Fire's footprint: Understanding soil heating and fire effects in Denali National Park & Preserve's prescribed pile burns
Behrens M. . 2025.
Abstract
Prescribed pile burning is increasingly used as a fuel-reduction treatment in boreal
forests. However, the belowground thermal and biogeochemical effects of pile burning at high
latitudes remain weakly quantified, and implementation occurs without empirical evidence to
support practitioner decisions. Clear links between practitioner-controlled factors and soil
outcomes are necessary to balance wildfire risk reduction with informed stewardship. We
evaluated soil heating and first-order fire effects at hand-constructed piles in Denali National
Park & Preserve. Treatments varied in season of burn, soil organic layer depth, and pile volume.
We instrumented 59 piles with temperature sensors at multiple depths and lateral distances, and
measured burn depth, belowground carbon and nitrogen loss, soil pH, and plant-available
nutrients during the first post-burn growing season. We found that heating was shallow, confined
to the pile footprint, and lower in Spring compared to Fall. Specifically, spring burns over frozen
soils limited peak temperature, exposure time, and depth relative to fall burns over thawed soils.
Soil organic layer depth buffered mineral soil heating. Larger piles modestly increased burn
depth into the organic layer but did not broadly intensify heating. Changes in belowground
carbon and nitrogen were driven primarily by pile volume and organic layer depth, and nitrogen
generally declined. Burned soils became more alkaline and exhibited a short-term nutrient pulse.
Together, these results show that season of burn and soil organic layer depth largely determine
soil heating, and belowground carbon and nitrogen loss, giving practitioners actionable guidance
for scheduling and siting pile burns that meet fuel-reduction goals in boreal forests and support
landscape stewardship decision-making.
