December Natural Events Calendar

It’s a rare December when snow doesn’t fall in Minnesota, and by the end of the month, snow covers most, if not all of the state. Surprisingly, these snowfalls in early winter actually help the propagation of many plants in the spring.

Prairie grasses and flowers that produce seed late in the summer and fall benefit from winter’s first snows – the seeds that land on a snowy surface are directly exposed to cold and moisture that over time soften their hard outer seed coat, making it easier for them to germinate in the spring. Dark colored seeds absorb sunlight, become warm and sink into the snow, traveling downward to make contact with the soil below. Freeze-thaw cycles open cracks in the soil, allowing the seeds to effectively plant themselves. This entire process works best in early winter, before the snow is deep or so frozen that seeds cannot penetrate its surface.

Prairie restorationists take advantage of this process by using a technique called “snow seeding” (also called frost seeding or dormant seeding). Gathered seed is scattered onto a fresh snow surface early in the month; the white snow makes it easy to see where the seed has landed causing the sowing process to be efficient as well as effective. This method has been used for years at several Nature Conservancy preserves, including Weaver Dunes Scientific and Natural Area, where the Conservancy has been restoring old fields to native sand prairie.

December’s snowfalls are also significant for many Minnesota mammals, including some that change their fur color to match the now white background of their surroundings. Perhaps the best-known example of this color-change is the snowshoe hare, also called the varying hare due to its changing fur color. Throughout the summer, snowshoe hares are dark brown, but as days shorten in the fall, they gradually turn entirely white (except for the tips of their ears); a transition that can take ten weeks to complete. Snowshoe hares are not the only Minnesota mammals to make this seasonal color change: whitetail jackrabbits also turn white (but are not found in the boreal forests of northern Minnesota where snowshoe hare live) and shorttail, longtail, and least weasels all turn white in the winter (and are found throughout most of the state).

Snowshoe hare are known for their fecundity, producing as many as four litters per year. This can result in dense populations – more than 500 hares per square mile – followed by population crashes (to fewer than ten per square mile) once food resources are exhausted. These boom-and-bust cycles repeat approximately every ten years and have an enormous impact on the hare’s predators, notably Canada lynx. Lynx are resident in northern Minnesota, although not common, and their numbers vary with the hare populations. When hares are scarce further north, it’s thought that more lynx wander south into Minnesota from Canada looking for food. Lynx have been studied extensively in the state, and information from radio-collared animals collected until 2010 provides clues for where a careful observer might spot one in the Arrowhead region. Seeing a snowshoe hare, however, will be much easier!