Fire regimes and the World’s biomes

1. Fire regimes and the World’s biomes 23 September 2010

2. What is a fire regime? • Characterization of the features of the historic (“natural”) fires for a particular ecosystem or ecoregion.

3. Fire Regime Components: Examples…? • Extent (size) • Frequency • Seasonality • Duration • Intensity • Severity Magnitude

4. Extent • Range of burned area • Can influence seed dispersal from neighboring systems. • Barriers to spread?

5. 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

6. 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

7. Seasonality • How likely fire might occur during each time of year • Affects plant survival and flowering

8. 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…

9. One Foot Intensity Direction of spread Burned Area Flamedepth

10. 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

11. 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

12. 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?

13. Fire Regime Exercise • Brief description of several major ecosystems in the world • TTYP: describe the fire regime for each ecosystem

15. Northern boreal forests • Boreal forests and tundra • Long winters, short summers • Lots of biomass

16. Mediterranean shrublands • Generally shrublands, also trees and grass • Wet, mild winters / hot, dry summers • Fire adapted biota

17. Tropical rainforests • High biomass • Ever-wet with occasional droughts

18. Tropical savannas (Africa) • Cyclic wet/ dry periods • Grazing x fire interactions • Shifting grasslands – savannas – forests

19. Brazilian cerrado • Fire-adapted grasses & shrubs • Dry winters • Summer rains

20. 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