Variability of tundra fire regimes in Arctic Alaska: millennial-scale patterns and ecological implications

Abstract

Tundra fires have important ecological impacts on vegetation, wildlife, permafrost, and carbon cycling, but the pattern and controls of historic tundra fire regimes are poorly understood. We use sediment records from four lakes to develop a 2000-yr fire and vegetation history in a highly flammable tundra region and compare this history with previously published fire records to examine spatial and temporal variability of tundra burning across Arctic Alaska. The four sites span a modern climatic gradient in the Noatak National Preserve, from warmer, drier down-valley locations to cooler, generally moister up-valley locations. Modern vegetation varies from herb-to shrub-dominated tundra from down-to upvalley sites, and pollen data suggest that this spatial pattern in vegetation persisted over the past two millennia. Peaks in macroscopic charcoal accumulation provide estimates of fireevent return intervals (FRIs), which did not vary significantly at millennial time scales but did vary across space. Down-valley sites burned relatively frequently over the past two millennia, with median FRIs of 150 years (95% CI 101-150) and FRI distributions statistically similar to those from ancient shrub tundra and modern boreal forest. At up-valley sites FRIs were significantly longer than those at down-valley sites, with a median FRI of 218 years (95% CI 128-285). These differences likely reflect the cooler growing-season temperatures and lower evaporative demand at up-valley sites, but local-scale variability in vegetation may have also shaped tundra fire regimes. Comparisons with other long-term fire records in Alaska reveal that the tundra biome can sustain a wide range of burning, with individual FRIs from as low as 30 years to more than 5000 years. These records together indicate that frequent tundra burning has occurred under a range of climatic and vegetation scenarios. The variety of tundra fire histories within Alaska suggests that the ecological impacts of tundra burning likewise vary widely, with important implications for wildlife-habitat maintenance and for the responses of tundra biophysical and biogeochemical processes to climatic change.

Biomass burning fuel consumption rates: a field measurement database

“…Fire regime in the Arctic is largely unknown, but historically fire is generally absent in the tundra biome compared to other biomes. However, the evidence of increasing fire frequency and larger extent of the fires in the arctic (Hu et al, 2010) may represent a positive feedback effect of global warming, so in the future more fires may occur in this biome (Higuera et al, 2011). There are still large unknowns of the impacts that fires have on the carbon stocks of the tundra ecosystems.…”

Climate-Driven Effects of Fire on Winter Habitat for Caribou in the Alaskan-Yukon Arctic

“…Fire return intervals in that region of Alaska (approx. 140–240 yrs) [58] are not indicative of tundra vegetation on the North Slope of Alaska where fire return intervals may exceed 1,000s years [6], [20]. The fire regime in western Alaska is more similar to fire regimes of lowland tundra interspersed amongst spruce forest that is common throughout the winter range of the Porcupine caribou herd [23].…”

Non-Destructive Lichen Biomass Estimation in Northwestern Alaska: A Comparison of Methods

“…Long-term studies of ungulate grazing exclosures are underway on Alaska's Seward Peninsula [33], [34], and conversion of lichen cover/height data to forage biomass will be an essential component of these studies. The National Park Service has other long-term lichen/vegetation studies in which both lichen cover and height are measured [33]; these may similarly be coupled with remote sensing modeling using our conversion factors for applications including changes in vegetation community structure with climate change effects [35], vegetation response to changing fire regimes [36], and carbon accounting [37]. The National Park Service's Arctic Network has sufficient density of ground-based measurements to model lichen biomass at a landscape scale [24].…”

“…Improved burn severity geospatial layers and historic fire perimeters would increase the resolution of these layers by allowing for the modeling of successional status, and hence lichen height and cover. Lichen winter range for the Western Arctic Caribou Herd is projected to suffer some decline with climate-driven shrub increase [1], [35], more frequent wildfire [36], and increasing inputs of nitrogen and sulfur from regional development [38]. Continued monitoring of lichen biomass will be critical for detecting and addressing ongoing changes.…”