Fossil Charcoal Research Articles

Preliminary study on pollen, charcoal records and environmental evolution of Alahake Saline Lake in Xinjiang since 4,700 cal yr BP

Human activity can affect the vegetation types and sedimentary records of a region. In this study, we used multiproxy records from a 140-cm sediment profile, including pollen, charcoal, organic carbon, conductivity, and hydrochemical analyses, to reconstruct a vegetation history for Alahake Saline Lake in northern Xinjiang, China. Fossil charcoal pieces (≥100 μm) were used to reconstruct fire history from the sedimentary record. A significant change in the presence of charcoal indicated an increasing occurrence of fire in the Alahake landscape over the past 4730 years. A peak charcoal concentration occurred at a depth of 0–28 cm, indicating intensified human activity since 790 cal. yr BP. For the same period, pollen assemblages revealed some distinct regional vegetation changes; from 4730 to 3600 cal. yr BP, the landscape was relatively rich in tree species and other vegetation types; from 3600–790 cal. yr BP, trees began to decline while the abundance of Chenopodiaceae increased sharply, indicating environmental degradation. The occurrence of Betula spp. (birch) pollen decreased markedly up to 410 cal. yr BP, suggesting the progressive disappearance of birch trees from the landscape, and the salinity of the lake increased (conductivity peaked above 14.16 ms/cm). High lake salinity and increasing anthropogenic activity have been the two most important factors driving historical changes in the abundance of birch in the Alahake Saline Lake region over the past 790 years. The results of this study are of significance for biodiversity conservation planning and wetland protection in semi-arid and arid areas of China.

Climate and human influence on late Holocene fire regimes in the British Virgin Islands

AbstractGlobal climate change poses significant threats to the Caribbean islands. Yet, little is known about the long-term disturbance regimes in island ecosystems. This research investigates 2000 yr of natural and anthropogenic fire disturbance through the analysis of a latitudinal transect of sediment records from coastal salt ponds in the British Virgin Islands (BVI). The two research objectives in this study are (1) to determine the fire regime history for the BVI over the last 2000 yr and (2) to explore ecological impacts from anthropogenic landscape modification pre- and post-European settlement. The magnitude of anthropogenic landscape modification, including the introduction of agriculture, was investigated through a multiproxy approach using sedimentary records of fossil pollen and charcoal. Our results suggest fire regimes from Belmont Pond, Thatch Island, and Skeleton Pond have been influenced by human activity, particularly during the postsettlement era, from 500 cal yr BP to modern. Our results suggest that fire regimes during the Medieval Climate Anomaly were responding to changes in climate via dominant atmospheric drivers. The presettlement fire regimes from these islands suggest that fires occurred every 90 to 120 yr. This research represents a significant data contribution to a region with little disturbance and vegetation data available.

Identification of fungal fossils and novel azaphilone pigments in ancient carbonised specimens of Hypoxylon fragiforme from forest soils of Châtillon-sur-Seine (Burgundy)

Fungal stromata were recently discovered in association with charcoal and burnt soil aggregates during an archaeological survey in the Châtillon-sur-Seine forest massif. The wood and soil in the samples were dated to the medieval period (between 738 and 1411 AD). Light microscopy and scanning electron microscopy revealed that a few of the stromatal fragments still contained ascospores. Their macromorphological characters were described and secondary metabolite profiles were generated using high performance liquid chromatography with diode array and mass spectrometric detection (HPLC–DAD/MS). The combination of these two data lines then allowed species identification. Most of the fragments were assigned to Hypoxylon fragiforme, the type species of the Hypoxylaceae (Xylariales). Two further species whose stromata grew on the fossil charcoal could be tentatively identified as Jackrogersella cohaerens and (more tentatively) as Hypoxylon vogesiacum. These three species are still commonly encountered in the forests of Central Europe today. Furthermore, the HPLC-HRMS data of H. fragiforme suggested the presence of unknown azaphilone dimers and of further new pigments. These archaeological compounds were compared to fresh stromata of H. fragiforme collected in Germany and subjected to the same analytical protocol. While the major components in both samples were identified as the known mitorubrin type azaphilones and orsellinic acid, the chemical structures of seven novel complex azaphilone pigments, for which we propose the trivial names rutilins C-D and fragirubrins A-E, were elucidated using spectral methods (NMR and CD spectroscopy, high resolution mass spectrometry). It appears that these pigments had indeed persisted for millennia in the fossil stromata.

Fruit collection and early evidence for horticulture in the Hexi Corridor, NW China, based on charcoal evidence

The reconstruction of fruit collection and cultivation based on plant remains plays an important role in understanding the subsistence strategies of ancient societies. Here, we report the identification of fossil charcoal from eight sites in the Hexi Corridor to give a clue to the early exploitation of fruit resources in the period 2300–400 bc. Charcoal assemblages show that millet farmers may have collected some tree fruits including bird cherry (Padus sp.), pear (Pyrus sp.) and whitebeam (Sorbus sp.) in the period 2300–2000 bc. From 2000 to 1500 bc there was continuing utilization of Padus sp., Sorbus sp. and cotoneaster (Cotoneaster sp.), at a time when cereal agriculture of wheat and barley had been introduced from outside. Based on analysis of ecological distribution, reproductive biology and the history of utilization, we infer that these fruits were gathered from the wild rather than cultivated. Later, the cultivation of non-native mulberry (Morus alba) began around 1500 bc in the context of an established high-yield wheat agriculture, probably indicating the earliest sign of horticulture in the Hexi Corridor. As with the beginning of agriculture, the horticulture is associated with cultivation of non-native species. In short, the variations in the presence of charred wood of fruit trees indicate that people might have collected wild fruits over a period of time, and that horticulture occurred much later than the spread of a variety of cereal and other crops in the Hexi Corridor.

Fossil charcoal quantification using manual and image analysis approaches

Charcoal particles are evidence of past fire events and macro-charcoal particles have been shown to represent local fire events. There are several methods for the preparation and quantification of macro-charcoal particles, none of which have been universally accepted as standard. Very few studies compare methodological differences and no studies to date compare quantification by mass with quantification by volume using image analysis. Using three cores taken from a peatland located in SE Norway, we compare these two established methods using a generalized linear mixed model (GLMM) and a split-plot ANOVA test. We show that charcoal volume (image analysis method) was a better predictor of charcoal mass than charcoal particle number and the same size classes of charcoal as size class distributions were not spatially and temporally correlated. Although there is still a need for a common and unifying method, our results show that quantification of charcoal particles by image analysis including size (e.g. height in mm) and area (mm2)/volume (mm3) measurements provides more significant results in cross-site or multiple-site studies than quantifications based on particle number. This has implications for the interpretation of charcoal data from regional studies that are used to model drivers of wildfire activity and environmental change in boreal–temperate landscapes during the Holocene.

Record of Charcoal from Early Maastrichtian Intertrappean Lake Sediments of Bagh Valley of Madhya Pradesh:Palaeofire Proxy

Presence of charcoal in intertrappean lake sediments associated with the Malwa Group of the Deccan trap, India is recorded. The finding provides the first evidence of palaeofire in the Indian late Cretaceous. Though previous studies have shown the presence of carbonaceous clays and coal bands in the Deccan volcanic associated sediments, the presence of fossil charcoal in the sediments is rarely reported. The fossil charcoal was identified based on optical microscope, Scanning Electron Microscope and Pyrolysis-Gas Chromatography Mass Spectrometer (Py-GC-MS). This study indicates that charcoal is derived from burning of plants caused by forest fire during the Maastrichtian (Chron 30N).

Nested cell strainers: An alternative method of preparing palynomorphs and charcoal

Centrifugation and sieving are essential techniques used in standard preparations of pollen and other palynological material. However, multiple centrifugation steps can potentially damage delicate palynomorphs and other microfossils, and the process of decanting after centrifugation can lead to loss of material. Traditional sieves often have a large surface area which makes manipulating smaller samples difficult and creates the need for potentially damaging techniques (e.g., sonication) to facilitate material through the sieve. We propose using stackable cell strainers as an alternative method for the preparation of pollen and charcoal samples. These sieves fit firmly on standard plastic 50ml centrifuge tubes and special rings allow the attachment of disposable syringes for suction. We demonstrate that the results of using cell sieves are comparable or better than those of traditional methods. Pollen counts from nine Holocene sites using the cell strainers showed similar concentrations of major palynomorphs in comparison to counts of samples processed following traditional methods. Visual comparison and counts of delicate pollen morphotypes, such as Pinaceae and Poaceae grains, indicated that fewer grains were damaged when cell strainers were used. Macrocharcoal preparations using cell strainers showed consistently lower counts than samples prepared using traditional methods, which may reflect lower rates of fragmentation of fossil charcoal during preparation. Finally, we demonstrate that nested cell strainers are also effective in processing lithified material and isolating and staining pollen from herbarium samples.

Changes of wood anatomical characters of selected species of Araucaria- during artificial charring - implications for palaeontology

ABSTRACT Charcoal is widely accepted as evidence of the occurrence of palaeo-wildfire. Although fossil charcoal remains have been used in many studies, investigation into the anatomical changes occurring during charring are few. The present study analyses changes in selected anatomical characters during artificial charring of modern wood of three species of the genus Araucaria (i.e. Araucaria angustifolia, Araucaria bidwillii and Araucaria columnaris). Wood samples of the studied species was charred under controlled conditions at varying temperatures. Measurements of anatomical features of uncharred wood and artificial charcoal were statistically analysed. The anatomical changes were statistically correlated with charring temperatures and most of the parameters showed marked decreases with increasing charring temperature. Compared to the intrinsic variability in anatomical features, both within and between growth rings of an individual plant, the changes induced by temperature account only for a comparatively small percentage of the observed variability. Regarding Araucaria charcoal, it seems possible that at least general taxonomic and palaeoenvironmental implications can be drawn from such material. However, it is not clear so far whether these results and interpretations based on only three taxa, can be generalized for the entire family and anatomically similar fossil taxa or not.

Does fuel type influence the amount of charcoal produced in wildfires? Implications for the fossil record

AbstractCharcoal occurrence is extensively used as a tool for understanding wildfires over geological timescales. Yet, the fossil charcoal literature to date rarely considers that fire alone is capable of creating a bias in the abundance and nature of charcoal it creates, before it even becomes incorporated into the fossil record. In this study we have used state‐of‐the‐art calorimetry to experimentally produce charcoal from 20 species that represent a range of surface fuels and growth habits, as a preliminary step towards assessing whether different fuel types (and plant organs) are equally likely to remain as charcoal post‐fire. We observe that charcoal production appears to be species specific, and is related to the intrinsic physical and chemical properties of a given fuel. Our observations therefore suggest that some taxa are likely to be overrepresented in fossil charcoal assemblages (i.e. needle‐shed conifers, tree ferns) and others poorly represented, or not preserved at all (i.e. broad shoot‐shed conifers, weedy angiosperms, shrub angiosperms, some ferns). Our study highlights the complexity of charcoal production in modern fuels and we consider what a bias in charcoal production may mean for our understanding of palaeowildfires.

Fossil charcoals from the Lower Jurassic challenge assumptions about charcoal morphology and identification

AbstractCharcoal morphometry is increasingly employed in the analysis of Quaternary sediments, but has not been applied in studies of earlier sediments. We present findings relating to charcoal morphometry and morphotypes in a Toarcian sequence, which contains a preponderance of highly elongate forms, and morphometric values well outside expected ranges. SEM imaging reveals elongate particles of two distinct kinds. One originates in conifer xylem, and may be associated with formation at high levels of heating. It is proposed that the other may derive from tree ferns, or from plants with similar growth forms. Our results show the importance of recognizing the wide morphological variation that exists in sedimentary charcoal. Failing to do so may result in serious errors in its identification, interpretation and quantification.

Wood types and human impact between 4300 and 2400 yr BP in the Hexi Corridor, NW China, inferred from charcoal records

Based on identification of fossil charcoals from 11 sites in the Hexi Corridor, we reconstruct the local vegetation community and human impact on it in the period from 4300 to 2400 cal. yr BP. More than 20 broadleaved taxa and 4 coniferous trees are present. The charcoal identifications show that vegetation in the period 4300–2400 cal. yr BP differed regionally because of variations in local topography and water supply, with limited diversity in the northwest Hexi Corridor and relatively rich diversity in the southeast area. In the northwest Hexi Corridor, the oasis woodland consisted mainly of Tamarix sp., Salix sp., and Populus sp. In the southeast region, the vegetation was a mix of coniferous forest and broadleaf woodland. By comparison with modern patterns of vegetation, broadleaf trees were much more abundant and the spruce forest extended down to relatively low altitudes, suggesting greater vegetation cover and richer diversity than today. There was also temporal variation. In the period from 4300 to 4000 cal. yr BP, woodland was relatively scarce, while the greatest diversity of plants appears in the period from 4000 to 3500 cal. yr BP, probably because of better moisture conditions at that time. After 3500 cal. yr BP, there was the appearance of woodland dominated by Morus alba, suggesting that cultivated trees may have played a key role in the lives of local people.

Macroscopic charcoal remains as evidence of wildfire from late Permian Gondwana sediments of India: Further contribution to global fossil charcoal database

Although there have been numerous reports of the occurrence of charcoal from the Indian Permian sediments (Kashmir and the Domodar Basin), here we report a new occurrence of charcoal from the Lopingian sediments of Central India, which is evidence of wildfire occurrence in the Permian of Gondwana and an addition to the global fossil charcoal database. Charcoal, a product of incomplete combustion of vegetation, is extensively reported from the Permian sediments of southern and northern hemisphere. Numerous reports have been generated from palaeobotanical and petrographical aspects of Gondwana sediments of India but the presence of macroscopic fossil charcoal has been somewhat overlooked until the past few years by many researchers, though the fusinite (charcoal equivalent term in petrographical studies) from many coalfields of Indian Gondwana has been attributed to pyrogenitic origin. Our study was carried out on macroscopic charcoal fragments retrieved from an exploratory drill core MBKW-3 from Mand-Raigarh Coalfield in the central part of the Mahanadi Basin, eastern India. The analysis involved Scanning Electron Microscopy for study of anatomical features and reflecting microscopy for estimation of the temperature of fire of charcoal formation where the inertinite reflectance data (average of 3.33%) indicate that these charcoals are formed at a temperature above 500°C. Palynomorph composition and their probable botanical affinity indicate that gymnosperms were the major type of vegetation that contributed to fuel load for wildfire while pteridophytes constituted a minor proportion. The palynological data reveal the predominance of arborescent vegetation over herbaceous elements. Fusinite reflectance data indicate that these charcoals are formed at a temperature in excess of 500°C. The almost unabraded edges of these charcoals, their high degree of preservation, and an assorted assemblage of different sizes clearly indicate their hypoautochtonous nature.

Observations of the structural changes that occur during charcoalification: implications for identifying charcoal in the fossil record

AbstractAll of our current understanding of fossil charcoal structure comes from observations of modern wood charcoal produced in furnaces. These charcoals consistently show cell wall homogenization after prolonged heating (>325°C) and this is therefore considered to be a key identifying feature of fossil charcoal. Yet furnaces are unable to replicate the full combustion processes that occur during a wildfire. Here, for the first time, we have studied the microscopic structural evolution of charcoal produced using calorimetry, wherein the wood is ignited under controlled conditions and the heat release rate and other parameters measured, and the resulting charcoal studied using reflected light microscopy. We show that homogenization of cell walls is actually only a short‐lived phase of charcoal formation that occurs during the early heating stages as the pyrolysis front traverses through the wood. Cell wall homogenization is then rapidly overprinted by the thinning, distortion and breakdown of cell walls, and a notable visual increase in reflectance. Our preliminary study therefore suggests that we need to first improve our understanding of charcoal formation in order to better understand the fossil record of wildfires.

Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia

The Toarcian Oceanic Anoxic Event (T-OAE) was characterized by a major disturbance to the global carbon(C)-cycle, and depleted oxygen in Earth’s oceans resulting in marine mass extinction. Numerical models predict that increased organic carbon burial should drive a rise in atmospheric oxygen (pO2) leading to termination of an OAE after ∼1 Myr. Wildfire is highly responsive to changes in pO2 implying that fire-activity should vary across OAEs. Here we test this hypothesis by tracing variations in the abundance of fossil charcoal across the T-OAE. We report a sustained ∼800 kyr enhancement of fire-activity beginning ∼1 Myr after the onset of the T-OAE and peaking during its termination. This major enhancement of fire occurred across the timescale of predicted pO2 variations, and we argue this was primarily driven by increased pO2. Our study provides the first fossil-based evidence suggesting that fire-feedbacks to rising pO2 may have aided in terminating the T-OAE.

Exploring the Ecological History of a Tropical Agroforestry Landscape Using Fossil Pollen and Charcoal Analysis from Four Sites in Western Ghats, India

Contrary to expectations, some human-modified landscapes are considered to sustain both human activities and biodiversity over the long-term. Agroforestry systems are among these landscapes where crops are planted under native shade trees. In this context, ancient agroforestry systems can provide insight into how farmers managed the landscape over time. Such insight can help to quantify the extent to which tropical forests (especially habitat-specialist trees) are responding to local and landscape-level management. Here, we extracted fossil pollen (indicator of past vegetation changes) and macroscopic charcoal (indicator of biomass burning) from four forest hollows’ sedimentary sequences in an ancient agroforestry system in Western Ghats, India. We used a mixed-modelling approach and a principal components analysis (PCA) to determine past trajectories of forest change and species composition dynamics for the last 900 years. In addition, we reconstructed the long-term forest canopy dynamics and examined the persistence of habitat-specialist trees over time. Our results show that the four sites diverged to a surprising degree in both taxa composition and dynamics. However, despite these differences, forest has persisted over 900 years under agricultural activities within agroforestry systems. This long-term analysis highlights the importance of different land-use legacies as a framework to increase the effectiveness of management across tropical agricultural lands.

Petrographic and mineralogical studies of fossil charcoal from Sierra de Bahoruco (Barahona Province, Dominican Republic)

The volcanic formations of the Sierra de Bahoruco mountain range (Barahona Province, Dominican Republic) contain charred fragments of plants, mainly tree trunks, which are composed of dense concentrations of hard mineralized fusain, with diverse microstructures. Petrographic examinations confirmed occurrence of two types of fusinite - structural fusinite with well-preserved tree tissue fragments, and detrital fusinite originating probably from softer tissues of tree phloem. In addition to the fusinite varieties developed from tree trunks and roots, charred tissues of dead external part of trunk epidermis affected by the microbiological process of rotting were identified. Poorly marked seasonal growth rings of trees, the shape and distribution of tree tissues, as well as the degrees of tissue destruction, indicated that the fragments originated from tropical trees growing in specifically marked rain and dry seasons, while wood tissues, charred by the fall of hot volcanic dust, suggested the existence of a monsoon tropical forest on the area. Fusinite was strongly impregnated with calcite and pectolite, sometimes zeolites (prehnite) and chlorite. It was accompanied by iron and copper sulphides, i.e. pyrite, chalcopyrite, and chalcocite. The latter minerals occurred in magma and pyroclastic formations, strongly associated with hydrothermal activities.

