KUCHLER TYPE FIRE ECOLOGY AND MANAGEMENT
KUCHLER TYPE: Nebraska sandhills prairie



FUELS, FLAMMABILITY, AND FIRE OCCURRENCE : 
Nebraska sandhills prairie occurs in a climate that is not conducive to
rapid decomposition of dead plant materials.  Therefore, dry fuel and
mulch build up within a short period of time [22].  Old stems and
leaves of little bluestem persist for several years, furnishing abundant
fuel for fires [47].

A single year's accumulation of plant material is capable of supporting
a grassland fire at any time of the growing season.  In addition,
regrowth following a spring fire produces enough fuel to support a fire
in the fall of the same year [8].  Fire during the same growing season
is less likely if the first fire occurred after May.  Summer and fall
fires are likely to decrease the potential for burning in the early
spring of the following year [8,9].  The flammability of grasses varies
to some extent over the growing season.  The probability of a fire
occuring in ungrazed, native bluestem grassland may be high even before
the grasses enter dormancy [8].

Ignition is probably more important than fuel availability or condition
in the initiation and spread of Nebraska sandhills prairie fires [8].
Early observers noted frequent prairie fires from spring through fall.
Fire is and was a frequent event in the central Great Plains.  Historic
fire frequencies were greatly influenced by human-caused ignitions, both
by Native Americans and European settlers [52].  Many fires were ignited
by lightning during electrical storms.  Peak lightning fire frequencies
occurred in July and August [8,9].  Moore [36] attributed 32 percent of
presettlement fires in the north-central plains to Indians, 14 percent
to Europeans, and the remainder he left unascribed due to lack of
information.  Most of those were probably caused by lightning.
Presently, range fires are not uncommon, but their extent and recurrence
are limited by human efforts at fire suppression and control [10].
Currently, lightning is the main source of ignition; sparks from trains
also start a number of fires each year [49].  Kirsch and Kruse [30]
observed four fires started by lightning in a single afternoon in 1958.
In South Dakota, eleven fires were ignited within a 20 by 40 mile (32 by
64 km) area within a 2-week period in 1971 [30].  In May 1965 a
lightning fire, driven by 48 mile-per-hour (76 k/hr) winds, burned over
18,000 acres (7,200 ha) of grassland and forest (including over 42% of
the 26,000 acres [10,400 ha] of planted pine) in the Nebraska sandhills
prairie [49].


FIRE EFFECTS ON SITE : 
Fire in grasslands generally causes soils to warm earlier in spring, and
achieve temperatures that average 9 degrees Fahrenheit (5 deg C) higher
than on unburned sites [5,31,52].  In Missouri little bluestem-big
bluestem grasslands, the maximum spring soil surface temperatures
were 5.22 to 17 degrees Fahrenheit (2.9-9.8 deg C) higher on burned
plots than on unburned plots [32].  Soils in burned grasslands usually
have slightly higher pH than in unburned grasslands due to the release
of alkaline earth metals.  In neutral or alkaline soils this usually has
little effect, but in acidic grassland soils, pH increases may improve
germination or have other effects on vegetative responses [46].

Spring and summer fires reduce vegetative cover and increase the
likelihood of blowout formation [39].  Burzlaff [13] suggested that the
limiting of fire has been of major importance in stabilizing dune soils
in the Nebraska sandhills prairie.

Burning recycles nutrients and releases energy stored in aboveground
plant biomass.  Fire effects differ depending on fire frequency and the
length of fire-free intervals.  The species- and nutrient-specific
effects of fire on nutrient uptake suggest that fire exclusion has the
potential to effect long-term changes in species composition in
nutrient-limited ecosystems, including Nebraska sandhills prairie [38].


FIRE EFFECTS ON VEGETATION : 
The effects of fire on grasses depend on climate, site and topography,
soil moisture, site condition (including fire frequency), species
composition, and timing of fire.  Spring burning usually favors
warm-season species over cool-season species.  The later the fire occurs
in spring, but still prior to the emergence of green shoots, the greater
the production of warm-season species in tallgrass prairie [31].
However, many grasses respond negatively to burning in dry areas
(approximately 275-300 mm summer rainfall) [31], or during drought
[14,52].  Fire followed by drought can kill enough little bluestem and
other bunchgrasses to create blowout conditions [39].  Fire combined
with drought reduced little bluestem cover as much as 42 percent in
Texas ranges; burning in wet years resulted in an 81 percent increase
in little bluestem cover [51].  In tallgrass prairie, big bluestem
almost always increases after burning, as does indiangrass and probably
switchgrass.  But the amount of increase depends on the community state
before burning, as well as the time of fire occurrence [16,31,53].

