In an International Polar Year "Back to the Future" project, researchers from the US and Australia examined test sites in Alaska where lemmings had been excluded for more than 50 years. The two-metre square plots of tundra had an increased abundance of lichens and mosses and less grass than control sites where lemmings had access.

"Our project has the explicit goal to visit historic research sites in the Arctic to try to understand how the Arctic has changed," David Johnson of the University of Texas at El Paso, US, told environmentalresearchweb. "The lemming exclosures in the landscape around Barrow represent what we believe to be the oldest such exclosures in the Arctic. Resampling [them] is one of the only ways we have to understand how ecosystems have been structured by herbivores in general, and lemmings specifically, in the Barrow landscape."

According to Johnson, lemming populations in the Arctic cycle between high and low animal densities; around Barrow population highs occur roughly every 4.5 years. Work on the exclosures in the 1950s showed that lemmings denude the landscape of their preferred – grasses and sedge species – during years when their populations are high. These plants then regrow during years with low lemming populations.

This latest study, which revisited 12 of the exclosures, found that over the long term lemmings promote grass and sedge growth in wet tundra.

"While there are a number of reasons why this may be, one recognized mechanism is simply suppressing lichen and moss abundance through trampling and removal of vascular plant litter," said Johnson. "These effects may be allowing grasses and sedges to grow to higher abundances, though an alteration of soil nutrient dynamics by lemmings is also a possible explanation."

The study highlights the need to appreciate how herbivore populations are affected by warming to fully understand Arctic greening, say the scientists. "Although the specific long-term effects of lemming we found are probably limited to areas that experience these population cycles, I think we demonstrate that herbivores can affect landscapes in such a way that could confound interpretations of warming-related greening if herbivores aren't considered," said Johnson.

Now the team is aiming to understand how lemmings may affect ecosystem function, particularly landscape-level carbon and energy balance, as well as looking into the effect of lemming exclusion on soil nutrient dynamics.

Johnson and colleagues from the University of Texas at El Paso, the Marine Biological Laboratory, University of Illinois at Urbana-Champaign, and Australian Antarctic Division reported their work in Environmental Research Letters (ERL).