Field Guide to December 2022

The Essence of Marcescense

By Steve Faccio

With stick season upon us, an end-of-year walk in the woods reveals a phenomenon known as marcescense; or some species of woody plants refusing to shed their dead leaves in autumn. In Vermont, the most common species that exhibit marcescense are young American Beech and Red Oak. Although beech and oak leaves wither in autumn, they remain firmly attached to the twigs until spring, instead of dropping to the ground. These leaves provide a unique soft rattling sound on breezy winter days, for those who brave the cold to listen.

Although it is unclear why marcescent plants have adapted this strategy, several hypotheses exist. One leading theory is that it may limit deer herbivory of developing buds that are obscured by the shriveled leaves. Marcescence also commonly occurs on young beech trees, which are more susceptible to deer browse.

Even in the Darkest Days, There’s a Butterfly Near You

By Kent McFarland

Mourning Cloak butterflies are one of the earliest to appear flying about in spring. They spent the fall fluttering about feeding and storing abdominal fat. Before winter arrived, they found a space to hide – in the woodpile, a hollow tree, a crack in a rock, or inside an old shed. In these protected and somewhat insulated hideouts they enter diapause, a state of dormancy. They become sluggish as the temperature drops. The freezing point of their cell tissue is lowered by an increased content of sugars, which act as an antifreeze. Mourning Cloaks produce sorbitol, a sugar alcohol obtained by the reduction of glucose. Sorbitol is also a sugar substitute that is often used in diet foods and it can also be found in plants in the genus Sorbus, represented by Mountain Ash in New England. Using electrical conductivity, biologists in Alaska found that Mourning Cloaks do not freeze until the temperature reaches -22 F, something that their cozy hideout should never experience. Learn more on the VCE Blog.

Tree Huggers

Micki Colbeck

Naturalists are often called tree huggers because—well because we are. There is nothing like throwing your arms around a big straight ash and hugging hard. This time of year however, with snow on the ground, the tree-huggers I notice are of the epiphytic bryological sort. Mosses and liverworts that call trees home, stand out against all that white and brown. One could gnash teeth trying to identify the hundreds of bryophytes found in our rich, wet woods, but a few are so common, you will see them on every hike.

The appropriately-named tree skirt moss, Pseudanomodon attenuatus, does grow like a thick skirt around the base of old trees. It’s usually higher on one side—perhaps the snowier side—than the other. Their cells have little bumps, called papillae which keep the light from passing through, and give the moss a dull green look. The branches thin out on the tips and curl up into little balls that look like dry poodle tails. This moss is abundant throughout eastern North America and Europe.

Tree-skirt Moss (Pseudanomodon attenuatus)

If you see a shiny yellow-green translucent moss with flattened complanate leaves attached to an old maple, you may be seeing Neckera pennata, the shingle moss. I use mnemonics to remember scientific names. This one is easy, because the leaves are pleated across horizontally, and look like a wrinkly neck—Neckera. Unlike the tree skirt moss, shingle moss grows higher up on the tree.

Shingle Moss (Neckera pennata)

Another species, called Porella platyphylla or wall scalewort, grows out from old trees and seems to reach up skyward like little branched fir trees. Liverworts differ from mosses in many ways, but there are three easy characteristics to look at when trying to identify one.

Are the leaves flattened in two rows—distichous, or are they whorled around the stem? Most moss leaves grow around the stem— liverworts lie flatter. Are the leaves lobed? Mosses, apart from Fissidens, never appear lobed, unlike liverworts. Do the leaves have a midrib, or central vein? Liverworts rarely do—mosses often do.

Wall Scalewort (Porella platyphylla)

Have you noticed small, tidy balls of moss growing up the sides of old trees? They are probably one of the tree cushion mosses of the family Orthotrichaceae. It is necessary to look closely at the sporophytes to tell if you are looking at the very common Ulota crispa—crispy when dry and holding a vase-shaped spore capsule up above the leaves—or the closely related Ulota coarctata, with pear-shaped spore capsules. But if the sporophytes are immersed among the leaves, you may be seeing an Orthotrichum. All spore capsules of this family have hairy caps called calyptrae when young.

So, the next time you are out skiing through an old forest and come face to face with a tree, take a break, give a hug, and see what you may see.

Hidden Jewels: Overwintering Augochlora

By Spencer Hardy

Heating season is well underway, which for many Vermonters means frequent trips to the woodpile. On a cold, blustery morning, the last thing someone wants to find is a puny, half-rotten piece of wood. However, other Vermonters seek out this degraded wood and use it to stay warm through the winter. Meet the Pure Green Sweat Bee (Augochlora pura), a common jewel-colored bee that’s likely tucked away in a log near you. Now that a hard freeze has killed the last of the flowers, the males of this bee species (and many others) are gone as well. All that remains are the fertilized females, trying to tough out the winter in a protected spot. Augochlora and several species of Metallic Sweat bees (genus Lasioglossum) have evolved to both nest and overwinter within cracks, beetle holes, and other openings of stumps, snags, and fallen logs. The larger size and bright green color of the Pure Green Sweat Bee means that it’s occasionally stumbled upon in mid-winter, when rotting logs are flipped or split. If you are so lucky, take a photo (and post to iNaturalist), then tuck her back into a similarly protected spot, where she can continue napping until early May.

Our Winter Warbler

By Kent McFarland

It is an aster in winter, spit in the wind, sun through the clouds – a force of nature called the Yellow-rumped Warbler. Find its buttery warmth even when life outside seems to groan or crunch or crack in the cold. In his tribute to “butter-butts,” VCE Research Associate Bryan Pfeiffer says that it takes guts to be a warbler in winter. Bryan describes the Yellow-rump’s “retrograde reflux of intestinal contents,” which allows the yellow-rump to eat far more than mere insects to make it through the cold. Read it on Bryan’s blog.