Don't Leaf Me This Way

For some of us, autumn stirs mixed feelings. Falling leaves, falling temperatures, cold rains and so forth remind us to prepare for the upcoming winter. They can get slippery after a rain, so watch your step. And those leaves keep on falling, getting into the rain gutters and on the lawn. People rake them up and put them in piles. Some cities allow them to be raked to the street to be picked up, and some clowns use half the street for their personal dumping ground, but I digress. Other people are able to burn the leaves, depending on where they live and whether doing so is a fire risk. Many people appreciate the fall foliage, often driving for many miles on a "color tour".
Image courtesy of antpkr /
Why do the leaves come down? Why can't the doggone trees just hold onto the things, anyway? It would be less work for us, yes? Actually, there is a purpose to trees dropping their leaves. And a science, all the way down into a sequential gene code! It's all the intricate product of the master Designer.
In Autumn, deciduous 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.
‘Leaves are designed to be disposable.’—Dr Kim Coder, University of Georgia.

The pre-fabricated ‘AZ’

The place where the leaf separates (abscises) from the tree is typically located at the base of the leaf stalk (petiole). It is called the abscission zone (AZ). The AZ is no random fracture point but is actually built-in, “pre-positioned” during leaf formation. As a publication from the University of Georgia (USA) puts it: “Leaves are designed to be disposable.” (Emphasis added.)

Retrieving valuable resources from the leaf

With the post-summer hint of coolness in the air, before the onset of wintry weather, trees initiate a “senescence sequence”2 to systematically retrieve the re-usable resources from the leaves. As this process begins, and the green chlorophyll pigment and other parts of the light-harvesting (photosynthetic) complex are dismantled, the leaf changes colour.
You can drop in and finish reading "Autumn leaves don’t Fall (by accident)".