Even as a 7 or 8 year old girl, I could sense that a profound change was in the air. There were still plenty of hot days of summer vacation left, but every once in a while a cool day would sneak in to remind me that Fall was coming, and the long days of playing outside with friends in the prairie, roller skating, playing Green Ghost, Hide and Seek and catching lightening bugs was about to end. Our legs and arms would be loaded with mosquito bites with little regard for what kind of diseases we might contract and the only treatment for the itch was a pink pasty film of calamine lotion on our skin. Night arrived faster as summer waned, shortening our time outside each evening.
Sometimes the temperatures of Labor Day weekend would send people back to work and school with sunburned faces and shoulders, and other times it was too cool to enjoy the last swim of the summer. No matter what, the changing temperatures were a signal that the leaves would soon be changing color and Fall was imminent. I think the brilliance of trees in the Fall is the present we receive for losing the lovely, warm days of Summer. The Sumac leaves in the image attached to this blog post are some of the first to transform their color each year, announcing that change is upon us.
Brilliant SumacSumac is one of the earliest trees to change color in the Fall. In the right lighting conditions, the leaves glow with shades of red, orange and yellow.
Multiple variables interact to produce the Fall color display each year. According to the U.S. National Arboretum, during the Spring and long days of Summer, chlorophyl is constantly replaced in the leaves, giving them their green color and storing the nutrients they will need for the next year. As the nights get longer in the Fall, the cells near the intersection of the stem and leaf divide rapidly but do not expand, creating a layer called the abscission layer. This layer blocks the transport of nutrients from the leaf to the branch and from the roots to the leaves. Since there is no transfer of materials, the chlorophyl gets blocked from the leaves and the green pigment disappears, which makes the yellow and orange colors more visible. Red and purple pigments from the sugars are trapped in the leaf and together this change results in vivid, Fall color. As Autumn progresses, the cells in the abscission layer become dry and corky, causing the leaves to break off from the stem and fall.
According to accuweather.com, cool air at night with abundant daytime sun increases the formation of more red and purple pigments, but freezing conditions destroys the leaf's ability to manufacture them. Early frost puts an end to the colorful foliage. If there is a drought during the growing season, the abscission layer forms early and causes the leaves to drop before they change color. Heavy wind or rain can also cause early leaf drop and a less than spectacular display. The Emerald Ash Bore Beetle has reduced the numbers of White and Green Ash trees known for their spectacular Fall color, so there is a reduction in the diversity of species in our communities and forests that used to add depth and variety to the color palette. All of these factors combined determine the kind of color we'll see each Fall.
What are the perfect conditions for beautiful Fall leaves? Brilliant Fall foliage requires a growing season with ample rainfall and a dry, cool and a sunny Autumn with warm days and cool, frostless nights.
Cooler temperatures create wonderful walking and hiking conditions, perfect for a stroll through one's neighborhood, forest preserve or arboretum. Summer is behind us, but there are still several weeks left to enjoy brilliantly colored leaves and nature's abundant gifts.
