Fire Severity Classes Research Articles

Fire severity alters the distribution of pyrogenic carbon stocks across ecosystem pools in a Californian mixed‐conifer forest

AbstractPyrogenic carbon (PyC) is hypothesized to play an important role in the carbon (C) cycle due to its resistance to decomposition; however, much uncertainty still exists regarding the stocks of PyC that persist on‐site after the initial erosion in postfire forests. Therefore, understanding how fire characteristics influence PyC stocks is vital, particularly in the context of California forests for which an increase of high‐severity fires is predicted over the next decades. We measured forest C and persistent PyC stocks in areas burned by low‐to‐moderate and high‐severity fire, as well as in adjacent unburned areas in a California mixed‐conifer forest, 2 to 3 years after wildfire. We measured C and PyC stocks in the following compartments: standing trees, downed wood, forest floor, and mineral soil (0–5 cm), and we identified PyC using the weak nitric acid digestion method. We found that the total stock of PyC did not differ among fire severity classes (overall mean 248 ± 30 g C m−2); however, fire severity influenced the distribution of PyC in the individual compartments. Areas burned by high‐severity fire had 2.5 times more PyC stocked in the coarse woody debris (p < 0.05), 3.3 times more PyC stocked in standing trees (p < 0.05), and a lower PyC stock in the forest floor (−22%, p < 0.05) compared to low‐to‐moderate fire severity areas. These results have important implications for the permanence time of PyC, which is putatively higher in standing trees and coarse woody debris compared to the forest floor, where it is susceptible to rapid losses through erosion.

Emissions of forest floor and mineral soil carbon, nitrogen and mercury pools and relationships with fire severity for the Pagami Creek Fire in the Boreal Forest of northern Minnesota

Forest fires cause large emissions of C (carbon), N (nitrogen) and Hg (mercury) to the atmosphere and thus have important implications for global warming (e.g. via CO2 and N2O emissions), anthropogenic fertilisation of natural ecosystems (e.g. via N deposition), and bioaccumulation of harmful metals in aquatic and terrestrial systems (e.g. via Hg deposition). Research indicates that fires are becoming more severe over much of North America, thus increasing element emissions during fire. However, there has been little research relating forest floor and mineral soil losses of C, N and Hg to on-the-ground indices of fire severity that enable scaling up those losses for larger-scale accounting of fire-level emissions. We investigated the relationships between forest floor and mineral soil elemental pools across a range of soil-level fire severities following the 2011 Pagami Creek wildfire in northern Minnesota, USA. We were able to statistically differentiate losses of forest floor C, N and Hg among a five-class soil-level fire severity classification system. Regression relationships using soil fire severity class were able to predict remaining forest floor C, N and Hg pools with 82–96% confidence. We correlated National Aeronautics and Space Administration Airborne Visible and Infrared Imaging Spectrometer-Classic imagery to ground-based plot-scale estimates of soil fire severity to upscale emissions of C, N and Hg to the fire level. We estimate that 468 000 Mg C, 11 000 Mg of N and over 122 g of Hg were emitted from the forest floor during the burning of the 28 310 ha upland area of the Pagami Creek fire.

Effect of fire severity on physical and biochemical soil properties in Zagros oak (Quercus brantii Lindl.) forests in Iran

Fire affects the physical and chemical properties and soil biological activity of natural ecosystems. This study was conducted in the Miyan Tang region, Ilam Province in western Iran. The study site was 110 hectares, where we sampled soils in areas that were classified by fire severity: low (LS), high (HS) and medium severity (MS), and unburned (UB), which served as the control. In each severity class, 25 transect points were randomly selected for measurement. Around each transect plot center, 3 soil samples were selected randomly and soils collected from the 0 to 20 cm depth were combined into a composite sample that was used in laboratory analysis to represent conditions at that point. Plots in the UB and LS fire classes had similar soil conditions and had higher values of factors such as saturated moisture, organic carbon, carbon dioxide, and silt and clay content. In contrast, plots in the HS and MS fire severity classes were clustered in the positive direction along the first axis that represented gradients in soil acidity, electrical conductivity, cation exchange capacity, accessible phosphorus, accessible potassium, bulk density, and sand. Soil attributes were similar in areas of HS and MS fire severity classes, whereas soil conditions in the LS class and UB controls were most similar. Fire in the LS areas either did not significantly alter the physical–chemical soil properties and microbial basal respiration, or soils were able to recover quickly after being burned.

