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Wildfires affect ecosystems depending on the fire regime. Long-term studies are needed to understand the ecological role played by fire, especially as regards its impact on soils. The aim of this study is to monitor the long-term effects (18 years) of a wildfire on soil properties in two areas affected by low and high fire severity regimes. The properties studied were total nitrogen (TN), total carbon (TC), C/N ratio, soil organic matter (SOM) and extractable calcium (Ca), magnesium (Mg), sodium (Na) and potassium (K). The study was carried out in three phases: short- (immediately after the wildfire), medium- (seven years after the wildfire) and long-term (18 years after the wildfire). The results showed that in both fire regimes TN decreased with time, TC and SOM were significantly lower in the burned plots than they were in the control in the medium- and long-terms. C/N ratio was significantly lower at short-term in low wildfire severity area. Extractable Ca and Mg were significantly higher in control plot than in the burned plots in the medium-term. In the long-term, extractable Ca and Mg were significantly lower in the area exposed to a high severity burning. No differences were identified in the case of extractable Na between plots on any of the sampling dates, while extractable K was significantly higher in the plot exposed to low wildfire than it was in the control. Some restoration measures may be required after the wildfire, especially in areas affected by high severity burning, to avoid the long-term impacts on the essential soil nutrients of TC, SOM, extractable Ca and Mg. This long-term nutrient depletion is attributable to vegetation removal, erosion, leaching and post-fire vegetation consumption. Soils clearly need more time to recover from wildfire disturbance, especially in areas affected by high severity fire regimes. [ABSTRACT FROM AUTHOR]

Western juniper ( Juniperus occidentalis Hook.) woodlands are replacing low elevation (<2100 m) quaking aspen ( Populus tremuloides Michx.) stands in the northern Great Basin. Restoring aspen woodlands is important because they provide wildlife habitat for many species and contain a high diversity of understory shrubs and herbaceous species. We measured herbaceous cover, density, and diversity for 15 years following two juniper control treatments in aspen woodlands. Treatments included cutting one-third of mature juniper trees followed by early fall burning (Fall), cutting two-thirds of the juniper followed by early spring burning (Spring), and untreated woodlands (Control). Junipers were selectivly cut to increase dry surface fuels to carry fire and kill the remaining conifers. The Fall treatment resulted in significant initial reductions in herbaceous cover and a long-term reduction in perennial forb cover and diversity. Herbaceous recovery in the Fall treatment was dominated by non-native species which represented about 68% of total herbaceous cover. By the end of the study the main non-natives in the Fall treatment were Kentucky bluegrass ( Poa pratensis L.) and cheatgrass ( Bromus tectorum L.). In contrast, native perennials in Spring and Control treatments represented, on average, above 60% of total herbaceous cover. Herbaceous cover in the Spring treatment increased and was greater than the Fall treatment and the Control. Perennial forb cover in the Spring treatment was 2- and 6-times greater than Control and Fall treatments, respectively. Perennial forb density was about 7 times greater in the Spring than Fall treatment. Because of lower fire severity, spring burning resulted in greater recovery of the herbaceous layer while maintaining a more diverse native understory than fall burning. The severe fire effects from fall burning aspen woodlands probably requires reseeding of native perennials to maintain understory composition and diversity and limit weed encroachment. [ABSTRACT FROM AUTHOR]

Western juniper ( Juniperus occidentalis spp. occidentalis Hook.) woodlands are replacing many lower elevation (<2100 m) quaking aspen ( Populus tremuloides Michx.) stands in the northern Great Basin. We evaluated two juniper removal treatments (Fall, Spring) to restore aspen woodlands in southeast Oregon, spanning a 15-year period. The Fall treatment involved cutting 1/3 of the juniper followed by a high severity broadcast burn one year later in October 2001. The Spring treatment involved cutting 2/3 of the juniper followed by a low severity broadcast burn 18 months later in April 2002. The cut trees increased the amount of dry fuels to carry fire through stands. We tested the effectiveness of treatments at removing juniper from seedlings to mature trees, assessed aspen ramet recruitment and development, and evaluated recovery of the shrub layer. In the Fall treatment, burning eliminated all remaining juniper trees and saplings, stimulated an 8-fold increase in aspen density (16,000 ha −1 ) and increased aspen cover 6-fold compared to the untreated controls. After 15 years, aspen density in the Spring treatment was about 1/3 of the Fall treatment, however, aspen cover did not differ from the Fall treatment. Because spring burning was less effective at removing juniper, leaving about 20% of the mature trees and 50% of the saplings, retreatment of conifers will be necessary to maintain the aspen community. In the Fall treatment, juniper began establishing within 15 years after conifer control indicating retreatment might be necessary earlier than expected. Total shrub cover and density in the Spring treatment was greater than the control and Fall treatments. Cover and density of sprouting shrub species, particularly western snowberry ( Symphoricarpus oreophilus Gray), increased and were greater in the Spring treatments than the Fall treatment where they had declined. Shrubs that increased in the Fall treatment were species where seed germination is enhanced by fire, especially snowbrush ( Ceanothus velutinus Douglas ex Hook) and wax currant ( Ribes cereum Dougl.). If an objective is to maintain or increase native understories the Spring treatment was more effective than the Fall treatment for recovering the shrub layer. [ABSTRACT FROM AUTHOR]

Increased fire frequency, extent and severity are expected to strongly affect the structure and function of boreal forest ecosystems. In this study, we examined 213 plots in boreal forests dominated by black spruce (Picea mariana) or jack pine (Pinus banksiana) of the Northwest Territories, Canada, after an unprecedentedly large area burned in 2014. Large fire size is associated with high fire intensity and severity, which would manifest as areas with deep burning of the soil organic layer (SOL). Our primary objectives were to estimate burn depth in these fires and then to characterise landscapes vulnerable to deep burning throughout this region. Here we quantify burn depth in black spruce stands using the position of adventitious roots within the soil column, and in jack pine stands using measurements of burned and unburned SOL depths. Using these estimates, we then evaluate how burn depth and the proportion of SOL combusted varies among forest type, ecozone, plot-level moisture and stand density. Our results suggest that most of the SOL was combusted in jack pine stands regardless of plot moisture class, but that black spruce forests experience complete combustion of the SOL only in dry and moderately well-drained landscape positions. The models and calibrations we present in this study should allow future research to more accurately estimate burn depth in Canadian boreal forests. [ABSTRACT FROM AUTHOR]

