From: Andy Soos, ENN
Published May 9, 2013 04:06 PM
Snow Blanket
Plants and animals adapt to their world so when the climate changes
they either change, move, or die. For plants and animals forced to tough
out harsh winter weather, the coverlet of snow that blankets the north
country is a refuge, a place beneath-the-snow that gives an essential
respite from biting winds and subzero temperatures. But in a warming
world, winter and spring snow cover in the Northern Hemisphere is in
decline, putting at risk many plants and animals that depend on the time
beneath the snow to survive the chill of winter. Snow, in this case, is
like a warm blanket.
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
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.
Subnivean climate refers to the zone in and underneath the snow pack.
From the Latin for under (sub) and snow (nives). This is the environment
of many animals that remain active during the winter. This zone provides
protection from predators and insulation from the elements. The
subnivean climate is formed by three different types of snow
metamorphosis: destructive metamorphosis, which begins when snow falls;
constructive metamorphosis, the movement of water vapor to the surface
of the snow pack; and melt metamorphosis, the melting/sublimation of
snow to water vapor and its refreezing in the snow pack. These three
types of metamorphosis transform individual snowflakes into ice crystals
and create spaces under the snow where small animals can move.
"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 Northern Hemisphere — 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.
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.
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.
For further information see
Subnivean.
Snow image via Wikipedia.
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