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By Holly Einess
On my drive to the Arboretum I call a friend to wish her a happy birthday. She tells me the trees in her North Dakota yard are decked in beautiful hoarfrost and asks whether I’m seeing the same. “No,” I lament, “It’s a little foggy here today, but the trees are bare.” Fifteen minutes later I pull into the Arb and see, to my surprise and delight, that the trees here ARE covered in hoarfrost!
The air must be quite moist in order for hoarfrost to form, and the fog of the last few days has provided that moisture. And of course temps must be at or below freezing. I’m eager to get a look at all the ways the frost is manifesting, so set off around Wood Duck pond, where the scene is lovely in a muted, silvery kind of way.
Heading uphill toward the Dog Commons, I notice a tree that appears to be eating the branch of its neighbor. I’ve seen trees in the past that have grown around objects such as rocks, park benches, or fences. And I’m familiar with inosculation, in which trunks, branches or roots of two trees grow together. But I’ve never seen something quite like this! (Once home at my computer, I can’t resist enhancing the effect…)
On the Dog Commons trails I keep a lookout for the barred owl a friend saw here a few days ago, but it’s apparently elsewhere today. Chickadees dart about among the trees as a nuthatch calls and a downy woodpecker drums. A pair of white-tailed deer in the distance pause in their foraging, then bound away as two walkers come into view. For as often as I see deer tracks at the Arboretum, I seldom see the animals themselves, as they tend to be most active at dawn and dusk. Members of the deer family (which also includes elk, moose, and caribou) are the only animals that grow antlers, which are composed of skin, nerves, blood vessels, fibrous tissue, cartilage and bone. Antlers are among the fastest-growing animal organs and should not be confused with horns, which are made of keratin (like hair, nails, claws, and hooves). Animals with horns (rhinos, rams, impala) grow them young and keep them their whole life. Antlers, by contrast, are shed and then grown anew each year, and each year they grow bigger.
I head back down to Wood Duck Pond and then over to Green Heron Trail, where I see my first gray squirrels of the day, one perched on a log eating a nut, two others chasing each other up and down a tree. Along the way I take in the beauty of the hoarfrost as it clings to branches, berries, and leaves, hoping it lasts at least a few more days!
***Correction: Thanks to readers Kyloe Fisher and Jo Frerichs for pointing out that frost from fog is normally rime frost, not hoarfrost!
Hoarfrost: clear and cold nights; water vapor creates crystals (looks like feathers)
Rime ice: foggy and cold nights; water droplets create ice (looks like needles or clumps of ice)
Holly Einess is a Minnesota Master Naturalist Volunteer.