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Rising global fire activity is increasing the prevalence of repeated short‐interval burning (reburning) in forests worldwide. In forests that historically experienced frequent‐fire regimes, high‐severity fire exacerbates the severity of subsequent fires by increasing prevalence of shrubs and/or by creating drier understory conditions. Low‐ to moderate‐severity fire, in contrast, can moderate future fire behavior by reducing fuel loads. The extent to which previous fires moderate future fire severity will powerfully affect fire‐prone forest ecosystem trajectories over the next century. Further, knowing where and when a wildfire may act as a landscape‐scale fuel treatment can help direct pre‐ and post‐fire management efforts. We leverage satellite imagery and fire progression mapping to model reburn dynamics within forests that initially burned at low/moderate severity in 726 unique fire pair events over a 36‐year period across four large fire‐prone Western US ecoregions. We ask (1) how strong are the moderating effects of low‐ to moderate‐severity fire on future fire severity, (2) how long do moderating effects last, and (3) how does the time between fires (a proxy for fuel accumulation) interact with initial fire severity, day‐of‐burning weather conditions, and climate to influence reburn severity. Short‐interval reburns primarily occurred in dry‐ and moist‐mixed conifer forests with historically frequent‐fire regimes. Previous fire moderated reburn severity in all ecoregions with the strongest effects occurring in the California Coast and Western Mountains and the average duration of moderating effects ranging from 13 years in the Western Mountains to >36 years in the California Coast. The strength and duration of moderating effects depended on climate and initial fire severity in some regions, reflecting differences in post‐fire fuel accumulation. In the California Coast, moderating effects lasted longer in cooler and wetter forests. In the Western Mountains, moderating effects were stronger and longer lasting in forests that initially burned at higher severity. Moderating effects were largely robust to fire weather, suggesting that previous fire can mediate future fire severity even under extreme conditions. Our findings demonstrate that low‐ to moderate‐severity fire buffers future fire severity in historically frequent‐fire forests, underlining the importance of wildfire as a restoration tool for adapting to global change. [ABSTRACT FROM AUTHOR]

Indigenous communities throughout California, USA, are increasingly advocating for and practicing cultural fire stewardship, leading to a host of social, cultural, and ecological benefits. Simultaneously, state agencies are recognizing the importance of controlled burning and cultural fire as a means of reducing the risk of severe wildfire while benefiting fire‐adapted ecosystems. However, much of the current research on the impacts of controlled burning ignores the cultural importance of these ecosystems, and risks further marginalizing Indigenous knowledge systems. Our work adds a critical Indigenous perspective to the study of controlled burning in California's unique coastal grasslands, one of the most biodiverse and endangered ecosystems in the country. In this study, we partnered with the Amah Mutsun Tribal Band to investigate how the abundance and occurrence of shrubs, cultural plants, and invasive plants differed among three adjacent coastal grasslands with varying fire histories. These three sites are emblematic of the state's diverging approaches to grassland management: fire suppression, fire suppression followed by wildfire, and an exceedingly rare example of a grassland that has been repeatedly burned approximately every 2 years for more than 30 years. We found that Danthonia californica was significantly more abundant on the burned sites, whereas all included shrub species (Baccharis pilularis, Frangula californica, and Rubus ursinus) were significantly more abundant on the site with no recorded fire, results that have important implications for future cultural revitalization efforts and the loss of coastal grasslands to shrub encroachment. In addition to conducting a culturally relevant vegetation survey, we used Sentinel‐2 satellite imagery to compare the relative severities of the two most recent fire events within the study area. Critically, we used interviews with Amah Mutsun tribal members to contextualize the results of our vegetation survey and remote sensing analysis, and to investigate how cultural burning contrasts from typical Western fire management approaches in this region. Our study is a novel example of how interviews, field data, and satellite imagery can be combined to gain a deeper ecological and cultural understanding of fire in California's endangered coastal grasslands. [ABSTRACT FROM AUTHOR]

Wildfires may facilitate climate tracking of forest species moving upslope or north in latitude. For subalpine tree species, for which higher elevation habitat is limited, accelerated replacement by lower elevation montane tree species following fire may hasten extinction risk. We used a dataset of postfire tree regeneration spanning a broad geographic range to ask whether the fire facilitated upslope movement of montane tree species at the montane‐to‐subalpine ecotone. We sampled tree seedling occurrence in 248 plots across a fire severity gradient (unburned to >90% basal area mortality) and spanning ~500 km of latitude in Mediterranean‐type subalpine forest in California, USA. We used logistic regression to quantify differences in postfire regeneration between resident subalpine species and the seedling‐only range (interpreted as climate‐induced range extension) of montane species. We tested our assumption of increasing climatic suitability for montane species in subalpine forest using the predicted difference in habitat suitability at study plots between 1990 and 2030. We found that postfire regeneration of resident subalpine species was uncorrelated or weakly positively correlated with fire severity. Regeneration of montane species, however, was roughly four times greater in unburned relative to burned subalpine forest. Although our overall results contrast with theoretical predictions of disturbance‐facilitated range shifts, we found opposing postfire regeneration responses for montane species with distinct regeneration niches. Recruitment of shade‐tolerant red fir declined with fire severity and recruitment of shade‐intolerant Jeffrey pine increased with fire severity. Predicted climatic suitability increased by 5% for red fir and 34% for Jeffrey pine. Differing postfire responses in newly climatically available habitats indicate that wildfire disturbance may only facilitate range extensions for species whose preferred regeneration conditions align with increased light and/or other postfire landscape characteristics. [ABSTRACT FROM AUTHOR]

Spatial and temporal variation in fire characteristics—termed pyrodiversity—are increasingly recognized as important factors that structure wildlife communities in fire‐prone ecosystems, yet there have been few attempts to incorporate pyrodiversity or post‐fire habitat dynamics into predictive models of animal distributions and abundance to support post‐fire management. We use the black‐backed woodpecker—a species associated with burned forests—as a case study to demonstrate a pathway for incorporating pyrodiversity into wildlife habitat assessments for adaptive management. Employing monitoring data (2009–2019) from post‐fire forests in California, we developed three competing occupancy models describing different hypotheses for habitat associations: (1) a static model representing an existing management tool, (2) a temporal model accounting for years since fire, and (3) a temporal–landscape model which additionally incorporates emerging evidence from field studies about the influence of pyrodiversity. Evaluating predictive ability, we found superior support for the temporal–landscape model, which showed a positive relationship between occupancy and pyrodiversity and interactions between habitat associations and years since fire. We incorporated the new temporal–landscape model into an RShiny application to make this decision‐support tool accessible to decision‐makers. [ABSTRACT FROM AUTHOR]

The projected rise in fire activity due to climate change challenges forest conservation efforts worldwide. Current non-intervention approaches, which rely on natural processes for ecosystem conservation, often overlook palaeoecological data depicting long-term, local interactions between fire regime components, forest structure and composition, soil, aquatic environment and anthropogenic disturbance. To explore whether palaeoecological information supports non-intervention strategies in the Picea abies – Fagus sylvatica – Abies alba closed temperate mountain forest under future fire risks, we conducted a multi-proxy, retrospective analysis (charcoal morphology, pollen, plant macro-remains, sedimentology, palaeoclimate models) on a Holocene lacustrine archive located in the Bavarian Forest National Park, Germany. Results show that climate shifts directly induced vegetation reorganizations and fire regime changes around 11.1, 9.3 and 7–6 ka BP, and gradually allowed the expansion of closed mixed forests dominated by the late successional Picea abies – Fagus sylvatica - Abies alba under a remarkably stable, low-fire environment. We emphasize the possible role of shade-related traits of these species as key bottom-up drivers of biomass burning over the past 6000 years likely due to their effects on microclimate, offsetting the species-specific fire traits. Although these forests tolerate low-severity surface fire, more subtle impacts were identified at the level of soil cover and lacustrine environment. First, our data demonstrate that lake browning processes developed naturally since the Early Holocene with the progression of chemical weathering and podzol formation, but an ecological threshold due to browning intensification was crossed ca. 6000 years ago, under maximum forest density and in the absence of fire disturbance. Second, fire likely reduced lake water browning and soil podzolisation processes by mineral erosion and the decrease in litter and soil organic matter due to direct burning or indirect aeration. Soil and aquatic ecosystem components appeared highly interconnected and responded even to low disturbance severities. Consequently, these components may react more sensitively to the predicted increase in fire frequency and severity, with yet unknown ripple effects on the forest ecosystem resilience. Given the critical role of the Picea abies - Fagus sylvatica - Abies alba closed-canopy forests in shaping the microclimate and catchment-lake interactions, our study suggests that non-intervention strategies are suitable for preserving ecosystem stability in these types of forests. By promoting natural recovery of shade-tolerant tree species and minimizing direct anthropogenic impacts, this approach would protect the soil, regulate erosion and delivery of soil organic substances, and potentially mitigate the effects of climate change on fire hazard and on individual forest tree species. • Shade-related traits of late successional trees reduced local fire frequency and severity. • Fire regime and forest dynamics controlled soil erosion and lake browning. • Picea – Fagus – Abies closed temperate mountain forests tolerate low severity, surface fire. • Soil and lake environments are interconnected and may react sensitively to increased fire. • Promoting natural forest recovery could buffer the climate-related increase in fire hazard. [ABSTRACT FROM AUTHOR]

