Fire Activity Research Articles

Fire Impacts on Recruitment Dynamics in a Seasonal Tropical Forest in Continental Southeast Asia

The effects of forest fires on tree recruitment dynamics in tropical forests is important for predicting forest dynamics and ecosystem function in Southeast Asia. To our knowledge, no studies have examined the effects of fire intensity on community-level recruitment patterns in tropical forests due to the rarity of long-term observation datasets in fire-impacted tropical forests and the difficulty of quantifying fire intensity. We addressed two questions: (1) is tree recruitment among species affected by fire intensity? and if so, (2) are there specific plant functional traits associated with these responses? We used data from a long-term forest dynamics plot at the Huai Kha Khaeng (HKK) Wildlife Sanctuary in Thailand. The HKK plot occurs in a strongly seasonal tropical environment and has experienced several fires since its establishment in 1994. We found 46 tree species (52% of the 89 species analysed) showed evidence of reduced recruitment rates with increasing fire intensities during the most recent fire in 2005. Tree species in this flammable landscape have various leaf and wood functional traits associated with fire. Spatial and temporal variability in fire activity may lead to alterations in long-term taxonomic and functional composition of the forest due to selection on fire-related traits.

Landscape dynamics and fire regime since 17,550 cal yr BP in the Cantabrian region (La Molina peat bog, Puente Viesgo, Spain)

Our aim with this paper is to provide insight into the landscape dynamics of the Cantabrian region (northern Iberian Peninsula) from the Last Glacial Period to the present. We present a multiproxy approach performed in a sedimentary record from La Molina peat bog, located at 484 m a. s. l. in Puente Viesgo, Cantabria (Latitude: 43.26° N; Longitude: 3.97° W), that covers the last c. 17,550 years. Analyses were performed on the organic matter, pollen and sedimentary charcoals, which have been used to characterise the fire regime at a local level. The results revealed a steppe-like formation from the basis of the sequence to the Bølling-Allerød chronozone, when the spread of woody species is detected. The dry and cold conditions of the Younger Dryas caused the decrease of mesophilous taxa until the onset of the Holocene. From that point onwards, a mixed deciduous formation composed of Betula and deciduous Quercus was established in the region. Besides, a series of biomass pulses was detected during the early Holocene, probably linked to intervals of increased rainfall. Fire episodes detected at the 9.3 and the 8.2 ka events created forest openings and probably favoured the establishment of Corylus, most likely also helped by a climate shift. There was a lack of fire activity until the Neolithic, when the fire signal increased probably linked to grazing and agricultural practices and triggered deeper changes in the Cantabrian plant landscape structure.

Marginal imprint of human land use upon fire history in a mire-dominated boreal landscape of the Veps Highland, North-West Russia

Dendrochronological reconstructions inform us about historical climate-fire-human interactions, providing a means to calibrate projections of future fire hazard. Most of these reconstructions, however, have been developed in landscapes with a considerable proportion of xeric sites that could potentially inflate our estimates of the historic levels of fire activity. We provide a 420-year long reconstruction of fires in a mire-dominated landscape of the Veps Nature Park, North-West Russia. The area has mostly escaped large-scale forestry operations in the past and is an example of pristine mid-boreal vegetation with a high (approximately 30% for the area studied) proportion of waterlogged areas with ombrotropic mires. The historical fire cycle was 91.4 years (90% confidence intervals, CI 66.2–137.6 years) over the 1580–1720 period, decreasing to 35.9 (CI 28.1–47.6 years) between 1730 and 1770, and then increasing again to 122.7 years (CI 91.0–178.0 years) over the 1780–2000 period. Early season fires dominated over late season fires during the reconstruction period. We documented a higher fire activity period between 1730 and 1780, resulting from the increase in early season fires. This period coincided with one of the largest multi-decadal declines in the reconstructed spring precipitation since 1600 CE, although we found no significant relationship between fire and precipitation over the whole reconstructed period. The nine largest fire years were associated with negative summer precipitation and positive summer temperature anomalies over the study region. Land-use history of the area did not appear to have an effect on historical fire dynamics. Modern (1996–2016) fire records indicate a regional fire cycle of ∼ 1300 years, featuring a pronounced pattern with early (April–May) and late (July–September) season fires. The uniform fire cycle in the area since 1780, occurrence of nine largest fire years during years with spring-summer droughts, and low ignition frequencies over the last 420 years (0.005 to 0.037 ignitions per year and km2) suggest that the fire regime of the Veps Highland remained largely natural until the onset of the 20th century.

Lightning patterns in the Pantanal: Untangling natural and anthropogenic-induced wildfires

The identification of fire causes and characteristics is of fundamental importance to better understand fire regimes and drivers. Particularly for Brazil, there is a gap in the quantification of lightning-caused fires. Accordingly, this work is a novel probabilistic assessment of the spatial-temporal patterns of lightning-ignited wildfires in the Pantanal wetland. Here, remote sensing information such as VIIRS active fires, MODIS burned area (BA) and STARNET lightning observations from 2012 to 2017, were combined to estimate the location, number of scars and amount of BA associated with atmospheric discharges on a seasonal basis. The highest lightning activity occurs during summer (December–February), and the lowest during winter (June–August). Conversely, the highest fire activity occurred during spring (September–November) and the lowest during autumn (March–May). Our analysis revealed low evidence of an association between fires and lightning, suggesting that human-related activities are the main source of ignitions. Weak evidence of natural-caused fire occurrence is conveyed by the low spatial-temporal match of lightning and fire throughout the studied period. Natural-caused fires accounted for only 5% of the annual total scars and 83.8% of the BA was human-caused. Most of the fires with extension larger than 1000 ha were not related to lighting. Lightning-fires seem an important element of the summer fire regime given that around half of the total BA during this season may be originated by lightning. By contrast, in the rest of the year the lightning-fires represent a minor percentage of the fire activity in the region. The density of lightning-ignited fires varies considerably, being higher in the north part of the Pantanal. This work provides a basis for a better understanding of lightning-related fire outbreaks in tropical ecosystems, particularly wetlands, which is fundamental to improve region-based strategies for land management actions, ecological studies and modeling climatic and anthropogenic drivers of wildfires.

Population decline in California spotted owls near their southern range boundary

AbstractSpecies worldwide have begun to shift their range boundaries in response to climate change and other anthropogenic causes, with population declines at the trailing edge of a species' range often foreshadowing future changes in core parts of the range. Therefore, we analyzed a 30‐year (1991–2019) data set for the California spotted owl (Strix occidentalis occidentalis) near its southern range boundary in southern California, USA, that included the largest regional population (San Bernardino Mountains) to estimate trends in territory occupancy and reproduction. We then assessed how these demographic rates were affected by habitat, wildfire, fuel treatments, and climate. Mean occupancy declined from 0.82 to 0.39 during our study, whereas reproductive output showed no temporal trends ( young/occupied territory). Territory extinction (extirpation) rates were relatively low in territories with more large trees (≥50 cm dbh), and colonization increased strongly with large tree density for low‐elevation territories within the shrub‐woodland ecotype but not for higher‐elevation territories within mixed‐conifer forest. High‐severity wildfire had an adverse effect on occupancy: territory extinction rates steadily increased with the amount of high‐severity fire within an owl territory during the previous 10 years, while colonization declined to nearly zero when ≥40% of a territory burned at high‐severity during the previous 10 years. The effects of high‐severity fire were unlikely to be confounded with post‐fire fuel treatments, which primarily consisted of the removal, burning, or scattering of brush and small trees and snags (<40.6 cm dbh) and affected much smaller areas than high‐severity fire. Of the 40 territories that received fuel treatments within 10 years of a fire, only 3 of them had post‐fire fuel treatments that affected >5% of the territory, whereas average area burned at high severity for all 40 territories was 17%. Fuel treatments intended to modify fire behavior and reduce the likelihood of large, high‐severity fires led to increases in territory extinction and colonization such that their net effect on occupancy was minimal. Our simulations of occupancy dynamics indicated that high‐severity fire accounted for 9.6% of the observed decline in occupancy, whereas fuel treatments effectively accounted for none of the decline. Spotted owl reproductive output was lower at territories where fuel treatments occurred, but low‐ to moderate‐severity fire resulted in much larger, population‐level reductions in reproductive output (141 fewer young) from 2006–2019 than treatments (19 fewer young). Thus, the benefits of fuel treatments that reduce fire occurrence and severity appear to outweigh potential short‐term costs to spotted owls and their habitat. Because high‐severity fire only explained a modest amount of the long‐term occupancy decline and much of the decline occurred in the 1990s before large fires occurred, additional factors are likely adversely affecting the owl population and merit further study. Nevertheless, the large observed population decline, limited evidence of owl dispersal among mountain ranges in the southern California metapopulation, and negative effects of increasingly large and severe fire suggest that California spotted owls at their southern range boundary are vulnerable to extirpation. In an era of climate change, owls in the core part of the range will likely become increasingly susceptible to warmer temperatures and increased severe fire activity in the future. Thus, the restoration of historical, low‐severity fire regimes through fuels management while maintaining large trees is important to improving owl persistence.

Scandinavian Forest Fire Activity Correlates with Proxies of the Baffin Bay Ice Cover

Understanding factors driving fire activity helps reveal the degree and geographical variability in the resilience of boreal vegetation to large scale climate forces. We studied the association between sea ice cover in the Baffin Bay and the Labrador Sea and observational records of forest fires in two Nordic countries (Norway and Sweden) over 1913–2017. We found a positive correlation between ice proxies and regional fire activity records suggesting that the Arctic climate and the associated changes in North Atlantic circulation exercise an important control on the levels of fire activity in Scandinavia. Changes in the sea cover are likely correlated with the dynamic of the North Atlantic Current. These dynamics may favor the development of the drought conditions in Scandinavia through promoting persistent high-pressure systems over the Scandinavian boreal zone during the spring and summer. These periods are, in turn, associated with an increased water deficit in forest fuels, leading to a regionally increased fire hazard. The Arctic climate will likely be an important future control of the boreal fire activity in the Nordic region.

Future expansion, seasonal lengthening and intensification of fire activity under climate change in southeastern France

Background An increase in fire weather is expected in a warming climate, but its translation to fire activity (fire numbers and sizes) remains largely unknown. Additionally, disentangling the extent to which geographic and seasonal extensions as well as intensification contribute to future fire activity remain largely unknown. Aims We aimed to assess the impact of future climate change on fire activity in southeastern France and estimate changes in spatial and seasonal distributions. Methods We projected future fire activities using a Bayesian modelling framework combined with ensemble climate simulations. Changes in numbers of escaped fires (>1 ha), large fires (>100 ha) and burned area were studied for different emission scenarios or degrees of global warming. Key results Fire activity could increase by up to +180% for +4°C of global warming, with large expansions of fire-prone regions and long seasonal lengthenings. Overall, changes will be dominated by intensification within the historical fire niche, representing two-thirds of additional future fire activity, half of this occurring during the high fire season. Conclusions This study confirms that major changes in fire niches would be expected in Euro-Mediterranean regions. Implications Long-term strategic policies for adapting prevention and suppression resources and ecosystems are needed to account for such changes.

Leveraging NASA Soil Moisture Active Passive for Assessing Fire Susceptibility and Potential Impacts Over Australia and California

Wildfires are a major concern around the globe because of the immediate impact they have on people's lives, local ecosystems, and the environment. Soil moisture is one of the most important factors that influence wildfire occurrences and spread. However, it is also one of the most challenging hydrological variables to measure routinely and accurately. Therefore, soil moisture is significantly underutilized in operational wildfire risk applications. Thus, the aim here is to use a well-established operational soil moisture product to isolate the soil moisture-fire relationship and assess the utility of using soil moisture as a leading indicator of potential fire risk. We evaluated the value of remotely-sensed soil moisture observations from the soil moisture active passive sensor for monitoring and predicting fire risk in Australia and California. We quantified the relationship between observed fire activity and soil moisture conditions and analyzed the soil moisture conditions for two extreme fire events. Our findings show that fire activity is strongly associated with soil moisture anomalies. Lagged correlation analysis demonstrated that a remote-sensing based soil moisture product could predict fire activity with a 1–2 month lead-time. Soil moisture anomalies consistently decreased in the months preceding fire occurrence, often from normal to drier conditions, according to a spatiotemporal analysis of soil moisture in two extreme fire events. Overall, our findings indicate that soil moisture conditions prior to large wildfires can aid in their prediction and operational satellite-based soil moisture products such as the one used here have real value for supporting wildfire susceptibility and impacts.

Disentangling the factors of spatio-temporal patterns of wildfire activity in south-eastern France

Background Identifying if and how climatic and non-climatic factors drive local changes in fire regimes is, as in many other human-dominated landscapes, challenging in south-eastern France where both heterogeneous spatial patterns and complex fire trends are observed. Aim We sought to identify the factors driving the spatial-temporal patterns of fire activity in southeastern France. Methods We incorporated several non-climatic variables into the probabilistic Firelihood model of fire activity and implemented an enhanced spatio-temporal component to quantitatively assess remaining unexplained variations in fire activity. Key results Several non-climatic drivers (i.e. orography, land cover and human activities) contributed as much as fire-weather to the distribution of fire occurrence (>1 ha) but less to larger fires (>10, 100 and 1000 ha). Over the past decades, increased fire-weather induced a strong increase in wildfire probabilities, which was actually observed on the western part of the region but not so in the east and Corsican Island, most likely due to reinforced suppression policies. Conclusions While spatial patterns in fire activity are driven by land-use and land-cover factors, temporal patterns were mostly driven by changes in fire-weather and unexplained effects potentially related to suppression policies but with large differences between regions.

Assessing the role of compound drought and heatwave events on unprecedented 2020 wildfires in the Pantanal

The year 2020 had the most catastrophic fire season over the last two decades in the Pantanal, which led to outstanding environmental impacts. Indeed, much of the Pantanal has been affected by severe dry conditions since 2019, with evidence of the 2020’s drought being the most extreme and widespread ever recorded in the last 70 years. Although it is unquestionable that this mega-drought contributed significantly to the increase of fire risk, so far, the 2020’s fire season has been analyzed at the univariate level of a single climate event, not considering the co-occurrence of extreme and persistent temperatures with soil dryness conditions. Here, we show that similarly to other areas of the globe, the influence of land-atmosphere feedbacks contributed decisively to the simultaneous occurrence of dry and hot spells (HPs), exacerbating fire risk. The ideal synoptic conditions for strong atmospheric heating and large evaporation rates were present, in particular during the HPs, when the maximum temperature was, on average, 6 °C above the normal. The short span of the period during those compound drought-heatwave (CDHW) events accounted for 55% of the burned area of 2020. The vulnerability in the northern forested areas was higher than in the other areas, revealing a synergistic effect between fuel availability and weather-hydrological conditions. Accordingly, where fuel is not a limiting factor, fire activity tends to be more modelled by CDHW events. Our work advances beyond an isolated event-level basis towards a compound and cascading natural hazards approach, simultaneously estimating the contribution of drought and heatwaves to fuelling extreme fire outbreaks in the Pantanal such as those in 2020. Thus, these findings are relevant within a broader context, as the driving mechanisms apply across other ecosystems, implying higher flammability conditions and further efforts for monitoring and predicting such extreme events.

