Randi R. Jandt

Carbon loss from an unprecedented Arctic tundra wildfire

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.

Fire behavior, weather, and burn severity of the 2007 anaktuvuk river tundra fire, North Slope, Alaska

Abstract In 2007, the Anaktuvuk River Fire (ARF) became the largest recorded tundra fire on the North Slope of Alaska. The ARF burned for nearly three months, consuming more than 100,000 ha. At its peak in early September, the ARF burned at a rate of 7000 ha d−1. The conditions potentially responsible for this large tundra fire include modeled record high summer temperature and record low summer precipitation, a late-season high-pressure system located over the Beaufort Sea, extremely dry soil conditions throughout the summer, and sustained southerly winds during the period of vegetation senescence. Burn severity mapping revealed that more than 80% of the ARF burned at moderate to extreme severity, while the nearby Kuparuk River Fire remained small and burned at predominantly (80%) low severity. While this study provides information that may aid in the prediction of future large tundra fires in northern Alaska, the fact that three other tundra fires that occurred in 2007 combined to burn less than 1000 ha suggests site specific complexities associated with tundra fires on the North Slope, which may hamper the development of tundra fire forecasting models.

Biomass offsets little or none of permafrost carbon release from soils, streams, and wildfire: an expert assessment

As the permafrost region warms, its large organic carbon pool will be increasingly vulnerable to decomposition, combustion, and hydrologic export. Models predict that some portion of this release w ...

Tundra Fire and Vegetation Change along a Hillslope on the Seward Peninsula, Alaska, U.S.A.

Abstract A 1977 tundra fire burned a hillslope where prefire soils and vegetation ranged from poorly drained moist tussock-shrub tundra on the lower slopes to well-drained dwarf shrub tundra on the back slope and very poorly drained wet sedge meadow on the flat crest. We sampled the vegetation on this slope before the fire and at 8 sites following the fire at irregular intervals from 1 yr to 25 yr. During the first decade after the fire, short-term recovery was dominated by bryophytes, sedges, and grasses from both regrowing sedge tussocks and seedlings. However, during the second and third decade, and by 24 yr after the fire, evergreen (Ledum palustre) and deciduous shrubs (mainly Salix pulchra willow) expanded dramatically so that shrub cover was generally higher than before the fire. Labrador tea has increased by vegetative means on the poorly drained lowest 3 tussock-shrub tundra sites. Upslope on the better-drained and more severely burned tussock-shrub and dwarf shrub tundra sites, willows became established from seed mainly during the first 10 yr after the fire and, based on their relatively large size (0.5–1 m tall) and cover, have grown rapidly during the past 15 to 20 yr. There has been very little or no recovery of Sphagnum moss and fruticose lichens after 24 yr at any site, except for Sphagnum moss in the wet meadow site. The permafrost active layer thickness has diminished to prefire levels at the lower slope tussock-shrub tundra sites but is much greater or degraded completely on the steeper slope, corresponding with the distribution of willow shrub colonization. These changes in tundra vegetation and permafrost following fire suggest that such fires could accelerate the predicted effects of climate warming on ecosystems in the Arctic.

Decrease of lichens in Arctic ecosystems: the role of wildfire, caribou, reindeer, competition and climate in north-western Alaska

We review and present a synthesis of the existing research dealing with changing Arctic tundra ecosystems, in relation to caribou and reindeer winter ranges. Whereas pan-Arctic studies have documented the effects on tundra vegetation from simulated climate change, we draw upon recent long-term regional studies in Alaska that have documented the actual, on-the-ground effects. Our review reveals signs of marked change in Arctic tundra ecosystems. Factors known to be affecting these changes include wildfire, disturbance by caribou and reindeer, differential growth responses of vascular plants and lichens, and associated competition under climate warming scenarios. These factors are interrelated, and, we posit, unidirectional: that is, they are all implicated in the significant reduction of terricolous lichen ground cover and biomass during recent decades. Lichens constitute the primary winter forage for large, migratory caribou and reindeer herds, which in turn are a critical subsistence resource for rural residents in Alaska. Thus, declines in these lichens are a major concern for rural people who harvest caribou and reindeer for subsistence, as well as for sport hunters, reindeer herders, wildlife enthusiasts and land managers. We believe a more widely distributed and better integrated research programme is warranted to quantify the magnitude and extent of the decline in lichen communities across the Arctic.

