A too-early transformation may signal a stressed tree, says Tchukki Andersen, staff arborist with the Tree Care Industry Association (TCIA).
“Premature colors can be an indication that a tree isn’t vigorous enough to withstand insects and disease organisms that may attack it, not to mention the usual changes that occur when the weather turns cold,” explains Andersen. “Occasionally, only one or two limbs of the tree will show premature fall color. This could a sign of a disease at work, weakening only the infected limbs.”
The more common situation is for the entire tree to exhibit premature fall coloration, a phenomenon usually linked to root-related stress. “Trees respond to these stresses by trying to curtail their above-ground growth,” says Andersen.
To better understand how leaves change prematurely, think of them as small factories containing raw materials, products and by-products, all in chemical form and some with color. As the leaf is “abandoned” by the tree, the green chlorophyll – the dominant chemical found in most leaves – is broken down and “recycled,” leaving behind other colored chemicals. Supply lines to the leaves also become clogged. If the major chemical remaining in the abandoned leaf is red, the leaf turns red. If it’s yellow, the leaf turns yellow.
“The yearly variation in color intensity is due to varying weather conditions, which can affect the balance of chemicals and their composition in the leaves,” Andersen says. Differing amounts of rainfall, sunlight, temperature, humidity and other factors may have an effect on how bright, how quickly and how long “leaf-peeping” season will be in any given year.
If the leaves on your trees seem to have gotten a jump start on fall compared to other similar species in the area, it may be time to consult with a professional arborist who can identify problems and offer solutions.