Ecosystem Dynamics E-Book

Richard H. W. Bradshaw

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 700

Veröffentlichungsjahr: 2014

Beschreibung

Ecosystem Dynamics focuses on long-term terrestrial ecosystems and their changing relationships with human societies.  The unique aspect of this text is the long-time scale under consideration as data and insights from the last 10,000 years are used to place present-day ecosystem status into a temporal perspective and to test models that generate forecasts of future conditions. Descriptions and assessments of some of the current modelling tools that are used, along with their uncertainties and assumptions, are an important feature of this book. An overarching theme explores the dynamic interactions between human societies and ecosystem functioning and services.

This book is authoritative but accessible and provides a useful background for all students, practitioners, and researchers interested in the subject.

Leseprobe

Table of Contents

Cover

Title Page

Copyright

Acknowledgements

About the companion website

Chapter 1: Where Are We and How Did We Arrive Here?

1.1 Why this book?

1.2 Ecosystems in crisis

1.3 Relevance of the past

1.4 Forecasting the future

1.5 Chapter details and logic

1.6 For whom is the book intended?

1.7 Four key questions and the links to policy

Chapter 2: Modelling

2.1 Introduction

2.2 Background ecosystem, vegetation and species models

2.3 Dynamic modelling

2.4 Integrating models

2.5 Further reading

Chapter 3: Data

3.1 Introduction

3.2 Which data are relevant?

3.3 Ecosystem dynamics: direct observation

3.4 Ecosystem dynamics: indirect measurement or proxy data

3.5 Drivers of ecosystem dynamics

3.6 Databases

3.7 Gaps in available data and approaches

Chapter 4: Climate Change and Millennial Ecosystem Dynamics: A Complex Relationship

4.1 Introduction

4.2 Reconstructing climate from biological data

4.3 The very long records of vegetation dynamics

4.4 Holocene records

4.5 Modelling of Holocene vegetation dynamics to help understand pollen data

4.6 Simulating Fennoscandian Holocene forest dynamics

4.7 Climate and megafaunal extinction

4.8 So how important is climate change for future millennial ecosystem dynamics?

Chapter 5: The Role of Episodic Events in Millennial Ecosystem Dynamics: Where the Wild Strawberries Grow

5.1 Introduction

5.2 Fire

5.3 Forest pathogens during the Holocene

5.4 Hurricanes and wind damage

5.5 Conclusion

Chapter 6: The Impact of Past and Future Human Exploitation on Terrestrial Ecosystem Dynamics

6.1 Introduction

6.2 Denmark: case study of human impact during the Holocene

6.3 Islands: sensitive indicators of human impact

6.4 Human influence on Mediterranean, temperate and boreal forests

6.5 The tropics

6.6 Spatial upscaling of the timing and ecosystem consequences of human impact

Chapter 7: Millennial Ecosystem Dynamics and Their Relationship to Ecosystem Services: Past and Future

7.1 Introduction

7.2 MEA classification

7.3 The current crisis in ecosystem services

7.4 Ecosystem services and the future

7.5 Relating the maintenance of biodiversity to ecosystem service provision

7.6 Scenarios of possible futures: some different approaches

7.7 So what do scenarios say about the possible futures for ecosystem services?

Chapter 8: Cultural Ecosystem Services

8.1 Introduction

8.2 Sacred sites and species

8.3 Cultural landscapes: biodiverse relicts of former land use systems

8.4 Hunting as a cultural ecosystem service

Chapter 9: Conservation

9.1 Conservation as we know it

9.2 Knowledge of the past: relevance for conservation

9.3 Conservation in practice: protected areas (Natura 2000)

9.4 Conservation and alien or invasive species

9.5 Global change, biodiversity and conservation in the future

9.6 Conclusion

Chapter 10: Where Are We Headed?

10.1 Introduction

10.2 Emergent themes and important underlying concepts

References

Glossary

Index

End User License Agreement

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Guide

Table of Contents

List of Illustrations

Figure 1.1

Figure 1.2

Figure 1.3

Figure 2.1

Figure 2.2

Figure 2.3

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Figure 2.6

Figure 2.7

Figure 2.8

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Figure 3.1

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Figure 4.1

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Figure 10.1

List of Tables

Table 2.1

Table 3.1

Table 5.1

Table 6.1

Table 6.2

Table 6.3

Table 7.1

Table 7.2

Table 7.3

Table 7.4

Table 9.1

Table 10.1

Ecosystem Dynamics

From the Past to the Future

Richard H.W. Bradshaw

University of Liverpool

Martin T. Sykes

Lund University

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Acknowledgements

This book has developed from the academic journeys that we have both enjoyed from the 1970s until today. Between us we have held various posts in academia in Denmark (R.B.), Ireland (R.B.), Sweden (R.B., M.T.S.), New Zealand (M.T.S.), the United Kingdom (R.B., M.T.S.) and the USA (R.B.), and both colleagues and experiences from all these countries have influenced the content of the book. R.B. proffers special thanks to John Birks, Colin Prentice and the other occupants of Room 28, Tom Webb III and Herb Wright, who all helped awaken my interest in palaeoecology. Many friends from the Faculty of Forest Sciences, SLU, Sweden combined to teach me both Swedish and Forest Science. Tack Olle Zackrisson och Pelle Gemmel for creating this opportunity. I also thanks special friends at the short-lived but exciting Department of Environmental History and Climate Change, GEUS, Denmark, where Bent Odgaard, the two Peters (Rasmussen, Friis Møller) and Anne Birgitte Nielsen, among others, showed me how Denmark was a true cradle of paleoecology and worthy of respect, despite being a small, flat country with little natural vegetation! In Sweden and Denmark, I led or participated in seven EU-funded projects, which generated important parts of the material covered here. A special thanks to Thomas Giesecke and other European Pollen Database colleagues for many of the good ideas in Chapter 4 and for introducing Teutonic rigour to my thinking.

M.T.S. would like to especially thank three people who provided significant opportunities: Bastow Wilson from Otago, New Zealand, who gave an anxious mature student the opportunity to do a PhD; Eddy van der Maarel from Uppsala, who provided the first postdoctoral position in 1989, albeit initially for 5 months, which provided a vital stepping stone to more than 24 years in Sweden; and Colin Prentice, then in Uppsala, who provided the opportunity to integrate my earlier computing background and ecology training into forest gap modelling and much more. I would also like to acknowledge the valuable discussions and informal contributions made by many colleagues, particularly those involved in various European-scale projects over a number of years, including ALARM, ATEAM, CLIMIT, CLIMSAVE, DECVEG, ECOCHANGE, EPIDEMIE, FIREMAN, MACIS, RUBICODE and others. I also thank various Lund scientists, including Almut Arneth, Dörte Lehsten, Veiko Lehsten, Paul Miller, Honor Prentice, Jonathan Seaquist, Ben Smith and others from the Departments of Physical Geography and Ecosystem Science and Ecology, as well as past PhD students, especially Thomas Hickler and Marie Vandewalle, who all gave support in myriad ways.

R.B. also acknowledges support from M.T.S.'s Lund colleagues while writing the book and thanks his old Lundian friends on the other side of the door in Kvartärgeologi, who were always ready for coffee and conversation. A special thanks to the DYNAMITE team for providing distraction from the book and good field discussions, plus some exceptional food and drink.

We both acknowledge the significant contribution Margaret P. Sykes made as a facilitator in a number of meetings between the authors, where much of the structure of the book was developed. She also read all chapters, more than once, and provided valuable editing, comments and corrections.

We both thank Sandra Mather for her cheery temperament and skilled help with figure production, even when all of the figures arrived at the last minute. Thanks also to readers Anne Birgitte Nielsen, Tom Webb III, Gina Hannon, Abigail G. Sykes and Julian M. Sykes-Persson for many useful comments and to Louise Bradshaw for help with the references. Krister Larsson, Thomas Giesecke, Gina Hannon, Peter Rasmussen and Jennifer Clear all provided photos or figures. A special thanks to Jean Clottes for the wonderful lions from the Chauvet Cave.

M.T.S. thanks the staff at the Geolibrary in the Geocentrum, Lund, in particular Rolf Hall and Robin Gullstrand, who responded with enthusiasm to his requests for books and articles.

We acknowledge with thanks financial support from:

The EU FP6 ERA BiodivERsA – FIREMAN (Fire Management to Maintain Biodiversity and Mitigate Economic Loss) 2009–2013, funded in Sweden by FORMAS and in the UK by NERC.

LUCCI (Lund University Centre for Carbon Cycle and Climate Studies), financed by a Linnaeus grant from the Swedish Research Council VR, who financed R.B. for a visiting professorship in Lund.

LUCID (Lund University Centre of Excellence for Integration of Social and Natural Dimensions of Sustainability), financed by a Linnaeus grant from the Swedish Research Council VR, who provided some funding to M.T.S.

STINT (The Swedish Foundation for International Cooperation in Research and Higher Education), who supported Lund–Liverpool exchange, including several book activities through project DYNAMITE.

The Hasselblad Foundation, who awarded M.T.S. the 2012 Natural Scientist writing stipend, which allowed a 2 month visit to the Hôtel Chevillon, Grez-sur-Loing, France in November and December 2012 in the final phase of the writing.

Dr Joel Guiot, Directeur de la fédération de recherché, CEREGE, Europole Mediterranéen de l'Arbois, Aix-en-Provence, France, who provided working space and fruitful discussions for 3 months in Spring 2011 to M.T.S. as visiting professor in the critical start-up phase of the book.

Finally, both authors would like to acknowledge the love and support of their families, without whom it would have been a whole lot tougher.

About the companion website

This book is accompanied by a companion website:

www.wiley.com/go/bradshaw/sykes/ecosystem

The website includes:

Powerpoints of all figures from the book for downloading

PDFs of tables from the book

Chapter 1Where Are We and How Did We Arrive Here?

‘I could calculate your chance of survival, but you won't like it.’

The Hitchhiker's Guide to the Galaxy, Douglas Adams, 1979

1.1 Why this book?

In January 2013 the Australian Bureau of Meteorology had to increase the temperature range of its standard weather forecasting chart by 4 °C to a maximum of 54 °C, adding deep purple and pink to its colour palette. The new colours were put into immediate action as old temperature records toppled in the latest heatwave, following what the government's Climate Commission called an ‘angry summer’. This is just one symptom of change that will influence global ecosystems, and it is important for all whose livelihoods and food are linked to the land to know what these impacts will be. Providing projections of the impacts is a challenge that we can meet either by studying records of past warmer periods or by using models to forecast the future. These two approaches are linked, as forecasting models have to build on knowledge and experience from the past. This link between models and data is one of the motivations and central themes of our book.

This book is about the long-term dynamics of the terrestrial ecosystems of the Earth. These ecosystems only cover 29% of the surface of the planet, but that is where we live, produce much of our food and gather most of our raw materials. The oceans and freshwaters of the world are also of vital importance for civilisations past and present, but in this book we concentrate on the dry land systems. We need to understand the changes taking place around us in order to be able to manage and exploit ecosystems in appropriate ways in the future. To do this we must have adequate descriptions, both of the system dynamics and of the forces that cause or shape these dynamics. The current state of many ecosystems is a consequence of dynamics, forces and events that have operated over very long periods; the timespan we cover stretches back over 20 000 years, to the coldest part of the last ice age, and reaches forward 100 years into the future. There are several factors that influence ecosystem dynamics but the most important are climate change, human impact and the physiological constraints of individual species. Specialised geological techniques are needed to explore the past, and modelling carries our analyses into the future. Our combination of data and modelling helps us understand how we arrived at the present state of the world and where we might be headed.

We two authors have expertise in long-term ecosystem dynamics that result in population and range changes of individual species. We both have a botanical background, so we use more plant than animal examples, although humans are the species most often mentioned. For long-lived trees, we examine both rapid events like forest fires and slow events like the range changes that occurred as Europe became revegetated after the last ice age. The ecosystem concept comprises species interactions with soils, water and the atmosphere, but inevitably our treatment reflects our own interests and experience and may be uneven. As biologists we are more conversant with the biotic components and processes than the abiotic, and there is more coverage of large plants and animals than of microorganisms. Humans are at the centre of this book. We analyse the development through time of the way people interact with the ecosystems that they have come to dominate. We write little about the present day as that is well covered in numerous other sources.

Models are another central topic in the book. They are sophisticated tools for integrating our knowledge of the Earth system and exploring the future. Models have a symbiotic relationship with data, which we examine in this book. Models draw on data during their construction and must be tested against yet more data. Models are not real life but can be used as experimental tools to explore the nature and relationships of the systems under study to generate future scenarios and even forecasts. They give outputs that may or may not be correct but can be assessed for validity against available data, for example through hindcasting: the comparison of known past events with model output. Hindcasting can increase understanding of past ecosystems and boost confidence in the explanatory power of models, and it is one important focus of this book. The overall aim of ecosystem modelling is to improve insight into and understanding of the complex interactions within an ecosystem, such as the responses to past or future variations in climate. Models can generate insight but do not necessarily provide definite answers, because they are, after all, only models. Once the model output has been validated against data, the model becomes a more effective and convincing tool with which to explore possible futures.

1.2 Ecosystems in crisis

The human race has now moved into the driving seat of all terrestrial ecosystems and the control panel is complex. There is no owner's manual and several systems are already careering out of control. There is an urgent need to understand these controls and to use our power wisely. This book provides the background information needed to ensure a long, sustainable relationship between planet Earth and its new managers and prepares the ground for writing that owner's manual. The control panel has warning lights and touch controls that alter land cover, emission of gases, hydrology, soil properties, genetic diversity and several other factors. Guidelines are needed for the appropriate settings and there is some urgency as several warning lights are flashing, including those labelled ‘greenhouse gas emissions’, ‘rapid climate change’, ‘biodiversity loss’, ‘food security’ and ‘water supply’. These warning lights show that the resilience of several ecosystems is being put to the test.

There are enormous issues at stake, including the future of ecosystem goods and services such as agriculture and silviculture, water and soil resources and the carbon and nitrogen cycles. There is active debate about how many people can survive on the planet in the longer term. Can the Earth support 12 000 000 000 people or are we threatened by severe and painful population reductions, such as occurred in the distant past? What are the prospects for the long-term survival of the human race? The term Anthropocene has been introduced to describe the last 200 years, in which ‘our societies have become a global geophysical force’, a process that has accelerated during the last 35 years (Steffen et al., 2007). It is not easy to put a precise date on when humans took over control of the planet from natural forces such as competition between species, natural selection, fire, weathering of rock and hydrological cycles, but the 200 years of the Anthropocene is one convenient estimate as good data exist from that period, although others have argued for the first millennium AD. Humans today move an order of magnitude more rock, soil and sediment during construction and agriculture than the sum of all other natural processes that operate on the surface of the planet put together. If the erosion of rock and soil caused by construction and agriculture were evenly distributed over ice-free continental surfaces, these human activities would now lower land surface by a few hundred metres per million years, as compared with an earlier estimated natural rate of a few tens of metres per million years (Wilkinson, 2005). We are also exploiting many of the same ecosystem processes that were operating in the past, but our exploitation is now so intensive that we have considerably amplified or modified their rates, properties and effects. Fire is one ecosystem process that has become totally altered through its deliberate use in agriculture and its suppression to protect forest resources, as well as the manipulation of fuels. The management of grazing animals and the selection of genotypes of plants and animals that are favourable for us are further examples of the ways in which we have modified ecosystem processes and properties. Our owner's manual draws on past experience to propose appropriate uses of the ecosystem controls.

Human society faces several developing crises in ecosystem services that are making warning lights flash on our control panel. The global economy is almost five times the size it was half a century ago and such a rapid increase has no historical precedent (Jackson, 2009). The associated increase in use of finite natural resources and management of increased land areas has led to rapid conversion of terrestrial biomes into agricultural land, plantations, wasteland and cities, with consequent loss of species and modification of ecosystem services. The Millennium Ecosystem Assessment (MEA) has identified those services that are rapidly degrading, which include freshwater, wild foods, wood fuel, soil volume and quality, genetic resources and natural hazard regulation by wetlands and mangroves (www.maweb.org). Terrestrial ecosystems provide key components of the natural capital and services that fuel much current economic growth. They probably always fulfilled this function for hunter-gatherer societies and subsequent civilisations, but never on the scale posed by current demands. Agriculture lies behind much ecosystem transformation and is a contributory factor to major environmental concerns, including loss of biodiversity, overexploitation of freshwater, soil degradation and even climate change. Yet about one in seven people are chronically malnourished (Foley et al., 2011). The amount of land dedicated to cereal production per person has been reduced from 0.23 ha in 1950 to 0.1 ha in 2007, increasing the challenge involved in feeding the growing global population. There is also growing competition between individual services as terrestrial ecosystems become more heavily exploited. Most of the Earth's surface that is suitable for arable agriculture is now utilised, and maize, rice and wheat provide over 30% of their essential daily food to more than 4.5 billion people (Shiferaw et al., 2011). However, competing demands for the use of maize, both as animal feed and for its conversion into bioethanol for fuel, have driven up prices in an alarming manner, with significant social consequences.

It is sobering to consider the global development of population size since AD 1750 and its consequences , which include demands on some major ecosystem services such as water use and fisheries (Figure 1.1; Steffen et al., 2004, cited in Dearing et al., 2010). No complex analysis is needed to understand that as the population curve climbs, reduction of tropical forest area, number of species extinctions and loss of sustainable fish stocks are likely to follow, along with global gross domestic product (GDP) and other economic indicators, such as the number of vehicles on the road (Figure 1.1).

Figure 1.1Changes in global states and processes since AD 1750—including ecosystem services, climate variables and economic data—all show acceleration in rates from the mid-twentieth century (after Steffen et al., 2004, Dearing et al., 2010 and Ehrlich et al., 2012)

All around us we can see the ecosystem consequences of the rapidly increasing human population, which is coupled to the demands we make on our environment and fuelled by technologies and energy sources developed during the industrial revolution. Recent and forecasted future global population dynamics are the herd of elephants in the room that underlie all that is written about current and future global change. While it is proving possible in several regions of the world to influence family size, which is usually closely linked to social equality and levels of education, the associated increasing consumption of natural resources is proving to be far harder to control (Ehrlich et al., 2012). The inexorable spread of consumer culture from developed to developing economies is driven by too powerful forces to be managed by normal governmental regulatory tools. The usually cautious United Nations Secretary-General has called for revolutionary action in the developed world to replace the prevailing model of economic growth, which is driven by extravagant use of natural resources. He has described this model as ‘a global suicide pact’.

Every previous period of human society has had its concerns, worries and prophets of doom. Here we are with more people than ever before, who are living longer and have access to resources and knowledge on an entirely different scale from previous generations, yet many researchers share the foreboding of the Secretary-General and feel that the increasing pressure on global ecosystems is precipitating a crisis that will be impossible to resolve by technological means alone and will result in social dislocation and suffering. This book provides a background to the consequences for terrestrial ecosystems of the current state of affairs and reviews the tools that can help explore possible future scenarios.

Rockström et al. (2009) introduced the concept of a safe operating space for the Earth, in which they feel their way towards the planetary boundaries of the Earth system (Figure 1.2). They identify nine critical processes for which thresholds of control variables such as atmospheric carbon dioxide concentration should be defined—although this is easier said than done. If these notional thresholds are crossed, the consequence could be ‘unacceptable environmental change’. They suggest that three processes have already exceeded these safe operating limits, namely climate change, the rate of biodiversity loss and interference with the global nitrogen cycle. A particular concern they raise relates to ‘tipping points’, which describe the tendency of complex Earth systems not to respond smoothly to changing pressures but rather ‘to shift into a new state, often with deleterious or potentially even disastrous consequences for humans’ (Rockström et al., 2009). There is an urgent need to identify potential thresholds within Earth systems, which once crossed will alter their states in ways that could have alarming consequences for civilisation. Our agriculture is highly dependent on the regularity of monsoon systems and the timing of spring, for example, so we need to understand any nonlinear responses of these climatic features to global warming. Could a reduction in the cover of arctic sea ice elicit a nonlinear response in the northern hemisphere growing season? This feels like an immediate concern as farmers bemoan one problem after another and survey the poor condition of their winter cereals during late, cold springs. Many of the Earth's subsystems do appear to react in a nonlinear, often abrupt, way and are particularly sensitive around threshold levels of certain key variables. If these thresholds are crossed then important subsystems, such as a monsoon system, could shift into a new state, posing problems for sustained agricultural production. The concepts of critical tipping points and nonlinear responses to pressure on Earth systems have become a significant research issue in global ecology and will be explored further in this book.

Figure 1.2Proposed safe operating space for nine planetary systems (inner green shading). The safe boundaries for three systems (rate of biodiversity loss, climate change and human interference with the nitrogen cycle) have already been exceeded (red wedges).

