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Effects of Fire in the Northern Great Plains

Effects of Fire on Some Undesirable Species


Cacti

Cacti are relatively fire susceptible (Wright and Bailey 1980). Plains prickly pear cactus (Opuntia polyacantha) is adversely affected by repeated burning (Martin 1983).

Bunting et al (1980) used prescribed burning to control the density of eight species of cacti on southern mixed prairie in west Texas. Seven of eight species suffered mortality of 49 to 100% by the fourth year after burning. Mortality was either a direct effect of fire or was a fire-induced interaction with insects, rodents, or disease.

Burning makes all cactus species more attractive to cattle, and the reproductive rate of most species is low. Burning at intervals of 5 to 6 years prevents development of dense stands of prickly pear. Fall burning of prickly pear killed more than 80% of the pads, while spring burns accomplished a 40% pad kill (Dodd et al 1985).

In Alberta, pronghorn antelope (Antilocapra americana) are known to readily consume prickly pear cactus after burning removes the spines. Over 50% of the green pads were utilized after a burn (Stelfox and Vriend 1977). The use of fire in prickly pear control along with the response of pronghorns and cattle to eating burned pads may warrant further investigation.

Kentucky bluegrass

Late-spring fire has been a particularly effective method of controlling Kentucky bluegrass (Hensel 1923).

In many mesic areas of the mixed prairie, prescribed burning has controlled cool-season grasses without reducing herbage yields or cover of warm-season grasses (Kirsch and Kruse 1973; Gartner and Thompson 1973); although Dwyer and Pieper (1967) report total herbage yield was reduced the first year following a burn. Zelder and Loucks (1969) found that growth began earlier and continued to be greater on burned plots.

Schacht and Stubbendieck (1985) indicated that bluegrasses were damaged but not eliminated from burned plots. Bluegrasses appeared to regain their vigor by the second year following the fire, but their herbage yields on burned plots remained lower than on control plots.

Zelder and Loucks (1969) found that the standing crop of Kentucky bluegrass was greater on unburned ridge sites. Bluegrass height was greater on the unburned than on the corresponding burned plots. This response, however, could be expected, since plots were burned after the plants had begun growth (Zelder and Loucks 1969).

Zelder and Loucks (1969) also reported a general trend for spring fires to decrease fruiting of early blooming grasses and to increase fruiting of late blooming grasses. They suggested that burning may damage flower primordia of early blooming grasses. On upland sites, burning reduced Kentucky bluegrass seed production and increased seed production of little bluestem.

The increase in fruiting that results from burning late blooming prairie grasses is well documented by other studies, as is the decrease of Kentucky bluegrass fruiting (Curtis and Partch 1950; Ehrenreich and Aikman 1963).

In summary, Kentucky bluegrass is more susceptible to damage by fire on ridge sites and little affected in depressions. The low fertility and high permeability of the ridge soils seem to make the effect of fire somewhat more devastating than on soils of deeper, heavier texture. It seems reasonable, then, to suggest that consecutive burning for several years running of areas where exposure is high would probably increase desirable species and decrease Kentucky bluegrass.

Cheat grass (Bromus secalinus)

Fire hazard in a stand of vegetation is increased by the presence of cheat grass. The extremely high flammability of the dry grass permits fires to start and spread with unusual rapidity.

Fire will also enhance establishment and spread of cheat grass (Klemmedson and Smith 1964; Schacht and Stubbendieck 1985; Young et al 1976).

In the Utah foothills, Pickford (1932) found that cheat grass made up less than 1% of the vegetative composition on ungrazed and unburned areas. On ungrazed but burned ranges, cheat grass made up 22%, whereas on unburned but grazed areas it comprised 15%. Cheat grass dominated vegetation under the combination of both burning and grazing, at 38% plant frequency.

Repeated burning every few years or burning in early summer will deplete a stand of perennial grasses and allow annual grasses, primarily cheat grass, to increase sharply (Young et al 1976). Once a sagebrush-grass community is depleted of perennial plant cover, secondary succession goes from Russian thistle (Salsola iberica) to mustard (Sisymbrium and Descurainia spp) to cheat grass within 5 years (Wright and Bailey 1982).

Pechanec and Hull (1945) found that burning reduced cheat grass plants, depending on the month of the burn. Early summer burns, at the time of year when climax perennials are easily killed by fire, were only a temporary setback for cheat grass (Wright and Bailey 1982). Therefore, the density of cheat grass increases over time while fewer perennials survive after each fire.

Young et al (1976) reported that after a late July burn there was an 80% or greater reduction in cheat grass and cheat grass seed production. However, in a burn study conducted by Barney and Frischknect (1974), the cover value of cheat grass varied from 12.6% in the 3-year-old burns to 0.9% in the oldest stands. Cheat grass declined in cover the first 22 years after fire, then leveled off and stayed about the same.

Pechanec and Hull (1945) showed that during the year following burning, cheat grass plants were far fewer on burned than on unburned ranges.

These studies give us considerable difference of opinion about the effectiveness of fire as a tool for reducing cheat grass stands.

Time of burning is evidently an important factor determining subsequent cheat grass stand density. Cheat grass was effectively controlled by burning in late spring, just as the seed matured but before it shattered (Stark et al 1946; Plummer et al 1955). Areas burned in early summer had light remnant stands, compared with fall-burned areas (Pechanec and Hull 1945). Their studies near Boise, Idaho, showed that June and July burns reduced plant numbers to 14 and 11 per square foot compared to 41, 45, and 124 plants per square foot, respectively, on August, October, and November burns.

Warg (1938), in disagreement with many other observers, felt that burning was not a satisfactory means of controlling cheat grass. Leopold (1941) agreed, stating, 'The more you burn cheat the thicker it grows next year, for the seeds shatter early and harbor in cracks in the ground."

The latter part of Leopold's statement is significant and has been stressed by others as a key to the success of cheat grass in competing with perennials.

Warg (1938) observed that cheat grass was damaged less by heat than were perennial natives. After 5 minutes at 257 F (125 C), germination of cheat grass was 87.25% as compared to 9.87% with the control. After 302 F (150 C) for 5 minutes, cheat grass seed failed to germinate.

Cheat grass fire hazard differs from that of most perennial grasses of the western range. The plant matures early in June and dries out within 1 or 2 weeks after maturing, remaining a hazard until fall.

The high flammability of cheat grass is not only a function of its early maturity and uniform stands, but may be at least partially explained by its low moisture content when mature (Klemmedson and Smith 1964).

Fire is a major cause of disturbance that has enhanced the establishment and spread of cheat grass, but fire can also be used to control the species.


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