FIRE EFFECTS
SPECIES: Bouteloua gracilis | Blue Grama 



IMMEDIATE FIRE EFFECT ON PLANT : 
Fire generally top-kills blue grama.  Rhizomes are usually unharmed.
This species is generally is less damaged when burned during the spring
than when burned during the summer or fall [11,53].  During the spring
when soils are moist, heat penetration into the soil is slight, and
damage to underground parts is minimal [53].  Blue grama is usually
unharmed by fires in years with above normal winter and spring
precipitation [58].  It can be severely damaged by fires that occur
during drought years [53,58].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
An Arizona study indicated that lethal temperatures of culm bases of
sensitive perennial grasses such as blue grama closely approximated
existing air temperatures at or near ground level during the hot, dry
months of summer.  During cooler, moister periods, the lethal
temperatures of culm bases were much higher.  Over 2 years, the lethal
temperature for blue grama growing in pinyon-juniper woodland ranged
from 108 to 128 degrees Fahrenheit (60.0-71.2 deg C) [25].


PLANT RESPONSE TO FIRE : 
Blue grama response to fire varies.  It may be harmed, largely
unaffected, or increased by fire.  Its response depends on season of
burning, soil moisture, temperature, plant community composition, and
five severity.  Recovery is more rapid during years of above average
precipitation.  Recovery time ranges from 1 to 4 years or more depending
on conditions [53,58].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
A Texas study compared postfire blue grama yields after fires carried
out in dry and wet years (winter-spring precipitation 0 to 40 percent
above normal).  Blue grama was tolerant of fire during wet years; there
was no loss in herbage yield by the end of the first growing season.
Results were as follows [58]:

        Burned-lb/ha (kg/acre)          Unburned-lb/ha (kg/acre)

               Current Growth   Litter           Current Growth   Litter
-----------------------------------------------------------------------------
Wet   1st Yr-  1,680 (1,888)      ---     ---    1,429 (1,606)    2,474 (2,780)
Yrs.  2nd Yr-  1,369 (1,530)      699    (784)   1,247 (1,401)    2,584 (2.904)
      3rd Yr-  2,142 (2,407)    1,750  (1,966)   1,754 (1,971)    1,932 (2,171)

Dry   1st Yr-  1,100 (1,236)      ---     ---    3,150 (3,539)      500  (562)
yrs.  2nd Yr-  1,840 (2,067)      250    (281)   3,000 (3,371)      500  (562)
      3rd Yr-  2,600 (2,921)      330    (371)   2,650 (2,978)      500  (618)

When a Central Great Plains blue grama-buffalo grass prairie was burned
during the spring of a dry year, yields recovered to 35, 62, and 97
percent at the end of the first, second, and third postfire growing
seasons [58].  In a New Mexico study, blue grama herbage was reduced by
30 percent the first year after an early spring fire, but with adequate
moisture recovered completely by the second year [15].

At the end of the first growing season after an October fire in
Nebraska, productivity of blue grama on burned plots was less than on
adjacent control plots [34]:

                       Blue Grama - Phytomass (g/sq m)

                  June        July        August       October 
Burned Area       21.2        21.5        23.1         12.1
Unburned Control  16.0        22.4        30.3         24.0

However, in Montana, White and Currie [53,59] found that spring burning
reduced blue grama yield early in the growing season, but increased
productivity later in the same season.  The following examples
illustrate the variability in response of blue grama to fire:
 
Location                   Recovery Time/Response         Reference

Shortgrass prairie         3 years                        Launchbaugh 1964
                           harmed by fire in drought      Wright & Bailey 1980 
                           yrs.; tolerant when spring-
                           winter precipitation is 
                           greater then normal 

Mixed-grass prairie        increased or unaffected        Schacht & 
                           by spring burning                Stubbendieck 1985
                                                          Wright & Bailey 1980

Mesic mixed prairie        reduced or increased           Wright & Bailey 1980

Tallgrass prairie          increased after early          Wright &  Bailey 1980
                           spring or winter fire

Blue Grama Steppe (ND)     4+ years                       Daubenmire 1968

Canadian Great Plains      3 years                        Daubenmire 1968
                                                          Wright & Bailey 1980 
                           reduced by spring fire         Daubenmire 1968

Central Great Plains       2-3 years                      Wright & Bailey 1980
                           harmed by fire in dry years

Chihuahuan Desert          3 years                        Ahlstrand 1982

Chihuahuan Desert          increased or recovered         Ahlstrand 1982
  mountain shrub           3 growing seasons  
                           after fire 

New Mexico                 2 years                        Dwyer & Pieper 1967


FIRE MANAGEMENT CONSIDERATIONS : 
Application of fertilizers such as ammonium sulfate significantly
influences yields of blue grama on burned and unburned plots.  In New
Mexico, plots burned but not fertilized produced 9.0, 11.3, 15.6, and
56.3 percent more blue grama during October, January, June, and April,
respectively, than did control plots [14].  Plots burned and fertilized
produced 103, 116.9, 164.4, and 173.6 percent more forage in October,
January, June, and April than did the control.  Plots fertilized in June
and left unburned produced 200.1 percent more blue grama than the
control [14].

The nutrient content of blue grama is altered by fire.  June crude
protein levels following a low-intensity April fire in New Mexico were
16.1 percent compared with 14.8 percent on unburned control plots [15].
In a Nebraska study, several species of grasshoppers showed a marked
preference for blue grama from burned areas, suggesting potentially
higher nutritional value of grama on burned sites [34].

A 3- to 4-month rest from grazing is recommended after fire [57].
Burning blue grama during drought years should be avoided if
productivity is to be maintained [59].

Related categories for Species: Bouteloua gracilis | Blue Grama