Past Fire Frequencies: Treerings, Charlocal & Sediments

METHODS OF RECONSTRUCTING FIRE FREQUENCY

• Fire scars sampled with Chain Saw or Increment Borers
  
  
• Fire history and extent reconstructed by collecting hundreds of trees in an area.
  
• Production depends on fire intensity. Intense fires may destroy all the trees in an area.
  

EXAMPLES

Note historic decline

SEDIMENTARY CHARCOAL = f(P,D,R,I)

Charcoal Dispersal:
Exponential decline away from fire
Particles range in size from pollen to large branches

Charcoal Preservation:
superb, it's already oxidized

Charcoal Identification:
difficult: charcoal vs. "carmalized" wood, opaque minerals
processing can break-up charcoal, increasing number of pieces

1. count fragments in pollen preparations, surface area, or volume
   
2. count burned macrofossils (positive identification by breaking)
   
3. mounting sediment in epoxy and sectioning (Clarke, 1988; Smith and Anderson, 1995)
   

WILDFIRE CHARCOAL = f(B,M,H,S)

Biomass (fuel type, fuel volume)
Meteorological conditions: temperature, moisture, wind
Habitat conditions (hills vs. flats)
Size and intensity of fire

Macroscopic-Microscopic Comparison

INTREPRETATION;

Changing charcoal frequency is an INDEX of fire frequency

Note historic decline

CLIMATIC CHANGE AND FIRE FREQUENCY

• Aridity
  Increased aridity, higher temperature, greater wind speed can increase both the frequency and intensity of fires. For example, the maximum charcoal percentages during the "early Holocene xerothermic" at Lost Trail Pass Bog (Mehringer et al.1977)
• Charcoal in loess more plentiful during cold dry glacials (Wang et al., 2005)
  
  
• Global Warming
  

  Cold climate favors more undergrowth and more frequent low-intensity fires. During Medieval Warm Period fire frequency peaked due to intense droughts and periodic stand-replacing fires (Pierce et al., 2004).

• Biomass
  Climatic change can also produce vegetation changes that create greater availability of fuel. For example the transition from open vegetation to forest at Lake Cleveland (Davis et al., 1986) and at Balsam Meadow (Davis et al., 1985)
  
  

ANTHROPOGENIC CONTROL OF FIRE FREQUENCY

a. wildlife and livestock management: game drives, improvement of forage
b. improve campsites and trails, remove dense vegetation, prevent wildfire
c. warfare: conceal movements, confound enemies

New Guinea: Goeff Hope (1980) suggests grasslands in high-elevation rainforest result from fires

Australia: Gerdip Singh (Singh & Geissler, 1985), at Lake George increased charcoal frequency during the last interglaciation is coincident with earliest human artifacts, vegetation change at that time may have been caused by fire.

Minnesota: Eric Grimm (1983), position of prairie/forest border determined by anthropogenic fires during the Late Holocene (fire shadows)

Western North America: Kay (1995 ff.) All ecosystems were impacted by Indian burning, restoration management toward pre-Columbian ecosystem states would require frequent human-caused fires.

California: Tulare Lake (Davis, 1992) Charcoal accompanies transition from Great-Basin woodland to valley grassland human & climate? [diagram]



Arizona, San Pedro Valley (Davis et al., 2001) Burning of wetlands much less frequent during historic period.




SPECIAL TOPICS Soot (industrial) in pollen preparations Fires destroy desert varnish of rocks by spalling


HISTORIC DECREASE IN FIRE FREQUENCY
Climate Change
Grazing and Timber Cutting
Governmental Fire Suppression





Charcoal Readings

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