Fire Episodes Research Articles

Influence of forest fire episodes on the distribution of gaseous air pollutants over Uttarakhand, India

ABSTRACTWidespread forest fire events occurred in the foothills of North Western Himalaya during 24 April to 2 May 2016 (Event-1) and 20–30 May 2018 (Event-2). Their impacts were investigated on the distribution of pollutant gases ozone (O3), carbon monoxide (CO), and oxides of nitrogen (NOx) over Uttarakhand using simulations of Weather Research and Forecasting model coupled with chemistry (WRF-Chem) and in-situ observations of these gases over Dehradun, the capital of Uttarakhand. During Event-1, the observed CO mixing ratio over Dehradun increased from 25 April 2016 onwards, attained maximum (705.8 ± 258 ppbv) on 2 May 2016 and subsequently decreased. The rate of increase of daily baseline CO was 29 ppbv/day during HFAP (High Fire Activity Period). During Event-2, daily average concentrations of CO, O3, and NOx showed systematic increase over Dehradun during HFAP period. The rate of increase of CO was 9 ppbv/day, while it was very small for NOx and O3. To quantitatively estimate the influence of forest fire emissions, two WRF-Chem simulations were made: one with biomass burning (BB) emissions and other without BB emissions. These simulations showed 52% (34%) enhancement in CO, 52% (32%) enhancement in NOx, and 11% (9%) enhancement in O3 during HFAP for Event-1 (Event-2). A clear positive correlation (r = 0.89 for Event-1, r = 0.69 for Event-2) was found between ∆O3 (O3with BB minus O3without BB) and ∆CO (COwith BB minus COwithout BB), indicating rapid production of ozone in the fire plumes. For both the events, the vertical distribution of ∆O3, ∆CO, and ∆NOx showed that forest fire emissions influenced the air quality upto 6.5 km altitude. Peaks in ∆O3, ∆CO, and ∆NOx during different days suggested the role of varying dispersion and horizontal mixing of fire plumes.

Air quality changes in Ukraine during the April 2020 wildfire event

The paper analyzes air quality changes in Ukraine during a wildfire event in April 2020 and a dust storm episode during the 16th of April 2020. The wildfire event contained two episodes of active fires and huge pollutants' emission: 4-14 April and 16-21 April, respectively. Using the Sentinel-5P data of CO and NO 2 column number density and ground-based measurements, there was estimated air quality deterioration. Advection of polluted air masses and analysis of affected territories were made in combination with a Web-based HYSPLIT model. Satellite data described air quality changes better than in-situ measurements. Data intercomparison showed better coincidence in regions that were not affected by wildfire emissions. The paper described the dust storm event based on absorbing aerosol index (AAI) data that occurred between two wildfire episodes.

Assessment of Urban Air Quality in Indonesia

ABSTRACT This study assessed the urban air quality in 16 large Indonesian cities on the islands of Java, Sumatra, Kalimantan, Sulawesi, Maluku, and Papua from 2010 till 2017. 24-h samples of airborne particulate matter (PM) in two size fractions, PM2.5 (< 2.5 µm in aerodynamic diameter) and PM2.5-10 (2.5–10 µm in aerodynamic diameter), were collected weekly using a Gent stacked filter unit sampler and then analyzed for their mass concentrations, black carbon (BC) content, and elemental compositions. The majority of the average annual PM2.5 concentrations measured at the Java sites (Bandung, Jakarta, Semarang, and Surabaya) exceeded the Indonesian annual ambient air quality standard (15 µg m–3), although the other tested locations, excluding Pekanbaru and Palangka Raya, exhibited values below the standard. During the forest fire episodes of 2015, the average daily PM2.5 concentrations in Pekanbaru and Palangka Raya rose above the national daily ambient standard (65 µg m–3). The percentage of BC, which is associated with traffic emission and biomass burning, averaged between 15% and 26% (a significant fraction) in the PM2.5. The concentrations of the major elements in the PM2.5, viz., Si, S, K, Fe, Zn, and Pb, varied widely from site to site, although all of the locations displayed enhanced levels of the crustal elements Si and S, which originated from unpaved roads and volcanic eruptions, and vehicle fuel, forest fires, and volcanic emissions, respectively. Significantly higher concentrations of heavy metals (Fe, Zn, and Pb in Surabaya and Pb in Tangerang) were found at the heavily industrialized sites, demonstrating the effect of local industrial emissions on air quality. Our results, which are based on a crucial survey of PM concentrations and compositions in Indonesia, provide a scientific basis for developing and improving various air quality policies in the nation, including an early warning system for severe pollution events.

Bushfires in Australia: a serious health emergency under climate change

Bushfires in Australia: a serious health emergency under climate change

Urban air pollution, climate change and wildfires: The case study of an extended forest fire episode in northern Italy favoured by drought and warm weather conditions

The aim of the paper is to describe the spread forest fire event occurred in the Italian Alps in 2017 under extremely drought conditions. In the study the root causes of wildfires and their direct relapses to the air quality of the Western Po valley and the urban centre of Torino have been assessed by means of air pollution measurements (focused to particulate matter with reference samplers and optical particle counters OPCs), meteorological indicators and additional public data. Results show a good correlation among different urban sites and instrument technologies. Concentration data, compared with environmental conditions and historical values describe the clear impact of fires on both local and regional air quality. Indeed, the deferred impact of wildfires on the local wood biomass energy supply chain is briefly outlined.

A high-resolution sedimentary charcoal- and geochemistry-based reconstruction of late Holocene fire regimes in the páramo of Chirripό National Park, Costa Rica

AbstractMultiproxy analysis of two sediment cores recovered from lagos Morrenas 3C and Ditkebi, located in the páramo of Costa Rica's Chirripó National Park, was undertaken to develop multidecadal-scale reconstructions of late Holocene fire regimes for the region. Analysis of macroscopic charcoal and sediment geochemistry (C%, N%, δ13C, δ15N, and C/N ratios) documents periodic burning of the páramo in Chirripó National Park during the past ~1700 yr. The charcoal records provide evidence of high fire frequency between AD ~560 and 720 and between AD ~980 and 1230. Severe fire episodes are reflected by a rapid increase in the flux of carbon (C) and nitrogen (N) from the surrounding catchment because of the volatilization of páramo vegetation. Additionally, δ15N, which sharply increases following local fire events, captures postfire changes in nutrient loading and, likely, the decadal-scale rate of postfire recovery of páramo vegetation. The consistently high δ13C and C/N values observed between AD ~700 and 1100 suggest an expansion ofMuhlenbergia, a native C4grass growing near shore, suggesting that the interval between AD ~700 and 1100, broadly corresponding to the Terminal Classic Drought and Medieval Climate Anomaly, was characterized by a decrease in effective moisture and temperature.

Chemical characterization of urban PM10 in the Tropical Andes

Complex inhalable particles have become one of the main causes to trigger health problems worldwide. While the level of concern depends on the chemical composition of these particles, some regions are poorly studied, particularly, the Andes. In this work, the chemical characterization of atmospheric PM10 filter samples, collected between January and October of 2017, was carried out for the first time in the world's highest capital, Quito, Ecuador. This study investigates PM10 relation with meteorological variables and criteria pollutants. Average PM10 concentrations ranged from 24.9 μg m−3 to 26.2 μg m−3, with some alarming peaks during the episodes of fires and New Year's celebration. The major elements at study sites were Ca, Na, S, Mg, P, K, Fe, Si and Al, while the major water-soluble ion was SO42−. Meteorology plays an important role at this complex terrain city. Factor analysis showed natural dust and soil resuspension as the main source of particulate matter. Moreover, two less urbanized sites showed evidence of industrial activities or airport emissions, while the central city site showed a very strong signal of traffic-related pollution. These results are compared with representative cities around the world. As is the case in developing countries, low-quality diesel fuel is recognized for emitting large amounts of heavy metals, resulting in higher levels of those tracers in traffic flow areas. This work demonstrates the problems facing a midsize city, such as the lack of stricter regulations and, thus compromised air quality. This may imply serious respiratory and cardiovascular health effects.

