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• Office hours: Fridays 9AM-12noon (or
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• Quiz Thursday (today’s lecture/discussion
only)
Fire Ecology:
Rocky Mountain Mixed
Conifer Forests
NREM390
October 5, 2010
Fire Regimes: Review
• Components of fire regimes
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–
–
–
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Extent
Frequency
Seasonality
Intensity
Duration
Severity
• Historic vs. Modern Fire Regime?
Fire classification:
severity and frequency (return interval)
• Short fire return intervals (<20 years)
– Low-severity surface fires are common .
– Fire tolerant herbaceous species or shrubs dominate.
– Species composition often similar.
• Intermediate fire return intervals (20-75 years)
– Fuel buildup and continuous in distribution
– Moderate-severity fires (patchy crown fires) or some high-severity fires
– Greater changes in plant composition
• Long fire return intervals (>100 years)
– Very high fuel loads possible
– High-severity fire commonly occur (stand-replacing crown fires)
– Postfire & prefire vegetation can be very different
• Mixed-severity fires
– Combination of frequent low-severity & infrequent high severity fires
How do historical (pre-settlement) and modern
(current) fire regimes differ – and why?
• In ecosystems with high frequency, low intensity
fire regimes (e.g., dry forests, grasslands,
woodlands, savannas):
– Significant changes to fire regime due to:
• Land use change (agriculture, urban)
• Fire suppression and fuel accumulation
• Change in vegetation type and structure
• Forests with low frequency, high severity standreplacing fire regimes:
– Much less change from historical fire regimes – Why?
Fire regimes in
Rocky Mountain
Conifer
Ecosystems
Spruce-Fir
9,000-11,000 ft
Lodgepole pine
(aspen, spruce-fir)
8,000-9,000 ft
Shortgrass
steppe
<5,500 ft
Alpine
Meadows
>11,000 ft
Ponderosa pine
5,500-6,500 ft
Douglas-fir
mixed conifer
6,500-8,000 ft.
Ponderosa Pine: Ecology
• Shade intolerant
• Early successional
• Fire resistant
– Thick bark
– Seedlings > 5 yr. old
• Mast seeding (episodic)
Ponderosa pine: fire regime
• Fire frequency: 5-30 yrs.
• Light surface fires
• Regeneration:
– Patches of old trees 
crown fire & seed bed
– Mast year + fire-free period
• 1900s: grazing &
fire suppression
– Many seedlings survive
– Fuel build up
– High severity,
stand-replacing fires
Ponderosa pine: Low intensity,
frequent surface fires (historic)
Stand-replacing fires
Fire regimes in
Rocky Mountain
Conifer
Ecosystems
Spruce-Fir
9,000-11,000 ft
Lodgepole pine
(aspen, spruce-fir)
8,000-9,000 ft
Shortgrass
steppe
<5,500 ft
Alpine
Meadows
>11,000 ft
Ponderosa pine
5,500-6,500 ft
Douglas-fir
mixed conifer
6,500-8,000 ft.
Douglas-fir, mixed conifer: Ecology
• Intermediate shade tolerance
• Early successional
– Seedlings can establish on moist,
cool sites
• Late successional
– Understory of Ponderosa Pine
– Understory of Lodgepole Pine
• Intermediate fire resistance
– mature trees only
Douglas-fir: fire regime
• Historic: Mixed fire severity
– Light surface fires, 20-60 yr.
– Severe stand-replacing fires, >60 yr.
• Fire suppression  shade tolerant species
– Douglas-fir seedlings
– Hemlock, white spruce,
blue spruce (low fire resistance)
• Shift: increased mixed-conifer
forests on landscape
• Favors high severity,
stand-replacing fires
Fire regimes in
Rocky Mountain
Conifer
Ecosystems
Spruce-Fir
9,000-11,000 ft
Lodgepole pine
(aspen, spruce-fir)
8,000-9,000 ft
Shortgrass
steppe
<5,500 ft
Alpine
Meadows
>11,000 ft
Ponderosa pine
5,500-6,500 ft
Douglas-fir
mixed conifer
6,500-8,000 ft.
Lodgepole pine: Ecology
•
•
•
•
Shade intolerant
Early successional
Intermediate fire resistance
Serotiny
– Young trees – low serotiny
– Old trees – low serotiny (high elevations with low fire
frequency
– Intermediate age – high serotiny
• requires intense ground fires
• Melt resin
• Exposed mineral soil (seed bed)
http://www.cfr.washington.edu/Classes.esc.202/LPBarkBFireRot.htm
Lodgepole pine: fire regime
• Mixed severity fire regime
• Low-intensity surface fires, 50-100 yr.
