High Burn Severity Research Articles

Post-Fire Regeneration and Diversity Response to Burn Severity in Pinus halepensis Mill. Forests

In recent decades, fire regimes have been modified by various factors such as changes in land use, global change or forest management policies. The vulnerability of Mediterranean terrestrial ecosystems is increasing due to more severe and frequent droughts. This study aimed to determine the plant response of ecosystems during the short-term post-fire period by relating alpha diversity, floristic richness and tree recruitment dynamics to burn severity 5 years after a wildfire. Our results conclude that in the short term, Pinus halepensis Mill. stands in southeastern Spain quickly recovered alpha diversity values, mainly in areas burned with low severity. We observed that moderate and high severities affected the ecosystem more significantly, showing higher values for the Shannon Index but lower for the Simpson index. Pine recruitment was higher in burned areas, and we found the highest number of Aleppo pine seedlings under a moderate burn severity. Post-fire regeneration functional groups (obligate seeders and resprouters) were promoted under moderate and high burn severity, increasing their abundance. Annual species (mainly herbs) colonized burned areas, persisting with higher presence under moderate burn severity. Restoration tools should be focused on reducing fire severity, mainly in areas at high risk of desertification, and promoting resistance, vulnerability and resilience of these ecosystems.

Long-term avian response to fire severity, repeated burning, and mechanical fuel reduction in upland hardwood forest

Forest restoration, fuel reduction, and wildlife conservation management requires understanding if, and how repeated prescribed fire, fire severity, or mechanical methods can promote goals. We examined breeding bird response to repeated fuel reduction treatments by mechanical understory reduction (twice; Mechanical-only), prescribed burning (four times; Burn-only), or mechanical understory reduction plus burning (then three subsequent burns; Mechanical + Burn). Initial burns were hotter in Mechanical + Burn than Burn-only resulting in heavy tree mortality, canopy openness, thick shrub density, and abundant snags lasting several years. Relative density and species richness of birds increased in Mechanical + Burn within three breeding seasons of high-severity burns, and remained greater throughout subsequent burns. Increases were due to an influx of species associated with young forest conditions, with little change in most mature forest species. Repeated burning in Mechanical + Burn likely impeded forest maturation, allowing many scrub-shrub bird species to persist. Species richness in Burn-only did not differ from any treatment, but modest increases over time were apparent as structural heterogeneity increased with delayed tree mortality. Cavity-nester density was highest in Mechanical + Burn, but remained high even as snags fell to pretreatment levels. Ground-nester density was lower in Mechanical + Burn than Control and Mechanical-only, but ground-nesting species responded differently. Open woodlands were not created by any treatment due to persistent re-sprouting of top-killed trees and shrubs. We note that breeding birds appear to respond similarly to high-severity burns and silvicultural treatments with heavy canopy reduction, offering possible alternatives in managing upland hardwood forests for diverse breeding bird communities.

Composition and Structure of Forest Fire Refugia: What Are the Ecosystem Legacies across Burned Landscapes?

Locations within forest fires that remain unburned or burn at low severity—known as fire refugia—are important components of contemporary burn mosaics, but their composition and structure at regional scales are poorly understood. Focusing on recent, large wildfires across the US Pacific Northwest (Oregon and Washington), our research objectives are to (1) classify fire refugia and burn severity based on relativized spectral change in Landsat time series; (2) quantify the pre-fire composition and structure of mapped fire refugia; (3) in forested areas, assess the relative abundance of fire refugia and other burn severity classes across forest composition and structure types. We analyzed a random sample of 99 recent fires in forest-dominated landscapes from 2004 to 2015 that collectively encompassed 612,629 ha. Across the region, fire refugia extent was substantial but variable from year to year, with an annual mean of 38% of fire extent and range of 15–60%. Overall, 85% of total fire extent was forested, with the other 15% being non-forest. In comparison, 31% of fire refugia extent was non-forest prior to the most recent fire, highlighting that mapped refugia do not necessarily contain tree-based ecosystem legacies. The most prevalent non-forest cover types in refugia were vegetated: shrub (40%), herbaceous (33%), and crops (18%). In forested areas, the relative abundance of fire refugia varied widely among pre-fire forest types (20–70%) and structural conditions (23–55%). Consistent with fire regime theory, fire refugia and high burn severity areas were inversely proportional. Our findings underscore that researchers, managers, and other stakeholders should interpret burn severity maps through the lens of pre-fire land cover, especially given the increasing importance of fire and fire refugia under global change.

Measuring short-term post-fire forest recovery across a burn severity gradient in a mixed pine-oak forest using multi-sensor remote sensing techniques

Understanding post-fire forest recovery is pivotal to the study of forest dynamics and global carbon cycle. Field-based studies indicated a convex response of forest recovery rate to burn severity at the individual tree level, related with fire-induced tree mortality; however, these findings were constrained in spatial/temporal extents, while not detectable by traditional optical remote sensing studies, largely attributing to the contaminated effect from understory recovery. Here, we examined whether the combined use of multi-sensor remote sensing techniques (i.e., 1 m simultaneous airborne imaging spectroscopy and LiDAR and 2 m satellite multi-spectral imagery) to separate canopy recovery from understory recovery would enable to quantify post-fire forest recovery rate spanning a large gradient in burn severity over large-scales. Our study was conducted in a mixed pine-oak forest in Long Island, NY, three years after a top-killing fire. Our studies remotely detected an initial increase and then decline of forest recovery rate to burn severity across the burned area, with a maximum canopy area-based recovery rate of 10% per year at moderate forest burn severity class. More intriguingly, such remotely detected convex relationships also held at species level, with pine trees being more resilient to high burn severity and having a higher maximum recovery rate (12% per year) than oak trees (4% per year). These results are one of the first quantitative evidences showing the effects of fire adaptive strategies on post-fire forest recovery, derived from relatively large spatial-temporal scales. Our study thus provides the methodological advance to link multi-sensor remote sensing techniques to monitor forest dynamics in a spatially explicit manner over large-scales, with important implications for fire-related forest management and constraining/benchmarking fire effect schemes in ecological process models.

Fire severity drives variation in post-fire recruitment and residual seed bank size of Acacia species

Very high-severity fires are a component of many fire-prone ecosystems, yet are often viewed as detrimental to vegetation. However, species in such systems are likely to have adapted to persist under a fire regime that includes high-severity fires. We examined how fire severity affects post-fire recruitment and residual seed banks of Acacia species and whether severity may affect plant responses to fire intervals. Nine sites of either high or low burn severity were identified after a large-scale mixed-severity fire in Warrumbungle National Park, south-eastern Australia. Transects were used to sample above-ground woody plant density. Seed bank size was surveyed by soil extraction from two depths and manual searching for seeds. Residual soil seed bank and recruitment were compared across the two burn severities. Acacia seedling density was higher in areas burnt at high severity, indicating that increased severity triggers increased germination from the seed bank. Size of residual seed bank was smaller after high-severity fire, but varied between species, with few Acacia cheelii seeds remaining despite high above-ground abundance. In contrast, A. penninervis retained a small residual seed bank. There was little evidence of negative effects on populations of Acacia species after high-severity burns. However, we found that high fire severity may impact on the ability of a species to persist in response to a subsequent short fire interval. Fire management for maintaining biodiversity needs to consider other key aspects of the fire regime, including severity and season, rather than focusing solely on fire frequency.

Spatial and temporal evapotranspiration trends after wildfire in semi-arid landscapes

In recent years climate change and other anthropogenic factors have contributed to increased wildfire frequency and size in western United States forests. This research focuses on the evaluation of spatial and temporal changes in evapotranspiration (ET) following the 2011 Las Conchas Fire in New Mexico (USA) using the Operational Simplified Surface Energy Balance Model (SSEBop ET). Evapotranspiration is coupled with soil burn severity and analyzed for 16 watersheds for water years 2001–2014. An average annual decrease of 120 mm of ET is observed within the regions affected by the Las Conchas Fire, and conifers were converted to grassland a year after the fire. On average, the post-fire annual ET in high, moderate, and low burn severity is lower than pre-fire ET by approximately 103–352 mm, 97–304 mm, and 91–268 mm, respectively. The ratio of post-fire evapotranspiration to precipitation (ET/P) is statistically different from pre-fire conditions (α = 0.05) in nine of the watersheds. The largest decrease in ET is approximately 13–57 mm per month and is most prominent during the summer (April to September). The observed decrease in ET contributes to our understanding of changes in water yield following wildfires, which is of interest for accurately modeling and predicting hydrologic processes in semi-arid landscapes.

