Beaver Invasion Welcomed in Alaska.

• Position: THERMOKARST LAKE BASINS

A population explosion of beavers on Alaska's Baldwin Peninsula near Kotzebue has been documented by scientists. Using satellite images, the researchers counted a jump from two to 98 beaver dams since 2002.

"Our study shows that beavers were responsible for two-thirds of the increase in surface-water area in the Kotzebue study region since 2002," says Ben Jones of the Institute of Northern Engineering at the University of Alaska, Fairbanks.

Ken Tape of UA's Geophysical Institute, notes that "equally important is that beavers are more dominant than climate--and anything else--in driving surface-water changes."

The scientists have documented what locals have been noticing for the past few decades: more beavers, which in turn means more lakes and different reactions of fish and game animals to the changes.

In making their dams, slowing streams, and pooling up water, beavers introduce a source of heat to permafrost landscapes, where soil has been frozen for perhaps hundreds or thousands of years.

The beavers also seem to be attracted to the depressions left behind when ground-ice chunks as large as city buses thaw. Scientists call this thermokarst, which often fill with water to become lakes. Jones...