FIRE CASE STUDIES
SPECIES: Abies lasiocarpa | Subalpine Fir 



CASE NAME : 
Table Mountain - Prescribed Crown Fire Study


REFERENCE : 
Woodard, P. M. 1977 [124]

SEASON/SEVERITY CLASSIFICATION : 
fall/severe


STUDY LOCATION : 
The study took place in the Cascade Mountains in central Washington
approximately midway between the towns of Ellensburg and Wenatchee.



PREFIRE VEGETATIVE COMMUNITY : 
The study area is within the subalpine fir (Abies lasiocarpa) zone.  Two
adjacent but different-aged stands were burned.  One area was a young,
lodgepole pine (Pinus contorta) thicket, the other was a old, decadent
stand of lodgepole pine with subalpine fir and Engelmann spruce (Picea
engelmannii) attaining dominance.  Each is described below.

Lodgepole pine thicket - Lodgepole pine is the overstory dominant, but
subalpine fir and Engelmann spruce are also principal components.
Subalpine fir and Engelmann spruce are codominants in the intermediate
size classes.  Subalpine fir is the only tree regenerating under the
canopy.  Understory plants include elk sedge (Carex geyeri), Hood sedge
(C. hoodii), heartleaf arnica (Arnica cordifolia), broadleaf arnica (A.
latifolia), bigleaf lupine (Lupinus polyphyllus), and dwarf bilberry
(Vaccinium myrtillus).

Snag area - This is a decadent lodgepole pine stand, with subalpine fir
and Engelmann spruce dominating the overstory canopy.  Fir and spruce
codominate the intermediate size classes, but subalpine fir is the only
tree regenerating under the canopy.  Predominant understory plants
include subalpine fir, elk sedge, broadleaf arnica, and mosses
(Rhacomitrium canascens, Polytridum commune).


TARGET SPECIES PHENOLOGICAL STATE : 
NO-ENTRY


SITE DESCRIPTION : 
The burned site is a southwest facing gentle slope at an elevation of
5,596 to 5,776 feet (1,706-1,761 m).  A total of 27 acres (10.9 ha) were
burned.  

Climate:  The climate is typical of most areas within the subalpine
zone.  The winters are cold and wet and the summers cool and dry.  Frost
and freezing temperatures can occur during any month of the year.  Over
70 percent of precipitation falls as snow between October and March.

Soil and duff:  The two stands have similar soils, but the soil in the
snag area is more fertile and better developed.  In both areas soils
are derived from basalt residium, have a clay-loam texture, and average
6 inches (15.2 cm) deep.  The effective rooting depth was about 20
inches (51 cm) in the thicket area, and 20 to 40 inches (51-102 cm) in
the snag area.  On both areas, duff was generally from 1 to 4 inches
(0.4-1.6 cm) thick.  The mean depth of duff was 2.3 inches (5.94 cm) on
the thicket area, and 1.9 inches (4.92 cm) on the snag area.  

Fuel loading:  Prior to burning, mean fuel loads were as follows:

          fuels                    thicket area          snag area
                                tons/acre tonnes/ha  tons/acre tonnes/ha

dead and down wood
 0.0-0.25 inch (0.0-0.6 cm)        0.6       1.3        0.9       2.0
 0.26-0.99 inch (0.61-2.5 cm)      2.1       4.6        2.9       6.4
 1.0-3.0 inches (2.6-7.6 cm)       4.4       9.8        5.1      11.4
 > 3.0 inches (7.6 cm) rotten     17.4      38.9       30.9      69.2
 > 3.0 inches (7.6 cm) solid      17.0      38.1       50.1     112.2
litter                            41.4      92.7       89.8     201.2
duff                              32.5      72.8       30.0      67.1


FIRE DESCRIPTION : 
The fire was ignited with drip torches on September 30, 1975, taking
approximately 1 hour and 20 minutes to ignite the entire 27 acres (10.9
ha).  Actual fire prescriptions at the time of ignition were as follows:

ambient air temperature = 60 to 63 degrees F (16-17 C)
relative humidity = 19-21 percent
wind = calm gusts to 15.6 miles/hr (26 km/hr), from the south-southwest
days since last rain = 15
fine fuel moisture content = 13 percent

Within about 10 minutes after ignition, trees began to crown out.
Fire behavior for each area is summarized below:

Snag area - Crowning occurred throughout most of the snag area.  Flame
heights were estimated to be 125 feet (38 m) by one observer, and 50
feet (15 m) above the tops of 90 foot (27 m) crowns by two other
observers.  The fire consumed all small downed and dead wood from 0.0 to
1 inch (0-2.5 cm) in diameter, as well as needles and small twigs on
live standing trees.  Ninety-six percent of down and dead fuels less
than 3 inches (7.6 cm) in diameter were consumed.  In general, 90 to 100
percent of the duff layer was removed.  Many trees less than 3 inches
(7.6 cm) in diameter at the base were completely consumed, and nearly
all standing snags were blown down or burned down.  Where crowning
occurred, the only thing that remained immediately following the fire
was reddened soil, ash-covered soil, large-diameter logs, and dead
trees.

Lodgepole thicket - Fire within the lodgepole thicket was much less
severe.  The crown fire which occurred within the snag area stopped when
it met the boundary of the lodgepole thicket.  Dead and down fuels less
than 3 inches (7.6 cm) in diameter were reduced by 70 percent.  Dead and
down fuels greater than 3 inches (7.6 cm) in diameter were reduced 34
percent.  Duff was reduced about 25 percent.


FIRE EFFECTS ON TARGET SPECIES : 
Where crowning occurred subalpine fir suffered 100 percent mortality.
Fire burning within the crown of live trees consumed all needles and
small twigs leaving scorched skeletons.  Many live trees less than 3
inches (7.6 cm) in diameter at the base were completely consumed.

One year after this fire, subalpine fir seedlings established from seed
produced by unburned trees adjacent to the burned area.  However,
stocking was considered low and attributed to a poor seed crop.
Seedling establishment was restricted to areas along the margin of the
burn.

Subalpine fir pre and postfire frequency and cover are summarized below:

                         thicket area              snag area
                      prefire   postfire        prefire   postfire

frequency             100%        38%            100%       12%
relative ground cover  37%        12%             20%        4%


FIRE MANAGEMENT IMPLICATIONS : 
High intensity crown fires which are common in subalpine fir forests,
kill all or nearly all seed trees within a burned area.  If subalpine
fir is to naturally regenerate on this type of burn, seeds must come
from adjacent unburned stands.  Because subalpine fir seeds are
dispersed over relatively short distances, initial seedling
establishment is restricted to the burn's edge.  Subalpine fir cone
production can be erratic from year to year, with the best regeneration
occurring during good seed crop years.

Related categories for Species: Abies lasiocarpa | Subalpine Fir