Fall Leaves

Have you been watching this season?
This has been one the the most spectacular autumns, the kind you remember fondly for years to come. How the vibrant colors come as a wave until we've been overtaken with gem-tones: the deep yellows, rusty oranges, dark burgundy, and the surprising maroon. 
First it was the bright yellow leaves of the honey locust and the walnut, then the sugar maples beginning from the tips of the branches moving inward, the hickories follow with the large yellow leaves and mast falling with every gust. The mighty oaks are just now coming into their glory (from where I sit today), their color forming more sporadic patterns than the maple gradients. This entire fall season I've also been watching the pines, red and white, they too have been turning - the needles closest to the trunk are slowly turning brown and forming the soft blanket at the base of the tree.
Of course there are many many many other types of trees putting on many different color displays, these are just the ones in my immediate view.
What does your season look like?

Why and how do the leaves change?

As the hours of daylight get shorter and the temperatures begin to drop, the trees no longer have the resources needed to continue making chlorophyll, so they begin the process of going dormant for the winter.
Chlorophyll is what gives the leaf its green color and what absorbs energy from the sunlight turning carbon dioxide and water into sugars and starch for the tree to “eat”. 
As the light and temperature change, the leaves stop making food for the tree and the chlorophyll breaks down exposing other pigments in the leaves.

Green: Chlorophyll
Yellow & Orange: Carotene
Red & Purple: Anthocyanins

The tree begins adding an additional layer of cells where the leaf stem attaches to the tree, sealing off the connection and creating a “leaf scar”. As the wind drifts by, the leaves then release and fall to the earth. 

Not all trees release their leaves - some oaks and beech trees will hold on to their leaves until the new growth begins the following spring. This is a process called marcescence. 
There is much debate about why they do this but we do know a few things…
It mainly occurs on juvenile trees. These trees often grow on dry, infertile sites. These trees are all in the same family (Fagaceae), this family also includes some evergreens. If there is an ecological benefit to holding on to these leaves, it has yet to be clearly defined.

Why are some years full of bright leaves and others brown?
The weather has a lot to do with the intensity of leaf color. Low temperatures that stay above freezing favor the formation of anthocyanin in leaves which produces the bright reds in maples. 
Early frost, however, will weaken the bright red colors.
Rainy and/or overcast days are great for observing fall colors as the gray backdrop really shows off the intensity of fall colors.