If you’ve been up above treeline, you know that it can be an extreme environment in any season. Winds are fierce, temperatures are cold, clouds can render the visibility to nothing in a blink of an eye—and that’s just in the summer! Winter takes it to a whole new level of extreme.
I love visiting alpine summits in the winter. The views can be stunning, and I like a reminder of the harsh winter world that exists just a few miles away from my desk. A down parka, Gore-tex jacket and pants, insulated mittens, wool hat, winter boots, a thermos of something warm, and plenty of layers make the summit of Algonquin a comfortable place for me to be, for a few minutes. But I wouldn’t want to stay up here too long—even with excellent equipment, I’d get cold. All of this has me wondering about the life that exists up here year-round. How do alpine plants survive this inhospitable environment?
Before answering this question, I think it’s worth considering just how severe winter conditions can be. Temperatures on Whiteface Mountain have hit a frigid -43°F, without wind chill. The average wind speed during the month of January is 40 mph, which translates to gale force winds strong enough to break branches, pelt ice, and make it hard to walk. Water droplets from clouds freeze on contact with any surface, coating everything in rime ice. For most plant species, this is just too unforgiving an environment for survival.
Alpine plants have a number of adaptations that allow them to survive and thrive in this landscape. During the short growing season, they prepare for winter by building up stores of carbohydrates in their root systems. Like hibernating animals, they are dormant throughout the winter, protected from the arctic conditions above by an insulating layer of snow. Under this protective blanket, the temperature stays constant at a relatively comfortable 26°F. While winter winds rage as high as 138 mph above, under the snow all is quiet. As the snows begin to melt, plants put fully half of their stored energy into production of a chemical called anthocyanin. This reddish-purple pigment allows the plants to begin growth and photosynthesis as soon as the temperatures are above 32°F. (In contrast, lower elevation plants won’t photosynthesize until temperatures are above 50°F, and won’t hit optimum rates until the temperatures are closer to 70°F.) The dark pigment traps additional heat, slowly radiating it back to the plant. This protects the new growth from late-season freezes, allowing them to survive up to five consecutive days of freezing temperatures.
Alpine plants are typically small and low to the ground. Many of them also have a cushion-shape growth form. This shape and size protect them from the worst of the wind and from damaging rime ice. Rime ice forms as super-cooled water droplets from the air freeze onto a surface. As the ice forms, more water droplets freeze and accumulate on existing ice, growing into the wind. Rime ice can grow at a rate of nearly 4 inches per hour in the right conditions. Ice-coated branches become heavy and break, causing the flagging that is seen on trees near the summits.
While adaptations such as size, shape, and chemistry help these plants survive the challenges of winter in the alpine zone, they are still vulnerable. A coating of ice makes plants brittle—a single misplaced footstep can shatter twigs and destroy decades of growth. I love visiting alpine summits in the winter, but I am always keenly aware of staying on the trail, solid rock, or at least on deep snow. This way, whether I’m enjoying a bluebird day with a crystal clear view, or fighting to stay upright in the swirling snow, I know I’m not making this environment any harsher for the species that live up here in winter’s extreme wonderland.
Rime Ice photo by Paul Casson