Andrew C. Scott

Fire in the Earth system.

Burn, Baby, Burn Wildfires can have dramatic and devastating effects on landscapes and human structures and are important agents in environmental transformation. Their impacts on nonanthropocentric aspects of the environment, such as ecosystems, biodiversity, carbon reserves, and climate, are often overlooked. Bowman et al. (p. 481) review what is known and what is needed to develop a holistic understanding of the role of fire in the Earth system, particularly in view of the pervasive impact of fires and the likelihood that they will become increasingly difficult to control as climate changes. Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

The Pre-Quaternary history of fire

Abstract Although evidence for land vegetation comes from the Silurian, and maybe even earlier, the first record of fossil charcoal (fusain) is from the late Devonian. For this period there are only one or two isolated records. Not until the Early Carboniferous is there a record of extensive charcoal deposits, mainly preserved in near-shore clastic sediments, which provide evidence of significant and widespread wildfires. By the late Carboniferous charcoal was common or abundant in a wide range of facies, including tropical wetland peats. Wildfire played an important role in shaping the environment at this time. The latest Palaeozoic and early Mesozoic records of charcoal are fewer, whereas important deposits of late Mesozoic age are found worldwide. The occurrence of charcoal at the Cretaceous–Tertiary Boundary has been highlighted as evidence for a global fire following a meteorite impact, but this interpretation is questionable. Charcoal has been widely reported from Tertiary sediments and its appearance in the Quaternary and Recent is not solely as a result of human impact. Through the past 400 million years there have been major changes in atmospheric oxygen levels that affected fire intensity and frequency. Fire systems thus have a long history and their impact on shaping the environment is assessed.

The human dimension of fire regimes on Earth

Humans and their ancestors are unique in being a fire-making species, but ‘natural’ (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from ‘natural’ background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.

Observations on the nature and origin of fusain

Abstract Evidence for a wildfire origin of fusain is examined. Charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance. Artificially charred leaves and naturally burnt wood are illustrated using the SEM. Reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis. The ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the Late Devonian.

Wildfire responses to abrupt climate change in North America

It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial–interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

The nature and influence of fire in Carboniferous ecosystems

Fusain occurs widely in Carboniferous coals and sediments. It is now recognised to represent charcoal and be the product of wildfire. The occurrence of fire is partly constrained by atmospheric oxygen levels, availability and nature of fuel and by aspects of climate (rainfall and seasonability in particular). The majority of fires in the Carboniferous were probably started by lightning strikes or by volcanic activity. Experiments on the charring of modern plants has shown that the reflectance of charcoal (and hence fusain) is directly related to temperature of formation. Different fire types may yield fusain assemblages of differing reflectance spectrums, but it may be significant that many modern charcoal assemblages yield only semifusinites (as seen by reflectance microscopy). The significance of these findings is assessed in relation to the use of fusinites and semifusinites as depositional indicators, as interpreted from coal petrology. Fires may have a dramatic effect on ecosystems, not only causing changes in vegetational succession but also severe erosion can occur following a major fire which can be traced in depositional systems. In this paper we document three major Carboniferous sedimentary systems affected by fire: clastic sedimentary systems, using extensive fusain deposits in mid-Lower Carboniferous, near-shore sediments in Donegal, Ireland; volcanic systems using late Early Carboniferous, volcaniclastic sequences in the Midland Valley of Scotland; and coal and coal-bearing sequences in the Upper Carboniferous (Westphalian B) of the Pennine Basin, England. In the later settings the influence of fire in peat formation and succession is assessed. In addition, data on the vegetational composition of charcoal assemblages is considered. It is concluded that fire plays a major role in many Carboniferous ecosystems.

Coal petrology and the origin of coal macerals: a way ahead?

The development of coal petrology and the establishment of a nomenclatural system have proved of major use both for the industrial utilization of coal and for the development of a broad understanding of coal formation and diagenesis. The development, over the past 30 years, however, of nomenclature that includes aspects of plant origin and process is a retrograde step (e.g. pyrofusinite, degradofusinite, and funginite). Equally problematic is the use of prescriptive formulae to indicate coal ‘origins’. This paper reviews some of the problems involved with coal petrology as it is usually practiced. In addition, new advances in organic geochemical techniques have led to a fuller understanding of the relationship of plants and coal macerals. Recent research on the origin of coal macerals is presented and there is a discussion of the problems and challenges facing coal petrologists. A holistic approach to studies of the origin of coal and coal macerals, which includes not only petrographic but also chemical and biological studies, is advocated. D 2002 Elsevier Science B.V. All rights reserved.

Plant/animal interactions during the upper carboniferous

This paper discusses evidence for plant/animal relationships in the Upper Carboniferous. Close interactions are examined from the study of fossil plants and animals preserved in coal swamp and coastal plain environments. Evidence for plant/animal interactions is in the form of: (1) animal morphology, including both vertebrates and invertebrates. The vertebrates are dominated by amphibians; however, a few reptiles are known and are mostly carnivores or insectivores. The invertebrate communities are dominated by arthropods, many of which are herbivores. Millipedes, springtails and mites are present on the forest floor and in peats, with insects dominating above ground environments. The diets of the animals have been studied using evidence from gut contents, coprolites, anatomy and comparisons to modern representatives. (2) Plant morphology, including positive stimulation (i.e., dispersal vectors) or in terms of negative stimulation such as protection against herbivory. These data include plant anatomy and morphology, evidence of herbivory in the form of chewed leaves, bored seeds and megaspores, etc. Evidence is provided that suggests that the medullosan seed fern pollen typeMonoletes may have been dispersed by animal vectors. Information on plant/animal relationships in a single environment is based on a study of coprolites extracted from permineralizations (coal balls). Assemblages of coprolites found in these coal balls suggest that they were formed principally from mites, Collembola and millipedes, and demonstrates that the association of soil arthropods, which is important in modern soil ecosystems, was already dominating similar environments in the late Carboniferous. The abundant fossil evidence for plant/animal interrelationships during the Upper Carboniferous should be evaluated when considering co-evolution.АбстрактВ этой статье рассмат ривается очевидност ь связи растениеживотное в Верхней каменноуго льной аормации. Их тес ное взаимодействие доказывалось путем и сследования окамене лых растений и животных, сохранивш ихся в угольных топях и на береговых равнинах. Очевидност ь взаимодействия растение-животное пр оявляется в виде: 1) морфологии жив отных, включая как поз воночные так и беспозвоночные. У позвоночных домини руют земноводные, однако, известны и нек оторые пресмыкающие и, главным образом, плотоядные или насек омоядные. У беспозвон очных доминируют членистоногие, многи е из которых являются травоядными. Многоно жки, ногохвостики и клещи находятся в лесном оп аде и в торфе, в то время как насеком ые доминируют в надзе мной среде. Питание животных изучалось п утем исследования со держания кишечника, копролитов, анатомии этих животных и их сра внения с современными особями. 2) Морфологии р астений, включая поло жительную стимуляцию (т. у. перено счики распыления) или с точки зрения негативной стимуляц ии, такой как защита от травоядных. Эти данные включают анат омию и морфологию рас тений, признаки присутствия травояд ных в виде прожеванны х листьев, проеденных семян, мегаспор и т.д. Пр иводятся доказатель ства которые указывают на то, что пыльца папор отника вида Monoletes может распыляться животны ми-переносчиками. Инф ормация о связи растение-животное в е диной среде основана на изучении копролитов, выделенных из минера лизации (угольных шар иков). Скопление копролитов предпола гает, что они были обра зованы, главным образом, от клещей, чле нистоногих вида Collembola и многоножек, и доказывает, что ассо циация почвенных чле нистоногих, которая важна в современных э косистемах почвы, был а уже доминирующей в подобных условиях в поздней каменноугол ьной формации. При рассмотрении совмес тной эволюции следуе т учтиывать значительное количество окаменел остей, указывающих на взаимосвязь растениеживотное в периодуе Верхней ка менноугольной форма ции.ResúmenEste trabajo discute evidencias de relaciones de planta/animal en el Carbonifero Alto. Se examinan interacciones recíprocas cercanas basadas en el estudio de plantas fósiles y animales consevados en ambientes de pantanos de carbón de piedra y llanos costeros. La evidencia de interacciones planta/animal existe en la forma de: (1) morfología animal incluyendo ambos vertebrados e invertebrados. Los vertebrados están dominados por anfibios, sin embargo, se conocen algunos reptiles que son en la mayor parte carnivoros o insectívoros. Las comunidades de invertebrados están dominadas por artrópodos, muchos de los cuales son herbivoros. Milpies, colémbolos (orden Collembola) y acaros están présente sobre el suelo del bosque y en turbas con insectos dominando los ambientes sobre el suelo. Las dietas de los animales han sido estudiadas usando evidencia de contenido del intestino, coprolitos, anatomia y comparaciones con representantes modernos. (2) morfología de planta, incluyendo estimulación positiva (i.e., agentes de dispersión) o estimulación negativa (i.e., protección contra herbivorías). Estos datos incluyen anatomía