Fire consumes excessive mulch, which builds up rapidly in Nebraska
sandhills prairie and retards plant growth.  However, the exposure
of bunchgrass bases contributes to drought stress [22].  

On Nebraska sandhills prairie choppy sands areas burned in May,
vegetative cover in August averaged 16 percent less on burned sites than
on adjacent unburned sites.  By 2 years following the fire, vegetative
cover averaged 8 percent less than on adjacent unburned sites [9].  One
growing season after a May, 1965 wildfire, forb cover and total
vegetative cover were reduced.  Vegetative growth was 53 to 91 percent
greater on unburned sited than on burned sites.  Species diversity was
unchanged.  Total grass cover was not substantially altered.  Sand
bluestem, sand dropseed, and sandhill muhly relative cover decreased;
prairie sandreed and needle-and-thread grass relative cover increased
[49].

A study to evaluate the effects of grazing on fire response was
conducted on choppy sands sites.  Both grazed and ungrazed sites burned
in May averaged 26 percent lower total cover in August than unburned
sites.  After 2 years, vegetative cover averaged 11 percent less on
burned sites than on unburned sites.  The decline in total cover as a
consequence of burning was greatest on north-facing slopes (where
prefire grass cover was greatest).  A suggested reason for this effect
was that greater grass cover on a site promotes a hotter, more intense,
and therefore more destructive fire [78].

The Arapaho Prairie has not been grazed since its purchase by the Nature
Conservancy in 1976.  Areas of this prairie were burned by wildfire
(lightning ignition) in October 1981.  Aboveground plant biomass was
measured the following growing season.  In early spring, prairie
sandreed exhibited a higher rate of growth on burned areas than on
unburned areas, but by mid-August, burned and unburned sites were
approximately equal in prairie sandreed aboveground biomass.
Needle-and-thread grass had greater biomass on burned sites than on
unburned sites in August, but the reverse was true in October,
indicating that growth slowed earlier on burned sites.  A similar
pattern was exhibited by blue grama [37].

No studies have been conducted on the long-term effects of fire on
Nebraska sandhills prairie vegetation [49].

Nebraska Sandhills Prairie Species In Other Communities:  In the loess
hills of Nebraska, a late spring prescribed fire was used to control
Kentucky bluegrass (Poa pratensis), Canada bluegrass (P. compressa), and
Japanese brome (Bromus japonicus).  Precipitation was lower than average
the first postfire growing season and above average the second year
following the fire.  Herbage yield of warm-season grasses (blue grama,
sideouts grama, and sand dropseed) was generally higher in June and
September on burned plots in both the first and second postfire years
[41].

In northern mixed prairie, the ratio of cool-season (needle-and-thread
grass, big bluestem, switchgrass) to warm-season (blue grama, sideouts
grama, little bluestem) species was unaffected by burning; however,
herbage production of cool-season species increased during the
warm-season growth period on spring-, summer-, and fall-burned plots.
Warm-season herbage increased with spring fire as expected.  The
increase in cool-season species is contradictory to the prevailing view
that spring burning is detrimental to cool-season grasses.  The author
suggested that there is a native cool-season guild of species that are
well adapted to fire, and that the warm-season species are less well
adapted to fire on dry northern sites [44].  In the mixed-grass prairie
of Wind Cave National Park, South Dakota, spring prescribed fires were
conducted for ponderosa pine control.  The fires were lit when
cool-season grasses were in the process of green-up and the fires were
relatively low-severity and slow-moving. Green needlegrass (Stipa
viridula), needle-and-thread grass, little bluestem, and western
wheatgrass decreased in ground cover the first growing season after the
fire, but showed rapid increases the 2 years following the fire.  Bare
ground cover increased 26 percent immediately after the fire but
decreased 29 percent to below prefire estimated levels by 2 years after
the fire [20].

