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Staying Alive

How plants survive the harsh Adirondack winter

Photograph by Robert Lubeck

Photograph by Robert Lubeck

Long before the snow flies, all but the hardiest birds have left, the bears are deep in slumber, insects have transformed to protective pupae and toads have buried themselves deep in the mud. Only the stalwart plants remain in a winter world inhospitable to life itself.

One February after a long snowshoe trek, we set up camp at Janacks Landing, on Cranberry Lake, under a sky filled with brilliant stars. The heat of our campfire barely made a dent in air so sharp it froze the inside of our noses, so we crawled early into our sleeping bags. But it was still cold. We donned down parkas, balaclavas and mittens inside our winter bags. We still had to fire up the stove to warm ourselves with tea. We knew better than to sip from the jar of brandy, which would only make us lose heat faster. Besides, it had frozen. Tossing and turning, my dreams that night were of vulnerability: all that stood between us and the deep freeze was our carefully assembled gear.

Any exposed skin was quickly frozen, yet the trees stood naked around us in the moonlit snow. No down, no tent and no tea—they endured the bitter cold. How do they survive when all other beings have fled to warmth? Except, of course, crazy winter campers.

There are three basic strategies for dealing with winter: migration, avoidance and tolerance. Plants can’t migrate like the birds or hibernate like the warm-blooded animals. Annual plants avoid winterkill by dying back with the frost, leaving behind dormant seeds to start over in the spring. Perennial plants re­treat underground to deep roots where the Earth’s stable temperature keeps them from freezing and they live on stored carbohydrates, almost like a hi­bernating bear. The forest floor becomes nearly bare, but for a few hardy evergreen herbs who tolerate winter by huddling beneath the blanket of snow.

The snowpack is a complex layered environment. The bottom layer, the “subnivean” zone, heated by the Earth and insulated by the snow above, stays a balmy 32 degrees. Warmer, moist and enriched in carbon dioxide from decaying vegetation, the subnivean zone creates a dim greenhouse for forest floor plants in winter. Light can penetrate the snowpack and some mos­ses even photosynthesize and reproduce under the snow. Think of the typical forest floor plants of the Adi­rondacks: waxy-leafed wintergreen, trailing stems of goldthread and partridgeberry, miniature forests of club mosses. All are evergreen and all grow close to the ground, to take shelter be­neath the subnivean tent. Christmas fern and the marginal shield fern have adopted this strategy. If they grew taller they would suffer the freezing temperatures and erosive forces of blowing snow, so in­stead they settle cozily be­neath the snow. Being evergreen en­sures that they can capture sunlight early in spring and get a jump on an already short growing season.

The subnivean zone is also critical to survival of many small mammals like mice and voles who move around within it. If snow repeatedly melts and freezes, this sliver of favorable habitat is destroyed and turns into an uninhabitable icy crust. As climate change produces more winters where the snowpack restlessly comes and goes, the multitude of species that rely on its protection will be in jeopardy.

The forest trees, however, cannot take cover and must bear the full brunt of winter. A snowshoer moving below their spare canopies may take their en­durance for granted, not aware of the remarkable behaviors that let them survive the frigid season. Deciduous trees like maples and birches resist winter’s ravages by dropping tender leaves that would succumb to freezing. While au­tumn’s brilliant foliage display dazzles, more subtle changes essential for survival escape our notice. Before the leaves drift away, sugars and nutrients are pulled back into the tree for conservation. Every time a red leaf falls, it has been pushed off by the growth of a corky layer between the twig and the leaf, forming a leaf scar. Look closely at a scar and you can see where the plumbing of the leaf and the twig were connected. The tree seals up the now useless water vessels to prevent water loss. Long be­fore the leaves are shed, the branches have been making their winter preparations, creating tiny copies of themselves in the form of buds. These embryonic shoots are as carefully packaged as campers’ gear, under waterproof scales to ensure safe passage through winter.

Just as we made detailed preparations for our winter camping trip, so too the trees get ready. Ice crystals are sharp and can puncture delicate cell membranes; trees expend a large effort to prevent tissue from freezing, such as the buds and the cambium, the living layer just below the bark. While the deciduous trees are taking sugar out of their leaves, the evergreens like spruces and firs are doing the opposite, accumulating sugars in their cells as a sort of antifreeze. The very membranes of the leaf cells are altered, becoming more permeable so water can move easily from inside the cell to the outside, where when it freezes it will do no harm. But sugars as antifreeze are only effective down to about 10 below, and Adirondack winters get colder than that. So evergreen leaves also make special proteins which inhibit the formation of ice crystals. The protoplasm of the cell becomes super-cooled to a viscous, almost glasslike substance that resists freezing.

All things are connected in nature, and this tree behavior benefits the winter survival of animals, including hu­mans. The loading of sugar into vulnerable living tissues means that buds be­come calorie rich and many mammals survive by browsing on them. Cambium, a vital living layer, is also protected by sugary antifreeze, making it sweet and nutritious. This process is at the heart of the na­tive name for the Adirondacks: Tata­ronta—or home of the bark eaters. The name reflects that the winters here are so tough that one would be reduced, like a porcupine, to eating bark. In fact, the cambium is well-known as an emergency food during starvation times.

Our night at Janacks Landing was broken by a nearly continuous barrage of what sounded like gunshots. While the trees protect their living tissue, the wood is not living and is susceptible to freezing. A tree is more than half water and when it freezes, the expansion of ice in­side the trunk can actually break the wood, creating the rifle-crack heard on frigid nights. The water-conducting vessels are ruptured; because they are linked end to end these can reduce a de­ciduous tree’s ability to transport water the next year.

Evergreens have a different wood structure that allows water to detour around areas broken by freezing, making them better suited to far northern habitats. Conifers are the masters of winter adaptation. Their tall spires intercept sunlight coming in at a low angle, and the drooping branches help snow slide off in a circle. Shed snow builds up where the branches meet the ground, creating “tree wells,” protected spots that can shelter winter wildlife.

We could have used that shelter at Janacks Landing. The next morning we broke camp in the weak winter sunshine. Our sleeping mats were as solid as boards and we had to strap them whole to our backpacks. The tent was so stiff that it couldn’t be stuffed into its sack, only folded in a crackling bundle. We hiked out to Wanakena and, stopping at the General Store for coffee, learned that a record had been set that night of –43 degrees. It’s a good thing we didn’t have a thermometer with us. We would have shivered with hypothermic worry in­stead of staying warm. But unlike us, with elegant adaptation to the deepest cold, the trees had nothing to fear.

Robin Wall Kimmerer is the author of Braiding Sweetgrass: Indigenous Wisdom, Scientific Knowledge, and the Teachings of Plants (Milkweed Editions, 2013). Kimmerer is a professor of environmental biology at SUNY College of Environmental Science.

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