By the calendar, autumn is here. We’ll still enjoy comforting, warm, summer-like days, but the night time temperatures and the crisp evening air that we breathe tell us a change in seasons is at hand.Our beautiful autumn color display is beginning in Flagstaff, and at its peak we enjoy a resplendent canopy of colorful yellow and orange aspen leaves among the pines in the forest, and entire colorful slopes on the Peaks.Autumn in Flagstaff is still a wonderful time for visiting, sightseeing and outdoor recreation! When you’re out hiking, and smell the change in the air, look up! Sunlight streams through the treetops and the bright colors are in contrast to the clear blue sky. In simple terms, what we experience as autumn colors are always in the leaves. Cartenoids are present on the leaf surface (yellow, orange and brown) throughout the growing season. Anthocyanins (red and blue) are produced in the autumn, in response to bright light and excess plant sugars within leaf cells. What gives leaves their green color during much of the growing season is chlorophyll, something we’ve heard of more commonly. Chlorophyll is necessary for photosynthesis, the chemical reaction that enables plants to use sunlight to manufacture sugars for their food. As the days grow shorter and the amount of sunlight per day diminishes, chlorophyll production slows and the colors are unmasked. Eastern hardwoods are known for their vibrant reds, but here in Flagstaff and on the slopes of the Rockies we enjoy stunning yellows with tinges of orange and sometimes red. The amount of brilliant color that develops is related to weather conditions during the time that the chlorophyll is dwindling. The amount of moisture in the soil also affects autumn color. It’s a fairly common myth that frost aids in autumn color production or intensity. Warm, sunny days and cool nights do promote color. As the progression of decay in the leaf structure closes off the cells at the base of each leaf, frost can actually accelerate the breakdown in the leaf’s connection to branches. As the connection weakens, physical disruption such as wind and rain bring down the leaves creating what we refer to as “fall.”Autumn colors can be fleeting, or the leaves can last longer. Some areas are, of course, more brilliant than others. Early snow squalls can add an exciting contrast to the enjoyment of autumn colors. The colors are a good excuse for a lot of locals and tourists to get out and enjoy Flagstaff’s forest wonderland. Most everyone has their favorite places to go look at leaves each year. Or you can check at the Visitor Center at the train station for tips on where to go “leaf peeping.”
– Excerpts from the USDA Forest Service.
• Average date of the first fall frost (32 degrees): September 21st.
• Average date of the first fall freeze (28 degrees or below): October 5th.