FIRE CASE STUDIES
SPECIES: Schizachyrium scoparium | Little Bluestem 



FIRE CASE STUDIES : 
1. Oklahoma fuel load study burn
2. Wind Cave National Park-Gobler's Ridge Fuel Moisture Treatments


1st CASE NAME : 
Oklahoma fuel load study burn


REFERENCE : 
Ewing, L. L.; Engle, D. M. 1988 [47]


SEASON/SEVERITY CLASSIFICATION : 
late summer/severe


STUDY LOCATION : 
The Oklahoma Agricultural Experiment Station Agronomy Research Range,
approximately 9 miles (15 km) southwest of Stillwater, Oklahoma.


PREFIRE VEGETATIVE COMMUNITY : 
Tall-grass prairie dominated by big bluestem (Andropogon gerardii var.
gerardii), indiangrass (Sorhgastrum nutans), switchgrass (Panicum
virgatum), little bluestem, and side-oats grama (Bouteloua
curtipendula).


TARGET SPECIES PHENOLOGICAL STATE : 
Little bluestem was in active growth stage at the time of the September
5 burn.


SITE DESCRIPTION : 
Two similar upland study sites approximately 2.1 miles (3.5 km) apart
were burned to represent different grazing intensities.  One site was
moderately grazed in recent years including the year of burning
(considered the low fuel site), while the other had not been grazed for
at least 3 years (considered the high fuel site).  Mean annual
precipitation is 32.7 inches (83.1 cm) with 75 percent falling between
April and October.
   


FIRE DESCRIPTION : 
The fire was a line head fire ignited by driptorch on September 5, 1985.
Precipitation was 17 percent above average during the 1985 growing
season.  Weather conditions were typical of wildfire conditions--hot and
dry.  Fire intensity and fire temperatures demonstrate that fire on the
high fuel plot was roughly four times as intense at the soil surface as
that on the low fuel plot.  Fire intensity and duration was measured in
degree seconds.  Degree seconds is the amount of time the sampled area
differs from the ambient postburn temperature by more than 2 degrees C
(sampled at 2-second intervals).  Data on fire intensity and duration
are presented below:

  Area Sampled                             degree seconds
                                    low fuel             high fuel
  soil surface                   10,400 +or- 1,900   43,600 +or- 3,200
6 in (15 cm) above soil surface   6,300 +or- 40      29,000 +or- 2,100
12 in (30 cm) above soil surface  3,900 +or- 180     20,300 +or- 1,400

Conditions reported:

Air temp. = 98.6 deg. F (37 deg. C)
RH = 36%
Wind speed = 13.8-24 mph (23-40 kph), low fuel plot
              7.8-18 mph (13-30 kph), high fuel plot
Fuel load = 443 plus or minus 74 g/m2, low fuel plot
            1,032 plus or minus 60 g/m2, high fuel plot 


FIRE EFFECTS ON TARGET SPECIES : 
This late summer fire resulted in a nearly complete combustion of
biomass, with the plots generally having blackened and bare soil with a
dusting of ash.  Regrowth following the fire was primarily from
surviving tillers; few new tillers were initiated on either burned plot.
Regrowth was minimal on the low fuel plot and very slight on the high
fuel plot.  Basal area was significantly reduced by both fires.  A 58
percent reduction in basal area occurred on the low fuel plot, and a 95
percent reduction in basal area occurred on the high fuel plot.  The
following growing season, peak biomass production of little bluestem on
the low fuel plot showed no significant decrease compared to the
unburned low fuel plot.  However biomass production on the burned high
fuel plot was only 5 percent of that on the unburned high fuel plot.


FIRE MANAGEMENT IMPLICATIONS : 
During the summer little bluestem has growing points which are not as
well protected as those of warm-season rhizomatous grasses.  This late
summer fire demonstrates that little bluestem may be damaged or killed
outright by intense fires during the summer.  Since little bluestem
elevates a high proportion of its apical meristems above the ground
surface, where they are vulnerable to a fire;s flames and heat, it is
sensitive to summer burning.  This study also demonstrated that reduced
fuel loads from moderate grazing kept fire intensity low so that plants
had almost fully recovered 1 year later.



FIRE CASE STUDIES
SPECIES: Schizachyrium scoparium | Little Bluestem 



2nd CASE NAME : 
Wind Cave National Park-Gobler's Ridge Fuel Moisture Treatments


REFERENCE : 
Worchester, L. L. 1979 [156]


SEASON/SEVERITY CLASSIFICATION : 
Dry Treatment - Late Spring/Severe
Medium Treatment - Late Spring/Severe
Wet Treatment - Late Spring/Moderate


STUDY LOCATION : 

Gobler's Ridge in Wind Cave National Park, South Dakota, approximately
50 miles (80 km) south of Rapid City, South Dakota, in the southern
Black Hills.


PREFIRE VEGETATIVE COMMUNITY : 
Burned communities were dominated by little bluestem and big bluestem
(Andropogon gerardii var. gerardii).  The area was protected from
grazing for 15 years prior to burning.  Preburn mean basal coverage and
preburn fuel quantities of little bluestem communities were:

                   Basal Coverage     Dead Fuel     Live Fuel
                                       (gm/m2)       (gm/m2)  
dry treatment          38%               369           10.2
medium treatment       48%               353           13.5
wet treatment          44%               390.2          9.7
         


TARGET SPECIES PHENOLOGICAL STATE : 
Early vegetative growth stage.  New growth comprised about 3 percent of
biomass.


SITE DESCRIPTION : 
Treatments on the Gobler's Ridge study area occured on plots between
3,084 and 3,349 feet (940 and 1,018 m).  Four replications of each
treatment including a control were applied on a west facing slope with
376 feet (114.5 m) of relief.  The dry and medium burns took place under
naturally occurring moisture conditions, while the surface soil and
mulch were artificially moistened for the wet burn.  The mean annual
precipitation is 18 inches (46 cm), with 70 percent falling between May
1 and September 30.  The frost-free period averages 120 days.


FIRE DESCRIPTION : 
Dry Treatment - burns on the dry treatment plots were rapid, producing
intense heat and very little smoke.  Consumption of vegetation took 3
minutes per 4x4 meter plot.  Flame height was 39 to 69 inches (100-174
cm) above ground level.  Flames appeared dense and covered the entire
plot rapidly.  Mineral soil was visible after burning.  The prescribed
burns took place on May 27, 1978.  Burning conditions were as follows:

    Mulch moisture content: 30%
    Soil moisture from 0 to.4 inches (0-1 cm): 33%
    Air temperature: 70 degrees F (21.1 C)
    Relative humidity: 37%
    Wind speed: 3 mph (4.8 kph)
    Maximum mean burn temperature: 1000 degrees F (538 C)

Medium Treatment - the general fire characteristics were the same as for
the dry burn treatment.  The prescribed burns took place on June 1,
1978.  Burning conditions were as follows:  

    Mulch moisture content: 37.6%
    Soil moisture from 0 to .4 inches (0-1 cm): 41%
    Air temperature: 51 degrees F (10.6 C)
    Relative humidity: 61%
    Wind speed: 2.6 mph (4.2 kph)
    Maximum mean burn temperature: 962.6 degrees F (517 C)
    
Wet Treatment - burns were slow to ignite, leaving a mosaic pattern with
much smoke produced.  Flame height was difficult to record due to the
intense smoke, which was apparently attributed to the high moisture
level of the mulch.  The prescribed burns took place on June 2, 1978.
Burning conditions were as follows: 

    Mulch moisture content: 45.6%
    Soil moisture from 0 to .4 inches (0-1 cm): 46%
    Air temperature: 55 degrees F (12.8 C)
    Relative humidity: 50%
    Wind speed: 2.6 mph (4.2 kph)
    Maximum mean burn temperature: 905 degrees F (485 C)
 


FIRE EFFECTS ON TARGET SPECIES : 
Initial consumption by weight was 47.2 percent for the dry burn, 30.2
percent for the medium burn, and 31.4 percent for the wet burn.
Vegetative recovery began within 2 weeks after burning.  Within a month
plants were green and succulent.  Wet burn treatments had slightly
taller vegetation, greater biomass, and faster growth during early
recovery stages.  Culm heights were taller after burning compared to
preburn measurements, but unburned controls had consistently taller
vegetation than burned areas.  Yield data showed no significant
differences in yield due to treatment.  Mean yields of little bluestem
in treatment plots are as follows:

Treatment                                   Yield
                                           (gm/m2)  
Control (unburned plots)                     106.5
Wet burn (45.6% mulch moisture)              117.1
Medium burn (37.6% mulch moisture)           116.9
Dry burn (30% mulch moisture)                114.9
  


FIRE MANAGEMENT IMPLICATIONS : 
Fuel moisture content at the time of ignition showed a significant
negative correlation to burn temperature and to percent consumption.  As
fuel mosisture content increased, more protective cover remained over
the soil after burning.  However, preburn and postburn vegetation
measurements indicate that fuel moisture levels did not have an adverse
effect on vegetive recovery, yield, or species composition.  All plots
showed rapid recovery.

Related categories for Species: Schizachyrium scoparium | Little Bluestem