– Fuel characteristics
– Topography & Weather
• Stand-replacing fires, 100-400 yr.
– Climate driven
– drought, winds
• Fire suppression
– Understory: spruce, fire
(low fire resistance)
– Low impact on fire dynamics
• Altitudinal gradient: Rockies
– Moisture, temperature
– Biomass accumulation
Fire regimes in
Rocky Mountain
Conifer
Ecosystems
Spruce-Fir
9,000-11,000 ft
Lodgepole pine
(aspen, spruce-fir)
8,000-9,000 ft
Shortgrass
steppe
<5,500 ft
Alpine
Meadows
>11,000 ft
Ponderosa pine
5,500-6,500 ft
Douglas-fir
mixed conifer
6,500-8,000 ft.
Mid-Elevation Lodgepole pine ecosystems (8,000-9,000 ft)
Relatively
rapid regeneration:
- Lodgepole pine
- Aspen
- Spruce
- Fir
High-Elevation
Spruce-Fir ecosystems
(10,000-11,000 ft)
Slow regeneration process
Alpine meadows and tundra forest
Ecosystems &
Lodgepole pine,
Spruce-Fir
fire regimes
Douglas-fir
mixed conifer
Ponderosa pine
PinyonJuniper
Tallgrass prairie
Short grass steppe
/ Sagebrush
Fire regimes
Ecosystem
Tallgrass prairie
Short Grass Steppe
/Sagebrush
Pinyon-juniper
(savannas, woodlands)
Ponderosa Pine
Mixed conifer
(Ponderosa pine,
Douglas fir, white fir,
larch)
Lodgepole pine
Subalpine (lodgepole
pine-spruce-fir)
Severity
class
Fire interval
Driving factor
Fire regimes
Ecosystem
Severity class Fire interval
Driving factor
Tallgrass prairie
Low severity
1-5 yrs
Fuel load
Short Grass Steppe
/Sagebrush
Low severity
20-50 yrs
Fuel load
Pinyon-juniper
(savannas,
woodlands, forests)
Low to moderate
severity
< 10 yrs
< 100 yrs
Weather, fuel
load, topography
Ponderosa pine
Low to moderate
severity
4-36 yrs
< 100 yrs
Weather, fuel
load, topography
< 60 yrs
> 100yrs
Weather, fuel load,
topography
50-100 yrs
> 400 yrs
Weather, fuel load,
topography
Mixed conifer
(Ponderosa pine,
Douglas fir, grand fir, Mixed severity
western larch)
Lodgepole pine
Mixed severity
Subalpine
(lodgepole pinespruce-fir)
High severity
> 400+ yrs
Weather
Lodgepole Pine regeneration after the 1988 Yellowstone Fires
Pre-Fire
Cougar Creek
Yellowstone Lake
Elevation
Low (< 2,000m)
High (>2,300 m)
Stand age
130 yr.
250 yr.
% serotiny
65%
1.9 %
Fire return interval
~ 180 yrs.
~ 300 yrs.
Pine seedling density
(stems/ha)
211,000 stems/ha
600 stems/ha
Post-Fire
LP regeneration
High (> 50/m2)
Low (< 10/m2)
Seed viability
High (ground fires,
melt resin, scarify soil)
Low (crown fires, serotiny)
Stand development
Similar to unburned
High herbaceous density,
forests
Slow forest recovery
* Effect of patch size on LP regeneration: Large > Small
* Effect of fire severity on LP regeneration: ground fires > crown & surface
Fire and Ecosystem Heterogeneity
• Mosaic pattern – “patchiness”
– Fire intensity
– Burned area
• Microclimate variation
– Light
– Moisture
– Nutrients
• Species composition & diversity
– Different microclimate requirements
– Different regeneration strategies
• Ecosystem diversity
– Successional communities
– Dynamic equilibrium (landscape scale)
Other examples of post-fire heterogeneity
• Herbaceous vegetation
– Light (larger patches)
– Seed dispersal high
• Aspen
– Root suckering (low fire intensity)
– Regeneration by seed (woody debris – elk browse)
• Spruce-fir
– Distance to seed trees
– Shade, moisture
• Wildlife
– Mosaic of different habitats
– Increased abundance of food
Initial vegetation cover: Lodgepole pine
Probably
ground fires,
some mortality,
new seedlings,
mixed-age
LP stand
No fire until 300 yrs.
Mixed LP,
spruce-fir,
crown fire,
slow regen
Fire every ~100 yrs.
Probably surface
fires, high survival
no new regeneration,
dense LP stand
Fire every ~40-50 yrs.