Dynamics of paleo-fires in the forest-steppe zone of the Western Siberia

Abstract. In this work we present the results of reconstruction of the dynamics of paleo-fires over the last 3300 cal. yr BP in the Barabinsk forest-steppe of the Western Siberia based on macrocharcoal analysis and radiocarbon dating of peat deposits of the Nikolaevsky ryam. The authors identified 18 local fire episodes using the CharAnalysis program. At the end of the Subboreal period, 6 local fires occurred, probably caused by dry and cold conditions. In the subAtlantic period of the Holocene, 12 fires were recorded with a peak of pyrogenic activity at 1200-1000 cal. yr BP. This peak of fires is probably associated with the warm and dry conditions of the Medieval Climate Optimum. As a result of the study, it was concluded that the intensity and frequency of paleo-fires in the area of Nikolaevsky ryam were influenced by climatic changes: in dry climatic periods, an increase in fire activity was observed.

Woody plant encroachment pervasive across three socially and ecologically diverse ecoregions

Woody plant encroachment in grasslands represents one of the greatest challenges for global biodiversity conservation. Furthermore, this is a social-ecological problem, where human activity and behavior have resulted in significant changes in ecological processes that control woody plants, and failure to fully recognize the role of human activity has led to continued loss of grasslands worldwide. It is therefore critical that conservation professionals understand how ecological systems, settlement patterns, and fragmentation from anthropogenic development interact to influence rates of woody plant encroachment. Using annual estimates of tree cover derived from regionally available remote-sensing data, our objectives were, first, to describe rates of woody plant encroachment over the last 20 years (2000–2019) across three ecologically and socially diverse ecoregions in the Southern Great Plains of North America. Then, we examined how anthropogenic and biophysical variables influenced rates of encroachment (both directly and indirectly) within the region. Results indicate that, despite marked differences in social and ecological characteristics, all three ecoregions have experienced consistent increases in woody plant encroachment during the study period. This included the Flint Hills ecoregion of Kansas and Oklahoma, an area that experiences widespread and frequent fires. At the regional scale, rates of encroachment were directly and negatively related to the average area burned in a county, initial cover of trees, and fragmentation from row crops. Percent cover of development and row crop agriculture also indirectly alter rates of encroachment in a county by influencing initial tree cover and fire activity. The pervasive nature of woody plant encroachment, even in regions that experience frequent fires, suggests that many grasslands are being managed outside of critical ecological thresholds needed to maintain grasslands and limit woody encroachment, which can have significant implications for biodiversity. Our results show that anthropogenic or ecological factors do not act in isolation in their influence on woody plant encroachment and can form complex relationships that shape regional trends in woody plant encroachment.

Forest fire and its key drivers in the tropical forests of northern Vietnam

Fire increasingly threatens tropical forests in northern Vietnam as climate changes and human population grows. Understanding fire occurrence patterns may support more effective forest management and reduce fire risk. We investigated spatiotemporal patterns and drivers of wildfire across three provinces in northern Vietnam and assessed the effectiveness of the Modified Nesterov index (MNI) fire danger rating system. We explored fire occurrence and size within and between years and forest types using descriptive analyses and developed spatiotemporal Maximum Entropy (Maxent) models incorporating variables representing potential drivers of fire, including weather, fuel, topography and human activity. Most fires occurred late in the dry season and fires were most common in natural forest. Maxent models successfully predicted fire occurrence (area under the receiver operating characteristic curve (AUC) values 0.67–0.79). While the contributions of drivers varied among provinces, MNI, temperature, elevation and distance to road were consistently important. The model for combined provinces showed that fire probability was greater under higher temperature and MNI, in areas with lower population, farther from roads, at higher elevations and in natural forests. This study suggests that an assessment integrating multiple drivers better predicts fire occurrence than a system based on weather alone and may support improved fire management and education in northern Vietnam.