Tree mortality and structural change following mixed-severity fire in Pseudotsuga forests of Oregon’s western Cascades, USA

Mixed-severity fires are increasingly recognized as common in Pseudotsuga forests of the Pacific Northwest and may be an important mechanism for developing or maintaining their structural diversity and complexity. Questions remain about how tree mortality varies and forest structure is altered across the disturbance gradient imposed by these fires. Therefore, we sampled live and dead trees at 45–1.0ha plots, each with four 0.10ha nested subplots, stratified across an unburned, low, moderate and high-severity fire gradient. Burned plots were primarily sampled 10 and 22years post-fire, except three plots sampled four years post-fire. We estimated probability of mortality for fire-tolerant (Douglas-fir, incense-cedar, sugar pine) and fire-intolerant (western hemlock, western redcedar, true fir) trees from 5079 samples. The probability of mortality varied across all species and fire-severity classes, but the greatest difference was observed between fire-tolerant and fire-intolerant functional groups. Probability of mortality decreased with increasing DBH for all species except western hemlock that did not increase its fire resistance with increasing size. Some large, fire-tolerant trees survived high-severity fire but only in 31% of our plots. Snag fall and fragmentation was estimated for trees killed by the fire from 2746 sampled snags and logs 10 and 22years post-fire. The proportion of snags fallen decreased with increasing DBH for all species, and was positively correlated with fire severity, except for Douglas-fir that had a higher proportion felled following low-severity fire. Snag fragmentation rates were positively correlated with DBH and fire severity for all species. Individual tree and snag estimates were scaled to plot-level structural attributes and contrasted by their coefficient of variation within- and among-plots from unburned to moderate-severity, as well as across all sampled conditions. Structural attributes varied more within- than among-plots, likely a result of patchy mortality that increased with fire severity. Although vertical and horizontal structural diversity increased at sub-hectare scales, the highest variability occurred for all structural attributes when compared across all sampled conditions. We conclude that the range of fire effects imposed by mixed-severity fire is important in creating structural diversity in Pseudotsuga forests of the Pacific Northwest and should be promoted through progressive fire management programs aimed at maintaining this forest’s fire regime now and in the future.

Effects of the fire regime on mammal occurrence after wildfire: Site effects vs landscape context in fire-prone forests

Wildfires have major impacts on ecosystems globally. Fire regimes (including fire frequency, intensity, season and type of fire) influence the status of species by altering habitat suitability at the site scale, and by creating heterogeneity at the landscape scale. The relative effects of site and landscape-scale fire attributes on animal species are rarely examined together. Such knowledge is important, given that fire regimes are sensitive to changing land management practices; and that fires are predicted to become larger and more frequent in some regions as a result of climate change. Here, we tested the relative influence of elements of the fire regime (fire severity, fire history) at the site-scale, and the landscape context (extent of surrounding unburnt forest, fire heterogeneity) on the occurrence of native terrestrial mammals after severe wildfire in south-eastern Australia. We conducted surveys by using automatically triggered, infrared cameras at 80 sites in fire-prone eucalypt forests, 2–3years post-wildfire. Thirteen native mammal species were recorded, eight of which were detected with sufficient frequency for analysis. Most species were widespread (35–90% of sites) and recorded in all fire severity classes. Fire effects at the site-level were more influential than landscape context effects arising from heterogeneity in the fire regime (e.g. extent of surrounding unburnt forest). Fire severity was the most influential of the fire-regime elements investigated, but it affected different species in different ways. This study highlights three main points relevant to conservation of terrestrial mammals after wildfire. First, spatial variation in fire severity associated with wildfire (ranging from unburned to severely burned stands) is an important contributor to the post-fire status of species. Second, post-fire environmental conditions are significant: here, rapid regeneration of vegetation following drought-breaking rains greatly influenced the suitability of post-fire habitats. Third, it is valuable to consider the effects of the fire regime at multiple scales, including both the site (forest stand) and its landscape context. Insights from short-term surveys, such as this, will be enhanced by complementary longitudinal studies, especially where they encompass environmental variation through the post-fire succession.

Fire severity mediates seedling recruitment patterns in slender mulga (Acacia aptaneura), a fire-sensitive Australian desert shrub with heat-stimulated germination

Members of the widespread arid Australian mulga (Acacia aneura) complex are fire-sensitive shrubs or small trees that can resprout epicormically following low-severity burning, but are readily killed by high-severity fire. The seeds of many species of mulga are stimulated to germinate by heat during burning, although post-fire regeneration rates are unpredictable. Here, we investigated whether variability in post-fire mulga recruitment relates to the relationship between fire severity and soil heating during fire, which may kill, leave unaffected, or stimulate the germination of buried seeds. This hypothesis was examined in central Australia on slender mulga (A. aptaneura), by experimentally investigating (a) seedling recruitment rates under different fire severity classes, (b) the germination and lethal temperature thresholds of seeds, (c) soil temperatures during fires of different severity classes and (d) the emergence depths of seedlings beneath high- and low-severity burnt plants. We found that post-fire recruitment was significantly lower beneath low-severity burnt and unburnt plants than high-severity burnt plants. This result was explained by the finding that maximum germinability of mulga seeds occurs after heating to between 80 and 100 °C, and that these temperatures are not achieved in unburnt patches or low-severity burns at depths where the majority of the seed bank is known to occur. Despite the increased regeneration observed after high-severity fire, post-fire recruitment was highly variable between sites, independent of fire severity. This indicates that while heat-stimulated germination may confer on mulga a risk-spreading strategy to a range of fire severities, post-burn recruitment may not always offset high adult death rates following high-severity fire.

Hydrological modelling for flood forecasting: Calibrating the post-fire initial conditions

Summary Floods and forest fires are two of the most devastating natural hazards with severe socioeconomic, environmental as well as aesthetic impacts on the affected areas. Traditionally, these hazards are examined from different perspectives and are thus investigated through different, independent systems, overlooking the fact that they are tightly interrelated phenomena. In fact, the same flood event is more severe, i.e. associated with increased runoff discharge and peak flow and decreased time to peak, if it occurs over a burnt area than that occurring over a land not affected by fire. Mediterranean periurban areas, where forests covered with flammable vegetation coexist with agricultural land and urban zones, are typical areas particularly prone to the combined impact of floods and forest fires. Hence, the accurate assessment and effective management of post-fire flood risk becomes an issue of priority. The research presented in this paper aims to develop a robust methodological framework, using state of art tools and modern technologies to support the estimation of the change in time of five representative hydrological parameters for post-fire conditions. The proposed methodology considers both longer- and short-term initial conditions in order to assess the dynamic evolution of the selected parameters. The research focuses on typical Mediterranean periurban areas that are subjected to both hazards and concludes with a set of equations that associate post-fire and pre-fire conditions for five Fire Severity (FS) classes and three soil moisture states. The methodology has been tested for several flood events on the Rafina catchment, a periurban catchment in Eastern Attica (Greece). In order to validate the methodology, simulated hydrographs were produced and compared against available observed data. Results indicate a close convergence of observed and simulated flows. The proposed methodology is particularly flexible and thus easily adaptable to catchments with similar hydrometeorological and geomorphological features.

The effects of fire severity on macroinvertebrate detritivores and leaf litter decomposition.

High severity wildfire events are a feature of forests globally and are likely to be more prevalent with climate change. As a disturbance process, fire has the potential to change important ecological functions, such as decomposition, through its impact on biodiversity. Despite the recognised importance of decomposition in terms of fuel loads and energy flow, little is known about the post-fire effects of fire severity on decomposition by litter-dwelling macroinvertebrate detritivores. We tested the hypotheses that: 1) increasing fire severity is associated with decreased rates of leaf litter decomposition by macroinvertebrate detritivores; and 2) the abundance and biomass of macroinvertebrate detritivores decreases with increasing fire severity, while body size increases. We used a litterbag experiment at long-unburnt, ground-burnt and crown-burnt sites (n = 7 for all treatments) to test the effect of fire severity on: a) macroinvertebrate-driven break-down of litter fuel loads; and b) the size and abundance of macroinvertebrate detritivores three years after fire. Microhabitat conditions differed among fire severity classes. Macroinvertebrate exclusion reduced litter decomposition by 34.7%. Macroinvertebrate detritivores were larger and less abundant following higher severity fires, possibly as a result of fire-induced changes in habitat structure. Opposing effects of fire severity on macroinvertebrate abundance and body size resulted in both similar detritivore biomass and, most interestingly, no differences in leaf litter decomposition under different fire severities. This suggests that the diversity of macroinvertebrates enhances functional resilience of litter decomposition to fire and that litter-breakdown is not inhibited within three years following a high severity fire in this forest type and where recolonisation sources are readily available. We found no support for the hypothesis that high severity fires reduce litter decomposition and therefore increase the likelihood of future fires.

