Scientists don’t yet fully understand all of the complicated actions and interactions that produce the spectacular displays of autumn leaf colors that are a highlight of the fall months. Although not fully understood, several factors affect when and how tree leaves change color and the hues they produce. These factors include:
- Shortening of day length
- Cooling temperatures
- Organic pigments in the leaf cells
- Sunlight intensity
- Tree genetic traits
- Site characteristics
Why are fall trees more intense some years?
Cool Night Temperatures
An extended period of cool night time temperatures below 45 degrees but above freezing helps to develop more anthocyanins in the leaves bringing out more intense fall colors in trees.
Bright sun filled days allow the leaves to trap the sugars from the dwindling chlorophyll creating fantastic fall color.
Stormy and windy days help to release the leaves on the trees. An extended period of calm days help to enhance the viewing time of fall foliage.
Original article at the Arbor Day Foundation.