Connecting research to management: Investigating pile burn effects on soil heating

Beneath the smoke from burning debris piles at Denali National Park & Preserve, there is also science in action. Debris cut and piled by wildland fire crews in summer 2023 and 2024, largely funded with assistance from the Bipartisan Infrastructure law, are not only reducing fire risk to nearby structures, but also creating a valuable experiment to study the effects of pile burning on subarctic soils and the potential impact on surface and subsurface values.

Left image

Slash cut and piled in the summer in preparation for winter burning.

Credit: NPS

Right image

Slash piles burning on snow-covered ground.

Credit: Chris Kopek, NPS

In March 2023, Northern Arizona University (NAU) graduate student Matt Behrens, with assistance from the NPS Alaska Western Area Fire Management fire ecology team, placed high-heat temperature sensors in several of the piles to record the flux of heat into the soil column. A first look at retrieved data showed a several hour delay in the transfer of heat through the organic-rich duff layers, and minimal soil heating effects beyond the pile edge.

NPS Alaska Western Area Fire Management program Fire Effects team of Chris Kopek and Mariana Perez create a trench in which Northern Arizona University researcher Matt Behrens then laid temperature sensors at different distances both horizontally from the pile center and vertically through the soil column at pile center. The organic soil collected on the blue tarp will be used to fill the trench. The trees and branches collected on the green tarp were re-piled over the trench prior to burning.

(Sarah Stehn, NPS)

Transect (measuring) tapes are used to locate holes which are dug using hand tools to find mineral soil and measure the depth between surface and mineral soil of the organic soil layer. The steel soil coring tool shown in the foreground is used to pull up soil samples for nutrient analysis. Matt Behrens, NAU

In fall 2024, Behrens will place instruments in additional piles to compare the effects of pile burning in the fall versus spring months, and across different fuels units and soil types. Understanding of how deep and to what degree soils are heated during these burn operations will assist fire practitioners throughout the state in minimizing potential damage to permafrost, soil seed banks, and undetected cultural resources.

Behrens’ work is supported financially by a Joint Fire Science Graduate Research innovation grant, NAU, and BIL funds via a Cooperative Ecosystems Studies Unit (CESU) agreement between NAU and the National Park Service (NPS). But importantly, it is also supported on the ground by collaboration between the Western Area Fire Management fire management officer and prescribed fire specialist, local and visiting fuels management crews, and the Alaska Region NPS fire ecology team. The coordination of all parties ensures desired fuels units are prioritized for cutting and burning and that the sequence of those activities allows for instrumentation of piles.

Continued collaboration is planned to ensure results remain focused and directive to fire and fuels management questions. Partnering throughout the research design and implementation process allows each party to bring their best assets forward and further the important integration of fire science and fire management for which NPS is known.

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