Putting people on the map
A new study remaps the earth and its ecosystems by including humans in the scene.
Nature is no longer pristine. It is merely embedded within human systems, say a pair of eco-geographers in a study published in December 2007 in Frontiers in Ecology and the Environment. By combining global data on human population distribution with those on land cover and land-use change, the researchers have remapped the biomes of the planet. Their findings reveal that humans dominate more than 75% of the earth's ice-free land and, of 21 newly identified biomes, only 3 are free of human influence.
Ecologists have long used biomes to distinguish areas according to their geographic and climatic signatures as well as their distinctive plant and animal communities. For example, a rain forest biome differs in climate, geography, and organisms from a chaparral grassland biome. Biomes have been helpful to scientists in understanding changes in land cover, land use, the impacts of climate change on ecosystems and ecosystem function, and the conservation of biomes. But until now, the most dominant organism, Homo sapiens, has been consistently missing from the picture.
"We consider the world mostly as either natural systems, or when we do include humans, it's either urban or agriculture," says study coauthor, Erle Ellis of the University of Maryland, Baltimore County. This is an oversimplification of the reality, he says. Earth systems expert Ruth DeFries of the University of Maryland, College Park, agrees. "It's not just that humans dominate the landscape, but both respond to the landscape and affect it at the same time," she says. "Humans are part of the integrated system."
So with an aim to illustrate the more complex and widespread reality of human interactions with the landscape, Ellis and coauthor Navin Ramankutty of McGill University (Canada) set out to remap the biosphere.
The so-called anthropogenic biomes or anthromes (biomes influenced by humans) include urban and dense settlements, various village biomes, cropland biomes, rangeland, and forested biomes. The researchers further classified these new biomes according to human population density. A chief distinguishing feature of the anthromes is that they are "mosaics," in which different types of ecosystems are mixed together to create complex, heterogeneous landscapes. For instance, one-third of global urban biomes are nested within densely populated village biomes or forested areas interspersed with croplands and housing. Traditional biomes, in contrast, are portrayed as homogeneous entities, spatially distinct from one another.
"It's a new map, it's not a new idea," says Ramankutty. "A lot of people who study land use in local communities or around the world know this for a fact," he adds. David Lobell, a researcher at Stanford University's Program on Food Security and the Environment, agrees. "I think the main contribution is to introduce this concept of formally talking about humans as a central part of the way we think about ecosystems."
The paper will "revolutionize how we think about the earth's biosphere," says ecologist Jonathan Foley, director of the Center for Sustainability and the Global Environment at the University of Wisconsin Madison. "We have always acknowledged that people affect ecosystems and landscapes, but we still called them the same old thing and mapped them as if they were still entirely natural. But now, thanks to this work, we can better describe the real biosphere—the one dominated by human actions—in our maps, models, and ecological field studies."
The results emphasize the "artificial dichotomy" between people who want a "Walmart world" (a world of supermarkets and consumption, with no place for nature in it) and those who want to preserve a more "pristine" nature, says Ramankutty. And that has a significant bearing on ecological restoration. Instead of attempting to restore ecosystems to their pristine state, scientists and managers should try to restore or conserve nature so as to allow the ecosystems to function in the presence of humans, he says.
