Effective post-fire management – including flood mitigation, revegetation, and salvage logging – depends on timely and reliable burn-severity assessments that characterize impacts to vegetation and soils. These assessments are typically derived from satellite-based change detection but can be delayed or degraded by aerosols (i.e., dust or smoke), clouds, and snow. Across 9,129 large fires (≥404 ha) in Canada and the United States from 2016–2024, we quantified sources of post-fire data obstruction and evaluated observational latency – the time to acquire the first usable scene – for four freely available, moderate-resolution datasets: Landsat, Sentinel‑1, Sentinel‑2, and the Harmonized Landsat Sentinel-2 (HLS) product. For 77 fires with field-derived burn-severity indicators, we also assessed mapping accuracy in forested ecosystems and quantified variation over time. Cloud cover was the dominant cause of data obstruction, especially in mesic and coastal regions. Sentinel‑1 exhibited the shortest observational latency (median = 4 days), followed by HLS (7 days), Sentinel‑2 (10 days), and Landsat (17 days). Composite imagery from Sentinel‑1 (89.6%) and HLS (82.8%) achieved near‑complete coverage of most fires within one month, substantially better than Sentinel‑2 (70.5%) and Landsat (56.1%). HLS, Landsat, and Sentinel‑2 produced maps of stand-replacing disturbance that exceeded 80% accuracy within one month of fire, only slightly lower than maps generated after the following growing season. Sentinel‑1 had lower initial accuracy (<70%), but outperformed other sensors in winter and improved over time. High‑frequency multispectral datasets such as HLS facilitate timely, accurate post‑fire assessments, informing critical management activities that can prevent the loss of human life and minimize economic losses following fire.

Aspen forests provide wildlife, watershed, and aesthetic value, and the potential for reduced fire occurrence, behavior, and severity. There is interest in planting aspen to achieve various management objectives. However, few studies have investigated the optimal conditions for aspen seedlings in the western US. We conducted two experiments to address this knowledge gap. First, we tested the effects of shading structures (i.e., logs) and biochar on the survival and growth of 960 outplanted aspen seedlings in three exclosures in a recent fire footprint. Second, we tested whether experimentally placing logs near 120 naturally-occurring post-fire aspen seedlings affected survival or growth. Survival of outplanted seedlings was high (66%) despite hot and dry conditions in the years of the study. Logs and biochar had minimal effects on planted seedling survival and growth, but in one exclosure, survival of planted seedlings was lower in log and log + biochar treatments, likely due to the protection logs provided to small mammalian herbivores. Survival was higher for naturally-occurring seedlings with logs placed on the south side compared to control seedlings in one site, and growth was higher for naturally-occurring seedlings with a nearby log, but not significantly so. In sites where aspen seedling survival and growth are relatively robust, management actions to modify the microsite may not be necessary.

Fire suppression is the primary management response to wildfires in many areas globally. By removing less-extreme wildfires, this approach ensures that remaining wildfires burn under more extreme conditions. Here, we term this the “suppression bias” and use a simulation model to highlight how this bias fundamentally impacts wildfire activity, independent of fuel accumulation and climate change. We illustrate how attempting to suppress all wildfires necessarily means that fires will burn with more severe and less diverse ecological impacts, with burned area increasing at faster rates than expected from fuel accumulation or climate change. Over a human lifespan, the modeled impacts of the suppression bias exceed those from fuel accumulation or climate change alone, suggesting that suppression may exert a significant and underappreciated influence on patterns of fire globally. Managing wildfires to safely burn under low and moderate conditions is thus a critical tool to address the growing wildfire crisis.

