Climate Change Is Drawing Alaska’s Moose Onto the Tundra
As longer and warmer summers increase the abundance and size of shrubs in far northern Alaska, moose have expanded beyond the boreal forest limits and onto the tundra, according to a new study.
University of Alaska ecologist Ken Tape, the lead author of the study, believes that the expansion of moose onto the tundra is one of the first definitive examples of a climate change–driven shift in a large land mammal’s distribution.
“We know these changes are occurring, but here’s an example where the wildlife is responding to these changes in real time, over about a century and a half,” Tape said, which by scientific standards is shorter than the blink of an eye.
Scientists have documented other wildlife species on the move because of climate change, such as southerly bird species shifting northward or equatorial fish leaving warming, low-oxygen waters.
While it’s well documented that polar bear habitat in the Arctic is contracting, the white bruins are considered marine mammals rather than land animals, and shrinking sea ice is the primary driver of their geographic shifts.
Moose are moving in Alaska because warming conditions have allowed tundra shrubs to grown taller, enough to stick well out of winter snow cover, Tape said. That’s made them accessible chow for moose, the largest member of the deer family, which can grow up to 7 feet tall at the shoulder.
Tape and his colleagues estimated that between 1860 and 2009, the height of tundra shrubs increased from 3.6 feet to about 6 feet and that shrub cover in parts of the tundra landscape jumped from 5 percent to 13 percent between 1950 and 2000. “We have repeat photography going back to the 1950s, but warming really started in the 19th century and took off in the 1970s,” he said.
The researchers based their findings about shrub growth on a combination of historical weather records, modeling, and photography of the tundra. They also used historical records to document the distribution of moose in Alaska. Combining the two analyses allowed them to rule out hunting as the primary reason there were no moose on the tundra in the early 20th century. “The lack of habitat supersedes hunting,” Tape said. “If anything, hunting probably delayed the expansion of moose into these regions.”
The study was published Wednesday in the journal PLOS ONE.
Expanded moose habitat may not sound problematic, particularly in a part of the world where many people rely upon hunting wildlife to feed themselves and their families. But it’s not that simple, said Tape, because there are already animals living in these environments that are not used to competing with more southerly species for space, food, or safety.
Add a moose to the mix, and you’ve got a voracious herbivore capable of munching 40 to 60 pounds of vegetation a day that other wildlife also need for forage and shelter, such as the ptarmigan, a tundra bird.
Tape noted the example of the red fox, a forest species moving northward with the warming climate. The species is already beginning to outcompete the smaller polar fox, a tundra dweller.
But now “you have these boreal species coming up and competing with Arctic species, like the ptarmigan. We don’t know what the outcome of that will be,” Tape added. “It’s the borealization of the Arctic.”