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Sugar maple fall color9/5/2023 Finally, the whole tree is orange, dusted with red, inlaid with yellow. Yellow spreads from the leaf margins inward. The higher the content of sugar trapped in the leaves, the more brilliant the color. The red moves down from the top of the tree and in from the sides. Sugar maple leaves turn yellow in the shade, red in the sun, and, depending on the proportion of sun and shade, and on genetics, they change hourly from yellow to red to orange. Sugar maple leaves contain all three pigments – xanthophyll, carotene, and anthocyanin – and as go the sugar maples, so goes fall color. The same tree that makes sugaring a unique spring experience is also the key to fall foliage. So why is New England foliage world-renowned for its brilliance? The sugar maple, of course. While a gentle nip may spur leaf petiole drying, a hard frost ruptures plant cells, causing their contents to leak out and destroying their brilliant color. Don’t believe the tales about Jack Frost painting fall color across the Northeast. Sunny days and cool nights, however, generate reds and oranges and purples. If late September and October are overlaid with clouds, little anthocyanin is produced. If the sap is alkaline, they turn blue or purple.Īnthocyanin is a sun pigment. If the leaf sap containing anthocyanin is acidic, leaves turn red. Anthocyanin yields the red of sumac, blueberry, red maple, and Virginia creeper, the purple-blue of white ash, and the purples of viburnum. While autumn yellows are produced by subtraction, autumn reds are produced by addition – the addition of sugars and leaf waste which cannot exit through the plugged petioles. Xanthophylls, the yellow pigment in egg yolk and butter, and carotene, the orange pigment in carrots – both of which are present in varying amounts in different tree species all summer but hidden by chlorophyll – transform the leaves of American elm, quaking aspen, paper birch, and black willow to a golden yellow. With chlorophyll production winding down, previously unseen pigments appear. In a dry summer, this de-greening of leaves may be obvious much earlier than in a wet summer as trees simply run out of water to maintain full chlorophyll production. As the flow of water into each leaf is cut off, the leaves become less and less green. A constant supply of water up through the trunk and into each leaf is required for the tree to continue manufacturing chlorophyll. Chlorophyll, the green pigment in leaves, is volatile. With the flow of water staunched, the production of chlorophyll stops. Just inside these cells a layer of tough, corky cells develops, stopping the flow of water into the leaf and stopping the export of carbohydrates and metabolic waste back to the tree. It starts in July and by late September, more than half of each leaf’s nitrogen (and phosphorous) has been returned to the woody tissue, where it acts as an antifreeze for the tree and will provide an infusion of nutrients for early spring growth.Ĭool September nights, meanwhile, stimulate cells at the base of each leaf stem, or petiole, to dry out. Subtly decreasing amounts of daylight trigger the beginning of nitrogen re-absorption from the leaves back into the tree’s woody tissue. What causes this display of color? And why is New England’s foliage so brilliant?įall color actually starts during the lazy days of high summer. Autumn color comes to the foliage of Vermont and New Hampshire in early September, crescendos in mid-October, and fades by November.
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