Changes In Fire Regimes Research Articles

Comparison of Post-fire Patterns in Brazilian Savanna and Tropical Forest from Remote Sensing Time Series

Monitoring of fire-related changes is essential to understand vegetation dynamics in the medium and long term. Remote sensing time series allows estimating biophysical variables of terrestrial vegetation and interference by extreme fires. This research evaluated fire recurrence in the Amazon and Cerrado regions, using Moderate Resolution Imaging Spectroradiometer (MODIS) albedo time series, enhanced vegetation index (EVI), gross primary productivity (GPP), and surface temperature. The annual aggregated time series (AAT) method recognized each pixel’s slope trend in the 2001–2016 period and its statistical significance. A comparison of time trends of EVI, GPP, and surface temperature with total fire recurrence indicates that time trends in vegetation are highly affected by high fire recurrence scenarios (R2 between 0.52 and 0.90). The fire recurrence and the albedo’s persistent changes do not have a consistent relationship. Areas with the biggest evaluated changes may increase up to 0.25 Kelvin/Year at surface temperature and decrease up to −0.012 EVI/year in vegetation index. Although savannas are resistant to low severity fires, fire regime and forest structure changes tend to make vegetation more vulnerable to wildfires, reducing their regeneration capacity. In the Amazon area, protection of forests in conservation units and indigenous lands helped in the low occurrence of fires in these sensitive areas, resulting in positive vegetation index trends.

Climate, landscape diversity, and food sovereignty in arid Australia: The firestick farming hypothesis.

Climate change has long been recognized as a significant driver of dietary diversity and dietary quality. An often overlooked aspect of climate change are shifts in fire regimes, which have the potential to drastically affect landscape diversity, species distributions, and ultimately, human diets. Here, we investigate whether the fire regimes shaped by Indigenous Australians change landscape diversity in ways that improve dietary quality, considering both the diversity and the quantity of traditional foods in the diet. We use structural equation modeling to explore two causal models of dietary quality, one focused on the direct effects of climate change and resource depression, the other incorporating the dietary effects of landscape diversity, itself a product of fire-created patchiness. We draw on a focal camp dataset covering 10 years of observations of Martu foraging income in the Western Desert of Australia. We find strong support for the hypothesis that fire-created patchiness improves diet quality. Climate change (cumulative 2-year rainfall) has only an indirect effect on dietary quality; the availability of traditional foods is mediated primarily through the landscape diversity shaped by fire. Our model suggests that the loss of the indigenous fire mosaic may lead to worsening availability of traditional foods, measured as both caloric intake and diet diversity. Because the effects of rainfall are mediated through landscape diversity, increased rainfall may not compensate for the recent changes in fire regimes resulting from the loss of Aboriginal fire from the landscape.

Ranking buffel: Comparative risk and mitigation costs of key environmental and socio-cultural threats in central Australia.

Changed fire regimes and the introduction of rabbits, cats, foxes, and large exotic herbivores have driven widespread ecological catastrophe in Australian arid and semi‐arid zones, which encompass over two‐thirds of the continent. These threats have caused the highest global mammal extinction rates in the last 200 years, as well as significantly undermining social, economic, and cultural practices of Aboriginal peoples of this region. However, a new and potentially more serious threat is emerging. Buffel grass (Cenchrus ciliaris L.) is a globally significant invader now widespread across central Australia, but the threat this ecological transformer species poses to biodiversity, ecosystem function, and culture has received relatively little attention. Our analyses suggest threats from buffel grass in arid and semi‐arid areas of Australia are at least equivalent in magnitude to those posed by invasive animals and possibly higher, because unlike these more recognized threats, buffel has yet to occupy its potential distribution. Buffel infestation also increases the intensity and frequency of wildfires that affect biodiversity, cultural pursuits, and productivity. We compare the logistical and financial challenges of creating and maintaining areas free of buffel for the protection of biodiversity and cultural values, with the creation and maintenance of refuges from introduced mammals or from large‐scale fire in natural habitats. The scale and expense of projected buffel management costs highlight the urgent policy, research, and financing initiatives essential to safeguard threatened species, ecosystems, and cultural values of Aboriginal people in central Australia.

