) stated that sand sagebrush is a non-sprouter whose seedlings come back vigorously following fire.

Burning controls three-tip sagebrush (A. tripartita), black sagebrush (A. nova), and low sagebrush (A. arbuscula) when sufficient fuel is available to support a fire (Wright et al 1979). Beetle and Johnson (1982) stated that black sagebrush is a good forage plant that is non-sprouting and fire susceptible and does not need to be controlled.

Silver sagebrush (A. cana) is completely top killed with spring and fall burns regardless of fire intensity. Plants with only foliage consumed, however, tended to resprout sooner than those that were completely burned (White and Currie 1983b). Beetle and Johnson (1982) found that dwarf sagebrush spreads extensively by root sprouting when stimulated by burning. Burning intensity acted to retard resprouting rather than to physically change the location of the resprouting point.

In spring, when soil moisture was high and silver sagebrush plants were just becoming physiologically active after winter dormancy, about a third of the plants burned to the stump, and 10% of those not burned so extensively were killed by fire. Considerably higher plant mortality was achieved by burning under dry fall conditions after sagebrush plants had completed their growth and reproductive cycles. After fall burning about three fourths of the plants that were completely burned to the stump died and almost 40% of those only partially burned were killed by fire (White and Currie 1983b).


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