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The interaction of fire and mankind

Event

Location

The Royal Society, London, 6-9 Carlton House Terrace, London, SW1Y 5AG

Overview

Scientific discussion meeting organised by Professor Andrew Scott, Professor William Chaloner FRS, Professor Claire Belcher and Dr Chris Roos

CC image courtesy of U.S. Department of Agriculture on Flickr

The complex interrelationships between fire and mankind transcend international borders and disciplinary boundaries. The spectre of climate change highlights the need to improve our understanding of these relationships across space and time.  This meeting will examine historical, evolutionary, and biophysical tensions inherent in the fire-climate-society nexus to advance the international, interdisciplinary science necessary to address contemporary and future fire challenges.

A draft programme and speaker biographies are available to download. The related publication of this meeting can be found online.

Attending this meeting

This event is intended for researchers in relevant fields and is free to attend. There are a limited number of places and registration is essential. An optional lunch is offered and should be booked during registration (all major credit cards accepted).

Enquiries: Contact the events team

Event organisers

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Schedule of talks

14 September

09:00-12:30

Fire and early humans

4 talks Show detail Hide detail

Chairs

Professor Bill Chaloner FRS, Royal Holloway, University of London, UK

09:00-09:30 Fire feedbacks to the Earth system on multi-million year timescales

Professor Claire Belcher, University of Exeter, UK

Abstract

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. 

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09:45-10:15 The discovery of fire by humans

Professor John Gowlett, University of Liverpool, UK

Abstract

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.

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11:00-11:30 Fire-climate-human linkages in lowland South America

Professor Mitchell J. Power, University of Utah, USA

Abstract

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. 

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11:45-12:15 Fire in the mind

Professor Stephen Pyne, Arizona State University, USA

Abstract

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.

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12:30-13:30 Lunch

13:30-17:00

The developing relationships between fire and humans

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Chairs

Professor Andrew Scott, Royal Holloway, University of London, UK

13:30-14:00 Fire and arrival of humans on the California Channel Islands

Dr Mark Hardiman, University of Portsmouth, UK

Abstract

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.

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14:15-14:45 Fire, climate and humans in Western North America: Continental to mountain range-scale insights from tree rings

Professor Tom Swetnam, University of Arizona, USA

Abstract

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.

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15:30-16:00 Fire and humans in Australian food webs from the Pleistocene to the Anthropocene

Professor David Bowman, University of Tasmania, Australia

Abstract

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.

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16:15-16:45 The deforestation story: testing for anthropogenic origins of Africa's flammable grasslands

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

Abstract

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. 

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15 September

09:00-12:30

Fire and humans: current conflicts

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Chairs

Professor Claire Belcher, University of Exeter, UK

09:00-09:30 Fire effects on soils: the human factor

Dr Cristina Santín, University of Swansea, UK

Abstract

Soils are perhaps the most valuable ‘non-renewable’ resource on Earth. They are the basis for Earth’s vegetation and human agroecosystems, present the largest terrestrial organic carbon stock, and act as stores and filters for water. Mankind has impacted soils from its early days in many different ways, with burning being one of the first. Fire has long been used as an agricultural tool to fertilise the soils and control plant growth, but it can also cause dramatic changes in vegetation cover, enhancement of soil erosion by several orders of magnitude or even desertification of previously productive areas.

Indeed fire is regarded by many as the seventh soil-forming factor. In this presentation the effects of fire on soils will be discussed focusing on the human factor. Human-induced fires have shape our landscape for several thousand years and they are currently the most common type of fire in many regions of the world. We will examine the effect of traditional land-use practices involving fire, such as slash-burning or vegetation clearing, on soils, and will also discuss how more modern uses of fire, such as fuel reduction burns, are affecting our soils. Finally, we will explore the potential effects on soils of the complex interactions between the human-induced climate change and fire dynamics.

