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• Inter-individual variability of tree drought responses within a stand has received little attention. Here we explore whether the spatial variations in soil/subsoil properties assessed through Electrical Resistivity Tomography (ERT) could explain variations in drought response traits among trees. • We used ERT to compute the percent variation in resistivity (PVR) between dry and wet conditions as an indicator of spatial variability in total available water content. PVR was computed in two different depth ranges (0–2 and 2–5 m) for eleven Quercus ilex stools in a Mediterranean forest stand. PVR values were compared to biological traits, including tree water status (predawn water potential (Ψ)), leaf traits (δ13C, leaf mass area (LMA)), and canopy defoliation measured after intense drought. • We found significant correlations between PVR and biological variables. For Ψ , the nature and strength of the correlations vary according to the level of drought intensity. The correlation between Ψ and PVR was positive during well-watered conditions in the upper layer (0–2 m) and during water-limited conditions in the deeper layer (2–5 m). During most severe droughts, however, the Ψ was negatively correlated with PVR in the upper layer. Trees with lower PVR in the upper layer were also associated with water use efficiency (higher δ13C), higher LMA, and a lower level of defoliation after extreme drought. • Overall, our results indicate that local differences in soil/subsoil properties affect tree response to drought and suggest that less favorable soil/subsoil conditions (lower PVR) can lead to lower water stress during the driest period and to lower defoliation after extreme drought. Plausible explanations for this better acclimation include higher stomatal regulation and improved deep soil and subsoil water exploration by trees located in more adverse conditions. We encourage the development of ERT in ecological studies to further explore the interrelated relationships between soil/subsoil, climate, and tree functioning. Unlabelled Image • ERT is used to assess spatial variability in soil/subsoil conditions in a forest. • Soil/subsoil conditions induce contrasted drought responses between individual trees. • Low TAW in shallow layer induce a strong water use efficiency. • High TAW in shallow layer induce more stress during severe drought. [ABSTRACT FROM AUTHOR]

In our original manuscript [[1]], we presented an evaluation of crown fire rate of spread predictions from two physics-based wildland fire behavior models: FIRETEC and the Wildland Urban Interface Fire Dynamics Simulator (WFDS). However, we disagree with them on the ability for the AC06 dataset to support such comparisons for physics-based models, given the number of required model input parameters and boundary conditions that are either unknown or unreported in the dataset. Although we believe that the wildland fire science community should continue to use established data sets such as AC06 in model performance studies, we also believe that advancements in physics-based modeling evaluation are most likely to occur through the initiation of new "validation experiments". [Extracted from the article]

Modeling the behavior of crown fires is challenging due to the complex set of coupled processes that drive the characteristics of a spreading wildfire and the large range of spatial and temporal scales over which these processes occur. Detailed physics-based modeling approaches such as FIRETEC and the Wildland Urban Interface Fire Dynamics Simulator (WFDS) simulate fire behavior using computational fluid dynamics based methods to numerically solve the three-dimensional, time dependent, model equations that govern, to some approximation, the component physical processes and their interactions that drive fire behavior. Both of these models have had limited evaluation and have not been assessed for predicting crown fire behavior. In this paper, we utilized a published set of field-scale measured crown fire rate of spread (ROS) data to provide a coarse assessment of crown fire ROS predictions from previously published studies that have utilized WFDS or FIRETEC. Overall, 86% of all simulated ROS values using WFDS or FIRETEC fell within the 95% prediction interval of the empirical data, which was above the goal of 75% for dynamic ecological modeling. However, scarcity of available empirical data is a bottleneck for further assessment of model performance. [ABSTRACT FROM AUTHOR]

Abstract: This study was conducted to increase understanding of possible roles and importance of local three-dimensionality in the forward spread of wildfire models. A suite of simulations was performed using a coupled atmosphere–fire model, HIGRAD/FIRETEC, consisting of different scenarios that varied in domain width and boundary condition implementation. A subset of the simulations was strictly two-dimensional in the streamwise and vertical directions, while another subset of simulations involved igniting a finite-length fireline. The remaining simulations were all three-dimensional and employed periodic boundary conditions in the cross-stream direction and a fireline spanning the entire cross-stream extent of the domain. The three-dimensional periodic simulations were compared with the two-dimensional simulations, and then briefly with the finite-length fireline simulations. The two-dimensional scenarios were constrained in their ability to represent inherently three-dimensional physical phenomena such as horizontal flow penetrating through the fireline between plumes of rising hot gas, and cross-stream heterogeneity in the windfield. Elimination of these three-dimensional flow patterns in two-dimensional simulations resulted in over prediction of spread rates in low velocity situations and under predicted spread rates in high wind speed scenarios. In the three-dimensional simulations, local cross-stream heterogeneities in temperature and velocities lead to penetration of hot gases through the fireline and onto unburned fuel. Three-dimensional fires presented a positive correlation between increasing ambient wind speed and rate of spread. Further investigation of finite length fires is required in order to understand the ramifications of fireline curvature. [Copyright &y& Elsevier]