Effects of wildfire and permafrost on soil organic matter and soil climate in interior Alaska |
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Authors: | JENNIFER W. HARDEN,KRISTEN L. MANIES,MERRITT R. TURETSKY&dagger , JASON C. NEFF&Dagger |
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Affiliation: | US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, USA,;Department of Plant Biology, Michigan State University, 166 Plant Biology Building, East Lansing, MI 48824, USA,;Geological Sciences and Environmental Studies, University of Colorado at Boulder, CB-399, Boulder, CO 80309, USA |
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Abstract: | The influence of discontinuous permafrost on ground‐fuel storage, combustion losses, and postfire soil climates was examined after a wildfire near Delta Junction, AK in July 1999. At this site, we sampled soils from a four‐way site comparison of burning (burned and unburned) and permafrost (permafrost and nonpermafrost). Soil organic layers (which comprise ground‐fuel storage) were thicker in permafrost than nonpermafrost soils both in burned and unburned sites. While we expected fire severity to be greater in the drier site (without permafrost), combustion losses were not significantly different between the two burned sites. Overall, permafrost and burning had significant effects on physical soil variables. Most notably, unburned permafrost sites with the thickest organic mats consistently had the coldest temperatures and wettest mineral soil, while soils in the burned nonpermafrost sites were warmer and drier than the other soils. For every centimeter of organic mat thickness, temperature at 5 cm depth was about 0.5°C cooler during summer months. We propose that organic soil layers determine to a large extent the physical and thermal setting for variations in vegetation, decomposition, and carbon balance across these landscapes. In particular, the deep organic layers maintain the legacies of thermal and nutrient cycling governed by fire and revegetation. We further propose that the thermal influence of deep organic soil layers may be an underlying mechanism responsible for large regional patterns of burning and regrowth, detected in fractal analyses of burn frequency and area. Thus, fractal geometry can potentially be used to analyze changes in state of these fire prone systems. |
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Keywords: | black spruce boreal carbon combustion fire emission fire fractal analysis ground fuel moss cover organic mat organic soil peat permafrost soil surface temperature |
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