Reconstruction of vegetation and climate of the past of the central Caucasus for materials from the Tarskoe swamp

Abstract. The reconstruction of vegetation changes of foothill zone in the central part of the North Caucasus based on the data of the Tarskoe swamp is presented. The swamp is the largest in this region of the Caucasus and is the most promising peat paleoarchive. It has been studied earlier, but the cores were poorly dated. The Tarskoe was re-drilled, the sediments were dated, and pollen and microcharcoal analysis were carried out. Twelve radiocarbon dates were obtained for the deposits, the age of the bottom sediments was about 4.6 cal. ka BP. Based on the data obtained, it was possible to establish that the of the bogging occurred against the background of more open landscapes, with a greater proportion of meadows than at present. Only after 4.4 cal ka BP broad-leaved forests become more closed, in their composition Fagus were dominant, with alternating admixture of Carpinus, Ulmus and Alnus. The increase of Alnus after Cyperaceae is most likely reflect local changes, since this tree species settled in the swamp at a late stage of its development. The dynamics of fire activity is interesting, it is most pronounced in the intervals between 4.4-3.3 cal. ka BP and than from 2.2 cal. ka BP until present. The frequency of fires is probably related not to climate, but to anthropogenic activities. In almost all cases, this coincides with the appearance of cultivated cereals pollen and with an increase in the diversity and quantity of grasses associated with humans (weeds). Thus, the obtained data for the first time give a possibility to construct a dated sequence of changes in the composition of broad-leaved forests of the belt of Caucasus piedmont and confirmed the appearance of cultivated cereals pollen about 4.3 cal. ka BP, which is probably associated with agriculture of the Maikop culture.

环境介质中左旋葡聚糖记录与植被火燃烧变化研究进展

<p indent="0mm">Vegetation fire, also called biomass burning, wildfire, landscape fire, bushfire, forest fire, scrub fire, crop residue burning, peat bog fire, savanna fire and grass fire, are spontaneous combustion of plants in a natural setting. Vegetation fires began soon after the appearance of terrestrial plants in the Silurian about 420 million years ago. The regime of vegetation fire has varied with long-term changes in global climate and shorter-term regional changes in climate and vegetation since then, and human beings have altered fire activity since the mid-Holocene, especially in recent years. Vegetation fire affects vegetation distribution, ecological structure, biogeochemical and hydrologic cycles, geophysical processes, and the climate system at local to global scales. Vegetation fire is one of the largest sources of trace gases and aerosols in the Earth’s atmosphere. It contributes more than half of black carbon and about 80% of primary organic aerosol worldwide. Besides, smoke aerosol from vegetation fire is composed of hundreds of chemical components, and many of which (e.g., polycyclic aromatic hydrocarbons) are known to be harmful to human health. Fire smoke causes more than 600000 premature deaths annually worldwide. Therefore, understanding the spatial-temporal changes of vegetation fire is of great importance. Using some specific biomarkers for tracing changes and emissions of vegetation fire has become a research focus in recent years. Among various chemical components, anhydro-sugars are mainly emitted by pyrolysis of cellulose and hemicellulose when burning temperature exceeds 300°C, whereas the contribution of fossil fuel emissions seems to be negligible. Levoglucosan accounts for more than 90% of anhydro-sugars in the nature. Levoglucosan has been reported with a lifetime longer than ten days under most atmospheric conditions, and thus could be transported far from the fire sources. The annual total levoglucosan emission is estimated at about 3.8 Tg (million ton) per year worldwide, however, when atmospheric degradation is considered, the atmospheric budget of levoglucosan is only about 1.9 Gg (kiloton) as calculated by the GEOS-Chem global 3-D chemical transport model. Eventually, levoglucosan is scavenged out the atmosphere to be deposited on earth surfaces by precipitation or gravitational processes. Its presence has been detected in various environmental medias including atmospheric aerosols, precipitation, lake/sea water, snowfall, glacier snow/ice, lake/marine sediments. High levoglucosan concentration/flux is usually found in middle and low latitudes where intense fire sources are nearby. In comparison, extreme low concentration/flux are found on highmountains, polar regions and marine sites where levoglucosan can only arrive by long distance transportation. Levoglucosan has been widely used as a biomarker for tracing fire emissions ranging from event to glacial-inter glacial timescales. For example, levoglucosan has been detected in lake sediments older than 430 ka years before present under anoxic environmental conditions. This work summarized the recent progress of levoglucosan records and vegetation fire changes in various environmental media. Levoglucosan in atmospheric aerosols can reflect fire emissions from event to seasonal scales, and levoglucosan records in glacial ice and lake/marine sediments can reveal fire evolution from seasonal to glacial-interglacial timescales. Overall, the current knowledge supports that levoglucosan should be an ideal biomarker for tracing vegetation fire changes on Earth’s surface. However, more evidences are needed in the near future to better understand its stability, interpret its records in ice core and sediments, as well as its relation with other proxies.