Stratigraphic distribution and significance of a 15 million-year record of fusain in the Upper Triassic Chinle Group, southwestern USA

We document the occurrence of Upper Triassic fusain in northern Arizona, southern Utah and northern New Mexico in latest Carnian(?) to Norian-age alluvial strata of the Monitor Butte Formation and the Sonsela and Painted Desert members of the Petrified Forest Formation (Chinle Group). The fusain, identified by standard techniques of macroscopic and microscopic morphology, and resistance to chemical oxidation, is present at multiple stratigraphic horizons at several locations that are approximately correlative, although separated by several hundred km. The morphology of this fossil charcoal includes large, partially charred silicified to coalified logs, completely charred smaller limbs, charcoal fragments reworked in fluvial deposits, and particulate fusain disseminated in sediments. The apparent rarity of fusain in Triassic strata previously was cited as evidence for relatively low levels (compared to modern) of atmospheric oxygen and the consequent infrequent occurrence of wildfire during this time interval. However, our findings demonstrate a significantly greater abundance of fusain in Upper Triassic strata than previously acknowledged. Therefore, we suggest that wildfire was not an unusual occurrence during the Late Triassic. This conclusion supports recent experimental studies and geochemical models that indicate atmospheric oxygen levels at or above modern levels during the Late Triassic.

The quantitative reconstruction of temperature and precipitation in the Guanzhong Basin of the southern Loess Plateau between 6200 BP and 5600 BP

Understanding the features of the paleoclimate and paleoenvrionment from key areas is crucial for predicting the climate variation of the future. In this study, fossil charcoal coupled with high-accuracy accelerator mass spectrometry (AMS) 14C dating from the Guanzhong Basin is analyzed to reconstruct the paleoclimate. Here, the coexistence approach (CA) was applied, and the result showed that the mean annual temperature (MAT) was about 14.8°C, and the annual precipitation (AP) was about 831.1 mm in the Guanzhong Basin during 6200–5600 cal. a BP. Comparing the climate between the mid-Holocene and present in the Xi’an area, the MAT was about 1.1°C higher than today and the AP was about 278 mm higher than today, similar to the modern climate of the Hanzhong area in the southern Qinling Mountains.

First report of Cisuralian (early Permian) charcoal layers within a coal bed from Baode, North China with reference to global wildfire distribution

Fossil charcoal is reported for the first time from a Cisuralian coal bed of the Shanxi Formation in the Qiaotou Section, Baode, Shanxi, North China. Based on anatomical characteristics, these charcoal fragments consist of coniferous or cordaitalean xylem, unidentified primary xylem and cordaitalean and possible fern leaves. These charcoal fragments represent the evidence of palaeowildfire taking place in tropical peat swamps during the Cisuralian in Cathaysia. The palaeowildfire is most likely to be a surface fire and burning litter and shrubby vegetation. Fire frequency for this early Permian peat swamp might have been on the order of 176–(294–588)–1429years, close to modern values. Compared with modern analogues, the North China Block during the Cisuralian was probably wet in general but could be occasionally seasonally dry for short time intervals. Previous charcoal and inertinite records moreover indicate that palaeowildfires were globally common during the Cisuralian. Overall, more wildfire evidence was found in the Artinskian–Kungurian than the Asselian-Sakmarian (except in the Euramerican Realm), probably due to more suitable regional climate, vegetation to fuel fires and taphonomic circumstances.

The influence of leaf morphology on litter flammability and its utility for interpreting palaeofire.

Studies of palaeofire rely on quantifying the abundance of fossil charcoals in sediments to estimate changes in fire activity. However, gaining an understanding of the behaviour of palaeofires is also essential if we are to determine the palaeoecological impact of wildfires. Here, I use experimental approaches to explore relationships between litter fire behaviour and leaf traits that are observable in the fossil record. Fire calorimetry was used to assess the flammability of 15 species of conifer litter and indicated that leaf morphology related to litter bulk density and fuel load that determined the duration of burning and the total energy released. These data were applied to a fossil case study that couples estimates of palaeolitter fire behaviour to charcoal-based estimates of fire activity and observations of palaeoecological changes. The case study reveals that significant changes in fire activity and behaviour likely fed back to determine ecosystem composition. This work highlights that we can recognize and measure plant traits in the fossil record that relate to fire behaviour and therefore that further research is warranted towards estimating palaeofire behaviour as it can enhance our ability to interpret the palaeoecological impact of palaeofires throughout Earth's long evolutionary history.This article is part of the themed issue 'The interaction of fire and mankind'.