Postfire influences of snag attrition on albedo and radiative forcing

AbstractThis paper examines albedo perturbation and radiative forcing after a high‐severity fire in a mature forest in the Oregon Cascade Range. Correlations between postfire albedo and seedling, sapling, and snag (standing dead tree) density were investigated across fire severity classes and seasons for years 4–15 after fire. Albedo perturbation was 14 times larger in winter compared to summer and increased with fire severity class for the first several years. Albedo perturbation increased linearly with time over the study period. Correlations between albedo perturbations and the vegetation densities were strongest with snags, and significant in all fire classes in both summer and winter (R < −0.92, p < 0.01). The resulting annual radiative forcing at the top of the atmosphere became more negative linearly at a rate of −0.86 W m−2 yr−1, reaching −15 W m−2 in year 15 after fire. This suggests that snags can be the dominant controller of postfire albedo on decadal time scales.

Post-Fire Effects in Wetland Environments: Landscape Assessment of Plant Coverage and Soil Recovery in the Paraná River Delta Marshes, Argentina

During 2008, under a region-wide drought, there were a large number of simultaneous fires in the Paraná River Delta region: the most affected vegetation was in marshes dominated by Schoenoplectus californicus (C.A.Mey.) Soják or Cyperus giganteus Vahl. The objective of this paper was to study fire severity in terms of fire effect on vegetation cover and soil properties, and the recovery of those properties after one growing season, using optical remote sensing techniques and fieldwork data. To this aim, we performed unsupervised classification of Landsat TM imagery and conducted vegetation censuses and soil sampling in November 2008 and May 2009. Our results show that we could identify three fire severity classes: low severity, medium severity, and high severity. These classes are characterized by a remnant vegetation cover of approximately 75 %, 25 %, and 5 %, respectively, and a diminution of soil organic carbon and nitrogen of 66 % and 59 % in the case of medium severity and high severity. Fire had almost no effect over pH and a slight effect on electrical conductivity. After one growing season, vegetation recovery is dependent on fire severity and hydrological condition, while soil properties did not show signs of recovery. This is one of the first studies of fire effects and recovery on fluvial herbaceous wetlands.

Fuel variability following wildfire in forests with mixed severity fire regimes, Cascade Range, USA

Fire severity influences post-burn structure and composition of a forest and the potential for a future fire to burn through the area. The effects of fire on forests with mixed severity fire regimes are difficult to predict and interpret because the quantity, structure, and composition of forest fuels vary considerably. This study examines the relationship between fire severity and post-burn fuel characteristics in forests with mixed severity fire regimes. We sampled live and dead canopy and surface fuels across four fire severity classes on three wildfires that occurred on the east side of the Cascade Range, USA, in 2007 and 2008. We used empirical fuels data and stand structure and composition characteristics to calculate potential surface fire behavior for the four fire severity classes. Post-burn average canopy cover is 25–30% in the low severity class and <10% in the high severity class and ranges from 0 to 50% for all fires. All variables representing post-burn canopy fuels differ by fire severity class. The average loading of dead and down woody fuels <7.6cm diameter and litter is 0.9–1.1kgm−2 in the low severity class and 0.6–0.8kgm−2 in the high severity class. Values for fuel loading variables span a wide range of values within and among fires, and substantial overlap exists among severity classes. Fire severity generally does not influence post-burn dead and down woody fuel loading. Estimates of potential fire behavior also cover wide ranges of values, particularly among fires. Flame lengths average 0.4–0.8m in the low severity classes and 0.3–1.1m in the high severity classes. The range of potential flame length values, modeled with a 16.1kmh−1 midflame wind speed, varies by up to 2.0m within a single severity class (0.6–2.6m). Fire severity does influence potential fire behavior, but typically just one severity class differs from the other three classes. These results indicate that fire severity influences immediate (2–3years) post-burn canopy fuels and potential fire behavior but does not influence dead and down surface fuel loading for the three fires studied. The wide ranges of values for the fuel components analyzed demonstrate the variability that is characteristic of forests with mixed severity fire regimes and emphasize the need to consider the natural heterogeneity of these forests in fire and fuels management. Quantification of post-burn fuel variability is critical for understanding the ecological significance of mixed severity fires and developing restoration strategies that emulate characteristics of the historical fire regime.