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09:45-10:15 At the nexus of fire, water and society

Deborah Martin, U.S Geological Survey, USA

Abstract

In 2015 the World Economic Forum declared that water crises (significant declines in water quality and quantity) are the greatest risks facing society. Water supplies are derived from several land cover types that are vulnerable to fire, but on a global basis, the highest percentage of water delivered to the world’s largest cities and numerous smaller communities comes from forested landscapes. Fire alters the hydrologic functions of forested catchments, including water interception, storage and discharge, and thus the timing and magnitude of water, sediment and chemical constituent export.   Two major themes emerge from research on burned catchments. First, in response to intense rain, burned catchments usually have higher peak flows compared to unburned catchments. Second, the altered hydrologic response of burned catchments leads to increased concentrations and loads of constituents dissolved in the water or associated with sediments. These changes can persist for decades. Post-fire studies have measured elevated concentrations and changes in the timing of the transport of carbon, nitrogen and other nutrients, sediment, heavy metals, and organic compounds like polycylic aromatic hydrocarbons (PAH’s). These constituents have the potential to affect the treatment of water for human consumption and can impact the quality of water stored in lakes and reservoirs. Efforts already exist in several parts of the globe to protect forested landscapes from disturbance because of their important role in providing ecosystem services and ability to act as “natural infrastructure” to deliver water-related services with minimal need for the construction of engineered infrastructure. However, we currently lack comprehensive tools to consider the effects of fire in planning, protecting and creating resilience in our water supplies.  Clearly, the need to understand the nexus of fire, water and society has become more pressing in the face of mega-fires, weather extremes and climate change.

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11:00-11:30 Smoke particles, air pollution and population health

Dr Fay Johnston, University of Tasmania, Australia

Abstract

The shift from open fires to internal combustion engines as the primary source of energy for human activity underpinned a shift from hunter-gatherer and agrarian to industrialised economies that defined the start of the Anthropocene. The accompanying changes in patterns of fertility, mortality and morbidity have been well described in terms of demographic, epidemiological, and health transitions. However any widespread change in human use of fire, by definition, produces a widespread change in human exposure to air pollution, now recognised as the single most important global environmental risk factor for human mortality. Using the framework of the Global Burden of Disease studies led by the World Health Organisation, I use the region of Southeast Asia as a case study for examining and comparing the direct mortality impacts of air pollution from different human patterns of burning. These include indoor domestic fires, agricultural and deforestation fires, the combustion of fossil fuels by industry and transport, and the epidemic of smoking made possible by mass production and global marketing of tobacco products.

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11:45-12:15 Community owned solutions for fire management in tropical forest and savanna ecosystems: case studies from Indigenous communities of South America

Dr Jay Mistry, Royal Holloway, University of London, UK

Abstract

Fire plays an increasingly significant role in tropical forest and savanna ecosystems, contributing to greenhouse gas emissions and impacting on biodiversity. Emerging research shows the potential role of Indigenous land use practices for controlling deforestation and reducing CO2 emissions. Analysis of satellite imagery suggests that Indigenous lands have the lowest incidence of wildfires, significantly contributing to maintaining carbon stocks and enhancing biodiversity. Yet, acknowledgement of Indigenous peoples’ role in fire management and control is limited, and in many cases dismissed, especially in policy-making circles. In this presentation, we analyse existing data on Indigenous fire management and impact, focusing on examples from tropical forest and savanna ecosystems in Venezuela, Brazil and Guyana. We highlight the key attributes of fire management techniques stemming from Indigenous communities themselves i.e. community owned solutions for fire management. These include Indigenous knowledge, local leadership and collective spirit/values, partnerships and networks. We suggest that through these cross-cutting themes and within the guiding principles that emerge from them, they become relevant from local to global scales. Our aim is to build a case for supporting Indigenous fire practices within government policy by combining different forms of knowledge systems to ensure more effective and sustainable fire management for all.

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12:30-13:30 Lunch

13:30-17:00

Fire and humans: current and future problems

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Chairs

Dr Chris Roos, Southern Methodist University, USA

13:30-14:00 Using fire observations from space for assessing atmospheric & air quality impacts

Professor Martin Wooster, King's College London and NERC National Centre for Earth Observation, UK

Abstract

Landscape fire is a globally prevalent but unpredictable phenomena that in many regions displays large interannual variability in its distribution, extent and intensity, and which burns on average across an area of the Earth similar to that of India every year. This activity has a very significant impact on our atmosphere, as well as on many biogeochemical cycles, and observations by Earth orbiting satellites represent the most successful approach to identifying and quantifying these impacts.  Since the late 1990's, many highly capable Earth Observing satellite instruments have been deployed in orbit, alongside a parallel development of methods required to extract more quantitative information on fires from these observations. This has led now to a much more complete understanding of global landscape fire activity and the associated atmospheric emissions, and ultimately to our ability to observe fire activity across the Earth in almost real-time. This presentation will review this capability, and will demonstrate how it enables the impact of fires on the atmosphere, and on the quality of the air we breathe, to be routinely monitored, permitting the delivery of forecasts to indicate how a situation of poor air quality for example may develop over the coming days (such that early warnings can potentially be provided). The newly operational Copernicus Atmosphere Service (www.copernicus-atmosphere.eu/) makes use of an explicit near real-time representation of fire and fire emissions to start to deliver this capability to the global community. 

