Soil heating in fire (SheFire): A model and measurement method for estimating soil heating and effects during wildland fires

Authors: BRADY, MARY - University Of Nevada; DICKINSON, MATTHEW - Us Forest Service (FS); MIESEL, JESSICA - Michigan State University; Wonkka, Carissa; KAVANAGH, KATHLEEN - Oregon State University; LODGE, ALEXANDRA - Texas A&M University; ROGERS, WILLIAM - Texas A&M University; STARNS, HEATH - Texas A&M Agrilife; TOLLESON, DOUG - Texas A&M Agrilife; TREADWELL, MORGAN - Texas A&M Agrilife; TWIDWELL, DIRAC - University Of Nebraska; HANAN, ERIN - University Of Nevada

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2022
Publication Date: 4/9/2022
Citation: Brady, M.K., Dickinson, M.B., Miesel, J.R., Wonkka, C.L., Kavanagh, K.L., Lodge, A.G., Rogers, W.E., Starns, H.D., Tolleson, D.R., Treadwell, M.L., Twidwell, D., Hanan, E.J. 2022. Soil heating in fire (SheFire): A model and measurement method for estimating soil heating and effects during wildland fires. Ecological Applications. 32(6). Article e2627. https://doi.org/10.1002/eap.2627.
DOI: https://doi.org/10.1002/eap.2627

Interpretive Summary: Fire has transformative effects on soil properties in ecosystems around the world. While methods for estimating fire characteristics and aboveground effect have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, nutrient cycling, and vegetation recovery following fire. In this paper we present a novel framework for characterizing belowground heating and effects. The framework includes (1) a model to estimate fire-driven soil heating, cooling, and the effects of heating across depths and over time (Soil Heating in Fire model; SheFire), and (2) a simple field method for recording soil temperatures at multiple depths using sensors installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many challenges associated with typical heat-measuring devices. Heating measurements provide inputs to the SheFire model and modeled soil heating can then be used to determine ecosystem responses, such as heating effects on plant and soil microbe tissues. To validate SheFire estimates, we conducted an experiment using a burn table where iStakes recorded temperatures that were used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by traditional measurement devices, we co-located both types of devices in the burn table experiment. We found that SheFire accurately estimated soil heating at unmeasured depths, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to traditional heat-measurement devices for recording soil temperatures during fires. Finally, we present a case study using SheFire and iStakes to estimate soil heating during a prescribed fire; we examined how that heating would have influenced seed survival and tree root survival at different soil depths. This measurement-modeling framework provides a cutting-edge approach for estimating how fire energy transfers through a soil profile and predicting biological responses.

Technical Abstract: Fire has transformative effects on soil physical, chemical, and biological properties in terrestrial ecosystems around the world. While methods for estimating fire characteristics and associated effects aboveground have progressed in recent decades, there remain major challenges in characterizing soil heating and associated effects belowground. Overcoming these challenges is crucial for understanding how fire influences soil carbon storage, biogeochemical cycling, and ecosystem recovery post fire. In this paper we present a novel framework for characterizing belowground heating and effects. The framework includes (1) an open-source model to estimate fire-driven soil heating, cooling, and the effects of heating across depths and over time (Soil Heating in Fire model; SheFire), and (2) a simple field method for recording soil temperatures at multiple depths using iButton sensors installed along a wooden stake inserted into the soil (i.e., an iStake). The iStake overcomes many logistical challenges associated with deploying thermocouples. Heating measurements provide inputs to the SheFire model and modeled soil heating can then be used to derive ecosystem response functions, such as heating effects on protein denaturation. To validate SheFire estimates, we conducted an experiment using a burn table where iStakes recorded temperatures that were used to fit the SheFire model. We then compared SheFire predicted temperatures against measured temperatures at other soil depths. To benchmark iStake measurements against those recorded by thermocouples, we co-located both types of sensors in the burn table experiment. We found that SheFire demonstrated skill in estimating soil heating at unmeasured depths, with the largest errors occurring at the shallowest depths. We also found that iButton sensors are comparable to thermocouples for recording soil temperatures during fires. Finally, we present a case study using SheFire and iStakes to estimate soil heating during a prescribed fire; we examined how that heating would have influenced Chamaecrista nictitans seed survival and tree root vascular cambium survival at different soil depths. This measurement-modeling framework provides a cutting-edge approach for estimating how fire energy transfers through a soil profile and predicting biological responses.