y morfología de plantas, evidencia de herbívoros en la forma de hojas masticadas, semillas y megaesporas excavadas, etc. Proveemos evidencias que sugieren que el polen del tipoMonoletes de helechos de medulosa con semillas puede haber sido dispersado por agentes de dispersión animal. Informatión sobre relaciones planta/animal en un solo ambiente está apoyado en un estudio de coprolitos sacado de permineralizaciones (bolas de carbón). Conjuntos de coprolitos sugieren que fueron formados principalmente de acaros, colémbolos (orden Collembola), y milipies, y demuestran que la asociación de artrópodos del suelo, que es importante en los ecosistemas de suelos modernos, ya había dominado ambientes semejantes a fines del Carbonífere La abundante evidencia fosíl de interrelaciones planta/animal durante el Carbonífero Alto debe ser evaluada cuando se considera la co-evolución.ZusammenfassungDer vorliegende Beitrag erörtert Beweismaterial für Wechselbeziehungen zwischen Pflanzen und Tieren im oberen Karbon. Enge Interaktionen sind durch das Studium fossiler Pflanzen und Tiere, die in Kohlsumpf-und Kustenebenen-Gemeinschaften konserviert wurden, beschrieben. Beweise für Interaktionen zwischen Pflanzen und Tieren treten in folgenden Formen auf: 1) Morphologie der Tiere, einschliesslich Vertebraten und Invertebraten. Amphibien sind die vorherrschended Vertebraten; auch einige Reptilien sind bekannt, diese sind aber meistens Carnivoren oder Insektivoren. Arthropoden dominieren die Invertebraten Gemeinschaften, und viele unter ihnen sind Herbivoren. Doppelfüssler, Springschwänze, Milben und Zecken in Mooren und Waldböden anzutreffen, während Insekten die höheren Schichtendominieren. Die Nahrung der Tiere wurde durch Analyse von Darminhalten, Koprolithen, Anatomie und Vergleiche zu modernen Vertretern studiert. 2) Morphologie der Pflanzen, einschliesslich positive (z.B. Verbreitungsvektoren) und negative Stimulation, wie Schutz vor Herbivoren. Diese Resultate schliessen Pflanzen Anatomie, Morphologie, Nachweis von Herbivoren in Form angefressener Blatter und eingebohrter Samen und Megasporen, etc. ein. Beweise, die Vermutung dass der Pollen der Medullosen Farnsamer des TypenMonoletes mit Hilfe von Tiervektoren verbreitet wurden nahelegen, sind gegeben. Informationen über Wechselbeziehungen zwischen Pflanzen und Tierenin einer bestimmten Umgebung sind auf das Studium der Koprolithen gestützt, die aus Permineralisationen (Dolomitknollen) extraktiert wurden. Anhaufungen von Koprolithen deuten dahin, dass sie vorallem von Milben, Zecken, Springschwänzen und Doppelfüsslern gebildet wurden. Dies zeigt, dass die Assoziation von Gliederfüsslern, welche in den modernen Boden-Oekosystemen so Wichtig ist, schon im oberen Karbon ähnliche Ausmasse angenommen hat. Bei einer Diskussion von K-Evolution sollte der reichliche Nachweis von Beziehungen zwischen Pflanzen und Tieren im oberen Karbon in Betracht gezogen werden.SommaireCette etude discute le rapport entre les plantes et les animaux dans le carbonifère supérieur. Les interactions discrètes sont examinées par l’étude des plantes et des animaux fossiles, préservés dans les marais du charbon et dans les environnementes des plaines costaux. Évidence des interactions est des classes suivi: (1) Morphologie des animaux, comprenant les vertébrés et les invertébrés. Les vertébrés était dominés par les amphibiens, pourtant, quelque amphibiens sont connus, mais ils sont pour la plupart des carnivores et des insectivores. Les communautés des invertébrés sont dominé par des arthropodes, une grande parties des celles-ci sont des herbivores. Les millipieds, les mites, et les Collembola sont presentés au sol de la forêt et dans les tourbes, avec des insects qiu dominent les environnements au-dessus des sols. Les régimes des animaux étont etudiés en faissons l’usage de l’evidence reçu des contenus des intestins, des coprolithes, de l’anatomie et des comparaisons avec des représentatives modernes. (2) La morphologie des plantes, comprenant la stimulation positive (par example, les vécteurs de la dispersion) ou la stimulation negative telle que la protéction contre l’herbivorie. Ces données comprennent l’anatomie et la morphologie des plantes, l’evidénce de l’herbivorie dans les formes de feuilles mâchées, les semances et les mégaspores percées. L’évidence qui propose que le pollen des pteridospermées du typeMonoletes était dispersé par un vécteur animal, est fourni. Les reseignements sur la relations entre les plantes et les animaux dans un environnement particulier est fondé sur l’étude des coprolithes extrayant des permineralizations (coal balls). Des assemblages des coprolithes proposent qu’ils étèrent formé principalement par les Acari, les Collembola, et les Diploda, et elles demonstrent que l’association des arthropodes du sol qui est important aux ecosystems des sols modernes, etait dominé déjà dans les environnements semblables du carbonifère supérieur. L’évidence abundante des interactions entre des plantes et des ani

