Why Are the Leaves Hanging On? by Susan Camp When You Live Among

Why Are the Leaves Hanging On? By Susan Camp When you live among many trees, you tend to think of them as a backdrop for the rest of the environment: house, lawn, garden, deck, outdoor furniture, and anything else on the property. If you look closely, you will see that the various species don’t always perform in the same way. They don’t all bud, leaf out, change color in fall, and drop their leaves at the same time. In fact, you may have noticed that some deciduous trees don’t drop their leaves at all until spring. Pale, papery leaves remain firmly attached to the branches until the new leaf buds appear. Jim and I first observed this phenomenon about 15 years ago when the young beeches and some of the oaks in our woods kept their leaves throughout the winter. We commented on the occurrence each year, but didn’t feel the need to research the topic until last fall, when one of our two dwarf Japanese maples (Acer palmatum) didn’t lose its leaves and the other one did. Pale reddish-brown leaves still remain on the tree, as they do on many young beech trees in the woods. A white oak behind the house used to retain its leaves, but no longer does so. What is this phenomenon and why does it occur? I found some answers by accident while researching another topic. The term for the retention of dead plant parts is marcescence, from the Latin root meaning, “to shrivel.” While marcescence can refer to retained flower parts or seed capsules, the word usually describes leaves of deciduous trees and shrubs that do not detach in the fall. Trees most often affected by marcescence are American beech (Fagus grandifolia), hornbeam (Carpinus), hophornbeam (Ostrya), witch hazel (Hamamelis), and many species of oak (Quercus). As the weather begins to cool at the end of summer, cells located at the junction of a twig and the end of a leaf stem, called the abscission layer, release enzymes that seal off the point where the two structures interface. Over time, the abscission layer weakens, and then disappears, and the leaf drops off. Sometimes, an early cold snap or frost will occur before the abscission process is complete and the leaves will remain on the trees. This is what may have caused marcescence in our one Japanese maple. In years, without an early killing frost, the reason for marcescence remains a matter of scientific speculation. The simplest explanation is that the age of the tree may dictate the occurrence of marcescence, but several related, underlying reasons are offered in the literature. Winter leaf retention may provide protection for young trees from the drying and destructive effects of harsh winds. Snow that is trapped in the branches provides water and helps prevent dehydration during the cold season. The old leaves are dry and bitter and offer little nutritional value, so by concealing the new spring growth, retained leaves discourage deer and other browsers. The rustling, rattling sound the old leaves make may discourage animals from feeding on or around the marcescent trees. A newer theory of marcescence involves nutrient cycling and availability of nutrients. Some scientists believe that juvenile understory trees with small root systems can’t compete with larger trees for nutrients, particularly if the soil is poor. The young trees may benefit by not releasing their leaves until spring, when the decomposing leaves will add extra organic matter around the root systems. Whatever the scientific reason for marcescence, the phenomenon provides some color, texture, and sound in the midst of the winter quiet in the woods. Some interesting articles on marcescence include “Winter Leaves that Hang On” from the Center for Private Forests, Penn State College of Agricultural Sciences; “When Leaves Don’t Leave” from the Arnold Arboretum, Harvard University; and “Marcescence: An Ecological Mystery” from “The Adirondack Almanack.” February 13, 2020 .

Load more