Growth and functional traits of Julbernardia globiflora (Benth) resprouts and seedlings in response to fire frequency and herbivory in miombo woodlands

Understanding the effects of fire and herbivory on vegetation is crucial for biodiversity conservation in miombo woodlands. Changes in fire regimes in miombo alter plant growth and functional traits, such as carbon and nitrogen content, specific leaf area (SLA), and the concentrations of polyphenols, which can also change herbivory patterns in these systems. We compared the relative growth rate in height and basal diameter of seedlings and resprouts of Julbernardia globiflora in areas of high and low fire frequency and in the presence and absence of herbivores in Gorongosa National Park. We also measured functional traits (SLA, phenolics) from resprouts and seedlings in high and low fire frequency areas. Overall, resprouts were more responsive to fire frequency than seedlings, perhaps because they may have already survived at least one fire. Resprout RGR in diameter was greatest in areas with a low frequency of fire and where herbivores were excluded. SLA was higher in areas with lower fire frequency, where canopy cover is likely greater. Higher concentrations of polyphenols were measured in seedlings from the high fire frequency area, indicating a greater investment in defenses in vulnerable seedlings. In sum, when fires occur every two years, plant growth was limited, leaves were thicker, and plants invested more in C-rich defenses. Lastly, we observed that Combretum adenogonium, a species favored by fire and not characteristic of true miombo, was more abundant in the frequently burned site, and J. globiflora regenerates more from resprouts than from seed in areas with a short fire return interval. This study suggests that high frequency fires affect miombo conservation, and efforts to prevent frequent fires are important for the integrity of the ecosystem.

Non-native plants exert strong but under-studied influence on fire dynamics

Altered fire regimes are among the most destructive consequences of anthropogenic environmental change. Fires have increased in frequency in some regions, and invasion by fire-adapted non-native species has been identified as a major driver of this change, which results in a feedback cycle promoting further spread by the non-native species and diminishing occurrence of natives. We notice, however, that non-native species are often invoked in passing as a primary cause of changing fire dynamics, but that data supporting this claim are rarely presented. We therefore performed a meta-analysis of published literature to determine whether a significant relationship exists between non-native species presence and increased fire effects and risk, examined via various fire metrics. Our analysis detected a strongly significant difference between fire metrics associated with non-native and native species, with non-native species linked to enhanced fire effects and risk. However, only 30 papers discussing this linkage provided data to support it, and those quantitative studies examined only eight regions, five biome types, and a total of 22 unique non-native taxa. It is clear that we are only beginning to understand the relationship between non-native species and fire and that results drawn from an extremely limited set of contexts have been broadly applied in the literature. It is important for ecologists to continue to investigate drivers of changing fire regimes as factors such as climate change and land use change alter native and non-native fuels alike.

Arctic fires re-emerging

Underground smouldering fires resurfaced early in 2020, contributing to the unprecedented wildfires that tore through the Arctic this spring and summer. An international effort is needed to manage a changing fire regime in the vulnerable Arctic.

Widespread short‐term persistence of frog species after the 2019–2020 bushfires in eastern Australia revealed by citizen science

AbstractFires change ecosystem composition and influence species extinction risk, yet information on the impact of fire on biodiversity is scant. The bushfires in southeastern Australia during the summer of 2019/20 were unprecedented in their extent and intensity, and postfire management decisions have been hindered by a lack of knowledge of the impact of fires on biodiversity. We examine the short‐term persistence of frog species across southeastern Australia after these fires using records of calling frogs from the national citizen science project FrogID. We demonstrate widespread short‐term persistence of frog species. Sixty‐six frog species were detected in the firegrounds before the fire, and within 125 days postfire, 45 of these were detected. All 33 frog species with more than five records that were detected in the months of December–March prefire were detected postfire. While the short‐term postfire persistence of so many frog species is a positive result, the population‐level and longer‐term consequences of the fires remain unknown, as does the ability of frogs to persist with the changing fire regimes predicted as a consequence of global climate change. We illustrate the value of citizen science in collecting large‐scale and rapid observations in response to increasing anthropogenically‐driven ecological events.

What drives grassland-forest boundaries? Assessing fire and frost effects on tree seedling survival and architecture.

Fire and frost represent two major hurdles for the persistence of trees in open grassy biomes and have both been proposed as drivers of grassland‐forest boundaries in Africa.We assess the response of young tree seedlings, which represent a vulnerable stage in tree recruitment, to traumatic fire and frost disturbances.In a greenhouse experiment, we investigated how seedling traits predicted survival and resprouting ability in response to fire versus frost; we characterized survival strategies of seedlings in response to the two disturbances, and we documented how the architecture of surviving seedlings is affected by fire versus frost injury.Survival rates were similar under both treatments. However, different species displayed different levels of sensitivity to fire and frost. Seedling survival was higher for older seedlings and seedlings with more basal leaves. Survivors of a fire event lost more biomass than the survivors of a frost event. However, the architecture of recovered fire‐ and frost‐treated seedlings was mostly similar. Seedlings that recovered from fire and frost treatments were often shorter than those that had not been exposed to any disturbance, with multiple thin branches, which may increase vulnerability to the next frost or fire event. Synthesis. Fire caused more severe aboveground damage compared with a single frost event, suggesting that fire is an important driver of tree distribution in these open grassland systems. However, the impact of repeated frost events may be equally severe and needs to be investigated. Also, woody species composition may be influenced by phenomena that affect the timing and frequency of seedling exposure to damage, as mortality was found to be dependent on seedling age. Therefore, changes in fire regime and climate are likely to result in changes in the composition and the structure of the woody components of these systems.

Impact of air intake position on fire dynamics in mechanically ventilated compartment

The effects of air intake position on the burning behaviour of liquid pool inside a mechanically ventilated compartment are analyzed by using both an experiment and a physics-based model. A series of compartment fire experiments has been undertaken from a reduced scale enclosure with a length/height and width of 2 m. An external ventilation system consists of an air admission duct placed in low or high position inside the compartment, providing an Air Change Per Hour (ACPH) in a range from 1 to 4. Lowering the inlet duct enhances fuel-air mixing in the compartment. The experimental and numerical studies highlight a faster fire growth for a low air intake with a rise of ACPH, implying more dangerous fire with regarding the more important peak in heat release rate and heat feedback to liquid fuel surface. For air intake in high position, the direction of air jet inside enclosure is found to be orthogonal to the direction of the buoyancy-induced flow. This results in an air entrainment restriction towards the fire base and a decrease of the heat feedback to liquid fuel surface due to cooling effect on the hot smoke layer near the ceiling. Thus a high inlet contributes to a reduction by a factor of 40% in HRR, and the fire growth power is practically independent to ACPH. Moreover, for a high inlet, fire exhaust occurs more easily because both the heat feedback and air entrainment are weaker than these for a low inlet. As a consequence, changing air intake position from low to high leads to a change in fire regime from an under-ventilated fire to an over-ventilated one.

Habitat selection by spotted owls after a megafire in Yosemite National park

As fires in the western United States have become larger and more severe over recent decades, understanding how the changing fire regime affects wildlife has become a key issue for conservation. Spotted owls (Strix occidentalis) associate with late-successional forest characteristics and therefore may be particularly sensitive to structural changes in habitat that result from fire. Previous studies have found varying responses of the owls to forest fire. We investigated the effects of the 2013 Rim Fire on territory selection by California spotted owls within Yosemite National Park, which, unlike the surrounding landscape, has been managed with no commercial logging since the early 1900s and minimal fire suppression since the 1970s. We examined specific habitat characteristics associated with spotted owl presence before and after the fire to understand how fire-induced changes in habitat structure may influence spotted owl territory selection. Spotted owls persisted and nested within the fire perimeter throughout the four post-fire years of our study at rates similar to what we observed in areas of Yosemite that were unaffected by the fire. However, within the fire perimeter, spotted owls avoided areas characterized by >30% percent high severity fire. Prior to the fire, spotted owls selected for areas of high canopy cover relative to the rest of the landscape; after the fire, even though territory centers shifted substantially from pre-fire locations, pre-fire canopy cover remained a stronger predictor of spotted owl presence than post-fire canopy cover, or any other pre- or post-fire habitat variables we assessed. The importance of pre-fire forest structure in predicting owl presence after fire suggests that reported variation in spotted owl population response to different fires across the Sierra Nevada may in part reflect variation in pre-fire forest characteristics, and perhaps different forest management regimes that shaped those characteristics. Pre-fire forest characteristics may impart a legacy of post-fire habitat conditions important to owls that commonly used forest and fire metrics do not effectively describe. Further study of owl response to fire in forests with a broader spectrum of pre-fire forest structure and management regimes is needed to better predict and manage effects of the changing fire regime on spotted owls.

Recent fire regime in the southern boreal forests of western Siberia is unprecedented in the last five millennia

Wildfires in Siberia are documented to have increased in frequency and severity over recent decades. However, in the absence of long-term records, it is unclear how far and why this trend deviates from centennial to millennial scale variability. Here we reconstruct past patterns of fire frequency and fire type, and explore how the fire-related traits of boreal species and plant functional types (PFTs) determine ecosystem responses to changing fire regimes. We use charcoal-based reconstructions of the fire regime in combination with a pollen-based assessment of vegetation composition in two boreal forest peat profiles from Plotnikovo Mire in western Siberia that span the last 2400 and 5000 years. We found moderate levels of biomass burning between 5000 and 4000 cal yr BP. Biomass burning and fire severity i.e., more biomass burning per fire episode, increased over the last 1500 cal yr BP associated with the dominance of fire invaders (Betula). Conversely, between 4000 and 1500 cal yr BP lower biomass burning, with perhaps fire types affecting mostly litter and understorey vegetation, coincided with the dominance of fire resisters (e.g., Pinus sylvestris, P. sibirica, Larix) intermixed with a considerable number of fire avoiders (e.g., Abies sibirica and Picea obovata). This long-term perspective shows that the current fire regime commenced 1500 years ago and deviates from the trends observed over the last 5000 years. This deviation is linked to a combination of climate conditions conducive to fire, the amount and composition of woody fuels, and land use changes. Although pines reacted more sensitively to increased fire severity, the fire avoider Picea obovata appears to be much more vulnerable to both frequent, severe fires than Abies sibirica. We anticipate that climatically driven changes in fire weather, with frequent warm and dry spells, and anthropogenic land use intensification will heighten fire severity and their impact, driving vegetation composition towards Betula species to the detriment of Picea obovata. This study also shows that charcoal morphotypes can provide useful information on fuel and fire type, and that, although all macro-charcoal size classes reliably indicate local-scale fires, the larger fraction (>300–500 μm) allows the identification of on-site fire episodes. We recommend multi-site palaeo-fire reconstructions in boreal peatlands to adequately reflect the influence of localised peat moisture content, and vegetation composition and structure variability on the small-scale heterogeneity of fire type and spread. This will ensure that trends in fire regime dynamics are representative and not limited to the local scale. We also propose future directions in fire research that can be tested using fossil records of fire, climate and vegetation ideally in an interdisciplinary approach.

A trait‐based approach to assessing resistance and resilience to wildfire in two iconic North American conifers

Abstract Ongoing changes in fire regimes have the potential to drive widespread shifts in Earth's vegetation. Plant traits and vital rates provide insight into vulnerability to fire‐driven vegetation shifts because they can be indicators of the ability of individuals to survive fire (resistance) and populations to persist (resilience) following fire. In 15 study sites spanning climatic gradients in the southern Rocky Mountains, USA, we quantified variation in key traits and vital rates of two co‐occurring, widely distributed conifers (Pinus ponderosa Douglas ex. P. Lawson & C. Lawson and Pseudotsuga menziesii (Mirb.) Franco). We used mixed‐effects models to explain inter‐ and intraspecific variation in tree growth, survival, bark thickness and seed cone production, as a function of species, tree life stage (i.e. diameter, height and age), average climate, local competition and site conditions. Pinus ponderosa was predicted to survive low‐severity fire at a 23% earlier age than P. menziesii. Pinus ponderosa had thicker bark and more rapid juvenile height growth, traits conferring greater fire resistance. In contrast, P. menziesii was predicted to produce seed cones at a 28% earlier age than P. ponderosa. For both species, larger individuals were more likely to survive fire and to produce cones. For P. ponderosa, cone production increased where average actual evapotranspiration (AET) was higher and local competition was lower. More frequent cone production on productive sites with higher AET is an important and underappreciated mechanism that may help to explain greater resilience to fire in these areas. Synthesis. Our analyses indicated that many plant traits and vital rates related to fire differed between Pinus ponderosa and Pseudotsuga menziesii, with trade‐offs between investment in traits that promote individual defence to fire and those that promote recolonization of disturbed sites. Future changes in fire regimes will act as a filter throughout North American forests, with our findings helping to infer which individuals and populations of two iconic species are most vulnerable to future change and offering a framework for future inquiry in other forests facing an uncertain future.

Paleolimnological Assessment of Wildfire‐Derived Atmospheric Deposition of Trace Metal(loid)s and Major Ions to Subarctic Lakes (Northwest Territories, Canada)

AbstractWildfires release terrestrial elements to the atmosphere as aerosols, and these events are becoming more frequent and intense in the Arctic boreal forest as the climate is warming. We quantified the impact of atmospheric deposition of aerosols from local wildfires on metal(loid) fluxes using macroscopic charcoal accumulation rates, historical fire mapping, and element concentrations in 210Pb‐dated lake sediment from five subarctic lakes with small catchments. Lake sediments showed small but significant increases in fluxes (median = 5–10%) for 22 trace metals, metalloids, or major ions following fire events. The impact of wildfire aerosols on element fluxes was mostly due to short‐term (≤2 years) increasing sedimentation rate (6 ± 41% increase), whereas sediment element concentrations were not strongly impacted. Wildfire‐associated deposition to lake sediments was mainly composed of Ca, Al, Fe, Mg, K, Mn, and Na, which are major constituents of ash from burned biomass, but changes in sediment flux were greatest for Sb, As, Ni, Ba, Mn, Mo, and Sr compared to pre‐disturbance conditions. Compared to anthropogenic sources of pollution, wildfire‐associated atmospheric fluxes of metal contaminants to the lakes (e.g., Hg, Pb, As, Sb, and Cd) were low. This study provides quantitative estimates of wildfire impacts on atmospheric geochemical fluxes to subarctic lakes, which can be used for modeling larger‐scale impacts under changing fire regimes.

Frequent planned fire can prevent succession to woody plant dominance in montane temperate grasslands

AbstractNatural temperate grasslands are endangered throughout their range, largely because of their almost complete conversion to agriculture, and by changes in fire and grazing regimes. Woody encroachment by shrubs is a global threat to the structure, function and composition of grasslands. We wished to determine the characteristics of fire regimes that prevent or reverse woody plant encroachment, maintain native species richness and minimise exotic plant invasion in temperate grassland at the Surrey Hills Tasmania, where a fire management plan with variable prescriptions had been implemented for two decades. We collected floristic, fire regime and environmental data from 105 quadrats (1 × 10 m) in 2016/2017, and compared the data from 2016/2017 to that from a 1994 survey using the same methods. A high frequency and cover of native shrubs characterised areas unburned for at least 20 years before 2017, but not those unburned in the 20 years before 1994. Shrub cover began to strongly increase after a decade without fire and was greater on larger plains. Native species richness declined with an increasing minimum interval between fires and increased with elevation. It began to decline at the quadrat scale when shrub cover attained 40%. In the data set as a whole, 17 of the 67 most abundant taxa were absent from all quadrats unburned for 20 years before 2017, indicating a high potential for loss of species at a landscape scale in the absence of fire. Exotic species cover was randomly distributed in relation to fire regimes and environment. The current fire management regime has largely been at a sufficient frequency and minimum interval (approximately a decade between fires) to maintain the grassiness and native species richness of treated plains, which is fortunate given that recent land‐use change appears to have resulted in increased frequency of shrubs independent of their cover.

Seed source pattern and terrain have scale-dependent effects on post-fire tree recovery

Distance to seed source is often used to estimate seed dispersal—a process needed for post-fire tree recovery. However, distance, especially in mountainous terrain, does not capture pattern or scale-dependent effects controlling seed supply and delivery. Measuring seed source pattern (area and arrangement) could provide insights on how these spatial dynamics shape recovery. We tested metrics and investigated how seed source pattern, tree regeneration traits, scale, and terrain interact to shape post-fire tree recovery. Our research questions were: Does seed source pattern outperform distance when modeling tree species presence and regeneration density? If yes, does seed source pattern have scale-dependent or terrain-dependent effects on regeneration density? We measured seed source pattern at nested spatial extents around 71 plots and related measurements to local post-fire tree recovery. We used generalized linear models to test metrics and visualize scale-dependent and terrain-dependent effects on regeneration density. Distance sufficiently modeled presence, but seed source pattern outperformed distance when modeling regeneration density. Relevant spatial extents and relationships were species-dependent. For wind-dispersed species, regeneration was associated with more seed source area and more complex arrangements, but terrain mediated these relationships. For serotinous and resprouting species, regeneration was associated with less seed source area and less complex arrangements, which are consistent with high-severity burn sites that promote recovery. Seed source pattern supports spatial resilience and interacts with scale and terrain to shape regeneration density. Accounting for these spatial dynamics could help steward forests facing changing fire regimes.

Soil Resistance to Burn Severity in Different Forest Ecosystems in the Framework of a Wildfire

Recent changes in fire regimes, with more frequent, extensive, and severe fires, are modifying soil characteristics. The aim of this study was to evaluate the effect of burn severity on the resistance of some physical, chemical, and biochemical soil properties in three different forest ecosystems affected by a wildfire in the northwest of the Iberian Peninsula. We evaluated burn severity immediately after fire using the Composite Burn Index (CBI) in three different ecosystems: shrublands, heathlands, and oak forests. In the same field plots used to quantify CBI, we took a composite soil sample to analyse physical (mean weight diameter (MWD)), chemical (pH; total C; total organic C (TOC); total inorganic C (TIC); total N; available P; exchangeable cations Na+, K+, Mg2+, and Ca2+; and cation exchange capacity (CEC)), and biochemical (β-glucosidase, urease, and acid phosphatase enzyme activities) properties. The resistance index of each property was then calculated. Based on our results, the values of the soil chemical properties tended to increase immediately after fire. Among them, total C, TOC, and exchangeable Na+ showed higher resistance to change, with less variation concerning pre-fire status. The resistance of chemical properties was higher in the oak forest ecosystem. MWD decreased at high severity in all ecosystems, but soils in shrublands were more resistant. We found a high decrease in soil enzymatic activity with burn severity, with biochemical properties being the least resistant to change. Therefore, the enzymatic activity of soil could be a potential indicator of severity in forest ecosystems recently affected by wildfires.

Dramatic recent changes in small mammal assemblages from Northern Patagonia: A caution for paleoenvironmental reconstructions

Temporal differences in fossil assemblages of small mammals can generate important insights into associated environmental conditions. Moreover, by including modern assemblages in such comparisons, it may also be possible to identify the effects of recent human colonization on mammal communities and their habitats. To explore potential signals of European colonization in northwestern Patagonia, we compared fossil and modern assemblages of small mammals from two newly characterized paleontological sites in the Limay Valley region of Río Negro Province, Argentina. The material analyzed consisted of 18 species of small-bodied terrestrial mammals identified from a sample of 27,992 specimens. Fossil assemblages dating from 6453 to 1002 calibrated years before present were relatively stable in taxonomic composition and displayed only minor differences in relative species abundances. In contrast, the modern assemblages examined were clearly distinct, containing a different suite of numerically dominant taxa and lacking three previously abundant grassland species that are presumed to have gone extinct in the vicinity of our study sites. We suggest that these changes reflect substantial post-colonization modifications of surrounding landscapes, including establishment of pine plantations, changes in fire regimes, and introductions of livestock and invasive species of plants. If correct, this supposition raises important concerns regarding the use of modern assemblages as a baseline for reconstructing paleoenvironmental conditions. To avoid potential misinterpretations associated with the use of modern faunal assemblages, we suggest two potential alternative strategies for inferring temporal changes in environmental conditions.