The area burned in Spain exceeded historical records in 2022, when exceptionally warm conditions influenced wildfire events. The predicted intensification of wildfire regimes includes an increase in frequency, severity, and size. Therefore, a study of the wildfires that occurred in 2022 is necessary to understand their behaviour and possible environmental impacts. The objective of this study is to analyse the applicability of using spectral indices and Geographic Information System (GIS) approaches to map the spatial distribution and estimate potential soil losses using Sentinel-2 imagery and fire severity field data. Soil losses were estimated using an empirical model based on soil burn severity data collected in the field after wildfire. The relationship between the Normalized Difference Infrared Index (NDII), Difference Normalized Wildfire Ash Index (dNWAI), and the Blue Normalized Difference Vegetation Index (BNDVI) with the estimated soil losses was then evaluated. In addition, the influence of different time scales of the satellite images was analysed. The first period considered (Date I) ranges from 8 to 20 days after the beginning of the wildfire, which coincides with the field data collection. The second period considered (Date II) ranges from 28 to 35 days after the start of the wildfire. The results obtained showed a significant dependence relationship between the BNDVI index (using satellite images of Date I) and the estimated soil losses (R2 = 0.756), while the results of the NDII (R2 = 0.31) and dNWAI (R2 = 0.061), showed no spatial relationship with the estimated soil losses. Three of the largest wildfires in 2022 in Spain were analysed, and the results showed strong correlations of BNDVI index for Folgoso do Courel (R2 = 0.808), for Carballeda de Valedorras (R2 = 0.906), and for Sierra de la Culebra (R2 = 0.939). In addition, these results allowed the mapping and quantification of potential soil losses in areas where fire severity was high, totalling ∼2,50,000 Mg ha−1 in Folgoso do Courel, ∼3,70,000 Mg ha−1 in Carballeda de Valdeorras, and ∼4,70,000 Mg ha−1 in Sierra de la Culebra. Moreover, BNDVI values for estimating soil loss vary by vegetation type, and there is a positive correlation between severity classes and the BNDVI index. This approach can inform post-fire land management decisions in future wildfires and could be applied to other regions. • The BNDVI index allows to map and estimate potential soil losses after wildfire. • Soil burn severity need to be evaluated separately from vegetation burn severity. • A positive correlation exists between soil burn severity and BDNVI index. • The BNDVI index varies according to vegetation type. [ABSTRACT FROM AUTHOR]

Wildfires are predicted to increase in frequency and severity with climate change but detailed understanding of their influence on forest wildlife is lacking for many species. Wildfires vary in their extent and severity among landscapes, limiting generalisations about impacts from a single wildfire. We investigated post-wildfire persistence in the threatened exudivorous yellow-bellied glider (Petaurus australis) in south-eastern Australia. The widespread occurrence of wildfires in the 'Black Summer' of 2019–20 enabled populations in three landscapes (90–160 km apart) to be studied. This species has a slow life history (one young per year and >1 year to mature) so post-fire recovery is predicted to be slow. We conducted repeat surveys over 3 years post-fire in each landscape at 25–29 sites that were occupied pre-wildfire. All survey sites were burnt in two landscapes but only 40 % were burnt in the third. We estimated declines in occupancy of 13 %, 40 % and 66 % in burnt forest. The factors driving the variation in decline appear to be a combination of fire severity and the abundance of very large (≥80 cm) hollow (i.e. cavity) -bearing trees that serve as den sites. The implications of this study are that the impacts of wildfires on populations of tree-hollow dependent species can be expected to vary in different landscapes as a consequence of fire severity, rainfall deficit and logging history. Our study suggests the importance of ensuring populations are conserved across a wide geographic gradient, and the value of very large hollow-bearing trees rather than simply the number of any hollow-bearing trees. • Knowledge of the response of wildlife to wildfires is a global deficiency. • The Australian Black Summer fires allowed unique landscape replication of wildfires. • We investigated post-fire persistence in an iconic arboreal mammal. • We estimated declines in occupancy in burnt forest landscapes of 13 %, 40 % and 66 %. • Very large hollow-bearing trees appear to influence survival through wildfire. [ABSTRACT FROM AUTHOR]

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Wildfires significantly impact biodiversity, with ecosystems exhibiting diverse short- and long-term responses. We investigated the effects of wildfire on bird communities in a Pinus yunnanensis forest, a dominant vegetation type widely distributed in southwest China's biodiversity hotspot. These forests are known to be flammable and exhibit fire-adapted traits. Using point count surveys, we compared breeding bird diversity in burned areas immediately and eight years post-fire. Our findings reveal that: (1) The effects of wildfire on bird diversity vary across spatial and temporal scales; (2) Pyrodiversity promotes bird diversity. Burned areas exhibited higher overall bird diversity (γ diversity) compared to unburned areas. However, species diversity within sites (α diversity) was lower in burned areas at both sampling periods; (3) Bird diversity in areas with the most severe burns was initially lower than all other areas but showed significant recovery eight years after the fire; and (4) The composition of bird communities across burn severities became more similar after eight years, suggesting a trend towards community convergence over time. These results highlight the varied effects of fire on bird communities in this fire-adapted ecosystem. We recommend implementing prescribed burning policies that create a mosaic landscape inclusive of different burn severities to promote bird biodiversity conservation and mitigate the risk of catastrophic wildfires. • The impact of wildfire on bird diversity depends on spatio-temporal scales. • Differences of α and β diversity among various fire severities weaken with time. • Frequent fires of various severity are beneficial for the conservation of birds in Pinus yunnanensis forests. [ABSTRACT FROM AUTHOR]

The formulation and planning of integrated fire management strategies must be strengthened by decision support systems about fire-induced ecological impacts and ecosystem recovery processes, particularly in the context of extreme wildfire events that challenge land management initiatives. Wildfire data collection and analysis through remote sensing earth observations is of utmost importance for this purpose. However, the needs of land managers are not always met because the exploitation of the full potential of remote sensing techniques requires a high level of technical expertise. In addition, data acquisition and storage, database management, networking, and computing requirements may present technical difficulties. Here, we present FIREMAP software, which leverages the potential of Google Earth Engine (GEE) cloud-based platform, an intuitive graphical user interface (GUI), and the European Forest Fire Information System (EFFIS) wildfire database for wildfire analyses through remote sensing techniques and data collections. FIREMAP software allows automatic computing of (i) machine learning-based burned area (BA) detection algorithms to facilitate the mapping of (historical) fire perimeters, (ii) fire severity spectral indices, and (iii) post-fire recovery trajectories through the inversion of physically-based radiative transfer models. We introduce (i) the FIREMAP platform architecture and the GUI, (ii) the implementation of well-established algorithms for wildfire science and management in GEE, (iii) the validation of the algorithm implementation in fifteen case-study wildfires across the western Mediterranean Basin, and (iv) the near-future and long-term planned expansion of FIREMAP features. • Fire management strategies must be strengthened by decision support systems. • Remote sensing (RS) data processing may involve technical difficulties for managers. • We developed an innovative RS-based software to estimate wildfire ecological impacts. • FIREMAP can auto-generate burned area, fire severity and vegetation recovery products. • FIREMAP meets accuracy standards for end-users in wildfire science and management. [ABSTRACT FROM AUTHOR]

Climate change is predicted to increase the frequency and severity of large-scale wildfires and threaten scores of wildlife species. However, the state of understanding of how medium-sized ground-dwelling mammals, of which many are threatened, respond to such wildfires remains limited. The Australian 'Black Summer' fires were unprecedented in their extent and severity, and burned large swathes of habitat for threatened species, providing an opportunity to address this information deficit. We used camera-trapping to investigate how populations of several small, threatened macropods and other medium-sized ground-dwelling mammals in five wildfire-affected subtropical study areas responded to the 'Black Summer' fires, two years on from the event. We examined whether occupancy was influenced by fire, habitat, or landscape variables to evaluate capacity to survive severe fire events and identify populations of conservation significance. Four species of small macropod (three threatened) were restricted to different subsets of the study areas but there was no evidence this was influenced by the wildfires. The red-legged pademelon showed a negative response to fire severity whereas occupancy of the other three was not influenced by fire. Two common species groups (bandicoots and brushtail possums), and the feral cat, were widespread and also showed no difference in occupancy in fire-affected areas. Vegetation cover positively influenced the occupancy of the northern long-nosed potoroo and the red-necked pademelon, and presumably offset any fire effect 2 years after the wildfires. Our study confirms that populations of threatened and non-threatened medium-sized mammals can recover following severe wildfires and suggests that conservation of most of the threatened macropods could be focused on threats other than wildfire in reserves where they appear to be most abundant. • Threatened macropods exhibited a robust recovery following a catastrophic wildfire event. • Most species' responses were consistent across both burnt and unburnt areas. • Fire-induced changes to vegetation structure benefit some threatened macropods. • Severe fire renders habitat unsuitable for red-legged pademelons for at least 3 years post-fire. [ABSTRACT FROM AUTHOR]

The primary objective of prescribed burning (PB) treatment is to promote increased ecosystem resistance to high fire severity and ecosystem adaptive resilience after unplanned wildfires under worsening climates. Yet, empirical evidence involving regional-scale assessments with enough spatial representativeness on how vegetation will respond to PB-wildfire interactions in Mediterranean shrublands is absent. This is particularly relevant to provide comprehensive insights on the effectiveness of PB policies and programs in southern European countries, where shrublands are the main PB target. Here, we investigated the PB effect on vegetation responses in the short-term (1–3 years) after subsequent wildfire encounters in Mediterranean shrublands at the regional scale across mainland Portugal. We leveraged geospatial cloud-computing platforms and remote sensing data (optical and synthetic aperture radar -SAR-) and techniques with physical basis to procure reliable proxies for vegetation fractional cover (FCOVER), vigor (normalized difference vegetation index; NDVI) and structural complexity (cross-polarization ratio of C-band SAR backscatter data; SAR-CR) at the landscape scale throughout the time series. The role of site productivity and topographic configuration variables as putative drivers of vegetation responses was also analyzed. We found that the mitigating effect of PB on wildfire severity translated into stronger vegetation responses in treated areas than in untreated counterparts after the first PB-wildfire encounter. Although FCOVER, NDVI and SAR-CR recovered gradually in both areas, the recovery rate was markedly higher in PB-treated areas 3-years after the PB-wildfire encounter than at earlier times in the time series. The effect of PB treatment was stronger for the FCOVER recovery response than for NDVI and SAR-CR. The effect of the PB treatment on FCOVER and NDVI responses was modulated by site environmental characteristics, such that their differences between PB-treated and untreated counterparts were maximal for both higher altitudes and warmer, drier locations in the landscape. • First regional-scale assessment of vegetation responses in PB-wildfire intersections. • PB mitigates fire severity in reburns and enhances short-time vegetation responses. • The strongest vegetation response was found 3-years after the PB-wildfire encounter. • PB effect was higher for vegetation cover than for vigor or structural complexity. • PB effect on vegetation responses was modulated by site environmental characteristics. [ABSTRACT FROM AUTHOR]

Increased understanding of how mechanical thinning, prescribed burning, and wildfire affect subsequent wildfire severity is urgently needed as people and forests face a growing wildfire crisis. In response, we reviewed scientific literature for the US West and completed a meta-analysis that answered three questions: (1) How much do treatments reduce wildfire severity within treated areas? (2) How do the effects vary with treatment type, treatment age, and forest type? (3) How does fire weather moderate the effects of treatments? We found overwhelming evidence that mechanical thinning with prescribed burning, mechanical thinning with pile burning, and prescribed burning only are effective at reducing subsequent wildfire severity, resulting in reductions in severity between 62% and 72% relative to untreated areas. In comparison, thinning only was less effective – underscoring the importance of treating surface fuels when mitigating wildfire severity is the management goal. The efficacy of these treatments did not vary among forest types assessed in this study and was high across a range of fire weather conditions. Prior wildfire had more complex impacts on subsequent wildfire severity, which varied with forest type and initial wildfire severity. Across treatment types, we found that effectiveness of treatments declined over time, with the mean reduction in wildfire severity decreasing more than twofold when wildfire occurred greater than 10 years after initial treatment. Our meta-analysis provides up-to-date information on the extent to which active forest management reduces wildfire severity and facilitates better outcomes for people and forests during future wildfire events. • Forest treatments that reduce surface fuels decrease subsequent wildfire severity. • Thinning with prescribed burning was the most effective and persistent treatment. • Treatment efficacy for reducing wildfire severity declined for older treatments. • Prior low or moderate severity wildfire can reduce subsequent wildfire severity. [ABSTRACT FROM AUTHOR]

Contemporary fire regimes in Californian forests are shifting, with fires becoming larger, more frequent, and increasingly severe. As landscapes transition back to active fire regimes, understanding how the physical environment and biological legacies of past disturbance interact with and determine forest development becomes an increasingly important management concern. We surveyed post-fire regeneration in a wilderness area of Lassen Volcanic National Park (LAVO) with a three-decade history of fires. We tallied conifer seedlings , and measured shrub and ground cover and mature trees in the field, and used geospatial data and water balance models to account for the possible effects of , terrain, live seed sources, vegetation characteristics, and immediate post-fire climate as measured by water balance on conifer regeneration. We used a Random Forest machine learning technique to model how landscape and local factors affect post-fire regeneration stocking and species regeneration occurrence. Post-fire conifer regeneration in LAVO was common: Median post-fire seedling density was close to desired stocking density, 73% of our plots had at least one conifer seedling, and only 16% of plots lacked tree regeneration or mature trees. Likelihood of stocking and individual species' occurrence was most strongly related to time since fire, distance to forest, elevation, and species of nearest seed source. Tree regeneration increased with time since fire, but this effect was more pronounced at high elevation suggesting an interaction between terrain and time since fire on regeneration. Stocking was most likely on cooler (northeastern) slopes and at lower (<1950 m) elevations, nearer (within 200 m) to live forest patches, and where shrub cover was present but low (<20%). Climatic conditions as represented by water balance for the first five years after a fire did not influence likelihood of stocking but it did influence species occurrence. Distance to conspecific trees was important for species' regeneration occurrence, and the landscape pattern of species occurrence was consistent with the elevational zonation of forest dominants in LAVO. Adequate tree regeneration of forests with an active fire regime in LAVO indicate that California montane forests are resilient to prescribed fire and managed wildfire and that expanded use of fire to reduce potential for severe fire promotes resilience in California forest landscapes. • Regeneration was surveyed in conifer forests 7–25 years post-fire. • Half the plots were stocked and 27% had no regeneration. • Time since fire, distance to forest, and elevation controlled regeneration. • Post-fire water balance had no discernable effect on stocking. [ABSTRACT FROM AUTHOR]

Bushfire severity mapping and analysis for Queensland's Gondwana Rainforests World Heritage Area properties following wildfires in 2019/20 was found to under-predict the ecological impact within closed-canopy rainforests, biasing against the prioritisation of rainforest-dependent threatened fauna for assessment and the allocation of recovery resources. By incorporating the fire tolerance of vegetation communities mapped within the bushfire extent, bushfire severity can be extended to predict the potential ecological impact of each severity class on ecosystems, and priority species. Prioritising threatened species based on potential ecological impact rather than fire severity alone allows post-fire survey and monitoring to be better targeted to those species likely most severely impacted. It also allows resources and recovery actions to be directed towards those areas of greatest concern, which may not have suffered the worst bushfire severity. [ABSTRACT FROM AUTHOR]

Infrequent, high‐intensity disturbances can have profound impacts on forested landscapes, changing forest structure and altering relative species abundance. However, due to their rarity and the logistical challenges of directly observing such extreme events, both the spatial variability of disturbance intensity and the species‐specific responses to this variability are poorly understood. We used observed patterns of mortality across a fire severity gradient following the 2009 Black Saturday fires in southeastern Australia to simultaneously estimate (1) species‐ and size‐specific susceptibility to fire‐induced mortality and (2) fire intensity. We found broad variation in patterns of fire susceptibility among the 10 tree species (five eucalypts and five non‐eucalypts) sufficiently abundant for analysis. Among the eucalypts, Eucalyptus obliqua was the most resistant to fire‐induced mortality, with trees of ~25 cm DBH having a 50% probability of surviving even the most intense fires. In contrast, E. regnans had 100% mortality across all size classes when subjected to high‐intensity fire. Basal resprouting occurred in six of the study species and, when accounted for, fundamentally changed the mortality profile of these species, highlighting the importance of resprouting as an adaptation to fire in these landscapes. In particular, the two iconic cool temperate rainforest species (Nothofagus cunninghami and Atherosperma moschatum) were strong resprouters (~45% of individuals were able to resprout after being top‐killed by fire). We also found evidence for compositional shifts in regeneration above threshold values of fire intensity in cool temperate rainforest and mixed forest sites, both of which have important conservation values within these landscapes. The observed patterns of species‐ and size‐specific susceptibility to fire‐induced mortality may be used to anticipate changes in forest structure and composition in the future. In addition, they may also help guide forest management strategies that reduce the length of time individual trees are exposed to potentially lethal fires, thereby increasing the resilience of these forests to future fires. [ABSTRACT FROM AUTHOR]

Exploration practices for oil sands developments in the boreal forest of western Canada create a network of thousands of kilometers of linear features, particularly seismic lines that dissect these forests posing significant environmental challenges. As wildfire is one of the prevalent stand‐replacing natural disturbances in the Canadian boreal forest, it is an important driver of environmental change and stand development that may contribute to the mitigation of such linear industrial footprint. Here, we evaluate the short‐term cumulative (also known as combined) effects of seismic lines and wildfire on biodiversity and site conditions. One year after the Horse River (Fort McMurray, Alberta, Canada) fire event in the spring of 2016, we compared dissected and undisturbed forests in burned and unburned boreal peatlands, assessing changes in overall stand structure and the responses of a variety of organisms. Soil moisture was significantly higher on seismic lines than in the adjacent forest, suggesting why most of the study sites within the fire perimeter showed little evidence of burning at the line in relation to the adjacent forest. Low fire severity on seismic lines seemed an important driver of local species diversity for ants, beetles, spiders, and plants in disturbed peatlands, resulting in similar species composition on seismic lines both within and outside the burned area, but different assemblages in burned and unburned adjacent forests. Our results suggest that fire did not erase seismic lines; rather, wildfire might increase the influence of this footprint on the recovering adjacent forest. Longer‐term monitoring will be necessary to understand how boreal treed peatlands respond to the cumulative effect of wildfire and linear disturbances. [ABSTRACT FROM AUTHOR]

Large wildfires (>50,000 ha) are becoming increasingly common in semiarid landscapes of the western United States. Although fuel reduction treatments are used to mitigate potential wildfire effects, they can be overwhelmed in wind‐driven wildfire events with extreme fire behavior. We evaluated drivers of fire severity and fuel treatment effectiveness in the 2014 Carlton Complex, a record‐setting complex of wildfires in north‐central Washington State. Across varied topography, vegetation, and distinct fire progressions, we used a combination of simultaneous autoregression (SAR) and random forest (RF) approaches to model drivers of fire severity and evaluated how fuel treatments mitigated fire severity. Predictor variables included fuel treatment type, time since treatment, topographic indices, vegetation and fuels, and weather summarized by progression interval. We found that the two spatial regression methods are generally complementary and are instructive as a combined approach for landscape analyses of fire severity. Simultaneous autoregression improves upon traditional linear models by incorporating information about neighboring pixel burn severity, which avoids type I errors in coefficient estimates and incorrect inferences. Random forest modeling provides a flexible modeling environment capable of capturing complex interactions and nonlinearities while still accounting for spatial autocorrelation through the use of spatially explicit predictor variables. All treatment areas burned with higher proportions of moderate and high‐severity fire during early fire progressions, but thin and underburn, underburn only, and past wildfires were more effective than thin‐only and thin and pile burn treatments. Treatment units had much greater percentages of unburned and low severity area in later progressions that burned under milder fire weather conditions, and differences between treatments were less pronounced. Our results provide evidence that strategic placement of fuels reduction treatments can effectively reduce localized fire spread and severity even under severe fire weather. During wind‐driven fire spread progressions, fuel treatments that were located on leeward slopes tended to have lower fire severity than treatments located on windward slopes. As fire and fuels managers evaluate options for increasing landscape resilience to future climate change and wildfires, strategic placement of fuel treatments may be guided by retrospective studies of past large wildfire events. [ABSTRACT FROM AUTHOR]

Collaborative efforts between indigenous peoples and government land managers are gaining recognition as important elements of forest restoration. Unique land allocations, such as the Research Natural Area (RNA) system of the US Forest Service, necessitate novel approaches to achieve desired outcomes among stakeholders. We describe a Traditional Ecological Knowledge (TEK) framework that integrates efforts among resource managers, tribal representatives, scientists, and a tribal youth intern program to conduct ecological restoration in a Jeffrey pine (Pinus jeffreyi) forest ecosystem of the western United States with a history of frequent fires. Reintroduction of TEK-based practices provided some moderation of fire effects during an unplanned wildfire event, benefiting both ecological conditions and a traditional Paiute Indian food source, piagi, the larvae of the Pandora moth (Coloradia pandora). Tribal youth learned about traditional food collection and land management practices, and federal managers discovered that TEK helped achieve ecological restoration goals. Our collaborative framework increased confidence in the mutual benefits of western science- and TEK-based forest management practices, creating a foundation for long-term partnership in ecosystem restoration. [ABSTRACT FROM AUTHOR]

• Stem density and canopy closure were significantly lower in burned sites. • Vegetative structure and burn history (i.e., burned or unburned) affect detection. • Bat occupancy was higher in burned sites for all species groups examined. • Burn severity had a negative effect on Myotis and tri-colored bat occupancy. Prescribed burning has become more common for the management of eastern forests in North America, so understanding if and how foraging bats respond to structural changes generated by fire is of increasing importance. Our objective was to investigate the effects of post-fire landscape conditions on the occurrence of foraging bats in mixed forests of the Cumberland Plateau physiographic region. We deployed Anabat II bat detectors in 164 paired burned and unburned forest sites for ≥2 nights from mid-May through August 2014 and 2015 to monitor bat foraging and commuting habitat use. We conducted vegetation surveys to quantify site-specific structural characteristics, which indicated that measures of structure were significantly lower in burned sites than unburned sites. We used Program Presence to test a priori hypotheses of species-specific probability of detection and site occupancy related to weather, burn history (i.e., site burned within the past 10 years or unburned), and site and landscape characteristics. Bats were detected at 94% of burned sites and 83% of unburned sites. Probability of detection was affected by weather conditions, vegetative structure, and burn history for most species. Occupancy for all species/species groups examined was positively associated with burning and generally associated with lower vegetative structure. Although burn severity did not affect most species groups, occupancy of Myotis species and tri-colored bats (Perimyotis subflavus) was lower in sites that received moderate severity burns than in sites that received low severity burns. Therefore, while prescribed fire may provide vegetative structure conducive to efficient foraging for all bats of the Cumberland Plateau, our results demonstrate that retaining some unburned forests while creating mosaics of lower and higher severity burns across the landscape will result in favorable foraging conditions for all resident bat species. [ABSTRACT FROM AUTHOR]

