FIRE CASE STUDIES
SPECIES: Cercidium microphyllum | Yellow Paloverde 



CASE NAME : 
Bulldog Canyon Prescribed Fire Study



SEASON/SEVERITY CLASSIFICATION : 
summer fire/low-severity


STUDY LOCATION : 
The study was located in Bulldog Canyon on the Tonto National Forest,
Arizona, at 33 degrees 15 minutes north latitude and 111 degrees 22
minutes west longitude.


PREFIRE VEGETATIVE COMMUNITY : 
A yellow paloverde-saguaro (Cercidium microphyllum-Carnegiea gigantea)
community covered Bulldog Canyon.  Standing dead biomass was assessed in
April before the fire.  Three microhabitats were evaluated:  (1) open
shrubless interspaces which covered 70 percent of the ground, (2) yellow
paloverde covered 8 percent, and (3) triangle bursage (Ambrosia
deltoidea) covered 15 percent.

Total perennial plant cover was measured prefire in April and
immediately postfire in June.  Twenty-three 12x26 feet (4x8 m) random
quadrats were located along parallel transects systematically placed
every 32.8 feet (10 m) throughout the study area.  Prefire mean total
perennial plant cover was 30.7 with a standard error of 3.4 percent.


TARGET SPECIES PHENOLOGICAL STATE : 
Phenological stages of the plants were not specifically mentioned.  At
the time of burning in June, yellow paloverde would be past flowering,
and fruits would be developing.


SITE DESCRIPTION : 
The study site was located in a desert canyon at 1,477 feet (450 m)
elevation.  Spring months are dry and warm in this semiarid climate.  No
appreciable precipitation was reported from the April prefire
assessments to the June prescribed fire.  No information was given on
specific topography, slope, or soils.


FIRE DESCRIPTION : 
Plots were placed to assess prefire surface fuels such as dead litter
and annual plants.  Twenty 7.9x7.9 inch (20x20 cm) plots were randomly
located in both the open and the triangle bursage microhabitats.
Thirty-two similar plots were located under eight yellow paloverde, one
at each of the four cardinal directions.  Average fuels are given in the
following table:

         microhabitat                   mean (standard error)g/sq m
        open                                     69.9 ( 7.5)
        triangle bursage                        143.3 (32.6)
        yellow paloverde                        319.4 (56.5)

The fire burned 12 June 1981.  Air temperatures ranged from 104 degrees
Fahrenheit (40 deg C) in the shade to 132.8 degrees Fahrenheit (50 deg
C) at 0.39 inch (1 cm) above an unshaded soil surface.  The relative
humidity remained at 29 percent during the fire.  Mean air movement
during the fire was low at 0.003 foot per second (0.001 m/sec) with
gusts up to 9 feet per second (2.75 m/sec).  Mean soil moisture in the
top 2 inches (5 cm) of soil was 0.61 and 0.80 percent for open and
shaded areas, respectively, with standard errors less than 0.1 percent.

Maximum temperatures for each microhabitat were estimated with
temperature sensitive pellets placed 0.39 and 0.78 inch (1 and 2 cm)
below the soil surface and 0.39 and 11.8 inches (1 and 30 cm) above the
soil surface.  Additional measurements were made with thermocouples at
0.39 inch (1 cm) below soil surface, at the soil surface, and 11.8
inches (30 cm) above the soil surface in the three microhabitats.

Temperatures were lowest in open microhabitats and highest in triangle
bursage areas (see table below).  Temperatures beneath yellow paloverde
were intermediate.  Fire had little influence on soil temperatures at
0.39 and 0.79 inch (1 and 2 cm) below the soil surface.  Temperatures at
0.39 inch (1 cm) above the soil surface burned the hottest.
Temperatures 0.39 inch (1 cm) above soil surface were significantly
(P<0.05) higher from temperatures 0.79 inch (2 cm) below the soil
surface for yellow paloverde and triangle bursage microhabitats.

                        mean maximum temperatures (deg C) during fire*
                                (standard error in parentheses)
vertical                                 microhabitat
location (cm)            open    yellow paloverde    triangle bursage
   30                  76(76)ax     167(33)abx         210(54)abx
    1                  88(51)ax     299(17) bxy        405(16) b y
  - 1                  61( 5) x      63( 7)  x          90( 9)  x
  - 2                  60( 0)ax      57( 2)a x          60( 2)a x

*Means not significantly different (P<0.05) within each vertical location
  are indicated by the same letter (a,b) and within microhabitats (x,y).

As fire moved through yellow paloverde microhabitats, it burned lightly
leaving some litter and duff unburned.  Additionally, the thick litter
and duff beneath yellow paloverde insulated the soil from the fire.

The increase in soil surface albedo after the fire was not significant
(P=0.08).  A small increase in water repellency was not expected to
create erosion or runoff problems.


FIRE EFFECTS ON TARGET SPECIES : 
No fire effects information specific to yellow paloverde was given.
Fires were low severity and did not consume all litter and duff below
yellow paloverde.  However, yellow paloverde has thin bark and
photosynthetic trunks that make it susceptible to top-kill by fire.


FIRE MANAGEMENT IMPLICATIONS : 
Desert fire temperatures are variable due to interactions of
microhabitats and fuel.  This prescribed fire did not alter physical
site characteristics such as albedo, soil water repellency, and
long-term microsite temperatures.  Perennial plant cover was
significantly (P=0.001) reduced which may lead to soil erosion.  Yellow
paloverde is very susceptible to fire, but no mortality data were given.

Related categories for Species: Cercidium microphyllum | Yellow Paloverde