Landscape-based fire scenarios and fire types in the Ayllón massif (Central Mountain Range, Spain), 19th and 20th centuries

Wildfires have been a major landscape disturbance factor throughout history in inland mountain areas of Spain. This paper aims to understand the interaction of fire regimes and landscape dynamics during the last two centuries within a socio-spatial context. The study area selected for this historical and spatial analysis is the Ayllón massif, in the Central Mountain Range. The theoretical background used to identify the driving forces of fire regime changes over the 19th and 20th centuries in this mountain area includes landscape-based fire scenarios and fire-type concepts. Both concepts have been addressed in recent studies from a spatial planning and fire management approach in an attempt to understand current fire landscapes and wildfire risk. However, this is the first time that these concepts have been applied to show that both spatial and temporal scales are crucial for an understanding of the current wildfire panorama, and that fire history related to landscape dynamics is fundamental in socio-spatial differences in fire regimes.Four variables (fire history, land use, population and settlement system, and forest management) were assessed to define historical landscape-based fire scenarios, and three fire feature variables (fire extent, fire cause, and spatial distribution pattern) were considered to define historical fire-types. We found that the non-linear evolution of fire regimes during the 19th and 20th centuries was determined by fire-type changes according to landscape dynamics. Moreover, population and forest management have been the main driving forces of fire regime tipping points or pyrotransitions. This study validates the hypothesis that fire regime changes are the result of the interaction of fire history and landscape dynamics.

Arctic and boreal paleofire records reveal drivers of fire activity and departures from Holocene variability.

Boreal forest and tundra biomes are key components of the Earth system because the mobilization of large carbon stocks and changes in energy balance could act as positive feedbacks to ongoing climate change. In Alaska, wildfire is a primary driver of ecosystem structure and function, and a key mechanism coupling high-latitude ecosystems to global climate. Paleoecological records reveal sensitivity of fire regimes to climatic and vegetation change over centennial-millennial time scales, highlighting increased burning concurrent with warming or elevated landscape flammability. To quantify spatiotemporal patterns in fire-regime variability, we synthesized 27 published sediment-charcoal records from four Alaskan ecoregions, and compared patterns to paleoclimate and paleovegetation records. Biomass burning and fire frequency increased significantly in boreal forest ecoregions with the expansion of black spruce, ca. 6,000-4,000 years before present (yr BP). Biomass burning also increased during warm periods, particularly in the Yukon Flats ecoregion from ca. 1,000 to 500yr BP. Increases in biomass burning concurrent with constant fire return intervals suggest increases in average fire severity (i.e., more biomass burning per fire) during warm periods. Results also indicate increases in biomass burning over the last century across much of Alaska that exceed Holocene maxima, providing important context for ongoing change. Our analysis documents the sensitivity of fire activity to broad-scale environmental change, including climate warming and biome-scale shifts in vegetation. The lack of widespread, prolonged fire synchrony suggests regional heterogeneity limited simultaneous fire-regime change across our study areas during the Holocene. This finding implies broad-scale resilience of the boreal forest to extensive fire activity, but does not preclude novel responses to 21st-century changes. If projected increases in fire activity over the 21st century are realized, they would be unprecedented in the context of the last 8,000yr or more.

Fire as a fundamental ecological process: Research advances and frontiers

Abstract Fire is a powerful ecological and evolutionary force that regulates organismal traits, population sizes, species interactions, community composition, carbon and nutrient cycling and ecosystem function. It also presents a rapidly growing societal challenge, due to both increasingly destructive wildfires and fire exclusion in fire‐dependent ecosystems. As an ecological process, fire integrates complex feedbacks among biological, social and geophysical processes, requiring coordination across several fields and scales of study. Here, we describe the diversity of ways in which fire operates as a fundamental ecological and evolutionary process on Earth. We explore research priorities in six categories of fire ecology: (a) characteristics of fire regimes, (b) changing fire regimes, (c) fire effects on above‐ground ecology, (d) fire effects on below‐ground ecology, (e) fire behaviour and (f) fire ecology modelling. We identify three emergent themes: the need to study fire across temporal scales, to assess the mechanisms underlying a variety of ecological feedbacks involving fire and to improve representation of fire in a range of modelling contexts. Synthesis: As fire regimes and our relationships with fire continue to change, prioritizing these research areas will facilitate understanding of the ecological causes and consequences of future fires and rethinking fire management alternatives.