Twentieth-century wildfire suppression and land management policies have promoted biomass accumulations in some ecosystems in the western United States where wildfire is a natural and necessary element. These changes have fueled large, stand-replacing crown fires in southwestern ponderosa pine forests, where they were rare under natural fire regimes [Allen et al., 2002]. Current policy contemplates massive ecosystem restoration involving prescribed fires and mechanical fuel reductions on millions of hectares and the subsequent re-introduction of pre-suppression fire regimes [USDA and USDI, 2002]. Success critically depends on understanding past and present fire regimes. The current western drought and the potential for climatic change to increase the frequency and magnitude of the region's droughts [Smith et al., 2001] further emphasize the need to understand short- and long-term climate-fire relations.