Photo: Vole tunnels revealed by melting snow, © John Fowler (johnfowler.photoshelter.com), used by permission.
Note: This is a science outreach piece belonging to a series I wrote for the newsletter of the Fredericton Botanic Garden. I’d be happy to see it modified for use elsewhere and so am posting the text here under a CC BY-NC 4.0 license. If you use it, though, I’d appreciate hearing where and how.
On a cold February day, when breath hangs visible in the frigid air and even our winter-resident birds are huddling out of sight, it’s easy to think that life outdoors waits suspended for a thaw. Think twice, though, because when that thaw comes it will bring evidence – like the networks of vole tunnels in the photo above – that this apparent suspension was just an illusion. There’s a lot going on, even on the coldest days of winter; but a lot of it is happening out of sight, under the snow.
The snow is just the ticket, for a lot of plants and animals, because it provides an insulating blanket. For example, with a 35 cm snow layer, ground-surface temperatures can stay at or just above freezing even when air temperatures drop below -30°C. Such temperatures are more than warm enough for most species to avoid freeze damage, and for many to remain active.
Among species using snow cover to avoid freeze damage are plants we call chamaephytes and hemicryptophytes. These are admittedly cumbersome words, but the concept is simple. Through winter, both kinds of plants maintain their living-but-dormant buds above ground level, but under the protective cover of snow. Chamaephytes, such as bunchberry and wild blueberries, bear buds on woody stems but less than about 25 cm above ground. Hemicryptophytes, such as daisies and many grasses, lack woody stems but maintain buds at or just above the soil surface. It’s not, of course, impossible for a plant to maintain overwintering buds exposed to winter air – our trees do it (and our conifers even maintain green foliage). It’s not cheap, though. Such plants need to prepare for winter cold stress by investing in thick, waxy leaf coatings, thick bracts to shelter buds, and high concentrations of antifreeze molecules (sugar, glycerol, and proteins) in their tissues. Chamaephytes and hemicryptophytes, comfortably ensconced under the snow, avoid the need for this investment and can put those resources to other uses, such as an earlier start to the next year’s growth.
The tunnel networks that become visible with spring thaws, though, remind us that other species don’t just rest under the snow. Instead, they move about down there, foraging all winter and seldom needing to surface. Among these are the tunnel architects, voles and shrews (two groups of abundant, but secretive, small mammals). Voles are herbivores, feeding on roots and bulbs, green buds, and bark. In high densities (it’s true) they can damage a garden, although we don’t begrudge them a modest taste of ours since they’re part of the natural web a garden can celebrate. Shrews, in contrast, are predators. They feed voraciously on worms, grubs, snails, and even mice and voles considerably larger than they are, in order to fuel their legendarily high metabolic rates. They can eat several times their body weight each day (and in doing so can provide excellent pest control). For these tunnelers, the snow provides warmth that makes winter-long activity possible. It also provides protection from their own predators – although not perfect protection, since ermines, foxes, and others have keen hearing and listen for scurrying feet to pounce upon.
There’s a lot going on under the snow. Life has found an impressive variety of ways to make it through winter – and that’s something to think about the next time you walk, ski, or snowshoe through our Garden.
© Stephen Heard (firstname.lastname@example.org) February 16, 2017 but licensed CC BY-NC 4.0
Other Botanic Garden newsletter outreach pieces: