Deforesting the Earth: From Prehistory to Global Crisis, An Abridgment / Edition 1 available in Paperback, eBook
Deforesting the Earth: From Prehistory to Global Crisis, An Abridgment / Edition 1
- ISBN-10:
- 0226899470
- ISBN-13:
- 9780226899473
- Pub. Date:
- 09/01/2006
- Publisher:
- University of Chicago Press
- ISBN-10:
- 0226899470
- ISBN-13:
- 9780226899473
- Pub. Date:
- 09/01/2006
- Publisher:
- University of Chicago Press
Deforesting the Earth: From Prehistory to Global Crisis, An Abridgment / Edition 1
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Product Details
| ISBN-13: | 9780226899473 |
|---|---|
| Publisher: | University of Chicago Press |
| Publication date: | 09/01/2006 |
| Edition description: | Abridged |
| Pages: | 561 |
| Product dimensions: | 6.00(w) x 9.00(h) x 1.70(d) |
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DEFORESTING THE EARTH
From Prehistory to Global Crisis An Abridgment
By Michael Williams
The University of Chicago Press
Copyright © 2006 The University of Chicago
All right reserved.
ISBN: 978-0-226-89947-3
Chapter One
The Return of the Forest
Ever since the dawn of Holocene time, when global conditions remotely like those of the present-day first evolved from the ice ages, humans have always impacted the natural environment. -W. R. Dickinson, "The Times are Always Changing: The Holocene Saga" (1995)
PROLOGUE: THE END OF THE ICE AGE
If ever there was a beginning to the modern forest it was at the end of the Ice Age just over 10,000 years ago when the great sheets of ice that covered much of the Northern Hemisphere began to melt and retreat. Then the Holocene, or most recent age of the Quaternary, was born, and the modern forest began to emerge around the world. Almost immediately humans began adapting and changing the evolving physical landscape. Before the thawing began, a wintry blanket had held the world in its grip for over 10,000 years. Ice over 4 km thick covered both North America and northern Europe, and smaller ice caps existed in the Alps, the southern Andes, and even parts of eastern Asia. Because of the water locked up in the ice, sea levels were up to 100 m lower than today. Land bridges were exposed between Britain and Europe, Alaska and Asia, and the islands of Southeast Asia were joined to mainland Asia, allowing humans to migrate between land masses.
Then, about 16,000 years before the present (hereafter BP), the great sheets of ice began to melt slowly and retreat. A new world vegetation map began to emerge. Europe had no forests except in isolated pockets or refugia in Iberia and southeastern Europe. A wide tundra zone covered most of the Continent, in which the predominant vegetation was shrubs and steppelike grasses capable of surviving the harsh climate. Forests did occur, however, in Japan, and in the pine and spruce woodland of eastern United States. A tundra zone also existed in North America, but in contrast with Europe it was much narrower, being only 100 km-200 km broad.
If the temperate areas were colder then the tropical areas were drier; ancient sand seas (ergs) extended to places where there is tropical and subtropical forest today, for example, in western Africa and Florida, and great dust plumes swept out to sea to leave revealing depositional sequences on the ocean bed. Throughout Africa and Latin America, aridity reduced the extent of the rain forest and left it as a series of isolated refugia where, it is thought, they may have developed their amazing biodiversity. Most rain forest existed in Southeast Asia, and surprisingly, in the currently arid Southwest of the United States.
When the ice began to melt the change was not sudden, and during the next 8,000 years temperatures moved slowly upward by some 4ºC or 5ºC to become something like those of today. What caused the climate to change then, or at other geological times, is not known. There are a number of hypotheses, the most likely being the Milankovitch hypothesis based on the regular variations in the earth's orbital geometry, which fluctuates as it circles the sun. In addition, toward the end of the Ice Age, the sheer bulk of the ice would have created conditions that would have deflected the moisture-bearing winds fueling the fresh supply of snow away from the ice. Also, the large quantities of cold freshwater on the ocean surface would have acted like a lid over the denser seawater, thus reducing evaporation in summer and leading to thick layers of ice in winter.
The retreat was long and uneven; oscillating climatic conditions, particularly in northwest Europe, caused it to advance again many times, only to retreat even farther later, always accompanied by changes in sea level. The water that had been locked in the ice began to melt and form huge rivers that gouged river channels across the northern continents, which must have had to cope with volumes of water up to 20 times that of modern rivers. The result was sandy and gravelly outwash plains that spread over vast areas. These were subsequently eroded by wind, the dust being carried away many thousands of miles from the edge of the ice front to create the enormous, thick loess deposits stretching from northern Europe into Central Asia and China, in the pampas of Argentina and Uruguay, and in the Great Plains of the United States, with pockets in Washington and Idaho. In the tropics, greater humidity acting on unconsolidated and bare soils caused massive erosion to produce the greatest sediment yields of the age.
