Elyse C. McCormick | October 22, 2025

If you’re anything like me, you’re a self-professed lover of all things autumnal – harvest vegetables, apples, cozy hot drinks, and of course, the changing colors that accompany autumn in deciduous forests.  I feel spoiled now living in New England, where fall unfolds in a kaleidoscope of color (and you’re never far away from an apple cider donut). Many other people seem to like it too, as a major part of New England tourism depends on “leaf-peepers” – tourists that travel from all over the world just to see the stunning forests before they shed their leaves. But what governs the fall colors we see? Why do some trees have colors at all, and why do they drop their leaves?  

Figure 1. Sugar maple (Acer saccharum) starts to turn colors. Photo by Elyse McCormick.

People have long been curious about how and why trees change color and lose their leaves in the autumn. It’s complicated to understand this phenomenon: botanists, biochemists, and evolutionary biologists alike have done many studies on fall color change. Thanks to their hard work, we know that leaves change color because there’s a shift in their pigment levels. In summer, leaves are green because they produce high levels of a pigment called chlorophyll, which is essential for photosynthesis, a process that produces sugars to feed the tree. However, once there are different light and temperature cues in fall, the tree gets a signal to reduce its chlorophyll production, causing green pigments to leave the leaf [1, 2]. This lets other colors, rich reds, oranges, and yellows, come to the surface (Figure 1). Some of these colors, like red, are caused by anthocyanins that are actually produced more in the fall as a response to changes in light signals. Other colors, like yellow, are caused by carotenoids that are present in the leaf all year long, but you can only see them as the chlorophyll die back [1,3].

The colors we see tend to stay similar across tree types, although there can be a lot of variation. Oak trees tend to be deep red, brown, or russet, while hickory trees have a golden bronze hue. Beech and birch trees show gold and bronze colors, while sorrel trees are vivid crimson. And the fall starlet in New England, maple trees, show an incredible amount of variation between species, ranging from orange-red sugar maples to golden black maples (Figure 2) [2]. 

Figure 2. A golden mixed maple stand. Photo by Elyse McCormick.

So then, why does fall color seem spectacular in some years, and just good in others, if color is caused by the same pigments? This is a puzzle scientists are still trying to solve. We know several factors are at play – the best fall foliage comes when days have been warm, nights have been crisp, and nights have started to get longer [2,3]. We still need scientists to study why trees have different colors and what the function of changing colors might be. Even now, evolutionary biologists are making new hypotheses about the function of leaf color change [4]. Additionally, we know climate change will impact fall foliage [5,6],  but further study will help us understand whether trees can adapt to these changes. Understanding this will give us better insights into the challenges trees and forests face in the future, and how we might keep seeing beautiful falls for years to come. 

References:

1. Hörtensteiner, Stefan. “Chlorophyll degradation during senescence.” Annu. Rev. Plant Biol. 57, no. 1 (2006): 55-77.
2. U.S. Forest Service. “Science of Fall Colors.” U.S. Forest Service. [Sept. 18, 2025] https://www.fs.usda.gov/visit/fall-colors/science-of-fall-colors
3. Michigan State University Extension. “How Weather Affects Fall Colors.” Michigan State University Extension. [Sept. 18, 2025] https://www.canr.msu.edu/news/how_weather_affects_fall_colors
4. Archetti, Marco, Thomas F. Döring, Snorre B. Hagen, Nicole M. Hughes, Simon R. Leather, David W. Lee, Simcha Lev-Yadun et al. “Unravelling the evolution of autumn colours: an interdisciplinary approach.” Trends in ecology & evolution 24, no. 3 (2009): 166-173.
5. Taylor, Gail, Matthew J. Tallis, Christian P. Giardina, Kevin E. Percy, Franco Miglietta, Pooja S. Gupta, Beniamino Gioli et al. “Future atmospheric CO2 leads to delayed autumnal senescence.” Global Change Biology 14, no. 2 (2008): 264-275.
6. Garretson, Alexis, and Rebecca E. Forkner. “Herbaria reveal herbivory and pathogen increases and shifts in senescence for northeastern United States maples over 150 years.” Frontiers in Forests and Global Change 4 (2021): 664763.