Using Pre-Fire High Point Cloud Density LiDAR Data to Predict Fire Severity in Central Portugal

[EN], The wall-to-wall prediction of fuel structural characteristics conducive to high fire severity is essential to provide integrated insights for implementing pre-fire management strategies designed to mitigate the most harmful ecological effects of fire in fire-prone plant communities. Here, we evaluate the potential of high point cloud density LiDAR data from the Portuguese áGiLTerFoRus project to characterize pre-fire surface and canopy fuel structure and predict wildfire severity. The study area corresponds to a pilot LiDAR flight area of around 21,000 ha in central Portugal intersected by a mixed-severity wildfire that occurred one month after the LiDAR survey. Fire severity was assessed through the differenced Normalized Burn Ratio (dNBR) index computed from pre- and post-fire Sentinel-2A Level 2A scenes. In addition to continuous data, fire severity was also categorized (low or high) using appropriate dNBR thresholds for the plant communities in the study area. We computed several metrics related to the pre-fire distribution of surface and canopy fuels strata with a point cloud mean density of 10.9 m−2. The Random Forest (RF) algorithm was used to evaluate the capacity of the set of pre-fire LiDAR metrics to predict continuous and categorized fire severity. The accuracy of RF regression and classification model for continuous and categorized fire severity data, respectively, was remarkably high (pseudo-R2 = 0.57 and overall accuracy = 81%) considering that we only focused on variables related to fuel structure and loading. The pre-fire fuel metrics with the highest contribution to RF models were proxies for horizontal fuel continuity (fractional cover metric) and the distribution of fuel loads and canopy openness up to a 10 m height (density metrics), indicating increased fire severity with higher surface fuel load and higher horizontal and vertical fuel continuity. Results evidence that the technical specifications of LiDAR acquisitions framed within the áGiLTerFoRus project enable accurate fire severity predictions through point cloud data with high density.SIPortuguese Foundation for Science and Technolog

Fuel build-up promotes an increase in fire severity of reburned areas in fire-prone ecosystems of the western Mediterranean Basin

​​​​​​​Fire Ecology is the official journal of the Association for Fire Ecology[EN] Background Fire‑vegetation feedbacks can modulate the global change effects conducive to extreme fire behavior and high fire severity of subsequent wildfires in reburn areas by altering the composition, flammability traits, and spatial arrangement of fuels. Repeated, high‑severity wildfires at short return intervals may trigger long‑term vegetation state transitions. However, empirical evidence about these feedbacks is absent in fire‑prone ecosystems of the west‑ern Mediterranean Basin, where the response of fire activity has been enhanced by contemporary socioeconomic and land‑use changes. Here, we evaluated whether fire severity differs between initial burns and subsequent wild‑fires in reburn areas (fire‑free periods = 10–15 years) of maritime pine and Aleppo pine forests, holm oak woodlands, and shrublands in the western Mediterranean Basin, and whether there is a relationship between the severity of such interactive wildfire disturbances. We also tested how the type of ecosystem and changes in vegetation structure after the initial wildfires influence these relationships. We leveraged Landsat‑based fire severity estimates for initial and last wildfires using the Relativized Burn Ratio (RBR) and Light Detection and Ranging (LiDAR) data acquired before the last wildfire. Results Fire severity of the last wildfire was significantly higher than that of the initial wildfire for each dominant ecosystem type in reburn areas. These differences were very pronounced in maritime pine forests and shrublands. For consistency, the same patterns were evidenced for the fire severity in reburn and first‑entry areas of the last wild‑fire for each dominant ecosystem type. Fire severity of the last wildfire in forests and woodlands (particularly maritime pine‑dominated) raised with increasing severity of the previous wildfire to a greater extent than in shrublands. Pre‑fire fuel density in the lower vegetation strata (up to 4 m high in maritime and Aleppo pine forests, as well as in shrub‑lands, and up to 2 m high in holm oak forests) was significantly higher in reburn than in first‑entry areas of the last wildfire. Conclusions Our results suggest that land managers should promote more fire‑resistant landscapes to high fire severity by minimizing fuel build‑up and thus fire hazard through pre‑fire fuel reduction treatments such as pre‑scribed burning[ES] Antecedentes La retroalimentación entre el fuego y la vegetación puede modular los efectos del cambio global que conducen al comportamiento extremo del fuego y a una alta severidad de fuegos subsiguientes en áreas de interacción entre incendios. Esto se puede producir mediante alteraciones en la composición, características de inflamabilidad, y la disposición espacial del combustible. Los incendios repetidos, de alta severidad en intervalos de tiempo cortos, pueden producir transiciones a largo plazo sobre el estado de la vegetación. Sin embargo, la evidencia empírica sobre estas retroalimentaciones está ausente en los ecosistemas propensos al fuego en la cuenca oeste del Mediterráneo, donde la respuesta a la actividad del fuego ha aumentado por las actividades socioeconómicas y el cambio en los usos del suelo. En este trabajo, evaluamos si la severidad del fuego difiere entre incendios iniciales y subsiguientes en áreas con fuegos recurrentes (período libre de incendios de 10–15 años), en bosques de pino marítimo y pino de Alepo, en bosques de encinas y en matorrales de la cuenca oeste del Mediterráneo, y si existe una relación entre la severidad de estas perturbaciones interactivas. Testeamos asimismo cómo el tipo de ecosistema y cambios en la estructura de la vegetación después de los incendios iniciales influencian esas relaciones. Potenciamos las estimaciones de severidad basadas en LANDSAT para los incendios iniciales y finales, usando el Ratio Relativo a de Quema (Relativized Burn Ratio o RBR en inglés), y datos LIDAR adquiridos antes del último incendio. Resultados La severidad del último incendio fue significativamente más alta que la del fuego inicial para cada tipo de ecosistema dominante en áreas de interacción de incendios. Estas diferencias fueron muy pronunciadas en bosques de pino marítimo y en matorrales. Consistentemente, los mismos patrones fueron evidenciados para la severidad de los incendios en áreas de interacción de incendios y en aquellas en que el fuego entró por vez primera durante el último incendio para cada tipo de ecosistema. La severidad del último incendio en bosques (particularmente los dominados por pino marítimo) aumentó con una la severidad del incendio anterior en mayor grado que en matorrales. La densidad del combustible preincendio en los estratos de vegetación bajos (hasta 4 m de altura en bosques de pino marítimo y de Alepo, como también en matorrales, y hasta 2 m de altura en bosques de encinas), fueron también significativamente más altos en las zonas de interacción de incendios que en la primera entrada del fuego durante el último incendio. Conclusiones Nuestros resultados sugieren que los gestores del territorio deben promover paisajes más resistentes a la alta severidad, minimizando el aumento de la carga de combustible y por lo tanto el riesgo de incendio, mediante tratamientos de reducción del combustible, como por ejemplo quemas prescriptasSIThis study was fnancially supported by the Spanish Ministry of Science and Innovation in the framework of LANDSUSFIRE project (PID2022-139156OBC21) within the National Program for the Promotion of Scientifc-Technical Research (2021-2023), and with Next-Generation Funds of the European Union (EU) in the framework of the FIREMAP project (TED2021-130925B-I00); by the Regional Government of Castile and León in the framework of the IA-FIREXTCyL project (LE081P23); and by the Portuguese Foundation for Science and Technology in the frame of project UIDB/04033/2020. José Manuel Fernández-Guisuraga was supported by a Ramón Areces Foundation postdoctoral fellowshi

Prescribed burning mitigates the severity of subsequent wildfires in Mediterranean shrublands

