Emerging Issue Summary
Overview and Management Relevance:
The 2007 Anaktuvuk River Fire was a unique event in the known fire regime of the North Slope that occurred concurrently with a record low sea ice extent and a record late summer drought. Its significance as a portent of change is unclear and we are unable to forecast whether it was the beginning of a trend.
For the purposes of this summary, fire regime was defined as the occurrence, number, extent, and severity of fires. Fire observations have been recorded since 1956. Before 1993, only fires greater than 1,000 acres were recorded, with a threshold of greater than 100 acres since. The fire return interval for the Arctic Coastal Plain and foothills was estimated to be 10,000 or more years based on records collected during 1957-79. More recently, the fire return interval has been estimated to be approximately 3,500 years for the foothills, but as short as about 600 years for other tundra areas in Alaska (e.g., Seward Peninsula). In areas that have reburned, tundra is 4.5 time more likely to reburn than forested areas.
Some paleoecological work assessing fire-deposited charcoal in lake cores is underway and should contribute to improved understanding of fire regime on the North Slope. For tundra fires, inference from coring sites is limited to a fairly small area around the coring sites. As fire return intervals have historically been on the order of several hundred years, detecting less than very dramatic changes in long-term fire regime may not be possible.
The measurable or observable factors that influence annual fire regime include frequency of lightning, length of snow-free period, temperature, and precipitation. Lightning activity levels have been monitored since the 1950s and a noticeable sustained increase in activity on the North Slope was detected beginning in 2002, but lightning data may not be very reliable. The instrumentation to detect lightning has improved in recent years, but greater coverage is desirable, particularly in the Central Arctic. Information on spatial extent of snow cover on specific dates is available through remote sensing (NDVI). The need for a better distribution of sites for collecting temperature and precipitation data to meet a variety of emerging issue data needs is discussed in the “Weather and Climate” summary.
Weather patterns in Alaska are influenced by the Pacific Decadal Oscillation (PDO), a 20-30 year pattern of Pacific Ocean temperature variability that is poorly understood. The PDO is a relatively short-term phenomenon influencing weather and climate within the much longer-term pattern of increases in average global temperatures. The warm phase of the last PDO contributed to the warmer, drier Alaska weather observed in 1976-2006. As the PDO cycles to the cool phase, cooler and wetter summer weather is expected for Alaska, including the North Slope. The wildland fire management issues that arise from variation in summer weather tend to be manifested at a statewide level and are not isolated to the North Slope. The Alaska Wildland Fire Coordinating Group helps deal with coordination of these management issues at a statewide level.
The 2007 Anaktuvuk River Fire was described as a variable stage fire (rapid surface burn while the ground smoldered longer), with reburning occurring in some areas after wet vegetation matter dried out. Following most North Slope fires, resprouting of vascular plants (tussocks and forbs) is often nearly immediate unless, as with some portions of the Anaktuvuk River Fire, the fire burns down to mineral soil. In contrast, lichen communities recover slowly and make take up to 80 years or longer to recover to prefire biomass abundance. Woody species (willow, poplar, and aspen) respond well to disturbance and increases in the parameters defining fire regime, if they occur, are expected to support the spread of these species.
The 2007 Anaktuvuk River Fire has not prevented the seasonal migration of caribou through that area. However, research indicates that caribou foraging on winter range in the boreal forest and tundra ecosystems will tend to decrease use in burned areas for up to 50 years post burn in mid-winter. There is the potential for large-scale burns to result in changes in the seasonal distribution of caribou, which thus affect their availability to subsistence users. However, the geographic extent of winter range used by Alaskan arctic caribou herds is large and range use varies annually. Most caribou of the Western Arctic and Porcupine herds and typically over half of the Central Arctic Herd winter in forest and tundra habitats south of the Brooks Range. In most years, less than 10 percent of the Teshekpuk Herd caribou will winter south of the Brooks Range. Credible prediction of the potential effects of changes in fire regime or fire management policy on caribou distribution and subsistence use is not possible in the foreseeable future.
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