Fire Ecology and Fire Regimes in Boreal Ecosystems
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Transcript of Fire Ecology and Fire Regimes in Boreal Ecosystems
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Fire Ecology and Fire Regimes in Boreal Ecosystems
Oct 19, 2010
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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, alder, willow, aspen
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Soil temperature, moisture, and fire influence vegetation types
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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
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Boreal Forests Fire Regime• Wildfires are episodic
Some years very large wildfires
• Relatively frequent firesContinuous layer of fuels:grasses, moss, shrubs, black spruce (~ lodgepole pine *)
• Dry summers Lightning, long days (midnight sun)
• Mixed fire-regimehigh intensity stand-replacing crown fires +
ground fires (smoldering in deep organic layers)
Natural fire cycles: ~50-200 years
After human use/protection:<100 years in remote regions to >500 in heavily protected(Beniston 2003)
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Smoldering?
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Boreal fires: high energy release rates
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Effects of fire on boreal landscapeFire 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
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Loss of protective insulation from vegetation
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Post-fire permafrost thaw: recycling of nutrients & water
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Fire creates mosaic of vegetation…
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and mosaic of stand types…
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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
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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.
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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?
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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)
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Relationship between climate change and fire in Boreal regions (2)
• Indirect effects of climate change– More fuel loads ?
CO2 fertilization insect outbreakstree 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
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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”?
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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 sourceBalance between CO2 sequestration and emissions = complex!
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Sink
Source
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CO2 fert
Climate
Fire
CO2, Climate, fire
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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?
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Climate change effects on permafrost…
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