Increasing fire severity and warmer, drier postfire conditions are making forests in the western United States (West) vulnerable to ecological transformation. Yet, the relative importance of and interactions between these drivers of forest change remain unresolved, particularly over upcoming decades. Here, we assess how the interactive impacts of changing climate and wildfire activity influenced conifer regeneration after 334 wildfires, using a dataset of postfire conifer regeneration from 10,230 field plots. Our findings highlight declining regeneration capacity across the West over the past four decades for the eight dominant conifer species studied. Postfire regeneration is sensitive to high-severity fire, which limits seed availability, and postfire climate, which influences seedling establishment. In the near-term, projected differences in recruitment probability between low- and high-severity fire scenarios were larger than projected climate change impacts for most species, suggesting that reductions in fire severity, and resultant impacts on seed availability, could partially offset expected climate-driven declines in postfire regeneration. Across 40 to 42% of the study area, we project postfire conifer regeneration to be likely following low-severity but not high-severity fire under future climate scenarios (2031 to 2050). However, increasingly warm, dry climate conditions are projected to eventually outweigh the influence of fire severity and seed availability. The percent of the study area considered unlikely to experience conifer regeneration, regardless of fire severity, increased from 5% in 1981 to 2000 to 26 to 31% by mid-century, highlighting a limited time window over which management actions that reduce fire severity may effectively support postfire conifer regeneration.

BackgroundWilderness areas are important natural laboratories for scientists and managers working to understand fire. In the last half-century, shifts in the culture and policy of land management agencies have facilitated the management practice of letting some naturally ignited fires burn, allowing fire to fulfill its ecological role and increasing the extent of fire-related research opportunities. With the goal of identifying the global scientific advances enabled by this paradigm shift in wilderness fire management, we conducted a systematic review of publications that either (1) selected protected areas for investigation because of an active fire regime enabled by wilderness fire management, (2) studied modern fires or fire regimes deliberately located in a wilderness area, or (3) conducted applied research to support wilderness fire management.ResultsOur systematic review returned a sample of 222 publications that met these criteria, with an increase in wilderness fire science over time. Studies largely occurred in the USA and were concentrated in a relatively small number of protected areas, particularly in the Northern Rocky Mountains. As a result, this sample of wilderness fire science is highly skewed toward areas of temperate mixed-conifer forests and historical mixed-severity fire regimes. Common principal subjects of publications included fire effects (44%), wilderness fire management (18%), or fire regimes (17%), and studies tended to focus on vegetation, disturbance, or wilderness management as response variables.ConclusionsThis work identifies major scientific contributions facilitated by fire in wilderness, including self-limitation of fire, the effects of active fire regimes on forest and aquatic systems, barriers and potential solutions to wilderness fire management, and the effect of fire on wilderness recreation and visitor experiences. Our work reveals geographic and bioclimatic areas where more research attention is needed and highlights under-represented wilderness areas that could serve to fill these gaps. Finally, we identify priorities for future wilderness fire research, including the past and potential role of Indigenous and prescribed burning, the effects of changing climate and fire regimes on ecosystem processes, and how to overcome barriers to wilderness fire management.

High-severity fires and short-interval reburns strongly influence forest structure and composition and may overwhelm forest ecosystem resilience and catalyze persistent shifts to non-forest conditions. Recent increases in annual area burned and severity in the western United States (US) highlight the need to better understand the long-term effects of high-severity fire, including interactions with subsequent fires. In the early 20th century, the northern US Rocky Mountains experienced several fire seasons with widespread, high-severity fires, under fire weather comparable with extreme conditions today. The Selway-Bitterroot Wilderness in north-central Idaho has remained an active fire regime with limited suppression and management, making it an ideal location to investigate long-term effects of initial high-severity fires, as well as ecosystem resilience to contemporary reburning. Using field sampling informed by fire history data from 1870 to 2020, we investigated the influence of fire frequency (once, twice, and thrice burned from 1910 to 2017) on forest structure, conifer regeneration, and fuel loading in mesic mixed-conifer forests that burned at high severity in either 1910 or 1934. Tree regeneration was abundant across all three burn histories, and 99% of sample sites were <200 m from the nearest conifer seed source when sampled in 2021. Abundance of snags and coarse woody material was less affected by fire frequency and more impacted by time since last fire. High shrub biomass occurred only on steep southwest aspects with low overstory basal area and was not related to burn history. Live tree composition and density differed across forests with contrasting recent fire histories, but even thrice-burned sites supported abundant conifer tree regeneration, indicating that northern Rocky Mountain mesic mixed-conifer forests that experienced fire during the twentieth century currently remain resilient to wildfire. Wildfire as an ecological process in the Selway-Bitterroot Wilderness likely contributed to ecosystem resilience.