Photo credit: Zane Miller, United States Forest Service. • Many burned areas (43%) in Yosemite had forest structure predictive of den habitat. • Cover >2 m, 95th p. height, and 25th p. height were most predictive of den habitat. • High den habitat probability occurred most often within low-severity burned areas. One challenge that land managers face in the southern Sierra Nevada is how to balance conservation of fisher (Pekania pennanti) habitat with the reintroduction of fire. The fisher population in the southern Sierra Nevada is of high conservation priority, due to its small population size, genetic isolation, and the risk of habitat loss due to wildfire and fuel reduction activities. It is unknown whether contemporary forests altered by fire suppression can support fisher habitat following the reintroduction of fire. We examined whether patch-scale forest habitat conditions used by fishers in a landscape with limited recent fire (Dinkey study area) also exist in a landscape with restored fire (Yosemite study area). We developed random forest and logistic regression models using lidar-derived forest structure metrics to distinguish reproductive den presence (n = 261) from randomly-generated "available" points (n = 261) within an estimate of the female population home range. The full logistic regression model correctly classified (under cross-validation) 69.5% of observations and the random forest model correctly classified 74.3%. The parsimonious logistic regression model we selected had comparable accuracy to the full model (correctly classified 68.8% of observations) and included the following variables: cover >2 m, 95th percentile height, and 25th percentile height. Partial dependence plots suggest thresholds at which predicted probability of reproductive den presence exceeds 50%: cover >2 m greater than 60%, 95th percentile height of at least 32 m, and 25th percentile height between 4 m and 14 m. We found that comparable thresholds of forest cover and tree height exist in burned areas in Yosemite; 43.0% of burned pixels had similar lidar-derived forest structural characteristics to those predictive of reproductive dens in Dinkey. Areas with similar forest structures occurred within a range of fire severities and years since the most recent fire, and particularly in low-severity fire conditions (mean differenced normalized burn ratio [dNBR] value: 128.4). These results are promising for land managers who face the challenge of simultaneously reducing the risk of high-severity fire and conserving fisher habitat, however more research is needed to conclude whether suitable fisher habitat can exist in burned areas at all scales of selection and for all activities of the fisher population. [ABSTRACT FROM AUTHOR]

Highlights • We proposed a new LiDAR-based profile area change (PAC) method for fire severity assessment. • PAC metrics are highly correlated to field measured changes in basal area and leaf area index. • PAC metrics outperformed traditional LiDAR-based canopy cover and tree height change metrics, and Landsat-derived RdNBR. • PAC metrics can be applied at multiple scales from individual trees to plot-level fire assessments. Abstract This study proposes a new method (profile area change, PAC) to quantify fire-induced forest structural changes at the individual tree and clump of trees scales using pre- and post-fire LiDAR data. The PAC measures the difference in profile area summarized from pre- and post-fire LiDAR points. We applied the PAC method to assess the effects of the 2013 American Fire in the Sierra Nevada, California, USA. Our LiDAR PAC metrics were compared to changes in commonly used LiDAR-derived canopy cover and tree height metrics at tree level, and to Landsat-8 imagery-derived relative differenced normalized burn ratio (RdNBR) at the 30m pixel level. A quantitative validation using field measured changes in basal area and leaf area index (LAI) confirmed that correlations between PAC metrics and field measurements (R2 ≥ 0.67) were significantly higher than those from canopy cover or tree height metrics (R2 ≤ 0.43), and much stronger than that from RdNBR (R2 ≤ 0.26). The PAC metrics can also be used to infer the extent of tree canopy disturbance caused by fire, based on whether the majority of biomass loss occurred above or below the tree crown base height. Mapping of canopy disturbance indicated that over half (57.0%) of the American Fire region had tree canopy loss from fire, 22.5% of trees had sub-canopy loss, while the remaining area had no detectable tree canopy change. Overall, the LiDAR PAC metric, as a simple and integrated method, demonstrated promising potential in characterizing fine-grained changes in forest structure. The method can be beneficial for forest managers in evaluating fire-induced environmental and economic losses, and provide useful information for forest restoration design. [ABSTRACT FROM AUTHOR]

Research Natural Areas (RNAs) are federal lands designated to protect exemplary, relatively undisturbed ecosystems where ecological processes may proceed unencumbered with minimal human intervention. Ideally, RNAs serve as properly functioning reference sites for more heavily managed landscapes. However, many RNAs have been modified to some degree by past and ongoing human actions. In the western United States, these actions commonly result in altered disturbance regimes, most notably fire. Ecological disturbance regimes are important components of natural ecosystems, and major changes to such regimes challenge the usefulness of the RNA system as a reference network. To assess the extent of modern departure from their pre-Euroamerican settlement (i.e., pre-1850) fire regimes, we examined 64 RNAs on Forest Service lands in California. We found that 76% exhibited moderate to high fire regime departure. Of these, 87% are burning much less frequently than they would have under the presettlement fire regime and 13% are burning more frequently. Within RNAs, ecosystems historically characterized by frequent, mostly low-severity fire have missed multiple fire cycles and tend to burn at higher fire severities than expected under the presettlement fire regime. We present four case studies that demonstrate how recent wildfires have affected California RNAs. We also indicate where and how future fire management strategies could address altered fire regimes and more effectively sustain target ecosystems within RNAs. Our findings suggest that a re-examination of the hands-off approach to management in some protected natural areas like RNAs is needed. [ABSTRACT FROM AUTHOR]

Highlights • Large trees and shade intolerant trees had a higher probability of surviving fire. • Radial growth in small trees in burned stands increased. • Radial growth in large trees remained suppressed for decades after fire. • Radial growth responses can be explained by changes in leaf area. • Smaller trees easily add leaf area following fire while larger trees often do not. Abstract Wildfire is an important disturbance process in western North American conifer forests. To better understand forest response to fire, we used generalized additive models to analyze tree mortality and long-term (1 to 25 years post-fire) radial growth patterns of trees that survived fire across a burn severity gradient in the western Cascades of Oregon. We also used species-specific leaf-area models derived from sapwood estimates to investigate the linkage between photosynthetic capacity and growth response. Larger trees and shade intolerant trees had a higher probability of surviving fire. Trees that survived fire tended to experience a reduction in growth immediately following fire, with the most pronounced growth suppression found in trees within stands burned at high severity. Radial growth response to fire over time differed markedly as a function of tree size. Smaller trees that survived fire generally experienced enhanced radial growth relative to small trees in unburned stands. Conversely, larger trees that survived fire experienced significant and persistent reductions in growth relative to large trees in unburned stands. There was a linear relationship between diameter and tree leaf area in stands burned at low severity, but a non-linear relationship between diameter and leaf area in stand burned at high severity. Generalized additive models are well suited to modeling non-linear mortality and growth responses to fire. This research provides a better understanding of how fire severity influences tree-growth, forest succession, as well as the long-term resilience of forests to disturbances. [ABSTRACT FROM AUTHOR]

Highlights • Fires are getting more frequent, larger, and more severe across all vegetation types in the Southwest. • Trends in area burned and area burned severely were increasing in all seven forest and woodland ecosystems across the Southwest from 1984 to 2015. • Trends in percent of high-severity fire were increasing in xeric mixed conifer and mesic mixed conifer/spruce-fir ecosystems across the Southwest from 1984 to 2015. Abstract In the last three decades, over 4.1 million hectares have burned in Arizona and New Mexico and the largest fires in documented history have occurred in the past two decades. Changes in burn severity over time, however, have not been well documented in forest and woodland ecosystems in the southwestern US. Using remotely sensed burn severity data from 1621 fires (>404 ha), we assessed trends from 1984 to 2015 in Arizona and New Mexico in (1) number of fires and total area burned in all vegetation types; (2) area burned, area of high-severity, and percent of high-severity fire in all forest and woodland areas; and (3) area burned, area of high-severity, and percent of high-severity in seven different grouped forest and woodland vegetation types (Ecological Response Unit [ERU] Fire Regime Types). Number of fires and area burned increased across the Southwest regardless of vegetation type. The significant increasing trends held for area burned, area of high-severity, and percent of high-severity fire in all forest and woodland ecosystems. Area burned and area burned severely increased in all seven ERU Fire Regime Types while percent of high-severity fire increased in two ERUs: Mixed Conifer Frequent Fire and Mixed Conifer with Aspen/Spruce Fir. Managers must face the implications of increasing, uncharacteristic high-severity fire in many ecosystems as climate change and human pressures continue to affect fire regimes. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Small (1 m2 ≤ area ≤ 900 m2) unburned patches occupied 5% of the area burned. • Areas with all fire severity classifications contained small unburned patches. • Tree survival was higher when trees were rooted in an unburned patch. • Small tree survival was higher towards the interior of unburned patches. Abstract Fire refugia – the unburned areas within fire perimeters – are important to the survival of many taxa through fire events and the revegetation of post-fire landscapes. Previous work has shown that species use and benefit from small-scale fire refugia (1–1000 m2), but our understanding of where and how fire refugia form is largely limited to the scale of remotely sensed data (i.e., 900 m2 Landsat pixels). To examine the causes and consequences of small fire refugia, we field-mapped all unburned patches ≥1 m2 within a contiguous 25.6 ha forest plot that burned at generally low-to-moderate severity in the 2013 Yosemite Rim Fire, California, USA. Within the Yosemite Forest Dynamics Plot (YFDP), there were 685 unburned patches ≥1 m2, covering a total unburned area of 12,597 m2 (4.9%). Small refugia occurred in all fire severity classifications. Random forest models showed that the proportion of unburned area of 100 m2 grid cells corresponded to pre-fire density and basal area of trees, distance to the nearest stream, and immediate fire mortality, but the relationships were complex and model accuracy was variable. From a pre-fire population of 34,061 total trees ≥1 cm diameter at breast height (1.37 m; DBH) within the plot (1330 trees ha−1), trees of all five of the most common species and those DBH < 30 cm had higher immediate survival rates if their boles were wholly or partially within an unburned patch (P ≤ 0.001). Trees 1 cm ≤ DBH < 10 cm that survived were located closer to the center of the unburned patch than the edge (mean 1.1 m versus 0.6 m; ANOVA; P ≤ 0.001). Four-year survival rates for trees 1 cm ≤ DBH < 10 cm were 58.8% within small refugia and 2.7% in burned areas (P ≤ 0.001). Species richness and the Shannon Diversity Index were associated with unburned quadrats in NMDS ordinations 3 years post-fire. Burn heterogeneity in mixed-conifer forests likely exists at all scales and small refugia contribute to diversity of forest species and structures. Thus, managers may wish to consider scales from 1-m2 to the landscape when designing fuel reduction prescriptions. The partial predictability of refugia location suggests that further work may lead to predictive models of refugial presence that have considerable potential to preserve ecological function or human habitation in fire-frequent forests. [ABSTRACT FROM AUTHOR]

Forests of the eastern United States provide numerous ecosystem services, including water filtration. Forest management activities of eastern forests often include prescribed fire to accomplish a variety of management objectives such as invasive species control, wildlife habitat improvement, ecosystem restoration, and hazardous fuel reduction. Despite widespread use of prescribed fire in this region and the need to maintain adequate water quality from forests impacted by this practice, there is a paucity of knowledge on prescribed fire's impacts on water quality. This article summarizes and consolidates known impacts of prescribed fire on chemical, physical, and biological properties related to water quality and freshwater ecosystems in moist-temperate eastern North America, including impacts on drinking water treatability. Based upon this synthesis, it appears that most prescribed fires in eastern forests are low intensity and low severity and cause minimal changes to forest soil properties, leading to minimal adverse impacts that might exacerbate soil erosion and adversely affect surface waters. In some cases, prescribed fire has been shown to enhance water quality in the region. Technological advancements in monitoring fire behavior have the potential to advance our knowledge regarding the effects of prescribed fire on water quality in the eastern forest region, particularly for fires of mixed or moderate severity and fires occurring in complex terrain. [ABSTRACT FROM AUTHOR]

Highlights • Fire vulnerability of cork oak tree depends on corkback roughness and cork quality. • Flammability analysis suggests forest management to mitigate fire severity. • Silvicultural treatments could improve cork production and cork quality. Abstract Quercus suber (cork oak tree) is an excellent epicormic resprouter that can keep cambium alive after high-intensity fires because of its plan traits, mainly its thick cork. Although tree bark harvesting is an important source of income, it may reduce protection against wildfires. This study aims to identify stem and cork characteristics that affect the probability of reaching lethal cambial temperature and hence the probability of survival of living tissues. Cork flammability was analyzed using a sample set comprised of 120 cork specimens and 120 cork pieces. Five experimental fires were used to test the results obtained at bench scale. Bench-scale flammability experiments could not simulate the real heat spread and presence of highly volatile isoprenoids. The results revealed differences in cambial temperature and lethal temperature rate (LTR) at both scales according to corkback roughness and cork quality. Peak cambial temperature and LTR show an increase in stems characterized by maximum roughness and worse cork quality. The LTR measurements showed a 30% difference between bench and field scales (0.35 mm s−1 and 0.5 mm s−1, respectively). The findings indicate that corkback roughness, cork thickness, cork porosity and cork quality could influence the vulnerability of cork oak forests to wildfires. A negative correlation was found between total thickness and cambial temperature. A total thickness of over 3.7 cm prevented reaching lethal cambial temperature. Forest managers can use this information to define silviculture and design forest treatments with a view to reducing fire severity and mitigating the ecological and socioeconomic impacts of fire in cork oak forests. [ABSTRACT FROM AUTHOR]

• Compared historical average annual area burned to contemporary fire years 1985–2020. • Inland Pacific Northwest forests averaged ≥ 224–291,000 ha burned historically. • Contemporary fire years in the region average only 49,000 forested hectares burned. • Current forest restoration treatment rates are far below historical burn rates. • Increased treatment rates & managed wildfire necessary for successful restoration. Wildfires and fire seasons are commonly rated largely on the simple metric of area burned (more hectares: bad). A seemingly paradoxical narrative frames large fire seasons as a symptom of a forest health problem (too much fire), while simultaneously stating that fire-dependent forests lack sufficient fire to maintain system resilience (too little fire). One key to resolving this paradox is placing contemporary fire years in the context of historical fire regimes, considering not only total fire area but also burn severity distributions. Historical regimes can also inform forest restoration efforts by illuminating the pace and scale at which fires historically maintained (i.e., 'treated') fire-resilient landscapes. Here we ask, for a broad extent of the inland Pacific Northwest (eastern Oregon and Washington, USA), a region predominated by drier forest types and recently experiencing record-breaking fire years: 1) How much annual fire area would have been needed to support historical fire regimes?; and 2) How do contemporary fire years (1985–2020) compare to historical fire amounts and severities? To meet historical fire frequencies for each forest type, annual area burned would have averaged at least 224,000–291,000 ha per year regionally prior to the 20th century (notwithstanding interannual variability) – presumably arising from both indigenous-cultural and lightning-ignited fires. Drier forests would account for 82–88% of annual burn area. In contrast, despite the seemingly fiery contemporary era, contemporary fire years average just ∼49,100 ha·yr−1 (∼17–22% of historical), with only one year approximating historical area burned. Contemporary years average well under historical rates for virtually all severity classes across dry and moist (but not cold) forests. Annualized fire deficits relative to historical rates are especially conspicuous for low-severity area in dry forests (on average missing 127,000–161,000 ha·yr−1 regionally) and moderate-severity area in both dry (missing 34,000–44,000 ha·yr−1) and moist (missing 9000–12,000 ha·yr−1) forests. Ten-year moving averages in burn area are increasing in recent years, but remain below historical levels. Trends are similar across states and major land ownerships. With current forest restoration efforts occurring at a fraction of historical fire rates, our findings highlight that successful restoration and maintenance will require a) increasing active treatment rates, and b) incorporating managed wildfire to attain substantially more treated area. As such, beneficial fire years may be those not with less, but rather more, area burned – with characteristic severity and patch distributions, minimal clearly-negative impacts (e.g. loss of life and property), and contribution to restoration/maintenance objectives. [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]

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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. [ABSTRACT FROM AUTHOR]

