Predictive heat transfer model for fire-induced injuries in tree stems

Abstract

This study introduces a physics-based mathematical model to predict the injury and mortality of tree stems during prescribed burns and in wildland fires. The two-dimensional transient model is developed in polar coordinates employing the finite volume method with an implicit time integration scheme. The model includes a source term in the heat transfer equation to account for the volumetric heat absorbed due to desiccation and pyrolysis processes. The thermophysical properties such as thermal conductivity, density, and specific heat are set to vary as a function of temperature. The model is verified against existing experimental and numerical studies (1D and 2D). The temperature history just underneath the inner bark shows that the temperatures predicted by the present model align closely with experimental data. The necrotic depth and viability factor of the tree stem are determined from the predicted temperature distribution in the tree stem. A parametric study is conducted by varying the area exposed to the heat flux, moisture content, and tree species. The depth of stem injury and mortality rate are analyzed for these cases. Results show that the coupled effect of thermo-property variation and moisture content in different layers can significantly affect the heat diffusion and the predicted temperature distribution within the inner layers of the stem. The model serves as a valuable tool for predicting tree mortality rates during wildfires and prescribed burns and helps land managers and fire managers foster better forestry management and ecosystem conservation strategies.