FIRE EFFECTS
SPECIES: Sporobolus wrightii | Big Sacaton 



IMMEDIATE FIRE EFFECT ON PLANT : 
In southeastern Arizona a February 1985 wildfire "consumed" all
available big sacaton forage [12].  At the Research Ranch in
southeastern Arizona, Bock and Bock [2] studied the impact of fire on an
ungrazed sacaton grassland community.  Height and percent cover of big
sacaton were reduced until postfire year 2 on sites burned in summer
or winter.  "Hot" early summer fires may kill big sacaton plants [2].  


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Big sacaton sprouts after top-kill by fire [53].  Big sacaton may
recover to prefire coverage in 2 to 3 years on ungrazed sites [4].
Postfire recovery is influenced by fire severity [2] and season of
burning [14].  In southeastern Arizona in 1975 and 1976 three wildfires
occurred in an ungrazed big sacaton grassland community [2].  The first
two fires occurred in mid-May and mid-June 1975, and the third in
February 1976.  Permanent study sites were established on the two summer
burns and on adjacent unburned (control) areas in August 1975.  In
February 1976 a wildfire occurred on one of the control sites which then
became the winter burn study site.  The summer burns occurred during
hot, dry weather and were probably more severe than the winter burn [2].
Big sacaton postfire percent cover on the four study sites is listed
below; prefire cover was not reported.

                           summer burns             winter burn
          control    first year    second year       first year

sacaton     74               35            70            50

In postfire year 1, big sacaton percent cover was less on burned than
unburned sites, and less on the summer than winter burns.  It was
similar to prefire cover in the second year [2].  

In southeastern Arizona the impacts of burning on big sacaton forage
quality and quantity were studied [14,15].  Plots were burned with a
headfire in winter (Feb. 6), summer (July 10), and fall (Oct. 2) 1980,
1981, and 1982.  Plots had been lightly grazed for 5 years prior to
burning.  The time from ignition to total forage consumption by fire was
recorded by plot.  Fuel moistures and weather conditions were as follows
[14]:

            fine fuel-moisture     wind speed     air temperature
            % oven-dry weight     mi/hr (km/hr)    deg F (deg C)

winter           10-30              10 (16)        50-64 (10-18)
summer           20-25              8-15 (13-24)   84-86 (29-30)
fall             45-55              8-10 (13-16)   66-77 (19-25)

Big sacaton green forage at the peak of the summer growing season (Aug.
21) 1,2, and 3 years after treatment was as follows:

                   number of growing seasons after treatment
  
                         1              2              3
                                    
                                      kg/ha

winter                400-735        690-850         595-695
summer                700-865        850-935         1,375-1,590
fall                  260-725        575-805         745-890
untreated             1,695-1,900    1,365-1,720     1,650-2,000

Green forage availability for the 3 treatment years was consistently
greater on untreated plots than on burned plots.  In postfire years 1
and 2, big sacaton green forage was greater on summer than on winter- or
fall-burned plots.  By postfire year 3 green forage on summer-burned
plots was nearly equivalent to that on unburned plots [14].  At postfire
year 1, standing crops were 60 percent less on spring- and fall-burned
plots.  At postfire year 2, live biomass on spring-burned plots was 30
percent less than on control plots.  On fall-burned plots, 50 percent of
plants failed to produce leaves the following spring.  Removing hte
standing dead biomass which insulates against cold temperatures may have
killed the plants [56].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Land managers have traditionally recommended burning big sacaton
grassland in either fall or winter [7,14].  According to Cox [14],
winter and fall burns have a detrimental effect on big sacaton plant
production for at least three summer growing seasons [14].  Loss of
summer-formed leaves inhibits formation of winter leaves, and root
crowns may be damaged by frost.  Winter burning may reduce plant litter,
making green foliage more available to livestock but reducing the
long-term viability of big sacaton plants [17].  

In Arizona seed-eating rodents are abundant on burned big sacaton sites.
Bock and Bock [2] propose that ideal wildlife habitat would be mosaic of
big sacaton stands in various stages of postfire succession.

Related categories for Species: Sporobolus wrightii | Big Sacaton