How Do Trees Survive Winter? The Science of Dormancy

What happens when trees shed their leaves? And why don't all trees do this?

French Broad River and dirt road, Hot Springs, NC
WendyOlsenPhotography / Getty Images

What happens when trees lose their leaves in autumn and remain bare throughout the winter? Are the trees still alive?

Deciduous trees survive winter through a process similar to hibernation, called dormancy. Certain conditions need to be in place for dormancy to occur. Here, we examine how trees live through winter.

What Is Dormancy?

Dormancy is similar to hibernation in that all the parts and processes of the plant, including the metabolism and energy consumption, slow down.

According to the Michigan State University Extension, there are two types of dormancy: endo-dormancy, when growth is inhibited regardless of the growing condition, and eco-dormancy, when day length and temperature impact growth inhibition. While plants in endo-dormancy rely on internal chilling requirements and develop cold hardiness, plants in eco-dormancy remain there only during cold weather, typically when temperatures are below the mid-40s.

Trees enter the first stage of eco-dormancy during seasonal temperature and day-length changes. These environmental signals ultimately cause deciduous trees to lose their leaves. Leaves, flowers, and fruit require energy to maintain, which is why they shed them in colder months.

When the trees lose their leaves, a chemical called abscisic acid (ABA) is produced in terminal buds—the part at the tip of the stem that connects to the leaf. ABA is produced in both deciduous and coniferous trees. It suspends growth and prevents cells from dividing—another key component of dormancy. It also saves a lot of energy to stall growth during the winter.

Why Dormancy Helps Trees

It is possible to force a tree to evade dormancy if you keep it inside and with a stable temperature and light pattern. However, this is usually bad for the tree. Dormancy ultimately keeps the tree alive, both in the short- and long-term. The lifespan of a tree or plant is dramatically decreased if the tree isn't allowed to go dormant for a few months.

Just as bears use hibernation to survive without their usual resources in warmer months, trees use dormancy to protect themselves so they can grow again in the warmer months.

Do All Trees Go Dormant in the Winter?

Close up image of a snowy evergreen tree in winter
Jeja / Getty Images

You may be wondering about trees in your area that tend to retain their leaves during winter. Those are likely evergreen trees, which do not undergo the same dormancy period that deciduous trees go through.

However, evergreen trees may drop some of their needles after a few years of maturing or if the trees are stressed due to various conditions.