FIRE CASE STUDIES
SPECIES: Bromus vulgaris | Columbia Brome 



CASE NAME : 
Fire Intensity Effects/Understory/Benewah Co., ID


REFERENCE : 
Armour, C. D.; Bunting, S. C.; Neuenschwander, L. F. 1984 [3]


SEASON/SEVERITY CLASSIFICATION : 
fall/low intensity
fall/high intensity


STUDY LOCATION : 
Coeur d'Alene Indian Reservation, Benewah County, Idaho


PREFIRE VEGETATIVE COMMUNITY : 
Prefire vegetation was dominated by seral stands of ponderosa pine
(Pinus ponderosa) with an understory of shrubs and perennial graminoids.
Prominent shrubs included oceanspray (Holodiscus discolor), ninebark
(Physocarpus malvaceus), chokecherry (Prunus virginiana), baldhip rose
(Rosa gymnocarpa), and common snowberry (Symphoricarpos albus).
Prominent graminoids included Columbia brome (Bromus vulgaris),
bluebunch wheatgrass (Pseudoroegneria spicatum), pinegrass
(Calamagrostis rubescens), blue wildrye (Elymus glaucus), and Idaho
fescue (Festuca idahoensis).


TARGET SPECIES PHENOLOGICAL STATE : 
Phenological state of Columbia brome was not given.  Since the fires
were conducted in the fall of 1978 it was probably approaching
senescence.


SITE DESCRIPTION : 
Elevation of the study area is approximately 2,887 feet (880 m) on
gently rolling hills.  Average annual precipitation is 22 inches (560
mm), the majority of which falls from October to March.  A 3.9-inch
(10-cm) layer of volcanic ash from the May 18, 1980, eruption of Mount
St. Helens was present on the soil.  The study area had been
selectively logged three times at 10-year intervals, the last in 1977.
The sites had not burned for 44 to 62 years.  Prior to fire suppression,
the sites had a mean fire return interval of approximately 22 years.
Grazing by domestic livestock had not occurred on the sites for at least
30 years.


FIRE DESCRIPTION : 
Three fire treatments were employed:  unburned control, low-intensity,
and high-intensity fires.  Three areas of similar stand history and
composition were each subdivided into nine 0.5 to 2.47 acre (0.2-1.0 ha)
units and burned under under varying temperature, fuel moisture, and
relative humidity conditions, resulting in fires of varying intensity.
Three replications of unburned, low-, and high-intensity treatments were
sampled within each location.  Fireline intensity ranged from 25 to 194
kcal/m-s on low-intensity sites; it ranged from 30 to 3,034 kcal/m-s on
high-intensity sites.  Flame length averaged 2.95 feet (0.9 m), with a
range of 0.33 to 5.58 feet (0.1- 1.7 m), for both fire intensities.
More duff was consumed on high- than on low-intensity sites.  The
average depth of duff on the unburned sites was 2.6 inches (6.6 cm); the
depth on low-intensity sites after burning was 1.6 inches (4.0 cm); the
depth on high-intensity sites was 0.5 inches (1.3 cm).


FIRE EFFECTS ON TARGET SPECIES : 
Columbia brome decreased after fire.  The reduction was the result of
prolonged duff smoldering which destroyed rhizomes.

Mean canopy cover and frequency of Columbia brome after fire treatments
were:

                             Fireline Intensity       

                     Control         Low          High

        Cover          0.7 a         0.3 b        0.3 b
        Frequency     15.5 a         7.7 b        4.6 b
   

                                Postfire Year

                         1            2            3

        Cover           0.5 a        0.7 a        0.2 b
        Frequency       9.1 b       14.5 a        4.2 c

Means within a row followed by the same letters are not significantly
  different (p<0.1).

There was an unexpected rise in Columbia brome frequency from 1979 to
1980 in all treatments.  This was probably due to the volcanic ash layer
resulting from the Mount St. Helens eruption rather than to any fire
effects.  The ash cap acted as a moisture barrier, retarding
evaporation.  By 1981 this cap had broken up.


FIRE MANAGEMENT IMPLICATIONS : 
The response of Columbia brome to fire appeared to vary with the amount
of duff reduction, regardless of fireline intensity.  High-intensity
fires were conducted when fuels were drier than they were for
low-intensity fires.  The reduction of Columbia brome was the result of
rhizome destruction.  In order to preserve as much Columbia brome cover
on a site as possible, fires should be conducted when the duff is moist.

Related categories for Species: Bromus vulgaris | Columbia Brome