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Why Do Some Trees Lose Their Leaves?

Trees lose their leaves to conserve energy over the winter and to prevent damage to the tree.
During the warmer months, leaves photosynthesize sunlight, producing chlorophyll.
Leaves photosynthesize sunlight in the spring and summer months.
Trees can conserve their moisture during the dry, cold winter by losing their leaves.
Some trees have leaves that change color before they fall.
A loss of sunlight causes some trees to drop their leaves.
Autumn is a noteworthy time for deciduous trees to drop their leaves.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 03 October 2014
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Deciduous trees lose their leaves every winter, rather than maintaining green foliage throughout the year like evergreens do. Often, the trees provide a radiant show of fall color before they lose their leaves, and in some regions, this fall color is a vacation attraction that visitors from all over enjoy. There are a number of reasons for leaf loss, but essentially, it happens to conserve energy over the winter and prevent damage to the tree. In the spring, the tree puts out new leaves so that the process can begin anew.

Many deciduous trees are found in regions which have cold, dark, harsh winters. Trees lose their leaves to protect themselves during the winter months, as the cold dry winds in these regions will readily strip moisture from the trees through the leaves, which have a large surface area. By losing their leaves, trees can conserve their moisture in the trunk and branches, rather than drying out and dying. In addition, the leaf loss puts the tree into a state of dormancy, and greatly reduces the amount of energy that the tree needs to stay alive.

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During the spring and summer, leaves photosynthesize the plentiful sunlight that falls on them, producing chlorophyll, which turns them green. The photosynthesis provides energy for the tree, and the tree feeds the leaves with nutrients it takes up from the ground to keep them healthy. The bright yellows, oranges, and reds that make fall color distinctive are actually already there all the time, but the chlorophyll masks them. As the days get shorter, the trees have less sunlight to work with, and the efficiency of the leaves starts to decrease. The leaves fall because they become a draw on the energy of the tree, as the tree would otherwise have to feed the leaves through the winter.

As the nights get longer, trees make preparations to lose their leaves, starting with the secretion of chemicals to cut the leaf off from the rest of the tree. As the leaves stop producing chlorophyll, they start to change color. Ultimately, trees lose their leaves once the chemicals they secrete have effectively cut the leaves off from the parent branch. These chemicals, primarily ethylene and abscisic acid, make the leaves fall by severing the link between the leaf and the tree. The leaves fall to the ground, providing a layer of protective mulch to insulate the roots, and the tree conserves its energy for the next year and a new growing season.

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lighth0se33
Post 21

I have a few trees that don't lose their leaves in my yard. I have several cedar trees that stay green year round, as well as a field of pine trees. My neighbor has some blue spruce that are gorgeous in winter, because they retain their foliage and their color.

However, the majority of my trees do shed their leaves. They just look so bare and ghostly against the cold sky! That's why I'm glad I do have a few green ones left during the winter.

Snow looks really cool on both kinds. On the skeleton trees that are bare and gray, it looks like a like frosting. On the evergreen trees, it looks like flocking!

feasting
Post 20

@giddion – I live in Mississippi, and I can tell you that fall does arrive later here. We have temperatures in the eighties well into October, so generally, we don't even see the beginning of the leaves changing color until the middle of October.

The trees that lose their leaves start shedding them on a major scale in the middle of November. By Thanksgiving, there will be a blanket of brown leaves on the grass.

I think that the warm climate here keeps the leaves from changing until late in the season. It's always interesting to travel northward in fall and watch the colors deepen along the way.

giddion
Post 19

When do trees lose their leaves in the southern United States? I know that in the northern region, they start to turn colors in September and fall soon afterward.

I've been as far south as northern Kentucky in the fall, but I've never traveled into the deep south. Can anyone tell me what autumn is like down there?

OeKc05
Post 18

This article is fascinating! I never knew all that was involved in the process of shedding leaves. I will look at deciduous trees differently now.

anon291769
Post 16

Is it the trees or the leaves that produce oxygen?

anon163013
Post 14

Your tree is suffering from a disease called the dutch elm tree disease.

anon123578
Post 13

what kind of trees lose their leaves?

anon115342
Post 12

Why do some trees lose their leaves earlier than others?

anon84799
Post 10

I have three trees in my back yard that are losing their leaves already and it is May in Minnesota. I noticed over the last two years branches were breaking and I at first thought it was from storms but now I am concerned they are dying?

anon74761
Post 9

why is that some trees lose their leaves in spring?

anon52141
Post 6

The changing of the colour of leaves is triggered by the shortening day length. If some trees are near street lights this can prolong the time before senescence and abscission because the trigger for it is not yet present.

neilc
Post 5

I posted these comments anonymously, but I registered now so I'll put them under this name. Just two notes: 1. Abscisic acid is not believed to be involved in leaf abscission any longer, as it says in your own article on abscisic acid. 2. Leaf color comes not only from the revealing of carotenoids already present in the leaves, but also from anthocyanin pigments produced in late summer that are not present earlier in the season. Great site, I am enjoying browsing your material!

anon19543
Post 1

Why is it that some trees, of exactly the same type, planted, for example in the same street, lose their leaves quicker than others? Some in our street are already yellow and have started to fall, while others are still almost completely green?

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