In Autumn, trees don’t lose their leaves—they loose them.
It is the final
step in a highly ordered and carefully controlled process initiated in preparation for a resting period (winter) in above-ground
portions of the tree.
The place where the leaf separates from the tree is called the
abscission zone (AZ). This separation or abscises is located at the base of the leaf stalk (petiolle). This fracture
point is built-in during leaf formation. Leaves don't just fall, there is a complicated chemical process that is designed
by God that allows nutrients to be recycled.
What's hiding under those green leaves just waiting to shine?
At the first hint of coolness in the air the trees begin to retrieve the re-usable resources from the leaves. As
this takes place the leaves begin to change color as initially the chlorophyll is drawn out. The green color of the chlorophyll
had been hiding the yellow and orange pigments (xanthophyll and beta-carotene) and as the tree draws the chlorophyll out,
the other colors that were there all the time are now displayed. When half of the chlorophyll is gone and the phosphate in
the leaves drops, anthocyanin pigments are produced which gives the leaves the beautiful deep orange and fiery red colors
to the leaves.
The recycling begins.
nutrients that the tree extracted from the leaves are stored in the roots, trunk, and branches. Next spring these are recycled
for leaf production. In order for all the nutrients from the leaves to be extracted this must take place before frost or freezing
temperatures as the cold will kill the leaves, along with the nutrients.
After the completion of the extraction of nutrients, the abscission
zone (AZ) becomes very active. The AZ is triggered by a bunch of chemical signals coming in that tells it to begin to secrete
enzymes that begin to loose the leaves. These enzymes dissolve the "glue" that holds the cells together and begin
to degrade the wall between the cells. With the weakening of the walls of the cells, along with increased internal water pressure,
the cells begin to swell. This causes tremendous shear forces which cause fracture lines between the cell walls. Wind, gravity,
rain and animal interference tug on these fracture lines, causing the cell walls to pull apart and open up the fracture line.
After the used up leaf falls, the tree begins to heal the open wound along the fracture line by depositing protective
material (tyloses, suberin and lignin) to seal off the leaf scar, defending it from cold, disease, and pests.
This information came from https://creation.com/autumn-leaves-fall-by-design.
I would recommend reading the entire article.