Effects of surface fuel consumption on patterns of permafrost in a black spruce forest complex in interior Alaska

A common characteristic of black spruce forests underlain by permafrost in interior Alaska is the presence of a deep (10 to greater than 50 cm) layer of organic material consisting of live and dead moss, lichen, grass tussocks, and organic soil This layer of organic material promotes permafrost development through insulation of the ground layer, as well as retention of soil moisture. This organic layer is also part of the fuel matrix that burns during the periodic (every 50 to 200 years) fires that are common to this forest type, and the level of surface fuel consumption strongly influences post-fire patterns of soil temperature and moisture. In this paper, we present the results of a study of the patterns of surface fuel consumption (SFC) in a black spruce forest complex in interior Alaska. In a single fire event from 1994, there was a wide range in SFC, from less than 20 percent to greater than 90 percent of the ground-layer organic material present before the fire. Based on field observations, a model of SFC is presented that takes into account seasonal climatic patterns, degree of permafrost melt at the time of the fire, and underlying site drainage. This model is used to explain the wide range of permafrost conditions observed in the mature, unburned black spruce forests in the study region.