Wright and others [54] charted information on the response of species by
prairie type and location.  Glenn-Lewin and others [23] determined the
flowering response of prairie species to burning.  In locations other
than Nebraska sandhills prairie, big bluestem, little bluestem, sideoats
grama, switchgrass, indiangrass, and prairie dropseed all increase
flower production after a fire [23].


FIRE EFFECTS ON RESOURCE MANAGEMENT : 
Annual spring fires in the Allwine Prairie Preserve (Douglas County,
Nebraska) appeared to cause minimal mortality to ground-nesting and
burrowing species.  The western harvest mouse, however, is quite
vulnerable to prairie fires since it constructs aboveground nests out of
prairie grasses and grass litter.  Considerable mortality occurred to
both adults and young [18].

Historically, prairie fires caused much mortality and injury to American
bison, deer, and wolves [36].  Animal use of burned prairie was also
affected; American bison, which used the same migration routes
repeatedly, would alter their migration pathway where burned areas were
depleted of forage.  As much as a month was required in some cases for
American bison to return to an area following a fire [36].


FIRE USE CONSIDERATIONS : 
Grassland fires can be intense and fast moving.  Most grassland fires
burn as headfires without completely consuming fuels [17,46].  Headfires
in tall grasses can generate big flames but do not usually produce
firebrands or spot fires due to the rapid consumption of fuels.  Despite
large and extensive fire fronts and a rapid spread rate, extremely high
temperatures at ground level are uncommon [46].  Damage to the basal
portions and rootstocks of plants is therefore also uncommon [17,46].
In dry conditions, backing fires generate more heat than headfires since
they are slower moving [22,46], and thus consume fuel more completely.
In dry conditions backing fires may cause more damage to roots and plant
bases than headfires [17,25,26].  The amount and rate of heat release in
grassland fires depends on weather conditions, topography (fire spreads
faster with steeper slopes), and fuel characteristics [17].

Grassland fires often develop broad fronts because of extensive and
unbroken terrain and continuous fuels.  Fire fronts become irregular
when topography and discontinuous fuel loads retard fire movement, and
when winds and developing fire storms speed up fire movement [46].  Fire
spread patterns in large fires may be very irregular, leaving patches of
unburned vegetation [37].  Burned areas cool off rapidly behind the
front allowing animals (and humans) to move into burned areas
immediately [46].  Specific guidelines on conducting prescribed fire in
grasslands are available [25,34] .

Significant differences in flammability during the growing season arise
due to vegetative moisture content and stage of development.  In one
study, the burn residue (inversely related to flammability, i.e. the
drier the vegetation the more complete combustion and less ash formed)
varied from a low of less than 1 percent of dry biomass in April to a
maximum of 16 percent in June.  Seasonal differences in flammability
appear to depend on both moisture content and stage of vegetative
development [8].

Summer prescribed fires can be successfully conducted in native bluestem
prairies, probably including Nebraska sandhills prairie, even without
forced ignition using petroleum-based fuels or artificial accumulation
of plant matter for fuel [8].


FIRE MANAGEMENT CONSIDERATIONS : 
The ecological role of fire in the Nebraska sandhills prairie is
unclear.  Current range management practices consist of total fire
exclusion.  Range managers believe that fire exclusion is the best
policy for maintaining domestic cattle forage [24].  The increase in
Nebraska sandhills rangeland productivity in the first half of this
century was at least partly attributed to fire control efforts because
of reduced vegetation loss and blowout occurrence [13].  However, this
may not be the most appropriate regime for the health of the ecosystem.
The stabilization of dune soils, due in part to fire suppression, has
contributed to the endangered status of blowout penstemon (Penstemon
haydenii).  This species occurs exclusively in blowouts, and is now on
the Federal List of Endangered Species [24].  There is ample evidence
that most types of grasslands soon begin to deteriorate when closed to
both grazing and fire; however, not all grasslands are fire dependent
[1,2].  In Nebraska sandhills prairie fire may not be completely
beneficial.  One year after an October wildfire on the Arapaho Prairie
total phytomass was 23 percent less on burned sites than on unburned
sites.  Morrison and others [37] concluded that these grasslands are not
positively affected by fire.  Observations made 2 years after the fire,
however, indicated that there were no long-lasting deleterious effects
[37].

