The influence of fire-free interval on carbon cycling in the Alaskan boreal fores

High Northern Latitude (HNL) (boreal) forests are an important world-wide carbon reservoir. Much of the carbon stored in North American boreal forests is in the deep organic soils of black spruce (Picea mariana) forests. In Alaska alone, these forests cover 26 million hectares and the deep organic soil layers located here store greater than eighty percent of the region’s non-peatland terrestrial carbon. The ability of this ecosystem to store carbon is strongly influenced by the fire regime. The boreal fire regime has seen increases in the frequency of large fire years and late season burning, as well as an increase in the total area burned each year. It has been shown that a shorter fire frequency, commonly referred to as the Fire-Free Interval (FFI), leads to changes in the successional trajectories of boreal forests and a reduction in the amount of organic matter sequestered by these forests. While there is extensive ongoing research on the size and severity of fire using ground and remote based studies in mature forest stands, research on the impacts of the FFI has thus far been limited to field-based studies. Detailed research on the changing FFI and its effects on boreal vegetation, using a combination of remote sensing, field-based and modeling efforts, will improve the understanding of carbon cycling in this region. In this study, the factors controlling the vulnerability of landscapes to more frequent reburning have been explored by integrating different geospatial data sets (including several derived from satellite remote sensing data) using GIS. Patterns of reburning have been examined, including the impacts of topography and climate, using a Landsat based land cover dataset, topographic datasets, MODIS Active Fire Hotspot data, fire weather indices and the delta Normalized Burn Ratio (dNBR) derived from Landsat TM/ETM+ data. Since 1950, over 30% of the interior of Alaska has been impacted by fire at least once, and over 10% of that has been impacted two or more times by fire. This pattern of frequent reburning can lead to shallower organic layers in black spruce stands and can have important implications for carbon cycling.