Simulating Surface and Subsurface Water Balance Changes Due to Burn Severity

Core Ideas Burn severity data informed a hydrologic model to assess water balance changes. Loss of vegetation and evapotranspiration exceeded impact of increased runoff. High burn severity may cause drier site conditions due to increased runoff. Change in evapotranspiration acts at long timescales while runoff is event based. Forest fires have a significant impact on hydrology, such as reduced infiltration rates leading to increased flooding. However, post‐fire water balance changes and the competing hydrologic response of increased runoff and evapotranspiration as a function of burn severity are not well understood. Comparing pre‐ and post‐fire water balance changes is challenging because measurements of fire‐disturbed landscapes with the previously undisturbed character are impractical due to non‐repetitive observational conditions. We used a physically based modeling experiment to incorporate burn severity data from the Las Conchas fire to approximate model parameterization to evaluate continuous water balance progression for pre‐ and post‐fire simulations using the same forcing conditions. Fire disturbance decreased evapotranspiration and increased overland flow response to precipitation events. The reduction of evapotranspiration often dominated the new water balance compared with the increase in overland flow, resulting in higher soil moisture. However, this modeling experiment also identified a tipping point where increased overland flow from high burn severity sites eclipses the effect of reduced evapotranspiration on the water balance, causing comparatively drier post‐fire soils. In particular, high burn severity sites approach a threshold that results in larger changes to overland flow than changes in evapotranspiration, potentially moving the site to an overland flow dominated regime. The shifts in water balance components have implications for how site conditions will change under a range of burn severity scenarios.

Did enhanced afforestation cause high severity peat burn in the Fort McMurray Horse River wildfire?

Climate change mediated drying of boreal peatlands is expected to enhance peatland afforestation and wildfire vulnerability. The water table depth–afforestation feedback represents a positive feedback that can enhance peat drying and consolidation and thereby increase peat burn severity; exacerbating the challenges and costs of wildfire suppression efforts and potentially shifting the peatland to a persistent source of atmospheric carbon. To address this wildfire management challenge, we examined burn severity across a gradient of drying in a black spruce dominated peatland that was partially drained in 1975−1980 and burned in the 2016 Fort McMurray Horse River wildfire. We found that post-drainage black spruce annual ring width increased substantially with intense drainage. Average (±SD) basal diameter was 2.6 ± 1.2 cm, 3.2 ± 2.0 cm and 7.9 ± 4.7 cm in undrained (UD), moderately drained (MD) and heavily drained (HD) treatments, respectively. Depth of burn was significantly different between treatments (p < 0.001) and averaged (±SD) 2.5 ± 3.5 cm, 6.4 ± 5.0 cm and 36.9 ± 29.6 cm for the UD, MD and HD treatments, respectively. The high burn severity in the HD treatment included 38% of the treatment that experienced combustion of the entire peat profile, and we estimate that overall 51% of the HD pre-burn peat carbon stock was lost. We argue that the HD treatment surpassed an ecohydrological tipping point to high severity peat burn that may be identified using black spruce stand characteristics in boreal plains bogs. While further studies are needed, we believe that quantifying this threshold will aid in developing effective adaptive management techniques and protecting boreal peatland carbon stocks.

Greater Temperature and Precipitation Extremes Intensify Western U.S. Droughts, Wildfire Severity, and Sierra Nevada Tree Mortality

AbstractExtensive drought in the western United States (WUS) during the twenty-first century and associated wildfire and tree mortality incidence has highlighted the potential for greater area of severity within widespread droughts. To place recent WUS droughts into a historical context, the authors analyzed gridded daily climate (temperature, precipitation, and climatic water deficit) data to identify and characterize the spatiotemporal evolution of the largest WUS droughts of the last 100 years, with an emphasis on severe cores within drought extents. Cores of droughts during the last 15 years (2000–02 and 2012–14) covered a greater area than in earlier droughts, driven by greater temperature and precipitation extremes. Comparing fire extent and severity before, during, and after drought events using the monitoring trends in burn severity dataset (1984–2014), the authors found fire size and high-severity burn extent were greater during droughts than before or after. Similarly, recent Sierra Nevada forest mortality was greatest in cores immediately after the drought. Climate simulations anticipate greater extremes in temperature and precipitation in a warming world; droughts and related impacts of the last 15 years may presage the effects of these extremes.

