I love this time of the year. The cooler air from the north signals the possibility of a beautiful fall color change across the Ozarks and Ouachitas, but what exactly causes the change? Our friends at www.arkansas.com have a great explanation I have included below.
Frost rarely triggers fall foliage. The first heavy frost seldom occurs until the colorful period is nearly over. Two factors are primarily responsible for starting the fall color process. The first is the changing of the season. Plants react to less light intensity as the earth tilts on its axis and the days grow shorter. To the human eye, the sun appears to move further south on the horizon. The second major contributor is weather during the critical period of mid-September to mid-October.
Many warm days and cool nights at the beginning of fall are very good for production of red colors. According to Dr. Don Culwell, a University of Central Arkansas botanist: “As the temperature drops, the cell’s machinery begins to shut down. Cool nights change sugars to red pigment.” Leaves produce some sugars for food during the day, but cooler temperatures at night keep these sugars from moving out of the leaves and into the tree.
Weather patterns during September and October (in Arkansas) are far more important. For instance, if it’s too rainy during this period, we will not have the warm, sunny days or the cool, crisp nights described earlier. If it turns too cold, we will have cool nights, but the lack of warm days will discourage leaves from manufacturing sugars while the sun is shining. If it stays too hot at night, sugars will continue to pass into the tree instead of collecting in the leaf until late in the critical period, when frost or heavy wind may strip the foliage from the trees before much color is apparent. When the right things happen at just the right time, we enjoy a statewide outbreak of the picturebook color that is always present in one area or another each year. Most years, great color appears in different regions at various times in October and November, which is why the weekly updates are valuable.
Speaking of updates, we’ll have a weekly update on the color change so you can plan your perfect hike or drive. Check back on the blog.