Forest wildfires consume fuel and are followed by post-fire fuel accumulation. This study examines post-fire surface fuel dynamics over 9 years across a wide range of conditions characteristic of California fires in dry conifer and hardwood forests. We estimated post-fire surface fuel loadings (Mg ha-1) from 191 repeatedly measured United States national inventory plots in dry conifer and hardwood stands of 49 California forest wildfires and identified differences across fire severity classes - low, moderate and high. No significant change in duff load was detected within the first 9 years post-fire across all forest types and fire severities. Litter, 1-h and 10-h fuels exhibited a quadratic trend over time in dry conifer stands, peaking ~6 years after fire, whereas hardwood stands displayed a constant rate of increase in those fuel types. For 100- and 1000-h fuels, the annual rate of change was constant for dry conifer and hardwood stands with differing rates of change across fire severity classes. This study was based on an extensive, spatially balanced sample across burned dry conifer and hardwood forests of California. Therefore, the estimated patterns of fuel accumulation are generally applicable to wildfires within this population. [ABSTRACT FROM AUTHOR]

A warming climate, fire exclusion, and land cover changes are altering the conditions that produced historical fire regimes and facilitating increased recent wildfire activity in the northwestern United States. Understanding the impacts of changing fire regimes on forest recruitment and succession, species distributions, carbon cycling, and ecosystem services is critical, but challenging across broad spatial scales. One important and understudied aspect of fire regimes is the unburned area within fire perimeters; these areas can function as fire refugia across the landscape during and after wildfire by providing habitat and seed sources. With increasing fire activity, there is speculation that fire intensity and combustion completeness are also increasing, which we hypothesized would yield smaller unburned proportions and changes in fire refugia patterns. We sought to determine (1) whether the unburned proportion of wildfires decreased across the northwestern United States from 1984 to 2014 and (2) whether patterns of unburned patches were significantly different across ecoregions, land cover type, and land ownership. We utilized a Landsat-derived geospatial database of unburned islands within 2298 fires across the inland northwestern USA (including eastern Washington, eastern Oregon, and Idaho) from 1984 to 2014. We evaluated patterns of the total unburned proportion and spatial patterns of unburned patches of the fires across different ecoregions, land cover types, and land ownership. We found that unburned area proportion exhibited no change over the three decades, suggesting that recent trends in area burned and overall severity have not affected fire refugia, important to post-fire ecosystem recovery. There were ecoregional differences in mean unburned proportion, patch area, and patch density, suggesting influences of vegetation and topography on the formation of unburned area. These foundation findings suggest that complex drivers control unburned island formation, and yield insights to locate potential important fire refugia across the inland northwest. [ABSTRACT FROM AUTHOR]

Burn severity (ecological impacts of fire on vegetation and soils) influences post-fire stand structure and species composition. The spatial pattern of burn severity may compound the ecological impacts of fire through distances to seed sources and availability of bud banks and seedbeds. Land managers require spatial burn severity data to manage post-fire risks, ecosystem recovery, and assess the outcomes of fires. This research seeks to characterize and explain variability in burn severity in the northwestern boreal forest. We assessed burn severity one year post-fire in six large wildfires that burned in 2014. We measured burn severity using the Composite Burn Index, surface Burn Severity Index, Canopy Fire Severity Index, and percent overstory mortality, describing a range of surface and overstory fire effects. Burn severity was variable, ranging from unburned residuals to complete overstory mortality and intense combustion. We related field measurements to remotely sensed multispectral burn severity metrics of the differenced Normalized Burn Ratio (dNBR), the Relativized dNBR, and the Relativized Burn Ratio. Diagnostic models of burn severity using relativized metrics had lower errors and better (though not significantly so) fits to the field data. Spatial patterns of burn severity were consistent with those observed in other large fires in North America. Stand-replacing patches were large, aggregated, and covered the largest proportion of the landscape. These patterns were not consistent across the four mapped burn severity field metrics, suggesting such metrics may be viewed as related, but complementary, as they depict different aspects of severity. Prognostic models indicated burn severity was explained by pre-fire stand structure and composition, topoedaphic context, and fire weather at time of burning. Wetlands burned less severely than uplands, and open stands with high basal areas experienced lower burn severity in upland vegetation communities. This research offers an enhanced understanding of the relationship between ground observations and remotely sensed severity metrics, in conjunction with stand-level drivers of burn severity. The diverse fuel complexes and extreme fire weather during the 2014 fire season produced the complex patterns and broad range of burn severity observed. [ABSTRACT FROM AUTHOR]

Forest management practices in Mediterranean ecosystems are frequently employed to reduce both the risk and severity of wildfires. However, these pre-fire treatments may influence the effects of wildfire events on soil properties. The aim of this study is to examine the short-term effects of a wildfire that broke out in 2015 on the soil properties of three sites: two exposed to management practices in different years – 2005 (site M05B) and 2015 (site M15B) – and one that did not undergo any management (NMB) and to compare their properties with those recorded in a plot (Control) unaffected by the 2015 wildfire. We analyzed aggregate stability (AS), soil organic matter (SOM) content, total nitrogen (TN), carbon/nitrogen ratio (C/N), inorganic carbon (IC), pH, electrical conductivity (EC), extractable calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K), microbial biomass carbon (C mic ) and basal soil respiration (BSR). In the managed plots, a clear-cutting operation was conducted, whereby part of the vegetation was cut and left covering the soil surface. The AS values recorded at the Control site were significantly higher than those recorded at M05B, whereas the TN and SOM values at NMB were significantly higher than those recorded at M05B. IC was significantly higher at M05B than at the other plots. There were no significant differences in C/N ratio between the analyzed sites. Soil pH at M05B was significantly higher than the value recorded at the Control plot. Extractable Ca was significantly higher at NMB than at both M05B and the Control, while extractable Mg was significantly lower at M05B than at NMB. Extractable K was significantly lower at the Control than at the three fire-affected plots. C mic was significantly higher at NMB than at the Control. BSR, BSR/C and BSR/C mic values at the fire-affected sites were significantly lower than those recorded at the Control. No significant differences were identified in C mic /C. Overall, a comparison of the pre-fire treatments showed that NMB was the practice that had the least negative effects on the soil properties studied, followed by M15B, and that fire severity was highest at M05B due to the accumulation of dead plant fuel. [ABSTRACT FROM AUTHOR]

