Why do Trees lose their Leaves?

Deciduous trees with and winter sunset
Deciduous trees and winter sunset

A long time ago, Kam asked me about trees losing their leaves.  In fact, so long ago they are beginning to bloom again.  It’s time to find out, before I need to answer questions about springtime blossom!

Falling Autumn leaves, glorious colours everywhere, but what’s it all about?

Trees losing Leaves

Autumn Leaves in the Park
Autumn Leaves in the Park

Every season many trees, though not all, lose their leaves.  At the end of summer, suddenly there is a nip in the air, or a fresher breeze.

Trees detect the change and act upon it.  They need to. Their delicate leaves, rich in nutrients, energy, water and full of life in the warmer months, could not withstand the change in season.

Before the tree loses it leaves, called shedding, it reabsorbs all the nutrients from the leaves, storing them in its roots to use later and to kickstart regrowth in springtime.  All this is part of a process called abscission.

Autumn leaves in wood
Autumn leaves

Hormones and enzymes in the trees begin abscission.

Chlorophyll, which gives leaves their green color, nitrogen and phosphorus are some of the absorbed nutrients.   The reabsorption  of chlorophyll is one of the reasons why trees turn red, orange, and gold colors in Autumn.

Then leaves are actually cut off by specialised cells in the tree.  A protective layer of cork cells grow over the area exposed to the elements by the fallen leaves.  This protects the tree trunk and branches.  It’s almost like the tree battens the hatches for the onset of winter.

Trees in spring
Springtime trees

Until spring time, the tree is dormant, conserving its energy and nutrients and using only what it needs.  In spring, stored nutrients spur new buds, branches and leaves until photosynthesis begins and brings fresh nutrients to the leaves and on to tree.

In climates which have cold winters, many trees species lose their leaves with autumn’s cooler weather. Trees that lose their leaves are  deciduous trees.

Long ago there would have been large forest areas.  most of these have disappeared due to farming and encroaching populations.  Deciduous trees are found in Asia, Europe and North America.

Winter trees
Wintertime trees

Also, deciduous trees are found in many sub-tropical and tropical regions which have heavy seasonal rainfall.

They lose their leaves at the start of the dry season. Such trees are common in the savannas and woodlands of Africa, South America and Asia.

A Note to You and Me

Shedding – to have a growth or covering fall because of a natural process.

Abscission – has the same Latin root word as that in scissors, scindere, which means “to cut.”

Deciduous – “the dropping of a part that is no longer needed” or “falling away after its purpose is finished”

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