The first hints of the Anthropocene appeared far earlier than you think

The “Anthropocene,” the current geological epoch in which humans are the dominant influence on the earth’s climate and ecosystems, is often considered to refer to the modern, industrialized world. But an analysis published June 7 in the Proceedings of the National Academy of Sciences shows that humans have been reshaping the planet’s landscapes and biological communities for many millennia.

The researchers, led by archaeologist Nicole Boivin of the University of Oxford and the Max Planck Institute for the Science of Human History, don’t propose a specific date for the start of the Anthropocene. Instead, their summary of a massive set of cross-disciplinary data, drawing on three decades’ worth of archaeological, paleoecological, and genetic studies, suggests that altering the planet is something very close to fundamental to the human condition.

Even before the Industrial Revolution, when the burning of fossil fuels began to alter the levels of carbon dioxide in the atmosphere, agriculture wrought large and essentially irreversible changes in the biosphere. Supposedly ancient forests in France actually contain the botanical signatures of Roman agriculture and settlement, for example. And some landscapes that we commonly think of as natural, such as open oak parkland in the Fertile Crescent, are actually human created.

“’Pristine’ landscapes simply do not exist and, in most cases, have not existed for millennia,” the researchers write. “Most landscapes are palimpsests shaped by repeated episodes of human activity.”

The spread of agriculture, which emerged around the start of the Holocene 11,700 years ago, has altered the abundance and range of many plant and animal species. Vast swaths of land are now covered with human crop plants, many growing far from the locations where they originated and having brought suites of invasive weeds along with them. And the biomass of domestic livestock now dwarfs that of wild vertebrate species, the researchers say. Dogs, domesticated even before the development of agriculture, are now the most widespread and abundant carnivore on the planet.

Until recently, it was difficult for scientists to identify the ecological effects of human activity in the more distant past. But now, they can use tools such as ancient DNA, stable isotopes, pollen and charcoal analysis, and new computational and statistical methods to gather clues about the effects of human activities during the late Pleistocene and early Holocene.

Homo sapiens began reshaping the environment almost as soon as we began migrating out of Africa, these new data suggest. Early inhabitants of many regions—Africa, Southeast Asia, Australia, and the Americas—burned vegetation to shape the movements of game and promote the growth of useful plants. And mounting evidence implicates humans in the extinctions of megafauna, or large animal species, that took place between 50,000 and 10,000 years ago.

As early as 23,000 years ago people were deliberately moving other species around: we brought the common cuscus, a primate-like marsupial that was hunted for meat, from its native New Guinea to eastern Indonesia, the Solomon Islands, and the Bismarck Archipelago. Later we also introduced fallow deer and foxes to Cyprus, and opossums and shrews to Caribbean islands.

The effects of our arrival have often been especially prominent on islands. Polynesians introduced at least 40 species of plants to the island of Tonga and burned and cleared rainforests to favor the growth of useful species. Analysis of pollen and charcoal shows the disappearance of dense palm forests on Rapa Nui (Easter Island) within 200 years of the arrival of Polynesian colonists, who also extirpated at least 18 species of plants.

But what the researchers refer to as “human niche construction”—our reshaping of the environment to better support our species—hasn’t been uniformly destructive. Scientists are trying to understand how to replicate the fertile “terra preta” soils created by indigenous Amazonians, which supported large human populations without drastic effects on ecosystem structure and biodiversity. Similar resilient, sustainable ecosystems were shaped by human activities in the Mediterranean, the Americas, Africa, and elsewhere.

And this suggests that instead of trying to restore an imaginary “natural” past, we need to make sure that today’s human-influenced landscapes can support both humans and other species, the researchers argue. “Cumulative archaeological data clearly demonstrates that humans are more than capable of reshaping and dramatically transforming ecosystems,” says Boivin. “Now the question is what kind of ecosystems we will create for the future.” – Sarah DeWeerdt | 21 June 2016

Source: Boivin N.L. et al. “Ecological consequences of human niche construction: Examining long-term anthropogenic shaping of global species distributions.” Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1525200113

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