An interesting article in the current issue of Science magazine:

Pleistocene Park: Return of the Mammoth's Ecosystem
Sergey A. Zimov
Science, Vol 308, Issue 5723, 796-798 , 6 May 2005

About 10,000 years ago, when the million-year-long Pleistocene epoch gave way
to the ongoing Holocene epoch, much of the world's ecosystems changed. In what
is now northern Siberia, vast numbers of large animals, among them mammoths,
woolly rhinoceroses, and yaks, both thrived on and nurtured the steppes that,
compared to other northern regions of the world, remained relatively unscathed
from the repeated advances and retreats of ice sheets. Even so, the steppes
there gave way to silt, dust, and ice-based tundra landscapes dominated in some
places by forests and in others by mosses. The large animals disappeared.
Sergey Zimov, director of the Northeast Science Station in Cherskii in the
Republic of Sakha (Yakutia), argues that climate change may not have been the
primary reason behind the demise of this Pleistocene ecosystem. Instead, he
says changing hunting practices wiped out the large animals whose absence led
to the ecosystem shifts. He and his colleagues now are reintroducing bison,
Yakutian horses, and other animals, eventually even tigers, in an attempt to
reconstitute the Pleistocene ecosystem. The experiment will test the hypothesis
that humans, rather than climate change, caused the ecosystem shift at the
beginning of the Holocene. The stabilization of the northern tundra soils that
this reconstitution could bring also could prevent the release of vast amount
of carbon now sequestered in the Siberian soils but in danger of being released
in the warmer times projected for the future.

Tom Billings