Source: Rockström et al. 2009. Reproduced by permission of Nature Publications

1.3 Relevance of the past

A case has been made that the Anthropocene began about AD 1800 as humans entered into a new phase of their relationship with the Earth and became a ‘global geophysical force’ that threatens important life support systems (Steffen et al., 2007). Does this mean that the earlier history of our relationship has little relevance for current issues? In some ways this would be convenient as there is a good deal of relatively well organised information about the changing state of the world during the last 200 years. To delve further back into the past (by several millennia) requires specialised research techniques, relying for example on pre-instrumental records for the reconstruction of past climate. Even philosophers are divided about the value of the past in planning for the future. ‘History is bunk’ is a view that is widespread. Its advocates argue that continually changing circumstances mean that little of value can be learnt from history, as shown by military commanders who use outdated strategies and fail to exploit opportunities presented by new technologies (Munro, 2001). Others argue for the value of analysis of past trends in forecasting the future, even if it is just to pick the winning horse in a race. A strong case has been made for the existence of uniform processes of change in physical Earth systems, such as mountain building or rock weathering; this idea was first proposed by Charles Lyell (1830–33) as the principle of uniformitarianism. Darwin was strongly influenced by Lyell's ideas and transferred this physical concept across to biological systems during the development of his theory expounding the slow but continuous evolution of species through natural selection. Whichever view one adopts concerning the value of the past, few can dispute that history is an inescapable part of our culture and helps define us as human beings. We all enjoy stories around the campfire and this book includes many such stories, as well as examples of how our long-term cultural heritage influences current management issues.

I (R.B.) have found from personal experience that understanding the history of a region can help resolve management conflicts. I saw this in the establishment of a National Park in Sweden, where landowners were upset by compulsory purchase orders for beech forests that they had managed for two generations. History showed that many of the features that the park was designed to protect, including the beech stands themselves, had largely developed as a consequence of earlier human activities. This knowledge surprised both the state authorities and the landowners and placed the negotiations on a new common footing, based around the idea that recent management would have to be explicitly acknowledged in the planning of the park and not simply ignored or eradicated. There are several other lines of research and policy that draw on evidence from the past. We use the models that form an integral part of this book to explore and understand past climate–vegetation interactions through hindcasting, adopting uniformitarian principles; if the models succeed in reproducing the important properties of past observations then our confidence in using them as forecasting tools is increased. It can be harder to model human impact on ecosystems, as human behaviour tends to be less predictable than that of plants. The Ruddiman hypothesis, which is discussed in Chapter 7, is a good example of how introducing the long-term history of anthropogenic deforestation into analyses of the biogeochemical cycling of CO2 and CH4 has stimulated debate and increased our understanding of atmosphere–biosphere interactions (Ruddiman et al., 2011a). The modern relevance of what we can learn from the archaeological record about the collapse of past civilisations is more controversial.

A debatable question for our time is whether the archaeological record provides evidence for over-exploitation of an irreplaceable natural resource and a consequent collapse of a civilization (Tainter, 2006). Tainter argues that there are probably no known examples from the past of pure ecological collapse brought about by overpopulation leading to resource depletion. The case of the Third Dynasty of Ur (c. 2100–2000 BC) in southern Mesopotamia comes close, but the final collapse can be attributed to poor management of agriculture—which may well have relevance for today. This civilisation built a canal from the River Tigris in modern Iraq into a fertile but arid region to generate high yields of wheat and barley, which facilitated population increase and city expansion (Jacobsen & Adams, 1958). A side effect of the irrigation was the raising of saline groundwater to the soil surface, which gradually reduced cereal yields and particularly affected the less salt-tolerant wheat. Written records and archaeological data show a slow but cumulatively large reduction in food supply and the consequent collapse of several cities (Jacobsen & Adams, 1958). There is evidence that methods for avoiding salinisation, including the use of frequent fallow periods, were known at the time but were not employed by those in charge. So, poor leadership decisions contributed to the collapse of this civilisation, rather than the direct over-exploitation of resources.

Soil salinisation is an example of a tipping point, where an ecosystem changes to another state, with consequences for the services that people have come to depend upon; such tipping points are obviously of concern to civilisation. Study of the past provides other examples of heavily exploited ecosystems or systems with low resilience that passed critical tipping points, leading to long-lasting and sometimes irreversible change, bringing undesirable social consequences. While these examples are unlikely to provide direct analogues for modern times, they illustrate certain principles that could influence current management. Prehistoric deforestation and the cultivation of soil on sloping ground or porous bedrock in the Mediterranean region and in the Burren of western Ireland caused soil erosion and loss of fertility (Figure 1.3). Early agricultural activities have interacted with climate change, leaving abandoned civilisations and cities that could no longer be sustained by the surrounding landscapes. Widely discussed examples include the collapse of the Central American Mayan civilisation c. AD 900 and of the Anasazi of New Mexico c. AD 1200, where severe drought sharply reduced the population size, resource consumption and political complexity that could be maintained in these societies (Tainter, 2006). Modern societies have developed more resilience to many of the types of localised environmental stress that caused serious problems to past isolated communities, but there are still lessons to be learnt that are surprisingly relevant today.

Figure 1.3Limestone pavement showing through the thin soils of the Burren, Co. Clare, Ireland. The Burren was covered by forest earlier in the Holocene and the soils were deeper (photo Richard Bradshaw)

1.4 Forecasting the future

Increasing numbers of scientists and commentators are pointing out the mostly negative outcomes that result from our current wholesale exploitation of the planet. Some of these are likely to occur in the immediate future or at least within the lifetimes of our children and grandchildren.

