Illinois Arboretum, fall 2014.
I like to press fall leaves so that they dry out and keep their color. Every year I’ll pick up leaves that are especially striking and stuff them in heavy books until further notice. Sometimes at the end of the school year I’ll find some still hidden in the back of a textbook. I learned about pressing leaves from my dad, so you can thank him for this topic.
Illinois is home to many deciduous trees, such as oaks, maples, elms, ash, and hickory trees. Deciduous means that they shed their leaves annually.
Leaf growth is actually all about planning ahead. By the time a tree has leafed out for the current year, the buds for next year’s leaves have also been prepared. The tree then spends its leaf season collecting carbohydrates that will be used for next year’s growth. The carbs are stored in the buds, roots, and branches.
The green color in tree leaves (and most of nature, for that matter) comes from chlorophyll. Leaves can actually fade in the sunlight like ink or cloth does over time, so the chlorophyll is constantly being renewed.
Trees are very sensitive to the length of each day and begin to transition when the nights are long enough. Cells in the leaf stem divide rapidly but do not expand, meaning that they become less and less attached to each other. Over time, transport of carbohydrates from the leaf to the rest of the tree, as well as minerals from the roots to the leaf, becomes blocked. Production of chlorophyll also stops around this time, revealing other colors in the leaf.
Leaves already contain xanthophylls and carotenoids, or yellow and orange pigments. Red and purple pigments come later from anthocyanins that are produced by the sugars (carbohydrates) that stopped being transported and got trapped in the leaf. Tannin, the brown pigment you see in dead leaves, is the only pigment that remains when all the others have broken down in the same way the chlorophyll did.
Temperature, soil moisture, and amount/intensity of sunlight affect the amount and variety of fall colors. The warm and sunny fall we’ve been having here in Champaign will make a difference in the colors we see compared to last year.