This week in the woods, needle ice pushed up like goofy inverted icicles from mud along a woodland stream in West Fairlee, Vermont. These formations occur in wet, saturated soil when air temperatures drop below freezing – most often in late autumn or early spring, when the ground has not completely frozen. Under such conditions, as Rachel Sargent Mirus explains in this Outside Story article, water freezes near the soil’s surface, where it meets the cold air, and more water moves up from deeper in the soil, freezes, and attaches to the ice above; when the liquid turns to ice, it expands and the top layer moves upward through pores in the soil, through capillary action. The arching columns might lift a layer of dirt or other material from the surface – like the cone, twig, and leaf seen here.
Around now, ponds and lakes start to get their first skims of ice. As Ted Levin explains, if not for one special property of water, ponds and lakes would freeze from the bottom up, and much aquatic life would not survive the winter. During the summer, ponds and lakes have three distinct strata, which circulate separately. The top, or epilimnion, keeps contact with the air and remains richest in oxygen but lowest in nutrients; the bottom, or hypolimnion, gains nutrients through falling detritus but loses oxygen to respiring decomposers. Over the course of the autumn, the warmer, lower-density epilimnion gives its warmth to the cooling air above, increases in density, and sinks. If not for water reaching its maximum density at 39.2 degrees Fahrenheit, this process would continue until the water at the bottom of the lake reached 32 degrees and froze. However, because water reaches its maximum density before it freezes, these bodies of water reach nearly uniform temperatures of 39.2 degrees, triggering “fall overturn”: wind stirs the lake from top to bottom, nutrients and oxygen redistribute, and water-dwelling organisms get what they need for the winter ahead. Because water in turn gets less dense as it cools below 39.2, the wind-whipped top layer remains in place, getting ever colder until it freezes. By the end of December or beginning of January (in a usual winter), the lake is sealed off from the wind.
The thrice-divided fronds of the intermediate wood fern give it a lacy, delicate look, but it has a toughness that allows it to remain green and keep photosynthesizing throughout the winter. Like its fellow evergreen fern the Christmas fern, it flattens to the ground in the colder months and thus stays sheltered from the wind and remains warmer than the air above it.
The dainty flowers of trailing arbutus have long since fallen away, but its leathery leaves remain evergreen. These creeping, low-growing, woody-stemmed members of the heath family prefer acidic, peaty environments without the risk of smothering leaf litter; these specimens appeared beneath pole-sized white pines reclaiming the margins of a beaver pond in Fairlee, Vermont.
Not quite evergreen but still green into December, American golden saxifrage forms mats in seeps and wet woodlands. It might become food for hungry bears emerging from hibernation in the spring.
In the winter months, moose move from a diet weighted toward aquatic vegetation toward more twigs and bark, especially of smooth-barked trees: red and striped (or “moose”) maple, aspen, willow, mountain ash, and fir. Lacking upper front teeth, they browse on bark by making incisor scrapes in an upward motion with their lower teeth. The scrapes begin cleanly at the bottom and taper into shreds where the bark leaves the tree, and the exposed white wood stands out in the drab, gray winter forests. The distance up the tree trunk (see second photo of the same marks) reflects the moose’s height.
A native insect but still a destructive pest, the sugar maple borer lays an egg in a crack in its host’s bark, and the larva spends two years below. It excavates galleries and, in the fall of its second year, a chamber to overwinter in the sapwood. The following summer, it chews a crooked route out. The exit path rarely girdles the tree completely, but the bark often swells and splits in response, as seen here, and the wound reduces sap flow and timber value.
Another classic wildlife sign on tree bark: yellow-bellied sapsucker tapholes. The migratory woodpecker left our region weeks ago, but their preferred aspens, birches, maples, and fruit trees still bear the scars – necklaces of pea-sized holes ringing branches and trunks. Sapsuckers sip sap that oozes from these fresh holes in the warmer months and eat any trapped insects.
Another woodpecker or, perhaps more likely, a black-capped chickadee made this hole in a goldenrod ball gall to get out the larva of the goldenrod gall fly. Downy woodpeckers tend to make neater holes, and chickadees tend to make ragged ones like this one. They make the effort to excavate these larvae when other food sources dwindle.
What have you noticed in the woods this week? Submit a recent photo for possible inclusion in our monthly online Reader Photo Gallery.
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