Fire Severity Research Articles

Shaded fuel breaks create wildfire-resilient forest stands: lessons from a long-term study in the Sierra Nevada

BackgroundIn California’s mixed-conifer forests, fuel reduction treatments can successfully reduce fire severity, bolster forest resilience, and make lasting changes in forest structure. However, current understanding of the duration of treatment effectiveness is lacking robust empirical evidence. We leveraged data collected from 20-year-old forest monitoring plots within fuel treatments that captured a range of wildfire occurrence (i.e., not burned, burned once, or burned twice) following initial plot establishment and overstory thinning and prescribed fire treatments.ResultsInitial treatments reduced live basal area and retained larger-diameter trees; these effects persisted throughout the 20-year study period. Wildfires maintained low surface and ground fuel loads established by treatments. Treatments also reduced the probability of torching immediately post-treatment and 20 years post initial thinning treatments.ConclusionsFuel treatments in conifer-dominated forests can conserve forest structure in the face of wildfire. Additionally, findings support that the effective lifespans of treatments can be extended by wildfire occurrence. Our results suggest that continued application of shaded fuel breaks is not only a sound strategy to ensure forest persistence through wildfire but may also be compatible with restoration objectives aimed at allowing for the use of more ecologically beneficial fire across landscapes.

Fire severity as a key determinant of aboveground and belowground biological community recovery in managed even-aged boreal forests.

Changes in fire regime of boreal forests in response to climate warming are expected to impact postfire recovery. However, quantitative data on how managed forests sustain and recover from recent fire disturbance are limited.Two years after a large wildfire in managed even-aged boreal forests in Sweden, we investigated how recovery of aboveground and belowground communities, that is, understory vegetation and soil microbial and faunal communities, responded to variation in the severity of soil (i.e., consumption of soil organic matter) and canopy fires (i.e., tree mortality).While fire overall enhanced diversity of understory vegetation through colonization of fire adapted plant species, it reduced the abundance and diversity of soil biota. We observed contrasting effects of tree- and soil-related fire severity on survival and recovery of understory vegetation and soil biological communities. Severe fires that killed overstory Pinus sylvestris promoted a successional stage dominated by the mosses Ceratodon purpureus and Polytrichum juniperinum, but reduced regeneration of tree seedlings and disfavored the ericaceous dwarf-shrub Vaccinium vitis-idaea and the grass Deschampsia flexuosa. Moreover, high tree mortality from fire reduced fungal biomass and changed fungal community composition, in particular that of ectomycorrhizal fungi, and reduced the fungivorous soil Oribatida. In contrast, soil-related fire severity had little impact on vegetation composition, fungal communities, and soil animals. Bacterial communities responded to both tree- and soil-related fire severity. Synthesis: Our results 2 years postfire suggest that a change in fire regime from a historically low-severity ground fire regime, with fires that mainly burns into the soil organic layer, to a stand-replacing fire regime with a high degree of tree mortality, as may be expected with climate change, is likely to impact the short-term recovery of stand structure and above- and belowground species composition of even-aged P. sylvestris boreal forests.

Contrasting effects of urbanization and fire on understory plant communities in the natural and wildland–urban interface

AbstractAs human populations expand and land‐use change intensifies, terrestrial ecosystems experience concurrent disturbances (e.g., urbanization and fire) that may interact and compound their effects on biodiversity. In the urbanizing landscapes of the southern Appalachian region of the United States of America (US), fires in mesic forests have become more frequent in recent years. However, 80 years of forest management practices aimed at fire suppression in this region may have decreased landscape resistance or resilience to high‐severity fires. At the same time, housing development is rapidly expanding in the wildland–urban interface, creating opportunities to examine the combined effects of urbanization and fire disturbances on plant communities when fires occur. Here, we investigated how understory plant communities were affected by a fire that varied in severity at sites in Gatlinburg, TN, and in the adjacent Great Smoky Mountains National Park. Our goal was to investigate the individual and combined effects of fire and urbanization on plant community composition in the second growing season after a fire. Overall, we found a significant interaction effect of fire severity and urbanization on total plant abundance and richness, such that increasing fire severity was associated with lower abundance and richness in natural areas but higher abundance and richness in exurban areas. Shannon diversity was significantly affected by fire severity and urbanization, but not interactively. Plant composition was affected by fire severity, urbanization, and their interaction effects. Understory plant communities in exurban locations (low‐density residential areas near protected lands) were resilient following the pulse disturbance event (fire), likely because of their consistent exposure to a press disturbance (urbanization). Our study indicates a press disturbance may change the way a subsequent pulse disturbance affects plant communities. Our findings contribute new insights into how disturbances can interact to alter patterns of biodiversity in the southeastern US.

