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Aims Areas affected by wildfire comprise spatially complex mosaics of burned patches in which a wide range of burn severities coexist. Rapid diagnosis of the different levels of soil burn severity and their extents is essential for designing emergency post-fire rehabilitation treatments. The main objective of this study was to determine whether visual signs of soil burn severity levels are related to changes in soil chemical and microbial properties immediately after fire. Methods Eight areas affected by wildfires in NW Spain were selected immediately after fire, and soil chemical and biological properties (pH, extractable Ca, K, Mg and P, SOC, total N, δC, basal soil respiration, Cmic, phosphatase activity, extractable NH₄⁺ and NO₃⁻, ammonification and nitrification rates and potential N mineralization) were analysed in relation to five levels of soil burn severity (0: Unburned; 1: Oa layer partially or totally intact; 2: Oa layer totally charred; 3: Bare soil and soil structure unaffected; 4: Bare soil and soil structure affected; 5: Bare soil and surface soil structure and colour altered). Results The five visually assessed levels of soil burn severity adequately reflected changes in SOC, pH, and phosphatase activity, which varied gradually with increasing soil burn severity. However, alterations in certain indicators related to the soil organic quality (C/N, Cmic/SOC, qCO₂, δ¹³C) were only detected in the most severely burned areas. Discriminant analysis revealed that the best combination of variables was acid phosphatase activity, SOC and pH, which correctly classified between 64 and 76 % of samples, depending on the levels of soil burn severity considered. Conclusions The results showed that the proposed soil burn severity categories may be useful for indicating the degree of degradation of important soil chemical and microbiological properties in sites similar to the study area. This, in combination with other factors, will allow prioritization of areas for rehabilitation.

Forest managers demand reliable tools to evaluate post-fire vegetation and soil damage. In this study, we quantify wildfire damage to vegetation and soil based on the analysis of burn severity, using multitemporal and multispectral satellite data and species distribution models, particularly maximum entropy (MaxEnt). We studied a mega-wildfire (9000 ha burned) in North-Western Spain, which occurred from 21 to 27 August 2017. Burn severity was measured in the field using the composite burn index (CBI). Burn severity of vegetation and soil layers (CBIveg and CBIsoil) was also differentiated. MaxEnt provided the relative contribution of each pre-fire and post-fire input variable on low, moderate and high burn severity levels, as well as on all severity levels combined (burned area). In addition, it built continuous suitability surfaces from which the burned surface area and burn severity maps were built. The burned area map achieved a high accuracy level (κ = 0.85), but slightly lower accuracy when differentiating the three burn severity classes (κ = 0.81). When the burn severity map was validated using field CBIveg and CBIsoil values we reached lower κ statistic values (0.76 and 0.63, respectively). This study revealed the effectiveness of the proposed multi-temporal MaxEnt based method to map fire damage accurately in Mediterranean ecosystems, providing key information to forest managers.

The remote sensing of fire severity and burned area is fundamental in the evaluation of fire impacts. The current study aimed to: (i) compare Sentinel-2 (S2) spectral indices to predict field-observed fire severity in Durango, Mexico; (ii) evaluate the effect of the compositing period (1 or 3 months), techniques (average or minimum), and phenological correction (constant offset, c, against a novel relative phenological correction, rc) on fire severity mapping, and (iii) determine fire perimeter accuracy. The Relative Burn Ratio (RBR), using S2 bands 8a and 12, provided the best correspondence with field-based fire severity (FBS). One-month rc minimum composites showed the highest correspondence with FBS (R2 = 0.83). The decrease in R2 using 3 months rather than 1 month was ≥0.05 (0.05–0.15) for c composites and <0.05 (0.02–0.03) for rc composites. Furthermore, using rc increased the R2 by 0.05–0.09 and 0.10–0.15 for the 3-month RBR and dNBR compared to the corresponding c composites. Rc composites also showed increases of up to 0.16–0.22 and 0.08–0.11 in kappa values and overall accuracy, respectively, in mapping fire perimeters against c composites. These results suggest a promising potential of the novel relative phenological correction to be systematically applied with automated algorithms to improve the accuracy and robustness of fire severity and perimeter evaluations.

Straw mulch is commonly applied to land after high-severity wildfires because of its effectiveness in reducing post-fire runoff and erosion. However, information about the effect on vegetation recovery is still scarce and usually limited to the first 2 years after wildfire. In this study, the effects of straw helimulching on vegetation recovery and species composition were assessed in 30 experimental plots established in four shrubland areas in north-west Spain 5 years after wildfire. The influence of the treatment on biomass accumulation in the medium term was also assessed. The relationships between soil burn severity, site characteristics (altitude, aspect, soil depth and percentage of stoniness) and the vegetation variables (total vegetation cover, weighted mean height of vegetation, total fuel load and litter and duff load) were also explored. Overall, the mulching treatment did not have significant effects on the variables studied. In the mulched plots, no non-native species were recorded 5 years after the wildfire. Site characteristics significantly affected the vegetation complex, but soil burn severity did not have any residual effect. The study findings indicate that straw helimulching has neutral effects on vegetation cover and composition in coastal shrublands in NW Spain in the medium term.

Background Forest fires have increased in extent and intensity in the Mediterranean area in recent years, threatening forest ecosystems through loss of vegetation, changes in soil properties, and increased soil erosion rates, particularly in severely burned areas. However, establishing the relationships between burn severity and soil properties that determine infiltration remain challenging. Determining where soil burn severity evaluation should be carried out is critical for planning urgent measures to mitigate post-fire soil erosion. Although previous research has indicated that spectral indices are suitable for assessing fire severity, most of the classifications used consider combined effects in vegetation and soil. Moreover, the relationship between spectral indices and soil burn severity has scarcely been explored until now. Results We selected three pine stands in Spain for study immediately after being burned by wildfires. We analyzed various soil properties (soil saturated hydraulic conductivity, mean weight diameter of soil aggregates, and soil organic carbon) in relation to six levels of soil burn severity in all three stands. In addition, we established 25 field plots in the burned areas. We computed ten spectral indices for each plot by using Sentinel-2 satellite data. The soil burn severity categories indicated the degree of degradation of important soil properties related to soil erosion susceptibility. Of the spectral indices considered, the relativized burn ratio (RBR) was the best predictor of cumulative infiltration and mean weight diameter of soil aggregates. The differenced mid-infrared bispectral index (dMIRBI) was most closely correlated with soil organic carbon content. Conclusions The findings demonstrate the potential applicability of remote sensing to determining changes in soil properties after fire.

Wildfires have nearly become a guaranteed annual event in most western National Forests. Severe fire effects can be mitigated with a goal of minimizing the hydrologic response and promoting soil and vegetation recovery towards the pre-disturbance condition. Sometimes, post-fire actions include salvage logging to recover timber value and to remove excess fuels. Salvage logging was conducted after three large wildfires on the Lolo National Forest in Montana, USA, between 2017 and 2019. We evaluated detrimental soil disturbance (DSD) on seven units that were burned at low, moderate, and high soil burn severity in 2022, three to five years after the logging occurred. We found a range of exposed soil of 5%–25% and DSD from 3% to 20%, and these values were significantly correlated at r = 0.88. Very-high-resolution WorldView-2 imagery that coincided with the field campaign was used to calculate Normal Differenced Vegetation Index (NDVI) across the salvaged areas; we found that NDVI values were significantly correlated to DSD at r = 0.87. We were able to further examine this relationship and determined NDVI threshold values that corresponded to high-DSD areas, as well as develop a model to estimate the contributions of equipment type, seasonality, topography, and burn severity to DSD. A decision-making tool which combines these factors and NDVI is presented to support land managers in planning, evaluating, and monitoring disturbance from post-fire salvage logging.

We analysed the relationship between burn severity indicators, from remote sensing and field observations, and soil properties after a wildfire in a fire-prone Mediterranean ecosystem. Our study area was a large wildfire in a Pinus pinaster forest. Burn severity from remote sensing was identified by studying immediate post-fire Land Surface Temperature (LST). We also evaluated burn severity in the field applying the Composite Burn Index (CBI) in a total of 84 plots (30 m diameter). In each plot we evaluated litter consumption, ash colour and char depth as visual indicators. We collected soil samples and pH, soil organic carbon, dry aggregate size distribution (MWD), aggregate stability and water repellency were analysed. A controlled heating of soil was also carried out in the laboratory, with soil from the control plots, to compare with the changes produced in soils affected by different severity levels in the field. Our results shown that changes in soil properties affected by wildfire were only observed in soil aggregation in the high severity situation. The laboratory-controlled heating showed that temperatures of about 300 °C result in a significant reduction in soil organic carbon and MWD. Furthermore, soil organic carbon showed a significant decrease when LST values increased. Char depth was the best visual indicator to show changes in soil properties (mainly physical properties) in large fires that occur in Mediterranean pine forests. We conclude that CBI and post-fire LST can be considered good indicators of soil burn severity since both indicate the impact of fire on soil properties.

