Trees with Leaves in Winter – Is It Possible?
The brilliant colors of Fall entice each one of us to get outside, go for a walk, and enjoy the beauty around us; and when we begin to see trees start to shed those colors, we know winter will soon be upon us. But what if those leaves haven’t yet fallen by February?
Abnormal weather patterns during the end of fall and early winter can cause trees to adapt in ways you may not expect. One way this may manifest is in trees holding on to their leaves much longer than you’d consider ordinary.
Trees That Lose Their Leaves
Maple, birch, willow, oak, hickory, dogwood, and redbud are all examples of deciduous trees, meaning that they periodically shed their leaves– namely, during the fall. The end of the summer usually brings a wave of color: beautiful yellows, oranges, purples, and reds. Some trees with longer-lasting leaf drops change their shade of color over the course of many weeks before finally falling; other trees’ leaves will turn brown and drop quickly, with much less in the way of a colorful show.
Why Might Some Trees Not Lose Their Leaves?
Are you wondering why your trees that normally lose their leaves during winter months still have leaves on them? Weather is the primary cause of your tree still holding onto its leaves.
When we’re talking about trees, the term persistence describes any tendency for something to stay put on a tree instead of falling. Fruits of crabapples are often persistent, which is less common for the larger apples on a typical apple tree since larger fruits are more prone to falling due to their weight and gravity’s influence. This persistence makes crabapples a great source of winter nutrients for deer and other wildlife. Oaks and beech trees are particularly persistent trees in that they consistently hold on to their leaves well into the winter and often until the next year’s new growth pushes the old leaves off.
There is another term that describes persistence when that trait is not a normal occurrence for that kind of tree. This is termed marcescence. Marcescence describes occasions when leaves would ordinarily fall off a tree you’re familiar with, but for some reason aren’t doing it now.
What Happens When a Tree Doesn’t Lose its Leaves?
First, let’s understand why trees lose their leaves in the first place. Trees that lose their leaves in the winter, deciduous trees, go through a series of changes as the weather cools and the length of daylight shortens; changes which enable them to drop leaves. Short and sunny days and cooler nights trigger a tree to accumulate sugar (to store for energy) and to decrease the production of chlorophyll (the compound that makes leaves green). The combination of more sugar and less chlorophyll unmasks other pigments contained in different leaves. This change in trees brings out the beautiful colors of autumn. Meanwhile, other cell changes cause leaf stems to form abscission zones, where they prepare to allow the leaf to “break off” and fall. This abscission zone also protects the newly exposed area on the stem, where the leaf was, from pests and pathogens.
Trees with leaves remaining in winter can be a result of temperatures dropping too rapidly in early fall. When this change is abrupt, leaves are killed instantly– going from green to brown. Those abscission cells do not form as they normally would, then, within the branches, altering the leaves’ ability to fall– resulting in leaves holding on during winter. Eventually these leaves will fall and the tree will begin its normal spring growth when the new growing season begins.
When Do Trees Lose Their Leaves in Wisconsin?
The past few years we have seen warmer weather extending later into the fall time frame in Wisconsin. The change in weather with cooler temperatures is one key to trigger leaf drop for deciduous trees. The temperatures provide an indicator for trees to prepare to enter their dormant winter state. However, with temperatures remaining warmer, that trigger is not recognized as readily so trees’ abscission cell formation is interrupted. Without those cells, leaves may persist on branches until they are forced off by wind or other factors.
Trees with leaves in winter can also be a result of a tree whose energy is so focused on growth that it doesn’t prepare for winter. Untimely use of excessive nitrogen fertilizer to assist the growth of a tree late into the growing season can cause this delayed dormancy.
If your tree still is holding its leaves in winter don’t be alarmed. In most cases, trees resume their usual seasonal changes when normal weather patterns return. Please contact a Wachtel Tree Science Certified Arborist for a consultation when you have questions about your trees, especially if something doesn’t look normal with your tree!