Charcoal in Organic Horizon and Surface Mineral Soil in a Boreal Forest Fire Chronosequence of Western Quebec: Stocks, Depth Distribution, Chemical Properties and a Synthesis of Related Studies

Wildfires are a major driver of carbon stocks and ecosystem development in Canadian boreal forests, but there is little information on amounts and properties of the charcoal produced. Using data and samples available from a previous study, we determined amounts, depth distribution and chemical properties of visually-determined charcoal (> 2 mm) in a boreal chronosequence in the Abitibi region of Quebec, Canada. Sites ranged from 24 to 2355 years since fire (ysf) and originated from low- and high-severity soil burns (> 5 cm or < 5 cm organic horizon unburned, respectively). Two or three pits were sampled at 1-cm depth intervals from 20 jack pine (Pinus banksiana) sites (one low severity and 19 high severity) and 31 black spruce (Picea mariana) sites (12 low severity and 19 high severity). Site-level charcoal stocks ranged from 50 to 5527 kg ha-1 with high within-site variability and lower stocks for the oldest sites. Depth distributions typically peaked around the organic-mineral interface, but some low-severity sites also had charcoal layers within the organic horizon. Means from 30 samples were 569 mg g-1 total C, 4.1 mg g-1 total N and 140 C/N (molar), with total C and C/N showing a trend of decline with time since fire, and total N showing an increase. Solid-state 13C CPMAS NMR spectra of nine samples showed high variability among the younger samples, but a trend to higher aromaticity for the older ones. A literature survey focusing on boreal forests similarly showed highly variable stocks and chemical properties of charcoal in organic horizon and upper mineral soil, with reduction of variance and lower stocks after several hundred years. This initial variation was also consistent with reports of highly variable temperatures and duration of charring in wildfires. Adding reports available for char production, and considering that most studies of char stocks and production are limited to the organic horizon (forest floor), suggests that initial production of charred material from boreal wildfires might be around 5-10 tonnes ha-1.

Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems

Summary Arid ecosystems are often vulnerable to transformation to invasive‐dominated states following fire, but data on persistence of these states are sparse. The grass/fire cycle is a feedback process between invasive annual grasses and fire frequency that often leads to the formation of alternative vegetation states dominated by the invasive grasses. However, other components of fire regimes, such as burn severity, also have the potential to produce long‐term vegetation transformations. Our goal was to evaluate the influence of both fire frequency and burn severity on the transformation of woody‐dominated communities to communities dominated by invasive grasses in major elevation zones of the Mojave Desert of western North America. We used a chronosequence design to collect data on herbaceous and woody cover at 229 unburned reference plots and 578 plots that burned between 1972 and 2010. We stratified the plots by elevation zone (low, mid, high), fire frequency (1–3 times) and years post‐fire (YPF; 1–5, 6–10, 11–20 and 21–40 YPF). Burn severity for each plot was estimated by the difference normalized burn ratio. We identified two broad post‐fire successional pathways. One was an outcome of fire frequency, resulting in a strong potential transformation via the grass/fire cycle. The second pathway was driven by burn severity, the critical aspect being that long‐term transformation of a community could occur from just one fire in areas that burned at high or sometimes moderate severity. Dominance by invasive grasses was most likely to occur in low‐and high‐elevation communities; cover of native herbaceous species was often greater than that of invasive grasses in the mid‐elevation zone. Synthesis. Invasive grasses can dominate a site that burned only one time in many decades at high severity, or a site that burned at low severity but multiple times in the same time period. However, high burn severity may predispose areas to more frequent fire because they have relatively high cover of invasive annual grass, suggesting burn severity and fire frequency have both independent and synergistic effects. Resilience in vegetation structure following fire in many arid communities may be limited to a narrow window of low burn severity in areas that have not burned in many decades.

Long-term impact of wildfire on soils exposed to different fire severities. A case study in Cadiretes Massif (NE Iberian Peninsula)

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 (18years) 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 (18years 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.

Spatial patterns of ponderosa pine regeneration in high-severity burn patches

Abstract 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.

Severe wildfire hinders renewal of soil P pools by thermal mineralization of organic P in forest soil: Analysis by sequential extraction and 31P NMR spectroscopy

Forest productivity is limited by soil P availability in several forest ecosystems worldwide. Most of the soil available P is probably produced by the mineralization of organic forms of P when these forms dominate in the soil. Severe wildfires lead to loss of soil organic compounds and therefore represent a strong risk of loss of soil P. The objective of the present study was to examine how the temperature reaching during burning affects the P fractions in organic horizons and soil. For this purpose, we conducted experimental burns of intact soil monoliths with their organic horizons. We then used Hedley chemical sequential fractionation and 31P MNR spectroscopy to determine the effects of temperature during burning on soil P fractions. In the unburned organic horizons, the organic P represented 70% of the total P and it was completely mineralized when the temperatures reached above 500°C. Similarly, in the unburned mineral soil, organic P forms represented 76% of the total P and the organic P was reduced by around 50% in the moderate soil burn severity (SBS) levels. In the highest SBS, the concentration of inorganic P (Pi) with a fast turnover rate (representing available P) was three times higher and the concentration of Pi with a slow turnover rate (representing the sum of inorganic fractions bound to Al and Ca) was eight times higher than in the unburned soil. By contrast, the organic P fractions decreased with the temperature reached during the fire, with 200°C considered a threshold for the total thermal mineralization of organic P, mainly the labile organic fraction. These findings suggest that high temperatures lead to release of Pi, most of which is precipitated by P forms such as Pi with a slow turnover rate. It appears that the high burn severity associated with temperatures higher than 200°C strongly disrupts soil P dynamics, increasing the occlusion capacity and decreasing the bioavailability.

Fire-climate history and landscape patterns of high burn severity areas on the California southern and central coast

There is mounting evidence that fire size and severity have been growing on the central and southern California coastal landscape over the past several decades. Landsat satellite data was analyzed for the 20 largest fires on the Central California coast since 1984 to determine the relationships between climate/weather conditions at the time of ignition and the size of high burn severity (HBS) areas. The study also examined the relationship between area burned and landscape patterns of HBS coverage, including patch size, edge complexity, perimeter-to-area ratio, and aggregation metrics. Results showed that climate conditions at the time of ignitions have been significant controllers of the total area of HBS and the complexity of HBS patches on the fire landscape. As maximum air temperatures for the month of ignition approached 40o C, the percentage of HBS to total area burned frequently exceeded 20%. The percentage of HBS to total area burned also exceed 20% when the precipitation total recorded during the previous 12 months was less than 25% of the annual average precipitation. Landscape analysis results showed that, as the total area burned in fires on the Central California coast grows, the edge lengths and areas of HBS patches also grows at a rapid rate. At the same time, the perimeter-to-area ratio of HBS patches decreases gradually and the HBS patches become more aggregated as total burned area grows.

Effect of Salvage Logging and Check Dams on Simulated Hydrological Connectivity in a Burned Area

