Why Do Trees Lose Their Leaves in Winter?

Leaves are nature’s food factories, plants’ powerhouses. Plants, including trees, take up water from the soil through their roots. They take in a gas called carbon dioxide in the air through small holes (pores) called “stomas” in their leaves. Plants use sunlight to convert water and carbon dioxide gas into glucose, a type of sugar. They form oxygen as a byproduct of this process. Plants use sugar as food, for energy and for growth. This process in which plants convert water and carbon dioxide gas into sugar is called photosynthesis. If there isn’t enough water around, the leaves can fail to function or be damaged, so they become a burden to the planet and shed their leaves to stay in better shape without these organs. Trees that lose (all at once) their leaves are called “deciduous trees” if the process occurs regularly or is seasonal. There are also trees that are evergreen, losing a few leaves at a time and staying green all year. These types of trees are called “evergreen trees”.

Leaves Are Shedding to Prepare for Winter?

By the end of autumn, most deciduous trees lose their leaves for the winter season. There are also a few deciduous trees that tend to shed their leaves in the fall. There are actually three common situations in which defoliation occurs.

-The first is the shedding of leaves in winter. The main reason most trees drop leaves is because that part of the world is pretty cold and dry when winter comes. During the winter months, especially in the northern hemisphere, precipitation is low and most of the water available to the plant freezes in the ground. If there is no water, it is better for the plant to lose its leaves, and moreover, the leaves can be damaged by cold and frost. Instead of wasting energy, trees shed their leaves to conserve resources. Fallen leaves help add nutrients to the soil. Therefore, leafless woodlands are common in our country, due to the European and North American winters and mid-latitudes.

-The second situation is the shedding of leaves when there is drought. Arid but caused by warm or hot climatic conditions. Many tropical or subtropical regions can experience notable dry seasons between the rainy seasons, which bring most of the annual precipitation. During these dry seasons, the forest dries up and some trees lose their leaves.

Leaves Change Color Before Falling

As with most things in nature, the behavior of trees depends on the sun. When trees detect a decrease in the amount of daylight, they begin to reduce the amount of chlorophyll they produce. Chlorophyll is the pigment that makes leaves green and is the primary energy producer for almost all plants. Before plants lose their leaves, they try to recover as many beneficial components as possible. The first component to be recovered is chlorophyll, which gives the leaves their green color. When chlorophyll production stops, it is broken down and taken back into the tree. As chlorophyll is recovered from the leaf and reabsorbed into the plant, other pigments (such as yellows, oranges, and reds) that are always present in the leaves but not visible due to excessive amounts of chlorophyll become visible. Therefore, in the autumn season, the color of the leaves changes from green to orange, yellow (when we can see the carotene pigments) and even red or purple (when we can see the anthocyanin pigments). The leaves often change color in this order. When all of the chlorophyll and potentially other pigments are recovered, the leaf dies. As the leaves dry, they begin to look brown and become brittle. At this stage, the leaves fall from the tree. Leafless trees or plants go into a reversible dormant state when new leaves grow, water and/or light become available again, and the cycle begins once again.

Why Do Trees Lose Their Leaves in Winter?

The falling (falling) of leaves from trees is called abscission. Low temperatures in winter cause slow production of auxin, the hormone that helps plants grow, causing them to turn towards the sun to absorb more light. Trees form a layer of cells known as the abscission layer between the petiole and the tree branch to adapt to the color change in the leaves seen during the recovery process of beneficial components and prepare for shedding. This layer stops the transport of nutrients and water to the leaves, becoming the main physical cause of trees losing their leaves. The abscission layer also helps protect this sensitive area of the plant from the cold and dryness of winter.


In some areas there are some trees with leaves that are dry, brown but still clinging to the tree throughout the winter. The corresponding term is “marcescence”. The abscission layer on these trees is not fully formed until spring, which allows them to keep their leaves much longer. Marcescence almost always occurs in sexually immature parts of the tree (parts that have not yet formed flowers). Generally, trees exhibit marcescence feature when young, but lose this feature as they age. As such, there are some oak species that do not shed their leaves in winter. It is also common for only one part of a tree to retain leaves; Usually the leaves remain on the branches closest to the ground. Some trees exhibit this behavior, such as white oak, marsh white oak, American hornbeam or blue beech, American rock or Iron Tree.

Is There Any Benefit From Keeping Leaf?

There is no real consensus among researchers as to why some tree species retain their leaves, but there are a number of theories. The most important of these is that keeping the leaves protects the buds of next year against deer or the drying winds of winter. As a result, trees with marcescent properties lose their leaves in the spring, while new plant parts push old leaves off the branches.


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