Early natural tree regeneration after wildfire in a Central European Scots pine forest: Forest management, fire severity and distance matters

In the last years, several wildfires destroyed large areas in Central European forest stands and the risk for fires is predicted to increase in the future. However, little is known about post-fire succession including the effect of forest management for this region. We studied recolonization patterns of natural regeneration of the pioneer tree species Betula pendula Roth (silver birch), Pinus sylvestris L. (Scots pine), Populus tremula L. (European aspen) and Salix caprea L. (goat willow) on 200 plots in a large, 334 ha burned pine forest stand two years after a severe wildfire. Natural regeneration in general was high, reaching higher densities than artificial regeneration on most plots. The influence of fire severity, post-fire forest management (complete and partial salvage logging and soil disturbance like skidder traffic, ploughing and raking) and distance to the next potential seed source on the number of tree regeneration was tested with multiple linear regression. High fire severities decreased abundance of pine, aspen and willow. The regeneration of all four investigated tree species was influenced by forest management. High birch regeneration was predicted for completely salvage logged plots in combination with skidder traffic or early ploughing and plots without any forest management. Pine regeneration was predicted to be highest on completely salvage logged and sites without any salvage logging. Forest management which includes partial salvage logging showed mostly lower predicted regeneration of birch, pine and aspen as probably an effect of timing. Willow regeneration was promoted by forest management which includes late ploughing. Regeneration of birch and pine decreased with increasing distance to the next potential seed tree, while aspen and willow sapling densities were not affected by distance due to their excellent dispersal by wind. For birch and especially pine, close seed trees are crucial for sufficient natural regeneration. Recolonization of burned areas is a highly dynamic process dependent on several factors. However, natural regeneration provides a fast, cost-effective way of reforestation which can be facilitated by suitable silvicultural treatments. We recommend to keep survived trees as green islands on site to provide close seed sources. To avoid seedling disturbance, forest management activities should be complied according to life cycles of naturally established tree seedlings. We also suggest using the benefits of deciduous pioneer trees in forestry in order to establish more diverse, less fire-prone forests after wildfires in the long term.

Forest Fire Mapping Using Multi-Source Remote Sensing Data: A Case Study in Chongqing

Forest fires are one of the most severe natural disasters facing global ecosystems, as they have a significant impact on ecological security and social development. As remote sensing technology has developed, burned areas can now be quickly extracted to support fire monitoring and post-disaster recovery. This study focused on monitoring forest fires that occurred in Chongqing, China, in August 2022. The burned area was identified using various satellite images, including Sentinel-2, Landsat8, Environmental Mitigation II A (HJ2A), and Gaofen-6 (GF-6). The burned area was extracted using visual interpretation, differenced Normalized Difference Vegetation Index (dNDVI), and differenced Normalized Burnup Ratio (dNBR). The results showed that: (1) The results of the three monitoring methods were very consistent, with a coefficient of determination R2 > 0.96. (2) A threshold method based on the dNBR-extracted burned area was used to analyze fire severity, with moderate-severity fires making up the majority (58.05%) of the fires. (3) Different topographic factors had some influence on the severity of the forest fires. High elevation, steep slopes and the northwestern aspect had the largest percentage of burned area.

Trends, Impacts, and Cost of Catastrophic and Frequent Wildfires in the Sagebrush Biome

Fire regimes in sagebrush (Artemisia spp.) ecosystems have been greatly altered across the western United States. Broad-scale invasion of non-native annual grasses, climate change, and human activities have accelerated wildfire cycles, increased fire size and severity, and lengthened fire seasons in many sagebrush ecosystems to the point that current wildfire-management practices and postfire restoration efforts cannot keep pace to ameliorate the ecological consequences of sagebrush ecosystem loss. The greatest impact of uncharacteristically frequent fire is the transition from native sagebrush-perennial grass communities to invasive, non-native, annual grasslands that are highly flammable. These community transitions are often permanent, owing to the low probability of reestablishing native perennial plants in non-native annual grass−dominated communities. Moreover, these grasses can form extensive and continuous fine fuel loads that promote more frequent fire and the continued expansion of invasive, non-native annuals. More frequent, larger, and severe wildfires necessitate greater resources for fire-prevention, fire-suppression, and postfire restoration activities, while decreasing critical ecosystem services, economic and recreational opportunities, and cultural traditions. Increased flexibility and better prioritization of management activities based on ecological needs, including commitment to long-term prefire and postfire management, are needed to achieve notable reductions in uncharacteristic wildfire activity and associated negative impacts. Collaboration and partnerships across jurisdictional boundaries, agencies, and disciplines can improve consistency in sagebrush-management approaches and thereby contribute to this effort. Here, we provide a synthesis on sagebrush wildfire trends and the impacts of uncharacteristic fire regimes on sagebrush plant communities, dependent wildlife species, fire-suppression costs, and ecosystem services. We also provide an overview of wildland fire coordination efforts among federal, state, and tribal entities.

Time since fire shapes plant immaturity risk across fire severity classes

BackgroundWhen fire intervals are shorter than the time required for plants to reproduce, plant populations are threatened by “immaturity risk.” Therefore, understanding how the time between fires influences plants can inform ecosystem management. Quantifying periods of immaturity risk requires investigating the influence of fire intervals across plant life stages, but most studies are indiscriminate of maturity. As fire regimes are multidimensional, it is also important to consider other characteristics of fires such as severity. We conducted a field study in heathy woodland that investigated how fire severity and fire interval influence immaturity risk to serotinous resprouter species, by examining if fire severity interacts with the time since the fire to influence the occurrence of mature individuals and relative abundance of three species: silver banksia (Banksia marginata Cav.), prickly teatree (Leptospermum continentale Joy Thomps), and heath teatree (Leptospermum myrsinoides Schitdl).ResultsRegression modeling revealed a strong, positive influence of time since the last fire on the proportion of quadrats at a site with mature plants, for all three species. We only detected a small and uncertain influence of fire severity on the proportion of quadrats with mature heath and prickly teatree, and did not observe an effect of fire severity on the maturity of silver banksia. Interestingly, no relationships were observed between time since fire and the relative abundance of plants. That is, only when plant life stages were considered did we detect an effect of fire on plants. Populations of the three species were mostly immature in the first 7 years post-fire, suggesting if sites were uniformly burnt in this time frame, there could be increased risk of local extinctions.ConclusionsOur study highlights the importance of examining population processes, such as reproduction, in addition to plant relative abundance. Surprisingly, we did not detect strong differences in plant maturation across fire severity classes; low occurrence of mature plants in recently burnt areas indicated that immaturity risk was high, regardless of fire severity. Ecological studies that distinguish between plant life stages will help to predict the impacts of fire on populations and enhance decision-making. We recommend fire intervals of ≥ 8 years to protect serotinous resprouter plants in heathy woodland vegetation of southern Australia.

