The annual changing of leaf colors in autumn is one of nature’s most spectacular shows. Vibrant hues of red, orange, yellow and purple decorate the landscape as green summer leaves make way for the colors of fall.
However, not all trees transform into this colorful display. Some trees simply drop their leaves while remaining green, or turn brown before shedding. Why do some trees put on such a show of changing colors in autumn while others do not?
Why Leaves Change Color
To understand why some trees change color yet others do not, we first need to explore why any leaves change color in autumn. The factors that cause the transformation from green to red, orange and yellow depend on:
- Leaf pigments
- Length of night
- Weather
During the spring and summer, leaves are green because they contain a pigment called chlorophyll. This pigment helps leaves capture sunlight and convert it into energy through photosynthesis. Trees need this energy to grow and thrive.
As days grow shorter in autumn, with less daylight and cooler temperatures, the chlorophyll in leaves begins to break down. The green color starts to fade as the chlorophyll diminishes. At this point, other pigments that have been present in the leaves all along start to show their colors.
These leaf pigments include:
- Carotenoids – Create yellow, orange and brown colors
- Anthocyanins – Create red and purple hues
- Tannins – Add brown colors
The mix of these pigments and their varying concentrations determine the resulting color we see in autumn foliage. Cool nights seem to spur production of anthocyanins in particular, bringing out more brilliant reds.
Weather conditions also play a role. Sunny fall days and cool evenings provide ideal conditions for vivid autumn displays. Early frost and windy or rainy weather can cut short the colorful show by causing leaves to wither and fall prematurely.
Why Some Trees Change and Others Don’t
Now that we understand the biology behind autumn leaf colors, we can look at why some trees put on spectacular shows of color change while others do not.
There are two main factors that determine the extent to which a tree’s foliage transforms in autumn:
- Leaf pigments – Some trees have more of the pigments that show red and purple colors
- Leaf structure – The physical makeup of leaves impacts color change
Trees like maples, oaks, aspens and gingkos put on stunning displays of fall foliage because they contain high levels of carotenoids, anthocyanins and tannins. