FIRE EFFECTS
SPECIES: Bromus tectorum | Cheatgrass 



IMMEDIATE FIRE EFFECT ON PLANT : 
Cheatgrass is a highly flammable species due to its complete summer
drying, its fine structure, and its tendency to accumulate litter
[14,24].  Fire reduces cured plants to ash, but fire intensity may not
be great enough to consume the litter layer, even if associated shrubs
burn [28].  Seed on or in the mineral soil will probably survive even if
some of the litter is consumed.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Because of its flammability, cheatgrass greatly increases the fire
hazard on a site.  The rate of spread, size, and frequency of fire all
increase.  In Oregon, cheatgrass ranges were found to be 500 times more
likely to burn than noncheatgrass ranges.  A forest stand with a
cheatgrass understory may suffer loss of regeneration because of
frequent burning.  Cheatgrass fires spread very rapidly and may extend
into nearby stands of native vegetation and reduce the cover of valuable
perennial species.

Besides increasing fire frequency, the length of time cheatgrass remains
a hazard is longer than that for perennial grasses.  Cheatgrass dries 4
to 6 weeks earlier than perennials and is susceptible to fire 1 to 2
months longer in the fall [23].  Several growth and habitat
characteristics of cheatgrass make it a fire hazard:

        (1) it produces large quantities of seed that usually develop 
            into dense stands
        (2) it can provide a continuous fuel between grassland and 
            forest stands
        (3) it grows in the 6 to 22 inch precipitation zone, an area 
            with severe fire weather
        (4) it cures early in the fire season
        (5) its finely divided stems and flowering stem ignite readily
            when dry
        (6) it responds easily to any change in moisture conditions 
            because of its  structure

There is a correlation between plant color and moisture status during
the curing process.  Cheatgrass passes from green to a purple hue to a
straw color as it dries.  The relationship is as follows:

      Plant Color       Moisture Content (%)
      -----------       --------------------
         green                 > 100
         purple               30-100
         straw                 <  30

The onset of purple coloring should be taken as a warning that hazardous
fire conditions will develop within about 2 weeks.  Observation of
coloration should be done close-up.  A stand may appear to be purple
when most plant parts are still fairly green.  In Montana, the average
time required to change from purple to straw color (100 to 30 percent
moisture) was 14 days [19].


PLANT RESPONSE TO FIRE : 
Burning cheatgrass may reduce the next spring's production.  On the
Snake River Plain near Dubois, Idaho fall-burned areas produced from 1/7
to 1/50 as much as unburned sites.  The rate of spring growth was also
retarded.  Early in the season, plants were half as large as those from
unburned areas.  The difference became less evident as plants matured
[20].

Early summer fires produce similar results.  Plant number may be
reduced, but those that do develop are often larger and produce great
quantities of seed.  The earlier the fire, the greater the degree of
reduction [23].  Fires in pure cheatgrass stands tend to be less common
in the spring or early summer [24].  Fires generally occur in the summer
after seed is shed and is less vulnerable to burning.  Reduction of
cheatgrass under these conditions is not great [24].  After a midsummer
fire in northern Nevada, cheatgrass density was reduced, but individual
plants were tremendously productive.  Tiller and seed production both
were enhanced by burning.  On an unburned control plot, the maximum
number of seeds on a plant was 250.  On the burned plot, the minimum was
960 [27].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
The amount of litter or ash left on a site is a good indicator of the
amount of cheatgrass seed still surviving.  Seed is concentrated in the
litter, especially around shrubs.  Since cheatgrass produces prolific
quantities of seed, even a large reduction in the seed pool will not
prevent it from regaining dominance on a site.  In a northern Nevada
study, cheatgrass seed was reduced approximately 96 to 99 percent, from
5,000 to 8,000 seeds per square meter to 20 to 300 seeds per square
meter [28].  However, as few as 43 seeds per square meter are required
to reduce establishment of crested wheatgrass (Agropyron cristatum) and
633 seeds per square meter may prevent the establishment of perennials
[7].


FIRE MANAGEMENT CONSIDERATIONS : 
NO-ENTRY

Related categories for Species: Bromus tectorum | Cheatgrass