Severe wildfires promoted by climate change negatively impact forest amphibian metacommunities

AbstractAimChanges to the extent and severity of wildfires driven by anthropogenic climate change are predicted to have compounding negative consequences for ecological communities. While there is evidence that severe weather events like drought impact amphibian communities, the effects of wildfire on such communities are not well understood. The impact of wildfire on amphibian communities and species is likely to vary, owing to the diversity of their life‐history traits. However, no previous research has identified commonalities among the amphibians at most risk from wildfire, limiting conservation initiatives in the aftermath of severe wildfire. We aimed to investigate the impacts of the unprecedented 2019–2020 black summer bushfires on Australian forest amphibian communities.LocationEastern coast of New South Wales, Australia.MethodsWe conducted visual encounter surveys and passive acoustic monitoring across 411 sites within two regions, one in northeast and one in southeast New South Wales. We used fire severity and extent mapping in two multispecies occupancy models to assess the impacts of fire on 35 forest amphibian species.ResultsWe demonstrate a negative influence of severe fire extent on metacommunity occupancy and species richness in the south with weaker effects in the north—reflective of the less severe fires that occurred in this region. Both threatened and common species were impacted by severe wildfire extent. Occupancy of burrowing species and rain forest specialists had mostly negative relationships with severe wildfire extent, while arboreal amphibians had neutral relationships.Main ConclusionMetacommunity monitoring and adaptive conservation strategies are needed to account for common species after severe climatic events. Ecological, morphological and life‐history variation drives the susceptibility of amphibians to wildfires. We document the first evidence of climate change‐driven wildfires impacting temperate forest amphibian communities across a broad geographic area, which raises serious concern for the persistence of amphibians under an increasingly fire‐prone climate.

Primary and pharmaceutical care usage concurrent associations with a severe smoke episode and low ambient air pollution in early life

BACKGROUND: Due to climate change, landscape fires account for an increasing proportion of air pollution emissions, and their impacts on primary and pharmaceutical care are little understood.OBJECTIVES: To evaluate associations between exposure in two early life periods to severe levels of PM2.5 from a mine fire, background PM2.5, and primary and pharmaceutical care.METHODS: We linked records of births, general practitioner (GP) presentations and prescription dispensing for children born in the Latrobe Valley, Australia, 2012–2014, where a severe mine fire occurred in February–March 2014 in an area with otherwise low levels of ambient PM2.5. We assigned modelled exposure estimates for fire-related (cumulative over the fire and peak 24-hour average) and annual ambient PM2.5 to residential address. Associations with GP presentations and dispensing of prescribed medications in the first two years of life (exposure in utero) and in the two years post-fire (exposure in infancy) were estimated using two-pollutant quasi-Poisson regression models.RESULTS: Exposure in utero to fire-related PM2.5 was associated with an increase in systemic steroid dispensing (Cumulative: IRR = 1.11, 95%CI = 1.00–1.24 per 240 μg/m3; Peak: IRR = 1.15, 95%CI = 1.00–1.32 per 45 μg/m3), while exposure in infancy was associated with antibiotic dispensing (Cumulative: IRR = 1.05, 95%CI = 1.00–1.09; Peak: IRR = 1.06, 95%CI = 1.00–1.12). Exposure in infancy to ambient PM2.5, despite relatively low levels from a global perspective (Median = 6.1 μg/m3), was associated with an increase in antibiotics (IRR = 1.10, 95%CI = 1.01–1.19 per 1.4 μg/m3) and in GP presentations (IRR = 1.05, 95%CI = 1.00–1.11), independently from exposure to the fire. We also observed differences in associations between sexes with GP presentations (stronger in girls) and steroid skin cream dispensing (stronger in boys).DISCUSSION: Severe medium-term concentrations of PM2.5 were linked with increased pharmaceutical treatment for infections, while chronic low levels were associated with increased prescriptions dispensed for infections and primary care usage. Our findings also indicated differences between sexes.

Vegetation recovery drivers at short-term after fire are plant community-dependent in mediterranean burned landscapes

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.

