Humans have altered North America’s ecosystems more than melting glaciers
https://www.sciencemag.org/news/2020/08/humans-have-altered-north-america-s-ecosystems-more-melting-glaciers
Source: By Elizabeth Pennisi, Science Magazine.
Source: By Elizabeth Pennisi, Science Magazine.
Excerpt: Recent human activity, including agriculture, has had a greater impact on North America’s plants and animals than even the glaciers that retreated more than 10,000 years ago. Those findings, presented this week at the virtual annual meeting of the Ecological Society of America, reveal that more North American forests and grasslands have abruptly disappeared in the past 250 years than in the previous 14,000 years, likely as a result of human activity. The authors say the new work, based on hundreds of fossilized pollen samples, supports the establishment of a new epoch in geological history known as the Anthropocene, with a start date in the past 250 years. ...For more than 10 years, researchers have debated when humans started to make their mark on the planet. Some argue agriculture transformed landscapes thousands of years ago, disrupting previously stable interactions between plants and animals. Others argue the launch of large-scale mining and smelting operations—seen in glacial records going back thousands of years—means the Anthropocene predates the industrial revolution. For geologists, however, the epoch starts with a different signal: nuclear explosions and a sharp uptick in fossil fuel use in the mid–20th century. But some skeptics suggest the ice ages have had an even greater effect on the world’s ecosystems. To test that idea, Stanford University paleoecologist M. Allison Stegner turned to Neotoma, a decade-old fossil database that combines records from thousands of sites around the world. Her question: When—and how abruptly—did ecosystems change in North America over the past 14,000 years? ...When the last ice age ended, forests and grasslands regrew across North America, creating a landscape that remained stable for thousands of years. But humans have changed all that, Stegner reports this week. Her team found just 10 abrupt changes per 250 years for every 100 sites from 11,000 years ago to about 1700 C.E. But that number doubled, to 20 abrupt changes per 100 sites, in the 250-year interval between 1700 and 1950....