The interaction of fire and mankind

We are becoming increasingly familiar with the potential influence of fire on modern short-term timescales, however the major feedbacks that operate on long timescales are inherently different. Changes in the abundance of atmospheric oxygen (O₂) are the main long-term forcing on fire-activity. Laboratory experiments have explored the sensitivity of fire to changes in O₂ and report that ~16% O₂ is required to enable self-sustaining combustion. The record of charcoals over the past 420Ma indicates that O₂ has never fallen below 16%. However, the amount by which it has risen to super-ambient levels remains debated because it involves consideration of a complex interplay between vegetation and fire. We have used the Cretaceous period to explore aspects of this interplay because it is a time that was likely characterised by high O₂ and major evolutionary innovations in land plants. We coupled laboratory experiments with mathematical models of fire spread to create the first predictions of palaeofire behaviour. These were based on changes to fuel driven by the invasion of early angiosperms. We explored the implications of these changes on long-term carbon and oxygen cycles, by imposing an increase in the flammability of ecosystems in the COPSE biogeochemical model between 135-100Ma. This coupled O₂-angiosperm flammability increase strengthens negative feedbacks that regulate O₂ revealing that by 80Ma atmospheric O₂ was lowered from ~28.5% to ~25%. We conclude that past evolutionary innovations in plants not only had major consequences for fire regimes, but that these altered the strength of Earth system feedbacks that affect the habitability of our planet. 

Professor Claire Belcher, University of Exeter, UK

Professor Claire Belcher, University of Exeter, UK

Claire is an Earth scientist specialising in the study of natural fires and the role that they play in regulating the Earth system. She graduated from Royal Holloway University of London with a degree in Geology in 2000. She then undertook an MSc in Micropalaeontology at University College London, graduating in 2001 before returning to Royal Holloway to undertake her PhD. She completed her PhD in 2005 entitled "Assessing the evidence for extensive wildfires at the Cretaceous-Tertiary Boundary" and has continued to build on this fiery start ever since.

She then moved to University College Dublin to work at the Programme for Experimental Atmospheres and Climate (PEAC) facility where she focused on the relationship between ancient wildfires and variations in palaeoatmospheric composition. In 2010 she moved to The University of Edinburgh to hold a unique position joint between BRE Centre for Fire Safety Engineering and the School of Geosciences. Since January 2012 she has been a Senior Lecturer in Earth System Science at the University of Exeter. Claire is the team leader of a 1.52 million euro European Research Council Starter Grant that seeks to understand the impact of plant evolution on wildfires in ancient ecosystems. Her research is internationally recognised for integrating state-of-the-art modern experimental methods into studies of Earth’s ancient past, an approach which is well highlighted by her recently published edited book "Fire Phenomena and the Earth System an Interdisciplinary Guide to Fire Science".

Numbers of animal species react to the natural phenomenon of fire, but only humans have learnt to control it and to make it at will. Natural fires caused overwhelmingly by lightning are highly evident on many landscapes. Birds such as hawks, and some other predators, are alert to opportunities to catch animals including invertebrates disturbed by such fires and similar benefits are likely to underlie the first human involvements with fires. Early hominins would undoubtedly have been aware of such fires, as are savannah chimpanzees in the present. Rather than as an event, the discovery of fire use may be seen as a set of processes happening over the long term. Eventually fire became embedded in human behaviour, so that it is involved in almost all advanced technologies. Fire has also influenced human biology, assisting in providing the high quality diet which has fuelled the increase in brain size through the Pleistocene. Direct evidence of early fire in archaeology remains rare, but from 1.5 million years ago onward surprising numbers of sites preserve some evidence of burnt material. By the Middle Pleistocene recognisable hearths demonstrate a social and economic focus on many sites. The evidence of archaeological sites has to be evaluated against postulates of biological models such as the ‘cooking hypothesis’ or the ‘social brain’, and questions of social co-operation and the origins of language. Although much remains to be worked out, it is plain that fire control has had a major impact in the course of human evolution.

