Trees Killed Mammoths

With a little help from humans (h/t Instapundit):

Dale Guthrie, a researcher at the University of Alaska in Fairbanks, has spent some 20 years examining more than 600 bones of large mammals from Alaska and the Yukon Territory.

His analysis points toward climate as the culprit.

Guthrie's data, published in tomorrow's issue of the journal Nature, shows that increases in moisture and warmer temperatures 13,500 to 11,500 years ago allowed for edible plants to migrate north.

This plant exodus provided more food sources for horses, mammoths, bison, and elks living in the far north, he suggests.

But then the milder climate backfired on the big mammals. It paved the way for trees, which eventually outshaded and outcompeted the low-lying plants the animals depended on, Guthrie says.

The upstart forests transferred the landscape's nutrients to the treetops, out of the reach of large mammals. Elks and bison, it seems, adapted better to the new landscape than mammoths and horses.