In short, the end of the Ice Age heralded a new era in the history of the world. Its physical, surface geography was largely made anew and the landscape began to take on something like its present day appearance, although its climate kept on fluctuating. Opportunistic species moved with bewildering speed and kaleidoscopic complexity to colonize the new land, and the forest mantle returned to something like its old, though now radically changed, habitats. And humans were not far behind.
WRITING THE BIOGRAPHY OF THE FOREST
It is a common notion that the world was a stable, pristine place before the industrial age. Deeply rooted in Western psyche and its culture is a myth that nature is a passive, harmonious, God-given backdrop against which the drama of human life is played out, the "sound and fury" of human existence contrasting strongly with the notion that "earth abides." But this is a myth. When George Perkins Marsh made the revolutionary and unfashionable statement in Man and Nature in 1864 that "man is everywhere a disturbing agent. Wherever he plants his foot, the harmonies of nature are turned to discords," it was rarely believed. How could the humans of the past with such low levels of culture and technology radically alter the natural world around them?
The forest, in particular, has never been still. Not only is it a living, ever-changing entity that is affected directly by both short- and long-term environmental changes, particularly climate, but it is also severely affected by quite minor human disturbances. Agriculture, domestication, and the control of fire have all been roughly coincident with the formation of the modern forests during the last 10,000 years, and their interaction is inseparable.
Consequently, if we want to understand how humans have changed present forests, we need to travel back along the distant corridors of time to when the forests were being formed after the end of the Ice Age. Just as people have biographies, so forests have their own histories that can be unraveled and documented. But unlike human biographies, the writing of forest histories needs something more than words alone. Pollen analysis and radiocarbon dating are essential components of the language of those histories.
Pollen analysis, or palynology, entails the boring of cores in peat deposits or lake and riverine sediments and counting the grains of different tree-pollen types preserved at different levels of the deposit. The quantities are indicative of past vegetation communities and, by implication, of past human disturbances of the environment. These data are usually presented in the form of pollen diagrams showing the concentration of the percentage values of the various pollen and spore types, arranged stratigraphically.
Pollen emissions can be prolific; for example, in areas of temperate vegetation they can reach up to 10 metric tons annually per square kilometer of land. Some trees produce more than others; beech (Fagus) produces twice as much pollen as lime (Tilia); elm (Ulmus) and spruce (Picea) twice as much again as beech; and alder (Alnus), birch (Betula), pine (Pinus), oak (Quercus), and hazel (Corylus) twice as much again as elm or spruce; in other words, eight times that of lime.
While the samples usually show a clear relative sequence of different pollens, an absolute chronology is difficult unless the samples are interbedded with datable human artifacts. The advent of radiometric techniques gave palynology a new certainty. Most natural, living elements (e.g., wood, charcoal, peat, seeds, bone, shell, cloth, rope, or soil) absorb a mixture of isotopes, of which the most common is radiocarbon ([sup.14]C). But following the death of the plant or animal, [sup.14]C decay occurs at a fixed and known rate. Hence the measurement of the [sup.14]C remaining in the fossil will provide an age for the death of that organism. Results are usually expressed as an age in years before present (BP)-present being ad 1950-with a standard deviation appended. Thus a date of 5000 ± 50 indicates that there is a 68 percent probability that the date is in the range 4950-5050.
THE RETURN OF THE FOREST
Armed with these techniques, sufficient data had been accumulated by the 1980s for the scattered information to be collated into continental histories of forest distribution and change in Europe and North America. Although the two continental analyses are not strictly comparable in terms of methods and detail, the overall conclusions stand close comparison. Vegetation belts migrated over several hundreds, if not thousands, of kilometers in response to fluctuating climate and followed a roughly similar sequence.
Europe
At 10,000 BP ice sheets still dominated Fennoscandia, Iceland, and a small ice sheet was present in Scotland. Europe's tundra, steppe, and birch-conifer boreal forest remained largely unchanged and dominated most of the lowlands of northern Europe, although some deciduous trees were beginning to move out of their southern refugia (fig. 1.1A). Around the Mediterranean, herb-dominated steppe was being colonized by the typical mediterranean plants, like olive, pistachio, and evergreen oak.
Then, with a rapid climate amelioration during the next 1,000 years, there were dramatic changes in vegetation everywhere, and by 9,000 BP the outlines of the modern forest were becoming evident (fig.1.1B). Certainly, by 8,000 BP the transition was complete; the mixed deciduous forest had moved from Spain and southern France to dominate the land area of the British Isles, Spain, France, central north Europe, and southern Scandinavia. In extreme southern Europe the deciduous forest gave way to the first substantial manifestations of a typical mediterranean evergreen oak and pine forest. The boreal (birch-conifer) forest was pushed northward to northern Scandinavia and Russia, and tundra and steppe all but disappeared, as had all permanent ice (fig. 1.1ITLITL).
During the next 4,000 years the vegetation change slowed down as temperatures stabilized, with the exception of the development of a well-marked western alpine zone of montane forest and the expansion of the mediterranean vegetation mix over much of Italy and the coastal littoral of the Balkan Peninsula. Thus, by 4,000 BP the distribution of trees was looking remarkably like that of today as the climate took on a contemporary complexion (cf. figs 1.1ITLITL and 1.1D). But while the distribution of the main biomes was similar to that of today, their composition was not. New trees, such as oak (Quercus), lime (Tilia), alder (Alnus glutinosa), and ash (Fraxinus excelsior), invaded and dominated locally. Hazel (Corylus avellana) and elm (Ulmus) spread even more rapidly. Other trees, such as spruce (Picea), did not expand to their present distribution until a slight deterioration of climate, which was noticeable by 2,000 BP. Between 2,000 BP and the present, there has, if anything, been slightly more cooling and the further expansion of boreal forest.
North America
Although glacial conditions were more fully developed in North America than in Europe, the absence of any marked thermal oscillations during the Holocene meant that the return of the temperate forests began earlier. At its maximum extent in 18,000 BP the Laurentide ice spread as far south as about latitude 40º, and a narrow belt of tundra separated it from a quite broad band of boreal forest. The temperate mixed forest was confined to the warm Gulf and south Atlantic plains.
The distribution of the forest had not changed significantly by 14,000 BP (fig. 1.2A), but after that time the retreat accelerated and there was a marked northward shift of temperate deciduous forest and mixed coniferous/northern hardwood forest, which pushed boreal forest and tundra ahead of them, with a corresponding expansion of the southern evergreen (pine) forests on their southern margin. By 10,000 BP the distribution of the forest was getting a decidedly modern appearance, although the ice still sat firmly over what is now the Canadian Shield (fig. 1.2B). By 6,000 BP the ice was all but gone and the forest had extended to very nearly its modern limits (fig. 1.2ITLITL).
It is thought that the migration northward of American vegetation was slower than in Europe because the wide distribution of pollens and seeds was inhibited by the dominantly east-west trending rivers compared to Europe's generally north-flowing rivers. The general northward movement of vegetation assemblages was accompanied by another trend, which was the progressive eastward shift of the prairie/woodland ecotone (not shown), which reached its maximum eastward extent about 6,000 BP, only to retreat somewhat in more recent times (fig. 1.2D).
The Tropical World
The temperate world was not the only part of the globe where vegetation was radically affected by climatic change during the last 10,000 years. Probably equally dramatic changes occurred in the tropics, but we know less about them. But the story is slowly being unraveled and is vastly more complex than thought. Since the 1950s, evidence has been accumulating for some tropical pollen sites, which, taken together with high lake levels, sediments, and artifactual data from Africa in particular, show that aridity was replaced by increasing moisture and that low temperatures were giving way to higher temperatures. This climatic change allowed the tropical forest to expand-both laterally so as to reclaim areas of fossil sand dunes, as in West Africa, and vertically so that montane vegetation climbed back up the mountains by as much as 1,500 m-2,000 m-especially in East Africa, New Guinea, and the Andes when glaciers melted and retreated. The long isolation of species in the remnant ice-free refugia of Latin America which had encouraged marked differences in species and flora type now ended with the onset of warm, pluvial conditions, so that a vast reservoir of biodiversity was created that still exists today.
THE HUMAN IMPACT
As the forest changed, so humans colonized the newly vegetated land with remarkable rapidity, doing all those things that humans do: foraging, firing, hunting, selecting species and rejecting others, turning the soil, fertilizing it, trampling it, and mixing it. Some trees moved, flourished, or were eliminated, just as surely as if they had been affected by changing climate. So, even as the forests were changing in the climatic seesaw of the millennia of the early Holocene era-slowly assuming their modern, historical distribution and form-the people who witnessed and survived that Ice Age from the tundra to the tropics were in the active process of changing their composition and density. It was a coevolution of humans and vegetation.
(Continues...)
Excerpted from DEFORESTING THE EARTH by Michael Williams Copyright © 2006 by The University of Chicago. Excerpted by permission.
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Table of Contents
List of IllustrationsList of Tables
Preface
PART I - CLEARING IN THE DEEP PAST
1. The Return of the Forest
2. Fire and Foragers
3. The First Farmers
4. The Classical World
5. The Medieval World
PART II - REACHING OUT: EUROPE AND THE WIDER WORLD
6. Driving Forces and Cultural Climates, 1500–1750
7. Clearing in Europe, 1500–1750
8. The Wider World, 1500–1750
9. Driving Forces and Cultural Climates, 1750–1900
10. Clearing in the Temperate World, 1750–1920
11. Clearing in the Tropical World, 1750–1920
PART III - THE GLOBAL FOREST
12. Scares and Solutions, 1900–1944
13. The Great Onslaught, 1945–95: Dimensions of Change
14. The Great Onslaught, 1945–95: Patterns of Change
Epilogue: Backward and Forward Glances
Acknowledgments
List of Measures, Abbreviations, and Acronyms
Notes
Bibliographic Essay
Index