FIRE CASE STUDIES
SPECIES: Panicum obtusum | Vine-Mesquite 



CASE NAME : 
Effects of fire on an ashe juniper community


REFERENCE : 
Wink, R. L.; Wright, H. A. 1973 [43]


SEASON/SEVERITY CLASSIFICATION : 
Spring 1970/light
Spring 1971/moderate


STUDY LOCATION : 
The study occurred on 2,632 acres (1,053 ha) of the Beckham Ranch in
Callahan County, 15 miles (24 km) southeast of Baird, Texas.
 


PREFIRE VEGETATIVE COMMUNITY : 
The vegetative community is a mixed-grass prairie interspersed with ashe
juniper (Juniperus ashei) and several species of oak (Quercus spp.).
The major grass species are little bluestem (Schizachyrium scoparium),
sideoats grama (Bouteloua curtipendula), buffalograss (Buchloe
dactyloides), vine-mesquite, Texas wintergrass (Stipa leucotricha), and
tall grama (Bouteloua pectinata).  The large junipers were dozed in
1965.


TARGET SPECIES PHENOLOGICAL STATE : 
Vine-mesquite was dormant.


SITE DESCRIPTION : 
The site is level to undulating with a few slopes greater than 20
percent.  Elevation is 1,205 to 1,405 feet (365-425 m).  The soils are
sandy loams which are slowly to moderately permeable.  Moisture
retention is moderate, and soils are fertile enough to provide good
grass production.  The limestone bedrock is cracked, forming deep
pockets capable of supporting deep-rooted grasses.  The average
precipitation is 24 to 28 inches (60-70 cm) per year.  During the course
of the study the precipitation varied from a near normal year in 1970,
with 23 inches (58.2 cm) falling from November 1969 to May 1970, to a
dry year in 1971, with 6.5 inches (16.5 cm) falling from November 1970
to May 1971.


FIRE DESCRIPTION : 
The amount of heavy fuels on the site varied from 40,000 to 60,000
pounds per acre (44,800-67,200 kg/ha).  Light fuels varied from
685 to 3,185 pounds per acre (768-3,568 kg/ha).  The leeward sides were
ignited prior to the start of the headfires.  

Atmospheric conditions at the time of the ignition of the headfires were
as follows:

                                25 March 1970   27 March 1971

air temperature                 75 degs F       86 degs F
                                (24 degs C)       (30 degs C)  
humidity                        35%             25%
wind speed                      10 mi/hr        15 mi/hr
                                (16 km/hr)      (25 km/hr)              

Fire intensity depended on the amount of fuels.  A cool to moderate fire
was carried in areas with 1,000 pounds per acre (1,120 kg/ha) of light
fuels.  Those areas with heavy fuels yielded hot fires. 


FIRE EFFECTS ON TARGET SPECIES : 
During the dry year (1971) vine-mesquite opportunistically used the
higher soil temperatures and litter removal to produce twice the
vegetative growth of the control.  During the wet year (1970)
vine-mesquite had a significant growth increase, but not as dramatic as
in the dry year.  The production of vine-mesquite (kg/ha) was as
follows:

Year            Burned          Unburned        Difference

1970            4458            3434            +30%
1971            7777            3669            +112%

The burn in the dry year (1971) resulted in the increased growth of
vine-mesquite because it occupies mesic microsites, but resulted in the
reduced growth of litle bluestem, tall grama, and side-oats grama.  This
reduced growth resulted from increased drought stress brought on by the
fire.  Because vegetative recovery was slow, the soil was exposed to
wind and water erosion for several months, thus increasing soil loss.

The burn in the wet year (1970) resulted in an increase in growth of all
species but one, side-oats grama.  With good soil moisture the plants
recovered rapidly, and soil loss was negligible.


FIRE MANAGEMENT IMPLICATIONS : 
When planning a prescribed burn, soil moisture should be a primary
concern for the land manager.  With high soil moisture, the vegetation
recovers rapidly, and the loss of soil from wind and water erosion is
minimal.

Related categories for Species: Panicum obtusum | Vine-Mesquite