Savanna Fires Research Articles

The threatened Gouldian finch preferentially forages in prescribed burnt savannas

Background The granivorous finches of Australia’s tropical savannas heavily rely on a sequence of perennial and annual grass seed production to feed throughout the year. An increase in late dry season wildfires has been suggested to detrimentally effect seed production sequence and has been attributed to poor physiological condition and a reduction in fitness of granivorous finches. Early dry season prescribed burning is an asset protection management strategy often implemented to reduce the incidence of late dry season wildfire, but has also been shown to improve the abundance and nutritional quality of grass seed Aims To assess whether the Gouldian finch (Chloebia gouldiae) preferentially used areas that were subject to early dry season prescribed burning over areas that were not burnt. Methods The creation of a landscape mosaic across the landscape with varying fire histories. Then the assessment of individual finch movement and site utilisation using VHF-radio telemetry transmitters, detected by an array of static receivers deployed across the landscape. Key results Finches significantly preferred to forage in areas burnt in the early season every 2–3 years. Conclusions The study demonstrates that early dry season prescribed burning creates preferred foraging habitat patches for Gouldian finches within savanna fire mosaics.

Fire on a tropical floodplain: a fine-scale fire history of coastal floodplains in the Northern Territory, Australia

Background The coastal floodplains of northern Australia are fire-prone, but the impact of fire on floodplain biota is not well understood. Aims In this study, we sought to characterise the fire history of six adjacent floodplains in coastal Northern Territory, Australia. Methods We built a fine-scale 31-year fire history (1988–2018) to compare fire regimes on floodplains across land tenures and floodplain fire regimes with the surrounding savanna fire regime, determine the extent to which current fire regimes are meeting existing ecological fire thresholds, and investigate the relationship between rainfall totals and the extent of burning. Key results Floodplains in conservation reserves burnt more frequently than those on pastoral lands, and savannas burnt more often than floodplains. Current floodplain fire regimes comfortably meet existing ecological fire thresholds. The proportion of floodplain burning is inversely proportional to the amount of rain in the previous wet season. Conclusions Floodplain fire regimes vary markedly between land-use types, and floodplain fire regimes differ to those of savannas. The current management thresholds for floodplain fire regimes would benefit from further evidence of conservation outcomes. Implications For more effective floodplain fire management, research is needed to generate floodplain-specific thresholds that best conserve their considerable conservation value.

Characterization of land cover-specific fire regimes in the Brazilian Amazon

Humans profoundly alter fire regimes both directly, by introducing changes in fuel dynamics and ignitions, and indirectly, by increasing the release of greenhouse gases and aerosols from fires, which can alter regional climate and, as a consequence, modify fuel moisture and availability. Interactions between vegetation dynamics, regional climate change and anthropogenic pressure lead to high heterogeneity in the spatio-temporal fire distribution. We use the new FireTracks Scientific Dataset that tracks the spatio-temporal development of individual fires to analyse fire regimes in the Brazilian Legal Amazon over the period 2002–2020. We analyse fire size, duration, intensity and rate of spread in six different land-cover classes. Particular combinations of fire features determine the dominant and characteristic fire regime in each of them. We find that fires in savannas and evergreen forests burn the largest areas and are the most long lasting. Forest fires have the potential for burning at the highest intensities, whereas higher rates of spread are found in savannas. Woody savanna and grassland fires are usually affected by smaller, shorter, less-intense fires compared with fires in evergreen forest and savanna. However, fires in grasslands can burn at rates of spread as high as savanna fires as a result of the easily flammable fuel. We observe that fires in deciduous forests and croplands are generally small, short and low intense, although the latter can sustain high rates of spread due to the dry post-harvest residuals. The reconstructed fire regimes for each land cover can be used to improve the simulated fire characteristics by models and, thus, future projections.

Linking resource- and disturbance-based models to explain tree-grass coexistence in savannas.

