The Role of Fire in Permafrost Terrain in the Boreal Forest

The boreal forest plays a potentially critical role in determining the rate of global climate change. First, changes in the extent of forest cover could have massive effects on regional warming and could greatly amplify or nullify the expected rapid climatic warming at high latitudes. Secondly, changes in the carbon balance of boreal forest could strongly influence global warming through impacts on atmospheric CO2. On the one hand, high-latitude forests could be an important component of the "missing sink" of CO2, if they are accumulating carbon. Alternatively, gradual climate warming could increase fire frequency or decomposition sufficiently that these forests become a net carbon source. The BOREAS project in Canada has documented the land-atmosphere exchange processes of mature boreal forests but has given less attention to the role of fire in the carbon balance of the boreal forest.

Fire return time in the boreal forest is less than 100 yr and is strongly influenced by climate and human activities (both as a source of ignition and an agent of fire control). Fire models that include CO2-induced climatic warming predict a 46% increase in fire severity rating and a 40% increase in area burned. Recent warming trends are correlated with a more than doubled annual area burned in the Canadian boreal forest. Thus, there is good reason to expect dramatic changes in fire regime in northern regions.

Given the importance of fire in the boreal forest, the fire-research community has planned a series of three large-scale experimental burns to study fire behavior and the ecological impacts of fire. These are crucial to management objectives (manipulating fire regimes and controlling undesirable fires) and to scientific objectives of understanding the ecological and climatic consequences of boreal fires. The first two experimental burns (Bor Island in central Siberia in 1995 and in the Northwest Territories of Canada in 1996) have focused largely on fire behavior in two important areas of non-permafrost terrain. The third experiment, FROSTFIRE, is planned for Alaska in 1998. It differs from the previous fire experiments in that (1) it will take place in permafrost-dominated terrain, which characterizes most of the circumpolar boreal forest, and (2) it will focus on the impact of fire on element cycles at the landscape and regional scales. The specific objectives of the proposed research are (1) to document the relationship between fire behavior and microclimate, vegetation and soil characteristics, (2) to document the carbon and nitrogen budgets of the fire and the immediate post-fire period, (3) to determine the role of fire in the regional carbon and nitrogen budgets of Alaskan boreal forest, and (4) to define the fuel and microclimatic determinants of stand-replacing vs. less severe fires. NSF has funded the basics of this research design, but we encourage involement of other groups to expand the research that could be accomplished.

The fire will take place in June 1998 in a 700 ha permafrost-dominated watershed at the Caribou-Poker Creek Research Watershed near Fairbanks Alaska. This watershed contains a permanent stream and the major forest types of the Alaskan boreal forest. The experiment is designed to vary fire intensity across the watershed in order to span the entire range of burn intensities observed in boreal forest. This range of burn intensities will be applied to both permafrost-dominated black spruce and muskeg ecosystems and to permafrost-free deciduous-forest ecosystems. We will also monitor an unburned control watershed. Prior to the burn, we will document the carbon and nitrogen stocks in vegetation and soils of the burned and control watersheds and their distribution into different fuel classes (i.e., classes of materials that differ in probability of combustion). We will also establish bore holes to monitor permafrost thermal regime because melting of ice-rich permafrost is a major ecological concern associated with climatic warming, particularly at times of surface disturbances such as fire. We have been monitoring N deposition at the site (NADP monitoring) and would measure carbon, water, and energy exchange of the major ecosystem types using eddy correlation and C and N outputs in streams through hydrologic monitoring.

Immediately following the fire, we will re-survey the watershed to estimate changes in C and N stocks (and their redistribution among major pools such as vegetation to ash) within the watershed. We will measure C and N fluxes to the atmosphere and losses in stream water beginning immediately after the fire and continue these measurements less frequently during winter and in the two subsequent years.

The final component of the proposed research will be an evaluation of the past and current role of fire in the Alaskan boreal forest. We have already determined the fire history of the site using fire scars and are studying the regional fire history through a more widespread analysis of fire scars. We are testing the feasibility of measuring charcoal inputs to annually laminated lake sediments in areas of known fire history. We would seek to extend these analyses in space and time through four efforts: (1) a regional analysis of charcoal input to lake sediments to determine the long-term history of fire in interior Alaska (the last 2000 yr, with emphasis on the last 100 yr), (2) an analysis of fire records to estimate fire return times and the frequency distribution of fire sizes in interior Alaska, and (3) comparison of a currently available vegetation map based on 1 km-resolution AVHRR with maps of historical fires to estimate regional fire probabilities during the 6 years for which AVHRR data are available. We would also hope to compare these to aerial photographs taken in the 1950s and 1960s that are currently being declassified by the military. We expect to be able to map prior fires through comparison of the historical record of pre-AVHRR fire locations with AVHRR-based vegetation maps. Finally, (4) we would combine this information in simple models to estimate regional C and N losses to the atmosphere as functions of regional variation in climate and vegetation and temporal variation in climate (using climate reconstructed from weather records and tree rings).

In addition to the NSF support for the experimental burn, three groups with separate funding will play a major role in this research. The Alaska Fire Service will prepare fire lines, carry out the controlled burn, and be responsible for containment of the fire within the burned watershed. Fire behavior specialists from the Canadian and U.S. Forest Services would instrument the site and monitor fire behavior. The boreal forest Long-Term Ecological Research (LTER) Program at Bonanza Creek will commit itself to process-based studies of processes occurring after the fire (e.g., decomposition, root growth, tree establishment and growth, stream C and N cycling, process-based modeling) for at least six years following the fire. The theme of the LTER project is the interaction of multiple disturbances (fire, logging, and insect outbreaks) in the boreal forest. This experimental burn will become the major fire research site for the long-term studies of the LTER program.

If you have any questions or comments about the project, contact:
Dr. Larry D. Hinzman (, Water and Environmental Research Center, University of Alaska Fairbanks,
441 Duckering Bldg., P.O. Box 755860, Fairbanks, Alaska 99775; Tel: (907) 474-7331, Fax: (907) 474-7979.

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