Century-Scale Fire Dynamics in a Savanna Ecosystem

(1) Background: Frequent fire, climate variability, and human activities collectively influence savanna ecosystems. The relative role of these three factors likely varies on interannual, decadal, and centennial timescales. Here, we tested if Euro-American activities uncoupled drought and fire frequencies relative to previous centuries in a temperate savanna site. (2) Methods: We combined records of fire frequency from tree ring fire scars and sediment charcoal abundance, and a record of fuel type based on charcoal particle morphometry to reconstruct centennial scale shifts in fire frequency and fuel sources in a savanna ecosystem. We also tested the climate influence on fire occurrence with an independently derived tree-ring reconstruction of drought. We contextualized these data with historical records of human activity. (3) Results: Tree fire scars revealed eight fire events from 1822–1924 CE, followed by localized suppression. Charcoal signals highlight 13 fire episodes from 1696–2001. Fire–climate coupling was not clearly evident both before and after Euro American settlement The dominant fuel source shifted from herbaceous to woody fuel during the early-mid 20th century. (4) Conclusions: Euro-American settlement and landscape fragmentation disrupted the pre-settlement fire regime (fire frequency and fuel sources). Our results highlight the potential for improved insight by synthesizing interpretation of multiple paleofire proxies, especially in fire regimes with mixed fuel sources.

Human-induced fire regime shifts during 19th century industrialization: A robust fire regime reconstruction using northern Polish lake sediments.

Fire regime shifts are driven by climate and natural vegetation changes, but can be strongly affected by human land management. Yet, it is poorly known how humans have influenced fire regimes prior to active wildfire suppression. Among the last 250 years, the human contribution to the global increase in fire occurrence during the mid-19th century is especially unclear, as data sources are limited. Here, we test the extent to which forest management has driven fire regime shifts in a temperate forest landscape. We combine multiple fire proxies (macroscopic charcoal and fire-related biomarkers) derived from highly resolved lake sediments (i.e., 3–5 years per sample), and apply a new statistical approach to classify source area- and temperature-specific fire regimes (biomass burnt, fire episodes). We compare these records with independent climate and vegetation reconstructions. We find two prominent fire regime shifts during the 19th and 20th centuries, driven by an adaptive socio-ecological cycle in human forest management. Although individual fire episodes were triggered mainly by arson (as described in historical documents) during dry summers, the biomass burnt increased unintentionally during the mid-19th century due to the plantation of flammable, fast-growing pine tree monocultures needed for industrialization. State forest management reacted with active fire management and suppression during the 20th century. However, pine cover has been increasing since the 1990s and climate projections predict increasingly dry conditions, suggesting a renewed need for adaptations to reduce the increasing fire risk.

Fire frequency and intensity associated with functional traits of dominant forest type in the Balkans during the Holocene

Disturbances by fire are among the most important processes that shape forest dynamics and diversity. However, the long-term variability of fire disturbance regimes in many European forests and specifically in the mountains of the Balkan Peninsula is not well understood. Here, we present the first Holocene record of fire regimes based on macrocharcoal morphologies in combination with pollen-based reconstruction of forest dynamics and fire-related strategies of prevailing mountain forests in the Rila Mountains, Bulgaria. While biomass burning followed the main trends in climate, the frequency and intensity of fire were strongly linked to fire-related coping strategies of dominant tree taxa (resisters, avoiders or invaders). Frequent fires of low intensity between 12,000 and 9000 cal year BP were concurrent with the dominance of invaders (Betula, herbs, ferns). Intermittent occurrence of low- and high-intensity surface and crown fires with longer return intervals between 9000 and 4000 cal year BP was associated with codominance of resister (Pinus sylvestris, Pinus peuce, Pinus mugo) and avoider (Abies alba and Picea abies) forest types, whereas a lengthening of the fire return interval over the past 4000 years was linked to increased abundance of P. abies. As a rising number of fire episodes may drive land cover towards more fire-adapted plant communities and towards less intense fire events, we expect increased dominance of invaders (resprouters that rapidly reach maturity stage) as well as resisters (properties protecting from fire damage) under future warmer and drier climate. This study also shows the potential of combining charcoal morphologies with pollen records to track variability in fire intensity and plant functional attributes over long timescales that are also relevant to forest management stakeholders.

Chemical Composition of Fine Particulate Matter from Peat Forest Fires at Palangka Raya and Its Dispersion using HYSPLIT

An air quality monitoring was conducted to investigate the chemical characteristics of particulate emissions in peat forest fires at Palangka Raya, Indonesia during 2012 where a peat forest fire episode occurred. Aerosol samples were collected at Palangka Raya where represents a sub urban site downwind of the peat forest fires. The samples were collected using Gent stacked filter unit sampler. The sampler provides two size fractions: coarse (2.5-10 μm equivalent aerodynamic diameters EAD) and fine (<2.5 μm EAD). Black carbon (BC) was measured using Smoke Stain Reflectometer, and elemental compositions were analyzed using X-ray Fluorescence (XRF). The concentrations of PM2.5 during a haze episode were significantly different about seven to eight times higher when compared to the concentrations in non-haze conditions. The major components of PM2.5 in peat smoke haze consist of sulphur, biomass burning component (BC, K), and crustal components (Al, Fe, Si). The sulphur mainly comes from the peat as it is the earliest stage of transition from compressed plant growth to the formation of coal. The dispersion pattern to show the effect of wind direction using the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) simulation was also applied.

Bryophytes Associated with Termite Mounds on the Northeastern Nigerian Highlands

Eighteen termite mounds on a stretch of undulating continuously grazed and burnt grasslands on the Mambilla Plateau, Eastern Nigeria, were surveyed for bryophytes. Bryophyte mats were present on all mounds investigated except one. The bryophyte mats were located at the base of the mounds, on a depression etched by raindrops and apparently serving to keep erosion at bay. We suggest that on grasslands with frequent fire episodes, the bryophyte mats may also play a role in fireproofing the mounds. In all, eight bryophytes species across five families were collected on the termite mounds. All species were new to the region but had been collected elsewhere from different substrates in Nigeria, except Fissidens ezukanmae Brugg.-Nann., which is a new species collected for the first time from termite mounds on Eastern Nigerian Highlands. Two species, Campylopus obrutus Ther. & P. de la Varde and Fissidens intramarginatus (Hampe) A.Jaeger, with estimated frequency of 24% each, were the most abundant species on the termite mounds.

Collective impacts of biomass burning and synoptic weather on surface PM2.5 and CO in Northeast China

Biomass burning has become one of the prominent sources of air pollution in Northeast China, where the land is largely covered by forest, grasslands, and agricultural crops. Nevertheless, the impact of biomass burning on air quality and the sensitivity of such impact to weather are rarely documented. In this study, we addressed these issues using satellite fire radiative power (FRP) and surface PM2.5 and CO data at 24 stations during fire seasons (March, April, October and November) in Northeast China from 2015 to 2017. Fire-polluted days were identified by tracing air parcels at the stations back to fire regions using a trajectory model, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results show that 60–80% the polluted days in Northeast China can be attributed to biomass burning in the fire seasons, varying among subregions due to the differences in landscapes, fire activities, and weather conditions. On fire-polluted days, the mean PM2.5 and CO concentrations from all observation stations in Northeast China reached 111 μg m−3 and 1.3 mg m−3, respectively. The hourly PM2.5 and CO concentrations on fire-polluted days could reach as high as 1000 μg m−3 and 10 mg m−3, respectively. By subregions, the mean PM2.5 concentrations were 128, 112, 102, 106 μg m−3, respectively, in the central, eastern, northern, and southern subregions, while mean CO concentrations were 1.2, 1.3, 0.8, 1.5 mg m−3, respectively, in the four corresponding subregions. On average, PM2.5 and CO concentrations on fire-polluted days elevated, respectively, by 22–54% and 4–11% from those on no-fire-polluted days, with the largest enhancement in the central subregion and the least in the southern subregion. We classified six predominant weather patterns during the fire seasons. When Northeast China was ahead of a strong Siberian High, fire-polluted days were least and FRP was weakest among the six patterns in most subregions, leading to lowest enhancement of PM2.5 and CO in the subregions. In contrast, two weather patterns exacerbated PM2.5 and CO pollution the most during fire episodes. Under one of the weather patterns, Northeast China was under a stagnant high-pressure system, resulting in poor dispersion conditions and thus high PM2.5 and CO pollution. The other pattern was characterized with high humidity and southwesterlies ahead of a trough, which brought about strong hygroscopic growth and regional transport of fire emissions. The degree to which the weather patterns impacted air pollution during fires varied largely among subregions. This study highlights the combined impacts of biomass burning and weather on air pollution. The findings and the developed methodology are helpful for forecasting air quality and implementing mitigation strategies during biomass burning.

Evaluation of the airborne pollution by emerging contaminants using bitter orange (Citrus aurantium) tree leaves as biosamplers

In this work, an analytical method has been applied to biomonitor airborne emerging pollutants in urban areas using bitter orange (Citrus aurantium) tree leaves, which is an evergreen species widely extended in the Mediterranean region, as biosampler. Leaves, from trees located in 20 different locations from Seville City (South of Spain) were sampled during one year period. Sampling sites were located in six highly populated areas, in seven lowly populated areas, in six urban parks and in one industrial area. Fifteen of the target compounds were detected in the analysed samples. The highest concentrations corresponded to plasticizers (up to 852ng/g dry matter (dm)) and surfactants (up to 752ng/gdm), especially di(2-ethylhexyl)phthalate and nonylphenol. Spatial distribution allowed assessing the influence of populated areas in the concentration of some of the studied compounds, such as plasticizers and perfluorinated compounds, and the influence of industrial areas, in the concentration of surfactants. No clear influence of the climatic conditions (temperature, solar radiation and rainfall) on the concentrations of studied compounds was observed. This fact could be due to the presence of diffuse sources of these compounds. In the case of the brominated flame retardant, the measured concentrations could be related with two fire episodes in the vicinity, but until now it has not been possible to rigorously demonstrate a causal relationship. This fact could reveal the suitability and valuable use of Citrus aurantium tree leaves for biomonitoring atmospheric pollutants, especially from unexpected emissions in atmospheric pollution episodes.

Phylogenetic community structure as an ecological indicator of anthropogenic disturbance for endemic lizards in a biodiversity hotspot

The expansion of human-altered landscapes affects biodiversity on every continent. In the Cerrado biodiversity hotspot of central Brazil, Eucalyptus plantations increasingly claim large tracts of native habitats thanks to favorable soils, climate and booming pulp firm profits. Yet, the highs and lows of the economy including government incentives over the years riddled the landscape with abandoned plantations, which are not subject to active restoration. Despite the well-documented pattern anthropogenic disturbances negatively affect Cerrado biodiversity, little is known about the processes driving species co-existence within these abandoned plantations.Herein, we use phylogenetic community structure indices to test if potential processes assembling lizard communities differ between undisturbed Cerrado habitats and disturbed abandoned Eucalyptus plantations; and if so, are these processes predictable. In addition, we explore the applicability of phylogenetic community structure indices as ecological indicators of anthropogenic disturbance in the Cerrado biodiversity hotspot.We address these questions at a local scale, recording lizard species richness and abundance along transects of undisturbed Cerrado and adjacent disturbed abandoned Eucalyptus plantations. Morphological measurements were collected from captured lizards to test for trait conservatism. We investigated if phylogenetic community structure is altered in a predictable manner by comparing (i) phylogenetic species variability, (ii) phylogenetic species richness and (iii) phylogenetic species evenness. To test for significant differences between undisturbed and disturbed communities, we performed two-tailed paired t-tests for each phylogenetic community index. We also test for phylogenetic clustering and overdispersion to determine if potential processes assembling lizard communities differ between undisturbed and disturbed communities. Furthermore, we compare phylogenetic community structure indices to other commonly used diversity indices (taxonomic, functional and phylogenetic diversity) to evaluate their applicability as ecological indicators of anthropogenic disturbance in the Cerrado.We demonstrated phylogenetic clustering in two out of three of the undisturbed Cerrado lizard communities supporting habitat filtering as the potential dominant assembly process; whereas 67% of the disturbed Eucalyptus communities showed phylogenetic overdispersion supporting competition as the potential predominate assembly process. This indicates anthropogenic disturbance, in the form of abandoned Eucalyptus plantations, may alter phylogenetic community structure in a predictable manner, leading to the loss of closely related species in the disturbed plantation forests. The highly endemic biota of the Cerrado is composed of closely related species that share similar traits for survival, most likely a consequence of frequent episodic fires during the dry season. Interestingly, phylogenetic community structure indices and diversity indices did not converge on the same disturbed site to prioritize for active restoration; thereby, providing a cautionary tale on the applicability of the indices as ecological indicators for the Cerrado biodiversity.

Stopping waves: geometric analysis of coupled bursters in an asymmetric excitation field

Bursting is a type of electrical activity seen in many neurons and endocrine cells where episodes of action potential firing are interspersed by silent phases. Here, we investigate partial synchrony and wave propagation in a population of square-wave bursters. In particular, by using a prototypical polynomial bursting model and slow/fast bifurcation analysis, we study why electrically coupled model bursters typically synchronize very easily, as reflected in the tendency for simulated excitation waves to propagate far into the region of silent cells when an excitation gradient is imposed. Such simulation is inspired by, but does not reproduce, experimentally observed Ca2+ waves in pancreatic islets exposed to a glucose gradient. Our analyses indicate a possible modification of the model so that the excitation waves stop at the border between “active” and “silent” cells. We verify this property by simulations using such a modified model for a chain, and for a cubic cluster, of coupled cells. Furthermore, we show how our one- and two-parameter bifurcation analyses allow us to predict where the simulated waves stop, for both the original model and the modified version.

Post‐fire vegetation and climate dynamics in low‐elevation forests over the last three millennia in Yellowstone National Park

Conifer forests of the western US are historically well adapted to wildfires, but current warming is creating novel disturbance regimes that may fundamentally change future forest dynamics. Stand‐replacing fires can catalyze forest reorganization by providing periodic opportunities for establishment of new tree cohorts that set the stage for stand development for centuries to come. Extensive research on modern and past fires in the Northern Rockies reveals how variations in climate and fire have led to large changes in forest distribution and composition. Unclear, however, is the importance of individual fire episodes in catalyzing change. We used high‐resolution paleoecologic and paleoclimatic data from Crevice Lake (Yellowstone National Park, Wyoming, USA), to explore the role of fire in driving low‐elevation forest dynamics over the last 2820 yr. We addressed two questions: 1) did low‐elevation forests at Crevice Lake experience abrupt community‐level vegetation changes in response to past fire events? 2) Did the interaction of short‐term disturbance events (fire) and long‐term climate change catalyze past shifts in forest composition? Over the last 2820 yr, we found no evidence for abrupt community‐level vegetation transitions at Crevice Lake, and no evidence that an interaction of climate and fire produced changes in the relative abundance of dominant plant taxa. In part, this result reflects limitations of the datasets to detect past event‐specific responses and their causes. Nonetheless, the relative stability of the vegetation to fires over the last 2820 yr provides a local baseline for assessing current and future ecological change. Observations of climate–fire–vegetation dynamics in recent decades suggest that this multi‐millennial‐scale baseline may soon be exceeded.

Modeling initial attack success of wildfire suppression in Catalonia, Spain

In southern European regions, the few fires that escape initial attack (IA) account for most of the burned area. Nonetheless, limited effort has been conducted to develop spatiotemporal models aiming at improving pre-positioning and deployment of fire-fighting brigades on the first dispatch. To this end, we calibrated a model to assess the probability of containment of fire by IA in Catalonia (northeastern Spain). The model was trained using machine learning algorithms from georeferenced historical fire ignition locations, fire response and weather conditions. Our results indicated that early detection, ground accessibility, and aerial support governed the broad spatial pattern of fire containment probability, with strong gradients that ranged from lowest chances of containment in northwestern mountains to highest in the coastal belt. In turn, weather conditions and fire simultaneity were crucial to explain the differences during wildfire season. We found that fires igniting above the 85th percentile of temperature and wind speed, during simultaneous fire episodes (n > 10), and 12.5 km away from the nearest fire station will probably escape IA, and grow into large events. These hazardous fire danger conditions were met 13 days per year on average during the period 1998–2015, with 5 fire simultaneous episodes escaping IA that burned 1546 ha in total. Results were provided as a set of high-resolution raster grids (100 m), which replicated the most typical weather and fire occurrence scenarios that first responders are likely to face during the wildfire season. This study reveals existing limitations in the dominant fire exclusion policy of Mediterranean areas and advocates for a comprehensive long-term wildfire management solution. Our model may help inform science-based decision-making on IA and general fire response planning in the study area.

