Download Slide 1

Fire Ecology and Fire Regimes in
Boreal Ecosystems
Oct 19, 2010
Fire ecology of boreal region
• Black spruce (Picea mariana)
– serotinous cones, highly flamable
– Early successional
• White spruce (Picea glauca)
– Non serotinous cones
– Late successional
• Other species: larch, birch,
willow, aspen
alder,
Soil temperature, moisture, and fire
influence vegetation types
Boreal region: land of fire & ice
• Vegetation shaped by fire and permafrost
– Heat and cold
– Aridity and moisture
• Permafrost: permanently frozen ground
– Impermeable boundary between surface and ground waters
– Active layer (thaw zone) – allows for shallow soil, rooted vegetation
• Dynamic equilibrium between vegetation and permafrost
determined by fire
Boreal Forests Fire Regime
• Wildfires are episodic
Some years very large wildfires
• Relatively frequent fires
Continuous layer of fuels:
grasses, moss, shrubs, black spruce
(~ lodgepole pine *)
• Dry summers
Lightning, long days (midnight sun)
• Mixed fire-regime
Natural fire cycles: ~50-200 years
high intensity stand-replacing crown fires +
ground fires (smoldering in deep organic layers)
After human use/protection:
<100 years in remote regions to
>500 in heavily protected
(Beniston 2003)
Smoldering?
Boreal fires: high energy release rates
Effects of fire on boreal landscape
Fire is the dominant disturbance in boreal forests
• Allows for massive decomposition and recycling of water and
nutrients
• Fires cause active zone of
permafrost to increase
temporarily
(vegetation = insulation)
• Replaces forest stands
Loss of protective insulation from
vegetation
Post-fire permafrost thaw:
recycling of nutrients & water
Fire creates mosaic of vegetation…
and mosaic of stand types…
Human influence on Boreal fires
• Fires deliberately set by Native Americans and
settlers
– Signal fires, campfires, hunting (ring of fire –
moose, caribou), mosquito control
– Gold rush in 1896 – “epidemic of forest fires”
• Railroad construction
• Expose mine deposits
• Create/improve pasture
• After railroad completed
(1923) – new emphasis
on fire suppression and control
Fire management in Alaska
• 1930-1950’s – emphasis on fire control
– Patrols and strong military presence
• 1950’s = enormous fires, mostly lightening caused
(5 mill acres burned in 1957)
– Smoke shut down “the state” for 2 weeks
• 1960’s and 70’s fire control in Alaska reached
similar levels as the lower 48 (under BLM)
– Emphasis on aircraft, helicopters, smokejumpers
• 17% of land is designated for fire suppression:
“valued areas” (proximity to communities and
roads)
• 83% of land (interior Alaska) under a natural fire
regime.
Fire and Climate Change
in the Boreal Region
TTYGroup on potential general impacts of CC on fire
dynamics:
• What has been predicted for temperature and precipitation
due to climate change in North American boreal region?
• What does this mean for the fire weather of the N. A.
boreal region?
• What are the direct effects of climate change on the
vegetation composition of boreal forests?
• What does this mean for fire behavior?
Relationship between climate change
and fire in Boreal regions (1)
• Climate change increases fire
activity:
– Warmer and drier climate (Higher
T, lower PP) = drier fuels
– Longer fire season
– Increased lightening
• More fire = positive feedback on
global warming
– Increased greenhouse gas
emissions enhancing warming.
– Increased CO2 = greater biomass
production, more fuel
(controversial)
Relationship between climate change
and fire in Boreal regions (2)
• Indirect effects of climate
change
– More fuel loads ?
CO2 fertilization
insect outbreaks
tree line expansion into tundra
– Less fuel loads / different fuel
loads? = negative feedback
Deciduous vs. coniferous
– Longer fire season = drier forest
floor = potential to alter depth of burn
+ deeper thaw of permafrost
Boreal forests: Carbon sink or source?
TTYGroup:
1. What factors determine whether a region
(or ecosystem) is a “sink” or “source,” and
why?
2. What does it mean to refer to the boreal
region as a “carbon sink” or a “carbon
source”?
Boreal forests: Carbon sink or source?
• Forests sequester carbon via
photosynthesis
– Carbon stored in biomass
– Long-term carbon storage: soil,
permafrost, peat
• Carbon released to atmosphere
by:
– Respiration
– Fire
– Decomposition of soil organic
matter, melting of permafrost
• Downward carbon flux: carbon
sequestration
• Upward carbon flux: carbon
emission
• Net carbon flux: sink or source
Balance between CO2 sequestration and
emissions = complex!
Sink
Source
CO2 fert
Climate
Fire
CO2,
Climate,
fire
Effects of post-fire succession and human activities
on future fire regimes in the boreal region?
•
•
•
•
•
•
Rate of biomass recovery
Species composition (deciduous vs. coniferous)
Tree line expansion into tundra
Fire severity – depth of burn, permafrost – feedbacks
Fire suppression efforts – successful?
Insects and disease – increase with warming?
Climate change
effects on
permafrost…