![]() ![]() 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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