What is the color when black is burned? Quantifying (re)burn severity using field and satellite remote sensing indices

BackgroundTrends of increasing area burned in many regions worldwide are leading to more locations experiencing short-interval reburns (i.e., fires occurring two or more times in the same place within 1–3 decades). Field and satellite indices of burn severity are well tested in forests experiencing a single recent fire, but the reliability of these indices in short-interval reburns is poorly understood. We tested how a commonly used field index (the Composite Burn Index, CBI) and satellite index (the Relative differenced Normalized Burn Ratio, RdNBR) compared to eight individual field measures of burn severity in short-interval reburns vs. areas burned in one recent fire, and whether results depended on whether the first fire was stand replacing (fire that is lethal to most dominant trees).ResultsCorrespondence between both CBI and RdNBR with individual burn severity measures differed in short-interval reburns compared to single fires for some metrics of burn severity. Divergence in the relationship between both CBI and RdNBR vs. field measures was greatest when short-interval reburns followed a prior stand-replacing fire, and measures were more comparable to single fires when the first fire was non-stand replacing (i.e., lower severity). When short-interval reburns followed prior stand-replacing fires, CBI and RdNBR underestimated burn severity in the second fire for tree-canopy metrics (e.g., canopy cover loss, tree mortality), as young forests in early developmental stages are more sensitive to a second fire. Conversely, when short-interval reburns followed prior less-than-stand-replacing fires, both CBI and RdNBR overestimated burn severity for forest-floor metrics, as past low severity fires leave behind live fire-resistant trees and can stimulate resprouting understory vegetation. Finally, neither CBI nor RdNBR accurately detected deep wood charring—an important phenomenon that occurs in short-interval reburns.ConclusionOur findings inform interpretability of commonly used indices of burn severity in short-interval reburns by identifying how individual burn severity metrics can be under- or over-estimated, depending on the severity of the fire preceding a reburn. Adjustments to burn severity measurements made in short-interval reburns are particularly critical as reburned areas increase.

Short-term drivers of post-fire forest regeneration in the Western Alps

BackgroundThe Mediterranean basin is currently facing major changes in fire regimes as a result of climate and land-use changes. These alterations could affect the ability of forests to recover after a fire, hence triggering degradation processes and modifying the provision of fundamental ecosystem services. Examining patterns and drivers of post-fire forest recovery, particularly for obligate seeders without specific fire-adaptive traits, thus becomes a priority for researchers and land managers. We studied the post-fire dynamics of Scots pine (Pinus sylvestris L.) stands affected by a mixed-severity fire in North-Western Italy, aiming to understand the impact of fire on soil properties and assess drivers, spatial distribution, and characteristics of short-term post-fire recovery.ResultsWe observed that fire did not significantly affect soil organic carbon (OC) content, while we detected significantly lower nitrogen (N) content in severely burnt sites. Regeneration density was particularly abundant in medium-severity areas, while it drastically decreased in high-severity patches. The most abundant tree species in the regeneration layer was Scots pine, followed by goat willow (Salix caprea L.), European aspen (Populus tremula L.), and, to a lesser extent, European larch (Larix decidua Mill.). Slope, fire severity, and distance from seed trees emerged as the most important drivers of post-fire forest regeneration patterns.ConclusionsOur results highlight the importance of preserving seed trees from salvage logging, even if they are damaged and have a low survival probability. Active post-fire management, such as tree planting, should be limited to large and severely burnt patches, where natural forest regeneration struggles to settle, increasing the risk of ecosystem degradation. These findings could be useful for informing land managers, helping them to enhance potential mitigation strategies in similar ecosystems and plan appropriate restoration approaches.

Carbon emissions and radiative forcings from tundra wildfires in the Yukon–Kuskokwim River Delta, Alaska

Abstract. Tundra environments are experiencing elevated levels of wildfire, and the frequency is expected to keep increasing due to rapid climate change in the Arctic. Tundra wildfires can release globally significant amounts of greenhouse gasses that influence the Earth's radiative balance. Here we develop a novel method for estimating carbon loss and the resulting radiative forcings of gaseous and aerosol emissions from the 2015 tundra wildfires in the Yukon–Kuskokwim Delta (YKD), Alaska. We paired burn depth measurements using two vegetative reference points that survived the fire event – Sphagnum fuscum and Dicranum spp. – with measurements of local organic matter and soil carbon properties to estimate total ecosystem organic matter and carbon loss. We used remotely sensed data on fire severity from Landsat 8 to scale our measured losses to the entire fire-affected area, with an estimated total loss of 2.04 Tg of organic matter and 0.91 Tg of carbon and an average loss of 3.76 kg m−2 of organic matter and 1.68 kg m−2 of carbon in the 2015 YKD wildfires. To demonstrate the impact of these fires on the Earth's radiation budget, we developed a simple but comprehensive framework to estimate the radiative forcing from Arctic wildfires. We synthesized existing research on the lifetime and radiative forcings of gaseous and aerosol emissions of CO2, N2O, CH4, O3 and its precursors, and fire aerosols. The model shows a net positive cumulative mean radiative forcing of 3.67 W m−2 using representative concentration pathway (RCP) 4.5 and 3.37 W m−2 using RCP 8.5 at 80 years post-fire, which was dominated by CO2 emissions. Our results highlight the climate impact of tundra wildfires, which positively reinforce climate warming and increased fire frequency through the radiative forcings of their gaseous emissions.

The extreme forest fires in California/Oregon in 2020: Aerosol optical and physical properties and comparisons of aged versus fresh smoke

Wildfire activity in the western United States during August to October 2020 was exceptional in terms of the fire severity and area burned. Extremely dry biomass fuels from near historic multi-year drought conditions were further exacerbated with very hot and dry conditions in 2020. These conditions when coupled with strong offshore flow allowed many ignitions to grow into extremely large and severe wildfires. Long-term monitoring at a few AERONET sites in California showed that the number of days with high Aerosol Optical Depth at 440 nm (AOD440>1) in 2020 was greater than any other year going back to the beginning of the data records in 2002. A wide range of fine mode particle volume median radii were retrieved from AERONET data over the course of these fires suggesting significant variability in combustion conditions and aging processes. Additionally, the fine mode radii in some of these smoke plumes in 2020 were very large especially at high AOD (∼0.22–0.32 μm volume median radius), likely due to both coagulation and condensation occurring during aging at very high particulate concentrations. The largest fine mode particle radii combined with narrow distributions resulted in some very rare AOD spectra showing peak AOD at 500 nm and decreasing to lower AOD at both shorter and longer wavelengths. The most extreme retrieved size distributions and associated measured AOD spectra were principally observed in long-distance transported smoke plumes from these western United States fires at sites in Colorado, Maryland and Virginia, possibly due to further aging during transport. Additionally, strong absorption was sometimes observed at short wavelengths with much lower single scattering albedo at 440 nm compared to 675 nm in some plumes consistent with significant brown carbon (BrC) and/or coated black carbon (BC) absorption in biomass burning particles. This strong spectral absorption signature observed at some California sites and dates remained similarly strong in some smoke plumes observed at some east coast sites in Maryland and Virginia, thereby suggesting that the lifetime of these particular BrC and/or coated BC absorbing species was greater than 5 days.

A multi‐scale assessment of forest treatment impacts on evapotranspiration and water yield in the Sierra Nevada

AbstractThe future of the Western United States is threatened by both an increase in wildfire frequency and a decrease in water availability. By reducing fuel loads, wildfire mitigation measures (forest treatments) can offer reduced fire severity and increased annual total runoff (water yield) via reduction in evapotranspiration (ET). While the benefits of forest treatments for fire management are well studied, their impact on ET and water yield remains largely unknown, and existing literature shows conflicting results. Here, we aim to resolve this ambiguity by quantifying the impact of forest treatments on ET and water yield, at spatially localized scales. Using daily average flow rates from sub‐basin and basin scale gauges, 100‐m LiDAR data, 800‐m PRISM precipitation data and 30‐m SSEBop ETa data, we analysed the impact of forest treatments on ETa and water yield in the Sagehen Experimental Watershed. Within treated areas of Sagehen, there is a linear relationship between loss of canopy cover and ETa reductions at the 100‐m pixel scale when canopy cover loss exceeds 10%. The impact of treatment was highly localized, and across the entire watershed (30 km2), treated areas with reduced ETa only made up 4 km2, ~10% of the Sagehen area. At sub‐basin and basin scale, the magnitude of year‐to‐year ETa reduction was <15%, and there was no quantifiable increase in water yield. Instead, precipitation alone explained 85% of water yield variability at sub‐basin and basin scale. Future forest management practices in the Sierra Nevada are essential for combating wildfire, but our results from Sagehen reveal that even at the sub‐basin scale (~3 km2), 56% thinning treatment by area did not result in increased water yield.

Post‐wildfire coastal dunefield response using photogrammetry and satellite indices

AbstractFire has been suggested to be an initiation mechanism of landscape instability and coastal dune transgression, but modern evidence showing a shift to a transgressive dune phase is lacking. Following the largest wildfire in historical records on Kangaroo Island, South Australia, bimonthly uncrewed aerial vehicle (UAV) surveys were conducted on three coastal dune sites to study their post‐fire responses. The three sites studied here represent the landscape diversity of the temperate dunes of Kangaroo Island with both active coastal and inland relict stabilised dune fields studied. UAV surveys were used to reconstruct landscapes with structure from motion (SfM) photogrammetry and compared over time to illustrate significant changes in the landscape. The geomorphic and vegetation changes are compared in net and intra‐survey comparisons to illustrate the post‐fire dunefield response and trends towards stabilisation. Because of a lack of reliable baseline pre‐fire data, satellite geomedians are used to compute spectral indices to show the trajectory of ground cover in the study sites in the years preceding and following the fire. Satellite indices are used to separate 3D changes according to ground cover types and show their differing post‐fire responses. Local and regional wind, temperature and rainfall records are presented to provide weather patterns of the years preceding and following the fire, illustrating the wet and mild post‐fire weather. The overall results indicate no significant landscape instability across the studied sites and that the ground cover of vegetation is nearing pre‐fire baselines, showing that a severe fire has not caused a transgressive dunefield to develop.

Exploration of the Burning Question: A Long History of Fire in Eastern Australia with and without People

Ethnographic observations suggest that Indigenous peoples employed a distinct regime of frequent, low-intensity fires in the Australian landscape in the past. However, the timing of this behaviour and its ecological impact remain uncertain. Here, we present detailed analysis of charcoal, including a novel measure of fire severity using Fourier transform infrared (FTIR) spectroscopy, at a site in eastern Australia that spans the last two glacial/interglacial transitions between 135–104 ka and 18–0.5 ka BP (broadly equivalent to Marine Isotope Stage (MIS) 6-5 and 2-1, respectively). The accumulation of charcoal and vegetation composition was similar across both periods, correlating closely with Antarctic ice core records, and suggesting that climate is the main driver of fire regimes. Fire severity was lower over the past 18,000 years compared to the penultimate glacial/interglacial period and suggests increasing anthropogenic influence over the landscape during this time. Together with local archaeological records, our data therefore imply that Indigenous peoples have been undertaking cultural burning since the beginning of the Holocene, and potentially the end of the Last Glacial Maximum. We highlight the fact that this signal is not easily discernible in the other proxies examined, including widely used charcoal techniques, and propose that any anthropogenic signal will be subtle in the palaeo-environmental record. While early Indigenous people’s reasons for landscape burning were different from those today, our findings nonetheless suggest that the current land management directions are based on a substantive history and could result in a reduction in extreme fire events.

Less fuel for the next fire? Short-interval fire delays forest recovery and interacting drivers amplify effects.

