fire regimes and the world’s biomes 23 september 2010
TRANSCRIPT
Fire regimes and the World’s biomes
23 September 2010
What is a fire regime?
• Characterization of the features of the historic (“natural”) fires for a particular ecosystem or ecoregion.
Fire Regime Components: Examples…?
• Extent (size)• Frequency• Seasonality• Duration• Intensity • Severity
Magnitude
Extent• Range of burned area
• Can influence seed dispersal from neighboring systems.
• Barriers to spread?
Fire Frequency – Data sources
• Dendrochronology (tree scars from non-lethal fires, cross-dating)• Paleoecology (charcoal in lake & soil sediments; wounds on tree
boles)• Data bases: reports, aerial photos, maps, atlases, satellite
images, remote sensing
Fire frequency: Fire return interval
• The number of fire events at a point or within a specific area.
• Short fire return intervals – < 25 years
• Intermediate fire return intervals – 25-100 years
• Long fire return intervals – >100 years
Seasonality
• How likely fire might occur during each time of year
• Affects plant survival and flowering
Duration
• The length of time a fire burns within a particular area
• For example…– Fast-moving prairie fires– Slow moving ground fires
• Important effect on intensity and severity…
Intensity
Burned Area
Direction of spread
One Foot Flame depth
Severity• Effect of fire on the ecosystem • Some measures of severity…
– % of organic biomass consumed by fire– % soil organic matter consumed– Mortality of plants and animals– Depth of heat penetration into the soil– Change in color of ash and soil– Description of fire behavior (surface, ground, crown)
• Most common measure of severity– Mortality in overstory vegetation
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 due to:– Land use change (agriculture, urban)– Fire suppression and fuel accumulation– Change in vegetation type and structure
• Forests with low frequency, high severity stand-replacing fire regimes:– Much less change from historical fire regimes – Why?
Fire Regime Exercise
• Brief description of several major ecosystems in the world
• TTYP: describe the fire regime for each ecosystem
Northern boreal forests• Boreal forests and
tundra• Long winters, short
summers• Lots of biomass
Mediterranean shrublands
• Generally shrublands, also trees and grass
• Wet, mild winters / hot, dry summers
• Fire adapted biota
Tropical rainforests
• High biomass• Ever-wet with
occasional droughts
Tropical savannas (Africa)
• Cyclic wet/ dry periods
• Grazing x fire interactions
• Shifting grasslands – savannas – forests
Brazilian cerrado
• Fire-adapted grasses & shrubs
• Dry winters
• Summer rains
Ponderosa pine – Douglas fir• Mountains in the West/Southwest• Dry summers, but also cooler and moister at high
elevations• Without fire, D-fir establishes in understory of
Ponderosa pine