|
Wildlife, Animals, and Plants
|
|
FIRE CASE STUDIES
SPECIES: Poa secunda | Sandberg Bluegrass
FIRE CASE STUDIES :
1. Prescribed Fire in Mt. Big Sagebrush/CA; OR
2. Summer Fire/Combustion Chamber/ID
1st CASE NAME :
Prescribed Fire in Mt. Big Sagebrush/CA; OR
REFERENCES :
Champlin, M. R. 1982 [14]
Champlin, M. R.; Winward, A. H. 1979 [73]
FIRE CASE STUDY AUTHORSHIP :
Janet L. Howard, 1997
SEASON/SEVERITY CLASSIFICATION :
Lava Beds: late spring/moderate
Crooked River: fall/severe
STUDY LOCATION :
The study was conducted at two locations. The first study area was on
Lava Beds National Monument, California. The second was on the Crooked
River National Grassland near Prineville, Oregon [1,2].
PREFIRE VEGETATIVE COMMUNITY :
Four plant communities on two locations were burned. Mountain big
sagebrush (Artemisia tridentata ssp. vaseyana) was the dominant prefire
shrub in all four communities. At Lava Beds National Monument, the
relatively mesic north-facing slopes were occupied by mountain big
sagebrush/Idaho fescue (Festuca idahoensis) communities that included
Sandberg bluegrass (Poa secunda), bluebunch wheatgrass (Pseudoroegneria
spicata), Thurber's needlegrass (Stipa thurberiana), prairie junegrass
(Koeleria macrantha), and cheatgrass (Bromus tectorum), in descending
order of frequency. Swales and hilltops were dominated by mountain big
sagebrush/bluebunch wheatgrass-Thurber's needlegrass communities.
Sandberg bluegrass and prairie junegrass were also present in these
communities, with lesser amounts of bottlebrush squirreltail (Elymus
elymoides) and cheatgrass. At Crooked River National Grasslands, the
prefire community was mountain big sagebrush/bluebunch wheatgrass.
Cheatgrass, Sandberg bluegrass, Idaho fescue, and bottlebrush
squirreltail were also present, in descending order of frequency [1,2].
TARGET SPECIES PHENOLOGICAL STATE :
Sandberg bluegrass was dormant and desiccated at time of burning on both
sites [2].
SITE DESCRIPTION :
Lava Beds site: Mean annual temperature is 47.7 degrees Fahrenheit (8.7
deg C); mean annual precipitation is 14.5 inches (363 mm). The site is
on a broken monocline at 4,465 feet (1,353 m) elevation. Slopes vary
from 0 to 8 percent.
Crooked River site: Mean annual temperature is 45.1 degrees Fahrenheit
(7.3 deg C); mean annual precipitation is 14.0 inches (349 mm). The
site is on a 60 percent, northwest-facing slope at 3,379 feet (1,024 m)
elevation. The upper 8 inches (20 cm) of soil is tuffaceous gravel less
than 0.8 inch (2 cm) in diameter with little soil between the coarse
material [1].
FIRE DESCRIPTION :
The purpose of the prescribed fires was to reduce mountain big sagebrush
cover and increase cover of bunchgrasses. Four plant communities were
burned in 1976. Ten 20 x 50 cm plots were located along four 15-m
transects for determining herbaceous frequency, basal cover, height, and
production [1]. The Lava Beds fire was a late spring burn conducted 2
days after 0.5 inch (13 mm) of rain. The Crooked River fire was a fall
burn conducted 4 days after 0.4 inch (10 mm) of rain. Shrub fuel
loading was similar at the four sites. Strip head fires were used to
ignite each area. Flame lengths were 3 times greater and rate of fire
spread 10 times faster at Crooked River than at Lava Beds, resulting in
a fire intensity much greater than at Lava Beds [2].
Average weather conditions at the two study locations during prescribed
burning were [1]:
Relative Wind Wind
Location Temperature Humidity Speed Direction
(deg F) (%) (mi/hr)
-------------------------------------------------------------
Lava Beds 73 25 6.6-9.6 NW
Crooked River 73 31 0.0-6.6 N-NE
-------------------------------------------------------------
Prefire grass loading (kg/ha) was as follows. Since big sagebrush was
the dominant shrub in all four communities, communities are identified
by the dominant bunchgrass [1].
