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Recent satellite observations showing "greening" of some Arctic regions - until now put down to global warming permitting plants to grow more easily in the frozen north - may in fact be explained by large numbers of lemmings defecating on the affected areas, so fertilising green plants.

"Our paper confirms that we really need to be careful attributing the greening of the Arctic to global warming alone. 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," said lead author of the study David Johnson, a biology prof at the University of Texas.

These results suggest that sustained lemming activity promotes a higher biomass of vascular plant functional types than would be expected without their presence and highlights the importance of considering herbivory when interpreting patterns of greening in the Arctic.

According to a statement announcing publication of the research:

The increase of grass and sedge could be due to changes in nutrient availability in soils from the addition of urine and faeces from the lemmings, or by simply reducing competition for space by keeping bryophyte and lichen abundance low, as well as reducing the amount of standing dead grass and sedge litter.

Lemming populations have historically gone through periods of highs and lows, which researchers believe have played a key role in regulating many properties and processes of tundra ecosystems.

The tiny rodents are best known perhaps for their tendency to migrate suddenly across long distances, sometimes including lengthy swims which may begin with a mass leap off a cliff (erroneously assumed to be mass suicide by some). In fact the lemmings do sometimes attempt swims too long for them and drown en masse, but normally they reach land again.

The migrations are thought to be driven in part by the lemmings' frequent sudden population increases. It now appears that the small sex-mad creatures may be causing green grasses and sedges to spread rapidly across tundra regions by fertilising the ground with their wastes and perhaps also by carrying the grasses' seeds about with them as well.

Arctic greening may actually reduce atmospheric carbon as the new plants suck it in: conversely higher temperatures in the north could cause soils to release more greenhouse gases, though recent research has cast doubt on such ideas. In any case, future forecasts will now have to factor in the Lemming Effect.

Johnson and his colleagues' research is published in the journal Environmental Research Letters. It can be read online here. ®

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