Abstract: Shifting disturbance regimes can have cascading effects on many ecosystems processes. This is particularly true when the scale of the disturbance no longer matches the regeneration strategy of the dominant vegetation. In the yellow pine and mixed conifer forests of California, over a century of fire exclusion and the warming climate are increasing the incidence and extent of stand‐replacing wildfire; such changes in severity patterns are altering regeneration dynamics by dramatically increasing the distance from live tree seed sources. This has raised concerns about limitations to natural reforestation and the potential for conversion to non‐forested vegetation types, which in turn has implications for shifts in many ecological processes and ecosystem services. We used a California region‐wide data set with 1,848 plots across 24 wildfires in yellow pine and mixed conifer forests to build a spatially explicit habitat suitability model for forecasting postfire forest regeneration. To model the effect of seed availability, the critical initial biological filter for regeneration, we used a novel approach to predicting spatial patterns of seed availability by estimating annual seed production from existing basal area and burn severity maps. The probability of observing any conifer seedling in a 60‐m2 area (the field plot scale) was highly dependent on 30‐yr average annual precipitation, burn severity, and seed availability. We then used this model to predict regeneration probabilities across the entire extent of a “new” fire (the 2014 King Fire), which highlights the spatial variability inherent in postfire regeneration patterns. Such forecasts of postfire regeneration patterns are of importance to land managers and conservationists interested in maintaining forest cover on the landscape. Our tool can also help anticipate shifts in ecosystem properties, supporting researchers interested in investigating questions surrounding alternative stable states, and the interaction of altered disturbance regimes and the changing climate. [ABSTRACT FROM AUTHOR]

Fire is one of the major factors that alter structure and function of forest in the Great Xing'an Mountains, with consequences on soil carbon cycling in forests. In this study, we collected soil samples (layers O, A, AB, BC, and C) under different fire-severity levels (low, moderate, and high) and post-fire recovery times (1987-2012) in the forests of Great Xing'an Mountains. Analysis of variance and multiple comparison were used to analyze effects of fire severity and reco-very time on content of soil organic carbon. The results showed that soil organic carbon (SOC) content in layer O presented a rising trend under both moderate- and high-severity fire disturbances. The content of SOC in layers A and B decreased year by year under low- and moderate-severity fires, which ranked in the order: 3 years > 5 years > 10 years > over 10 years since fire. The content of SOC under high-severity fire presented an increasing trend within 10 years since fire distur-bance and then decreased rapidly over 10 years. The content of SOC in layer BC presented no obvious changes. [ABSTRACT FROM AUTHOR]

Abstract: Many studies have examined how fuels, topography, climate, and fire weather influence fire severity. Less is known about how different forest management practices influence fire severity in multi‐owner landscapes, despite costly and controversial suppression of wildfires that do not acknowledge ownership boundaries. In 2013, the Douglas Complex burned over 19,000 ha of Oregon & California Railroad (O&C) lands in Southwestern Oregon, USA. O&C lands are composed of a checkerboard of private industrial and federal forestland (Bureau of Land Management, BLM) with contrasting management objectives, providing a unique experimental landscape to understand how different management practices influence wildfire severity. Leveraging Landsat based estimates of fire severity (Relative differenced Normalized Burn Ratio, RdNBR) and geospatial data on fire progression, weather, topography, pre‐fire forest conditions, and land ownership, we asked (1) what is the relative importance of different variables driving fire severity, and (2) is intensive plantation forestry associated with higher fire severity? Using Random Forest ensemble machine learning, we found daily fire weather was the most important predictor of fire severity, followed by stand age and ownership, followed by topographic features. Estimates of pre‐fire forest biomass were not an important predictor of fire severity. Adjusting for all other predictor variables in a general least squares model incorporating spatial autocorrelation, mean predicted RdNBR was higher on private industrial forests (RdNBR 521.85 ± 18.67 [mean ± SE]) vs. BLM forests (398.87 ± 18.23) with a much greater proportion of older forests. Our findings suggest intensive plantation forestry characterized by young forests and spatially homogenized fuels, rather than pre‐fire biomass, were significant drivers of wildfire severity. This has implications for perceptions of wildfire risk, shared fire management responsibilities, and developing fire resilience for multiple objectives in multi‐owner landscapes. [ABSTRACT FROM AUTHOR]

Setting suitable conservation targets is an important part of ecological fire planning. Growth-stage optimisation (GSO) determines the relative proportions of post-fire growth stages (categorical representations of time since fire) that maximise species diversity, and is a useful method for determining such targets. Optimisation methods can accommodate various predictor variables, but to date have only been applied using post-fire growth stages as the primary landscape variable. However, other aspects of fire regimes such as severity may influence species diversity but have not yet been considered in determining conservation targets in fire planning. Here we use a space-for-time substitution to address two objectives, 1. To determine the effects of growth stage and fire severity on plant and vertebrate species’ occurrence, and 2. To determine the optimal mix of growth stages and fire severities for sustaining the diversity of these groups. We used the tall wet forests of southeast Australia as the focal system because fire severity is expected to create distinct successional pathways and influence species’ responses. We found that growth stage predicted the occurrence of many species, and severity of the most recent fire was an important factor over and above growth stage for a small subset of species. The optimal distribution of growth stages for both plants and animals included a substantial proportion of young forest, however when fire severity was considered, areas burned at low severity were most important in driving the diversity of both groups. Growth stage is a good surrogate for developing conservation targets in tall wet forests, however growth stage alone does not capture the full range of species’ fire responses. More complex versions of growth stage optimisation that accommodate multiple fire-regime variables need to be explored to yield ecologically meaningful conservation goals. [ABSTRACT FROM AUTHOR]

Abstract: An understanding of how historical fire and structure in dry forests (ponderosa pine, dry mixed conifer) varied across the western United States remains incomplete. Yet, fire strongly affects ecosystem services, and forest restoration programs are underway. We used General Land Office survey reconstructions from the late 1800s across 11 landscapes covering ~1.9 million ha in four states to analyze spatial variation in fire regimes and forest structure. We first synthesized the state of validation of our methods using 20 modern validations, 53 historical cross‐validations, and corroborating evidence. These show our method creates accurate reconstructions with low errors. One independent modern test reported high error, but did not replicate our method and made many calculation errors. Using reconstructed parameters of historical fire regimes and forest structure from our validated methods, forests were found to be non‐uniform across the 11 landscapes, but grouped together in three geographical areas. Each had a mixture of fire severities, but dominated by low‐severity fire and low median tree density in Arizona, mixed‐severity fire and intermediate to high median tree density in Oregon‐California, and high‐severity fire and intermediate median tree density in Colorado. Programs to restore fire and forest structure could benefit from regional frameworks, rather than one size fits all. [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]

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]

• 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]

• RTMs allowed to disentangle vegetation recovery drivers of specific plant communities. • Fire severity and post-fire soil moisture were relevant recovery predictors. • Climate and landscape configuration did not explain vegetation recovery. • Driving factors shaping vegetation recovery dynamics were plant community-dependent. Large, severe wildfires can cause unpredictable changes in Mediterranean plant communities that undermine ecosystem resilience. Understanding the geophysical drivers shaping vegetation dynamics after fire is vital to provide integrated knowledge into plant community recovery feedbacks in the context of global change. We investigated the role of fire severity and a comprehensive set of geophysical drivers in the post-fire vegetation recovery of Mediterranean landscapes. We used physical-based remote sensing techniques to estimate vegetation recovery and examined whether this recovery is plant-community dependent in the short-term (one year) after the fire. The fractional vegetation cover (FCOVER) recovery was selected as a resilience indicator for Pinus sylvestris L. (Scots pine) forests, Quercus ilex L. (holm oak) woodlands, shrublands dominated by Cytisus oromediterraneus Rivas Mart. et al. (black broom) and grasslands. To obtain the pre- and post-fire FCOVER, we used the Gaussian processes regression algorithm trained with the PROSAIL-D radiative transfer model. The algorithm was parameterized to account for the variability of biophysical conditions in the plant communities considered and was applied to the Sentinel-2 multispectral imagery. Validation of remotely-sensed FCOVER with field data in burned and control plots was successful (R2 = 0.84 and RMSE = 10.83%), without significant under or overestimation. We selected 31 variables pertaining to fire severity, climate, post-fire soil moisture, pre-fire soil condition, and landscape configuration as putative predictors of FCOVER recovery percentage (FCOVER %rec), calculated as the ratio of post-fire to pre-fire FCOVER. Random Forest regression (RFR) was used to disentangle the influences of fire severity and geophysical drivers on community-specific FCOVER %rec. Fire severity and post-fire surface soil moisture variables were relevant predictors in RFR models in all plant communities. However, their importance was largely community-dependent. In grasslands, surface soil moisture in the early summer season one year after fire was the major variable explaining variability in FCOVER %rec. In holm oak woodlands, the contribution of fire severity and surface soil moisture was balanced. Conversely, fire severity largely outweighed other variables in driving FCOVER %rec in black broom shrublands and Scots pine forests. Pre-fire climate, soil condition and landscape configuration variables were not meaningful predictors in general. Our findings offer novel insights into the processes that underlie resilience in fire-prone plant communities located in the western Mediterranean Basin. This establishes a baseline to help prioritize adaptive management strategies for the most vulnerable areas in the region. [ABSTRACT FROM AUTHOR]

