Got Nature? Blog

The bright, crisp colors of summer begin to fade with the arrival of fall, revealing a riot of new colors on our foliage. These colors range from vivid reds and golds to deep oranges and browns before finally falling from the trees. For decades, travelers have chased the rainbow of colors across the United States in hopes of taking breathtaking photos or just for personal gratification.

Weather conditions throughout the year contribute to autumn colors but the primary driving factor is day length. Numerous warm, sunny days and cool evenings seem to be the harbingers of the best fall colors. Idyllic weather conditions allow trees to produce significantly higher volumes of sugar in leaves and the cool nights slow sugar export.

Surplus leaf sugars stimulate anthocyanin (red and purple) pigment production. Carotenoid (yellow and gold) pigment levels tend to remain steady throughout the growing season though masked by chlorophyll until autumn. Chlorophyll In addition to sunshine, soil moisture also contributes to leaf color. Predictors of vibrant fall color: spring (warm, wet); summer (warm/hot with sufficient rain); fall (warm sunny days, cool nights). Delayed spring showers or an extended summer drought can delay fall color for weeks.

Color change is initiated in the northeastern United States before continuing southward and can be species-specific. Aspens and hickories (primarily bronze, gold, and yellow), dogwood and oaks (ranging from deep red to dark brown), and maples (most often bright red to yellow-orange) represent the wide range of hues. In contrast, some species (elm) rarely exhibit any fall color. The map below, currently pinpointed to November 5th, can be used to visualize progression of fall color nationwide. For details of fall color across the nation, a fall color hotline 1-800-354-4595 has been created by the Forest Service to give travelers updates.

References:
Figure 1- Fall leaf photo
Figure 2- Fall foliage prediction act, smokymountains.com

Resources:
Autumn Leaves – what influences the color? – Got Nature?, Purdue FNR-Extension
Why Leaves Change Color, The Education Store, Purdue Extension
Why Leaves Change Color, USDA Forest Service, Northeastern Area

Shaneka Lawson, USDA Forest Service/HTIRC Research Plant Physiologist/Adjunct Assistant Professor
Purdue University Department of Forestry and Natural Resources