Abstract Background Wilderness areas are important natural laboratories for scientists and managers working to understand fire ecology. In the last half-century, shifts in agency culture and policy have encouraged the management practice of letting some naturally ignited fires burn, allowing fire to fulfill its ecological role and increasing the extent of fire-related research opportunities. With the goal to identify the global scientific advances enabled by this paradigm shift in wilderness fire management, we conducted a systematic review of studies in which 1) protected areas were selected for investigation because of an active fire regime enabled by wilderness fire management, or 2) applied research was conducted to support wilderness fire management. Results Our systematic review returned a sample of 222 papers that met these criteria, with an increase in wilderness fire science over time. Studies largely occurred in the United States of America and were concentrated in a relatively small number of protected areas, particularly in the Northern Rocky Mountains. As a result, this sample of wilderness fire science is highly skewed toward areas of temperate mixed conifer forests and historical mixed severity fire regimes. Common principal subjects of papers included fire effects (44%), wilderness fire management (18%), or fire regimes (17%), and studies tended to focus on vegetation, disturbance, or wilderness management as response variables. Conclusions This work identifies major scientific contributions facilitated by active fire management, including concepts such as self-limitation of fire, forest dynamics in active fire regimes, and the effect of fire on wilderness recreation. Our work also identifies areas—both geographic and conceptual—where more research attention is needed and highlights under-represented wilderness areas that could serve to fill these knowledge gaps.

Quaking aspen (Populus tremuloides) is an important component of western U.S. forests, however knowledge concerning processes of aspen seedling establishment, survival, and growth is limited and frequently anecdotal. Following a widespread post-fire establishment event in southern Utah, we explored spatial establishment patterns of >1000 aspen seedlings and tracked their survival and growth for two growing seasons. Specifically, we assessed the influence of landscape-level variables, microsite factors, and competition with suckers on aspen seedling establishment, survival, and growth. Aspen seedlings occurred across large areas of the 29,000 ha fire footprint, with an average plot density of 23,033 seedlings ha-1, and establishment more likely at higher elevations and closer to seed sources. Aspen seedlings preferentially established in concave microsites and were tightly associated with burned soil. A total of 33% of tagged seedlings remained alive after two growing seasons. Seedling persistence was strongly impacted by competition with co-occurring aspen suckers, with survival lower for aspen seedlings closer to nearby suckers and seedling growth reduced in plots with high sucker density. Given the long dispersal distances of aspen seeds and the ability of seeds to take advantage of initial post-disturbance conditions, sexual regeneration in aspen may represent an important pathway for maintaining forest resilience and associated ecosystem services, especially following fires with large patches of high burn severity.

Sexual regeneration is increasingly recognized as an important regeneration pathway for aspen in the western United States, a region previously thought to be too dry for seedling establishment except for during unusually wet periods. Because of this historical assumption, information on aspen seedling establishment and factors influencing its occurrence is limited and frequently anecdotal. We conducted a systematic field survey of 15 recent fire footprints that burned in 2018 in the western United States to quantify how common aspen seedling establishment is following fire and to identify factors associated with establishment. We found aspen seedling establishment in 12 of 15 (80%) of fire footprints surveyed, although densities were mostly low. Establishment probability was positively associated with mean annual precipitation and negatively associated with seed-source distance and the density of asexual aspen regeneration. Our results suggest that aspen seedling establishment may be a widespread, if often low-density, feature in postdisturbance areas. Even in low numbers, aspen seedlings may play a disproportionately large role in aspen regeneration ecology, providing adaptive capacity and facilitating local range expansion.