The objective of this article is to create soil burn severity maps to serve as field support for erosion tasks after forest fire occurrence in Spain (2017–2022). The Analytical Spectral Device (ASD) FieldSpec and the CIMEL CE-312 radiometers (optical and thermal, respectively) were used as input data to establish relationships between soil burn severity and reflectance or emissivity, respectively. Spectral indices related to popular forest fire studies and soil assessment were calculated by Sentinel-2 convolved reflectance. All the spectral indices that achieve the separability index algorithm (SI) were validated using specificity, sensitivity, accuracy (ACC), balanced accuracy (BACC), F1-score (F1), and Cohen’s kappa index (k), with 503 field plots. The results displayed the highest overall accuracy results using the Iron Oxide ratio (IOR) index: ACC = 0.71, BACC = 0.76, F1 = 0.63 and k = 0.50, respectively. In addition, IOR was the only spectral index with an acceptable k value (k = 0.50). It is demonstrated that, together with NIR and SWIR spectral bands, the use of blue spectral band reduces atmospheric interferences and improves the accuracy of soil burn severity mapping. The maps obtained in this study could be highly valuable to forest agents for soil erosion restoration tasks.

PurposeSoil erosion is one of the most detrimental consequences of forest fires. The present study aimed to compare the effectiveness of helimulching and needle cast for reducing soil loss after wildfire in NW Spain.Materials and methodsSediment yields were determined during the first 2 years after fire in 30 plots (80 m2) established in an area affected by wildfire in the summer of 2015. Thus, 10 plots were established for monitoring each of the following treatments: combusted canopy, combusted canopy + helimulching and scorched canopy. The effect of each type of treatment on soil erosion was tested using a general linear mixed model.Results and discussionImmediately after helimulching, the mean soil cover was 90%, whereas the fallen needles from the scorched trees totally covered the burned soil. Soil erosion was significantly higher in the combusted canopy treatment than that in the combusted canopy + helimulching and scorched canopy treatments. The latter two treatments yielded similar results (0.3 and 0.5 Mg ha−1, respectively). The similarity in effectiveness is probably due to the similar initial degree of soil cover provided by both treatments.ConclusionsNeedle cast from totally scorched crowns significantly reduced soil erosion after wildfire. Helimulching resembled the effects of the litter fallen from the scorched trees with a similar reduction in soil loss.

The objective of this study was to characterize the effects of soil burn severity and initial tree composition on long-term forest floor dynamics and ecosystem biomass partitioning within the Picea mariana [Mill.] BSP-feathermoss bioclimatic domain of northwestern Quebec. Changes in forest floor organic matter and ecosystem biomass partitioning were evaluated along a 2,355-year chronosequence of extant stands. Dendroecological and paleoecological methods were used to determine the time since the last fire, the soil burn severity of the last fire (high vs. low severity), and the post-fire tree composition of each stand (P. mariana vs. Pinus banksiana Lamb). In this paper, soil burn severity refers to the thickness of the organic matter layer accumulated above the mineral soil that was not burned by the last fire. In stands originating from high severity fires, the post-fire dominance by Pinus banksiana or P. mariana had little effect on the change in forest floor thickness and tree biomass. In contrast, stands established after low severity fires accumulated during the first century after fire 73% thicker forest floors and produced 50% less tree biomass than stands established after high severity fires. Standing tree biomass increased until approximately 100 years after high severity fires, and then decreased at a logarithmic rate in the millennial absence of fire. Forest floor thickness also showed a rapid initial accumulation rate, and continued to increase in the millennial absence of fire at a much slower rate. However, because forest floor density increased through time, the overall rate of increase in forest floor biomass (58 g m⁻² y⁻¹) remained constant for numerous centuries after fire (700 years). Although young stands (< 200 years) have more than 60% of ecosystem biomass locked-up in living biomass, older stands (> 200 years) sequester the majority (> 80%) of it in their forest floor. The results from this study illustrate that, under similar edaphic conditions, a single gradient related to time since disturbance is insufficient to account for the full spectrum of ecosystem biomass dynamics occurring in eastern boreal forests and highlights the importance of considering soil burn severity. Although fire severity induces diverging ecosystem biomass dynamics in the short term, the extended absence of fire brings about a convergence in terms of ecosystem biomass accumulation and partitioning.