[EN] Background Prescribed burning (PB) is becoming relevant in fuel reduction and thus fire hazard abatement in fire‑prone ecosystems of southern Europe. Yet, empirical evidence on the effectiveness of this practice to mitigate wildfire severity in Mediterranean shrublands is non‑existent, despite being the focus of PB efforts in this region. Here, we intended to quantify the protective effect of PB treatment units (2005–2021) to subsequent wildfire severity in shrublands across mainland Portugal, as well as the relative contribution and complex interactions between drivers of wildfire severity in PB‑treated areas and untreated neighboring counterparts through Random Forest regression. We leveraged cloud‑computing remote sensing data processing in Google Earth Engine to estimate fire severity (PB and wildfire) as the Relativized Burn Ratio (RBR) using Landsat data catalog.Results PB treatment was particularly effective at mitigating wildfire severity at the first PB‑wildfire encounter in shrublands, with a mean reduction of around 24% in RBR units. Fuel age (i.e., time since prescribed burning) in PB‑wildfire intersection areas overwhelmed to a large extent the effect of fire weather, burning probability, and PB severity. The mitigating effect of PB on wildfire severity persisted for a fuel age of around 5 years. However, this effect decreased with increasingly adverse fire weather conditions, such that variation in wildfire severity was somewhat insensitive to fuel age under extreme fire weather. Similarly, the lowest wildfire severity experienced in sites with high burning probability, along with the interaction effect observed between burning probability and fuel age, suggest that repeated PB treatments may be useful in controlling fuel accumulation and mitigating wildfire severity. The relative contribution of fire weather in explaining wildfire severity was exceedingly high in untreated areas, doubling that of the other variables in the model in the absence of PB treatment variables.Conclusions Our results suggest that the implementation of PB treatments at intervals of less than 5 years is of para‑mount importance to control fuel build‑up and fire hazard under extreme fire weather in productive Mediterranean shrublands. Further research on this topic is warranted in other shrublands worldwide, namely in Mediterranean‑type climate regions[ES] Antecedentes: Las quemas prescritas (PB) se han tornado relevantes en la reducción de combustibles y por lo tanto en la disminución del riesgo de incendios en ecosistemas proclives al fuego. Así todo, la evidencia empírica sobre la efectividad de esta práctica para mitigar la severidad del fuego en matorrales de ecosistemas del Mediterráneo es inexistente, a pesar de ser el foco de los esfuerzos de las PB en la región. En este trabajo, intentamos cuantificar el efecto protector en unidades de tratamientos de PB (2005‑2021) sobre la severidad subsecuente de incendios en matorrales a lo largo del centro de Portugal, como así también, la contribución relativa e interacciones complejas entre los factores conducentes a la severidad del fuego en áreas tratadas con PB y aquellas vecinas sin tratar (PB y No tratadas), a través de regresión Random Forest. Utilizamos la capacidad de procesamiento de sensores remotos en Google Earth Engine para estimar tanto la severidad del fuego (en PB y áreas no tratadas ) como la Ratio Relativa de Quemado (Relativized Burn Ratio, RBR) usando los datos del catálogo de Landsat. Resultados: Los tratamientos de PB fueron efectivos para mitigar los efectos de severidad del fuego en las primeras interacciones de PB con áreas incendiadas no tratadas, con una reducción media de alrededor del 24% en unidades de RBR. La edad del combustible (i.e. el tiempo transcurrido desde la PB) en la intersección PB‑incendio superó en gran medida los efectos de la meteorología del incendio, la probabilidad de quema, y la severidad de la PB. El efecto mitigador de la PB en la severidad de los incendios persistió en el combustible por unos 5 años luego de la PB. Desde luego, este efecto decreció con el incremento de condiciones adversas en la meteorología del incendio, tal como que la variación en la severidad del incendio fue no sensible a la edad del combustible bajo condiciones meteorológicas extremas. Similarmente, las severidades más bajas experimentadas en sitios con alta probabilidad de quema, junto con los efectos de las interacciones observadas entre probabilidad de quema y la edad del combustible, sugiere que la repetición de los tratamientos de PB puede ser útil para controlar la acumulación de combustible y mitigar la severidad de los incendios. La contribución relativa de las condiciones meteorológicas en la severidad del fuego fue notablemente alta en áreas no tratadas, duplicando el efecto de otras variables del modelo en ausencia de las variables de las PB. Conclusiones: Nuestros Resultados sugieren que la implementación de tratamientos de PB a intervalos menores de 5 años es de una alta importancia para controlar la acumulación de combustible y reducir el riesgo de incendios bajo eventos meteorológicos extremos en matorrales de ecosistemas Mediterráneos. Más investigaciones en este tema deben garantizarse en otros matorrales del mundo, fundamentalmente en aquellos que se desarrollan bajo climas de tipo MediterráneoSIThis study was financially supported by the Portuguese Foundation for Science and Technology in the frame of project UIDB/04033/2020. José Manuel Fernández-Guisuraga was supported by a Ramón Areces Foundation postdoctoral fellowshi

Modeling Pinus pinaster forest structure after a large wildfire using remote sensing data at high spatial resolution

P. 257-271In the Mediterranean Basin, wildland fires are major drivers of forest ecosystem dynamics. In the current context of global change, these fires are becoming more severe and recurrent because of climatic conditions, land use changes and invasive species. In areas affected by mega-fires (burned area > 10,000 ha), the patterns of regeneration may be heterogeneous due to local variations in fire regime, community composition and environmental features. The goal of this study was to analyze the post-fire structure of both Pinus pinaster Aiton. seedlings population and understory community in a Mediterranean fire-prone ecosystem at short-term by means of high spatial resolution satellite imagery within the perimeter of a full stand replacing mega-fire that burned around 12,000 ha of a Pinus pinaster forest in NW Spain. We established 234 field plots of 2 × 2 meters to cover four recurrence-severity scenarios. In each plot, we sampled 15 vegetation structural variables at both pine seedlings population and understory community levels. From the WorldView-2 satellite imagery, we obtained three sets of spectral variables (reflectance, spectral indices and image textures) that were used as predictors of vegetation recovery in generalized linear models. At population level, the number and cover of pine seedlings were successfully modeled with spectral indices and textural information (normalized root mean square error of 16% and 17%, respectively). At understory community level, woody species cover was correlated with first order textures (normalized root mean square error of 9%). Other understory structure variables (height and richness of woody species, percentage of bare soil, necromass and leaves) were predicted with an error lower than 20%. The predictive capacity of the models was similar for all recurrence-severity scenarios. Our results highlight the usefulness of spectral indices and textural data at high spatial resolution in the analysis of post-fire recovery in large and heterogeneous burnt areas. Given the accuracy and predictive capacity of the models obtained in this study, high spatial resolution satellite imagery together with field data provide useful information in post-fire decision making in fire prone ecosystems.S

The Effects of Fire Severity on Vegetation Structural Complexity Assessed Using SAR Data Are Modulated by Plant Community Types in Mediterranean Fire-Prone Ecosystems

This article belongs to the Special Issue The Use of Remote Sensing Technology for Forest Fire[EN] Vegetation structural complexity (VSC) plays an essential role in the functioning and the stability of fire-prone Mediterranean ecosystems. However, we currently lack knowledge about the effects of increasing fire severity on the VSC spatial variability, as modulated by the plant community type in complex post-fire landscapes. Accordingly, this study explored, for the first time, the effect of fire severity on the VSC of different Mediterranean plant communities one year after fire by leveraging field inventory and Sentinel-1 C-band synthetic aperture radar (SAR) data. The field-evaluated VSC retrieved in post-fire scenarios from Sentinel-1 γ0 VV and VH backscatter data featured high fit ( R2 = 0.878) and low predictive error (RMSE = 0.112). Wall-to-wall VSC estimates showed that plant community types strongly modulated the VSC response to increasing fire severity, with this response strongly linked to the regenerative strategies of the dominant species in the community. Moderate and high fire severities had a strong impact, one year after fire, on the VSC of broom shrublands and Scots pine forests, dominated by facultative and obligate seeder species, respectively. In contrast, the fire-induced impacts on VSC were not significantly different between low and moderate fire-severity scenarios in communities dominated by resprouter species, i.e., heathlands and Pyrenean oak forestsSIThis study was financially supported by the Spanish Ministry of Science and Innovation in the framework of the LANDSUSFIRE project (PID2022-139156OB-C21) within the National Program for the Promotion of Scientific-Technical Research (2021–2023), and with Next-Generation Funds of the European Union (EU) in the framework of the FIREMAP project (TED2021-130925B-I00); by the Regional Government of Castile and León in the framework of the IA-FIREXTCyL project (LE081P23); and by National Funds from FCT—Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020. José Manuel Fernández-Guisuraga was supported by a Ramón Areces Foundation postdoctoral fellowshi