Sustaining the terrestrial carbon (C) sink requires knowledge of the forest properties supporting stable production under increasingly variable climate conditions. We examined how stand disturbance history and age, structural complexity and species diversity, and leaf properties relate to the 10-yr stability of above-ground wood net primary production (NPPw) in northern temperate forests of Michigan, USA. Our investigation centered on separate deciduous, evergreen, and mixed late successional stands initiated over a century ago and free of recent disturbance, a "Cut Only" chronosequence established following clearcut harvesting, and a "Cut and Burn" chronosequence that regenerated following experimental clearcut harvesting and fire. The temporal stability of stand production was calculated from the 10-yr coefficient of variation (CV) of annual NPPw estimated from tree cores; canopy rugosity, a measure of structural complexity, was estimated using terrestrial LiDAR; and > 1500 subcanopy leaves were sampled for leaf mass area and chlorophyll fluorescence intensity. The temporal stability of stands differed by > 2-fold, from 5% to 11% CV of NPPw. Counter to expectations, we found that NPPw stability was greatest in the more severely disturbed Cut and Burn stands and lowest in late successional stands. Despite similar successional patterns of species diversity and structural complexity, NPPw stability increased in Cut Only stands and declined in Cut and Burn stands as age, diversity and canopy rugosity increased. The NPPw of more diverse, late successional deciduous forests was more temporally stable than that of evergreen forests. We conclude that management for maximal rates of production may not confer temporal stability, indicating future studies are needed to elucidate the stand and canopy properties that support both high production rates and stability.

Quaking aspen is a common component of postdisturbance landscapes, in part because of its ability to regenerate via asexual suckers. Previously viewed as exceedingly rare in the western United States, sexual seedling establishment is increasingly seen as another important natural regeneration pathway for aspen, because sexual regeneration increases genetic diversity and facilitates long-distance dispersal. However, aspen seedling research is hampered by difficulties in visually distinguishing seedlings from suckers in the field, and few resources exist to guide managers and researchers. We present methods for distinguishing aspen seedlings from aspen suckers, suitable for use in field studies. Using these methods, we achieved 99 percent predictive accuracy in a recently burned area in southern Utah, although accuracy decreased to 90 percent following one summer's growth, as seedlings and suckers became more similar in appearance. Study Implication: Sexual regeneration may play an important role in aspen's response to climate change, as it increases genetic diversity and adaptive capacity, and allows aspen populations and their ecological associates to better track changing climate through increased dispersal distances. The methods we present allow managers and researchers to accurately identify aspen seedling populations, which can then be protected and monitored through time to better understand aspen demography and the factors limiting establishment and survival of new clones. Aspen seedling ecology is an area with many knowledge gaps currently, and these methods remove a barrier that has hindered research in the past.

Globally, planted forests are rapidly replacing naturally regenerated stands but the implications for canopy structure, carbon (C) storage, and the linkages between the two are unclear. We investigated the successional dynamics, interlinkages and mechanistic relationships between wood net primary production (NPPw) and canopy structure in planted and naturally regenerated red pine (Pinus resinosa Sol. ex Aiton) stands spanning ≥ 45 years of development. We focused our canopy structural analysis on leaf area index (LAI) and a spatially integrative, terrestrial LiDAR-based complexity measure, canopy rugosity, which is positively correlated with NPPw in several naturally regenerated forests, but which has not been investigated in planted stands. We estimated stand NPPw using a dendrochronological approach and examined whether canopy rugosity relates to light absorption and light–use efficiency. We found that canopy rugosity increased similarly with age in planted and naturally regenerated stands, despite differences in other structural features including LAI and stem density. However, the relationship between canopy rugosity and NPPw was negative in planted and not significant in naturally regenerated stands, indicating structural complexity is not a globally positive driver of NPPw. Underlying the negative NPPw-canopy rugosity relationship in planted stands was a corresponding decline in light-use efficiency, which peaked in the youngest, densely stocked stand with high LAI and low structural complexity. Even with significant differences in the developmental trajectories of canopy structure, NPPw, and light use, planted and naturally regenerated stands stored similar amounts of C in wood over a 45-year period. We conclude that widespread increases in planted forests are likely to affect age-related patterns in canopy structure and NPPw, but planted and naturally regenerated forests may function as comparable long-term C sinks via different structural and mechanistic pathways.