Maine is a beautiful place to watch the changing colors of the seasons, with abundant trees, wide open space and beautiful light, the glorious colors of Fall reflect across the landscape from September 15th through October 15th give or take a week depending on where in the state you are. In Millinocket, we anticipate the leaves to start turning around the 20th or 21st of September, when they do it is a sight to behold – plan a visit for leaf peeping to the New England Outdoor Center and be right in the heart of the transition from green to yellow to red and gold.
What causes the leaves to change color?(1) Is it the day or night-time temperature? Is it the geographic location, the frost? Actually, it is a number of factors – and according to the US National Arboretum the process that starts the cascade of events that result in fall color is actually a growth process. In late summer or early autumn, the days begin to get shorter, and nights are longer. Like most plants, deciduous trees and shrubs are rather sensitive to length of the dark period each day. When nights reach a threshold value and are long enough, the cells near the juncture of the leaf and the stem divide rapidly, but they do not expand. This abscission layer is a corky layer of cells that slowly begins to block transport of materials such as carbohydrates from the leaf to the branch. It also blocks the flow of minerals from the roots into the leaves. Because the starting time of the whole process is dependent on night length, fall colors appear at about the same time each year in a given location, whether temperatures are cooler or warmer than normal. (1)
During the growing season, chlorophyll is replaced constantly in the leaves. Chlorophyll breaks down with exposure to light in the same way that colored paper fades in sunlight. The leaves must manufacture new chlorophyll to replace chlorophyll that is lost in this way. In autumn, when the connection between the leaf and the rest of the plant begins to be blocked off, the production of chlorophyll slows and then stops. In a relatively short time period, the chlorophyll disappears completely. This is when autumn colors are revealed. Chlorophyll normally masks the yellow pigments known as xanthophylls and the orange pigments called carotenoids — both then become visible when the green chlorophyll is gone. These colors are present in the leaf throughout the growing season. Red and purple pigments come from anthocyanins. In the fall anthocyanins are manufactured from the sugars that are trapped in the leaf. In most plants anthocyanins are typically not present during the growing season.
As autumn progresses, the cells in the abscission layer become more dry and corky. The connections between cells become weakened, and the leaves break off with time. Many trees and shrubs lose their leaves when they are still very colorful. Some plants retain a great deal of their foliage through much of the winter, but the leaves do not retain their color for long. Like chlorophyll, the other pigments eventually break down in light or when they are frozen. The only pigments that remain are tannins, which are brown. Temperature, sunlight, and soil moisture greatly influence the quality of the fall foliage display and temperature may dictate the color and its intensity. (1)
If you are planning to check out the fall foliage in the Katahdin Region – plan your visit with a getaway package – find that here: Fall Getaway Package, dinner at The River Driver’s Restaurant & Lodging at NEOC | Twin Pines – package for $119/per person per night.
(1) Source: The United States National Arboretum http://www.usna.usda.gov/PhotoGallery/FallFoliage/ScienceFallColor.html