Fire Ecology Lecture Outline
Part I: BASICS
Fire Triangle
fuels, oxygen, heat (energy/ignition
source)
Fire Environment
Fuels –
weather - topography
1) Fuel: continuity, size, shape,
arrangement
2) Fire Weather
§
Temp
§
Winds
Diurnal
Foehn: chinook,
mono, north, santa ana, east
§
Fuel Moisture
§
RH
§
Atmospheric stability
Clouds: cumulo-nimbus w/
anvil top
Dust
devils
*Weather
obs on fire crews -- importance of fire weather, dictates behavior, causes
effects
*South
Canyon/Storm King -- cold front passage
Fire
Generated Weather
Fire
whirls
Convection
column, cloud
Wind:
up/indrafts, downdrafts (360 fire
spread)
wind uprooting
trees
Rain, signal to column collapse
3) Topography
steep slopes: fire runs upslope, preheating
saddles: funneling, winds
chutes/chimneys: funelling, preheating
narrow canyons: spotting
Fire Behavior
Fire line
intensity
Heat/unit
area
Flame
length
Rate of
spread
Surface: Flame length < 1m
Understory: Flame length 1 – 3m
Crown: Flame length > 3m
Spotting
Torching
Crowning
Part II: FIRE
ECOLOGY
Case Study
E. Cascades
Dry
forests: PP and dry DF
Principals
-equilibrial
to non-equilibrial view of natural systems
steady
progression to climax state, disturbances detrimental
disturbance
interrupts succession, more complicated
-communities
adapted to fire
-require
fire to maintain structure and “health”
-manage
disturbances, protect all parts of system, even those you don’t know about
-maintains/promotes
biological diversity,
interrupts
sucessional processes
intermediate
disturbance hypothesis
Disturbance Regime
Characterized
by frequency, extent, severity, seasonality
Frequency
1-30 yrs in west
100’s of yrs w. cascades
1000’s
of yrs in rainforest (drought and s. slopes)
Table 1:
|
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|
|
|
|
Area in type (1,000 ha) |
Fire cycle(yr) |
Area burned per yr(1000 ha) |
Area in type (1,000 ha) |
Fire cycle(yr) |
Area burned per yr(1000 ha) |
|
Mixed Conifer |
399 |
30a |
13.3 |
504 |
50b |
10.1 |
|
Ponderosa Pine |
3,142 |
15c |
209.4 |
1,438 |
15 |
95.8 |
Extent
Inland
NW forests, avg. 6mill acres of forest burned annually, mostly in the dry
forest
100,000+ac
fires burned regularly in late 1800s (1920 WA)
variability,
acreage could double from one season to next
Severity
Measure
of ecological change
High
Severity:
low
frequency, high intensity
historically
rare in dry forest
Ex:
lodgepole pine, Yellowstone NP, 30mi fire –high elevation (5000ft+)
Moderate:
Varied frequency,
varied intensity
Regime least understood
Most difficult to manage
Ex: wet DF, mixed conifer,
mid-elevations in WA
Low:
High frequency,
intensity
Important in urban
interface
Ex. ponderosa
pine, dry DF
Seasonality
Summer/early
fall
Most
lightning in Aug.
Foehn
winds in summer/early fall
Varied
spatially (s. vs n. watersheds)
Least
understood
RESULT
Open pk
like stands
PP dominate
and seral dominant
Isolated
refugia of shade tolerant trees
Wildflowers
and grass more than brush
High
severity fire discouraged
Fire Suppression
Lg fires at
turn of century
1911 Weeks Act, federal $ for fire
protection
protect timber resource
Other factors:
decrease ignitions
by Native Americans
increased livestock
grazing
roads and farms
>>profoundly changes fire regime
RESULT
Increase
fuel loading
Denser
stands
Change
species composition
^ shade tolerant
species (true firs), decrease in shade intolerant species
Increase in
disease: dwarf mistletoe, bark beetle, spruce bud worm
Altered Disturbance
Regime
Frequency
Study
on Wen. NF
Mud
Ck -- 7.0 yrs, pre-1910
38.3 yrs (1910 to
1996)
Extent
Yakima
R. watershed
1900
- 1920 over 95,000 acres burned, avg size = 248 acres
1946 - 1966 4,833 ac, avg size = 31 acres
1967 - 1992 18,790 ac, avg size = 40 acres (Oliver et al. 1994)
Severity
Transformation:
low >> mod – high severity
Dinkleman fire –
pre-1889 fire intervals of 19, 10,
10, 20, & 13 years, but no scars were found after 1889
tree survived multiple fires but
could not survive intensity of Dinkleman
-Ironically, denser stands shade
forest floor fuels, ^ fuel moistures to the point of limiting fire spread in stands
that fire formerly burned through regularly.
-Under dry conditions these stands
will now burn more intensely than they could have in their pre-1900 state
Seasonality
No
change in seasonal dist. of precip
Prescribed
fire increases late fall and spring fires
Spring
fire
Inappropriate
ecologically
Preferred
for less smoke and control
Damage
trees prior to stress of dry season
Fall
fire
Allow
recovery over winter
Summer
fire
Changes
in stand structure mk summer undesirable
Abnormally
severe fires
Part III: FIRE
MANAGEMENT
Native Use
Varied
depending on location
Purpose: clearing brush from the forest floor
make travel
easier
cultivation of
edible and medicinal plants improvement
of game hunting communication
-evidence suggests
extensive knowledge of ecological function of fire
Fire Use
1940s recognition of ecological role of fire (Weaver)
1970’s policies implemented to restore natural fire regimes
PNF
“let burn” policy
came under fire during 1988 Yellowstone Fires
specific guidelines about weather conditions for PNF
Prescribed fire
1. prepare logging units for planting
2. reduce the risk of catastrophic fire events
3. reintroduce fire into the ecosystem
normally successful
few accidents – Cerro Grande Fire,
Fuels Reduction
Thinning
Thin & burn
Current debate
Importance of fire accepted – can we achieve fire effects w/o fire?
Thin and burn seems to be very effective, especially w/ high fuel loading
Fire Suppression
Will remain an important part of fire management
Urban interface
BIBLIOGRAPHY
Agee,
J.K. “The Landscape Ecology of
Barrett, S.W., and
Arno, S.F. “Indian Fires as an Ecological Influence in the
Camp, A.E. “Age
Structure and Species Composition Changes Resulting from Altered Disturbance
Regimes on the Eastern Slopes of the
Cooper,
C.F. “Pattern in
Harrod,
R.J., B.H. McRae, and W.E. Hartl. “Historical Stand Reconstruction in Ponderosa
Pine Forests to Guide Silvicultural Prescriptions.”
Hemstrom, M. A.
"Vegetative Patterns, Disturbances, and
Hessburg, P. F., B. G. Smith, and B. Salter.
"Detecting Change in
Mutch, R. W. "Fighting Fire with Prescribed Fire - A Return to Ecosystem Health." Journal of Forestry 92,11 (1994): 31-33.
Weaver,
H. “Fire as an Ecological and Silivicultural Factor in the Ponderosa Pine
Region of the Pacific Slope.” Journal of Forestry 41 (1943): 7-14.