Background: Many forests within the southern Appalachian region, USA, have experienced decades of fire exclusion, contributing to regeneration challenges for species such as oaks (Quercus spp. L.) and pines (Pinus spp. L.), and threatening the maintenance of oak-dominated forests in the future. While the use of prescribed fire as a forest management tool is increasing within this region, there remains a lack of information on the potential role of wildfire. A wildfire within the Daniel Boone National Forest, Kentucky, USA, provided an opportunity to investigate how wildfire affected forest vegetation response. Results: We examined the effects of fire severity, quantified using composite burn index (CBI), on basal area, stem density, and sapling recruitment for several key species. We also examined the effects of fire severity on understory species richness and illuminated the consequence of non-native species invasions following fire. Our results demonstrated a negative relationship between fire severity and basal area (stems ≥2 cm diameter at breast height; P ≤ 0.001), and a positive relationship with the recruitment of oak and pine saplings (both P ≤ 0.001), oak sapling density (P = 0.012), and non-woody understory species richness (P ≤ 0.001). We also found that increasing fire severity heightened likelihood of invasion by non-native species, specifically princess tree (Paulownia tomentosa [Thunb.] Siebold & Zucc. ex. Steud; P = 0.009) and Chinese silvergrass (Miscanthus sinensis Andersson; P = 0.028). Conclusions: Where it is feasible, public land managers may be able to generate a range of fire severity during future prescribed fires that approximate some characters of wildfire. These fires, when implemented in southern Appalachian upland forests, may help recruit oaks and pines and boost their potential as future canopy dominants. However, the increased occurrence of non-native invasive species invasion following fire conveys the importance of targeted and timely eradication treatments before new populations of non-native species may become established or reproduce, contradicting the ecological benefits of fire. [ABSTRACT FROM AUTHOR]

In fire-adapted forest ecosystems around the world, there has been growing concern about adverse impacts of post-fire logging on native biodiversity and ecological processes. This is also true in conifer forests of California, U.S.A. which are home to a rare and declining owl subspecies, the California spotted owl (Strix occidentalis occidentalis). While there has been recent concern about the California spotted owl occupancy in large fire areas where some territories have substantial high-severity fire effects, the influence of post-fire logging on the California spotted owl occupancy has been investigated very little, leading to some uncertainty about interpretation of conflicting results in different large fires. Research has found these owls preferentially select high-severity fire areas, characterised by high levels of snags and native shrubs, for foraging in forests that were not logged after fire, suggesting that removal of this foraging habitat might impact occupancy. The authors assessed the effect of post-fire logging and high-severity fire, on occupancy of this subspecies in eight large fire areas, within spotted owl sites with two different levels of high-severity fire effects. They found a significant adverse effect of such logging and no effect of high-severity fire alone. These results indicate it is post-fire logging, not large fires themselves, that poses a conservation threat to this imperilled species. [ABSTRACT FROM AUTHOR]

• Stand-replacing fire threatens the persistence of dry conifer forests in the western US. • The prevalence of stand-replacing fire since 1985 is much higher compared to the historical reference period (∼1600–1875). • The prevalence of contemporary stand-replacing fire in wilderness is slightly lower than in non-wilderness. • The prevalence of stand-replacing fire in the Gila Wilderness is much lower than that observed in the broader ecoregion. • Fire will continue to erode the extent of dry conifer forests unless they are restored to conditions resilient to stand-replacing fire. Dry conifer forests in the western US historically experienced frequent fire prior to European American colonization. Mean fire return interval ranged from about 5–35 years, with the majority of fires burning at low-to-moderate severity. The arrival of European Americans initiated notable reductions in fire frequency through the cessation of Indigenous burning, livestock grazing, and fire suppression. These activities effectively excluded fire from most dry conifer forests, thereby allowing live and dead fuels to accumulate. There are concerns that this fuel accumulation is causing contemporary fires (since 1985) to burn more severely compared to pre-colonization time periods, thereby increasing potential for enduring fire-catalyzed conversions to non-forest. Here, we used satellite-derived fire severity data to characterize the prevalence of contemporary (1985–2020) stand-replacing fire in dry conifer forests within four broad ecoregions for all fires, non-wilderness fires, wilderness fires, and prescribed fires. Our results indicate, that as a proportion of area burned, contemporary fires experienced 2.9 to 13.6 times more stand-replacing fire (depending on the ecoregion) compared to the pre-colonization period. Non-wilderness areas exhibit somewhat higher prevalence of stand-replacing fire, relative to the historical fire regime, than wilderness areas (where logging is prohibited). The relatively small difference between non-wilderness and wilderness suggests that fuel accumulation resulting from fire exclusion has played a larger role than historical logging activities on the prevalence of contemporary stand-replacing fire. Prescribed fires do not exhibit a higher prevalence of stand-replacing fire compared to the historical fire regime. We conducted a parallel analysis in the Gila Wilderness in New Mexico, USA, is it is arguably the best example of an unrestrained fire regime (many fires are not suppressed) in western US dry conifer forests. The Gila Wilderness proportionally experienced only 1.8 times more stand-replacing fire compared to the historical reference period; in contrast, the southwest ecoregion experienced 5.9 times more stand-replacing fire. Fire will inevitably burn a given forest no matter how much money and personnel we commit to fire prevention and suppression, and because of the high prevalence of stand-replacing fire, the long-term persistence of dry conifer forests is jeopardized. Unless forest managers are provided the social license and enabling conditions to substantially accelerate efforts to restore conditions resistant to stand-replacing fire, we anticipate that the extent of dry conifer forests will continue to erode as fire-catalyzed conversions increasingly unfold across the western US. [ABSTRACT FROM AUTHOR]

Soil microorganisms are a fundamental component of ecosystems and mediate biogeochemical cycles and ecosystem productivity. The frequency and extremity of fire weather is expected to increase under global warming; however, postfire soil microorganisms' patterns and trends remain unclear. By performing a global meta-analysis of 1019 paired observations of burned and unburned sites from 123 publications, we show that fungal biomass, microbial biomass carbon (C), soil respiration, autotrophic respiration, and C acquisition enzymes decrease in response to fire. The recovery times of microbial biomass and functional groups were shorter than those of soil C emissions and extracellular enzymes. Importantly, the postfire recovery of microbial biomass C and/or N as well as soil respiration and its components varied with mean annual temperature and precipitation, fire severity and type, and ecosystem type, with longer recovery times under high-severity fire/wildfire and in forests. Our study highlights the differential recovery patterns of microbial attributes after fire across global terrestrial ecosystems and reveals the importance of climate and the fire regime in regulating the postfire recovery of the soil microbial community and functioning. • We performed a global meta-analysis of soil microorganisms in response to fire. • Fire effects on MBC, SR, and C and P acquisition EEA increased with postfire time. • The recovery time of MBC was shorter than those of SR and C acquisition EEA enzymes. • MBC and SR need more time to recover under high-severity fire/wildfire or in forests. [ABSTRACT FROM AUTHOR]

• High severity fire had significant impacts on community composition. • Experimental warming and high burn severity altered plant trait expression and ecosystem function. • High severity fire and increased ambient temperatures may alter successional trajectories in the future. Uncharacteristically severe wildfires are occurring at higher frequency, across larger spatial extents, and in new seasons in many parts of the globe. At the same time, climate change is elevating temperatures and altering precipitation patterns. High severity fires have the potential to produce shifts in ecosystem type and function in communities that are adapted to low severity fire via changes in community composition, functional trait values, and nutrient cycling processes. However, interactive effects between climate warming and fire severity on community composition, trait values, and ecosystem functioning are rarely studied and poorly understood. We assessed the impact of experimental warming via open top warming chambers across a burn severity gradient on the understory plant community of a Ponderosa pine (Pinus ponderosa) forest in northern Arizona, USA. Specifically, we examined community composition, three plant functional traits (specific leaf area (SLA), leaf dry matter content (LDMC), and plant height) and one ecosystem function (decomposition rate) in the first post-fire growing season. High burn severity produced significant shifts in community composition. The combination of experimental warming and high burn severity significantly decreased community weighted mean LDMC and plant height, and increased decomposition rate. Our study demonstrates significant and rapid responses of community composition, trait expression, and ecosystem function in response to burn severity, experimental warming, and their interaction. This suggests that ecosystems experiencing atypically severe fire under future climate and wildfire conditions may recover in fundamentally different ways than in the past, favoring a different suite of species and traits, with altered ecosystem function. [ABSTRACT FROM AUTHOR]

With the effects of fire, weather and post-fire management on soil properties having been studied mostly individually, there is little understanding of the combined effects of wildfire, heavy storm and straw mulching. In this study, we evaluated the changes in soil properties following a high-severity fire, post-fire soil treatment using straw mulch, and a torrential storm in a forest stand in north-western Portugal. The main physicochemical properties of the soil were evaluated in different soil conditions: a) burnt and untreated, b) burnt and mulched areas, and c) unburnt sites on three survey dates 1) soon after wildfire, 2) after the rainstorm, and 3) one year after wildfire. We found that soil water repellency strongly increased ephemerally immediately after wildfire, decrease after the storm and disappeared after one year. Fire reduced the soil organic matter (by 50%, on average), total nitrogen (by 85–90%) and available phosphorous (by about 45%) at both the mulched and untreated sites, and this effect was not changed by the ensuing rainfall. In comparison to the unburnt sites, the pH increased in the burnt soils, and the electrical conductivity decreased. Finally, the dynamics of the major cations and minor elements were affected differently by the wildfire and rainfall under the different soil conditions. One year after the fire, the most notable changes compared to the unburnt soil were detected in magnesium, potassium and almost all the minor elements. Based on these findings, instructions were given to the land managers (aim to control soil hydrophobicity following wildfire, supply more soil organic matter to the soil to avoid a decline in soil fertility, and use alternative actions to straw mulching to control the soil chemistry) that were aimed at more effective post-fire management in severely burnt areas in Mediterranean forests. • Wildfire produces important changes on forest soils. • Torrential rainfall can damage soils affected by high severity fire. • Most soil changes produced by fire are ephemeral. • Post-fire straw mulching can avoid soil degradation. [ABSTRACT FROM AUTHOR]

Remote sensing data can usefully support the fire management operational applications in different spatial and temporal scales with a synoptic point of view and low cost technologies. The satellite monitoring systems together with other geographic information, historical data and field measurements, can provide the fire management operators useful tools of fire danger assessment, fire prevention, fire-fighting and post-fire planning. The FIRE-SAT monitoring system was applied to a fire event which developed in a wildland-urban interface area of the Potenza town (Basilicata, Italy) on July 2015, in order to assess the fire occurrence danger, to evaluate the fire effects and to simulate the fire propagation.

In most ecosystems, disturbance is an important agent of variation in community structure and composition. Determining the diversity and composition of soil seed bank is essential for designing conservation and restoration programs because it can markedly contribute to future plant communities. Despite the important role of soil seed banks in the composition of different plant communities, and thus in their conservation, the floristic studies in Zagros forests have only focused on aboveground vegetation. In this study, the characteristics of soil seed banks were examined in three conditions after one year of fire high severity burned, low severity burned and control (not burned) in Shirvanchardavol city in northeast of Ilam Province. The result of DCA showed that different fire severities and their effects on site conditions have been reflected clearly in the composition of the soil seed bank. The results also indicated that soil seed bank composition between control and high severity burned spots was specifically different. The shanon diversity, Margalef richness and evenness indices differed significantly between three treatments and the highest diversity was observed at low severity. In this regard the proportion of annual forbs tended to decrease with increasing severity of fire. In soil seed bank, Therophytes were the dominant life form of low severity burned and control spots and Hemichryptophytes were dominant in high severity burned spots.

Mediterranean pine forests in Spain experience wildland fire events with different frequencies, intensities, and severities which result in diverse socio-ecological consequences. In order to predict fire severity, spectral indices derived from remotely sensed images have been used extensively. Such spectral indices are usually used in combination with ground sampling to relate detected radiometric changes to actual fire effects. However, the potential of the tridimensional information captured by Airborne Laser Scanners (ALS) to severity mapping has been less explored. With the objective of addressing this question, in this paper, explanatory variables extracted from ALS point clouds are related to field estimations of the Composite Burn Index collected in four fires located in Aragón (Spain). Logistic regression models were developed and statistically tested and validated to map fire severity with up to 85.5% accuracy. The canopy relief ratio and the percentage of all returns above one meter height were the most significant variables and were therefore used to create a continuous map of severity levels.

The fire-tolerant eucalypt forests of south eastern Australia are assumed to fully recover from even the most intense fires; however, surprisingly, very few studies have quantitatively assessed that recovery. The accurate assessment of horizontal and vertical attributes of tree crowns after fire is essential to understand the fire’s legacy effects on tree growth and on forest structure. In this study, we quantitatively assessed individual tree crowns 8.5 years after a 2009 wildfire that burnt extensive areas of eucalypt forest in temperate Australia. We used airborne LiDAR data validated with field measurements to estimate multiple metrics that quantified the cover, density, and vertical distribution of individual-tree crowns in 51 plots of 0.05 ha in fire-tolerant eucalypt forest across four wildfire severity types (unburnt, low, moderate, high). Significant differences in the field-assessed mean height of fire scarring as a proportion of tree height and in the proportions of trees with epicormic (stem) resprouts were consistent with the gradation in fire severity. Linear mixed-effects models indicated persistent effects of both moderate and high-severity wildfire on tree crown architecture. Trees at high-severity sites had significantly less crown projection area and live crown width as a proportion of total crown width than those at unburnt and low-severity sites. Significant differences in LiDAR -based metrics (crown cover, evenness, leaf area density profiles) indicated that tree crowns at moderate and high-severity sites were comparatively narrow and more evenly distributed down the tree stem. These conical-shaped crowns contrasted sharply with the rounded crowns of trees at unburnt and low-severity sites and likely influenced both tree productivity and the accuracy of biomass allometric equations for nearly a decade after the fire. Our data provide a clear example of the utility of airborne LiDAR data for quantifying the impacts of disturbances at the scale of individual trees. Quantified effects of contrasting fire severities on the structure of resprouter tree crowns provide a strong basis for interpreting post-fire patterns in forest canopies and vegetation profiles in Light Detection and Ranging (LiDAR) and other remotely-sensed data at larger scales.

Satellite-derived spectral indices such as the relativized burn ratio (RBR) allow fire severity maps to be produced in a relatively straightforward manner across multiple fires and broad spatial extents. These indices often have strong relationships with field-based measurements of fire severity, thereby justifying their widespread use in management and science. However, satellite-derived spectral indices have been criticized because their non-standardized units render them difficult to interpret relative to on-the-ground fire effects. In this study, we built a Random Forest model describing a field-based measure of fire severity, the composite burn index (CBI), as a function of multiple spectral indices, a variable representing spatial variability in climate, and latitude. CBI data primarily representing forested vegetation from 263 fires (8075 plots) across the United States and Canada were used to build the model. Overall, the model performed well, with a cross-validated R2 of 0.72, though there was spatial variability in model performance. The model we produced allows for the direct mapping of CBI, which is more interpretable compared to spectral indices. Moreover, because the model and all spectral explanatory variables were produced in Google Earth Engine, predicting and mapping of CBI can realistically be undertaken on hundreds to thousands of fires. We provide all necessary code to execute the model and produce maps of CBI in Earth Engine. This study and its products will be extremely useful to managers and scientists in North America who wish to map fire effects over large landscapes or regions.

Improved predictions of tree species mortality and growth metrics following fires are important to assess fire impacts on forest succession, and ultimately forest growth and yield. Recent studies have shown that North American conifers exhibit a ‘toxicological dose-response’ relationship between fire behavior and the resultant mortality or recovery of the trees. Prior studies have not been conclusive due to potential pseudo-replication in the experimental design and time-limited observations. We explored whether dose-response relationships are observed in ponderosa pine (Pinus ponderosa) saplings exposed to surface fires of increasing fire behavior (as quantified by Fire Radiative Energy—FRE). We confirmed equivalent dose-response relationships to the prior studies that were focused on other conifer species. The post-fire growth in the saplings that survived the fires decreased with increasing FRE dosages, while the percentage mortality in the sapling dosage groups increased with the amount of FRE applied. Furthermore, as with lodgepole pine (Pinus contorta), a low FRE dosage could be applied that did not yield mortality in any of the replicates (r = 10). These results suggest that land management agencies could use planned burns to reduce fire hazard while still maintaining a crop of young saplings. Incorporation of these results into earth-system models and growth and yield models could help reduce uncertainties associated with the impacts of fire on timber growth, forest resilience, carbon dynamics, and ecosystem economics.

Fire severity is a key factor for management of post-fire vegetation regeneration strategies because it quantifies the impact of fire, describing the amount of damage. Several indices have been developed for estimation of fire severity based on terrestrial observation by satellite imagery. In order to avoid the implicit limitations of this kind of data, this work employed an Unmanned Aerial Vehicle (UAV) carrying a high-resolution multispectral sensor including green, red, near-infrared, and red edge bands. Flights were carried out pre- and post-controlled fire in a Mediterranean forest. The products obtained from the UAV-photogrammetric projects based on the Structure from Motion (SfM) algorithm were a Digital Surface Model (DSM) and multispectral images orthorectified in both periods and co-registered in the same absolute coordinate system to find the temporal differences (d) between pre- and post-fire values of the Excess Green Index (EGI), Normalized Difference Vegetation Index (NDVI), and Normalized Difference Red Edge (NDRE) index. The differences of indices (dEGI, dNDVI, and dNDRE) were reclassified into fire severity classes, which were compared with the reference data identified through the in situ fire damage location and Artificial Neural Network classification. Applying an error matrix analysis to the three difference of indices, the overall Kappa accuracies of the severity maps were 0.411, 0.563, and 0.211 and the Cramer’s Value statistics were 0.411, 0.582, and 0.269 for dEGI, dNDVI, and dNDRE, respectively. The chi-square test, used to compare the average of each severity class, determined that there were no significant differences between the three severity maps, with a 95% confidence level. It was concluded that dNDVI was the index that best estimated the fire severity according to the UAV flight conditions and sensor specifications.

While operational fire severity products inform fire management decisions in Grand Canyon National Park (GRCA), managers have expressed the need for better quantification of the consequences of severity, specifically forest structure. In this study we computed metrics related to the forest structure from airborne laser scanning (ALS) data and investigated the influence that fires that burned in the decade previous had on forest structure on the North Rim of the Grand Canyon in Arizona. We found that fire severity best explains the occurrence of structure classes that include canopy cover, vertical fuel distribution, and surface roughness. In general we found that high fire severity resulted in structure types that exhibit lower canopy cover and higher surface roughness. Areas that burned more frequently with lower fire severity in general had a more closed canopy and a lower surface roughness, with less brush and less conifer regeneration. In a random forests modeling exercise to examine the relationship between severity and structure we found mean canopy height to be a powerful explanatory variable, but still proved less informative than the three-component structure classification. We show that fire severity not only impacts forest structure but also brings heterogeneity to vegetation types along the elevation gradient on the Kaibab plateau. This work provides managers with a unique dataset, usable in conjunction with vegetation, fuels and fire history data, to support management decisions at GRCA.

Variation in the structure of ground fuels, i.e. the moss and litter (M/L) layer, may be an important control on fire severity in heather moorlands and thus influence vegetation regeneration and soil carbon dynamics. We completed experimental fires in a Calluna vulgaris -dominated heathland to study the role of the M/L layer in determining (i) fire-induced temperature pulses into the soil and (ii) post-fire soil thermal dynamics. Manually removing the M/L layer before burning increased fire-induced soil heating, both at the soil surface and 2 cm below. Burnt plots where the M/L layer was removed simulated the fuel structure after high severity fires where ground fuels are consumed but the soil does not ignite. Where the M/L layer was manually removed, either before or after the fire, post-fire soil thermal dynamics showed larger diurnal and seasonal variation, as well as similar patterns to those observed after wildfires, compared to burnt plots where the M/L layer was not manipulated. We used soil temperatures to explore potential changes in post-fire soil respiration. Simulated high fire severity (where the M/L layer was manually removed) increased estimates of soil respiration in warm months. With projected fire regimes shifting towards higher severity fires, our results can help land managers develop strategies to balance ecosystem services in Calluna -dominated habitats. [ABSTRACT FROM AUTHOR]

The carbon stability of fire-tolerant forests is often assumed but less frequently assessed, limiting the potential to anticipate threats to forest carbon posed by predicted increases in forest fire activity. Assessing the carbon stability of fire-tolerant forests requires multi-indicator approaches that recognize the myriad ways that fires influence the carbon balance, including combustion, deposition of pyrogenic material, and tree death, post-fire decomposition, recruitment, and growth. Five years after a large-scale wildfire in southeastern Australia, we assessed the impacts of low- and high-severity wildfire, with and without prescribed fire (≤10 yr before), on carbon stocks in multiple pools, and on carbon stability indicators (carbon stock percentages in live trees and in small trees, and carbon stocks in char and fuels) in fire-tolerant eucalypt forests. Relative to unburned forest, high-severity wildfire decreased short-term (five-year) carbon stability by significantly decreasing live tree carbon stocks and percentage stocks in live standing trees (reflecting elevated tree mortality), by increasing the percentage of live tree carbon in small trees (those vulnerable to the next fire), and by potentially increasing the probability of another fire through increased elevated fine fuel loads. In contrast, low-severity wildfire enhanced carbon stability by having negligible effects on aboveground stocks and indicators, and by significantly increasing carbon stocks in char and, in particular, soils, indicating pyrogenic carbon accumulation. Overall, recent preceding prescribed fire did not markedly influence wildfire effects on short-term carbon stability at stand scales. Despite wide confidence intervals around mean stock differences, indicating uncertainty about the magnitude of fire effects in these natural forests, our assessment highlights the need for active management of carbon assets in fire-tolerant eucalypt forests under contemporary fire regimes. Decreased live tree carbon and increased reliance on younger cohorts for carbon recovery after high-severity wildfire could increase vulnerabilities to imminent fires, leading to decisions about interventions to maintain the productivity of some stands. Our multi-indicator assessment also highlights the importance of considering all carbon pools, particularly pyrogenic reservoirs like soils, when evaluating the potential for prescribed fire regimes to mitigate the carbon costs of wildfires in fire-prone landscapes. [ABSTRACT FROM AUTHOR]

Contemporary wildfires in southwestern US ponderosa pine forests can leave uncharacteristically large patches of tree mortality, raising concerns about the lack of seed-producing trees, which can prevent or significantly delay ponderosa pine regeneration. We established 4-ha plots in high-severity burn patches in two Arizona wildfires, the 2000 Pumpkin and 2002 Rodeo-Chediski Fires, to determine if: (1) distance from forest edge influences the density and spatial patterns of regenerating ponderosa pine and sprouting tree species, (2) interactions with re-sprouting trees affect spatial patterns of ponderosa pine regeneration, and (3) distance from forest edge and species competition affect regenerating ponderosa pine height. Plots were located in high-severity burn patches (defined as 100% tree mortality) and either adjacent to residual live forest edges (edge plots), or >200 m from any residual live trees (interior plots). We found higher ponderosa pine regeneration densities in the edge plots (13–154 (median = 69) stems ha −1 ) than the interior plots (12–124 (median = 29) stems ha −1 ) on both wildfires, but no differences in spatial patterns between edge and interior plots. Ponderosa pine regeneration displayed patterns of small-scale spatial aggregation in all plots, except one edge and one interior plot on the Pumpkin Fire, which displayed random distributions. These patterns suggest both short- and long-distance dispersal play important roles in ponderosa pine regeneration in high-severity burn patches. Sprouting trees dominated tree regeneration on the Rodeo-Chediski Fire, but they were spatially independent of ponderosa pine and did not influence ponderosa pine height. Regenerating ponderosa pine height was positively correlated with neighboring ponderosa pine densities and height, suggesting that intraspecific facilitation or similar habitat preferences occur in high-severity burn patches. Collectively, these results indicate that ponderosa pines are re-establishing with heterogeneous spatial patterns in large high-severity burn patches, but often with low densities. Also, ponderosa pine regeneration could be more strongly influenced by intraspecific facilitation than interspecific competition from dense sprouting species. Future forest spatial patterns and composition are still unclear, but at this stage of development, these heterogeneous patches, characterized by drought-tolerant sprouting species or low pine densities, could be more resilient to climate change and severe wildfires than the overly-dense ponderosa pine forests that were present before the wildfires. [ABSTRACT FROM AUTHOR]

Thinning is recommended in overstocked thickets to improve forest structure and reduce high-intensity stand replacing fires. Many studies have outlined the benefits of thinning for forest growth and reproduction but effectiveness in fire intensity needs more attention. Moreover, the effect that slash generated by thinning may have on fire behavior has been seldom explored. Here we simulated fire behavior on unthinned and thinned Aleppo pine ( Pinus halepensis ) thickets in Catalonia (Northeast Spain) where woody residues were left in situ . Furthermore, we simulated fire behavior one year later considering the reduction in the dead fuel load, using decomposition rates empirically determined under high and low rainfall. We could also assess the accuracy of our simulations by measuring fire severity on trees in the same study area after a real wildfire. Simulations predicted that thinning prevents the occurrence of active crown fires and reduces mean flame length (from 6.2 ± 0.8 to 1.5 ± 0.2 m), the rate of fire spread (from 5.4 ± 0.9 to 0.9 ± 0.1 m min −1 ) and the fireline intensity (from 3631 ± 686 to 446 ± 70 kW m −1 ) compared to unthinned thickets. In the thinned stands these parameters further decrease one year later owing to the decomposition of woody residues. Decomposition of woody residues was observed to be faster under a high rainfall scenario leading to a reduction in simulated flame length and fire intensity twice as fast as under low rainfall. In accordance with the lack of active crown fires and the lower flame length predicted for thinned thickets, fire severity observed after a real wildfire in the study area was lower in thinned than in unthinned stands (respectively, 2.02 ± 0.13 vs. 2.93 ± 0.15 in a scale of 0–4). The agreement between simulations that predicted a reduction in fire intensity in thinned thickets and the lower fire damage (fire severity) observed confirms the benefits of thinning young P. halepensis thickets to reduce fire effects. Moreover, our results indicate that leaving woody residues in situ after the thinning of these young thickets does not increase fire intensity. Yet, the influence of precipitation on the decomposition of woody residues highlights the uncertainties that an increase in drought in Mediterranean-type climates may have in the behavior of future fire events. [ABSTRACT FROM AUTHOR]

Multidecadal trends in areas burned with high severity shape ecological effects of fires, but most assessments are limited to ~30 years of satellite data. We analysed the proportion of area burned with high severity, the annual area burned with high severity, the probability areas burned with high severity and also the area reburned (all severities and high burn severity only) over 133 years across 346 265 ha within the Selway-Bitterroot Wilderness (SBW) Area in Idaho, United States. We used burn severity class inferred from digitised aerial photography (1880-2000) and satellite imagery (1973-2012). Over this long record, the proportion burned with high severity did not increase, despite extensive area burned in recent decades. Much greater area burned with high severity during the Early (1880-1934) and Late (1975-2012) periods than during the Middle period (1935-1974), paralleling trends in area burned. Little area reburned with high severity, and fires in the Early period limited the extent of fires burning decades later in the Late period. Our results suggest that long-term data across large areas provides useful context on recent trends, and that projections for the extent and severity of future fires must consider prior fires and fire management. [ABSTRACT FROM AUTHOR]

Over the past few decades, the frequency and number of large fires has increased in the western United States following a paucity of fire activity in many forests during most of the 20th century. Areas of repeated burning are of particular interest for understanding where there may be qualitative shifts in fire severity and the ecological consequences related to ecosystem resilience and climate change. In the context of recent increases in fire activity, we evaluated the relative importance of potential factors contributing to reburn severity (fire severity in areas that have burned twice) from 1985 to 2012 in the Klamath Mountains ecoregion of California. A unique component of our study was the evaluation of different scales of analysis within the ecoregion. The variables prior burn severity (continuous relative difference-normalized burn ratio values from 1 to 1300), time since fire, biophysical setting, and average monthly weather were evaluated using generalized additive models to identify the relative importance of factors related to reburn severity patterns for 28 individual repeat fires (>375 ha), shorter (<15 yr) and longer (≥19 yr) fire interval categories, and across all repeat fires combined (79,112 ha). We found that evaluation of all repeat fires combined had masked important trends occurring across individual reburn areas of study particularly when dominated by one or more large fires. Averaging the variance of reburn severity explained across individual reburn areas (equal representation) yielded more explanatory power of predictor variables compared to the composite of all reburn areas combined. Over the period of analysis, topographic controls were relatively consistent regardless of fire interval, but vegetation characteristics had a stronger relationship than weather on reburn severity at longer fire intervals compared to shorter intervals. Likewise, we found greater similarity between prior and reburn severity at longer fire intervals than at shorter fire intervals. Our results underscore the presence of a self-reinforcing pattern of fire severity related to the biophysical setting in the Klamath Mountains ecoregion, but also highlight the importance of spatial and temporal scale of evaluation and the interactions of vegetation characteristics, time since fire, and fire weather on reburn fire severity. [ABSTRACT FROM AUTHOR]

In fire-prone forests, self-reinforcing fire behavior may generate a mosaic of vegetation types and structures. In forests long subject to fire exclusion, such feedbacks may result in forest loss when surface and canopy fuel accumulations lead to unusually severe fires. We examined drivers of fire severity in one large (>1000 km2 ) wildfire in the western United States, the Rim Fire in the Sierra Nevada, California, and how it was influenced by severity of 21 previous fires to examine the influences on (1) the severity of the first fire since 1984 and (2) reburn severity. The random forest machine-learning statistical model was used to predict satellite-derived fire severity classes from geospatial datasets of fire history, topographic setting, weather, and vegetation type. Topography and inferred weather were the most important variables influencing the previous burn. Previous fire severity was the most important factor influencing reburn severity, and areas tended to reburn at the same severity class as the previous burn. However, areas reburned in <15 yr burned at lower severity than expected. Previous fire severity and Rim Fire severity were higher on ridges, at intermediate elevations (~750–1250 m), and on slopes <30°, indicating a consistent effect of topography on fire severity patterns in these forests. Areas burned with low severity prescribed fires burned at low severity again in the Rim Fire, and areas with long fire-free periods burned at higher severity. This fire history effect suggests that prescribed burning was an effective management tool, leading to lower fire severity in the previous burns and the subsequent reburn. Our results show that self-reinforcing fire behavior results mainly from effects of vegetation structure and fuels on fire severity and that this behavior is mediated by topographic setting and the time since last fire. [ABSTRACT FROM AUTHOR]

Remote sensing data can usefully support the fire management operational applications in different spatial and temporal scales with a synoptic point of view and low cost technologies. The satellite monitoring systems together with other geographic information, historical data and field measurements, can provide the fire management operators useful tools of fire danger assessment, fire prevention, fire-fighting and post-fire planning. The FIRE-SAT monitoring system was applied to a fire event which developed in a wildland-urban interface area of the Potenza town (Basilicata, Italy) on July 2015, in order to assess the fire occurrence danger, to evaluate the fire effects and to simulate the fire propagation. [ABSTRACT FROM AUTHOR]

Following changes in vegetation structure and pattern, along with a changing climate, large wildfire incidence has increased in forests throughout the western United States. Given this increase, there is great interest in whether fuels treatments and previous wildfire can alter fire severity patterns in large wildfires. We assessed the relative influence of previous fuels treatments (including wildfire), fire weather, vegetation, and water balance on fire-severity in the Rim Fire of 2013. We did this at three different spatial scales to investigate whether the influences on fire severity changed across scales. Both fuels treatments and previous low to moderate-severity wildfire reduced the prevalence of high-severity fire. In general, areas without recent fuels treatments and areas that previously burned at high severity tended to have a greater proportion of high-severity fire in the Rim Fire. Areas treated with prescribed fire, especially when combined with thinning, had the lowest proportions of high severity. The proportion of the landscape burned at high severity was most strongly influenced by fire weather and proportional area previously treated for fuels or burned by low to moderate severity wildfire. The proportion treated needed to effectively reduce the amount of high severity fire varied by spatial scale of analysis, with smaller spatial scales requiring a greater proportion treated to see an effect on fire severity. When moderate and high-severity fire encountered a previously treated area, fire severity was significantly reduced in the treated area relative to the adjacent untreated area. Our results show that fuels treatments and low to moderate-severity wildfire can reduce fire severity in a subsequent wildfire, even when burning under fire growth conditions. These results serve as further evidence that both fuels treatments and lower severity wildfire can increase forest resilience. [ABSTRACT FROM AUTHOR]

Previous studies have suggested that bark beetles and fires can be interacting disturbances, whereby bark beetle-caused tree mortality can alter the risk and severity of subsequent wildland fires. However, there remains considerable uncertainty around the type and magnitude of the interaction between fires following bark beetle attacks, especially in drier forest types such as those dominated by ponderosa pine (Pinus ponderosa Lawson & C. Lawson). We used a full factorial design across a range of factors thought to control bark beetle-fire interactions, including the temporal phase of the outbreak, level of mortality, and wind speed. We used a three-dimensional physics-based model, HIGRAD/FIRETEC, to simulate fire behavior in fuel beds representative of 60 field plots across five national forests in northern Arizona, USA. The plots were dominated by ponderosa pine, and encompassed a gradient of bark beetle-caused mortality due to a mixture of both Ips and Dendroctonus species. Non-host species included two sprouting species, Gambel oak (Quercus gambelii Nutt.) and alligator juniper (Juniperus deppeana Steud.), as well as other junipers and pinyon pine (Pinus edulis Engelm.). The simulations explicitly accounted for the modifications of fuel mass and moisture distribution caused by bark beetle-caused mortality. We first analyzed the influence of the outbreak phase, level of mortality, and wind speed on the severity of a subsequent fire, expressed as a function of live and dead canopy fuel consumption. We then computed a metric based on canopy fuel loss to characterize whether bark beetles and fire are linked disturbances and, if they are, if the linkage is antagonistic (net bark beetle and fire severity being less than if the two disturbances occurred independently) or synergistic (greater combined effects than independent disturbances). Both the severity of a subsequent fire and whether bark beetles and fire are linked disturbances depended on the outbreak phase of the bark beetle mortality and attack severity, as well as the fire weather (here, wind). Greater fire severity and synergistic interactions were generally associated with the "red phase" (when dead needles remain on trees). In contrast, during the "gray phase" (when dead needles had fallen to the ground), fire severity was either similar to, or less than, green-phase fires and interactions were generally antagonistic, but included both synergistic and neutral interactions. The simulations also revealed that the magnitude of the linkage between these two disturbances was smaller for fires occurring during high wind conditions, especially in the red phase. This complexity might be a reason for the contrasted or controversial perception of bark beetle-fire interactions reported in the literature, since both fire severity and the type and magnitude of the linkage can vary strongly among studies. These results suggest that, for fires burning in the gray phase following moderate levels of mortality, bark beetle-caused mortality may buffer rather than exacerbate fire severity. However, for fires burning under high wind speeds, regardless of the outbreak phase or level of mortality, the near complete loss of canopy fuels may push this ecosystem into an alternative state dominated by sprouting species. Estudios previos han sugerido que los escarabajos de la corteza y el fuego pueden ser disturbios interactivos, por lo que la mortalidad de árboles causada por estos escarabajos puede alterar el riesgo y la severidad de incendios subsecuentes. Sin embargo, una considerable incertidumbre persiste en torno al tipo y magnitud de la interacción entre los incendios que siguen al ataque de insectos, especialmente en tipos de bosques secos como los dominados por pino ponderosa (Pinus ponderosa Lawson & C. Lawson). Usamos un diseño factorial a través de un rango de factores que pensamos controlaban la interacción entre el escarabajo de la corteza y los incendios, incluyendo la fase temporal del estallido del insecto, el nivel de mortalidad y la velocidad del viento. Para simular el comportamiento del fuego en camas de combustible en 60 parcelas representativas a lo largo de cinco bosques nacionales en el norte de Arizona, EEUU, usamos el modelo físico tridimensional HIGRAD/FIERETEC. Las parcelas estaban dominadas por pino ponderosa, y abarcaban un gradiente de mortalidad causado por escarabajos de diversas especies, tanto de los géneros Ips como de Dendroctonus. Las especies no hospedantes de estos escarabajos incluían a dos rebrotantes como el roble de Gambela (Quercus gambelii Nutt.) y el táscate (Juniperus deppeana Steud.), como así también otras especies de juníperos y de pino edulis (Pinus edulis Engelm.). Las simulaciones representaron explícitamente las modificaciones de la biomasa combustible y la distribución de humedad causada por la mortalidad inducida por estos escarabajos. Primeramente analizamos la influencia de la fase del estallido poblacional, el nivel de mortalidad, y la velocidad del viento, en la severidad de un incendio subsecuente, expresado en función del consumo de combustible vivo y muerto del dosel. Luego computamos una medida basada en la pérdida del combustible del dosel para caracterizar si los escarabajos de la corteza y el fuego son disturbios relacionados entre sí y, si lo son, si esa relación es antagónica (daño por el escarabajo y severidad del fuego son menores que cuando ambos disturbios ocurren independientemente), o sinérgica (mayores efectos combinados que si ocurriesen independientemente). Ambos, la severidad de un incendio subsecuente y si los escarabajos y el fuego son disturbios relacionados, dependen de la fase del estallido, de la mortalidad, y de la severidad del ataque, y también del entorno meteorológico del fuego, en este caso la velocidad del viento. Una mayor severidad e interacciones sinérgicas fueron generalmente asociadas con la fase "roja" (cuando las acículas muertas permanecen en los árboles). En contraste con esto, durante la fase "gris" (cuando las acículas han caído al suelo), la severidad del fuego fue similar a, o menor que, las fases de fuego "verde" y las interacciones fueron generalmente antagónicas, pero incluyeron también interacciones sinérgicas y neutras. Las simulaciones también revelaron que la magnitud entre ambos disturbios fue menor durante la ocurrencia de vientos fuertes, especialmente en la fase roja. Esta complejidad podría ser una razón sobre la percepción controversial o contrastante de las interacciones entre estos escarabajos y el fuego reportados en la literatura, dado que ambos, la severidad y el tipo y magnitud de la relación, pueden variar fuertemente entre estudios. Estos resultados sugieren que, para incendios que queman en la fase gris seguidos de moderados niveles de mortalidad, la causa de mortalidad debida a los escarabajos puede atemperar, más que exacerbar, la severidad del fuego. Sin embargo, para incendios que queman bajo fuertes velocidades de viento, independientemente de la fase del estallido o el nivel de mortalidad, el casi completo consumo del dosel puede derivar este ecosistema a un estado alternativo dominado por especies rebrotantes. [ABSTRACT FROM AUTHOR]