Snowy hikes inevitably cause me to be more delicate in my attention—more intentional. I pay more attention to where I place each foot on slick trails, which in turn awakens me to what other tracks are nearby and who else uses these pathways. Meanwhile, the snow quiets both the exterior landscape and the landscape of my mind. Hiking around Montana in the wintertime, my senses are heightened as my eyes hungrily seek colors and textures that stand out from otherwise gray and white monotones. I love the contrast in color of evergreen conifer trees against a snowy backdrop, or the contrast in texture of soft snow resting against the prickle of Doug-fir needles.
I am always surprised to see moss exposed in wintertime. Hiking on trails or backcountry roads, I encounter moss-covered rocks, or mossy ledges that crop out on the slope, like a bed where the quilt has been pulled back part way and you can see the sheets peeking out underneath. The richness of the emerald green and saturation of moisture make these encounters feel like I’m discovering moss at its peak “mossiness.”
Recently I began to wonder—how does moss seemingly thrive in winter, when most ground vegetation is dead or dormant? Does moss melt snow, or does snow melt on moss first, revealing the green that I so crave?
Mosses, like liverworts and hornworts, are bryophytes. In contrast with vascular plants that contain xylem, a tissue used to transport water internally, bryophytes instead absorb water and nutrients through their leaves. Bryophytes are some of the oldest plants on earth, dating back 450 million years. It turns out that mosses have a wide range of adaptations that have allowed them to survive this long in extreme climatic conditions like those in arid deserts, tropical forests, and even the Arctic and Antarctic. Like vascular plants, moss photosynthesizes by converting sunlight, water, and carbon dioxide to make glucose and oxygen. The presence of both moisture and light is critical for moss survival.
Many mosses have indeed adapted to not just survive but thrive in winter. Some live in exposed areas where wind clears the snow, granting them access to sunlight. Other species have adapted to grow exclusively under “snowbeds,” areas which experience prolonged snow, like crevices and depressions in alpine regions. Still others grow on rocks and cliffs that experience a lot of “snow water,” or snow melt. Here, the mosses take advantage of periods of extended hydration. Moss may also grow on bare tree limbs that receive more light in winter than during other times of the year.
It turns out that moss can actually photosynthesize under snow. In mixed forests where some trees have dropped their leaves, sunlight filters more easily through the canopy and can penetrate shallow layers of snow. Snowmelt can occur even while snowpack is still present, providing the moisture necessary for photosynthesis. And while photosynthesis stops if temperatures fall below a level at which the enzymes that carry out the process can do so efficiently, because snow insulates, it provides a buffer for higher temperatures that allows photosynthesis to proceed.
Perhaps even more fascinating, research suggests that moss also has antifreeze properties! Ice crystals can rupture cell walls, causing the cell—and eventually the animal or plant—to die. Some scientists believe mosses contain a combination of sugars and sugar alcohols that become more concentrated in the fall and winter and stop the ice crystals from developing, much like how antifreeze regulates temperature in a car. There’s some speculation about whether the moss itself has the antifreeze property or whether it’s secreted by bacteria living on the surface of the moss; either way, the result is that the sugar alcohols melt the snow around it. Some species of animals that survive harsh winter conditions such as lemmings, voles, and even caribou have been known to consume moss or lichen in the wintertime. Since moss has no nutritional value, scientists hypothesize that these animals eat the moss for these antifreeze properties, to keep their blood warm.
Perhaps it is no coincidence that the tiny leaves of star moss mirror the crystalline snowflakes they catch. The melting snow glints and glistens, calling me to pause in delight, crouch down to absorb the fractals in my mind, and take a photograph—sometimes on my phone, sometimes in my mind. This snapshot of green carries me through the winter.
I’m Elizabeth Domenech for Field Notes, brought to you by the Montana Natural History Center, providing natural history education for schools and the public throughout Montana. For information on upcoming events and programs at the Center, please call 406.327.0405 or visit our website at MontanaNaturalist.org.