Savannas cover a significant fraction of the Earth's land surface. In these ecosystems, C3 trees and C4 grasses coexist persistently, but the mechanisms explaining coexistence remain subject to debate. Different quantitative models have been proposed to explain coexistence, but these models make widely contrasting assumptions about which mechanisms are responsible for savanna persistence. Here, we show that no single existing model fully captures all key elements required to explain tree-grass coexistence across savanna rainfall gradients, but many models make important contributions. We show that recent empirical work allows us to combine many existing elements with new ideas to arrive at a synthesis that combines elements of two dominant frameworks: Walter's two-layer model and demographic bottlenecks. We propose that functional rooting separation is necessary for coexistence and is the crux of the coexistence problem. It is both well-supported empirically and necessary for tree persistence, given the comprehensive grass superiority for soil moisture acquisition. We argue that eventual tree dominance through shading is precluded by ecohydrological constraints in dry savannas and by fire and herbivores in wet savannas. Strong asymmetric grass-tree competition for soil moisture limits tree growth, exposing trees to persistent demographic bottlenecks.

Indonesian savanna fire-related spectral analysis

Peat fires in Indonesia frequently result in ecological degradation and loss. Public attention has shifted to savanna fires, which are usually overlooked but have increased in frequency in recent years, surpassing the area of controlled peat fires in Indonesia. Mapping the short-lived burns in Indonesia’s savanna is challenging. Only a few studies have examined fires in the Indonesian savanna, specifically the spectral responses associated with fires. Our study aims to analyse spectral changes caused by fires in Sumba Island, East Nusa Tenggara, Indonesia using field data and satellite images (Sentinel-2 and Landsat 8). We plotted the spectral values from blue to middle infrared bands for each burned and unburned site. In addition, we investigated the time series associated spectral indices for each site to determine how long spectral changes can be noticed immediately following fire incidents. Our research discovered that vegetation regrowth occurred rapidly (within two months), obscuring the detection of burned areas in the savanna. The red, near infrared, and middle infrared bands (>1,300 nm) were found to be the optimal spectral bands for discriminating between savanna vegetation regrowth and newly burned areas. Our findings will assist the Indonesian government in improving the mapping of burned areas for the purposes of national fire management.

Atmospheric Black Carbon Loadings and Sources over Eastern Sub-Saharan Africa Are Governed by the Regional Savanna Fires.

Vast black carbon (BC) emissions from sub-Saharan Africa are perceived to warm the regional climate, impact rainfall patterns, and impair human respiratory health. However, the magnitudes of these perturbations are ill-constrained, largely due to limited ground-based observations and uncertainties in emissions from different sources. This paper reports multiyear concentrations of BC and other key PM2.5 aerosol constituents from the Rwanda Climate Observatory, serving as a regional receptor site. We find a strong seasonal cycle for all investigated chemical species, where the maxima coincide with large-scale upwind savanna fires. BC concentrations show notable interannual variability, with no clear long-term trend. The Δ14C and δ13C signatures of BC unambiguously show highly elevated biomass burning contributions, up to 93 ± 3%, with a clear and strong savanna burning imprint. We further observe a near-equal contribution from C3 and C4 plants, irrespective of air mass source region or season. In addition, the study provides improved relative emission factors of key aerosol components, organic carbon (OC), K+, and NO3-, in savanna-fires-influenced background atmosphere. Altogether, we report quantitative source constraints on Eastern Africa BC emissions, with implications for parameterization of satellite fire and bottom-up emission inventories as well as regional climate and chemical transport modeling.

Canadian and Alaskan wildfire smoke particle properties, their evolution, and controlling factors, from satellite observations

Abstract. The optical and chemical properties of biomass burning (BB) smoke particles greatly affect the impact that wildfires have on climate and air quality. Previous work has demonstrated some links between smoke properties and factors such as fuel type and meteorology. However, the factors controlling BB particle speciation at emission are not adequately understood nor are the factors driving particle aging during atmospheric transport. As such, modeling wildfire smoke impacts on climate and air quality remains challenging. The potential to provide robust, statistical characterizations of BB particles based on ecosystem type and ambient environmental conditions with remote sensing data is investigated here. Space-based Multi-angle Imaging SpectroRadiometer (MISR) observations, combined with the MISR Research Aerosol (RA) algorithm and the MISR Interactive Explorer (MINX) tool, are used to retrieve smoke plume aerosol optical depth (AOD) and to provide constraints on plume vertical extent; smoke age; and particle size, shape, light-absorption properties, and absorption spectral dependence. These tools are applied to numerous wildfire plumes in Canada and Alaska, across a range of conditions, to create a regional inventory of BB particle-type temporal and spatial distribution. We then statistically compare these results with satellite measurements of fire radiative power (FRP) and land cover characteristics, as well as short-term climate, meteorological, and drought information from the Modern-Era Retrospective analysis for Research and Applications (MERRA-2) reanalysis and the North American Drought Monitor. We find statistically significant differences in the retrieved smoke properties based on land cover type, with fires in forests producing the thickest plumes containing the largest, brightest particles and fires in savannas and grasslands exhibiting the opposite. Additionally, the inferred dominant aging mechanisms and the timescales over which they occur vary systematically between land types. This work demonstrates the potential of remote sensing to constrain BB particle properties and the mechanisms governing their evolution over entire ecosystems. It also begins to realize this potential, as a means of improving regional and global climate and air quality modeling in a rapidly changing world.

Tracking and classifying Amazon fire events in near real time

Exceptional fire activity in 2019 sparked concern about Amazon forest conservation. However, the inability to rapidly separate satellite fire detections by fire type hampered fire suppression and assessment of ecosystem and air quality impacts. Here, we describe the development of a near–real-time approach for tracking contributions from deforestation, forest, agricultural, and savanna fires to burned area and emissions and apply the approach to the 2019 fire season in South America. Across the southern Amazon, 19,700 deforestation fire events accounted for 39% of all satellite active fire detections and the majority of fire carbon emissions (63%; 69 Tg C). Multiday fires accounted for 81% of burned area and 92% of carbon emissions from the Amazon, with many forest fires burning uncontrolled for weeks. Most fire detections from deforestation fires were correctly identified within 2 days (67%), highlighting the potential to improve situational awareness and management outcomes during fire emergencies.

A quadcopter unmanned aerial system (UAS)-based methodology for measuring biomass burning emission factors

Abstract. Biomass burning (BB) emits large quantities of greenhouse gases (GHG) and aerosols that impact the climate and adversely affect human health. Although much research has focused on quantifying BB emissions on regional to global scales, field measurements of BB emission factors (EFs) are sparse, clustered and indicate high spatio-temporal variability. EFs are generally calculated from ground or aeroplane measurements with respective potential biases towards smouldering or flaming combustion products. Unmanned aerial systems (UAS) have the potential to measure BB EFs in fresh smoke, targeting different parts of the plume at relatively low cost. We propose a light-weight UAS-based method to measure EFs for carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) as well as PM2.5 (TSI Sidepak AM520) and equivalent black carbon (eBC, microAeth AE51) using a combination of a sampling system with Tedlar bags which can be analysed on the ground and with airborne aerosol sensors. In this study, we address the main challenges associated with this approach: (1) the degree to which a limited number of samples is representative for the integral smoke plume and (2) the performance of the lightweight aerosol sensors. While aerosol measurements can be made continuously in a UAS set-up thanks to the lightweight analysers, the representativeness of our Tedlar bag filling approach was tested during prescribed burning experiments in the Kruger National Park, South Africa. We compared fire-averaged EFs from UAS-sampled bags for savanna fires with integrated EFs from co-located mast measurements. Both measurements matched reasonably well with linear R2 ranging from 0.81 to 0.94. Both aerosol sensors are not factory calibrated for BB particles and therefore require additional calibration. In a series of smoke chamber experiments, we compared the lightweight sensors with high-fidelity equipment to empirically determine specific calibration factors (CF) for measuring BB particles. For the PM mass concentration from a TSI Sidepak AM520, we found an optimal CF of 0.27, using a scanning mobility particle sizer and gravimetric reference methods, although the CF varied for different vegetation fuel types. Measurements of eBC from the Aethlabs AE51 aethalometer agreed well with the multi-wavelength aethalometer (AE33) (linear R2 of 0.95 at λ=880 nm) and the wavelength corrected multi-angle absorption photometer (MAAP, R2 of 0.83 measuring at λ=637 nm). However, the high variability in observed BB mass absorption cross-section (MAC) values (5.2±5.1 m2 g−1) suggested re-calibration may be required for individual fires. Overall, our results indicate that the proposed UAS set-up can obtain representative BB EFs for individual savanna fires if proper correction factors are applied and operating limitations are well understood.

Impact of image acquisition lag-time on monitoring short-term postfire spectral dynamics in tropical savannas: the Campos Amazônicos Fire Experiment

The use of optical remote sensing to monitor short-term postfire dynamics in rapidly recovering ecosystems is a complex task, requiring strong spectral separability and high temporal resolution. Thus, characterizing the effects of temporal lag in image acquisitions in relation to fire occurrence is of fundamental importance to improve our understanding of how fire-related environmental and ecological processes are connected to multitemporal spectral information. We used a harmonized series of Sentinel-2A/2B and Landsat-7/8 images paired with a fire experiment specifically designed for remote sensing assessment to evaluate short-term spectral responses of fire in tropical savannas. Our experimental design included strategic geolocation of experimental plots and separate prescribed burnings during the early- and mid-dry seasons. The M-statistic was used to assess spectral separability between burned and control treatments, and the temporal stability was assessed using fire scar latency, a custom statistic adapted to capture scar spectral responses over time. Finally, linear regressions were fitted to explore the association between consumed fuel load and spectral indices. The variation of normalized burn ratio and mid-infrared bispectral index indices stood out with the highest separability (M-statistic > 3) in both treatments and moderate-high association with consumed fuel load (R2 > 0.54). We observed that burned areas spectral sensitivity depends not only on timing of image acquisition but also on fire season and their interactions with land surface phenology. Our characterization provides a solid benchmark for future experimental assessments of fire spectral responses and provides new insights for improving fire monitoring algorithms.

Reconstruction of the holocene climate and environmental changes of Niayes peat bog in northern coast of Senegal (NW Africa) based on stable isotopes and charcoals analysis

A core from a peat bog in the “Niayes” region, northwest of Senegal, provides a valuable insight into the evolution of the landscape and fire regime related to the West African Monsoon rainfall and to human impact over the Holocene. The high-resolution multiproxy approach based on stable carbon isotopic composition (δ13C), Rock-Eval® thermal analysis, and charcoal analysis, provides an understanding of vegetation composition (C3/C4) and fire regime in the continental watershed. The analysis of our data indicates a more woody landscape and a higher water table level, related to increased monsoonal rainfall during the African Humid period (AHP) between 9.5 and 5.5 cal kyr BP. High insolation and orbital changes account for a northward migration of the African Rain Belt and a reinforced West Africa monsoon. The amount of forest fires was low and most likely of natural occurrence, as human density was very low. A short dry event interrupts the AHP and gives rise to a weakly grassy landscape at around 8.2 cal kyr BP. This drought of centennial scale (400 years) occurring between 8.4 and 8 cal kyr BP is concomitant with the general cooling observed in the Northern Hemisphere. After a period of transition, the millennial-scale Late Holocene dry period begins at 4.8 cal kyr BP. The low water table level, resulting from a decrease in precipitation, coincides with the appearance of a grassy savanna landscape. Insolation decrease and reduced vegetation were likely driven by a southward migration of the African Rain Belt and a weakening of the monsoon. During the late Holocene the “Niayes” zone evolved into a phase of environmental stress often interrupted by Little Humid Periods (LHP) of centennial scale (500 and 600 years) respectively between 4.4 and 3.9 and between 1.1 and 0.5 cal kyr BP. After 0.5 cal kyr BP the decrease in precipitation and the increase in savanna fires, probaly of anthropogenic origin, favor the landscape opening.

Flammability in tropical savannas: Variation among growth forms and seasons in Cerrado

AbstractThe herbaceous layer is the dominant fuel for fire in tropical savannas, the world's most fire‐prone biome. However, little is known about variation in flammability among different growth forms, as well as how flammability varies seasonally. Here, we describe such variation in Brazilian Cerrado, the world's most phytodiverse tropical savanna. We measured three components of flammability (maximum burning temperature, burning rate, and burnt biomass) and morphophysiological traits (dead biomass percentage, moisture content, and specific leaf area) of five species of each of grasses, forbs, and shrubs throughout the wet and dry season. We found that grasses were the most flammable growth form and that their flammability was highest in the middle of the dry season when the percentage of dead biomass was highest (60%), and moisture content was low (25%). Flammability did not vary across seasons for either forbs or shrubs. Dead biomass, moisture content, and specific leaf area were all strongly correlated with flammability. These findings explain the dominant role played by grasses as drivers of flammability in tropical savannas, and they improve our understanding of how savanna flammability varies across space and time depending on the composition of the grass layer and its level of seasonal curing. This enables a better prediction of fire spread and behavior in different savanna types based on grass‐layer composition.

A compound event-oriented framework to tropical fire risk assessment in a changing climate

Tropical fire activity closely follows the co-occurrence of multiple climate stressors. Yet, it remains challenging to quantify how changes in climate alter the likelihood of fire risks associated with compound events. Recent abrupt changes in fire regimes in iconic landscapes in Brazil (namely the Pantanal and Xingu) provide a key opportunity to evaluate how extremely dry and hot conditions, both together and individually, have influenced the probability of large fires. Here we quantify the relationships between climate and fire across these regions and provide evidence on the extent to which fire risk and the associated impacts could be constrained if anthropogenic global warming is limited. We investigate the burned area, differentiating between fire types according to land use (forest fires, savanna fires, farming fires and grassland and wetland fires), and derive present and future fire risks linked to multiple climate variables. We show that concurrent air dryness (high vapour-pressure deficit (VPD)) and low precipitation have driven fire occurrence in both Xingu and the Pantanal, with VPD playing a dominant role. Historical climatic change has already increased compound event-related (CE-related) fire risks of all fire types (5%–10%), and these risks are likely to increase in the future due to global warming. The likelihood of CE-related increase in fire risk may be reduced by up to 14.4% if global warming is constrained to +1.5 °C instead of +3 °C. Nevertheless, substantially increased CE-related fire risks are still expected even if restricting global mean warming to 1.5 °C, particularly in the Pantanal. We thus conclude that climate action should be coordinated with environmental protection to reduce ignition sources and promote effective conservation measures to preserve these biomes.

Smoke pollution must be part of the savanna fire management equation: A case study from Darwin, Australia

Savanna fire management is a topic of global debate, with early dry season burning promoted as a large-scale emissions reduction opportunity. To date, discussions have centred on carbon abatement efficacy, biodiversity and cultural benefits and/or risks. Here we use a case study of Darwin, Australia to highlight smoke pollution as another critical consideration. Smoke pollution from savanna fires is a major public health issue, yet absent so far from discussions of program design. Here, we assess the likely impacts of increased early dry season burning on smoke pollution in Darwin between 2004 and 2019, spanning the introduction and expansion of carbon abatement programs. We found increased smoke pollution in the early dry season but little change in the late dry season, contributing to a net annual increase in air quality standard exceedances. Geospatial analysis suggests this relates to increased burning in the path of early dry season trade winds. This study highlights the complex health trade-offs involved with any large-scale prescribed burning, including for carbon abatement.

Climatological Aspects of Active Fires in Northeastern China and Their Relationship to Land Cover

Biomass burning (BB) is a driving force for heavy haze in northeastern China (NEC) and shows distinct seasonal features. However, little is known about its climatological aspects, which are important for regional BB management and understanding BB effects on climate and environment. Here, the climatological characteristics of active fires and their dependence on land cover in NEC were studied using Moderate Resolution Imaging Spectroradiometer (MODIS) products. Moreover, the influence of meteorological factors on fire activities was explored. The number of fires was found to have increased significantly from 2003 to 2018; and the annual total FRP (FRPtot) showed a generally consistent variation with fire counts. However, the mean fire radiative power for each spot (FRPmean) decreased. Fire activity showed distinctive seasonal variations. Most fires and intense burning events occurred in spring and autumn. Spatially, fires were mainly concentrated in cropland areas in plains, where the frequency of fires increased significantly, especially in spring and autumn. The annual percentage of agricultural fires increased from 34% in 2003 to over 60% after 2008 and the FRPtot of croplands increased from 12% to over 55%. Fires in forests, savannas, and grasslands tended to be associated with higher FRPmean than those in croplands. Analysis indicated that the increasing fire count in NEC is mainly caused by agricultural fires. Although the decreasing FRPmean represents an effective management of BB in recent years, high fire counts and FRPtot in croplands indicate that the crop residue burning cannot be simply banned and a need instead for effective applications. More efforts should be made on clean utilization of straw. The accumulation of dry biomass, high temperature, and low humidity, and weak precipitation are conducive to the fire activities. This study provides a comprehensive analysis of BB in NEC and provides a reference for regional BB management and control.

Fire effects on riparian vegetation recovery and nutrient fluxes in Brazilian Cerrado

AbstractFire can change gallery forest vegetation structure, thereby altering nutrient fluxes between terrestrial and aquatic ecosystems. In Brazilian savannas, which are fire‐prone ecosystems, the fire regime is changing due to human activities such as converting native vegetation to farmland and urban areas. Uncontrolled wildfires in these savannas can reach gallery forests, which are more sensitive to fire impacts, leading to concerns about the effects of fire on gallery forest vegetation structure and freshwater ecosystems. We analysed the relationships between fire severity (the degree to which the fire has changed an area), percentage of burned area, variation in precipitation with gallery forest and savanna vegetation structure recovery and input of nutrients (NH4, , and ) to streams for 16 months after a fire event in five watersheds associated with small streams. One year after the fire, vegetation recovery (NDVI) was lower in gallery forest areas than in savanna woodlands, despite the more severe fires in savannas. The short‐term effects of fire on gallery forest vegetation included increased nitrate concentrations in streams, which were also influenced by increased precipitation and the extent of the burned area. The nutrient inputs into the stream stabilized within 1 year. However, gallery forest vegetation did not fully recover at that time and may continue to alter the functioning of the aquatic ecosystem. Together, these results demonstrate the need for an integrated fire management plan that considers both gallery forests and the surrounding savannas in the landscape to address consequences to aquatic ecosystems.

Australian Fire Emissions of Carbon Monoxide Estimated by Global Biomass Burning Inventories: Variability and Observational Constraints

AbstractAustralian fires are a primary driver of variability in Australian atmospheric composition and contribute significantly to regional and global carbon budgets. However, biomass burning emissions from Australia remain highly uncertain. In this work, we use surface in situ, ground‐based total column and satellite total column observations to evaluate the ability of two global models (GEOS‐Chem and ACCESS‐UKCA) and three global biomass burning emission inventories (FINN1.5, GFED4s, and QFED2.4) to simulate carbon monoxide (CO) in the Australian atmosphere. We find that emissions from northern Australia savanna fires are substantially lower in FINN1.5 than in the other inventories. Model simulations driven by FINN1.5 are unable to reproduce either the magnitude or the variability of observed CO in northern Australia. The remaining two inventories perform similarly in reproducing the observed variability, although the larger emissions in QFED2.4 combined with an existing high bias in the southern hemisphere background lead to large CO biases. We therefore recommend GFED4s as the best option of the three for global modeling studies with focus on Australia or the Southern Hemisphere. Near fresh fire emissions, the higher resolution ACCESS‐UKCA model is better able to simulate surface CO than GEOS‐Chem, while GEOS‐Chem captures more of the observed variability in the total column and remote surface air measurements. We also show that existing observations in Australia can only partially constrain global model estimates of biomass burning. Continuous measurements in fire‐prone parts of Australia are needed, along with updates to global biomass burning inventories that are validated with Australian data.

Demography of the dominant perennial grass species of a humid African savanna

Perennial grasses are the main source of fuel during fires in savannas. The demography of these grasses likely varies between species although they have the same general architecture and coexist in savannas. However, very few studies compare their demography. Similarly, their demography likely varies between years because of the variability in weather condition and fire intensity. We described and compared the demography and life-cycle of the four dominant perennial grass species (Andropogon canaliculatus, Andropogon schirensis, Hyparrhenia diplandra and Loudetia simplex) of the Lamto savanna (Ivory Coast) and assessed the influence of their demographic features (stasis, fecundity, growth, fragmentation and retrogression) on this demography. Grass species were monitored over three consecutive years (2015–2016, 2016–2017 and 2017–2018) on three 5 m × 10 m plots. We used a size-classified matrix model with 5 circumference classes (3–10 cm, 10–20 cm, 20–35 cm, 35–50 cm and >50 cm). Results showed differences in the age-based parameters, asymptotic growth rates (λs) and elasticities of the λs of the grass species. The population of A. canaliculatus, A. schirensis and H. diplandra were slowly declining while L. simplex was significantly declining. There were noticeable year-to-year variations in the demography of these four species. The most important demographic parameter influencing λs was the stasis in all species, while retrogression and fragmentation contributed to a relative homogeneity of ages between size-classes 2 to 5. This study provides new insights about the demography of Guinean savanna grasses that could be used to describe the mechanisms of their coexistence, and inform fire management policies.

环境介质中左旋葡聚糖记录与植被火燃烧变化研究进展

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

The Influence of Periodic Fires on the High Guinean Savannas and the Carbon Stock in Cameroun

The influence of periodic fires in the high Guinean savannas of Cameroon on woody plants and carbon stock is poorly documented. To fill this gap, work was carried out in the high Guinean savannas of Cameroon with the aim of contributing to the assessment of the effects of periodic fires on the woody cover and the carbon stock. The methodology used consists of carrying out semi-structured household surveys and floristic inventories in the Arrondissement of Ngaoundéré III and Ngan’ha, in the Department of Vina. A total of 50 households were interviewed at a rate of 25 per Borough according to a questionnaire prepared beforehand. For the botanical inventories, 02 types of savannah were selected: regularly burnt savannas (shrub savannas, wooded savannas) and those not burned for at least 10 years (shrub savannas, tree savannas). The choice of control savannas was made according to the indications of the peasants. In each of them, the 1km x 20m transects were covered and the diameter at breast height (dbh) of the woody plants was measured using a dbh meter at 1.3 m from the ground for large trees. and at 30 or 50 cm from the ground for shrubs and shrubs. The results show that climate change is palpable in the area. The rains are increasingly rare, the drought has become severe and the agricultural calendar is no longer respected. The specific diversity has become relatively low with 51 species having been inventoried, divided into 46 genera and 23 families. Savannahs that are not burnt produce more biomass than those that are burnt. The perfect illustration is given by the non-burnt tree savannah of Ngaoundere III with an above-ground and root biomass of 102.23 t/ha and 20.70 t/ha respectively. <i>Annona senegalensis</i> (1.27 tC/ha) is the species contributing massively to carbon sequestration in the high savannas of the Vina. Thus, by acting on the availability of plant biomass, fires contribute to the erosion of biodiversity. Adequate measures are urgently needed to limit bushfires.