By Lawrence J. Winship Gazette Contributing Writer
I really enjoy fall in the Pioneer Valley, for so many reasons—the changing and changeable weather, a shift from producing to storing away and, of course, the marvelous color show. I watch trees in all seasons, just as some folks watch birds, with the advantage that trees don’t move around nearly as much. Each tree is an individual, its shape and size influenced by more than just its species. Sure, looking closely one can assign each tree to a taxonomic category, but the ravages of time, weather and competition with near neighbors all play a role. A tree’s bark, limb arrangement, girth and wounds make each as unique as each of us. I watch to notice differences one day to the next, and in fall, wow! Do these changes speed up!
In the summer, trees all wear a camouflage coat of greens and browns. Looking at a hillside from a distance, one can often pick out hemlocks and pines. But it is sometimes hard to see where one hardwood species leaves off and another begins. As autumn progresses, first the red maples break cover, sporting scattered scarlet branches here and there. Finally yielding to the imperatives of temperature and day length, they soon become deep red all over. An exclamation point, red maples drop the starting flag on color season.
Soon sugar maples and birches join in, turning similarly to a brilliant yellow—but I can tell them apart, even at a distance. Sugar maples are among nature’s first photographers. The leaves exposed to the brightest sun turn orange and finally a bold red as anthocyanins are synthesized in response to light. Close up, one can peel back a bright red leaf to find a greenish yellow “shadow” on the leaf below. Ash leaves do the same thing, with reddish purple leaves casting yellow shadows. On a whole tree the sequential shading from red to orange to yellow to green calls to mind an impressionist painting, layer upon layer of paint globs dancing in the low-angle autumn light. Give me a grove of sugar maples with a light glaze of moisture from a passing shower, just before sunset, against an azure sky, and I am transfixed.
Another of my favorite trees looks like a stained-glass window in the apse of a great cathedral. Leaves of the black gum, often called tupelo, each turn at different rates. At one point in each season these trees sport shiny little patches of greens, yellows and reds all on the same branch, a crazy quilt of pigment.
Ginkgos, while not native to our continent, are ever-welcome guests at our feast of color, turning a translucent yellow that seems to glow. In fact, some of the pigments in these leaves are colorless to our eyes, yet are fluorescent. They absorb light we don’t see and then re-emit that light, adding to reflected sunlight.
Eventually, all too soon, all of the leaves on each tree senesce completely and the little layer of fragile cells that seals off the leaf stem from the branch, the abscission zone, forms completely. Fall really begins.
Depending upon the conditions during the growing season, some leaves hang on longer than others. Some are diseased, as many were this year, by a fungus that causes premature browning and leaf fall, robbing us of a full display. Ginkgos have another trick. On a very still morning, after a cold clear night, at dawn, as the first light brushes the tree, the leaves will begin to fall. Silently, one by one, they let go and drift to the ground. While you can see the same leaf ballet performed by other species, the leaves of ginkgos seem to be ready to go almost all at once. So, if you are there at the right moment, a gentle tap on the trunk—and all of the remaining leaves will rain down upon you in a golden cloud.
But maples, birches, ash and hickory are not the end. In time beeches turn a glorious yellow-brown and their cousins, the oaks, bring out the deep umbers and burgundies. Some oaks produce scarlet reds that rival the maples and whole hillsides proclaim the last crashing chord of color before winter’s white. We are surrounded by an abundance of woody diversity—we just don’t notice until the razzle-dazzle of autumn.
Happy fall! And enjoy walking with a crunch below and color above.
Lawrence J. Winship, a member of the Hitchcock Center board, is a professor of botany in the School of Natural Science and director of the Southwest Studies Program at Hampshire College.
Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week. For more information, call 413-256-6006, or write to us.Click here to return to full list of Earth Matters articles.