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Beneath the snow lies the subnivium (from the Latin nivis for snow, and sub for below), a small, protected area that is insulated and maintains a constant temperature. This microhabitat turns traditional thinking about snow on its head. Thanks to the emerging field of winter ecology, we now know that snowy environments have lives of their own. "Without snow, plant and animal life would be completely different," says biologist Jonathan Pauli of the University of Wisconsin-Madison. Pauli and scientists such as Ben Zuckerberg, are members of a new breed of researchers called winter ecologists who study the relationships among animals, plants and their snow-covered environments.

Their studies have shown that tiny mammals like shrews don't migrate but spend their winters in the subnivium. For some of the tiniest forms of life - fungi, invertebrates, soil bacteria and plant roots- snow maintains a mild winter temperature in which they can survive, compared to the killing cold up above. Plants and soil benefit from this layer because the lack of a hard frozen surface lets plant roots function. The active fungi release important nutrients to plants. As the temperature warms, the snow slowly melts and provides water for spring flowers. On an average, snow covers almost 18 million square miles of the planet each year. However, climate change is upsetting that chilly balance. Winter ecologists are studying how the lack of snow cover directly affects the ecology of many subnivium ecosystems, exposing organisms to temperatures for which they are not adapted.