Past Fire Frequencies: Treerings, Charlocal & Sediments

Fire is present in all ecosystems, from tundras to deserts. All vegetation burns (at different frequencies) under certain circumstances.

Fire is a dominant ecological process in some ecosystems: chaparral, grasslands, xeric forests (ponderosa pine, pinyon-juniper woodland, oak woodland).

METHODS OF RECONSTRUCTING FIRE FREQUENCY

1. FIRE-SCARRED TREES (Heinselman, 1973):
Produced by repeated burnings of individual trees. Initial burning makes trees more susceptible, and older trees burn easier, so there is an exponential decline in abundance of older trees.

EXAMPLES

Note historic decline




CHARCOAL IN LAKE SEDIMENTS:
Techniques:
  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)

Charcoal Production Factors (Albini, 1983)
AREA REPRESENTED
In general, smaller (microscopic) particles represent a regional geograpical area, and larger (macrofossil-sized) particles represent a local geograpical area (Carcaillet et al., 2001; MacDonald et al., 1991)

Macroscopic-Microscopic Comparison


after MacDonald et al., 1991


INTREPRETATION;

Note historic decline



CLIMATIC CHANGE AND FIRE FREQUENCY

ANTHROPOGENIC CONTROL OF FIRE FREQUENCY

Reasons to burn vegetation: (Williams & Reed, 1994)
Examples: