Ah, the bittersweet moments near the end of the summer. The nights are starting to cool, but the lake is still an incredible 76.5 degrees, at least here in Burlington, and the first of fall colors are poking into the green canopy. In this series, we celebrate the rainbow of fall (though a bit out of the ROYGBIV order) and explore the reasons behind the different colors we see in plants.


Sure, purple and red are spectacular on the hillsides, but the oranges are a quiet burn that extend fall’s tenure into the beginnings of winter as they seem to persist on the forest floor much longer. And there’s nothing quite like standing under the quiet glow of a sugar maple in the golden hour of a crisp fall afternoon.

The brilliant oranges and yellows of sugar maples in the fall (Shelburne Pond, Shelburne)

Much like how you’d mix red paint with yellow to land on orange, so too are the warm oranges a sort of bridge between the red anthocyanin pigments from the previous newsletter and the underlying yellow carotenoid pigments we’ll talk about in more depth in the next newsletter. 

Gold and orange hues of big-toothed aspen leaf in fall foliage

Carotenoids are a class of pigments found in some plants, imparting various shades of yellow, orange, or red. They make corn yellow, carrots and pumpkins orange, and tomatoes red. And in the fall, they add to the bounty of resplendent warm tones. While anthocyanins offer protection from UV radiation, carotenoids primarily serve as accessory pigments that extend the range of light chloroplasts can use for photosynthesis. As such their concentration within the plant remains relatively constant throughout the growing season. Leaves don’t appear orange in the summer, however, because the abundant green of chlorophyll overwhelms and masks the yellow pigments. As chlorophyll begins to break down in the fall, the underlying yellows are revealed. And the displays can be stunning.

Sugar maple leaf caught on a glossy buckthorn twig (Rock Point)

In the leaves of our trees, carotenoids tend to be a golden yellow. When carotenoid-rich trees – sugar maples, big-toothed aspens, tulip poplar, etc. – begin to produce red to purple anthocyanins in the fall, the colors blend into a vibrant orange tone. Trees that produce carotenoids but lack anthocyanins (notably quaking aspens, the hickories) take a striking golden yellow color in the fall.

Orange-red of the 4-lobed tulip poplar leaf (Centennial Woods, Burlington)

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