Fire severity as a key factor in post-fire regeneration of Pinus pinaster (Ait.) in Central Portugal

& Context Mediterranean pine woodlands are strongly affected by wildfires; however, there are knowledge gaps in the role of fire severity on Pinus pinaster Ait. regeneration. & Objectives The principal questions were: (a) does post-fire regeneration of Maritime Pine differ where canopies were consumed to a low vs. high degree and (b) which factors, besides fire severity, could explain these differences. & Methods Pine recruitment was monitored from 2 to 36 months after a summer wildfire in 18 25 m 2 plots, equally divided over two fire severity classes based on crown consumption. Besides the degree of crown consumption, three quantitative fire severity indices as well as post-fire site conditions, seed input and understory vegetation recovery were measured. & Results Pine seedling densities were consistently higher in the plots with low than high crown consumption but due to marked spatial variability, they were only significantly different at two out of the eight sampling occasions. This variability could be explained by a quantitative index based on the diameter of twigs, as well as by seed input and postfire site conditions (ash and litter cover). & Conclusion Fire severity was found to strongly affect the pine recruitment following wildfire, using both a qualitative visual severity index and a quantitative, more labourintensive one.

Ground and satellite-based assessments of wet eucalypt forest survival and regeneration for predicting long-term hydrological responses to a large wildfire

Large fires can have marked impacts on forest ecology and consequently on hydrology, including catchment water yields. Decisions on levels of fire protection and post-fire forest management require accurate information on the consequences of fire, including forest hydrological responses. In February 2009, wildfires burnt large areas of wet sclerophyll eucalypt forest in catchments supplying water to the city of Melbourne, Australia. Fire intensity was highly spatially variable, ranging from low intensity surface fire to high intensity crown fire. A survey of forest survival in three catchments 10–15months after the fires revealed a good correspondence between overstorey survival and a satellite-based fire severity rating.In forests dominated by Eucalyptus regnans and Eucalyptus delegatensis, overstorey survival was close to zero in the two highest fire severity classes (crown burn and crown scorch). However, in areas mapped as intermediate fire severity (moderate crown scorch), survival varied markedly both spatially and between forest age classes.In fire tolerant eucalypt species, in mixed stands of Eucalyptus obliqua, Eucalyptus radiata, Eucalyptus cypellocarpa, and Eucalyptus baxteri, and in pure stands of Eucalyptus nitens, survival was >90% at high and intermediate fire severity. For all overstorey eucalypt species, survival in the lowest two fire severity classes (light or no crown scorch) was >75% but in most of these areas the fire temporarily removed the understorey.The fire severity mapping and ground survey indicate large areas of senescing (approximately 250–300years old) and smaller areas of 70, 83 and 158year old E. regnans and E. delegatensis forest were killed. Based on past research, this would be expected to result in very dense seedling regeneration, increasing evapotranspiration and decreasing catchment yields over the coming 2–3 decades. However, 2years after the fire there were substantial differences between the three catchments in the density of seedling regeneration in these fire-killed areas. Where seedling densities are high, water yields are likely to decline. Areas with little or no eucalypt regeneration, however, might provide a persistent water yield increase. In addition, large areas of 70–158year old E. regnans and E. delegatensis overstorey survived the fire where fire severity was low. Removal of the understorey from these areas and suppression of understorey regrowth by the intact overstorey canopy might result in water yield increases persisting for years to a decade or more.

Factors Associated with the Severity of Intersecting Fires in Yosemite National Park, California, USA

In 1972, Yosemite National Park established a wilderness fire zone in which lightning fires were allowed to run their courses under prescribed conditions. This zone was expanded in 1973 to include the 16 209 ha Illilouette Creek basin, just to the southeast of Yosemite Valley. From 1973 through 2011, there have been 157 fires in the basin. Fire severity data were collected on all 28 of those fires that were larger than 40 ha. The proportion burned in each fire severity class was not significantly associated with fire return interval departure class. When areas were reburned, the proportion of unchanged severity fire decreased while the proportion of high severity fire increased. The proportion of fire severity of the subsequent fires was associated with the number of years since last burned, the burning index, and the severity of the previous fires. The main effects were significant for unchanged severity and low severity, and the interaction between return interval class and burning index class was significant for high severity. Most vegetation types remained the same when burned with unchanged, low, or moderate severity, while high severity often resulted in conversion to montane chaparral. The factors that were associated with reburn severity worked in combination with each factor influencing some aspect of severity. Managers and scientists can use this information to better understand the role fire plays in these ecosystems and how to best manage this dynamic ecological process.

Growth Response of Pinus ponderosa following a Mixed-Severity Wildfire in the Black Hills, South Dakota

Abstract In late summer 2000 the Jasper Fire burned ∼34,000 ha of ponderosa pine forest in the Black Hills of South Dakota. Although regarded as a catastrophic event, the Jasper Fire left a mosaic of fire severity across the landscape, with live trees present in areas burned under low andmoderate fire severity. In October 2005, we cored 96 trees from unburned, low-severity, and moderate-severity stands and assessed whether tree growth differed among fire severity classes during the 5 years postfire. We observed no differences in basal area increment (BAI) 10 years prefireamong fire severities with BAI averaging 9.6 cm2 per year. Despite severe drought conditions, BAI in moderate severity sites 2 years postfire was 58% greater than in unburned and low-severity stands. Although significant, this growth increase was short-lived. Three, 4, and 5 yearspostfire, no differences in growth among unburned, low-severity, and moderate-severity sites were detected, as BAI averaged 8.3, 7.5, and 7.0 cm2, respectively. The lack of a consistent and prolonged growth response suggests that the Jasper Fire did not result in any short-termchanges in growth patterns. Data extending beyond 5 years postfire are required to infer potential long-term changes in tree growth and productivity.

Effects of fire severity on early survival and growth of planted jack pine, black spruce and white spruce

Two boreal mixedwood stands burned by the 1999 Black River wildfire in southeastern Manitoba, Canada were selected to study the effect of fire severity on early survival and growth of planted jack pine (Pinus banksiana), black spruce (Picea mariana) and white spruce (Picea glauca) seedlings. In each stand, three fire severity classes (scorched, lightly burned, and severely burned) were identified based on the degree of forest floor consumption. Fire severity was not a significant factor on mortality. No mortality difference was found among species, except for year 5 when jack pine had significantly higher mortality than both black spruce and white spruce. Jack pine and black spruce had their highest mortality in year 4, while white spruce had its highest mortality in year 1. Under natural competition, seedling growth increased with increasing fire severity. When competition was removed, fire severity did not affect seedling growth. Regardless of fire severity and competition, jack pine had better diameter and height growth than black spruce, which, in turn, grew slightly taller than white spruce. Planted seedlings faced less intense vegetation competition on severely burned plots compared to scorched or lightly burned plots. Regardless of fire severity and species, competition increased with time since planting. Our study results indicate that planting immediately after a wildfire is a viable option to establish conifer components on burned boreal mixedwood stands. Key words: fire severity, plantation, regeneration, Pinus banksiana, Picea mariana, Picea glauca

Fire and vegetation type effects on soil hydrophobicity and infiltration in the sagebrush-steppe: II. Hyperspectral analysis

