At this time of year, the ground around my house and garden is carpeted with leaves fallen from deciduous trees. The process of leaf fall is such a dominant feature of autumn in this part of the United States that the season is usually known as “Fall.”
Since I last checked in on my red maple (Acer rubrum) tree, it has dropped all its leaves. The red maples, along with the birches, are among the first trees on my property to lose their leaves. By the end of the October, the red maple at the side of the driveway was pretty much bare of leaves – at a time when many of the oak (Quercus) and beech (Fagus) still had mostly green foliage.
The United States National Arboretum’s wonderfully clear explanation of the science of fall foliage notes that when the hours of darkness reach a certain threshold level, deciduous trees form an “abscission layer,”
a corky layer of cells that slowly begins to block transport of materials such as carbohydrates from the leaf to the branch. It also blocks the flow of minerals from the roots into the leaves.
Over time, the abscission layer becomes more and more dry and corky and the connections between cells weaken until the leaf breaks off and falls to the ground. The amount of time it takes the abscission layer to reach this point seems to vary from species to species. While my red maple drops its leaves fairly quickly, many of the leaves on my red oak (Quercus rubra) trees and virtually all the leaves on American beech (Fagus grandifolia) trees hang on until early spring.
Now that my red maple is bare of leaves, I can spend the coming months admiring its spare skeletal form and bark and watching for signs of new growth.
This post is part of the Tree Following meme, formerly at Loose and Leafy and now hosted by Pat English at The Squirrel Basket.