FIRE EFFECTS
SPECIES: Poa pratensis | Kentucky Bluegrass 



IMMEDIATE FIRE EFFECT ON PLANT : 
Plant phenological stage at time of burning greatly influences fire
damage to herbaceous plants.  In general, as new foliage of perennial
grasses reaches full development major food reserves have been depleted,
so that plants are injured most from fires occurring at this time
[24,93].  Because Kentucky bluegrass is a cool-season grass, active in
the spring and fall, it is most susceptible to fire damage at those
times.  Late spring fires, after plants have been growing for about a
month or more, are the most damaging to Kentucky bluegrass.  Sampling at
the end of the first growing season after late spring burning shows that
Kentucky bluegrass basal cover and tiller density are typically much
lower in burned areas than in nearby unburned areas
[11,26,31,43,83,86,87,94,106].

Cool fires conducted when plants are dormant have little effect on
Kentucky bluegrass [62].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Kentucky bluegrass's fire response varies greatly depending on season of
burning, fire frequency, and postfire precipitation and soil moisture.

Season of burning:  Kentucky bluegrass postfire cover, biomass, and
flower stalk density are often greatly reduced during the first postfire
growing season by a single late spring fire.  Three examples are
presented to demonstrate rather typical first-year responses to late
spring burning: (1) in mixed-grass prairie unburned for several years in
north-central Nebraska, a single prescribed fire in mid-April or mid-May
greatly reduced Kentucky bluegrass basal cover in October, with cover on
burned plots only half that found on unburned plots [83], (2) after a
single mid-April fire on a tallgrass prairie site unburned for several
years in Iowa, Kentucky bluegrass relative biomass decreased from 80
percent to 25 percent during the first postfire growing season [53], and
(3) in the mountains of western Montana, Kentucky bluegrass frequency
was reduced 27.5 percent by a single late May fire in a
sagebrush/bunchgrass habitat type [18].

Kentucky bluegrass biomass production and density may be unaffected or
increase after burning at other times of the year, such as early spring,
summer, or fall.  It consistently recovers more quickly from burning at
these times of year than from burning in late spring.

In fields dominated by cool-season grasses in Wisconsin, Kentucky
bluegrass was reduced to one-fifth of its original density after 6 years
of annual burning in May; annual burning in March or October did not
affect Kentucky bluegrass density [23].  A different study in Wisconsin
showed that flower stalk density was reduced 70 percent by three annual
mid-May prescribed fires but was slightly increased by annual burning in
late March or early April [51].  Although summer grass fires can be
relatively intense, Kentucky bluegrass is dormant at this time.  It may
not be harmed by summer burning, and if precipitation is favorable, it
may even increase.  In mixed-grass prairie in north-central South
Dakota, Kentucky bluegrass frequency increased or remained unchanged on
uplands burned in early August followed by a wet spring, but decreased
on uplands burned in summer following a dry spring [103,104].  Kentucky
bluegrass's density tripled 1 year after late October and early November
low-intensity prescribed fires in aspen stands in Colorado [99].  In
ponderosa pine habitat types in British Columbia, Kentucky bluegrass
biomass was unchanged by an October prescribed fire [110].

Fire frequency:  Even after late spring burning, unless burned a second
time, Kentucky bluegrass density and cover often return to preburn
levels within 1 to 3 years.  For example, burning in May or June in Wind
Cave National Park, South Dakota, consistently reduced Kentucky
bluegrass canopy coverage, height, shoot density, flower stalk density,
and biomass during the first postfire growing season but not during
postfire years 2 and 3 [87].  In fact, biomass and density were often
greater on burned plots than on control plots during postfire year 2.
Other studies in mixed-grass prairie have shown Kentucky bluegrass cover
can be reduced for 2 or 3 years by a single late spring fire [34,83,94].

Kentucky bluegrass cannot withstand frequent spring burning.  In the
tallgrass prairie, its density decreases with increased fire frequency,
and it may be eliminated from sites that are burned annually for several
years [1,5,28,44,65,77].  In the Flint Hills of northeastern Kansas,
Kentucky bluegrass canopy coverage under different burning regimes was
30.3 percent on an area unburned for 11 years, 7.0 percent on an area
burned 1 and 5 years before sampling, and 0 percent on an area burned
annually for 5 years [1].  A similar response was observed on a
reconstructed tallgrass prairie in Illinois subjected to the following
burning treatments [44]:

not burned = unburned for 19 years
burned twice = burned Feb. 28, 1952 and April 16, 1959
burned three times = burned Feb. 28, 1952; April 16, 1959; and May 2, 1961 
burned four times = burned Feb. 28, 1952; April 16, 1959; May 2, 1961; and
                    May 10, 1962

Sampling at the end of the 1962 growing season showed the relative
percentage of bluegrass (P. compressa and P. pratensis) shoot biomass
decreased with increased burning frequency in two community types as
follows:

                               Burning Treatment  
                 not burned     burned twice    burned      burned
                                               3 times     4 times
Community type
big bluestem        23.4             18.3         4.6          0
indiangrass         18.6             15.9         3.3          0

Vogl [117] sampled several pine barrens in northern Wisconsin and
reported that Kentucky bluegrass frequency either increased or decreased
within 1 year of a single spring fire but that Kentucky bluegrass was
eliminated on sites spring burned more than once every few years.

Influence of postfire moisture:  Kentucky bluegrass is more susceptible
to fire damage on ridge sites than in depressions, especially in dry
years [52].  In fact, in swales and low prairie sites that receive
upslope moisture, Kentucky bluegrass often increases after spring
burning.  In bluegrass fields in Wisconsin, Kentucky bluegrass density
and biomass increased in depressions but decreased or remained unchanged
on ridgetops after two successive mid-April fires [129].  In eastern
South Dakota, Kentucky bluegrass recovered well from early May burning
if irrigated.  On burned but unirrigated plots, however, biomass
decreased sharply [12].  In eastern North Dakota, lowland and upland
prairies were burned on May 8, 1966.  Postfire data on August 4, 1966
showed that Kentucky bluegrass frequency increased on lowlands but
remained unchanged on uplands.  Biomass on both uplands and lowlands
decreased, but the decrease was much greater on uplands [43].  When
postfire growing season precipitation was "considerably below normal" in
Wind Cave National Park, South Dakota, Kentucky bluegrass biomass on
burned areas was less than half that found on unburned areas whether
burned on September 18, February 13, or April 10 [37].

In a sagebrush/rough fescue habitat type in Montana, Kentucky bluegrass
biomass increased the first summer after a mid-May prescribed fire [95].
This increase was unexpected because bluegrass should be susceptible to
burning at this time.  This increase may be due to the high moisture
availability in surface soils at this site due to concave slope shape.
In contrast, another study in western Montana found Kentucky bluegrass
decreased after a prescribed fire on May 24 in a sagebrush/fescue
habitat type [18].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
In the Mountain West, Kentucky bluegrass is often more abundant in
recently burned areas than in nearby unburned areas.  Sampling 2- to
36-year-old burns in sagebrush/grassland habitat types in southeastern
Idaho, Humphrey [56] found that Kentucky bluegrass was more abundant in
recent than in old burns.  McKell [76] compared four different-aged
burns in the Gambel oak (Quercus gambelii) zone of north-central Utah.
Kentucky bluegrass cover and density were higher 1 year after a November
fire and 2 years after a January fire, but on 9- and 18-year-old burns
cover and density were the same as on nearby unburned areas.

In the Klamath Mountains of southern Oregon, Kentucky bluegrass was a
codominant grass in open ponderosa pine stands that were burned annually
in the spring for 16 years [123].


FIRE MANAGEMENT CONSIDERATIONS : 
Burning for bluegrass control:  Frequent (annual or biennial) late
spring burning can be used to control Kentucky bluegrass and promote the
growth of warm-season grasses in the Midwest.  The timing of burning is
critical and should take place just prior to the resumption of
warm-season grass growth.  Such burning favors warm-season grasses
because they are dormant at the time of burning.  Conversely,
cool-season species like Kentucky bluegrass are harmed by late spring
fire because they resume growth in the early spring and are thus
actively growing at the time of burning.

In mixed-grass prairie, mid-May has proven to be the most effective time
to burn for Kentucky bluegrass control and has resulted in concomitant
increases in warm-season grasses [31,83].  In native bluestem prairie in
eastern Kansas, Kentucky bluegrass has been nearly eliminated from sites
annually spring burned for decades [112].  In aspen parkland in
northwestern Minnesota, 13 years of annual spring burning in late April,
when bluegrass was 4 to 6 inches high (10-15 cm), reduced Kentucky
bluegrass to about half its original percent composition [107].  After
10 years of biennial spring burning on the Curtis Prairie on the
University of Wisconsin Arboretum, Kentucky bluegrass frequency
decreased from 60 to 13 percent [6].

Burning to promote bluegrass growth:  When using prescribed fire to
promote the growth of cool-season species in the Northern Great Plains,
Kentucky bluegrass will probably respond best to very early spring
(March-April) or late summer (August-September) fires [130].

Disease control:  In Kentucky bluegrass commercial seed fields, burning
after harvest successfully controls several diseases.  It is effective
in controlling ergot (Claviceps purpurea); silver top, caused by the
fungus Fusarium trianctum; and the mite, Siteroptes cerealium.  Burning
also helps control leaf rust (Puccinia poae-nemoralis) and other fungi
harbored in crop residue [48].

Wildlife considerations:  Succulent new grass shoots arising from burned
mountain grasslands are highly palatable to wildlife.  On the Front
Range in Colorado, mule deer and bighorn sheep ate considerably more
Kentucky bluegrass on areas burned in late September than on nearby
unburned areas [102].  Following late October and early November fires
in aspen stands in Colorado, Kentucky bluegrass cover increased and thus
provided more forage to wildlife [99].

Where Kentucky bluegrass is desired for providing ruffed grouse drumming
ground cover, it can be burned when the soil is damp and plants are
dormant [122].

Burning under aspen:  Powell [90] reported that in south-central
Colorado, aspen/Kentucky bluegrass communities have only a moderate
probability of carrying a prescribed fire and only if livestock grazing
is deferred for at least one season.  For fall prescribed burning, the
likelihood of a relatively uniform burning treatment may be increased by
burning after aspen leaf fall [99].

Related categories for Species: Poa pratensis | Kentucky Bluegrass