Science and nature

INFORMATIONAL: This passage is from the essay "What the Beeches Keep" by Nadia Ferreira-Holm. (Original practice text; the author, the work, the people and the place are fictional.) Line numbers appear in the left margin every 5 lines.

Every November, the woods behind my house on Calder Ridge go gray and bare, all except for the young beeches. While the maples and ashes drop their leaves within a week or two of the first hard frost, the small beeches along the creek hold on to 5 theirs. By January the leaves have faded to the color of paper bags, and they rattle in the wind with a sound my daughter once compared to someone turning the pages of a very old book. Many of them will still be hanging there in April, when the new buds finally push them off. 10 Botanists call this habit marcescence, from a Latin word meaning "to wither." A marcescent leaf dies on schedule, like the leaf of any other tree that sheds its leaves each year, but it does not fall. In most such trees, as autumn days shorten, a layer of special cells forms where each leaf stalk 15 joins the twig. These cells weaken the connection until the leaf drops at the slightest touch. In a marcescent tree, that layer does not fully form before winter, and the dead leaf stays attached, sometimes for months. For years I assumed the beeches were simply slow, that 20 they had been caught by winter before they finished the work of letting go. What made me doubt this was the pattern. On Calder Ridge, the trees that keep their leaves are almost always young ones, rarely taller than twice my height, and on the older beeches the dead leaves cling mostly to the lowest 25 branches. If the trees were merely running late, I would expect lateness to strike at random. Instead, the habit seemed to belong to a particular age and a particular height. Scientists who study marcescence have offered several explanations, and the question has not yet been settled. One 30 possibility is that the dry leaves protect the buds of young trees from deer and other browsing animals, which may find a mouthful of papery leaves less appealing than a bare twig tipped with buds. Browsing animals can reach only so high, which would fit my observation about the lower branches. 35 Another possibility concerns nutrients. A leaf that falls in autumn lies on the forest floor all winter, and much of what it releases as it breaks down may wash away before the tree can use it. A leaf that falls in spring, by contrast, would begin breaking down just as the tree's roots are becoming 40 active again. A third idea is that the leaves catch snow and so gather extra moisture around the base of the tree. Last winter I tried, in a small way, to test the first idea. I chose twenty young beeches along the creek and, with my neighbor Oren Stabile, pulled every dead leaf from ten of 45 them in December. The other ten we left alone. Each week we walked the row and counted the buds that had been bitten off. By March, the trees we had stripped had lost about three times as many buds as the trees that kept their leaves. I would like to say that this proves something, but I know 50 better. Twenty trees on one ridge in one winter is not a study; it is a hint. The deer on Calder Ridge might have favored the stripped trees for some reason I did not notice, such as their position along the path the animals travel. And even if the leaves do discourage deer, that would not rule out 55 the other explanations. A habit can serve more than one purpose, and a tree that keeps its leaves for one reason may benefit from them in several ways. Oren, a retired surveyor who distrusts any conclusion that cannot be measured with a tape, says the only thing we have 60 learned for certain is that deer prefer an easy meal. Maybe so. But I walk the creek differently now. When I hear the beech leaves rattling in February, I no longer hear a tree that forgot to finish its autumn. I hear a question that the tree has been answering, one way or another, for a very long 65 time.