Fire in the range of the Western Arctic Caribou Herd

Wildfire is the dominant ecological driver in boreal forest ecosystems. Although much less is known, it also affects tundra ecosystems. Fires effectively consume fruticose lichens, the primary winter forage for caribou, in both boreal and tundra ecosystems. We summarize 19502007 fire regime data for northwestern Alaska and subregions. We also identified meteorological factors that help explain the variability in fire extent across this landscape. We review information and inferences from recent studies on tundra fire regimes for managing caribou winter range. Climate warming may increase fire size and frequency in this region, which may substantially impact the vegetation, wildlife, and people of this region. Introduction Although much attention has been focused on the role of wildfire in boreal forest ecosystems, its role in tundra ecosystems has largely been overlooked (but see Miller 1985, Racine et al. 1985). Wildfires effectively consume ground-dwelling lichens that are the primary winter forage for Western Arctic Herd (WAH) caribou. These lichens can take decades to recover to pre-fire levels in northwestern Alaska (Jandt et al. 2008). Wildfires potentially limit caribou winter range by destroying preferred forage (Rupp et al. 2006). The WAH has undergone a population expansion starting in 1976 until reaching a high of 490,000 caribou in 2003 (Dau 2005). The herd has expanded and shifted its primary winter range to the Nulato Hills and the Seward Peninsula from its historic winter range in the Buckland Valley and Selawik National Wildlife Refuge (Figure 2). Both density dependent (i.e., increasing herd size leading to reduced lichen biomass) and density-independent (i.e., increasing area burned by wildfires leading to less mature habitat) may factor into the changes in winter range distribution exhibited by the WAH. Temperatures, in Alaska, including northwestern Alaska, have been rising and the rate of climate warming is predicted to increase (Stafford et al. 2000, ACIA 2005). Summer precipitation has decreased at many locations throughout Alaska, and Barrow has seen declines in annual precipitation as well (Stafford et al. 2000). Warmer and drier summers are associated with greater area burned in Alaska (Duffy et al. 2005). In the tundra ecosystem, wildfires are also predicted to increase (Higuera et al. 2008). Regional temperature and precipitation are correlated with large scale climatic regimes, such as the Pacific Decadal Oscillation (PDO) (Hartmann and Wendler 2005). Our goals were to 1) elucidate the fire regime in northwestern Alaska and in tundra ecosystems, 2) test whether wildfires are increasing in extent and frequency in the range of the WAH and 3) identify meteorological variables that correlate with annual area burned. Methods We summarized the data contained in the Alaska Fire Service’s geodatabase, which catalogs the extent, number and location of large fires mapped from 1950-2007 (Figure 3; data at http://agdc.usgs.gov/data/fire/index. html). Kasischke et al. (2002) performed similar analyses for Interior Alaska, but we calculated them for northwestern Alaska and various subsets including the WAH core winter range, outer range, and potential future winter range defined as a 30-mile (50-km) wide buffer around the outer range (Figure 2A). We also summarized burn area by conservation unit, ecoregion, tundra ecosystem, boreal forest ecosystem and also the area north of the 68th latitude (Figures 2 and 3). Tundra ecosystems were differentiated from forested areas using the 33-yard (30-m) National Land Cover Database – Alaska 2001 coverage (http://www.epa.gov/mrlc/nlcd-2001.html). For all of these areas, we also calculated the percentage of burned area that burned two or more times during the 58-year study period. Similarly, we calculated the fire cycle (i.e., the number of years required to burn over an area) (Kasischke et al. 2002) for these areas. We calculated this by dividing 1 by the proportion of area burned and multiN PS p h o to g ap h b y R o b rt W in free Figure 1. Grazing caribou.