Few studies on fire frequency have been done for Nebraska sandhills
prairie [8,9].  Ponderosa pine is increasing in some areas of Nebraska
sandhills prairie due to cattle grazing and decreased fire frequency
[43].  Historically, fire played a beneficial role in the preservation
of tallgrass prairie, and fire protection/suppression has led to an
increase in woody vegetation, particularly in the eastern portions of
the tallgrass prairie zone.  Fire in tallgrass prairies suppresses the
encroachment of trees and shrubs, and reduces competition from
cool-season invaders (i.e., Kentucky bluegrass and smooth brome) [42].
In the absence of fire, mixed-grass prairie in the Black Hills, South
Dakota, has also been invaded by ponderosa pine in the last 100 years.
It is estimated that 50 percent of presettlement prairie has been
converted to ponderosa pine woodlands [22].  In the Black Hills,
prescribed fire can be used in bluestem grasslands to reduce pine
invasion without decreasing forage production if the fire is conducted
prior to May 1 [21].

Nebraska sandhills prairie contains many tallgrass prairie species.  The
response of these species to fire has been more extensively studied in
true tallgrass prairie types than in Nebraska sandhills prairie.  The
particular soil and precipitation properties of Nebraska sandhills
prairie may have a unique effect on these species, particularly during
drought.  Bailey [3] stated that wildfire during the growing season is
detrimental to arid (9.6 to 16 inches [240-400 mm] mean annual
precipitation) mixed prarie range, but on wetter (16 to 20 inches
[400-500 mm] mean annual precipitation) areas, the vegetation is better
able to withstand the detrimental effects of fire.  Several major
grasses that are harmed by fire in the arid areas of North Dakota were
found to increase in cover after fire in the wetter eastern part of the
state [30].

In tallgrass prairies, the accumulation of dead plant material reaches
growth inhibiting quantities in only 3 to 5 years.  This accumulation
retards the warming of soil and reduces available light at the bases of
grass plants [48].  Occasional fires (every 2 to 3 years) renovate
unmowed prairies and are distinctly beneficial if they occur in spring
before growth is renewed [48].  Vegetation is generally more palatable
and more nutritious on burned sites than on unburned sites; coarse
grasses such as little bluestem that have a tendency to accumulate
litter are particularly improved [42,52].  Gartner and White [22] stated
that prescribed fire could be used to stimulate production of desirable
herbaceous species, reduce mulch accumulation, and reduce competition
from unwanted species within the prairie-forest ecotone.

Fire is recognized as having benefits to tallgrass prairie during
periods of average to above average precipitation [15].  In tallgrass
prairie, productivity of big bluestem, measured as aboveground biomass,
generally increases after a fire [45].  Most experimental fires in
tallgrass prairies are conducted between late March and April.  In
prairies dominated by warm-season grasses, growth and production are
stimulated by spring burning [6].  Spring burning enhances the growth,
tillering, and flowering-stem density of big bluestem and other
warm-season grasses [15].  For big bluestem, the increase is greater
with late-spring fires (mid- to late April) than with early (mid-March)
fires [6].  Over a period of 56 years in tallgrass prairie, big bluestem
increased under an annual spring fire regime and little bluestem
decreased [45].  Summer (prescribed) fire effects are likely to differ
substantially from those during dormant periods [8].

In tallgrass prairies, timing of burning greatly affects individual
species response to fire.  Early spring burning favors little bluestem
and prairie dropseed; late spring burning favors big bluestem,
indiangrass, and switchgrass [5,42].  Burning too early may depress big
bluestem production rather than stimulating it [45].  Repeated burning
of big bluestem communities favors indiangrass [5].  Wildfires during
the growing season, especially in drought years, appear to cause some
plant mortality [22].  Other factors including target species,
geographic location and rainfall must be considered in predicting and
interpreting response to burning [45].


REHABILITATION OF SITES FOLLOWING WILDFIRE : 
Blowout formation is sometimes triggered by denudation due to fire.
Blowouts can be stabilized with mulch and/or establishment of
vegetation.  A test of the efficacy of various grass species in
stabilizing blowouts determined that prairie sandreed had the highest
stand density and greatest freqency of occurrence on seeded blowout
plots.  It was also rated the msot effective at holding sand in place;
the authors recommend planting prairie sandreed and/or intermediate
wheatgrass (Thinopyrum intermedium) under a layer of prairie hay mulch
for the most rapid and complete stabilization of blowouts [35].

Related categories for Kuchler Type: Nebraska sandhills prairie