______________________________________________________________________________
| Lava Beds Crooked River|
| -------------------------------------- -------------|
| Wheatgrass- Wheatgrass- |
| Fescue Needlegrass Needlegrass Wheatgrass |
|----------------------------------------------------------------------------|
|Sandberg bluegrass 10.0 10.0 10.0 10.0 |
|Total 540.0 811.5 343.6 549.9 |
|____________________________________________________________________________|
Fuel moisture contents (%) during prescribed burning were [1]:
Location Grass Shrub Foliage 1-hour Fuel 10-hour Fuel
-----------------------------------------------------------------------
Lava Beds 39.9 96.9 7.5 5.4
Crooked River 35.2 118.3 26.9 26.2
------------------------------------------------------------------------
Fire behavior on four plant communities follows [1].
Lava Beds Crooked River
----------------------------------- -------------
Swale Hilltop
----- -------
Wheatgrass- Wheatgrass-
Fire Behavior Fescue Needlegrass Needlegrass Wheatgrass
-------------------------------------------------------------------------
grass flame height 2.6 ft 3.0 ft 1.65 ft 8.9 ft
shrub flame height 11.2 ft 7.2 ft 7.2 ft 20.1 ft
rate of fire spread 3.0 ft/min 3.0 ft/min 17.8 ft/min 265.65 ft/min
fireline intensity* 340 350 220 2000
-------------------------------------------------------------------------
*BTU/ft/min
FIRE EFFECTS ON TARGET SPECIES :
Sandberg bluegrass productivity generally increased after prescribed
burning, although response differed by site, fire intensity, and
postfire weather conditions. At Lava Beds, precipitation in the first
postfire winter was 130 percent of normal. Precipitation at Crooked
River in the first postfire winter was 86 percent of normal [1,2].
Sandberg bluegrass on the driest site at Lava Beds (hilltop) showed no
response. Production increased on the north slope and swale sites of
Lava Beds and on the Crooked River site [2].
Two years after burning at Lava Beds, Sandberg bluegrass had
significantly increased basal cover in Idaho fescue communities, and had
regained prefire basal cover in swale and hilltop bluebunch
wheatgrass-Thurber's needlegrass communities. Sandberg bluegrass showed
little change on bluebunch wheatgrass communities at Crooked River.
Basal cover of Sandberg bluegrass before burning (1976) and after
burning (1977 and 1978) was [1]:
Lava Beds Crooked River
-------------------------------------- -------------
Swale Hilltop
----------- -----------
Wheatgrass- Wheatgrass-
Fescue Needlegrass Needlegrass Wheatgrass
------------------------------------------------------------------
1976 0.9a 1.3 1.4a 1.0
1977 0.6a* 1.1 0.9b* 1.5
1978 1.4b* 1.3 1.8a* 0.3
------------------------------------------------------------------
Means followed by different letters differ at the 5% significance
level. Means followed by an asterisk differ at the 1% significance
level.
Height growth increased significantly. Height (cm) of Sandberg
bluegrass before and after burning was [1]:
Lava Beds Crooked River
-------------------------------------- -------------
Swale Hilltop
----------- -----------
Wheatgrass- Wheatgrass-
Year Fescue Needlegrass Needlegrass Wheatgrass
-----------------------------------------------------------------
1976 1.07a 1.20a 1.16a 1.06a
1977 2.55b 3.76b 3.16b 4.20b
1978 3.40c 3.38c 3.60c 4.72b
-----------------------------------------------------------------
Values followed by different letters within each site differ at
the 1% significance level.
FIRE MANAGEMENT IMPLICATIONS :
The prescribed fires generally favored Sandberg bluegrass growth,
especially on the more mesic sites. At both Lava Beds and Crooked
River, the fires reduced mountain big sagebrush cover to less than 1
percent. Removal of shrubs and litter contributed to increased soil
temperatures and therefore, to earlier growth of Sandberg bluegrass.
Early growth and Sandberg bluegrass' shallow, spreading root system
enabled Sandberg bluegrass to take advantage of early spring rains.
With reduced competition from other species, Sandberg bluegrass
increased in height and basal area [1,2]. At Lava Beds, Sandberg
bluegrass and bluebunch wheatgrass apparently increased at the expense
of Idaho fescue and Thurber's needlegrass. This advantage was
especially evident on the relatively moist Idaho fescue and swale sites,
but also evident on the hilltop site [2].
