Decline in snow cover spells trouble for many plants, animals

May 7, 2013 by Terry Devitt

For plants and animals forced to tough out harsh winter weather, the coverlet of snow that blankets the north country is a refuge, a stable beneath-the-snow habitat that gives essential respite from biting winds and subzero temperatures.

But in a warming world, winter and spring in the Northern Hemisphere is in decline, putting at risk many that depend on the space beneath the snow to survive the blustery chill of winter.

In a report published May 2 in the journal Frontiers in Ecology and the Environment, a team of scientists from the University of Wisconsin-Madison describes the gradual decay of the Northern Hemisphere's "subnivium," the term scientists use to describe the seasonal 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.

"Underneath that homogenous blanket of snow is an incredibly stable refuge where the vast majority of organisms persist through the winter," explains Jonathan Pauli, a UW-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."

Since 1970, snow cover in the —the part of the world that contains the largest land masses affected by snow—has diminished 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 Pauli and his colleagues, Benjamin Zuckerberg and Warren Porter, also of UW-Madison, and John P. Whiteman of the University of Wyoming in Laramie.

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

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 the cupboard bare when the protective snow cover goes missing.

"There are thresholds beyond which some organisms just won't be able to make a living," says 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," says Pauli. "We're seeing a trend. The subnivium is in retreat."

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2.4 / 5 (7) May 07, 2013
Curious how 2012/13 winter would do to these calculations. I'm afraid there are just too many variables and not enough sample data to determine any kind of trend. As soon as you think you have enough data what happens when 2 to 4 years of years of opposing data do to your trend? How do you explain that away?

My favourite two years are these last two. 2011/12 winter was dry and very short. 2012/13 winter was extremely wet and very long. There is still ice on many northern lakes in MN and WI. How two dramatically different years impact a trend? Throw them out because they are extremes? How many winters does one have to throw out before the amount of data left is not very useful in developing a trend?

I don't have answers, but the # of variables in the calculation exceeds 100 and that's about how many reliable years we have of data. This is the challenge we're facing. We're trying to develop models on such tiny sets of data :( In the end, we're guessing.
2.3 / 5 (6) May 07, 2013
And a quick follow-up. Because we're guessing, the real problem of pollution and the 3 Rs are forgotten in the noise. If we continue to do small steps, then more progress will be made then trying to scare everyone, Because if people feel scared, they will feel they can't change anything and do nothing.
3.4 / 5 (5) May 07, 2013
Lol ya definitely bucked the trend this winter, at least in North America. The thing of it is, Gunzo, such wild swings are exactly what has been predicted from the very earliest of reports on global warming. You are also wrong when you suggest that 3 to 4 years is indicative of a trend; that's weather, The trend, covering the last 100 or so years, is a warmer and warmer average temperature over the whole planet.
And yes, it IS a challenge to model weather It is an extremely complex and dynamic system, and the minutia of the day to day, year to year or decade to decade predictions will get more and more complex the further forward you try to project. The physics behind the modelling is robust, however there is never going to be 100% accuracy. The best you can do is plug in the numbers you have, and then refine tem as time goes by with updated data and better numbers, That is, after all, how science works.
2.3 / 5 (6) May 07, 2013
Maggnus, my example was 2 to 4 years of opposing data impacting a trend. I totally agree even 10 years is nothing. I would argue based on the # of variables, 100 years is a blip as well.

I have pictures of me in the winter of 1967 and tons of snow; the 70s and prediction of the global cooling craze; 1996 and how many record cold days we had, the winter of 82/83 Christmas to New Years where it was so cold, engines only started if they were inside. I can also remember late March/early April in the late 90s where I was outside coaching soccer because it was so nice.

Trend? No, just a lot of different data points. If we try to make any meaning of it and shout so loud immediate issues will be drowned out. Things right infront of our faces will be missed. We will miss the pesticides killing the bees and yet another year of crops under pollinated or the unintended reaction of Triclosan in liquid soap in the environment.
3.4 / 5 (5) May 07, 2013
I would argue based on the # of variables, 100 years is a blip as well.

And normally, as seems to be indicated by paleoclimate records, you would be right. The difference is the amount and the speed, neither of which is seen in the past records. It is the feedback that is the worry; feedback effects have so far not been documented. That appears to be changing.
Things right infront of our faces will be missed. We will miss the pesticides killing the bees and yet another year of crops under pollinated or the unintended reaction of Triclosan in liquid soap in the environment.

Both of which are important, and both of which should be studied. But these are short term problems, CO2 loading of the atmosphere will last for literally tens of thousands of years if something is not done. It is a slow-motion catastrophe that has no previous episode, so far as we can see, in the history of the planet. It demands our attention in a way nothing else quite equals.
no fate
3 / 5 (6) May 08, 2013
What humanity is doing to the earth from a loss of species standpoint alone will dwarf any previous natural extinction event (besides a meteor hit) in both scope and speed. It will ultimately end with our own in the worst case scenario. The best case scenario is worse than where we are now. Wrong direction if we are as smart as we think we are.

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