1317 Ecological Applications, 15(4), 2005, pp. 1317–1330  2005 by the Ecological Society of America IMPACTS OF LARGE-SCALE ATMOSPHERIC–OCEAN VARIABILITY ON ALASKAN FIRE SEASON SEVERITY PAUL A. DUFFY, 1,5 JOHN E. WALSH, 2 JONATHAN M. GRAHAM, 3 DANIEL H. MANN, 4 AND T. SCOTT RUPP 1 1 Ecological Dynamics Modeling Group, Department of Forest Sciences, University of Alaska, Fairbanks, Alaska 99775 USA 2 International Arctic Research Center, Fairbanks, Alaska 99775 USA 3 Department of Mathematical Sciences, University of Montana, Missoula, Montana 59812 USA 4 Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775 USA Abstract. Fire is the keystone disturbance in the Alaskan boreal forest and is highly influenced by summer weather patterns. Records from the last 53 years reveal high vari- ability in the annual area burned in Alaska and corresponding high variability in weather occurring at multiple spatial and temporal scales. Here we use multiple linear regression (MLR) to systematically explore the relationships between weather variables and the annual area burned in Alaska. Variation in the seasonality of the atmospheric circulation–fire linkage is addressed through an evaluation of both the East Pacific teleconnection field and a Pacific Decadal Oscillation index keyed to an annual fire index. In the MLR, seven explanatory variables and an interaction term collectively explain 79% of the variability in the natural logarithm of the number of hectares burned annually by lightning-caused fires in Alaska from 1950 to 2003. Average June temperature alone explains one-third of the variability in the logarithm of annual area burned. The results of this work suggest that the Pacific Decadal Oscillation and the East Pacific teleconnection indices can be useful in determining a priori an estimate of the number of hectares that will burn in an upcoming season. This information also provides insight into the link between ocean–atmosphere interactions and the fire disturbance regime in Alaska. Key words: Alaska boreal forest; East Pacific teleconnection; ecological disturbance regimes; fire regimes; multiple linear regression; Pacific Decadal Oscillation; teleconnections. INTRODUCTION The boreal forest covers 12  10 6 km 2 of the northern hemisphere and contains roughly 40% of the world’s reactive soil carbon, an amount similar to that held in the atmosphere (Melillo et al. 1993, McGuire et al. 1995, IPCC 2001). The biophysical phenomena af- fecting carbon storage and high-latitude albedo make the boreal forest an integral component of the global climate system (IPCC 2001). Fire-initiated succession underlies the biophysical factors, and there is a pressing need to characterize sensitivities and potential respons- es of the boreal forest disturbance regime to climatic change (Schimel et al. 1997, Gower et al. 2001, Chapin et al. 2003). The impact of forecast climatic warming on fire regimes in North America varies from a pre- diction for increased burning for Alaska and Canada (Flannigan et al. 2000, 2001) to reduced fire frequency in eastern Canada (Carcaillet et al. 2001). Quantifica- tion of the links between climate and fire in Alaska is not only essential for understanding the dominant land- scape-scale disturbance processes in Alaska, but it is also a valuable tool for planning fire management ac- Manuscript received 12 May 2004; revised 4 August 2004; accepted 13 September 2004; final version received 6 December 2004. Corresponding Editor: M. Friedl. 5 E-mail: paul.duffy@uaf.edu tivities and developing a better understanding of how forecast climate change might impact the dominant dis- turbance mechanism. Within the North American boreal forest, Interior Alaska (i.e., the region between the Alaska and Brooks Ranges) contains 56  10 6 burnable hectares and in- cludes the largest national parks and wildlife refuges in the United States. Most of this huge area is roadless. For the period 1950–2003, wildland fires burned an average of roughly 270 000 ha in Interior Alaska each year and they routinely threaten the lives, property, and timber resources of the sparse but growing population (see Plate 1). Wildland fires can threaten human values, yet they play a crucial role in the maintenance of In- terior Alaskan ecosystems. Despite the pervasive eco- nomic and ecological impacts, fundamental aspects of the fire regime in Interior Alaska are poorly understood. Fire regimes consist of many components including frequency, duration, intensity, severity, seasonality, ex- tent, and spatial distribution. When complicating fac- tors such as interactions with other components of the ecosystem (e.g., human impacts, weather, vegetation) and the importance of spatial and temporal scales are taken into account, the characterization of a fire regime requires a tremendous amount of data and appropriate analysis. One of the most basic aspects of a fire regime is the fire cycle (i.e., the fire recurrence interval for an