PARENT SESSION
Oral Session #15: Paleoecology and Climate Change.
Presiding: J. Betancourt
Monday, August 5. 1:00 PM to 3:45 PM. Graham Meeting Room, TCC.

Reconstructing fire regimes with charcoal and pollen from small hollows: A calibration with tree-ring records.

Higuera, Philip^*,1, Brubaker, Linda², Sprugel, Douglas³, ¹ University of Washington, Seattle, Washington² University of Washington, Seattle, Washington³ University of Washington, Seattle, Washington

ABSTRACT- Small hollows offer valuable records of environmental change with a unique combination of temporal depth and spatial resolution. In this study charcoal and pollen in eight ²¹⁰Pb-dated small-hollow records were compared to the timing and severity of 12 fires reconstructed with tree age structures and fire scars from stands adjacent to each hollow. Charcoal peaks recorded 3 of 3 high-severity, 2 of 4 moderate-severity, and 2 of 5 low-severity fires. The absence of charcoal peaks from some low- and moderate-severity fires is consistent with a positive relationship between fire severity and charcoal production. Sediment mixing and the taphonomic history of charcoal are other likely explanations for the absence of peaks from low- and moderate-severity fires. In contrast, the existence of a charcoal peak in absence of fire (false positive) occurred only once, which appeared to be due to a fire greater than 55 m from the hollow. Although we were not able to infer fire severity from charcoal peaks alone, some inferences were possible using a combination of pollen and charcoal evidence. All high-severity fires were associated with distinct increases in the ratio of background to local pollen, while this signature only occurred in half of the moderate- and none of the low-severity fires. With an understanding of their limitations and sensitivities, small hollows can provide valuable records of fire regimes and vegetation change that are unattainable with other methods.

KEY WORDS: fire history, disturbance history, sediment charcoal, paleoecology