The European heatwave of the summer of 2003 was probably the hottest summer for at least the last 500 years. It was focused on France, Germany and Italy, where there were thousands of heat-related deaths, especially among the elderly. Agricultural crops were also badly affected. Was this just natural variability or can the effects of anthropogenically increased CO2 concentrations on climate be blamed, at least in part? As with anything to do with climate change, there are both believers and nonbelievers. Stott et al. (2004) tried to address the issue using a method involving both the decadal-mean seasonal mean changes in summer temperatures and the change in risk of exceeding a threshold to estimate the contribution of increased greenhouse gases on risk of high mean summer temperatures in continental Europe. They concluded that it was very likely that anthropogenic effects on climate at least doubled the risk of a heatwave of the magnitude seen in 2003. In addition, it is likely that such heatwaves will be occurring frequently by 2050 and that unless atmospheric CO2 concentrations are controlled, the 2003 heatwave will be considered relatively mild in comparison to those that will occur. Current climate change has no known endpoint and the prospect of temperatures rising beyond human endurance in some parts of the world, in addition to rising sea levels, will present a serious challenge to future generations.

In reality, forecasting the future is impossible, but it is possible to build scenarios that can allow explorations of ‘what if?’ questions. In this book we use three different types of scenario to explore possible futures over the next 50–100 years. Of course, we must bear in mind that political timescales are usually short and that there are few recent examples of successful implementation of policy on longer ones. In practice, much of the focus on forecasting of the future has to do with relevance to the short-term political cycles that exist in most countries. A typical example is the European commitment to halt biodiversity loss by 2010, which has clearly failed. There may have been some improvements as a result, but the goal was always unrealistic given the lack of will or even interest among many politicians, as well as the general public in many places. However, around 2050 is when model projections indicate that significant climatic changes will be showing their effects. It is also quite clear that in order to reduce these possible effects, serious action needs to be taken now or in the immediate future, and even as we write windows of opportunity are closing.

Of course, many initiatives have value and contribute at least to our understanding of the present situation and do give warnings about the future, whether they are ignored or not. For example, the MEA was initiated by the United Nations in 2000 ‘to assess the consequences of ecosystem change for human well-being and the scientific basis for action needed to enhance the conservation and sustainable use of those systems’. The MEA places human welfare in focus and emphasises the importance of ecosystem integrity for sustained welfare. It also strives to forge new links between science and policy, which is an area in need of support in several nations.

The MEA, in common with most ecosystem research, has a limited time perspective, chiefly combining observations from recent decades with forecasts for the future. This book accesses specialised data from the past and adopts a much longer timeframe, designed to place the current state of terrestrial ecosystem affairs into a broader perspective, as Michael Mann did with his famous ‘hockey stick’ portrayal of northern hemisphere mean temperatures over the last 600 years (Mann et al., 1998). A deeper background outlining how the current state of affairs developed does influence interpretation and helps choose between the various ways ahead. This book contests the belief that the present is so different from the deep past that there is little to be learnt from ecosystem states thousands of years ago. Many important ecosystem processes still operate and there is much to be learnt from past experience.

1.5 Chapter details and logic

The book comprises 10 chapters. Following this introduction, two introduce the data and the models that respectively provide and explore the evidence discussed in the subsequent chapters. The models of Chapter 2 are a central feature of the book. They are tools for integrating our knowledge of the Earth system and exploring the future. Models come in many forms and the focus here is on both equilibrium and dynamic models of climate, ecosystems and species, as well as models of complex socioecological systems. Earth system models integrate general circulation models with dynamic ecosystem models and can, for example, incorporate the important feedbacks from ecosystems to climate. The vegetation models are presented in the order they were developed and linked to a brief history of global plant geography. The chapter covers the important linking of biogeochemistry to biogeography and reviews dynamic vegetation modelling from the landscape to the global scale, and introduces the concept of plant functional types. Finally, it discusses agent-based modelling and how human land use decisions are or can be incorporated into model frameworks.

Chapter 3 presents the data used to describe and interpret past ecosystem dynamics. Models are built from generalisations that are largely consistent with data, they are parameterised using data and they are validated by comparison with data. Modellers and their models would like to have ecosystem data of high spatial and temporal resolution, neatly organised into accessible databases. Unfortunately, data are rarely available in this form. Some recent climatic data and remotely sensed data on land cover are fairly well organised, but they cover rather short periods compared with the timespan of this book. A myriad of data types, including directly observed phenological data, ‘proxies’ such as pollen data from which past vegetation dynamics can be reconstructed and even cave paintings, must be evaluated to piece together a fragmentary story of past ecosystem dynamics that can then be explored with models. Chapter 3 introduces the major data sources from the past and outlines the assets and limitations of each data type.

The past relationships between climatic change and ecosystem dynamics are examined in Chapter 4. We wrestle with some complexity here because past ecosystem dynamics are a useful source of information about past climates, but they also provide important feedbacks to the climate system. Our main interest, however, is in discovering how past climatic change influenced ecosystems, because this provides a good basis for forecasting the effects of future climatic change on terrestrial ecosystems and their services. Models do help to tease apart these complex interactions and develop our understanding of climate-forced ecosystem change. Climatic changes during the last ice age resulted in global-scale vegetation dynamics that appear to be synchronous on different continents, allowing for some limitations of dating control. The climatic changes that define the Late Glacial period (21 000–11 500 years ago) were synchronous throughout Europe and resulted in rapid ecosystem responses that have been analysed in some detail. The reforestation of Europe during the Holocene (11 500 years ago to the present day) was a seemingly more complex process, influenced by climate but also by the location of species refugia, dispersal biology, competition, atmospheric CO2 concentrations and human activities. There is more and better-dated ecosystem evidence from the Holocene than from earlier periods and the apparent increase in complexity probably arises because we can examine the records with greater spatial and temporal resolution than before. Examples comparing the model results with data from Europe and Africa illustrate a range of climate–ecosystem relationships. The chapter concludes with a look at megafaunal extinctions, taking genetic evidence into account, and a review of recent, directly observed species range shifts and plant productivity changes.

Short-lived, irregular episodic events can be difficult to incorporate into models, yet they prove to have made a significant impact on ecosystem dynamics during the Holocene. Chapter 5 examines the role of fire, pathogens and wind on ecosystems. People and their domestic animals have been an important source of these hard-to-model disturbances, and their ecosystem impacts are covered in more detail in Chapter 6, just as longer-term climatic events, such as drought, were examined in Chapter 4. Increasing knowledge of the profound ecosystem effects of short-lived, episodic events in the past has rendered the classical concept of successional climax of limited practical value for many ecosystems. Past disturbance of natural and human origin has caused long-term changes of state for major ecosystems in Australia, New Zealand and elsewhere, pointing to the existence of alternative stable states. Fire is a disturbance agency with a very long history of human influence that is forecast to increase its ecosystem impact under future climates in many regions. Interactions between disturbance agencies are increasing and are likely to pose management issues for the maintenance of several ecosystem services in the future.

We begin to unravel the very long relationship between human activities and ecosystem dynamics in Chapter 6. The use of fire is the oldest management tool employed by early peoples, stretching back for quite possibly millions of years, so there are few convenient baselines from which we can assess the extent of current human impact on ecosystems. The transition from hunter-fisher-gatherer societies to settled agriculture began ecosystem conversions that still continue today. The timing and scale of these conversions are under continual revaluation and are important because of their influence on the global carbon cycle and feedbacks to the climate system. A 300 year period of frenzied construction of megalithic monuments accompanied the spread of agriculture into the northwest margins of Europe, with at least 30 000 monuments built in Denmark alone. A subsequent socio-economic collapse with the return of forest on to recently established fields was an early example of the boom-and-bust dynamics so familiar to Western societies today. Island systems are sensitive recorders of the biological impact of human settlement, and mass extinction of birds in particular has been a typical outcome on islands in the South Pacific during recent millennia. Island floras also change rapidly following settlement, through the introduction of exotic species, the increased abundance of previously rare species and the consequent loss of dominance of other plants. Total extinction of plant species has not been recorded as often as has extinction among large animals. Modelling human activities can be difficult, but one attempt suggests that considerable modification of the global land surface had already taken place prior to industrialisation, which supports a general conclusion from this chapter that past human impact on ecosystems has often acted over longer periods of time and to greater effect than many researchers previously believed to be the case. The last 200 years of human impact have been more intensive, but it is important not to underestimate the significance and scale of earlier human ecosystem impact.

Chapter 7 examines the changing demands made by the global community and the expectations that societies have become accustomed to in the form of goods and services provided by ecosystems. Rapid increases in human population are placing pressures on these services—pressures that need to be understood and reacted to through appropriate management. Here we explore the long-term development of these pressures and show how different services have been valued through time. The multiple origins of agriculture and abandonment of hunter-gathering lifestyles are examples of major past transitions in the development of provisioning services.

The first two chapters of Charles Darwin's Origin of Species are titled ‘Variation Under Domestication’ and ‘Variation Under Nature’ and emphasise how easily human intervention in natural processes can result in large effects. In this case, breeding programmes exploit natural variation in species for the benefit of society, which is an example of the use of genetic resources as an ecosystem service. It can be argued that we exploit several ecosystem properties in the same way to maximise the benefits we derive from such ecosystem services as food, fibre and water. We explore future scenarios for ecosystem services, which show that food security is likely to remain beyond reach for many people. Some ecosystem services are already being degraded through the increased demand for provisioning services. Biodiversity and its services suffer to some degree under all scenarios.

It can be hard to evaluate the commercial importance of cultural ecosystem services for society, but we argue in Chapter 8 that these are no luxury. They have been central to social behaviour through time and have influenced mythology and religion. Cultural services contribute to the humanity of our species and have inspired artistic creation for millennia. Cultural services retain importance through our relationship with and love of both the ‘natural’ world and the diverse cultural landscapes we have created through time. Hiking, camping, hunting and visits to the zoo pay homage to cultural ecosystem services. Support for traditional, nonmechanised methods of food production link to our fond memory of earlier landscapes and rural life. All these cultural attributes contribute to conservation policies, which are complex expressions of how we value many ecosystem properties, but particularly their cultural services.