Distribution of anatomically-preserved floras in the Lower Carboniferous in Western Europe

Twelve localities of Lower Carboniferous strata in Scotland (Loch Humphrey Burn, Glenarbuck, Pettycur, Oxroad Bay and the Berwickshire localities of Cove, Burnmouth, Gavinton, Edrom, Foulden) and in France (Esnost, Roannais, Montagne Noire) have been investigated with particular regard to their anatomically preserved floras. New data on the composition and preservation of the assemblages, their geological setting and stratigraphical age, using palynology in particular, are presented. Present data suggest that four successive groups of floras obtained from these localities can be recognised: from the Montagne Noire (mid to late Tournaisian), from the Berwickshire localities and Oxroad Bay (late Tournaisian to early Visean), from Loch Humphrey Burn and possibly Glenarbuck (mid Visean) and from Roannais, Esnost, and Pettycur (late Visean). The similarities and differences between the floras are discussed with particular emphasis on stratigraphical as opposed to ecological controls. Comparisons are made with the New Albany Shale floras of the U.S.A., the Saalfeld and Glatzish-Falkenberg floras from the German Democratic Republic. The data suggest that the ferns and pteridosperms show the most striking changes through the Lower Carboniferous strata.

Experiments in waterlogging and sedimentology of charcoal: results and implications

Abstract Fossil charcoal has a sporadic occurrence in sedimentary rocks since Devonian time. It is moderately common as a component of the organic material found in a wide variety of facies, but there are also some notable concentrations which occur locally. These occurrences have considerable palaeobotanical and palaeoecological value because the process of charring may result in excellent preservation of plant tissue. If assemblages of charred material are to be used to interpret palaeoenvironments, it is important to understand the behaviour of charcoal during transport from the site of the fire. Charcoal is an unusual sedimentary material because most fresh material floats, but with prolonged immersion becomes waterlogged and sinks. We carried out a series of waterlogging experiments on uncharred material and charcoal from a range of different plant types and tissues. These show considerable variations in the rates of waterlogging of different charred and uncharred plant tissues, and it is suggested that buoyancy contrasts are likely to result in separation during transport and deposition. Furthermore, experiments in a flume tank have shown that the process of deposition of charcoal in sand is controlled by the rate of migration of bedforms, which is in turn determined by depth, flow velocity and sediment supply. Allochthonous assemblages of charred and uncharred plant debris will most probably be biased and not fully representative of the contemporaneous plants or vegetation. The presence of charcoal concentrations may be used as an aid in interpreting palaeohydraulic conditions.