Many organisms—including plants, insects, amphibians, birds, and small mammals—in the upper-Midwest survive the harsh winter months tucked away in the subnivium: an insulated zone between the ground and snowpack where temperatures hold steady at around 32° F. However, in Wisconsin and across the Great Lakes region, this vital habitat is changing as the climate changes. According to the Wisconsin Initiative on Climate Change Impacts (WICCI), Wisconsin is becoming “less cold.” Between 1950 and 2006, the warming has been greatest in winter, with an average increase of 2.5° F. Future warming is also projected to be greatest in winter, resulting in later onset of snow and earlier melt in the spring. Researchers predict snow depth and duration will decrease, resulting in a subnivium that is colder and less thermally stable—and thus less hospitable for plants and animals.
To test this hypothesis, researchers in the Pauli and Zuckerberg labs at the UW–Madison Department of Forest and Wildlife Ecology have installed 27 micro-greenhouses in open and wooded habitats in Duluth, Minnesota; Houghton, Michigan; and Madison, Wisconsin, including three at the Arboretum. These 8′ x 8′ x 10′ greenhouses have fully automated roofs that open during precipitation events, allowing the same amount of rain or snow to accumulate inside and outside the houses. After each precipitation event, one of the greenhouses is kept at ambient temperature, while the other two are kept slightly warmer. This allows researchers to stimulate the effects of projected warming on snow pack characteristics and subnivium temperature.
One animal that would have to adjust to subnivium changes is the wood frog. Larry Werner, a PhD student and one of the lead researchers on the project, is asking the question “How do wood frogs respond to a more dynamic subnivium space?” Common in Wisconsin, wood frogs over-winter in the subnivium, usually under leaf litter, rocks, or logs near their breeding ponds. They are capable of withstanding freezing temperatures—by freezing themselves. Werner wants to investigate how these frogs will adapt to warmer winter temperatures and, potentially, to more frequent freeze-thaw cycles. “In 2018, subnivium temperature data collected from the greenhouses will be used in environmental chambers at the UW–Madison BioTron facility to mimic winter conditions in order for researchers to take real-time measurements of wood frog glycogen reserve and other metabolic activity. This will provide a model organism’s response to climate change,” says Werner.
Climate change will have real, and still undetermined, impacts on native plants and animals. This project demonstrates how the Arboretum is a valuable site for researching what climate change could mean for plants and animals that rely on the subnivium to survive the winter. Data from this project will not only provide needed information about regional (Great Lakes) effects of climate change on the subnivium zone and animals that utilize this winter habitat, but also provide the Arboretum with site specific climate change data.
—Brad Herrick, Arboretum ecologist
Subnivium research project benefits from win-win collaboration, UW–Madison CALS, 1/10/16
There’s a Secret World Under the Snow, and it’s in Trouble, Alison Gillespie, Smithsonian Magazine, 1/27/16
Beneath the snowpack lies a secret ecosystem: the subnivium, Kimberly Thompson, Aeon, 5/31/16