Leaves of Change was originally published in the BFEC Newsletter, Vol. 17/No. 4, Fall 2013.
Nothing is as constant as change itself. Whether you welcome it or not, summer changing to fall offers Ohioans a feast for the eyes. We all know that leaves change brilliant colors and fall from trees, but why?
The green that dominates summer forests is provided by chlorophyll, the pigment that allows plants to make food from the sun's energy (via photosynthesis). But lurking in smaller quantities behind chlorophyll are other pigments.
When shortening days cue trees to stop producing chlorophyll, green fades and the yellow hues of carotene pigments shine forth. Meanwhile, the declining intensity of sunlight causes leaf stalk veins to slowly close off, trapping sugars in the leaf. This revs up the production of another pigment, anthocyanin, which creates the red hues of red maple, sumac and oaks. Leaves fall from limbs once the veins are completely closed.
While declining sunlight wields the largest influence on changing colors, other factors like temperature, moisture and cloud cover play accompanying roles that interact to produce an infinite variety of color displays.
The pigment responsible for red colors, anthocyanin, is most active with sunny skies. When warm, sunny days are combined with crisp (but not freezing) colors, the reds really dazzle. Warmth pumps up sugar production in the leaf and anthocyanin pigments, while cool nights prevent the sugars from exiting the leaf through the closing leaf stalk. A wet spring and at least adequate moisture through the growing season also helps bring out the most brilliant colors.