Hyperspectral remote sensing methods were developed to identify and differentiate post-fire characteristics in burned sagebrush-steppe. This shrub-steppe environment is typical of the Intermountain West, where wildfire intervals are frequent. After a 78,000ha wildfire in 2005 in southern Idaho, soil water repellency and fire severity were evaluated with field and airborne spectroscopy measurements. A hyperspectral analysis correctly identified bare ground, low and high fire severity grass areas and low fire severity shrub areas, with accuracies between 74 and 92%. The differentiation of moderate and high fire severity areas was ambiguous, resulting in accuracies between 39 and 54%. The hyperspectral analysis of soil water repellency resulted in a representative map of its distribution with an accuracy of 65%. The analysis techniques conducted in this project signify spectroscopy to be beneficial for differentiating soil characteristics and fire severity classes in burned shrub-steppe areas, where the mostly bare, spectrally homogenous soils exhibit subtle but significant changes in reflectance. The spatial representation of post-fire soil and vegetation conditions may provide a better understanding of post-fire vegetation and surficial processes (water and wind erosion) in shrub-steppe.

Combining spectral mixture analysis and object-based classification for fire severity mapping

This study shows an accurate and fast methodology in order to evaluate fire severity classes of large forest fires. A single Landsat Enhanced Thematic Mapper multispectral image was utilized in this study with the aim of mapping fire severity classes (high, moderate and low) using a combined-approach based in an spectral mixing model and object-based image analysis. A large wildfire in the Northwest of Spain is used to test the model. Fraction images obtained by Landsat unmixing were used as input data in the object-based image analysis. A multilevel segmentation and a classification were carried out by using membership functions. This method was compared with other simplest ones in order to evaluate the suitability to distinguish between the three fire severity classes above mentioned. McNemar’s test was used to evaluate the statistical significance of the difference between approaches tested in this study. The combined approach achieved the highest accuracy reaching 97.32% and kappa index of agreement of 95.96% and improving accuracy of individual classes.

Estimation of fire severity using pre- and post-fire LiDAR data in sagebrush steppe rangelands

Reflectance-based indices derived from remote-sensing data have been widely used for detecting fire severity in forested areas. Rangeland ecosystems, such as sparsely vegetated shrub-steppe, have unique spectral reflectance differences before and after fire events that may not make reflectance-based indices appropriate for fire severity estimation. As an alternative, average vegetation height change ( dh ) derived from pre- and post-fire Light Detection and Ranging (LiDAR) data were used in this study for fire severity estimation. Theoretical deductions were conducted to demonstrate that LiDAR-derived dh is related to biomass combustion and thus can be used for fire severity estimation in rangeland areas. The Jeffreys–Matusita (JM) distance was calculated to evaluate the separability for each pair of fire severity classes, with an average JM distance of 1.14. Thresholds for classifying the level of fire severity were determined according to the mean and standard deviation of each class. A fire-severity classification map with 84% overall accuracy was obtained from the LiDAR dh method. Importantly, this method was sensitive to the difference between the moderate and high fire-severity classes.

Interactions Among Wildland Fires in a Long-Established Sierra Nevada Natural Fire Area

We investigate interactions between successive naturally occurring fires, and assess to what extent the environments in which fires burn influence these interactions. Using mapped fire perimeters and satellite-based estimates of post-fire effects (referred to hereafter as fire severity) for 19 fires burning relatively freely over a 31-year period, we demonstrate that fire as a landscape process can exhibit self-limiting characteristics in an upper elevation Sierra Nevada mixed conifer forest. We use the term ‘self-limiting’ to refer to recurring fire as a process over time (that is, fire regime) consuming fuel and ultimately constraining the spatial extent and lessening fire-induced effects of subsequent fires. When the amount of time between successive adjacent fires is under 9 years, and when fire weather is not extreme (burning index <34.9), the probability of the latter fire burning into the previous fire area is extremely low. Analysis of fire severity data by 10-year periods revealed a fair degree of stability in the proportion of area burned among fire severity classes (unchanged, low, moderate, high). This is in contrast to a recent study demonstrating increasing high-severity burning throughout the Sierra Nevada from 1984 to 2006, which suggests freely burning fires over time in upper elevation Sierra Nevada mixed conifer forests can regulate fire-induced effects across the landscape. This information can help managers better anticipate short- and long-term effects of allowing naturally ignited fires to burn, and ultimately, improve their ability to implement Wildland Fire Use programs in similar forest types.