Using fire regimes to delineate zones in a high-resolution lake sediment record from the western United States

a r t i c l e i n f o Keywords: Charcoal Fire regime Fire season Forest disturbance Lake sediments Pollen Paleoecology Regime shift Spruce-fir forest Wildfire Paleoenvironmental reconstructions are important for understanding the influence of long-term climate variability on ecosystems and landscape disturbance dynamics. In this paper we explore the linkages among past climate, vegetation, and fire regimes using a high-resolution pollen and charcoal reconstruction from Morris Pond located on the Markagunt Plateau in southwestern Utah, USA. A regime shift detection algorithm was applied to background charcoal accumulation to define where statistically significant shifts in fire regimes occurred. The early Holocene was characterized by greater amounts of summer precipitation and less winter precipitation than modern. Ample forest fuel and warm summer temperatures allowed for large fires to occur. The middle Holocene was a transitional period between vegetation conditions and fire disturbance. The late Holocene climate is characterized as cool and wet reflecting an increase in snow cover, which reduced opportunities for fire despite increased availability of fuels. Similarities between modern forest fuel availability and those of the early Holocene suggest that warmer summers projected for the 21st century may yield substantial increases in the recurrence and ecological impacts of fire when compared to the fire regime of the last millennium. Introduction Recent episodes of historically unprecedented tree mortality suggest that forest ecosystems in western North America (WNA) are undergoing substantial and rapid reorganization (Williams et al., 2010). Forest disturbance regimes are decoupling from historic norms due to warming temperatures, advancing spring snowmelt, and increasing aridity that are resulting in novel ecological outcomes and states (Scheffer et al., 2001; Westerling et al., 2006; Raffa et al., 2008). Long-term ecological records , such as those reconstructed from sediments archived in lakes, offer key insights into abrupt changes in climate and disturbance regimes. During the coming century, new ecological challenges will require a re-evaluation of land stewardship policies that will benefit greatly from consideration of longer term ecological records (Willis and Birks, 2006). Because fire is a keystone ecological process across a diversity of landscapes , the fire-regime concept is often emphasized as a common and accessible construct for interdisciplinary discourse (Falk and Swetnam, 2003; Conedera et al., 2009; Whitlock et al., 2010). Fire regimes are timescale-dependent, and therefore may include numerous biotic and abiotic attributes to describe fire variability (Whitlock et al., 2010). Over longer temporal scales, fire regimes are …