All Things Natural: The Last of the Leaves
Down they come, fluttering like earthbound butterflies, the red, orange, yellow, and brown leaves of autumn. As I gaze out my office window, I see a white ash, a red maple, and an American elm standing gaunt and naked. Stripped of the leaves that clothe them grandly in summer, they look almost embarrassed in their tattered lingerie of lichens.
Among deciduous trees only tamarack, quaking aspen, and American beech still bear green leaves. But not many. Hour by hour, day by day, even their foliage succumbs to the cold, the diminishing light, and the hormonal ebbs that characterize the season.
Why, I wonder, do beeches go last? These are essentially tropical plants, heirs to a lineage of woody plants that evolved in Southeast Asia before spreading around the world. When I roamed the hot, steamy, hurricane-adapted forests of the Gulf coast as a national park ranger, American beeches were my daily companions. Now I live in northern New York, in one of the coldest places in the Lower 48. Here, although it seems a little peculiar, our continent's only native beech remains very much with me.
Logic seems to call for beech, a tree borne of balmy climes, to drop its leaves at the first touch of frost. But it stubbornly refuses to do so. Not only does it remain green longer than other trees, yielding to gold and bronze only after multiple frosts have assaulted it, but it hangs onto its leaves, typically, long after they're dead.
A dozen days short of my fifty-sixth birthday, I find my head filled with odds and ends gathered over the course of an eventful lifetime. It's a congenial clutter I carry, and it includes botanical lingo I was taught in college. For example, I can't look at a beech from October through April and not think "marcescent abscission."
Abscission is, among other things, the process by which deciduous trees shed leaves. Most of our trees form abscission layers at the bases of the leaf stems, or petioles. These bands of cells include built-in zones of weakness that allow leaves to pop off when their working lives are done.
Maples and birches practice abscission. So do beeches. But according to my botany professor at Middlebury (the guy who planted "marcescent abscission" in my brain), beech abscission layers are incomplete. And so beech leaves hang on. If wind, snow, and ice go easy on them, they keep hanging on until the growth of new leaves forces them to fall in spring.
Which inclines me to wonder, as other deciduous trees shed colorful costumes while beeches remain fully dressed, whether there's value in hanging on to dead leaves through winter. Surely the stratagem involves risks. Ice storms can be hard on beeches. Those that have retained lots of leaves have extra surface area on which heavy, damaging ice can form. Yet maybe all those corpses rattling on the twigs help keep off deer, moose, snowshoe hares, and every other animal that wants to gnaw on beech twigs and buds. Who knows? There's a Ph.D. thesis in it for someone.
Ed Kanze owns and operates The Adirondack Naturalist Company, offering full and half-day excursions into the Adirondack Mountain wilderness. He is a licensed naturalist and lives with his family in the Adirondacks. His column runs weekly in Saratoga Wire
PHOTO CREDIT: Dale Willman
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