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Effects of Fire in the Northern Great Plains

Effects of Fire on Upland Grasses and Forbs

One of the simplest and least expensive practices to improve poor quality grassland is prescribed burning. Selective suppression or promotion of a particular plant species depends primarily upon the date of the fire in relation to the phenology of the particular species.

Usually, those species actively growing when the area is burned are much more susceptible to injury and death than dormant species or those just initiating growth (Anderson et al 1970).

The proper time to burn can be based on physiological stages (e.g., root reserves) or morphological stages (e.g., when buds are exposed). A sequence of fires may be necessary to restore grasslands to proper condition.

Fire severity (which is closely related to fuel amounts and distribution, weather, and moisture content of soil and fuel) is also a major factor affecting fire damage to plants (Wright and Bailey 1982).

Research within the past few decades has shown that fire has been an important natural component of many grassland communities (Daubenmire 1968). Although historical records of fire in the Great Plains are limited (Higgins 1986a), fire suppression since the early 1900s has changed the structure and composition of many plant communities, particularly those subject to frequent fires (Daubenmire 1968; Wells 1970; Bailey and Wroe 1974; Gartner and White 1986; Gartner et al 1986).

Numerous factors affect the response of plants to fire. The biotic and abiotic factors generally recognized are grassland type, fire history, season, fuel and soil moisture conditions, wind speed and direction, air temperature, and time of day of the fire. Because of the complexity and interaction of factors and the lack of data concerning burns in the same community under similar circumstances, results of fire effects are often confusing and misleading.

Not burning may have as much effect upon grass production as burning itself. Tomanek (1948) stated that although mulch reduces soil temperatures and evaporation, it also increases filtration rates. Excessive amounts of litter can accumulate under light or no grazing or lack of fire. Buildup of litter usually causes degeneration of grass stands and lower yields.

Burning native prairie in northeastern Iowa increased grass seedstalk production (Ehrenreich and Aikman 1957). Possible causes for this increase were removal of large quantities of litter, stimulation of floral bud induction resulting from the direct heat of the fire, and higher temperatures earlier in spring. The authors concluded that burning resulted in an increased accumulation of carbohydrates due to improved plant growth conditions.

After a burn the soil warms more rapidly in the spring. Removal of the litter permits soil temperatures to average as much as 52 F (11 C) higher than on unburned sites in early spring (Peet et al 1975). Soil temperatures in early spring are inversely related to the amount of litter and duff (Ehrenreich 1959).

Early rising soil temperatures stimulate the increase of certain bacteria that decompose organic matter. This allows warm-season grasses to grow at an optimum rate if moisture is adequate. Most of the fertilizing effects after a fire result from nitrates released by bacteria consuming organic matter, not from nutrients in the ash (Sharrow and Wright 1977a).

On the other hand, Launchbaugh (1973) stated that yield reductions were associated with the removal of dormant growth by burning. The net effect was less soil moisture available for plant growth due to exposure to extreme winter temperatures and increased respiration. He added, however, that when mulch accumulations are excessive, burning will result in greater yields.

Cool- and warm-season species growing together may respond differently to the same fire; seasonal timing is critical (Bragg 1982; Wright and Bailey 1982). Some plants may be actively growing and especially susceptible at the time of the fire while others will be dormant and less susceptible.

Many cool-season plants will be actively growing during spring and fall fires, but most warm-season plants either will be dormant or will have not yet expended a significant amount of stored energy on new growth. In summer, cool-season plants have nearly stopped growth or are dormant. Fire at this time is usually detrimental to warm-season species (Vogl 1974).

Spring burning will reduce species competition. Repeated burning on March 1 resulted in a sharp decrease in the number of Kentucky bluegrass (Poa pratensis) plants in Iowa (Ehrenreich 1959). Bluegrass, a cool-season exotic, also decreased sharply by repeated burning in early March (Bailey 1978; Engle and Bultsma 1984). Most native grasses are still dormant at this time when Kentucky bluegrass, beginning to grow, becomes highly susceptible to heat injury from fire. Thus, warm-season native grasses have higher yields because of decreased competition from cool-season invaders such as Kentucky bluegrass.

Native annuals are usually encouraged by burning if the fires occur at the appropriate time (Daubenmire 1968). Many annuals, as well as shortlived perennials, are opportunistic or pioneer species which require the open soil, reduced competition, and full sunlight characteristic of many post-burn sites (Vogl 1974).

Besides creating favorable sites for pioneer species, grassland fires directly affect seed germination and seedling establishment of native annuals. Vareschi (1962) found that soil temperature in many grasslands can reach 140 F (60 C) for several hours after a fire due to solar radiation. This was not detrimental to the seeds of native annuals; soil surface temperatures of even 194 F (90 C) for a few seconds were not harmful to most seeds.

The leaves and stems of annuals are frequently dry while the seeds contained in the inflorescence are still ripening. Fire occurring while the seeds are held aloft usually kills most of them (Daubenmire 1968). Fire also is detrimental to most actively growing annuals. Recurring fires during active growth can eliminate some annual plants (Vogl 1974).

Many perennial species are capable of vegetative reproduction, which gives them a competitive advantage in colonizing open or post-burn sites and aids the species in surviving damage from fire or other catastrophes (Vogl 1974).

The effect of fire on perennial plants varies with stage of development, fire intensity, and relative position of the perennating buds. Some species have perennating buds on above- ground stems where they are easily killed by fire. Others have their buds underground on roots or rhizomes. Buds at or below the soil surface are less susceptible to damage by fire than those above the soil surface. Hot or prolonged fire is detrimental to perennials when high temperatures destroy the perennating buds (Daubenmire 1968).

Perennial plants are also susceptible to fire after food translocation has taken place. Generally, as new foliage reaches maturity, the major portion of the food reserves has been withdrawn from the underground organs. Leaf and stem destruction at this time injures the plant most severely (Aldous 1934).

Although many environmental factors alter the effects of burning, drought conditions are the most limiting to grass production in the NGP (Wright and Bailey 1980; Engle and Bultsma 1984). During a drought, first post-year herbage yields were not increased by burning even though excessive mulch accumulations were removed by fire (Engle and Bultsma 1984).

Shortgrass prairie

Although shortgrass prairie occurs only in southern Alberta, southeastern Wyoming, northeastern Colorado, and western Kansas within the NGP, we believe it is important enough to include as part of these guidelines. One of the greatest benefits from burning shortgrass prairie is an increase in utilization by livestock (Wright and Bailey 1982).

The primary grass species dominating shortgrass prairies are buffalograss (Buchloe dactyloides) and blue grama (Bouteloua gracilis). Fire tolerance of most species in the shortgrass prairie under different moisture regimes appears to be similar to that for buffalograss and blue grama.

Red threeawn (Aristida longiseta) and sand dropseed (Sporobolus cryptandrus) are usually harmed by fire. However, sand dropseed tolerated fire when winter and spring precipitation was 40% above normal.

During dry years, most species of the shortgrass prairie are harmed by fire. Following a spring wildfire, when soil was dry, the recovery time for a buffalograss-blue grama community was three growing seasons (35%, 62%, and 97% recovery following the first, second, and third growing seasons, respectively) (Wright and Bailey 1982).

Other species harmed by a wildfire during a year of below normal precipitation included slim stem muhly (Muhlenbergia filiculmis), ring muhly (M. torreyi), wolftail (Lycurus phleoides), and galleta (Hilaria jamesii).

In the shortgrass area of southern Alberta, spring burning reduced forage production by 50% in the first year and by 15% in the second year, with recovery completed by the third year. Fall burning was less serious, reducing production by 30% the first year with recovery complete by the end of the second year (Clarke et al 1943).

A wildfire in a western Kansas shortgrass range reduced the basal cover of buffalograss and blue grama grasses by 48% and 67%, respectively. Shortgrass areas with heavy litter were severely damaged by burning, based on basal cover and forage production, compared to lighter damage on areas with less litter (Hopkins et al 1948).

Near Hays, Kan., March burning decreased first-year yields in a buffalograss-blue grama community by 65% and in a western wheatgrass (Agropyron smithii) shortgrass type on two locations by 82% and 48% (Launchbaugh 1964). By the third growing season, production differences were no longer significant.

Reduced production following a fire is attributed to (1) partial killing of the forage present, (2) reduction of plant vigor of the remaining forage plants, and (3) reduced moisture penetration associated with reduced ground cover and greater evaporation of soil moisture.

Although grasses are the major plants in shortgrass prairie, many species of forbs occur during years with above normal precipitation. Total forb yields are usually reduced more by spring burns than fall burns. In all cases, however, forb composition will be increased by burning when plants are dormant. Young, actively growing forbs will be severely harmed by fire.

The average basal diameters of bunches of blue grama increased regardless of treatment type. Basal diameter of red threeawn and sand dropseed decreased on plots burned 2 years in succession. Blue grama continued to increase except when burned 2 consecutive springs with a headfire.

Height reduction following fire has often been noted. A spring burn in western Kansas (Launchbaugh 1964) resulted in decreased heights of blue grama, buffalograss, and western wheatgrass. Height of blue grama was less in all burned plots, compared to unburned plots during the first burn year, with apparent recovery after the second year.

Wright and Bailey (1980) concluded that burning during dry years is apt to have negative results on shortgrass range. However, from his work in Texas, Vallentine (1971) suggested that infrequent burning should not harm grasses if done during moist periods. A burn may provide little benefit, however, unless an excessive litter buildup has occurred (Vallentine 1971). These studies appear to suggest that burning shortgrass sites is undesirable because production and ground cover are both reduced. However, much of the evidence is based largely on wildfires or prescribed burns made without consideration of weather or soil moisture conditions.

Mixed prairie

The mixed prairie of the NGP is located in eastern Montana, eastern Wyoming, all but the eastern edges of North and South Dakota, southeastern Alberta, and southern Saskatchewan (Wright and Bailey 1980). Annual precipitation varies from 15 to 19 inches (38-48 cm) per year in some mesic areas to less than 15 inches (38 cm) in semiarid regions.

Prescribed burning on mixed prairie in the NGP has become a controversial management technique during the past two decades. Negative attitudes toward burning have limited funding of fire ecology research in most NGP states (Gartner and White 1986) and have limited the use of fire as a possible management tool (White and Currie 1983a).

The effects of fire on native grasslands are indeed varied, but evidence shows that prairie closed to both grazing and fire soon begins to deteriorate (Anderson et al 1970; Kirsch and Kruse 1973; Schacht and Stubbendieck 1985).

Anderson et al (1970) burned upland mixed prairie in the Flint Hills of Kansas in early spring (March 20), midspring (April 10), and late spring (May 1).

Big bluestem increased under mid- and late spring burning, but increased only slightly under early spring or no burning. Sideoats grama (Bouteloua curtipendula) herbage remained constant under all burning systems.

Kentucky bluegrass was nearly eliminated from the treatment sites regardless of the time of burning. Buffalograss declined in the late spring burned pastures and was stable in the others. Blue and hairy grama (B. hirsuta) were favored by early and midspring burning.

Periodic droughts have a strong influence on recovery of mixed prairie grasses after a fire (Hopkins et al 1948; Wright and Bailey 1980; White and Currie 1983a).

Semiarid mixed prairie.  In the more arid regions of the mixed prairie, fire can result in decreased herbage yield (Gartner et al 1978) and critical reductions in litter (Dix 1960).

However, effects differ, primarily with season of burning, pre- and post-burn precipitation, and plant species composition (Clarke et al 1943; Coupland 1973).

Forde et al (1984) burned different areas of mixed prairie on the same day in the Wind Cave National Park in South Dakota. In the Red Valley burn, most of the perennial species decreased in percentage of ground cover the year of the burn, but cover rapidly increased during the next 2 years. In the Bison Flat burn, frequency of perennials decreased 25%, but air-dried biomass increased 38%, meaning fewer but larger plants remained after the fire.

Burning at various fuel moisture levels was investigated in two plant communities in Wind Cave National Park in South Dakota. Burning vegetation at 30%, 38%, and 46% fuel moisture had no significant effect on either little bluestem or a mixed grass community. With the exception of a decrease in cool-season species due to burning in late May and early June, no major species alterations were noted (Worcester 1979).

On April 25,1980, a mixed prairie in the Loess Hills of southern Nebraska was burned with backing fires (Schacht and Stubbendieck 1985). One study tract was dominated by a shortgrass community, but showed remnants of some desirable species of the mixed prairie such as big bluestem, sideoats grama, and little bluestem. The purpose of the burn was to shift species composition to higher yielding, native mixed grasses.

The initial effect of the fire was to greatly suppress the herbage yields of cool-season species. Annual bromes were nearly eliminated, and bluegrasses were damaged to a degree. Yields of both blue grama and sand dropseed were significantly higher on burned plots than on unburned plots.

Sand dropseed is a prolific seed producer and is drought resistant. It is one of the first species to grow on denuded rangeland where soil texture is sandy to silty.

Yield responses for western wheatgrass, blue grama, and threadleaf sedge (Carex filifolia) were measured after both spring and fall burning on a mixed prairie in eastern Montana (White and Currie 1983a).

Overall, blue grama responded better under spring burning. Western wheatgrass production was unaffected by spring and fall burning. Threadleaf sedge was found to decrease in production following fall burning. Spring burning resulted in higher total productivity than fall burning.

Redmann (1978) studied plant and soil water status throughout the growing season following an October fire in northern mixed prairie. Lower water potentials in the burned sites resulted in decreased production of western wheatgrass and Junegrass (Koeleria pyramidata).

DeJong and MacDonald (1975) also indicated that burning can alter the microclimate, resulting in unfavorable plant and water status.

Gartner et al (1978) conducted burns in western South Dakota to determine the effect of seasonal burning on Japanese brome (Bromus japonicus). Winter, late spring, and fall fires significantly reduced this annual grass, while at the same time the yield of western wheatgrass increased after winter and fall burns but declined with late spring burning.

Vegetative changes attributed to wildfire in the timbered breaks of central Montana were observed over a 10-year period (Eichhorn and Watts 1984). Although differences between the five plant associations were noted, some general trends existed:

Burning eliminated non-sprouting woody species such as big sagebrush (Artemisia tridentata) and Rocky Mountain juniper (Juniperus scopulorum). Sprouting shrubs such as choke cherry (Prunus virginiana), snowberry (Symphoricarpos spp), and rose (Rosa spp) increased. Forbs peaked 3 to 4 years after the burn and then decreased.

Mesic mixed prairie.  Wright and Bailey (1982) summarized numerous burning studies conducted in the mesic mixed prairie. Most concerned the effect of fire relative to seasonal changes in plants.

Engle and Bultsma (1984) studied the effect of burning during a period of below-average precipitation at the Samuel H. Ordway Memorial Prairie in north-central South Dakota. Mid-May and mid-June fires reduced Kentucky bluegrass and green needlegrass (Stipa viridula). The authors noted a similarity between plant responses following a burn in a mesic mixed prairie during drought to plant responses after burning in semiarid or xeric mixed prairie.

Burns were made on a mesic mixed prairie in Iowa on March 1 (Ehrenreich 1959). Dominant grass species were prairie dropseed (Sporobulus heterolepis), little bluestem (Andropogon scoparius), and big bluestem (A. gerardii). Areas were burned 1, 2, and 3 consecutive years.

Vegetation on areas with two burns began growing the earliest, matured earlier, and produced more flower stalks. This was attributed to a decrease in litter and higher soil temperatures. Grass growth began earlier, and the number of native plants which flowered increased. This occurred in the first growing season after a burn, but declined until the third growing season after burning, when both burned and unburned areas appeared very similar.

Some general statements may be made regarding production of mixed grass species in the NGP following prescribed burning.

Big bluestem increased in herbage during all periods of spring burning. Little bluestem seemed productive under burning, but not to the degree of big bluestem. Although sideoats grama yields remained constant, blue grama yields increased after spring burning. Finally, responses of Stipa species varied with spring burning.

Prescribed spring burning has increased production of many warm-season grasses in the mixed prairie. These increases vary, depending on rainfall and litter accumulation prior to and after burning (Smith and Owensby 1973).

Time of burning may affect certain species in a variety of ways because of differing phenological characteristics (Anderson et al 1970).

Prescribed burning is a viable management technique for mixed-prairie grassland management but is not recommended under drought conditions in the NGP (White and Currie 1983a; Engle and Bultsma 1984).

Tallgrass prairie

The tallgrass prairie occurs mainly on the eastern edge of the NGP. Precipitation varies from approximately 18 inches (46 cm) annually in southwestern Manitoba to 30 inches (76 cm) in south-central Minnesota. Glacial till soils are predominant (Wright and Bailey 1982).

Of all the grassland ecosystems in North America the tallgrass prairies seem to benefit most from fire.

Many species, including big bluestem, little bluestem, Indian grass, and switchgrass (Panicum virgatum), increase after burning (Wright and Bailey 1982).

Grasses such as sideoats grama and buffalograss, which are sometimes found in the tallgrass prairie understory, do not seem to be adversely affected by burning (Anderson et al 1970).

Cool-season grasses such as Bromus, Elymus, and Poa do not benefit and actually may be harmed by spring burning. Kentucky bluegrass, an exotic species which did not evolve under fire, can be almost eliminated by spring burning in tallgrass prairie (Wright and Bailey 1982; Svedarsky et al 1986).

Fire helps control woody plants (Bragg and Hulbert 1976) and Eurasian "weeds" in tallgrass prairies, and it enhances the growth of native prairie plants (Pauly 1982). The absence of natural fire or prescribed burning has allowed woody vegetation to increase in many areas of the tallgrass prairie.

Some possible results of burning in tallgrass prairie include litter reduction, suppression and eradication of unwanted species, shifts in species composition, and increases in production and diversity (Vogl 1974).

Heitlinger (1975) found that white sweet clover (Melilotus alba) can be controlled on Minnesota native prairie by one of the following three burning strategies: (1) burning annually in early May when the second year shoots are clearly visible; (2) burning every second year in early July before seed of second year plants ripens; and (3) burning annually in early September near the beginning of the critical growth period. Sweetclover is a biennial producing vegetative growth in year one and reproductive growth in year two.

Dziadyk and Clambey (1980) compared six plant communities in western Minnesota after a fall wildfire. Post-burn herbage production on five communities, was largely attributed to an unusually cool spring following the burn.

Peet et al (1975) found that big bluestem herbage in Wisconsin was higher on burned sites due to more favorable environmental conditions after litter removal. Year-end big bluestem biomass was 0. 11 lb/sq ft (531 g/sq m) on the burned site and 0.03 lb/sq ft (173 g/sq m) on the unburned control.

Controlled burning was used in the Cedar Creek Natural History Area in central Minnesota to promote grasses and forbs and reduce northern pin oak (Quercus ellipsoidalis) stands. Annual spring burning for 13 years increased the understory forb and grass species and decreased smaller oaks (less than 10 inches, or less than 25 cm dbh). Burned areas averaged 25 species of grasses and forbs, while unburned controls averaged only 13 species (White 1983).

Tester and Marshall (1962) found that burning a tallgrass prairie in Minnesota did not cause any noticeable shifts in vegetation composition, but the density of some undesirable species declined. Curtis and Partch (1948) reported that regardless of the burning schedule, Canada bluegrass (Poa compressa) and Kentucky bluegrass declined in abundance in a Wisconsin fire study.

In Missouri, Kucera and Dahlman (1968) observed 39% less root biomass on plots of big bluestem after 6 years of fire exclusion than on plots that had been burned annually for 10 years. They suggested a maximum of 3 years between burnings to avoid stand depletion of big bluestem, from litter accumulation.

On the Trelease Prairie near Urbana, Ill., Hadley and Kieckhefer (1963) found that one year without burning resulted in marked decreases in living shoot and flowering stalk production of big bluestem and Indian grass.

They also noted that root biomass increased with burning frequency and Kentucky bluegrass biomass was reduced following late spring burns. However, Hadley and Buccos (1967) found herbage production on the Oakville Prairie in the Red River Valley of North Dakota was comparable on burned and unburned sites,

For North Dakota tallgrass communities, Hadley (1970) said, "continued burning of the upland communities probably will stimulate herbage yields and seed production by most of the grasses, while maintaining the forb and small shrub components. Sustained burning may or may not decrease yields and species diversity in the lowland communities." Burning on uplands produced 22% more biomass but 15% less herbage than on lowland saline sites.

In Wisconsin, Pauly (1982) found that the most successful prairie burns were conducted in late March, April, or early May. Drier sites should be burned earlier in the spring than wet sites due to earlier onset of growth. Spring fires were easier to control because the vegetation was usually packed down by snow, the fire moved more slowly, and flame height was reduced.

At Buena Vista Marsh in central Wisconsin, little bluestem was stimulated by burning to produce greater germination and seed production (Zelder and Loucks 1969).

Tallgrass prairie vegetation will respond dramatically if prescribed burns are conducted at the proper time of year. Towne and Owensby (1984) and Launchbaugh and Owensby (1978) reported from the Kansas Flint Hills that the closer the time of burning is to the beginning of spring growth, the more favorable the response.

Owensby and Anderson (1967) found early spring burns reduced forage yields but late spring burns increased yield, compared to controls. Towne and Owensby (1984) further suggested that the discrepancies between past studies regarding the effects of fire on herbage yield are due to the differences in time of burning. They maintained that manipulation of the vegetation is possible with fire.

Tallgrass prairie burning reduces mulch cover and increases the number of reproductive grass shoots (Ehrenreich and Aikman 1957; Zelder and Loucks 1969; Hickey and Ensign 1983), and it also results in a more rapid phenological development of young plants and an increase in flower production (Hadley and Keickhefer 1963).

Curtis and Partch (1950) also found big bluestem plants to bloom profusely after burning. Ehrenreich and Aikman (1957) found the number of big bluestem seedstalks to be seven times greater in burned compared to unburned prairie in an Iowa study. Little bluestem and prairie dropseed showed an eightfold increase, and Indian grass had a threefold increase. Canada wildrye (Elymus canadensis) was unaffected by burning.

The increase in seedstalk numbers corresponded with an increase in total seeds and more noticeably erect flower stalks. Percentage purity and germination was greater for seed harvested from the burned area as opposed to the unburned area, with the exception of Canada wildrye.

Hickey and Ensign (1983) reported burning increased panicle number and increased seed yield 1.6-fold compared to mechanical thatch removal in Kentucky bluegrass fields. Hulbert (1969) increased tiller numbers 1.5 to 2.7 times by mulch removal in undisturbed bluestem prairie in Kansas; however, inflorescences were rare in both mulched and unmulched plots.

Seed production of western ironweed (Vernonia baldwinii), a common tallgrass prairie forb, was 32 to 43% lower (in seeds/plant) on burned sites than on sites where two or more seasons had passed since the last burn (Knapp 1984).

Weaver and Rowland (1952) found that when the mulch layer was removed by hand the flower stalk of big bluestem more than doubled in height. Big bluestem and switchgrass yields also increased after the removal of mulch. Ehrenreich (1959) found that vegetation of burned areas grew and matured earlier and produced more flower stalks than nearby unburned areas, but he pointed out that the greater height and increase in numbers of seedstalks were only temporary. He found little difference in burned and unburned areas after the second growing season.

Peet et al (1975) noted that 5 weeks after a burn, stem density of big bluestem was three times higher in burned areas. After only 3 more weeks there was little difference in stem density between burned and unburned plots in Wisconsin.

Fire affects big bluestem in three ways: (1) direct effect of the heat of the fire on the buds in the plant crown, (2) removal of accumulated litter from previous growth, and (3) the liberation of mineral fertilizers from the ashes (Curtis and Partch 1950).

The most important appears to be the removal of litter. Dark, bare soils warm faster in the spring than those shaded by litter, thereby enhancing seed germination (Hopkins 1954). Hadley and Kieckhefer (1963) attributed the increase in number of flower stalks to many factors but mainly to removal of litter. Curtis and Partch (1950) considered the presence of litter over the crowns to be the most important factor influencing flowering of big bluestem. When litter cover was removed, flower production increased six times and plant height increased by 60%.

Ehrenreich and Aikman (1957) agreed that increases in seedstalk production could be stimulated by the removal of large quantities of litter, but they felt the addition of ash and induced heat stimulation of buds to be important as well. They proposed that the most likely factor increasing seedstalk production was the increased accumulation of carbohydrate material in the plant from improved growth conditions, but they did not clarify what these improved growth conditions might be.

Hulbert (1969) reported soil temperatures on denuded plots in undisturbed bluestem prairie to be 34 to 41 F (1 to 5 C) higher than on mulched plots during the entire season. He concluded that earlier and greater growth and increased tiller numbers on denuded plots were due to higher temperatures and increased light intensity.

Weaver and Rowland (1952) reported that an accumulation of mulch thinned a stand of big bluestem and other tallgrasses to about a third the usual number of stems. They found soil temperatures under the mulch to be about 25 F (14 C) lower than on plots where mulch had been removed. They also found that only 1 to 5% of light penetrated through even the first inch of the normally compacted mulch. Decreased soil temperatures and less light resulted in a 3-week delay in spring growth, and production of flower stalks was delayed in the grasses which remained mulched.

Peet et al (1975) attributed production increases of big bluestem in a field following burning to more favorable environmental conditions for net photosynthesis from the time of leaf emergence through late June because of more light and higher soil temperatures.

In research by Old (1969), grass seed yields increased following burning due to litter removal, removal of competing cool-season plants, and increased nitrification due to increased soil temperatures.

Hardison (1980) reported that fire has been used for 30 years by commercial grass seed producers in the Pacific Northwest to reduce weed seeds and to control insects and several plant diseases.

In summary, fire does have a measurable positive effect on the yield of most tallgrass prairie grasses. Soil moisture is an important determining factor in the yield potential of seed and foliage. Native grasses on upland sites respond favorably, but tallgrass species on moist lowland or saline sites may not be as competitive with other species.

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