Last weekend, the American Beech trees (Fagus grandifolia) in Falmouth’s Beebe Woods seemed to be the the only species still clinging to their now yellow leaves. In fact, many American Beech branches, particularly those lower to the ground, will cling to their brown leaves throughout much of the winter. Botanists call this retention of dead plant matter marcescence. Although most commonly observed on young trees and on lower branches, there is considerable debate about why some species, such as American Beech, would delay the physiological process of leaf shedding. Some researchers suggest that this trait is more common in areas of dry, infertile soil, and that by not dropping their leaves until the spring the trees can deliver organic material to the forest floor at a time when it is most needed by the growing parent tree. Others have posed that persistent leaves could provide some frost protection for buds and new twigs over winter.
Yellow American Beech leaves stand out in an otherwise leaf-less forest.
In addition to their still present yellow leaves, beech trees are also notable for their smooth, pale gray bark and their slender, elongated buds. The relatively smooth bark of American Beeches not only helps with winter tree identification, but is also indicative of their rate of bark renewal. In Peter Wohlleben’s book The Hidden Life of Trees, he explains that beech trees have a very high rate of bark renewal, which allows their bark to remain thin and fit the tree’s girth almost exactly, not needing to crack in order to expand. Conversely, an example of a tree with a slow rate of renewal would be a pine. Because their bark is shed so slowly, a really thick outer bark will build up. That means that the outer layers of bark originated at a time when the tree was much younger and thinner. As the tree grows and increases in diameter, the outer layer of bark must crack to accommodate the increased trunk size.
This smooth bark also protects beech trees in thunderstorms. When it rains, water flows down the smooth bark in sheets, creating a continuous film. If lightning then strikes the tree, the electricity will be carried through the film of water on the outside of the tree down to the ground because water conducts electricity better than wood. The rough bark of other tree species, such as oaks and pines, disrupts this continuous flow of water, causing the damp wood of the outer growth rings to be the best conductor of the electricity, which often caused the tree to split or crack when hit by lightning.
Smooth American Beech bark.
The shiny chestnut brown buds contain miniature leaves developing for next spring, folded in intricate patterns. American Beech leaves are pleated along the central rib within the bud casing. Because all the buds for next year’s growth are completely formed by autumn, they carry a legacy of the past summer’s conditions. Next spring’s number of leaves and the length of the shoots produced by each bud are greatly influenced by the previous summer’s temperature and moisture levels.
Elongated American Beech buds.