Professor John Gowlett, University of Liverpool, UK

Professor John Gowlett, University of Liverpool, UK

John Gowlett has been involved with studies of early human fire use since his group made discoveries of burnt material at the 1.5 million year old site of Chesowanja in Kenya in the 1970s.  Subsequently he was engaged with colleagues in the investigation of combustion features at the 400,000 year old site of Beeches Pit in East Anglia UK, where refitting flints showed a link with human activities.  He has recently participated in bush fire studies in S. Africa, alongside other hearth experiments.  He was a director of the British Academy’s centenary project Lucy to Language (co-authoring Thinking Big, (2014) with Clive Gamble and Robin Dunbar), and has a particular interest in tracing the preconditions and origins of human conceptualising abilities. He is a Professor of Archaeology in the University of Liverpool.

Fire history reconstructions from lowland Amazonia provide insights into millennial-to-centennial scale trends and drivers of Neotropical fire activity since the Ice Ages.  Sedimentary proxies are used to reconstruct the development of fire and vegetation within lowland tropical ecosystems, including the seasonally-deciduous tropical forest, Cerrado, tropical rainforest, and flood-adapted forests and savanna systems in lowland Amazonia.  Sedimentary charcoal archives were compared to regional paleoclimate reconstructions and evidence for human land-use in the lowland Neotropics to understand drivers of past fire regimes. A network of Neotropical charcoal records captures long-term trends in fire activity, suggesting regional heterogeneity that is likely linked to natural climate variability.  In recent decades, and on long-time-scales, fire activity has been more prevalent in tropical ecosystems with greatest seasonality, which also corresponds to regions with elevated human land-use. Results of this research suggest fire frequency has been decreasing in the tropical lowland tropics during the last several thousand years, reaching a nadir in the past millennia, particularly following the demographic collapse after the Columbian Encounter around ~AD 1500. The long-term history of fire in the Neotropics is linked to natural climate variability, and potentially, may have been amplified (or dampened) at times by changing human demographics. The present view of Amazonia as a landscape without fire and containing pristine forests needs to be reevaluated. 

Professor Mitchell J. Power, University of Utah, USA

Professor Mitchell J. Power, University of Utah, USA

Associate Professor Mitchell Power holds a split position at the University of Utah with partnerships between the Natural History Museum of Utah and the Department of Geography.  His interests include botany, paleoecology, biogeography, fire history, and paleoclimatology. His research investigates vegetation change through time as influenced by climate and natural disturbances.  Currently he is involved in global and regional studies on drivers of fire activity during glacial and Holocene times and is a founding member of the Global Palaeofire Working Group. 

Since ancient times people have recognized fire as fundamental yet different.  For centuries Westerners tried to imagine it as a substance or an informing principle; but however conceived, it was integral and central, as it was in daily life.  This changed with the Enlightenment.  Fire disintegrated into subcategories of chemistry, physics, and engineering.  Interestingly, this transformation occurred at the same time that fire as a source of general power shifted from burning living biomass to fossil biomass.  With industrialization working fire has increasingly disappeared from the quotidian world, as it did from the intellectual world. Today, in developed societies it flourishes primarily in nature preserves and amid sites of social unrest.

Yet it may be reasserting a claim to significance.  It is the source of power behind the many global changes wrought by humanity and summed in the expression Anthropocene.  It has also become fundamental to the management of nature preserves, where its removal has unhinged ecosystems.  An increasing number of phenomena connect to humanity, as the keystone species for fire on Earth, shifted its fire practices.   Perhaps the time has likewise come to reassert a claim for fire's intellectual presence.  The other ancient elements have academic disciplines devoted to their study.  The only fire department on a university is the one that sends emergency vehicles when an alarm sounds.

Professor Stephen Pyne, Arizona State University, USA

Professor Stephen Pyne, Arizona State University, USA

Steve Pyne is a professor in the Human Dimensions Faculty, School of Life Sciences, Arizona State University in Tempe, Arizona, USA.  He has written over two dozen books, mostly on the history and management of fire, including big-screen histories for America, Australia, Canada, Europe, and Earth.  He is currently updating the fire history of the U.S. since 1960.  Other interests include the history of exploration, with books on Antarctica, the Grand Canyon, and the Voyager mission.  He also teaches graduate courses on nonfiction writing.  In an earlier life he spent 18 seasons working on wildland fire crews for the National Park Service.

Recent studies have suggested that the first arrival of humans in the Americas during the end of the last ice age is associated with non-trivial anthropogenic influences on landscape, in particular with the use of fire which would have given even small populations the ability to have broad impacts on the landscape. Understanding the impact of these early people is complicated by the dramatic changes in climate occurring with the shift from full glacial to full interglacial conditions. Despite these difficulties here we attempt to test the extent of anthropogenic influence using the Californian Channel Islands as a smaller, landscape scale test bed.

In 1954 Phil C. Orr discovered two human femora on Santa Rosa Island, California Channel Islands deposited in water lain sediments at the mouth of Arlington Springs Canyon which have become known as ’Arlington Springs Man’ direct and indirect radiocarbon suggest an age no younger than c.13,000 yrs BP. The probable stratigraphic positioning of the human remains has also been recently ascertained. This presentation places these existing investigations into a wider stratigraphic framework of the California Channel Islands. Over 20 field sections from Arlington Canyon coupled with >30 new radiocarbon dates (dating from c.20-11,000 yrs BP) has allowed a detailed chronostratigraphy to be developed for the Last Glacial-Interglacial Transition. Landscape changes and development both before and after ’Arlington Springs Man’ are discussed including possible changes in fire activity, vegetation, soil development and fluvial processes.

Dr Mark Hardiman, University of Portsmouth, UK

Dr Mark Hardiman, University of Portsmouth, UK

Mark Hardiman is a Lecturer in Physical Geography at the University of Portsmouth interested in understanding abrupt climate change and Earth system response. Mark has an MSc and PhD in the field of Quaternary Science from Royal Holloway, University of London where he was supervised by Professor John Lowe and Dr Simon Blockley. Specifically his research interests include understanding the potential role of wildfire to rapid geomorphic and environmental events via the analysis of charcoal in both complex and high-resolution palaeoenvironmental records during the Quaternary. His other research specialism is in geochronology, in particular using tephrochronology as a tool for directly synchronising palaeo archives.    

Forests and human communities in western North America are now extremely vulnerable to large, severe wildfires as a consequence of fire exclusion and other land use practices and increasingly warm and persistent droughts. Combined paleoecological and archaeological studies of climate, fire and human histories from the same landscapes can help reveal the relative roles of people and climate in driving past and modern trends in fire regimes. In this paper we evaluate human and climate controls of wildfire using (1) a mountain range-scale network of more than 1,000 fire scarred trees from the Jemez Mountains, New Mexico (~2,000 km²), and (2) a continental-scale network of fire history reconstructions from more than 800 sites in western North America (~3,000,000 km²), including 2,000 year-long fire histories from giant sequoia groves in the Sierra Nevada of California. The Jemez Mountains are an instructive case of the influences of long-time human occupation on fire-prone, forested landscapes. Here, in ponderosa pine and mixed conifer forests, we find that humans eliminated widespread surface fires during peak populations prior to 1650 CE, whereas many small fires still occurred at locations distant from villages and agricultural fields.  After depopulation of forested areas circa 1680 CE, widespread surface fires became much more regular and these extensive fires were highly correlated with wet/dry switching of moisture regimes. Continental-scale fire climate patterns emphasize the consistently important roles of inter-annual to decadal-scale climate variations on spatial and temporal fire activity, regardless of human influences at finer spatial scales during recent millennia.

Professor Tom Swetnam, University of Arizona, USA

Professor Tom Swetnam, University of Arizona, USA

Tom Swetnam studies changes in climate and forest disturbances using dendrochronology. He is Regents’ Professor at the world’s premier and largest laboratory dedicated to all aspects of tree-ring research and education, the Laboratory of Tree-Ring Research, University of Arizona. He has worked extensively on wildfire history and ecology in pine and giant sequoia forests of the western U.S., Mexico, South America, and Siberia, Russia. He received a BS in Biology and Chemistry at the University of New Mexico and a MS and PhD in Watershed Management at the University of Arizona. His most cited papers include: Swetnam and Betancourt, “Fire-Southern Oscillation relations in the Southwestern United States” Science 249:1017-1020, 1990; Swetnam, “Fire history and climate change in giant sequoia groves” Science 262:885-889, 1993; and Swetnam and Betancourt “Mesoscale disturbance and ecological response to decadal climatic variability in the American Southwest” Journal of Climate 11:3128-3147, 1998.

