FIRE CASE STUDIES
SPECIES: Pinus ponderosa var. ponderosa | Pacific Ponderosa Pine 



CASE NAME : 
Impact of prescribed burning on a sequoia-mixed conifer forest


REFERENCE : 
Kilgore, B. M. 1072 [80]


SEASON/SEVERITY CLASSIFICATION : 
Fall burn / Low- to Moderate-severity


STUDY LOCATION : 
The study site was located on the ridge of Redwood Mountain which runs
north and south within the 3,100-acre Redwood Mountain Grove of giant
sequoia (Sequoiadendron giganteum) in Kings Canyon National Park, Three
Rivers, California. 


PREFIRE VEGETATIVE COMMUNITY : 
Giant sequoia, white fir (Abies concolor), and sugar pine (Pinus
lambertiana) dominate the forest, with incense-cedar (Libocedrus
decurrens), Pacific ponderosa pine, and California black oak (Quercus
kelloggii) represented except in the extreme southern plots.  Shrubs and
herbs are present but rare, and grasses are almost absent.  Major shrub
species include Sierra mountain misery (Chamaebatia foliolosa) and
Sierra gooseberry (Ribes roezlii).  Graminoids include sedges (Carex
spp.).
  


TARGET SPECIES PHENOLOGICAL STATE : 
The target phenological states were not recorded.


SITE DESCRIPTION : 
The elevation along the ridge ranges from 6,400 feet (1,950 m) at the
saddle to nearly 7,000 feet (2,134 m).  Hygrothermograph records show a
yearly low of 17 degrees F (-8.4 deg C) and a high of 82 degrees F (28
deg C).  Temperatures in November just before the burn ranged from 32 to
58 degrees F (0-15 deg C).  Relative humidity fluctuated between 30 and
80 percent.  Winds in and near the study plots were moderate when
present, varying from 0 to 5 mph (0.3 kmh).  Average slope was 35
percent.  Large portions of this study area are found on soils derived
from metamorphic schists.

Burn day conditions were as follows:
                    
                      Temperature: 59 degrees F (15 deg C)
                      Humidity: 20 percent
                      10-hour fuel sticks: 10 grams
                      Wind speed: 0 mph
 


FIRE DESCRIPTION : 
Twelve 60- by 100-foot (18x30 m) study plots were laid out about 600
feet (183 m) east of the ridge of Redwood Mountain at an elevation of
6,300 feet (1,920 m).  Two additional plots were established just below
the saddle parking area as demonstration plots.  These were selected as
being represenative of the range of vegetative and fuel conditions found
on this east-facing slope of the mountain.  Seven of the 12 plots and
one demonstration plot were burned, while the remaining plots were
retained as controls.  For each plot, the following information was
measured before and after ignition:

1. Species, diameter, height class > 6 inches d.b.h. (15 cm) or 4.5 feet
   (1.4 m) tall.
2. Number of white fir and sugar pine saplings per acre in four height 
   classes.
3. Extent and approximate height of white fir sapling thickets.
4. Coverage and frequency values.
5. Litter and duff weights.
6. Length and diameter of down trees.
7. Chemical light meter indices for light reaching the forest floor.
8. Vegetation appearance recorded by black and white/color photographs
   from 102 permanent photo points.

After all preburn measurements were made, a 2-foot (0.6 m) wide
fire-line was built along the two sides and the bottom of the proposed
5-acre (2 ha) burn area.  The burning indices for the burn day were as
follows:

                       Forecast     Actual       Prescription (range)
                       --------     ------       --------------------
Fine Fuel Moisture        6           5                 7-10
Spread Index              8           8                 5-12
Intensity Index          59          56                37-49
Timber Burning Index      5           5                 3-5
Ignition Index           45          55                15-49

All test plots were ignited at 0900 by drip torch along the upper
boundary of the burn area.  A strip-head fire method of ignition was
used and it burned briskly from 0900 to 1200.



FIRE EFFECTS ON TARGET SPECIES : 
Ninty-four percent of the 210 2- by 3-foot (0.6x0.9 m) sample plots
showed evidence of fire impact.  Eighty percent burned almost
completely, while 14 percent burned partially or lightly.  Only 6
percent of the sample plots remained unburned.  Pacific ponderosa pine
trees greater than 12 inches (0.3 m) d.b.h. showed an increase in
relative density from 7.9 percent to 8.2 percent.  This increase may be
attributable to the reduction in white fir density.  Overall, Pacific
ponderosa pine cover percent increased 0.9 percent for all size classes.
This suggests that it is relatively resistant to low- to
moderate-severity fires under these burn conditions.

Preburn measurement of litter and duff was 50 tons/acre (124 tons/ha).
Following burning, litter fuels were reduced by more than 75 percent and
duff fuels by more than 85 percent, resulting in a postburn measurement
of 7.7 tons/acre (19 tons/ha).



FIRE MANAGEMENT IMPLICATIONS : 
This study investigated methods by which the impacts of prescribed fire
on certain biotic and abiotic elements of the sequoia-mixed conifer
forest ecosystem could be measured.  Pacific ponderosa pine was present
as a codominant species with an estimated 3.1 trees per acre (7.6/ha).
Different fire severities were found to produced different results.  In
an earlier study, a high-severity fire created more canopy openings,
prepared better seedbeds, dispersed smoke more effectively, and consumed
surface fuels more completely than this low- to moderate-severity fire.
Options for fire management in this type of stand include a
high-severity fire followed by another moderate-severity fire 7 to 10
years later; or, alternatively implement two low-severity fires in
closer sequence in order to gradually kill young seedlings and cleanup
heavy fuels.  Both strategies would allow for more natural regeneration
of seral species, while reducing the potential threat of hazardous
wildfires.

Related categories for Species: Pinus ponderosa var. ponderosa | Pacific Ponderosa Pine