Warming temperatures and longer summer seasons may have triggered a tundra growth spurt in Alaska and across the Far North. But a new study of plant ecology outside of Barrow has uncovered another factor scurrying through the regional green-up: lemmings.
A research team found that Arctic tundra crawling with the 3-ounce herbivores appears to thrive -- lush with the very grasses and sedges these furry rodents love to munch. Experimental plots where fences have excluded lemmings for the past 50 years pale by comparison -- with higher concentrations of moss and lichen, and much browner vegetation.
One reason might be the generous application of, ahem, lemming fertilizer, in the form of their scat and urine. And then there's the complex ecological impact that a legion of tiny nibblers exerts over the health of its tundra plant community.
"We have shown that lemmings can promote similar greening, through the increase of grasses and sedges, as warming does in Arctic regions where lemmings are present and go through dramatic population cycles," he explained in a story about the project.
"We are not saying that lemmings are causing the greening, because greening is occurring in areas where lemmings don't occur at high densities and we are not sure how lemming populations across the Arctic are themselves responding to warmer conditions. However, it is clear from our study that lemmings, and other herbivores, are more important in some of these Arctic ecosystems than people historically give them credit for."
The study, published this week in the journal Environmental Research Letters, suggests that lemmings help maintain the biomass of certain plants at a time when satellite monitoring and field work has found evidence of thicker and brushier vegetation.
And that leads to a startling insight. Lemmings -- the mass-migrating rodents of Arctic lore -- might just play a measureable role in the warming of the planet.
How do the lemmings fit in?
Lemmings are tiny, ubiquitous rodents found throughout the Arctic, members of the same subfamily that includes voles and muskrats. Like many other species of rodents and small mammals, the creatures can experience furious population booms and die-offs, and are important prey food for predatory birds and weasels.
The brown lemmings of Alaska's Arctic slope are among the toughest denizens of the Far North, able to survive in the harshest tundra through the months of frigid conditions. They remain active all winter in their subnivean world of tunnels and nests.
"To come across the intricately patterned and well-traveled raceways of a group of lemmings while traveling across apparently barren frozen ground gives one a sense of the wonderful and delicate balance of life in all climes," wrote Paul Whitney, in the lemmings entry of the Alaska Department of Fish and Game Wildlife Notebook.
Their tendency to migrate to new habitat in large groups — sometimes swimming across bodies of water en route — helped generate the myth that lemmings will commit mass suicide by swarming off cliffs. (A notorious and bogus 1958 Walt Disney documentary perpetuated the nonsense.) They figure in Native Alaskan folklore too.
"One of the native names for lemmings is 'kilangmiutak,' which means one-who-comes-from-the-sky," says Whitney wrote here. "The legend of lemmings falling from the sky is common from the eastern Canadian Arctic to western Alaska, and is also found in Scandinavia. Perhaps it arose because of the sudden appearance of lemmings when the snow melts in the spring of a peak population year."
Aside from their grip on the human imagination, lemmings can have a profound influence on their grassy world, sometimes stripping it to the dirt.
"The boom-bust population dynamics of the brown lemming (Lemmus trimucronatus), has long intrigued researchers in northern Alaska," wrote Johnson and his four co-authors in their paper. "Early observers of periodic outbreaks of high lemming densities noted that lemmings could denude the landscape of (grasses and sedges), resulting in the depletion of their own food and nesting supply and increasing rates of their own predation."
To study the long-term impact of lemmings on the ecology, scientists built a series of exclosures on the tundra outside of Barrow beginning in 1959 -- basically small plots surrounded by fences that kept lemmings out.
Various groups have studied the plots over the past half century. Over time, they found a curious dynamic. While the lemming population booms -- following a 4.5-year cycle near Barrow -- could temporarily nibble the grass to stubble, over the long haul, lemmings seemed to be good for the tundra.
New field work in the time of Arctic warming
Johnson has spent nine summers in Alaska investigating plant communities, both as a student and researcher, along the way visiting North Slope tundra and other Alaska Peninsula and Aleutian locations.
"I've had the most of the typical Alaska experiences," he wrote in an email message. "Insane amounts of bugs, many weather experiences, and a number of bear experiences. All in all, I love it!"
One Alaskan critter he likes to avoid? Lemmings. The scientists didn't need to trap them for the current study, and that was fine with Johnson.
"I've had them run across my XtraTuffs on multiple occasions though," he said in an email. "And in previous work, I have trapped animals. Oddly enough, rodents are the only group of animals that freak me out."
To find out what role these sneaky, furtive creatures now play in the climate-triggered greening of the tundra, Johnson and his team visited the long-time study site about three miles outside Barrow in 2002 and 2010 and examined 12 of the original plots. They analyzed the plant growth inside and outside the plots, and compared what they found to other measurements from the past.
"The 50+ year exclusion of lemmings from the coastal tundra near Barrow resulted in radical changes to plant community structure, but the specific effects varied with vegetation type," the scientists wrote in the paper.
"Our resampling of the historic herbivore exclosures in the coastal tundra near Barrow, Alaska revealed that lemming exclusion decreases the cover and biomass of (grasses and sedges) markedly and increases the biomass of lichens and (mosses.) Because these plants respond similarly to warming, lemmings may have partially contributed to the recent greening of arctic landscapes."
Why lemmings don't overgraze their ecosystem and ultimately destroy it is complicated. For one thing, the tiny rodents appear to fertilize their habitat with droppings. Nibbling at grasses and sedges, and disrupting the area with their ceaseless activity, might also contribute -- comparable to how mulching a lawn makes it greener and thicker.
"Many grasses and sedges have evolved with herbivores so it's plausible that moderate levels of herbivory (eating leaves by lemmings and other herbivores) maximizes plant growth," Johnson explained in an email.
Anything that dramatically promotes plant growth could play a role in climate change.
A "greener" tundra could absorb and store ever more carbon dioxide, contributing to the Far North's role as a "sink" for the most influential greenhouse gas. On the other hand, this same "greener" Arctic would be darker -- less reflective -- and would tend to absorb more solar energy, thus contributing to regional warming. Warmer temperatures might also thaw permafrost, boosting the activities of soil microbes -- some releasing greenhouse gases and others consuming them.
"We still don't know the relative magnitude of these two feedbacks to warming," Johnson said. But "it is plausible that herbivores, in some situations, may provide a mechanism for higher plant growth maintaining these ecosystems as carbon sinks."
As a result, lemmings -- and other Arctic plant eaters like caribou and musk ox -- need to be included in climate models because of their potential influence over vegetation.
"There has been a call for this in the climate community for at least the past five years," Johnson told Dispatch. "The link is not straight forward though. The same herbivore can have entirely opposite effects depending on the location. … Still other situations, we may find that they play no role."
Johnson and his team are working on more scientific papers about lemmings and plan to return to Alaska for more field work in 2012.
Contact Doug O'Harra at doug(at)alaskadispatch.com.