FIRE EFFECTS
SPECIES: Panicum virgatum | Switchgrass 



IMMEDIATE FIRE EFFECT ON PLANT : 
Fire removes aboveground parts of switchgrass.  Switchgrass litter is
resistant to matting down.  This standing dead material is apparently a
good fuel source which readily carries fire.

Most switchgrass plants survive fire because of protected underground
rhizomes, but the vigor and extent of postfire tiller growth is
dependent upon season of burning, fire intensity, and plant growth form
(sod- or bunch-forming ecotype).  If burned when dormant, switchgrass is
not harmed by fire and, drawing upon stored carbohydrate reserves,
resumes growth in the spring as usual.  Regrowth following summer
burning, however, is hampered because (1) switchgrass's apical meristems
are elevated above the soil surface at this time and can be consumed by
fire and (2) carbohydrate reserves for initiation of new growth are low
at this time of year.  If the apical meristem is destroyed by fire, new
growth must come from the initiation of new tillers from crown or
rhizome buds [64].  In Nebraska, switchgrass meristems protrude above
the soil surface beginning in mid-June, and extend more than 1 inch (2.5
cm) above the soil surface by late June [9,33].

During summer grass fires, fire intensity is dependent upon fuel
quantity.  Where fuel loads are heavy, grass fires can be relatively
intense, resulting in the consumption of switchgrass's aboveground
meristems.  Conversely, under light fuel loads, meristems may survive.
For example, during summer prescribed fires in Oklahoma tallgrass
prairie (Andropogon-Sorgastrum-Panicum), fire intensity at the soil
surface (measured by fire temperature and duration) was four times as
high on ungrazed plots (fuel load = 1,031 grams/meter square) than on
grazed plots (fuel load = 443 grams/meter square).  Postfire recovery on
grazed plots was quicker, with regrowth coming mostly from tillers free
of apical meristem damage.  On ungrazed plots, new growth came from
newly initiated tillers from rhizomes, but was not vigorous, and 2
months after the fire tiller density remained well below preburn levels
[25].

Both sod- and bunch-forming switchgrass ecotypes were burned annually in
January in Georgia [7].  No sod-forming types were harmed by fire, but
numerous bunch type clones were killed.  Bunch types often had the
center of the bunch elevated above the soil surface, leaving the roots
and rhizomes exposed.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Switchgrass cover and biomass often increase slightly to moderately
following dormant-season burns.  It generally responds best to burning
in late spring, just prior to the start of new growth.  For example, in
moderately grazed pastures that were annually burned over a 16-year
period in the Flint Hills of Kansas, switchgrass cover was higher under
late spring burning (May 1) than under early spring (March 20),
midspring (April 10), or no burning [4,47].  Prescribed early and
mid-May burning in North Dakota increased switchgrass canopy coverage,
but late June burning did not.  First and second year increases were as
follows [57]:

                               Switchgrass Canopy Coverage (%)
  
                     June 1973  August 1973      June 1974  August 1974

burned May 8, 1973      1.2        2.7              0.6         1.9  
control                 0.7        0.4              0.15        1.2

burned May 14, 1973     2.8        5.85             1.55        5.1
control                 2.1        3.5              0.65        2.7

Numerous other studies have documented increases in switchgrass biomass,
density or cover in the first postfire growing season following dormant
season burns [16,39,60,62,66].  

Seedstalk production may increase dramatically following burning.
Following mid-May burning in North Dakota, switchgrass seedstalk density
on burned plots was more than double that of unburned plots (25.2 vs
10.4/meter square) during the first postfire year [57].  A nearly
identical flowering response occurred in central Iowa following a
mid-April prescribed fire, where the number of switchgrass
inflorescences was more than double on burned versus unburned plots
[60].  In eastern Kansas, a 5-year-old planted switchgrass stand burned
in late April yielded 250 pounds of seeds per acre (280 kg/ha), while an
unburned portion of the same stand yielded only 190 pounds of seeds per
acre (212 kg/ha) [13].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Switchgrass may increase modestly following late spring burning if
moisture conditions following the fire are favorable, but it does not
exhibit as dramatic an increase as other warm-season grasses such as big
or little bluestem.  Knapp [41] attributes this to switchgrass's growth
form.  It has a high ratio of reproductive to vegetative shoots and is
therefore much less leafy than big bluestem.  Furthermore, switchgrass
litter does not matt down, and sunlight reaches emerging shoots even in
unburned stands.  In comparison, little sunlight reaches shoots in
unburned big bluestem stands.  Thus big bluestem often increases
dramatically with the favorable conditions of increased solar radiation
and warmer soil temperatures following burning, while preburn and
postburn environments in switchgrass stands are not as different.

Morrison and others [53] felt that fires in the Nebraska Sandhills may
affect the vegetation differently than fires in other grasslands because
the sandy soils become droughty late in the growing season, and thus
increases in grass cover do no occur.  On uplands of the Sandhills, they
found that switchgrass cover 1 year after an October wildfire was
slightly lower on burned areas than unburned areas.


FIRE MANAGEMENT CONSIDERATIONS : 
Switchgrass needs periodic fire to maintain its vigor and abundance.  On
the Konza Prairie in Kansas, it showed a linear decrease in abundance
with time since burning.  On areas burned annually in the spring, it was
a codominant with big bluestem, little bluestem, and indiangrass [32].  

In prairie plantings and in newly seeded stands, prescribed late spring
burning can be used to maintain or increase switchgrass biomass and
control undesirable cool-season grasses.  Cool-season grasses are harmed
by this treatment, because they begin growth early in the spring, and
are actively growing at the time of burning.  Conversely, warm-season
grasses begin growth in late spring, and are thus dormant at the time of
burning.  Switchgrass was the dominant warm-season grass on a 6-year-old
prairie planting in Wisconsin.  In late August following a prescribed
fire on May 15, warm-season grass biomass on the Wisconsin planting
increased 10 percent, while cool-season grass biomass decreased 81
percent [19].  Summer fires, however, favor cool-season grasses.  For
example, in north-central South Dakota, switchgrass and big bluestem
dominated lowlands burned in late April, while cool-season grasses
(Agropyron, Poa, Stipa) dominated lowlands burned in August [66].

In central North Dakota, Duebbert and others [21] recommend burning
warm-season grasses between May 15 and June 15.  Prescribed burning
guidelines have been outlined for the Northern Great Plains [80].  

Related categories for Species: Panicum virgatum | Switchgrass