Weather pattern associated with climate change during Canadian Arctic wildfires: A case study in July 2019

Wildfire is one of the major novel disturbances to the Arctic forest ecosystem. Relevant Weather and climate regimes are the most important elements affecting fire activity. However, these factors could be considered under changing due to Arctic warming. This paper discusses understanding relevant atmospheric weather and climate conditions over western Canada in July 2019 with a significant burned area fraction over western Canada, Alaska, and Siberia. Here, we show that daytime area-averaged Methane mole fraction for the month of July during recent two decades obtained from Modern-Era Retrospective Analysis for Research and Applications (MERRA) database has significant growth trend over Siberia-Alaska and western Canada with the highest value for the west part of Canada in July 2019. Also, the Pearson correlation coefficient displays the strong negative relationship between north hemisphere sea ice extent and daytime areas averaged Methane mole fraction during the month of July for Siberia-Alaska and western Canada at −0.72 and −0.69 correspondingly. However, during the last two decades, the average Carbone monoxide (CO) column burden for these areas has been slightly decreased. This research demonstrates that the Arctic region has faced an albedo decrease with a maximum value of around 40% departure from mean values in some parts mostly over the northern Canadian Arctic and northern Alaska boundary for this time. Monthly weather and climate map analysis have revealed that Canadian July 2019 wildfires were linked to different factors including the rather lower humidity (with a maximum of 17.5% in North Territories) and higher surface air temperatures. Besides, the composite mean weather map analysis for the middle troposphere shows strong climate–fire links, with effects of the local blocking anti-cyclonic high-pressure systems dominated over the western Canadian Arctic, Alaska, Siberia (mostly over the south and central parts). Daily weather analysis for the peak day, July 24 reveals a tilted mid-tropospheric long-wave ridge formation accompanies by a very dry surface air (relative humidity ∼30-% 40) and warm tongue extended from the northwest of the United State to western Canada and Alaska. During the wildfire case of July 24, 2019, south-westerlies to south easterlies winds caused the fire to spread mostly over western and southwestern areas in the local afternoon time.

Silviculture can facilitate repeat prescribed burn programs with long-term strategies

A significant expansion of prescribed fire activity will be necessary to mitigate growing wildfire hazard in California forests. Forest managers can facilitate this expansion by promoting forest structures that allow for more effective implementation of prescribed fire, for both initial-entry and repeat burns. We analyzed changes in surface fuel during a series of three burns in replicated mixed-conifer stands following a period of over 100 years of fire suppression and exclusion. Total fuel load, proportion of pine present, canopy cover and basal area of live trees were relevant forest-structure components that influenced plot-scale fuel consumption. The study highlighted the importance of pre-fire fuel load and the relative proportion of pine in the overstory, which both led to greater amounts of fuel consumption. The initial-entry burn dramatically reduced all fuel categories (fine fuel, coarse wood and duff). Following each burn, fuel recovered until the next burn reduced loads enough to maintain low fuel levels. We apply the results to provide an example of how to determine the timing of prescribed fires.