AbstractThis study assessed the effect of a wildfire and different post‐fire practices (salvage logging, skid trails and check dams) and vegetation recovery (eight scenarios) on the hydrological connectivity (HC) in 11 sub‐catchments (SubCs; 330 ha) affected by a wildfire (213 ha) in 2012 in Spain. According to the Landsat 8 Operational Land Imager/Thermal Infrared Sensor images, moderate, high and extreme burn severity affected 42·1% of the area. HC was calculated with an updated version of the Borselli index. Within the burned area (BA), HC increased in all SubCs after the wildfire (PostF‐1), the salvage logging and the new skid trails (PostF‐2), and the development of new gullies (PostF‐3). Check dams reduced connectivity but did not prevent the general trend. Afterwards, the incipient (PostF‐4 and PostF‐5) and future vegetation recovery made slightly decrease HC. In the three forestry SubCs with check dams and large BA (67% of the study area), connectivity markedly increased (11·4%, 18·2% and 22·9%) during the three first post‐fire scenarios. In the three SubCs with urban areas and small BA (5%), HC decreased a little because the linear elements connected the hillslopes between them. In the three SubCs with urban areas and large BA (12%), HC increased less than in the forestry SubCs (3·0%, 8·2% and 9·1%). In the two forestry SubCs without check dams and small BA (16%), the increment of connectivity was low (2·5%, 4·6% and 6·3%). Monitoring of check‐dam siltation and of the actual vegetation regrowth is necessary to minimize the off‐site consequences of high HC. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Differential impacts of wildfire on the population dynamics of an old-forest species.

Ecological disturbances shape and maintain natural communities, but climate change and human land use can alter disturbance regimes and affect population persistence and vital rates in unpredictable ways. Species inhabiting landscapes shaped by wildfire have evolved mechanisms allowing them to persist under this dynamic disturbance type, which creates habitats of varying quality for these species. We utilized data from a 26-yr demographic study of northern spotted owls to analyze the influence of wildfire on apparent survival and recruitment rates. Wildfires occurred across different years and affected different spotted owl territories, which allowed us to implement a retrospective Before-After-Control-Impact (BACI) analysis and model the potential effect of wildfire extent and severity. Our results indicated that mixed-severity fires that burned at predominantly low-severity had little effect on survival and recruitment while fires characterized by more medium to high burn severities negatively affected spotted owl survival, with varying effects on recruitment. Reduced survival and increased recruitment rates on some territories affected by medium to high severity fires suggested that post-fire habitat quality was reduced resulting in territories that were marginally capable of supporting owls. We hypothesize these territories may have represented "sinks" that were supported by nearby "source" territories in a spatially heterogeneous landscape created by the mixed-severity fire regime of the region.

Impacts of wildfires on interannual trends in land surface phenology: an investigation of the Hayman Fire

Land surface phenology (LSP) derived from satellite data has been widely associated with recent global climate change. However, LSP is frequently influenced by land disturbances, which significantly limits our understanding of the phenological trends driven by climate change. Because wildfire is one of the most significant disturbance agents, we investigated the influences of wildfire on the start of growing season (SOS) and the interannual trends of SOS in the Hayman Fire area that occurred in 2002 in Colorado using time series of daily MODIS data (2001–2014). Results show that the Hayman Fire advanced the area-integrated SOS by 15.2 d and converted SOS from a delaying trend of 3.9 d/decade to an advancing trend of −1.9 d/decade during 2001–2014. The fire impacts on SOS increased from low burn severity to high burn severity. Moreover, the rate of increase of annual maximum and minimum EVI2 from 2003–2014 reflects that vegetation greenness could recover to pre-fire status in 2022 and 2053, respectively, which suggests that the fire impacts on the satellite-derived SOS variability and the interannual trends should continue in the next few decades.

Does the presence of large down wood at the time of a forest fire impact soil recovery?

Fire may remove or create dead wood aboveground, but it is less clear how high severity burning of soils affects belowground microbial communities and soil processes, and for how long. In this study, we investigated soil fungal and bacterial communities and biogeochemical responses of severely burned “red” soil and less severely burned “black” soil from a burned forest on the eastern slope of the Cascade Range in Oregon. Specifically, we examined the effects of burn severity on soil nutrients and microbial communities for 1–4years after wildfire. Soil nutrients were significantly reduced in red soils. Soil fungi and bacteria, assessed with molecular methods, steadily colonized both burn severities and soil biodiversity increased throughout the study showing that microbial communities seem to have the capacity to quickly adjust to extreme disturbances. Although richness did not vary by soil type, the fungal and bacterial community compositions varied with burn severity. This difference was greatest in the early time points following the fire and decreased with time. However, nutrient-limited conditions of red soils were detected for four years after the wildfire and raise concern about soil productivity at these sites.

Multidecadal trends in area burned with high severity in the Selway-Bitterroot Wilderness Area 1880–2012

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 346265ha 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.