GUYETTE, R. (1), STAMBAUGH, M. (1), AND DEY, D. (2).

(1) Missouri Tree-Ring Laboratory, University of Missouri, 203 ABNR Building, Columbia MO 65211, (2) USDA Forest Service, North Central Research Station, 202 ABNR Building, Columbia MO 65211.

Fire regimes are influenced by the interactions of humans, their population density, and climate. Relationships among these factors can be used to address questions concerning past and present fire regimes. How does human population density influence the relationship between drought and wildfire? Are past wildfires the result of climate conditioned fuels and drought-inspired human ignitions? We examine the evidence and logic in human-climate-fire interactions and address problems in analysis that result from the asynchronous seasonality of fuels and tree growth in deciduous forests. In fire regimes with few lightning ignitions the effects of drought on fire occurrence are often not realized without human ignitions. For example, in the Ozark Highlands, the extent of wildfire is highly correlated (r = -0.44, p = 0.004) with drought (PDSI) during periods (1850-1890) with abundant anthropogenic ignitions but weakly correlated (r = -0.15, p = 0.014) during periods (1700-1849) with low human population density. While there is no necessary causation, logic, or connection between drought and the number of incendiary fires there is an association. For example, drought (PDSI) is significantly correlated with the number of arson fires in Missouri: r = -0.76, Oregon: r = -0 .42, and Washington: r = -0.46. Overall, human ignitions can amplify the impact of drought in fire regimes.