Simulations of the Waroona fire using the coupled atmosphere–fire model ACCESS-Fire

The Waroona fire burned 69 000 ha south of Perth in January 2016. There were two fatalities and 170 homes were lost. Two evening ember storms were reported and pyrocumulonimbus (pyroCb) cloud developed on consecutive days. The extreme fire behaviour did not reconcile with the near- surface conditions customarily used to assess fire danger. A case study of the fire (Peace et al. 2017) presented the hypothesis that the evening ember storms resulted from interactions between the above-surface wind fields, local topography and the fire plume. The coupled fire–atmosphere model ACCESS-Fire has been run in order to explore this hypothesis and other aspects of the fire activity, including the pyroCb development. ACCESS-Fire incorporates the numerical weather prediction model ACCESS (Australian Community Climate and Earth System Simulator, described by Puri et al. 2013) and a fire spread component. In these simulations, the Dry Eucalypt Forest Fire (Vesta) fire spread model is used. In this study we first show that the reconstruction of surface fire spread and simulated fire spread are a good match for the first day; second, we show that the model produces deep moist convection as an indicator of pyrocumulonimbus cloud and, third, we show the fire–atmosphere interactions surrounding the ember showers provided an environment conducive to the observed mass spotting. The simulation results demonstrate that ACCESS-Fire is a tool that may be used to further explore the complex processes and potential impacts surrounding pyroCb development and short-distance ember transport.

Comparing geostationary and polar-orbiting satellite sensor estimates of Fire Radiative Power (FRP) during the Black Summer Fires (2019–2020) in south-eastern Australia

Background We compared estimates of Fire Radiative Power (FRP) from sensors onboard geostationary Himawari-8 (BRIGHT_AHI) and polar-orbiting TERRA/AQUA (MOD14/MYD14) satellites during the 2019/2020 Black Summer Fires in South-Eastern Australia. Aim/methods Analysis was performed on a pixel, bioregion, and wildfire event basis to assess the utility of the new BRIGHT_AHI FRP product. Key results Results show a high agreement between the products (r = 0.74, P &lt; 0.01) on a pixel level, with BRIGHT_AHI generally underestimating FRP compared to MOD14/MYD14. Regional spatiotemporal trends were captured in more detail by BRIGHT_AHI due to its higher temporal resolution, with MOD14/MYD14 systematically underestimating the total and sub-diurnal FRP values. Nevertheless, both datasets captured similar fire ignition and spread patterns for the study region. On the event level, the correlation between the datasets was moderate (r = 0.49, r = 0.67), when considering different temporal constraints for hotspot matching. Conclusions The results of this study indicate that BRIGHT_AHI approximates the well-established MOD14/MYD14 product during concurrent observations, while revealing additional temporal information for FRP trends. Implications This gives confidence in the reliability of BRIGHT_AHI FRP estimates, opening the way for a denser observation record (10-min intervals) that will provide new opportunities for fire activity reporting, some of which are presented here.

Effect of Irrigation on the Control of Red Imported Fire Ants (Hymenoptera: Formicidae) by Water-Resistant and Standard Fire Ant Baits.

The red imported fire ant, Solenopsis invicta (Buren), is an invasive pest of agricultural, urban, and natural areas. It is also considered a public health pest due to its painful stings. While it can be efficiently controlled by commercially available fire ant baits formulated with a corn-grit carrier, rain or irrigation is thought to degrade the carrier, compromising bait effectiveness. This study assessed the effect of irrigation on the efficacy of water-resistant and standard fire ant bait formulations, by comparing worker number, brood volume, and queen survivorship after access to water-soaked baits and to irrigated, bait-treated sod. In initial testing, wetted water-resistant and standard baits reduced fire ant colonies less than dry baits, both when baits were given to colonies directly and when colonies were given access to baits broadcasted (i.e., scattered) atop sod. Comparisons of the efficacy of piled versus broadcast applications of water-resistant and standard baits revealed reductions of >88% in adults and brood and no surviving queens for all bait treatments. This result was unexpected because piled baits were hypothesized to be better protected from irrigation than broadcast bait applications. In a field study, irrigated water-resistant and standard baits caused similar and significantly higher reductions in fire ant foraging activity relative to an untreated control. These results indicated that both the water-resistant and standard fire ant bait provided significant fire ant reductions even after irrigation.