Harvesting the Biosphere
What We Have Taken from Nature
Publication Year: 2012
Published by: The MIT Press
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The Earthâs biosphere â that thin envelope of life permeating the planetâs hydrosphere, the lowermost part of its atmosphere, and a small uppermost volume of its lithosphere â is of surprisingly ancient origin: the first simple organisms appeared nearly four billion years ago (the planet itself was formed about 4.6 billion years ago), ...
Part I: The Earthâs Biomass: Stores, Productivity, Harvests
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In December 1990, the Galileo spacecraft came as close as 960 km to the Earthâs surface in order to get a gravitational assist from the planet on its way to Jupiter. This flyby was used by Sagan et al. (1993) as an experiment in the remote detection of life on Earth: just imagine that the spacecraft, equipped with assorted detection devices, belonged to another civilization, ...
1. Biomass: Definitions and Compositions
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The classic life sciences â botany, zoology, plant and animal anatomy and physiology â were for centuries preoccupied with classification. This concern was later extended to lifeâs assemblages, that is (in ascending order), communities, ecosystems, and biomes. Such a focus is now seen as antiquated: the preoccupation has shifted to the intricacies of genetic makeup and metabolism ...
2. Biomass Stores: Means and Extremes
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In contrast to regularly conducted inventories of wood volumes in commercially exploited forests and the frequent (now satellite-aided) monitoring of crop productivity, accurate quantifications of phytomass in natural ecosystems remain relatively uncommon. But they do support some easily defensible generalizations, illustrate some important exceptions, and help correct some stereotypes. ...
3. Biomass Productivities
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The biosphereâs productivity can be quantified as a cascading series of variables: the most inclusive ones, the two rates at the cascadeâs top, gross and net primary productivity, cannot be measured directly and can be quantified (far from accurately) only thanks to our improved understanding of photosynthetic processes, the environmental responses of autotrophs, ...
4. Phytomass Harvests
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Modern phytomass harvests fit mostly into four distinct categories. Food harvests have been transformed as humans have evolved from simple foragers collecting edible plants, hunting animals, and catching aquatic species to agriculturalists relying first on extensive shifting cultivation and later on intensive methods of farming, ...
5. Zoomass Harvests
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Terrestrial trophic pyramids are invariably broadly based, with phytomass (primary producers) being commonly 20 times more abundant than the mass of herbivores (primary consumers), and the zoomass in the highest trophic level (this may be the third level in the simplest ecosystems, and only a few terrestrial communities go beyond the fifth level) ...
6. Land Cover and Productivity Changes
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For a few million years of their early evolution, hominins made a limited claim on the biosphere, as they foraged for food and ate it raw. This began to change with the controlled use of fire for cooking and defense against predatory animals. Inevitably, this led to accidental fires, whose unchecked progress added to the phytomass destruction that had been taking place naturally by fires ignited by lightning. ...
Part II: History of the Harvests: From Foraging to Globalization
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The predecessor species belonging to our genus â starting with Homo habilis, who appeared nearly 2.5 million years ago â spent all of their evolution as simple heterotrophs. Our species, Homo sapiens, has spent no less than 95% of its evolution (assuming it evolved by about 200,000 years ago) in a similarly simple foraging mode. ...
7. The Evolution of Foraging
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A reliable quantification of the resulting impact on the biosphere is impossible, as we lack any realistic assessments of total populations engaged in specific foraging activities, but there can be no doubt that in parts of several biomes (in the richest tropical rain forests and in boreal forests), it remained marginal for millennia. ...
8. Crops and Animals
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The most important force driving the evolution from foraging to crop cultivation and the domestication of animals is clear: gathering and hunting cannot support population densities higher than about one person per square kilometer, even in benign environments with abundant standing biomass. ...
9. Biomass Fuels and Raw Materials
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Wood supplied virtually all the energy needed for space and water heating, cooking, and a growing range of artisanal manufactures and industrial processes for far longer than most people think. Fossil fuels were known, both in Asia and in Europe, since antiquity, but the first society in which coal became more important than wood was England of the early seventeenth century ...
Part III: Adding Up the Claims: Harvests, Losses, and Trends
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Three fundamental limitations make any large-scale, long-term accounting of human claims on the biosphereâs production challenging â and uncertain. First, these claims belong to three different categories that might simply be labeled extraction, management, and destruction, but a closer look shows that there are overlaps and blurred boundaries. ...
10. Changing Land Cover and Land Use
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The most obvious, and conceptually the simplest, indicator of the human impact on the biosphereâs productivity and phytomass storage is the total area of the natural ecosystems that have been transformed by human action. To put these changes into an evolutionary context, I will begin with a brief review of phytomass storage during the past 20 millennia, ...
11. Harvesting the Biosphere
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In an attempt to quantify what clearly appeared to be a disproportionate share of the Earthâs photosynthetic production that is claimed (directly and indirectly) by its most sapient species, Vitousek et al. (1986) chose net primary productivity (NPP) as the baseline and expressed the overall effect of harvests and modifications as the fraction of NPP appropriated by humans. ...
12. Long-Term Trends and Possible Worlds
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Our species has evolved to become the planetâs dominant heterotroph in what has been (when measured on the biospheric time scale of more than three billion years) a very brief period of time. Less than 2.5 million years have elapsed since the emergence of our genus (with Homo habilis), our species became identifiable about 200,000 years ago, ...
Scientific Units and Prefixes
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Page Count: 312
Publication Year: 2012