• In the Iguaque mountains forest, Q. humboldtii trees showed high resprouting ability (about 80%) two years after burning. The resprouting ability depended on fire severity, frequency, and tree size. • Quercus humboldtii acorn density was higher in burned areas than in unburned areas. However, in unburned forests, the density of healthy acorns was higher. • Quercus humboldtii seedling density was low in all sites, particularly in burned areas. • In the Iguaque Mountains, during the years following the wildfire, the natural regeneration of burned areas depended more on the Q. humboldtii resprouting ability than on the recruitment of Q. humboldtii seedlings or other forest species. • To restore Q. humboldtii forests in the Iguaque mountains disturbed areas, it is necessary to decrease the severity and frequency of wildfires and use assisted regeneration. Anthropogenic disturbances, including wildfires, threaten the diversity of tropical Andean ecosystems. However, the response of tropical Andean plant communities to wildfires in human-modified landscapes has to be discovered. Quercus humboldtii is the southernmost species of this genus in the Neotropics and is almost exclusively distributed in Colombia. While the extent of Q. humboldtii forests has decreased recently, to what time these results from the species' inability to thrive under the current climate and disturbance regimes are still being determined. In this study, we describe post-fire resprouting and acorn and seedling density in and around Q. humboldtii forest patches in the Iguaque mountains in Colombia. We discuss the implications for the conservation and restoration of these forests. Resprouting probability was high in burned trees two years after the fire (ca. 80%). Resprouting ability depended on fire severity and tree size. The proportion of trees resprouting from the stump was related to the severity of fire damage and tree size. Acorn density was higher in burned than unburned areas and depended on the slope, distance to the forest edge, and distance to the nearest oak. Conversely, the density of healthy acorns was low across all sites, particularly in burned areas. Seedling density was relatively high in unburned areas, but seedlings could not withstand recurrent fires. The density of acorns and seedlings decreased in the periphery of forest patches. Despite the strong impact of fire on forest structures, Quercus humboldtii adults may withstand the current fire regime thanks to their strong capacity for vegetative and sexual regeneration. However, the ability of this species to establish in areas where oaks are no longer present is scarce. As Q. humboldtii forest cover and spatial continuity have decreased in response to the increasing frequency of wildfires, the current fire regime represents a threat to the recovery of this species. Our results have important implications for the management of Q. humboldtii and Andean forests as they emphasize the need to control the severity and frequency of wildfires and to use assisted regeneration to restore Q. humboldtii forests in degraded areas. [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]

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]

Fuel moisture is a key driver of forest flammability as it influences ignition likelihood, fire intensity and resultant fire severity. Changes to forest canopy cover following disturbances like wildfire or logging may alter forest flammability by changing the microclimatic conditions that influence fine fuel moisture. Wet forests dominated by Mountain Ash ( Eucalyptus regnans ) are highly valued for their flora and fauna, timber, carbon and water. Wildfires are an important part of the lifecycle of these forests, but too frequent fire can threaten post-fire regeneration. With large tracts of Mountain Ash forest recovering from recent wildfires (in 2009 and 1983) there is a need to understand the mechanisms driving flammability in these forests, particularly as the forest structure changes following fire. This study sought to understand the effects of fire history on the flammability of Mountain Ash forests by specifically considering fuel moisture for different times since fire and fire severities. We measured canopy cover (plant area index) and fuel moisture within 8 forest sites last burnt between 7 and 200 years ago by wildfires of low or high severity. Fuel moisture and fuel availability (i.e. number of days when fine fuels are dry enough to ignite and sustain spreading fire) were strongly associated with canopy cover; with denser canopied forests having higher fuel moisture. The largest differences in canopy cover occurred between the recently burnt high and low severity forests. For the longer-unburnt forests there were no systematic differences evident in canopy cover with time since fire or fire severity. The fuel moisture was higher and fuels only available to burn on one day in the forest recently burnt by high severity fire (in association with a dense canopy). In contrast, fuels were drier and available to burn on 238 days in the forest recently burnt by low severity fire (in association with a sparser canopy). For the longer-unburnt forests (33 or more years since fire) there were no clear trends between fuel moisture and time since fire and fire severity suggesting that fires do not have a lasting impact on fuel moisture within these wet forests. Overall, this study shows that wildfires have immediate impacts on fuel moisture in Mountain Ash forests but as the time since fire increases, moisture appears to be more a function of canopy properties than fire history. [ABSTRACT FROM AUTHOR]

This study examines spatially variable stand structure and fire-climate relationships at a low elevation forest-grassland ecotone in west central British Columbia, Canada. Fire history reconstructions were based on samples from 92 fire-scarred trees and stand demography from 27 plots collected over an area of about 7 km2. We documented historical chronologies of widespread fires and localized grassland fires between AD 1600 and 1900. Relationships between fire events, reconstructed values of the Palmer Drought Severity Index, and annual precipitation were examined using superposed epoch and bivariate event analyses. Widespread fires occurred during warm, dry years and were preceded by multiple anomalously dry, warm years. Localized fires that affected only grassland-proximal forests were more frequent than widespread fires. These localized fires showed a lagged, positive relationship with wetter conditions. The landscape pattern of forest structure provided further evidence of complex fire activity with multiple plots shown to have experienced low-, mixed-, and/or high-severity fires over the last four centuries. We concluded that this forest-grassland ecotone was characterized by fires of mixed severity, dominated by frequent, low-severity fires punctuated by widespread fires of moderate to high severity. This landscape-level variability in fire-climate relationships and patterns in forest structure has important implications for fire and grassland management in west central British Columbia and similar environments elsewhere. Forest restoration techniques such as prescribed fire and thinning are oftentimes applied at the forest-grassland ecotone on the basis that historically high frequency, low-severity fires defined the character of past fire activity. This study provides forest managers and policy makers with important information on mixed-severity fire activity at a low elevation forest-grassland ecotone, a crucial prerequisite for the effective management of these complex ecosystems. [ABSTRACT FROM AUTHOR]

Clearcutting practices combined with the predicted increase in fire activity may induce post-fire regeneration failure in boreal forest landscapes. This study aims (1) to evaluate if recently managed landscape by clear cut logging is susceptible to be affected by post-fire regeneration failure; and (2) to explore the ecological drivers of black spruce ( Picea mariana (Mill.) BSP) post-fire regeneration. In 2014, we surveyed the regeneration of 36 stands in northwestern Quebec that had burned in a major fire in 2005. Fire severity was evaluated for each site with the differenced Normalized Burn Ratio. Using linear models, we explored the relationship between environmental variables (fire severity, pre-fire stand maturity, nature of the seedbed, and physiographic variables) and black spruce post-fire regeneration. Black spruce post-fire seedling density was highly variable (range: 25–16 000 seedlings/ha; mean ± standard deviation: 4549 seedlings/ha ± 4752) within the studied fire, but did not significantly differ between stands that had been logged 50 years prior to fire and those that were mature prior to the 2005 fire. However, post-fire regeneration failure (defined as <40% stocking that corresponds in our study region to a regeneration density <1750 seedlings/ha) was observed in 48% of the stands that had been logged, but only in 29% of the stands that were mature prior to the fire. The presence of residual trees left after clearcutting may explain why regeneration level was relatively good (>50%) in stands affected by past logging activities. Our study illustrates how biological legacies, environmental conditions and fire severity determine post-fire recovery and resilience of black spruce-dominated ecosystems of eastern Canada. By identifying the drivers of post-fire regeneration success, our study will help forest managers allocating resources where restoration of productive forest are truly needed. [ABSTRACT FROM AUTHOR]