Physical short-term changes after a tussock tundra fire, Seward Peninsula, Alaska

The Kougarok area, situated on the central Seward Peninsula, Alaska, experienced a severe fire in August 2002. This may be the only tundra fire where high-quality prefire (1999-2002) and postfire (2003-2006) active layer and meteorology measurements have been collected in the same locations. After fire, near-surface soil showed increased moisture at the burned tussock site, remaining close to saturation throughout the thawed season 2003-2006. Despite wetter soil after the fire, freezing occurred earlier at the burned tussock site than at the control, indicating the importance of a reduced organic layer. Severe combustion of lichen and moss left 15-25 cm high tussocks, resulting in a doubling of the surface roughness coefficient. Average September temperature at the tussock site increased 2.3 +/- 0.7 degrees C throughout the 1 m soil profile, doubling the active layer depth, although this is due partly to favorable meteorological conditions. The shrubby control station experienced a mean annual temperature increase of 1.1 +/- 0.3 degrees C in the upper 0.5 m. A similar annual change was found at the burned tussock site. Cooler weather conditions in 2006 stagnated the soil-warming trend, which occurred after 2002. How the thermal and moisture regimes in tundra will be affected after fire is highly influenced by weather, fire severity, vegetation regrowth, prefire vegetation, and ground ice conditions.