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The subnivium, a secret world beneath the snow, is at risk from global warming

Declining spring snowcover will impact plants and animals use deep snow cover as a refuge from winter cold

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Spring snow cover in the northern hemisphere is in decline. Graphic courtesy Rutgers Global Snow Lab.

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Melting snow reveals the subniveal world.

By Bob Berwyn

FRISCO — Beneath winter’s deep snows there is a secret world of frozen insects and amphibians in quasi-hibernation, where small mammals scoot about eating bugs and fungi. It’s an ecoogical world that’s mostly invisible but functions as a critical part of larger ecosystems. The subnivium, as scientists have dubbed it, is now at risk from global warming.

Since 1970, snow cover in the Northern Hemisphere has declined by as much as 3.2 million square kilometers during the critical spring months of March and April. Maximum snow cover has shifted from February to January and spring melt has accelerated by almost two weeks, according to a team of university researchers who set out to discover some of the ecological impacts of the loss of snow cover. Visit the Rutgers Global Snow Lab for more details on snow cover.

“Underneath that homogenous blanket of snow is an incredibly stable refuge where the vast majority of organisms persist through the winter,” said Jonathan Pauli, a University of Wisconsin-Madison professor of forest and wildlife ecology and a co-author of the new report. “The snow holds in heat radiating from the ground, plants photosynthesize, and it’s a haven for insects, reptiles, amphibians and many other organisms.”

“The thing that’s often most surprising to people is that, small mammals like shrews and voles, because of that insulative layer of snow, are active all winter long,” said John P. Whiteman of the University of Wyoming in Laramie.

The article in the journal  Frontiers in Ecology and the Environment, describes the seasonal microenvironment beneath the snow, a habitat where life from microbes to bears take full advantage of warmer temperatures, near constant humidity and the absence of wind.

The study focused on Wisconsin and the Upper Midwest in particular, but the findings could be applicable to other regions with seasonal snow cover.

“The winter ecology of Wisconsin and the Upper Midwest is changing,” said Benjamin Zuckerberg, a UW-Madison professor of forest and wildlife ecology. “There is concern these winter ecosystems could change dramatically over the next several years,” Zuckerberg said.

As is true for ecosystem changes anywhere, a decaying subnivium would have far-reaching consequences. Reptiles and amphibians, which can survive being frozen solid, are put at risk when temperatures fluctuate, bringing them prematurely out of their winter torpor only to be lashed by late spring storms or big drops in temperature.

Insects also undergo phases of freeze tolerance and the migrating birds that depend on invertebrates as a food staple may find that the menu shrinks dramatically as spring snow continues to shrink.

“There are thresholds beyond which some organisms just won’t be able to make a living,” said Pauli. “The subnivium provides a stable environment, but it is also extremely delicate. Once that snow melts, things can change radically.”

For example, plants exposed directly to cold temperatures and more frequent freeze-thaw cycles can suffer tissue damage both below and above ground, resulting in higher plant mortality, delayed flowering and reduced biomass. Voles and shrews, two animals that thrive in networks of tunnels in the subnivium, would experience not only a loss of their snowy refuge, but also greater metabolic demands to cope with more frequent and severe exposure to the elements.

The greatest effects on the subnivium, according to Zuckerberg, will occur on the margins of the Earth’s terrestrial cryosphere, the parts of the world that get cold enough to support snow and ice, whether seasonally or year-round.

“The effects will be especially profound along the trailing edge of the cryosphere in regions that experience significant, but seasonal snow cover,” the Wisconsin scientists assert in their report. “Decay of the subnivium will affect species differently, but be especially consequential for those that lack the plasticity to cope with the loss of the subnivium or that possess insufficient dispersal power to track the retreating range boundary of the subnivium.”

As an ecological niche, the subnivium has been little studied. However, as snow cover retreats in a warming world, land managers, the Wisconsin researchers argue, need to begin to pay attention to the changes and the resulting loss of habitat for a big range of plants and animals.

“Snow cover is becoming shorter, thinner and less predictable,” said Pauli. “We’re seeing a trend. The subnivium is in retreat.

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3 Responses

  1. The article does not describe whether the warming has made the hazardous interval when snow may have melted, but freezing still occurs, longer or simply earlier. Absent indications that it is longer, this does not represent an increased threat, but simply another poleward shift of temperature zones.

  2. Bob, You forgot to include 2013 spring cover in your graph, which is probably going to be a record high.

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