The footprint of large wildfires on the multifunctionality of fire-prone pine ecosystems is driven by the interaction of fire regime attributes

[EN], Background Mediterranean ecosystems dominated by Pinus pinaster Ait. (maritime pine) are subject to a shift from fuel-limited to drought-driven fire regimes, characterized by an increasing wildfire extent, recurrence, and severity. Previous studies have not addressed the interacting effects of fire recurrence and severity on the ecosystem multifunctionality (EMF) of maritime pine forests, although complex relationships between such fire regime attributes are expected. Here, we evaluated the medium-term effects of fire recurrence and severity on the EMF response of unmanaged, native pine ecosystems dominated by Pinus pinaster in the western Mediterranean Basin. We considered four key ecosystem functions computed from functional indicators (carbon regulation, decomposition, soil fertility, and plant production), which were pooled into an EMF construct. The fire regime effects on the trade-offs and synergies between the considered ecosystem functions were also analyzed. Results Multiple ecosystem functions responded differentially to fire recurrence and severity. Fire recurrence had a strong effect on soil fertility, decomposition, and plant production functions. No significant effects of fire severity on any of the individual functions were detected. However, both fire regime attributes interacted to determine soil fertility and decomposition functions, suggesting that their performance is only impaired by fire severity when fire recurrence is low. The differing responses to the fire regime attributes among ecosystem functions fostered a significant EMF response to fire severity and its interaction with fire recurrence, indicating that the effect of fire severity on EMF was stronger under low fire recurrence scenarios, even when relationships between individual functions and fire severity were weak. Fire recurrence caused significant trade-offs between functions to emerge. However, these trade-offs were not strong enough to differ significantly from the intrinsic trade-offs (i.e., regardless of the fire regime) of maritime pine ecosystems. Conclusions Our results indicated the need to use an integrative approach to assess the response of ecosystem functioning to the fire regime in maritime pine ecosystems. Adaptive management responses are necessary towards the minimization of repeated burnings and the reduction of the fuel load in unmanaged maritime pine stands of the western Mediterranean Basin with similar characteristics to those analyzed in this study.[ES], Antecedentes Los ecosistemas mediterráneos dominados por pino marítimo (Pinus pinaster Ait.) están sujetos a cambios en regímenes de fuego limitados por el combustible hacia regímenes conducidos por la sequía, y caracterizados por un incremento en la extensión, recurrencia y severidad de los incendios. Estudios previos no han abordado los efectos interactivos de la recurrencia y severidad del fuego en la multifuncionalidad de los ecosistemas (EMF) en bosques de pino marítimo, aunque cabe esperar relaciones complejas entre estos atributos del regimen de fuego. En este trabajo, evaluamos los efectos a medio plazo de la recurrencia y severidad en la respuesta de la multifuncionalidad de los ecosistemas (EMF) de bosques nativos dominados por pino marítimo no gestionados en la cuenca Mediterránea occidental. Consideramos cuatro funciones clave calculadas a partir de indicadores funcionales (regulación del carbono, descomposición, fertilidad del suelo, y producción egetal) los cuales fueron agrupados en un constructo EMF. Los efectos del régimen de fuego sobre las sinergias y contrapartidas entre las funciones ecosistémicas también fueron analizados. Resultados Múltiples funciones ecosistémicas respondieron diferencialmente a la recurrencia y severidad. La recurrencia del fuego tuvo un efecto muy fuerte en la fertilidad del suelo, en la descomposición y en las funciones de producción. Ningún efecto significativo de la severidad del fuego fue detectado en ninguna de las funciones individuales. Sin embargo, los atributos de ambos regímenes de fuego interactuaron para determinar las funciones de fertilidad y descomposición, sugiriendo que su rendimiento es afectado por la severidad solo cuando la recurrencia del fuego es baja. Las diferentes respuestas a los atributos de los regímenes de fuego entre las funciones ecosistémicas promueven una respuesta significativa de la EMF a la severidad del fuego y su interacción con la recurrencia, indicando que el efecto de la severidad sobre la EMF fue más fuerte bajo escenarios de baja recurrencia, aun cuando las relaciones entre funciones individuales y la severidad fueran débiles. La recurrencia del fuego causó la aparición de ontrapartidas significativas entre funciones. Obviamente, estas contrapartidas no fueron lo suficientemente fuertes para diferir significativamente de aquellas intrínsecas (i.e., independientemente del régimen de fuego) en los ecosistemas de pino marítimo. Conclusiones Nuestros resultados indican la necesidad de usar una aproximación integrada para determinar la respuesta del funcionamiento al régimen de fuego en ecosistemas de pino marítimo. Respuestas de manejo adaptativo son necesarias para la minimización de quemas repetidas y la reducción de la carga de combustible en rodales de pino marítimo no gestionados en la cuenca Mediterránea, con características similares a aquellos analizados en este estudio.SIAEIBritish Ecological SocietyPortuguese Foundation for Science and Technolog

