FIRE SIZE AND FIRE SEVERITY: IMPLICATIONS OF SMALL HOLLOW CHARCOAL RECORDS FROM THE PUGET SOUND LOWLANDS, WA

BRUBAKER, L (1) AND CRAUSBAY, S (2)

(1) Linda Brubaker, College of Forest Resources, University of Washington, Seattle WA; (2) Shelley Crausbay, Department of Botany, University of Wisconsin, Madison WI

The ecological consequences of fire regimes depend on three key parameters:  fire frequency (1 / return interval), severity and extent.  Most sediment-charcoal research has focused on fire frequency, with little attention to fire severity or extent.  Small-hollow pollen and charcoal records, supported by a calibration study (Higuera et al., 2005), reveal stand-level fire histories from Pseudtsuga menziesii/Tsuga heterophylla forests in the central Puget Sound Lowlands.  This forest type is characterized by low frequency (1/300-500yrs), stand replacing fires.  The similar ages of infrequent charcoal peaks at 2 hollows, separated by ~1 km and a distinct wetland, suggest that these sites experienced the same fire events over the past 7000 years.  Thus high-severity fires appear to have spread >1 km across distinct fire breaks.  A third site reveals vegetation and charcoal histories 14,000-6000 cal BP.  Between 12,000-7000 cal BP, when regional climates were warmer/drier than present, pollen assemblages indicate open vegetation near the site, although trees (P. menziesii and Alnus rubra) were present in the general landscape.  Despite the ubiquitous role of fire in maintaining treeless plant communities in this region, sediment-charcoal content is low during this period.  We interpret that frequent, low severity fires maintained open communities, but produced too little charcoal to be faithfully recorded in the sediment.