Slow Recovery of Lichen on Burned Caribou Winter Range in Alaska Tundra: Potential Influences of Climate Warming and Other Disturbance Factors

ABSTRACT Lichen regeneration timelines are needed to establish sound fire management guidelines for caribou (Rangifer tarandus) winter range. Paired burned and unburned permanent vegetative cover transects were established after 1981, 1977, and 1972 tundra fires in northwestern Alaska to document regrowth of tundra vegetation including caribou forage lichens in the wintering range of Alaskas largest caribou herd. Following fire, lichen had recovered very little compared to unburned transects (1% cover vs.15% cover) after 14 years. After 24 or 25 years, lichen cover in the burns remained low (3–4%), whether or not caribou were present during the recovery period. In addition, lichen cover on unburned transects at one study site had decreased from 14% to 6%. Shrub cover was higher on the burned plots than the unburned plots. Cover of cottongrass (Eriophorum vaginatum) initially increased following the fire and tussocks quickly became more vigorous than on paired unburned transects, remaining so for more than 14 years. Persistent changes in vegetation following fire likely reflect the cumulative impacts of seasonal caribou use and favorable growing conditions (warmer soils, longer growing season) for rooted vascular species during the recovery period. The actual recovery of forage lichens after fire on our study sites is slower than predictions based on ideal growth potential.

Changes in vegetative cover on Western Arctic Herd winter range from 1981 to 2005: potential effects of grazing and climate change

The population of the Western Arctic Herd, estimated at 490 000 caribou (Rangifer tarandus granti) in 2003, is at its highest level in 30 years. Twenty permanent range transects were established in the winter range of the Western Arctic Herd in 1981 to assess the impacts of grazing. These transects were revisited in 1995 and 1996 (1995/96). Only 18 of the transects were re-located, so an additional 7 transects were established in 1996. In 2005, all 25 remaining transects were revisited. Lichen coverage dropped by a relative 45.1% between 1981 and 1995/96 and by an additional relative 25.6% between 1995/96 and 2005. There was a significant decline in primary forage lichens between 1995/96 and 2005. Caribou use was greater in areas with high lichen abundance. Graminoid cover increased by a relative 118.4% from 1981 to 1995/96 and again by a relative 26.1% from 1995/96 to 2005. Shrub cover increased during the study whereas forb cover declined. The decline in lichen abundance on the winter range of the Western Arctic Herd over 24 years is an index of caribou habitat condition. The observed changes in vegetation cover can be attributed to caribou grazing, fire, and possibly global climate change. Continued declines in lichen cover could lead to population declines within the herd, range shifts, or both.

Fire in arctic tundra of Alaska: past fire activity, future fire potential, and significance for land management and ecology

A multidecadal analysis of fire in Alaskan Arctic tundra was completed using records from the Alaska Large Fire Database. Tundra vegetation fires are defined by the Circumpolar Arctic Vegetation Map and divided into five tundra ecoregions of Alaska. A detailed review of fire records in these regions is presented, and an analysis of future fire potential was performed based on future climate scenarios. The average size of tundra fire based on the data record is 22 km2 (5454 acres). Fires show a mean size of 10 km2 (2452 acres) and median of 0.064 km2 (16 acres), indicating small fires are common. Although uncommon, 16 fires larger than 300 km2 (74 132 acres) have been recorded across four ecoregions and all five decades. Warmer summers with extended periods of drying are expected to increase fire activity as indicated by fire weather index. The implications of the current fire regime and potential changes in fire regime are discussed in the context of land management and ecosystem services. Current fire management practices and land-use planning in Alaska should be specifically tailored to the tundra region based on the current fire regime and in anticipation of the expected change in fire regime projected with climate change.