Radar and multispectral remote sensing data accurately estimate vegetation vertical structure diversity as a fire resilience indicator

The structural complexity of plant communities contributes to maintaining the ecosystem functioning in fire-prone landscapes and plays a crucial role in driving ecological resilience to fire. The objective of this study was to evaluate the resilience to fire off several plant communities with reference to the temporal evolution of their vertical structural diversity (VSD) estimated from the data fusion of C-band synthetic aperture radar (SAR) backscatter (Sentinel-1) and multispectral remote sensing reflectance (Sentinel-2) in a burned landscape of the western Mediterranean Basin. We estimated VSD in the field 1 and 2 years after fire using Shannon’s index as a measure of vertical heterogeneity in vegetation structure from the vegetation cover in several strata, both in burned and unburned control plots. Random forest (RF) was used to model VSD in the control (analogous to prefire scenario) and burned plots (1 year after fire) using as predictors (i) Sentinel-1 VV and VH backscatter coefficients and (ii) surface reflectance of Sentinel-2 bands. The transferability of the RF model from 1 to 2 years after wildfire was also evaluated. We generated VSD prediction maps across the study site for the prefire scenario and 1 to 4 years postfire. RF models accurately explained VSD in unburned control plots (R2 = 87.68; RMSE = 0.16) and burned plots 1 year after fire (R2 = 80.48; RMSE = 0.13). RF model transferability only involved a reduction in the VSD predictive capacity from 0.13 to 0.20 in terms of RMSE. The VSD of each plant community 4 years after the fire disturbance was significantly lower than in the prefire scenario. Plant communities dominated by resprouter species featured significantly higher VSD recovery values than communities dominated by facultative or obligate seeders. Our results support the applicability of SAR and multispectral data fusion for monitoring VSD as a generalizable resilience indicator in fire-prone landscapes.SIEuropean Regional Development Fund (ERDF)Spanish Ministry of Economy and CompetitivenessRegional Government of Castilla and LeónBritish Ecological Societ

Using Unmanned Aerial Vehicles in Postfire Vegetation Survey Campaigns through Large and Heterogeneous Areas: Opportunities and Challenges

17 p.This study evaluated the opportunities and challenges of using drones to obtain multispectral orthomosaics at ultra-high resolution that could be useful for monitoring large and heterogeneous burned areas. We conducted a survey using an octocopter equipped with a Parrot SEQUOIA multispectral camera in a 3000 ha framework located within the perimeter of a megafire in Spain. We assessed the quality of both the camera raw imagery and the multispectral orthomosaic obtained, as well as the required processing capability. Additionally, we compared the spatial information provided by the drone orthomosaic at ultra-high spatial resolution with another image provided by theWorldView-2 satellite at high spatial resolution. The drone raw imagery presented some anomalies, such as horizontal banding noise and non-homogeneous radiometry. Camera locations showed a lack of synchrony of the single frequency GPS receiver. The georeferencing process based on ground control points achieved an error lower than 30 cm in X-Y and lower than 55 cm in Z. The drone orthomosaic provided more information in terms of spatial variability in heterogeneous burned areas in comparison with theWorldView-2 satellite imagery. The drone orthomosaic could constitute a viable alternative for the evaluation of post-fire vegetation regeneration in large and heterogeneous burned areasS