As 21st-century climate and disturbance dynamics depart from historic baselines, ecosystem resilience is uncertain. Multiple drivers are changing simultaneously, and interactions among drivers could amplify ecosystem vulnerability to change. Subalpine forests in Greater Yellowstone (Northern Rocky Mountains, USA) were historically resilient to infrequent (100-300 year), severe fire. We sampled paired short-interval (<30-year) and long-interval (>125-year) post-fire plots most recently burned between 1988 and 2018 to address two questions: (1) How do short-interval fire, climate, topography, and distance to unburned live forest edge interact to affect post-fire forest regeneration? (2) How do forest biomass and fuels vary following short-interval versus long-interval severe fires? Mean post-fire live tree stem density was an order of magnitude lower following short-interval versus long-interval fires (3240 vs. 28,741 stems ha-1 , respectively). Differences between paired plots were amplified at longer distances to live forest edge. Surprisingly, warmer-drier climate was associated with higher seedling densities even after short-interval fire, likely relating to regional variation in serotiny of lodgepole pine (Pinus contorta var. latifolia). Unlike conifers, density of aspen (Populus tremuloides), a deciduous resprouter, increased with short-interval versus long-interval fires (mean 384 vs. 62 stems ha-1 , respectively). Live biomass and canopy fuels remained low nearly 30 years after short-interval fire, in contrast with rapid recovery after long-interval fire, suggesting that future burn severity may be reduced for several decades following reburns. Short-interval plots also had half as much dead woody biomass compared with long-interval plots (60 vs. 121 Mg ha-1 ), primarily due to the absence of large snags. Our results suggest differences in tree regeneration following short-interval versus long-interval fires will be especially pronounced where serotiny was high historically. Propagule limitation will also interact with short-interval fires to diminish tree regeneration but lessen subsequent burn severity. Amplifying driver interactions are likely to threaten forest resilience under expected trajectories of a future fire.

Climate and fire impacts on tree recruitment in mixed conifer forests in Northwestern Mexico and California.

Frequent-fire forests were once heterogeneous at multiple spatial scales, which contributed to their resilience to severe fire. While many studies have characterized historical spatial patterns in frequent-fire forests, fewer studies have investigated their temporal dynamics. We investigated the influences of fire and climate on the timing of conifer recruitment in old-growth Jeffrey pine-mixed conifer forests in the Sierra San Pedro Martir (SSPM) and the eastern slope of Sierra Nevada. Additionally, we evaluated the impacts of fire exclusion and recent climate change on recruitment levels using statistical models with realized as well as fire suppression and climate change free counterfactual scenarios. Excessive soil drying from anthropogenic climate change resulted in diminished recruitment in the SSPM but not in the Sierra Nevada. Longer fire-free intervals attributable to fire suppression and exclusion resulted in greater rates of recruitment across all sites but was particularly pronounced in the Sierra Nevada where suppression began > 100 years ago and recruitment was 28 times higher than the historical fire return interval scenario. This demonstrates the profound impact of fire's removal on tree recruitment in Sierra Nevada forests even in the context of recent climate change. Tree recruitment at the SSPM coincided with the early Twentieth Century North American Pluvial, as well as a fire quiescent period in the late 18th and early 19th centuries. Episodic recruitment occurred in the SSPM with no 'average' recruitment over the last three centuries. We found that temporal heterogeneity, in conjunction with spatial heterogeneity, are critical components of frequent-fire adapted forests. Episodic recruitment could be a desirable characteristic of frequent-fire adapted forests and this might be more amenable to climate change impacts that forecast more variable precipitation patterns in the future. One key to this outcome would be for frequent-fire to continue to shape these forests versus continued emphasis on fire suppression in California.

Process safety management lessons learned from a fire and explosion accident caused by a liquefied petroleum gas leak in an aromatics reforming unit in Taiwan

A severe fire and explosion accident was caused by a liquefied petroleum gas leak in Taiwan in 2019. This accident resulted in the loss of approximately US$3.5 billion in output value due to a one-and-a-half-year shutdown after the accident; however, no casualties were recorded at the accident scene. An analysis of the accident pipelines demonstrated that the pipeline leak had been caused by hydrochloric acid corrosion. Cause analysis based on the accident timeline, fault tree analysis, and causal factor charting indicated inadequacies in five elements of process safety management (PSM) namely mechanical integrity (MI), management of change, emergency planning and response, process hazard analysis (PHA), and process safety information (PSI) as the root causes of the accident. Furthermore, insufficient PSI (i.e., a lack of comprehensive understanding regarding corrosion mechanisms) was deemed to have been the core problem leading to the accident. This accident revealed common shortcomings that are often overlooked in PSM implementation in Taiwan; thus, the present research can serve as a vital reference for improving PSM programs in Taiwan.