Humans take control of fire-driven diversity changes in Mediterranean Iberia’s vegetation during the mid–late Holocene

Fire regime changes are considered a major threat to future biodiversity in the Mediterranean Basin. Such predictions remain uncertain, given that fire regime changes and their ecological impacts occur over timescales that are too long for direct observation. Here we analyse centennial- and millennial-scale shifts in fire regimes and compositional turnover to track the consequences of fire regime shifts on Mediterranean vegetation diversity. We estimated rate-of-change, richness and compositional turnover (beta diversity) in 13 selected high-resolution palaeoecological records from Mediterranean Iberia and compared these with charcoal-inferred fire regime changes. Event sequence analysis showed fire regime shifts to be significantly temporally associated with compositional turnover, particularly during the last three millennia. We find that the timing and direction of fire and diversity change in Mediterranean Iberia are best explained by long-term human–environment interactions dating back perhaps 7500 years. Evidence suggests that Neolithic burning propagated a first wave of increasing vegetation openness and promoted woodland diversity around early farming settlements. Landscape transformation intensified around 5500 to 5000 cal. yr BP and accelerated during the last two millennia, as fire led to permanent transitions in ecosystem state. These fire episodes increased open vegetation diversity, decreased woodland diversity and significantly altered richness on a regional scale. Our study suggests that anthropogenic fires played a primary role in diversity changes in Mediterranean Iberia. Their millennia-long legacy in today’s vegetation should be considered for biodiversity conservation and landscape management.

Impact of wildfires on particulate matter in the Euro-Mediterranean in 2007: sensitivity to some parameterizations of emissions in air quality models

Abstract. This study examines the uncertainties on air quality modeling associated with the integration of wildfire emissions in chemistry-transport models (CTMs). To do so, aerosol concentrations during the summer of 2007, which was marked by severe fire episodes in the Euro-Mediterranean region especially in the Balkans (20–31 July, 24–30 August 2007) and Greece (24–30 August 2007), are analyzed. Through comparisons to observations from surface networks and satellite remote sensing, we evaluate the abilities of two CTMs, Polyphemus/Polair3D and CHIMERE, to simulate the impact of fires on the regional particulate matter (PM) concentrations and optical properties. During the two main fire events, fire emissions may contribute up to 90 % of surface PM2.5 concentrations in the fire regions (Balkans and Greece), with a significant regional impact associated with long-range transport. Good general performances of the models and a clear improvement of PM2.5 and aerosol optical depth (AOD) are shown when fires are taken into account in the models with high correlation coefficients. Two sources of uncertainties are specifically analyzed in terms of surface PM2.5 concentrations and AOD using sensitivity simulations: secondary organic aerosol (SOA) formation from intermediate and semi-volatile organic compounds (I/S-VOCs) and emissions' injection heights. The analysis highlights that surface PM2.5 concentrations are highly sensitive to injection heights (with a sensitivity that can be as high as 50 % compared to the sensitivity to I/S-VOC emissions which is lower than 30 %). However, AOD which is vertically integrated is less sensitive to the injection heights (mostly below 20 %) but highly sensitive to I/S-VOC emissions (with sensitivity that can be as high as 40 %). The maximum statistical dispersion, which quantifies uncertainties related to fire emission modeling, is up to 75 % for PM2.5 in the Balkans and Greece, and varies between 36 % and 45 % for AOD above fire regions. The simulated number of daily exceedance of World Health Organization (WHO) recommendations for PM2.5 over the considered region reaches 30 days in regions affected by fires and ∼10 days in fire plumes, which is slightly underestimated compared to available observations. The maximum statistical dispersion (σ) on this indicator is also large (with σ reaching 15 days), showing the need for better understanding of the transport and evolution of fire plumes in addition to fire emissions.