FIRE CASE STUDIES
SPECIES: Ambrosia deltoidea | Triangle Bursage 



CASE NAME : 
Bull Dog Canyon/Arizona Prescribed Fire


CREFERENCES : 
Cave, G. H., III. 1982. [7]
Patten, Duncan T.; Cave, George H. 1984 [23]


SEASON/SEVERITY CLASSIFICATION : 
summer/low-severity


STUDY LOCATION : 
The study was located in Bulldog Canyon in Tonto National Forest,
Arizona, at 33 degrees 15 minutes north latitude and 111 degrees 33
minutes west longitude.


PREFIRE VEGETATIVE COMMUNITY : 
The prefire vegetative community was typical of the Upper Sonoran Desert
paloverde-cactus-shrub association (Cercidium spp.-Opuntia spp. and
Carnegiea gigantea-Ambrosia spp.).  Plants occupied about one-third of
the total ground cover.  Triangle bursage (A. deltoidea) occupied about
15 percent of the total ground cover.  Annual forbs and grasses in this
association are abundant after winter and heavy summer rains, providing
enough fuel to carry a fire.


TARGET SPECIES PHENOLOGICAL STATE : 
At the time of the fire, triangle bursage would have been flowering
and/or fruiting.


SITE DESCRIPTION : 
Topography is flat except for one small, dry wash bisecting
the site.  The soil is composed of sandy loam argids with a desert
pavement surface.  Elevation at the site is 1,485 feet (450 m).

The burn site is adjacent to an area burned by wildfire on April 26,
1980.  The 1980 wildfire may have been more severe since both 1979 and
1980 were years of above average precipitation, and the standing
herbaceous vegetation was probably relatively lush.  The study compares
the prescribed fire and the wildfire sites.


FIRE DESCRIPTION : 
The fire was ignited on June 12, 1981.  Conditions were typical for
summer months in the Upper Sonoran Desert.  Air temperatures ranged from
104 degrees Fahrenheit (40 deg C) in the shade to 132.8 degrees
Fahrenheit (56 deg C) 0.4 inches (1 cm) above the unshaded soil surface.
Relative humidity remained at 29 percent during the fire.  Mean air
movement for the duration of the fire was low at 0.001 meters per
second.  Mean wind velocity for gusts was 2.75 meters per second.  Mean
soil moisture percent in the upper 2 inches (5 cm) of soil was 0.61
percent in open areas and 0.80 percent in shaded areas.  Litter fuel
averaged 143.3 grams per square meter.


FIRE EFFECTS ON TARGET SPECIES : 
In 1981, 1 year after the wildfire and immediately following the
controlled burning, the density of triangle bursage was greater on the
wildfire site than on the prescribed fire site, mainly because of the
establishment of triangle bursage seedlings on the wildfire site.
Postfire cover measurements were nearly the same.

Triangle bursage density was reduced by 82 percent on the prescribed
fire site immediately after the controlled burning.  The prefire density
of triangle bursage on the prescribed fire site was 6,275 plants per
hectare.  Immediately after the controlled burning, triangle bursage
density was 1,141 plants per hectare.  One year later, triangle bursage
density had not changed significantly.


FIRE MANAGEMENT IMPLICATIONS : 
NO-ENTRY

Related categories for Species: Ambrosia deltoidea | Triangle Bursage