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Arctic tundra soils store large amounts of carbon (C) in organic soil layers hundreds to thousands of years old that insulate, and in some cases maintain, permafrost soils. Fire has been largely absent from most of this biome since the early Holocene epoch, but its frequency and extent are increasing, probably in response to climate warming. The effect of fires on the C balance of tundra landscapes, however, remains largely unknown. The Anaktuvuk River fire in 2007 burned 1,039 square kilometres of Alaska's Arctic slope, making it the largest fire on record for the tundra biome and doubling the cumulative area burned since 1950 (ref. 5). Here we report that tundra ecosystems lost 2,016?±?435?g?C?m?2 in the fire, an amount two orders of magnitude larger than annual net C exchange in undisturbed tundra. Sixty per cent of this C loss was from soil organic matter, and radiocarbon dating of residual soil layers revealed that the maximum age of soil C lost was 50 years. Scaled to the entire burned area, the fire released approximately 2.1?teragrams of C to the atmosphere, an amount similar in magnitude to the annual net C sink for the entire Arctic tundra biome averaged over the last quarter of the twentieth century. The magnitude of ecosystem C lost by fire, relative to both ecosystem and biome-scale fluxes, demonstrates that a climate-driven increase in tundra fire disturbance may represent a positive feedback, potentially offsetting Arctic greening and influencing the net C balance of the tundra biome. [ABSTRACT FROM AUTHOR]

Amplified climate warming at high northern latitudes is challenging societies that depend on local provisional and cultural ecosystem services, e.g., subsistence resources, for their livelihoods. Previous qualitative research suggests that climate-induced changes in environmental conditions are affecting rural residents' ability to travel across the land and access local resources, but detailed information on the nature and effect of specific conditions is lacking. Our objectives were to identify climate-related environmental conditions affecting subsistence travel and access, and then estimate rural resident travel and access vulnerability to those environmental conditions. We collaborated with nine Interior Alaskan communities within the Yukon River basin and provided residents with cameraequipped GPS units to document environmental conditions directly affecting subsistence access for 12 consecutive months. We also conducted comprehensive interviews with research participants to incorporate the effects of environmental conditions not documented with GPS units. Environmental conditions reported by rural residents were categorized into seven condition types. We assessed vulnerability to each condition by accounting for both likelihood (number of times a condition was documented) and sensitivity (magnitude of the effect from the condition) information derived from GPS observations and interviews. We also tested for differences in mean vulnerability values among environmental conditions and between community types (road-connected vs. remote) using a oneway analysis of variance. Rural community travel and access were most vulnerable to changes in ice conditions, erosion, vegetative community composition, and water levels. Environmental conditions that impeded natural travel corridors, e.g., waterways, more strongly influenced remote communities than those connected by roads. Increased vulnerability to environmental change puts remote communities at increased risk for food-security issues. Our study used a novel community-based approach to integrate local knowledge with scientific analysis to document and estimate the relative effects that specific environmental conditions are having on access to subsistence resources across Interior Alaska. [ABSTRACT FROM AUTHOR]