Australia is an island continent with ecosystems renowned for their flammability, high endemism of plants and animals, the keystone role of marsupial herbivores and carnivores, ancient Aboriginal traditions of landscape burning, and more recently, extraordinarily high mammalian extinctions and irruptions of mammalian herbivores and carnivores introduced by Europeans.

There much debate about the causes and consequences of the recent extinctions in uncleared Australia landscapes. Several prominent theories have stressed, to differing degrees, the importance of change fire regimes following the breakdown of Aboriginal land management and the introduction of non-native herbivores and carnivores.  Some of these theories have also highlighted the legacy effects of the initial impact of Aboriginal colonisation in the late Pleistocene, including the extinction of very large marsupial herbivores and carnivores, collectively known a ‘megafauna’. 

It is possible that specific spatiotemporal patterns of landscape burning (pyrodiversity) influences habitat quality and hence mammal diversity and abundance. Recursively, pyrodiversity is reinforced by mammalian food webs via a range of ecological processes (such as nutrient cycling, soil turnover, plant regeneration and growth, plant species diversity because mammals affect ecosystems process via digging, trampling, phytomass off-take, seed and spore dispersal, and concentrating nutrients) all of which directly and indirectly influence fire regimes. Critically, humans are both keystone predators that regulate herbivores and affect pyrodiversity by controlling the frequency, extent and seasonality of landscape fire.

This human controlled food web – pyrodiversity hypothesis has substantial management implications for restoring ecosystems in the Anthropocene globally. While manipulating fire regimes, humans must simultaneously manage mammalian food webs, possibly by introducing new species to compensate for the extinction of herbivorous and carnivorous vertebrates that have occurred recent and more distant past.

Professor David Bowman, University of Tasmania, Australia

Professor David Bowman, University of Tasmania, Australia

Professor David Bowman holds a research chair in Environmental Change Biology in the School of Biological Sciences at the University of Tasmania at Hobart, Australia.  After completing his PhD in forest ecology and silviculture at the University of Tasmania in 1984, he spent two decades in the undertaking full time research throughout northern Australia working closely with Aboriginal people before returning to Tasmania. He has received fellowships from the Australian Academy of Science, Harvard, Kyoto, Leeds and Arizona universities. His research is collaborative, transdisciplinary and focused on understanding how fire influences the Earth system, humans alter ecologies with fire, fire shapes landscapes, and achieving socially and ecologically sustainable fire management.  Collectively he describes his research program as pyrogeography. 

The African continent has the largest extent of savannas and associated grasslands in the world. The savannas support frequent fires so that Africa also accounts for the largest fraction of the world’s annual burnt area than anywhere else. Thus Africa is an interesting test case for the influence of fire on vegetation and of humans in shaping fire regimes and thereby shaping the vegetation.  For more than a century, Africa’s grasslands have been widely interpreted as the products of deforestation promoted by anthropogenic burning. The deforestation hypothesis has led to official policies of fire suppression in many African countries. It has motivated plans for large-scale ‘reforestation’ projects targeting, in particular, Africa’s humid savannas and grasslands. Here I review different lines of evidence for the age and origins of African savannas and the fires that maintain them. These point to ancient origins of the grassy biomes long before intensive human use of fire. Nevertheless, except for the last few decades, there is considerable uncertainty as to the influence of people in expanding the area of derived savannas at the expense of the forest they are supposed to have displaced.  A better understanding of the attributes of ancient versus secondary grasslands is needed to evaluate human impacts on the spread of savannas. 

Professor William Bond, South African Environmental Observation Network and University of Cape Town, South Africa

Professor William Bond, South African Environmental Observation Network and University of Cape Town, South Africa

William Bond is Chief Scientist at South Africa’s Environmental Observation Network and Emeritus Professor in Biological Sciences at the University of Cape Town. He is known particularly for his studies of fire as a major process shaping the ecology, geography, and evolutionary history of plant life. His research is centred on the puzzle of shrublands, grasslands and savannas growing in climates capable of supporting closed forests. Diverse lines of evidence are revealing ancient origins for the biota of these open ecosystems. He has explored both physical and biotic controls on their distribution using a variety of tools, from remote sensing and physiologically-based global vegetation models, to field studies and glasshouse experiments. Switches between open and forested ecosystems are an under-appreciated aspect of global change with implications for land management and global change policy at local, regional and global scales. Bond is a foreign associate of the National Academy of Sciences of the USA.