Visual rewards are plentiful for winter forest walkers.
It was perfectly still and quiet while I walked in the Sourlands on a cold December morning. Usually, on winter mornings I can count on seeing squirrels busying themselves, but this morning they were sleeping late. It is also common to see a little flock of birds, mixed species with titmice, nuthatches, chickadees, sometimes a brown creeper or downy woodpecker, that have joined forces to protect themselves from hawks while they forage. These hardy little birds were also absent during my walk. Crows or overhead Canada geese can often supply some action and voice to a winter forest but even they were conserving their energy by lying low.
I loved being in that forest when it was so still and quiet; I took this walk, and I am writing this essay, at a time when the coronavirus is raging and the dangerous and crazy outgoing President is frightening even his allies. The calm of a winter forest is reassurance that the natural world can go on as usual, but I found it unsettling how very quiet and how very still the woods can be on a winter morning.
I think of the vast interconnectedness of the forest as a dynamic phenomenon. In spring and summer tree leaves make glucose out of air and water, send that glucose down hair-thin phloem tubes to the roots, and from there connect to the web of mycorrhizal fungi. The fungi network connects the tree to other trees and shrubs and it shares the bounty of glucose with plants that might need it. Flowers open and they attract insects that want the pollen and nectar and that inadvertently carry some of the pollen to flowers on other plants, making fruits that enclose seeds. Insect larvae eat new leaves and are being eaten themselves by songbirds that are building nests and raising families. In my imagination all that is going on in a forest causes there to be a great humming sound; like the sound of bees’ wings. I cannot imagine this hum on cold winter mornings because everything, everything, is pausing.
Trees and shrubs have expelled their leaves, they have stopped growing, and the moisture in their cells has been expelled so that the cells won’t burst when the water freezes. The grasses, sedges, and forbs have died down to the ground while the roots of these perennials also expel water. Roots convert the glucose that they have stored into a kind of antifreeze. Leaves and other dead plant parts on the forest floor help protect the roots from freezing, as does a nice coat of snow when that is available. Water is also withdrawn from the seeds of annual plants so that they won’t rupture when they freeze.
Many insects, including mosquitoes, die after they have laid their eggs in the fall. The eggs survive the winter and hatch when warmer weather arrives. Dragonfly adults die but the larvae survive by remaining underwater; the larvae of other insects burrow into the soil or the wood of a tree or log. Honeybees form a cluster in their hives and stay together for up to three months of cold. Most wasps die but impregnated queens hibernate and start a new colony in the spring. Other insect larvae find protection by living out the winter in a gall. Many insect larvae do something similar to plant roots, they replace the water in their bodies with glycerol, which works like antifreeze. A few insects, monarch butterflies are a well-known example, migrate in winter. Some insects, like mourning cloak butterflies, hibernate until spring.
Squirrels sleep more than usual in winter—often for several days at a time—but they do not hibernate. They find a cozy tree cavity or a nest that they built in the fall and snuggle down to protect themselves from the cold. They rely on caches of food that they stored in autumn for winter nourishment. Raccoons also do not hibernate, but they enter a state of torpor and spend most of the winter in dens—with other raccoons for warmth if possible. White-tailed deer are active through the winter, and they grow a winter coat that has hollow hairs so it provides better insulation than the coat they have the rest of the year. They also are less active when it is quite cold, conserving their energy. Bears, skunks, and groundhogs find that their sources of food are unavailable in winter and consequently they enter dens and lower their body systems. Their metabolism, breathing, heart rate, and their body temperature are greatly reduced during hibernation. It is more because of lack of available food than low temperatures that cause mammals to hibernate. Incidentally, I found out that it is not a good idea to poke a bear when it is hibernating; they can rouse themselves quickly and will surely be annoyed.
Terrestrial turtles, frogs, toads and snakes burrow into the ground, rotten logs, or they find rock crevices that protect them from winter’s privation. Like hibernating animals, they lower all their body functions but do not require the same amount of sleep as hibernating animals. This process is called brumation.
Aquatic turtles and frogs survive the winter by burrowing into the mud at the bottom of a water body. Wood frogs can survive even if their bodies are frozen solid because they produce glucose for antifreeze. Aquatic turtles stop breathing for up to five months and their hearts will beat once every ten minutes in winter.
The Sourland forest in winter does not possess the silence of the tomb, but it is the silence of a place where everything is enjoying a very deep sleep.