Fire regimes of the Alaskan boreal forest James Cronan, Donald McKenzie, and Diana Olson DRAFT James Cronan is a research scientist, Donald McKenzie is a research ecologist, and Diana Olson is a University of Idaho-FRAMES project manager, U.S. Department of Agriculture, Forest Service, Pacific Wildland Fire Sciences Lab, 400 N 34th Street, Suite 201, Seattle, WA 98103. Fire regimes of the Alaskan boreal forest James Cronan, Donald McKenzie, Diana Olson Authors U.S. Department of Agriculture, Forest Service Pacific Northwest Research Station Portland, OR DRAFT General Technical Report PNW-GTR-XXX Month 201x Published in cooperation with: University of Washington, School of Forest Resources Yale School of Forestry and Environmental Studies University of Idaho U.S. Department of the Interior, Bureau of Land Management, Alaska Fire Service Abstract Cronan, J; McKenzie, D; Olson, D. 201X. Fire regimes of the Alaskan boreal forest. Gen. Tech. Rep. PNW-GTR-XXX. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. XXX p. Fire regimes are described for the boreal forest of Alaska. Information was compiled from published and unpublished work and represents a comprehensive literature review. Contemporary fire regimes are discussed based on six components: ignitions, seasonality, intensity, fire size, severity, and fire frequency. Fire regimes are stratified by major vegetation types present within the boreal forest including black spruce forest, white spruce forest, hardwood forest, and tundra. Multi-scale temporal patterns of fire regimes are presented and future changes to fire regimes and impacts on the boreal forest are discussed. Keywords: fire regime, fire history, boreal forest, Alaska, literature review. DRAFT Contents 1 Chapter 1: Introduction 1 History of Fire in Boreal Alaska 2 Statement of Purpose 2 Methods 3 The Regional Environment 6 Chapter 2: Alaskan Boreal Fire Regimes 6 Reconstructing and Interpreting Fire Regimes 7 Ignitions 8 Seasonality 10 Intensity 11 Fire Size 13 Severity 16 Fire Frequency 21 Chapter 3: Fire Regimes of Major Vegetation Types 21 Black Spruce Forest 23 White Spruce Forest 25 Hardwood Forest 27 Boreal Tundra 28 Other Vegetation Types 29 Chapter 4: Temporal Trends in Boreal Fire Regimes 29 Millennial Trends for the Late Quaternary Period 35 Centennial to Decadal Scale Trends in Late Holocene Fire Regimes 37 The Impacts of Human-caused Climate Change on Fire Regimes in Boreal Alaska DRAFT 40 Chapter 5: Key Findings and Conclusions 45 English Equivalents 46 References 68 List of figures and tables 69 Appendix 1: Alaskan Fire History Study Summaries DRAFT Chapter 1: Introduction History of Fire in Boreal Alaska The boreal fire regime of interior Alaska was summarized succinctly some 50 years ago when a pioneering ecologist in Alaska said “In one respect all forest trees in the Alaskan interior are similar; they are killed by severe fires” (Lutz 1956). While today that statement remains largely true (French et al. 2008, Johnson 1992a, Murphy et al. 2008), a great deal has been learned about the patterns of fire in the intervening decades. Most importantly, research has revealed the complexity of the disturbance regime and shown important changes in the characteristics of fire over time and space that are influenced by a number of environmental factors. Once viewed as a relatively simple system linked to irresponsible human actions (Lutz 1956) and as a cause of environmental degradation (Hutchison 1968), fire was rapidly accepted as a disturbance integral to ecological function (Rowe and Scotter 1973, Viereck 1973, Viereck and Schandelmeier 1980), which has continually shaped and been shaped by the natural and human environment since the Laurentide Ice Sheet, and its influence on Alaska’s climate, began receding some 20,000 years ago (DeWilde and Chapin 2006, Hu et al. 2006). The modern day fire regime in boreal Alaska was established ca. 5500 BP (calendar years before Common Era [CE] 1950) (Hu et al. 2006). Since that time, fire has been integral to the ecology of boreal forests. The mainly even-aged stand age structure is almost purely maintained by periodic large stand- replacing fires (Johnson 1992a, Ryan 2002). The fire regime interacts with terrain, soil drainage, forest succession, and flooding in riparian areas to create a mosaic of distinct vegetation types distributed in large patches across the landscape (Fastie et al. 2002, Kasischke et al. 2002, Kane et al. 2007, Mann et al. 1995, Mann and Plug 1999, Viereck et al. 1993). Successional pathways (Epting and Verbyla 2005, Johnstone and Chapin 2006, Johnstone and Kasischke 2005, Kasischke et al. 2000), nutrient cycling (Simard et al. 2007, Viereck and Dyrness 1979), forest productivity (Fenton et al. 2005, van Cleve et al. 1983), permafrost (Harden et al. 2006, Viereck and Dyrness 1979), and wildlife habitat (Collins and Helm 1997, Johnson and Rowe 1975, Maier et al. 2005, Nelson et al. 2008) are all influenced by the boreal fire regime. DRAFT Resilient plant species have evolved with the stand-replacing fire regime and rapidly recolonize burned areas following fire. Adaptive strategies revolve around prolific seed production timed in various ways to coincide with fire, and regeneration from rootstock (Black and Bliss 1978, Foote 1983, Viereck and Dyrness 1979, Zasada and Gregory 1969). In general, higher severity favors species that regenerate from seed (Dyrness and Norum 1983, Greene et al. 2004, Johnstone and Kasischke 2005). To a large extent, the composition of the boreal forest in Alaska is dependent upon the current fire regime and vice versa (Brubaker et al. 2009; Higuera et al. 2009; Mann and Plug 1999; Rupp et al. 2000a, 2000b); and both are ultimately regulated by climate (Camill et al. 2009, Duffy et al. 2005, Tinner et al. 2008), which varies at multiple temporal scales (Bartlein et al. 1998, Berger and Loutre 1991, Hess et al. 2001, Hu et al. 2003, Papineau 2001). The relative impacts of climatic shifts depend on their magnitude and duration. Acknowledging these impacts is critical to understanding the nature of the boreal fire regime and has implications for appropriate management of natural resources. The current statewide wildland fire management plan recognizes the ecological importance of fire and strives to maintain natural fire regimes while achieving primary goals of safely protecting life and 1 property against damage from fires (Alaska Wildland Fire Coordinating Group 1998). This management strategy, incorporating tiered response to fire that balances societal, economic, and ecological priorities, was instituted nearly three decades ago (figure 1). The option to let fires burn in remote areas was slowly embraced by large public land-management agencies (Todd and Jewkes 2006), which were developing policy that recognized the ecological value of fire (Pyne et al. 1996). There is little evidence to suggest that earlier suppression policy had a substantial impact on the fire regime of boreal Alaska (DeWilde and Chapin 2006, Drury and Grissom 2008). This is primarily due to the prohibitive costs of firefighting over such a large and remote area and fire intervals that are generally longer than the period of suppression. Current policy has likely averted major continued ecological impact of suppressing fire by allowing for most fire to burn. Knowledge of the boreal fire regime is integral to successful land management as the boreal forests in Alaska are fire-dependent ecosystems. Accurate spatially and temporally defined estimates of the fire regime are important for monitoring deviations of the current fire regime from reference fire regime conditions and tailoring management strategies to best suit management goals. Well described fire regimes aid land and fire management agencies in anticipating ecological impacts of interannual and decadal shifts in fire activity, assessing risk to sensitive resources, efficient use of suppression resources, evaluating severity, and forecasting future landscape changes. As anthropogenic climate change begins to influence the fire regime in the boreal forest of Alaska (Kasischke et al. 2010, Senkowsky 2001) and Canada (Gillett et al. 2004), accurately identifying the drivers of fire regimes and potential feedback loops is increasingly important for several reasons (Hu et al. 2006). Alterations to fire regimes and landscapes caused by climate change will undoubtedly have repercussions for land use patterns across the state and management plans must be adaptive to these changes and have thoughtfully conceived strategies for mitigating negative impacts. A well developed framework to describe drivers of fire regimes is a necessary component of ecological models used to forecast the impacts of climate change. Statement of Purpose The purpose of this paper is to provide land and fire management agencies with a comprehensive review of the boreal fire regime in Alaska.DRAFT New fire history studies in Alaska have been produced nearly every year for the past three decades (table 1), but no comprehensive literature reviews addressing fire regimes in Alaska have been published since the early 1980s (Viereck and Schandelmeier 1980). The large number of studies, occasional lack of accessibility, and difficulty of interpreting results from studies with different methodologies can create an informational burden on land managers. Methods We focus on publications that describe fire history of the Alaskan boreal forest. Considerable effort was expended to identify