The timing of the two fires in relation to drought conditions of 1977
may have influenced the rapid recovery of Sandberg bluegrass cover at
the Lava Beds site. At Lava Beds, a heavy 3.1-inch (79-mm) August rain
occurred less than 1 month after the fire. At Crooked River, drought
followed immediately after the fire. In addition, Lava Beds received 61
percent of its normal precipitation between September 1976 and June
1977, while Crooked River received only 41 percent of its normal
precipitation during that period.
FIRE CASE STUDIES
SPECIES: Poa secunda | Sandberg Bluegrass
2nd CASE NAME :
Summer Fire/Combustion Chamber/ID
REFERENCE :
Wright, H. A.; Klemmedson, J. O. 1965 [71]
FIRE CASE STUDY AUTHORSHIP :
Anne F. Bradley, 1986
SEASON/SEVERITY CLASSIFICATION :
summer/moderate
STUDY LOCATION :
55 miles (88.5 km) southeast of Boise, Idaho
PREFIRE VEGETATIVE COMMUNITY :
Plants chosen for this study were part of a big sagebrush (Artemisia
tridentata)-Thurber needlegrass (Stipa thurberiana) community. Sandberg
bluegrass (Poa secunda) was generally subdominant, but sometimes
dominated disturbed areas. Individual Sandberg bluegrass plants studied
were on a site which had been burned and seeded to crested wheatgrass
(Agropyron cristatum) in 1957 (3 years prior to the study). Crested
wheatgrass establishment was poor to fair. Cheatgrass (Bromus tectorum)
and Russian-thistle (Salsola kali) dominated the stand, with lesser
amounts of crested wheatgrass, Sandberg bluegrass, Thurber needlegrass,
Indian ricegrass (Oryzopsis hymenoides), and needle-and-thread (Stipa
comata) present.
TARGET SPECIES PHENOLOGICAL STATE :
Plants were burned on three different dates in 1960. Dates and plant
condition follow:
June 9 plants dry but seed not cast
July 8 plants dry with some seed cast
August 18 plants dry with seed stalks (culms) broken by the wind
SITE DESCRIPTION :
Data on the burn site are presented below:
Elevation: 2,950 feet (890 m)
Mean annual
precipitation: 8 inches (203 mm)
Topography: undulating
Soils: soils are part of the Sierozem great soil
groups with surface soils a light,
grayish-brown, loosely structured noncalcareous,
sandy loam low in organics; subsurface soils are
light gray, calcareous and compact; color of the
subsoils and depth to lime vary
Geology: sedimentary deposits in the Bruneau Formation;
detrital material is dominated by massive lake
beds of white-weathering fine silt, diatomite,
clay, and minor amounts of alluvial silt and
sand
FIRE DESCRIPTION :
Sandberg bluegrass plants were burned individually. Plants were
selected by two basal area size classes. Classes were 0.5 to 1.5 inches
(1.27-3.81 cm) in diameter, and greater than 2 inches (5.08 cm) in
diameter. A combustion chamber made from a 55-gallon oil drum and a
metal ring restricted the fire to the vicinity of the study plant.
Other plants and litter within a 1-foot (30.5-cm) radius from the study
plant were removed. Shredded paper was used for fuel. Fuel levels were
predetermined to give maximum soil temperatures of 200 degrees
Fahrenheit and 400 degrees Fahrenheit (93 and 204 deg C). Burning
treatments occurred on June 9, July 8, and August 18, 1960.
FIRE EFFECTS ON TARGET SPECIES :
Sandberg bluegrass was burned on three different dates and at two
different temperatures. The following results were obtained:
Percentage of original basal area alive 1 year after treatment
----------------------------------------------------------------------------
June July August Control
---------- ---------- ------------ -------
temperature (F)* 200 400 200 400 200 400
---------- ---------- ------------ -------
small (0.5-1.5 in) 183 231 148 163 141 213 166
large (>2 in) 120 111 95 92 98 98 106
----------------------------------------------------------------------------
*200 deg F = 93 deg C; 400 deg F = 204 deg C
There was no significant change in basal area at any season for either size
class.
FIRE MANAGEMENT IMPLICATIONS :
Sandberg bluegrass was relatively unaffected by fire in this study.
Dormancy and the unpedestaled condition of the plants were probably
responsible for their survival. Pedestaled plants may be more
susceptible to fire damage, since their growing points are uninsulated
by soil.
Related categories for Species: Poa secunda
| Sandberg Bluegrass
|
 |