Comparison of Physical-Based Models to Measure Forest Resilience to Fire as a Function of Burn Severity

This article belongs to the Special Issue Remote Sensing in Forest Fire Monitoring and Post-fire Damage Analysis[EN] We aimed to compare the potential of physical-based models (radiative transfer and pixel unmixing models) for evaluating the short-term resilience to fire of several shrubland communities as a function of their regenerative strategy and burn severity. The study site was located within the perimeter of a wildfire that occurred in summer 2017 in the northwestern Iberian Peninsula. A pre- and post-fire time series of Sentinel-2 satellite imagery was acquired to estimate fractional vegetation cover (FVC) from the (i) PROSAIL-D radiative transfer model inversion using the random forest algorithm, and (ii) multiple endmember spectral mixture analysis (MESMA). The FVC retrieval was validated throughout the time series by means of field data stratified by plant community type (i.e., regenerative strategy). The inversion of PROSAIL-D featured the highest overall fit for the entire time series (R2 > 0.75), followed by MESMA (R2 > 0.64). We estimated the resilience of shrubland communities in terms of FVC recovery using an impact-normalized resilience index and a linear model. High burn severity negatively influenced the short-term resilience of shrublands dominated by facultative seeder species. In contrast, shrublands dominated by resprouters reached pre-fire FVC values regardless of burn severitySIThis study was financially supported by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (ERDF), in the framework of the FIRESEVES (AGL2017-86075-C2-1-R) project; by the Regional Government of Castilla and León in the framework of the WUIFIRECYL (LE005P20) project; and by the British Ecological Society in the framework of the SR22-100154 project, where José Manuel Fernández-Guisuraga is the Principal Investigator. José Manuel Fernández-Guisuraga was supported by a Ramón Areces Foundation postdoctoral fellowshi

ALOS-2 L-band SAR backscatter data improves the estimation and temporal transferability of wildfire effects on soil properties under different post-fire vegetation responses

Remote sensing techniques are of particular interest for monitoring wildfire effects on soil properties, which may be highly context-dependent in large and heterogeneous burned landscapes. Despite the physical sense of synthetic aperture radar (SAR) backscatter data for characterizing soil spatial variability in burned areas, this approach remains completely unexplored. This study aimed to evaluate the performance of SAR backscatter data in C-band (Sentinel-1) and L-band (ALOS-2) for monitoring fire effects on soil organic carbon and nutrients (total nitrogen and available phosphorous) at short term in a heterogeneous Mediterranean landscape mosaic made of shrublands and forests that was affected by a large wildfire. The ability of SAR backscatter coefficients and several band transformations of both sensors for retrieving soil properties measured in the field in immediate post-fire situation (one month after fire) was tested through a model averaging approach. The temporal transferability of SAR-based models from one month to one year after wildfire was also evaluated, which allowed to assess short-term changes in soil properties at large scale as a function of pre-fire plant community type. The retrieval of soil properties in immediate post-fire conditions featured a higher overall fit and predictive capacity from ALOS-2 L-band SAR backscatter data than from Sentinel-1 C-band SAR data, with the absence of noticeable under and overestimation effects. The transferability of the ALOS-2 based model to one year after wildfire exhibited similar performance to that of the model calibration scenario (immediate post-fire conditions). Soil organic carbon and available phosphorous content was significantly higher one year after wildfire than immediately after the fire disturbance. Conversely, the short-term change in soil total nitrogen was ecosystem-dependent. Our results support the applicability of L-band SAR backscatter data for monitoring short-term variability of fire effects on soil properties, reducing data gathering costs within large and heterogeneous burned landscapesS