Mistakenly, most folks think the cooler temperature of the Fall season triggers the annual autumnal coloration of our deciduous trees. Actually, photoperiod length, or the lengthening of nights, causes a chemical to be formed in the tree that begins to close off the vascular connections between the tree and its leaves. Crisp cool nights without severe freezing will contribute to more vivid colors, as will sufficient moisture and a successful growing season.
As nights lengthen, chlorophyll production, which gives leaves their green color, slows and stops. Without the masking chlorophyll, other chemicals become visible. Carotenoids and anthocyanins combine with sugars trapped in the leaf tissue to produce all the various colors.
Oaks turn red, brown, or russet; Hickories, golden bronze; Aspen and Yellow-Poplar, golden yellow; Dogwood, purplish red; Beech, light tan; and Sourwood and Black Tupelo, crimson. Maples differ species by species: Red Maple turns brilliant scarlet; Sugar Maple, orange-red; and Black Maple, glowing yellow.
If you want to go leaf watching, autumn color is not very predictable, especially in the long term. Half the fun is trying to outguess Nature! But it generally starts in late September in New England and moves southward, reaching the Smoky Mountains by early November. It also appears about this time in the high-elevation mountains of the West. Remember that cooler high elevations in Northern New Jersey will color up before the valleys and other areas to the South. The Forest Service’s Fall Color Hotline (1-800-354-4595) can provide you with details as the autumn color display progresses.
Northeast Fall Foliage Guide
Foliage guide graphic© Weather.com