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14:15-14:45 Tropical peatlands: In the line of fire

Professor Susan Page, University of Leicester, UK

Abstract

Tropical peatlands are one of the world’s largest near-surface pools of terrestrial organic carbon - storing some 90 billion tonnes. Yet, as a result of land use change, this vast pool of carbon is increasingly vulnerable to destabilisation, contributing to an increased flux of greenhouse gases to the atmosphere and acceleration of human-induced climate change. Focusing on Southeast Asia, this talk considers the link between contemporary land use activities, in particular the use of fire in land clearing, and the increased vulnerability of tropical peatlands to fire. It considers the principal causes of and controls on fire occurrence, contrasting the low vulnerability of undisturbed peat swamp forest with the increasingly fire-prone peatlands of deforested and drained landscapes. Recent research on the scale and variability of fire-derived greenhouse gas emissions, including both direct atmospheric emissions and less direct fluvial carbon exports, will be presented.  The impact of increasingly frequent, recurrent fires on ecosystem recovery and longer-term rehabilitation will also be considered, as well as the wider environmental and socio-economic costs of peatland fires in  a densely populated region of the world. The talk will conclude by considering the scope for improved fire management. 

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15:30-16:00 Invasive plants initiate novel fire regimes

Professor Jennifer Balch, University of Colorado, Boulder, USA

Abstract

Invasive grasses are increasing fire activity globally, yet the mechanisms driving the initiation and perpetuation of these novel fire regimes remain largely unknown. This work compares how short-term climate, long-term climate and land use interact with land cover across the western U.S. to alter the probability and behavior of fires. At a regional scale, invasive grasses can establish a strong grass-fire cycle. This work shows how fires in cheatgrass (Bromus tectorum), a non-native grass introduced in the 1800s, are larger, faster spreading and more frequent than fires in any native vegetation. This study tests whether cheatgrass fires are related to coupled wet-dry climate conditions and human ignitions, compared with native forest fires. This research integrates Earth observations from satellites into statistical models to create spatial predictions of wildfire vulnerability. These analyses are critically needed given that this invasive grass doubled the likelihood of fire and played a prominent role in the largest fire events in the intermountain west during the last decade. Assessing the relative influence of climate and anthropogenic drivers will also provide insights into how the cheatgrass-fire cycle can be prevented or reversed. While climate-induced shifts in fire activity have already been observed and predicted in forest ecosystems, little is known about how invasive grass fuels will concurrently change fire activity on regional to global scales. This study provides new mechanistic insights and foundational methods to characterize and quantify the current and future influence of feedbacks between climate, land use, and invasive grasses on native fire regimes.

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16:15-16:45 Fire and climate change

Dr LeRoy Westerling, UC Merling, USA

Abstract

Warming over recent decades has coincided with increased wildfire activity.  A diverse array of forest ecosystems in North America has been affected,  including cold boreal forests and Rocky Mountain forests with characteristically infrequent, high severity fire, and drier mixed conifer forests in the Sierra Nevada and Southwest with historically more frequent, mixed severity fire.  

Recent work indicates that some of these ecosystems may be near climatic tipping points, where recent or near term prospective changes in climate can interact with fire and other distrubance to drive ecosystems across thresholds. Wildfire in Alaskan and Rocky Mountain ecosystems has been limited by climatic controls on fuel flammability, and climate warming is lifting that constraint.  These ecosystems are exposed to increasingly frequent fire. Future fire activity may be limited more by fuel availability than climatic constraints on flammability, as changing ecosystem composition, climate and disturbance regimes interact.

Wildfire in mid-elevation mixed conifer forests of the Sierra Nevada and Southwest was historically more frequent, but less severe than recent decades.  Fire exclusion due to land use and fire suppression changes contributed to less fire, but increased fuel loads and greater fire severity.  Warming in these forests, combined with this fuels legacy, is contributing to an increase in uncharacteristically high severity wildfire.  Analysis of historical fires in Sierra Nevada forests indicates that restoring fuels to pre-fire suppression densities could significantly reduce high severity burned area, even under extreme climate change scenarios.  

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The interaction of fire and mankind The Royal Society, London 6-9 Carlton House Terrace London SW1Y 5AG UK