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Why do Leaves Fall in Autumn?
The question may sound funny, but have you ever asked yourself? And it leads to another question: why do conifers never lose his leave. Let’s have a scientific look around!
The falling of leaves in the autumn is proof that nature is intelligent! Most trees don’t lose their leaves on a whim – they do so out of necessity. This mechanism of falling leaves is, in fact, vital for the tree’s survival, allowing it to protect itself from the winter cold.
To best confront the cold, trees must slow down their growth.
Everything which uses up energy is therefore sacrificed. Like the trunk, the branches and the roots are well isolated from the cold, they need hardly any energy to stay alive. Leaves, on the other hand, consume enormous amounts of energy in an effort to resist the cold. To save energy, these sources of energy waste are therefore eliminated by the tree.
The alarm is sounded off when the weather becomes colder and the days shorter. The leaves contain sensors which send this information to the tree by producing an excess of ethylene. The tree senses that the cold is coming back and it secretes a plethora of small corks which appear in the leaves’ peduncles, thereby cutting off the supply of sap.
Leaves and nutrients
The leave has thus their supply of water and mineral salts severed and are therefore unable to produce chlorophyll by photosynthesis. They gradually change colour from green to their original red and orange colour. When they become too weak, they dry out and fall naturally with the first gusts of wind. The scars that they leave on the branch are quickly filled in by a fine layer of isolating cork.
The tree thus isolated can now concentrate its sap in its vital organs to better fight off the cold weather. This natural mechanism can be seen every autumn in regions which undergo temperatures which vary greatly with the seasons.
Conifer trees are better armed to protect themselves against the cold. Their leaves are covered with a fine layer of isolating wax, rendering them harder and stronger than the leave of other types of trees. They also possess particular substances which make them more resistant to the cold. As they protect themselves naturally, they are not considered as energy-wasting elements. Therefore, the tree allows them to survive because they don’t prevent it from slowing down its growth in winter.