Chapter 9 describes how current conservation policy is beset by potential paradoxes when viewed with a long-term perspective. We fight the spread of recently introduced species while protecting others that were introduced as a result of human activities long ago. We prize rarity for its own sake. We sometimes try to mimic ‘natural’ conditions that that we know little about. Often we fight change, and conservation can be a case of ‘keeping the landscape the way it was when I was young’, as Sir Arthur Tansley once wisely said. We can enter into costly interventions and fight losing battles against very successful invaders to atone for our earlier misdeeds. In my garden, I (R.B.) continually intervene to protect losers from successful species with rapidly increasing populations such as magpies, crows, pigeons, the whining collared dove and the neighbours' cats. It is estimated that Swedish cats kill over 16 million small garden birds each year, and with a mere 70 million nesting pairs in the country it feels like the neighbours have introduced a new and unnatural threat to the nation's wildlife. Another neighbour traps and kills the numerous and wily magpies that rob the nests of the smaller birds we all like to see. Magpies were first recorded in Ireland in 1676 and bred in Dublin in 1852. Their numbers expanded in urban Dublin during the late 1900s and an elderly colleague told me that he was amazed at the increase in numbers of magpies in Dublin during his lifetime as we watched a group of five squabbling outside his window. These beautiful and intelligent birds do eat eggs and young birds but are often unfairly blamed for the similar work of cats, squirrels and rats. A non-specialist predator like the magpie is unlikely to have any lasting effect on small bird populations. With so many changes to nature over such long periods of time and so many shifting demands on ecosystem services, it feels appropriate to assess how we have arrived at the current situation and our conservation policies. Given likely future scenarios it feels timely to explore the current priorities for human–ecosystem interactions, management and conservation, which is what we cover in Chapter 9.

Finally, in Chapter 10 we pull all the threads together and return to some of the issues raised in this chapter with fresh insight gained from the book as a whole.

1.6 For whom is the book intended?

Long-term ecosystem dynamics influence everyone on the planet, whether they are aware of it or not. This book has developed from joint research and teaching undertaken by both authors and the primary targets are graduate students and graduate courses or seminars that cover ecosystem dynamics. We also believe it should be of interest to a wider audience that is not engaged in academic research but wants some background to the issue of global change and wishes to understand the importance of a time perspective in ecosystem dynamics. We hope that the book has much to offer to students from the undergraduate level onwards and to researchers looking for background in subjects complementary and relevant to their own special field of knowledge. We intend to use it as the basis for a Master's course at Lund University, Sweden, which attracts students from the fields of ecology, geography, geology, archaeology and other disciplines within the biological and Earth sciences. While many readers will select groups of chapters, a few may choose to read the book from cover to cover following the logic of our chapter structure. The topics covered are not of interest only to researchers, teachers and students. Anyone with a garden or smallholding is aware of the seasonal and annual changes in vegetation and will have opinions about longer-term changes, whether they be the arrival of Spanish killer slugs, wetter summers or the ability to sit out in the garden later in the year than usual. Ecosystem dynamics also brush up against policy in many nations, because ‘degradation and loss of habitats and species are compromising the ecosystem services that sustain the quality of life for billions of people worldwide’ (Bradshaw et al., 2010a). As well as containing valuable biodiversity, forests help regulate the global carbon cycle and lock up considerable quantities of carbon. Deforestation has been estimated to account for 20% of global emissions of CO2 during the last 50 years (Global Carbon Project, 2012).

This book is not light reading, but its analysis of part of the science underlying current concerns about the effects of global change is of relevance to everyone. We have tried to make it accessible to the interested but nonacademic reader. The book lies between the subject of biology and that part of Earth sciences that deals with the recent ice ages and interglacials, where the records lie in the roughly 2.6 million year ‘soft rock’ deposits of the Quaternary period. Most of the text focuses on the Holocene and uses models to explore future scenarios, touching on a range of disciplines, including biological and environmental sciences, Earth sciences, archaeology, ethnology, climatology and genetics. The book will present the biological basis for ecosystem models and will introduce readers with backgrounds in Earth sciences, physics or modelling to the fascinations of long-term vegetational and ecosystem dynamics. The background, rationale and use of ecosystem models will introduce palaeoecologists and biologists to these powerful research tools. We have tried to make the text authoritative but readable. We hope that we have also made the contents accessible to interested members of a broader public outside the immediate research community. The book is intended to summarise evidence for the current state of global ecosystems and explore potential future developments, which are topics that affect us all.

1.7 Four key questions and the links to policy

The book aims to show how and why ecosystems change, on a day-to-day basis, seasonally, annually and on millennial timescales. There has been a widespread tendency to take ecosystems and the goods and services they provide for granted. Many can see the consequences when we alter ecosystems by our own actions but are surprised when they alter as a result of other influences, such as climate change or their own internal dynamics. It is important to know more about the variability of individual ecosystems and to investigate how they respond to and recover from disturbance. Nature can be portrayed in the media as delicate and sensitive, but many ecosystems have long histories so are probably quite resilient. We need to know how much punishment they can really withstand.

Human exploitation and manipulation of ecosystems and climate change are two of the major forces affecting ecosystems today. It is important to know what their effects are, how they interact and what the consequences will be, both for the ecosystems themselves and for the human race. If an important ecosystem service such as the pollination of food crops falters, we need to know the reasons why, if we are to fix the problem. We have identified four key questions that have guided the planning of this book. (1) How have ecosystems changed in the past? (2) How much of this change is attributable to human activities? (3) How much change is anticipated for the future? (4) What are the appropriate ecosystem management measures by which to prepare for the future?