Variability In Fire Regimes Research Articles

Spatial variability in Arctic–boreal fire regimes influenced by environmental and human factors

Wildfire activity in Arctic and boreal regions is rapidly increasing, with severe consequences for climate and human health. Regional long-term variations in fire frequency and intensity characterize fire regimes. The spatial variability in Arctic–boreal fire regimes and their environmental and anthropogenic drivers, however, remain poorly understood. Here we present a fire tracking system to map the sub-daily evolution of all circumpolar Arctic–boreal fires between 2012 and 2023 using 375 m Visible Infrared Imaging Radiometer Suite active fire detections and the resulting dataset of the ignition time, location, size, duration, spread and intensity of individual fires. We use this dataset to classify the Arctic–boreal biomes into seven distinct ‘pyroregions’ with unique climatic and geographic environments. We find that these pyroregions exhibit varying responses to environmental drivers, with boreal North America, eastern Siberia and northern tundra regions showing the highest sensitivity to climate and lightning density. In addition, anthropogenic factors play an important role in influencing fire number and size, interacting with other factors. Understanding the spatial variability of fire regimes and its interconnected drivers in the Arctic–boreal domain is important for improving future predictions of fire activity and identifying areas at risk for extreme events.

Promoting Optimal Habitat Availability by Maintaining Fine-Grained Burn Mosaics: A Modelling Study in an Australian Semi-Arid Temperate Woodland

The pyrodiversity–biodiversity (P–B) hypothesis posits that spatiotemporally variable fire regimes increase wildlife habitat diversity, and that the fine-grained mosaics resulting from small patchy fires enhance biodiversity. This logic underpins the patch mosaic burning (PMB) paradigm and reinforces the benefits of Indigenous fire management, which tends to promote pyrodiversity. However, tests of the P–B hypothesis and PMB paradigm are few. One of the most comprehensive field evaluations—a snapshot study of pre-existing fire mosaics in south-east Australian semi-arid mallee eucalypt woodlands—found little support. To explore the longer-term effects of fire mosaic grain size on habitat availability and biodiversity, we combined published data from the mallee study with a simple fire simulation. We simulated 500 years of landscape burning under different fire sizes. In the resulting mosaics, we assessed the proportional mixture and patch configuration of successional habitat states, then summarised habitat availability through time using a composite index based on the published fire history responses of 22 vertebrate taxa from the mallee study. Small fires formed fine-grained mosaics with a stable habitat mixture and with habitat diversity occurring at fine scales. Large fires formed coarse-grained mosaics with the opposite properties. The fine-grained mosaics maintained optimal habitat availability for vertebrate diversity over 500 years, while the fluctuating habitat mixture in the coarse-grained mosaics was unlikely to maintain maximum vertebrate diversity. Broadly, our results support the P–B hypothesis and justify further field-testing and evaluation of PMB programs to manage both pyrodiversity and biodiversity in the mallee and other flammable landscapes.

Fire regimes of the Southern Appalachians may radically shift under climate change

BackgroundIncreased drought due to climate change will alter fire regimes in mesic forested landscapes where fuel moisture typically limits fire spread and where fuel loads are consistently high. These landscapes are often extensively modified by human land use change and management. We forecast the influence of varying climate scenarios on potential shifts in the wildfire regime across the mesic forests of the Southern Appalachians. This area has a long history of fire exclusion, land use change, and an expanding wildland urban interface. We considered interactions among climate, vegetation, and anthropogenic influences to forecast future fire regimes and changes to the forest structure. We used climate scenarios representing divergent drought patterns (overall drought trend and interannual variability) within a process-based fire model that captures the influence of climate, fuels, and fire ignition on wildfire patterns and suppression.ResultsCompared to simulations using historical climate (1972–2018), future total burned area (2020–2100: 782,302.7 (716,655.0–847,950.3) ha) increased by 42.3% under high drought variability (1,134,888.4 (1,067,437.2–1,202,339.6) ha), 104.8% under a substantial increase in drought trend (1,602,085.7 (1,511,837.5–1,692,334.0) ha), and 484.7% when combined (4,573,925.0 (4,434,910.5–4,712,939.5) ha). Landscape patterns of fire exclusion and suppression drove the spatial variability of fire return intervals (FRI). Our projections indicate wide spatial variability in future fire regimes with some areas experiencing multiple fires per decade while others experience no fire. More frequent fires corresponded with increased oak prevalence and a reduction in the biomass of mesic hardwoods and maple; however, mesic hardwoods remained prevalent under all fire intervals because of their contemporary dominance.ConclusionsOur study illustrates how future drought–fire–management interactions and a history of fire exclusion could alter future fire regimes and tree species composition. We find that increasing trends in drought magnitude and variability may increase wildfire activity, particularly in areas with minimal fire suppression. In ecosystems where fuel moisture (and not load) is the standard limitation to fire spread, increased pulses of drought may provide the conditions for more fire activity, regardless of effects on fuel loading. We conclude the effects of climate and human management will determine the novel conditions for both fire regime and ecosystem structure.

Exceptional variability in historical fire regimes across a western Cascades landscape, Oregon, USA

AbstractDetailed information about the historical range of variability in wildfire activity informs adaptation to future climate and disturbance regimes. Here, we describe one of the first annually resolved reconstructions of historical (1500–1900 ce) fire occurrence in coast Douglas‐fir dominated forests of the west slope of the Cascade Range in western Oregon. Mean fire return intervals (MFRIs) across 16 sites within our study area ranged from 6 to 165 years. Variability in MFRIs was strongly associated with average maximum summer vapor pressure deficit. Fire occurred infrequently in Douglas‐fir forest stands seral to mountain hemlock or silver fir, but fire frequency was much shorter than predicted by theory in other forest types. MFRIs within Douglas‐fir stands seral to western hemlock or grand fir ranged from 19 to 45 years, and MFRIs in stands seral to Douglas‐fir ranged from 6 to 11 years. There was little synchrony in fire occurrence or tree establishment across 16 sites separated by 4 km. The lack of synchrony in fire suggests that large, wind‐driven fire events that are often considered to be characteristic of coast Douglas‐fir forests were not an important driver of succession in our study area during the last ~400–500 years. Climate was more arid than normal during fire years in most forest types, but historical fire in stands seral to Douglas‐fir was strongly associated with antecedent moisture and less strongly associated with drought. We interpret the extraordinary tempo of fire we observed in stands seral to Douglas‐fir and the unique climate pattern associated with fire in these stands to be indicative of Indigenous fire stewardship. This study provides evidence of far more frequent historical fire in coast Douglas‐fir forests than assumed by managers or scientists—including some of the most frequent fire return intervals documented in the Pacific Northwest. We recommend additional research across the western Cascades to create a comprehensive account of historical fire in highly productive forests with significant cultural, economic, and ecological importance.

The history of fire, human and climate in black pine forests of western Anatolia: The Taurus mountains

The interactions between fire occurrence-human-climate are highly complex to understand and also difficult to predict due to having many sources of variations in fire regimes. However, we can gather information about the effect of human influence on the regional fire regimes where human influence is high, and the history of locations is well-known by conducting retrospective fire history studies in locations. Here, we present the impact of human settlements on fire occurrence by comparing and discussing the previous drought-driven tree-ring-based fire history reconstruction sites in western Anatolia. For this purpose, we collected cross-sections from Miyarcık highland, Antalya, and developed a 519–y long (1503–2021 CE) composite fire chronology using dendrochronological methods. Our study site location is known for the seasonal inhabitants of “Yörüks”, who led a nomadic life in the Taurus Mountains for centuries, and forests were used for livestock grazing. Since the temperatures increase significantly at the beginning of spring in the lower elevations of Antalya, the yörüks move towards the upper highlands with their animals from May to November. We found lower fire frequency and no fire-climate association compared to other sites that experienced drought-driven wildfires, even though this site is located in a high-fire-risk region. Low-frequency fires might be due to moderate-level livestock grazing by yörüks in this area. Grazing contributes to reducing the amount of accumulated combustible materials, causes discontinuity of fuel in the understory of forests, and affects the dynamics of the spatial distribution of wildfires. This study showed that moderate-level grazing might support effective fire management activities as fuel management because of modifying the fuel properties, changing the fuel-fire interaction (e.g., the fuel continuity and amount of accumulated fuel), and reducing the wildfire probability over space and time.

Effects of long‐term fixed fire regimes on African savanna vegetation biomass, vertical structure and tree stem density

Abstract Fire plays an integral role in shaping the vegetation structure of savanna ecosystems. However, the effects of fire regime characteristics, such as frequency and season of burn, on savanna vegetation structure, biomass and tree abundance across landscape types are largely unknown. We used high‐resolution airborne light detection and ranging (LiDAR) to investigate the long‐term effects of fire manipulation on savanna vegetation in Kruger National Park, South Africa. We analysed the effects of fire exclusion and experimental burns every 1, 2, 3, 4 and 6 years and during different seasons on aboveground biomass (AGB), tree stem densities and vegetation vertical height profiles across a rainfall gradient and on contrasting geologies. Across savanna types, and especially in drier savannas, fire season was more influential for constraining AGB than fire frequency. Plots experiencing fires during the late‐ and mid‐dry season had 44.50% and 43.60%, respectively, lower AGB relative to unburnt plots than wet‐season fires. However, in mesic savannas, fire frequency interacted with fire season to influence AGB: plots subjected to high frequency, dry‐season fires had 55.35% lower AGB than unburnt plots, whereas plots burnt in the wet season at lower frequencies had lower AGB (24.40% lower than unburnt plots) than plots subjected to high frequency, wet‐season fires (13.74% lower AGB than unburnt plots). Fire regimes had variable effects on tree densities, and effects varied with the savanna type. Woody vertical vegetation profiles showed the largest differences in response to dry‐season fires, with the greatest divergence in vegetation height classes <5 m. Synthesis and applications. Understanding the influence of fire regimes on vegetation structure has important implications for the management of savanna heterogeneity and for predicting trajectories of change in savanna vegetation as fire regimes vary with climate change. We show that the magnitude of the effect of fire on woody vegetation structure varies with savanna context. Our results suggest that heterogeneous vegetation structure can be achieved by applying fires in the dry season in mesic savannas, whereas in dry savannas, variation in fire regimes is less consequential for constraining biomass accumulation and altering vegetation structure.

Species-Specific Responses of Medium and Large Mammals to Fire Regime Attributes in a Fire-Prone Neotropical Savanna

Fire occurrence affects the distribution of key resources for fauna in natural ecosystems worldwide. For fire management strategies adequate for biodiversity conservation, the understanding of how species respond to fire-induced changes is essential. In this study, we investigated the role of fire regimes on spaces used by medium and large mammals at multiple spatial scales (0.8 ha to 78.5 ha) in a fire-prone savanna ecosystem (Brazilian Cerrado). We sampled mammals using 60 camera traps distributed in 30 sampling units located in grassland and typical savanna formations. We applied single-species occupancy models and AIC-based model selection to assess how mammals use the space in response to pyrodiversity (both diversity of fire frequencies and diversity of fire ages), the proportion of recently burned area, and the proportion of long-unburned area while accounting for detectability. Our results showed that fire regime variables affected the study species differently. Deer species used the space regardless of mosaic pyrodiversity and the proportion of specific fire ages. Fire-related variables, however, affected space use by tapirs and maned wolves. Tapirs preferred to use fire mosaics with lower diversity of fire frequencies, whereas maned wolves more intensively used mosaics with high fire age diversity and a high proportion of recently burned areas. Based on our findings, we recommend that fire management targeting specific mammal species should not necessarily focus on maximum pyrodiversity. Instead, we suggest a management strategy combining “patch mosaic burning” with the maintenance of specific fire-age patches suitable for different species’ requirements.

Stratigraphic evidence for culturally variable Indigenous fire regimes in ponderosa pine forests of the Mogollon Rim area, east-central Arizona

AbstractThe impact of Indigenous populations on historical fire regimes has been controversial and beset by mismatches in the geographic scale of paleofire reconstructions and the scale of land-use behaviors. It is often assumed that anthropogenic burning is linearly related to population density and not different cultural practices. Here we take an off-site geoarchaeology strategy to reconstruct variability in historical fire regimes (<1000 years ago) at geographic scales that match the archaeological, ethnohistorical, and oral tradition evidence for variability in the intensity of Indigenous land use by two different cultural groups (Ancestral Pueblo and Western Apache). We use multiple, independent proxies from three localities in ponderosa pine (Pinus ponderosa) forests in east-Central Arizona to reconstruct fire regime variability during four phases of cultural use of different intensities. Elevated charcoal with domesticate pollen (Zea spp.) but otherwise unchanged forest pollen assemblages characterized intensive land use by Ancestral Pueblo people during an early phase, suggesting fire use to support agricultural activities. By contrast, a phase of intensive pre-reservation Western Apache land use corresponded to little change in charcoal, but had elevated ash-derived phosphorus and elevated grass and ruderal pollen suggestive of enhanced burning in fine fuels to promote economically important wild plants.

Climate and socioeconomic drivers of biomass burning and carbon emissions from fires in tropical dry forests: A Pantropical analysis.

Global burned area has declined by nearly one quarter between 1998 and 2015. Drylands contain a large proportion of these global fires but there are important differences within the drylands, for example, savannas and tropical dry forests (TDF). Savannas, a biome fire-prone and fire-adapted, have reduced the burned area, while the fire in the TDF is one of the most critical factors impacting biodiversity and carbon emissions. Moreover, under climate change scenarios TDF is expected to increase its current extent and raise the risk of fires. Despite regional and global scale effects, and the influence of this ecosystem on the global carbon cycle, little effort has been dedicated to studying the influence of climate (seasonality and extreme events) and socioeconomic conditions of fire regimen in TDF. Here we use the Global Fire Emissions Database and, climate and socioeconomic metrics to better understand long-term factors explaining the variation in burned area and biomass in TDF at Pantropical scale. On average, fires affected 1.4% of the total TDF' area (60,208 km2 ) and burned 24.4% (259.6Tg) of the global burned biomass annually at Pantropical scales. Climate modulators largely influence local and regional fire regimes. Inter-annual variation in fire regime is shaped by El Niño and La Niña. During the El Niño and the forthcoming year of La Niña, there is an increment in extension (35.2% and 10.3%) and carbon emissions (42.9% and 10.6%). Socioeconomic indicators such as land-management and population were modulators of the size of both, burned area and carbon emissions. Moreover, fires may reduce the capability to reach the target of "half protected species" in the globe, that is, high-severity fires are recorded in ecoregions classified as nature could reach half protected. These observations may contribute to improving fire-management.

Size requirements of intact forest landscapes for effective biodiversity conservation under regional fire regimes and climate change

Conserving large intact forest landscapes (IFLs) is one forest management strategy to mitigate industrial impacts on the environment. Measuring the IFL inventory at national scales has also been proposed as a means of assessing the conservation status at global scales. This paper explores the relationship between fire regimes and the size of intact forest landscapes required to meet specific conservation targets. In this paper, we demonstrate that variation in fire regimes results in changes in the minimum size of IFL required to meet habitat targets. In addition, minimum IFL size is also dependent on the nature of the habitat targets. Larger IFLs are required to improve likelihood of providing sufficient older habitat. There is significant risk of not meeting older forest age-class targets at higher annual area burned (AAB) rates, especially under climate change. In general, there is more risk of not meeting habitat targets associated with smaller IFLs, higher annual area burned (both due to spatial differences and between historical and projected burn rates under climate change), and for provision of older forests. We used habitat age-related targets as outlined in the recovery strategy for woodland caribou as an example to demonstrate the usefulness of this type of simulation experiment and risk curves to identify appropriate IFL size along a gradient of natural disturbance intensity.

Resistance of termite mounds to variation in long-term fire regimes across semi-arid African savannas.

Fire regimes are expected to change with climate change, resulting in a crucial need to understand the specific ways in which variable fire regimes impact important contributors to ecosystem functioning, such as mound-building termites. Termite mounds and fire are both important agents of savanna ecosystem heterogeneity and functioning, but there is little understanding of how they interact across savanna types. We used very high-resolution LiDAR remote sensing to measure the size and distribution of termite mounds across approximately 1300 ha of experimental burn plots in four South African savanna landscapes representing a wide range of fire treatments differing in seasonality and frequency of burning. In nutrient-poor granitic savannas, fire had no impact on termite mound size, densities and spatial distributions. In nutrient-rich basaltic savannas with high mammalian herbivore abundance and intermediate rainfall, very frequent fires caused a decrease in termite mound size, whereas in arid nutrient-rich basaltic savannas, fires that occurred at intermediate frequencies and in transitional seasons (i.e. late dry season and late wet season) decreased the degree of spatial overdispersal exhibited by mounds. Overall, our results suggest that termite mounds are resistant to variation in fire seasonality and frequency, likely indicating that ecosystem services provided by mound-building termites will be unaffected by changing fire regimes. However, consideration of changes to termite mound size and distribution could be necessary for land managers in specific savanna types, such as nutrient-rich soils with high mammalian herbivore abundance.

Pyrogeography across the western Palaearctic: A diversity of fire regimes

AbstractAimThe aim was to characterize fire regimes and estimate fire regime parameters (area burnt, size, intensity, season, patchiness and pyrodiversity) at broad spatial scales using remotely sensed individual‐fire data.LocationWestern part of the Palaearctic realm (i.e., Europe, North Africa and the Near East).Time period2001–2021.MethodsInitially, I divided the study area into eight large ecoregions based on their environment and vegetation: Mediterranean, Arid, Atlantic, Mountains, Boreal, Steppes, Continental and Tundra. Next, I intersected each predefined ecoregion with individual‐fire data obtained from remote sensing hotspots to estimate fire regime parameters for each environment. This allowed me to compute annual area burnt, fire size, fire intensity, fire season, fire patchiness, fire recurrence and pyrodiversity for each ecoregion. I related those fire parameters to the climate of the ecoregions and analysed the temporal trends in fire size.ResultsFire regime parameters varied across different environments (ecoregions). The Mediterranean had the largest, most intense and most recurrent fires, but the Steppes had the largest burnt area. Arid ecosystems had the most extended fire season, Tundra had the patchiest fires, and Boreal forests had the earliest fires of the year. The spatial variability in fire regimes was largely explained by the variability of climate and vegetation, with a tendency for greater fire activity in the warmer ecoregions. There was also a temporal tendency for large fires to become larger during the last two decades, especially in Arid and Continental environments.Main conclusionThe fire regime characteristics of each ecoregion are unique, with a tendency for greater fire activity in warmer environments. In addition, fires have been increasing in size during recent decades.

Lowering the rate of timber harvesting to mitigate impacts of climate change on boreal caribou habitat quality in eastern Canada

Many boreal populations of woodland caribou (Rangifer tarandus caribou) have declined in Canada, a trend essentially driven by the increasing footprint of anthropogenic disturbances and the resulting habitat-mediated apparent competition that increases predation pressure. However, the influence of climate change on these ecological processes remains poorly understood. We evaluated how climate change will affect boreal caribou habitat over the 2030–2100 horizon and in a 9.94 Mha study area, using a climate-sensitive simulation ensemble that integrates climate-induced changes in stand dynamics, fire regime, and different levels of commercial timber harvesting. We assessed the relative importance of these three drivers under projections made using different radiative forcing scenarios (RCP 2.6, 4.5, 8.5). Habitat quality was estimated from resource selection functions built with telemetry data collected from 121 caribou between 2004 and 2011 in 7 local populations. At the beginning of our simulations, caribou habitat was already structured along a south-to-north increasing quality gradient. Simulations revealed changes in forest cover that are driven by climate-induced variations in fire regime and scenarios of harvesting levels, resulting in the loss of older coniferous forests and an increase in deciduous stands. These changes induced a generalized decrease in the average habitat quality and in the percentage of high-quality habitat for caribou, and in a northward recession of suitable habitat. Timber harvesting was the most important agent of change for the 2030–2050 horizon, although it was slowly replaced by changes in fire regime until 2100. Our results clearly showed that it is possible to maintain the current average habitat quality for caribou in future scenarios that consider a reduction in harvested volumes, the only lever under our control. This suggests that we still have the capacity to conciliate socioeconomic development and caribou conservation imperatives in the face of climate change, an important issue debated throughout the species distribution range.

Future fire predictions in light of millennial fire regime variability in Corsica, France

Future fire predictions in light of millennial fire regime variability in Corsica, France

Changing fire regimes during the first olive cultivation in the Mediterranean Basin: New high-resolution evidence from the Sea of Galilee, Israel

Throughout the Mediterranean biome, fire has been a dominant natural agent of change and an important tool for anthropogenic landscape modifications for millennia. However, fundamental knowledge on the complex linkages among fire, vegetation, and early agricultural practices remains limited. This research explores the role these processes have in shaping the landscape in the southern Levant – a key region with a long tradition of agriculture and horticulture. Olive horticulture is among the oldest and most widespread agricultural forms in the Mediterranean Basin. The earliest palynological evidence for olive horticulture is recorded in the Sea of Galilee in Israel and suggests that the first major olive cultivation began during the end of the 8th millennium BP. We present a multi-proxy dataset from the Sea of Galilee before and during the first olive cultivation (~7700–6680 a cal BP). Quantitative analyses of a charcoal time series categorized into distinct charcoal morphotypes indicate changes in fire regimes and sources of biomass burning. With a two-year-resolution, our study offers one of the highest resolution sedimentary charcoal records yet available worldwide. Isotopes from lake carbonates provide new evidence for the climatic setting of this phase, providing an independent evaluation of climatic impacts on vegetation and fire. Combined with palynological evidence, this multi-proxy dataset provides new insights into the linkages between fire, climate, fuel, and early horticultural practice. The fire regime changed with the start of olive cultivation in the Sea of Galilee's catchment. Fire frequency increased just before and during the expansion of olive cultivation, probably driven by the anthropogenic use of fire for clearing the landscape and promoting fertile soils. Once olive orchards were established, low magnitude fires became common, suggesting anthropogenic manipulation of the fire regime with frequent, low intensity, controlled burnings. Fuel limitation and low fuel connectivity likely played a role in both pre-cultivation and cultivation phases, resulting in low fire activity during times of reduced grass and woody vegetation cover. This study allows a new perspective into the temporal variability of middle-Holocene fire regimes in the Levant and an increased understanding of the dynamic role of fire during early horticulture practices. Our data also have relevance for future challenges that cultural legacies such as olive cultivation will face.

Large fires or small fires, will they differ in affecting shifts in species composition and distributions under climate change?

Climate change is expected to increase fire activity, which has the potential to accelerate climate-induced shifts in species composition and distribution in the boreal-temperate ecotone. Wildfire can kill resident trees, and thus provide establishment opportunities for migrating tree species. However, the role of fire size and its interactions with tree species with varied life-history attributes in driving climate-induced shifts is not understood. Future fire regimes could be characterized by many small fires or a few large fires. Large and small fires create and regulate distinct burn patterns, which may influence tree-species responses and post-fire successional trajectories. Here we investigated the effects of future fire-regime variability on the boreal-temperate ecotone of northeastern China under climate change using a coupled forest dynamic model (LANDIS PRO) and ecosystem process model (LINKAGES). We simulated fire regimes using the LANDIS PRO fire module. We designed two fire scenarios (frequent, small fires and infrequent, large fires) to represent different fire regimes in terms of fire size. Results showed fire-catalyzed, climate-induced transitions from boreal to pioneer and temperate forest communities. Frequent, small fires resulted in 13% and 23% higher increases in pioneer and temperate species respectively, relative to infrequent, large fires. Therefore, species composition shifts were faster following frequent, small fires than infrequent, large fires. The results can help policymakers and forest managers determine tradeoffs among strategies to mitigate or adapt to climate change under altered fire regimes.

The fire regime response of a reintroduced endangered species

Reintroduction and translocation are widely employed actions in restoration ecology. The broad aim of these activities is to re‐establish populations in places where they formerly existed. However, the success of re‐establishment efforts in terms of responses to key ecosystem processes such as natural disturbances like fires has rarely been quantified. Using the iconic and endangered Australian Eastern Bristlebird (Dasyornis brachypterus) as a case study, we quantified associations with fire regime variables in an intact population (surveyed for 17 years) and a translocated population (surveyed for 10 years). Both populations occurred in a similar environment and were surveyed on an (almost) annual basis using the same field protocols. We found that both the intact population and the translocated population of the Eastern Bristlebird were associated with the same key fire regime variable, time since fire, in a broadly similar way. In addition, the probability of species persistence was found to lowest on recently burnt sites. We tentatively suggest that the translocation program has not only successfully re‐established a population of the Eastern Bristlebird but associations with (and resilience to) fire as a key ecological process are similar in both populations. On the basis of our findings, we recommend that in areas where the Eastern Bristlebird occurs prescribed fire management should focus on ensuring there are patches of unburnt vegetation within the fire footprint. This is especially important given the widespread wildfires that have recently occurred throughout south‐eastern Australia.

Fire Regime Impacts on Postfire Diurnal Land Surface Temperature Change Over North American Boreal Forest

AbstractWildfire is the most prevalent natural disturbance in the North American boreal forest (NABF) and can cause postfire land surface temperature change (ΔTfire) through biophysical processes. Fire regimes, such as fire severity, fire intensity, and percentage of burned area (PBA), may influence ΔTfire through their impacts on postfire vegetation damage and, if so, there may be important feedbacks between fire regime and climate warming through biophysical effects. Here, we employ satellite observations to investigate postfire diurnal ΔTfire across NABF. We further use a stepwise multiple linear regression model to examine the driving factors for ΔTfire by incorporating latitude, fire regime variables, and their interactions. Our results demonstrate a pronounced asymmetry in diurnal ΔTfire, characterized by daytime warming in contrast to nighttime cooling. Clear latitudinal patterns are found in ΔTfire, with stronger effects in lower latitudes. Such latitudinal patterns of ΔTfire, especially the daytime one, are driven by both latitudinal patterns in fire regimes and an increased sensitivity of ΔTfire to fire regime as the latitude decreases. The multiple linear regression model explains 37% of the variance in daytime ΔTfire, whereas for the nighttime ΔTfire the explanatory power is rather low (5%). For daytime ΔTfire, fire severity accounted for most (43.65%) of the model explanatory power, followed by PBA (24.60%) and fire intensity (13.10%). Our results highlight important fire regime impacts on daytime ΔTfire and, further, on the annual ΔTfire, suggesting that fire might amplify future boreal climate change through positive feedbacks between fire regime and postfire surface warming.

Bat activity response to fire regime depends on species, vegetation conditions, and behavior

Disturbances such as fire play an important role in shaping forests and the wildlife they support. As such, forest managers employ prescribed fire to restore ecosystem function, promote forest biodiversity, and maintain wildlife habitat. To better understand how bats respond to variation in fire regime, we used acoustic recorders to quantify bat activity in forests maintained by frequent fire in southern Florida, USA and modelled this variation as a function of both fire regime and vegetation characteristics. Next, to better understand the mechanisms underlying these responses, we quantified variation in bat foraging efficiency and activity during the important early evening period. We found that even in regions historically maintained by frequent fire, bat activity was more closely associated with vegetation conditions, such as canopy cover and woody understory volume, than fire regime. When vegetation and fire frequency were considered together, the bat activity response was nuanced. Activity across the bat community was greater in forests that had burned more frequently in the previous two decades, but bats appeared more likely to encounter prey in forests that burned less frequently. Species-specific responses added additional complexity, potentially related to size and wing morphology, with larger bats responding more strongly to fire, whereas activity of smaller bats was primarily related to vegetation characteristics. Similarly, activity during the early-evening shifted as a function of fire frequency, but in different directions for different species. Our results suggest that investigations of occurrence or overall bat activity may provide an incomplete understanding of the complex responses to fire regimes that become more apparent when activity is partitioned into more refined metrics. These nuances have implications for management of fire-maintained forests. Though frequent burning may best promote the ecosystem services associated with insectivorous bat activity, a more heterogenous approach to fire management that considers bat species diversity, bat behavior, and vegetation conditions may provide additional benefits to bats.

Historical fire regimes of North American hemiboreal peatlands

Peatlands contain one-third to one-half of global soil carbon, and disturbances, specifically fire, directly influence these carbon stocks. Despite this, historical variability of peatland fire regimes is largely unknown. This gap in knowledge partly stems from reconstructions of peatland fire regimes with methods limited to evaluating infrequent, severe fire events and not capturing frequent, low-severity events. Furthermore, variability in fire regimes is likely higher in heterogenous landscapes like the hemiboreal subzone, the transition between boreal and temperate biomes, where peatlands are embedded in landscapes including forests with high proportions of fire-dependent species, such as red pine (Pinus resinosa), that are well adapted to frequent low-severity fires. Here, we sought to evaluate the role of low- and moderate-severity fires within hemiboreal peatlands in central North America to better understand historical variability in fire regimes. We reconstructed historical fire regimes using fine-scale (temporal and spatial) dendrochronology methods to estimate frequency of low- and moderate-severity fires, identify synchronous fire events among forested uplands within and surrounding individual peatlands as well as among sites, and assess fire-climate relationships. We collected 220 cross-sections or partial-tree sections within three poor fen peatlands across the Great Lakes Region. Using standard dendrochronological techniques, we crossdated 129 samples, assigning dates to 414 fire scars (128 unique fire years) comprising a 500-year tree-ring record (1520–2019). Prior to the mid-1900s, fire events were frequent and widespread within peatlands we evaluated, with mean fire return intervals (MFRI) ranging from 7 to 31 years. Fire events were also synchronous among forested uplands within and surrounding peatlands. Fires predominantly occurred in the dormant and latewood (growing season) positions and during regionally dry conditions corresponding to mild and moderate drought (Palmer Drought Severity Index ≥ −2.99) but interestingly not during regionally severe drought (Palmer Drought Severity Index ≤ −3.00). While large-scale, high-severity fires are important to the ecology of peatlands and to changing climate-fire interactions, our results suggest that widespread low- to moderate-severity fires were historically frequent in hemiboreal peatlands and likely central to their development and maintenance. Evaluating whether peatlands will continue to be carbon sinks or become carbon sources due to climate change requires an understanding of the inherent variability in fire regimes, especially in hemiboreal systems.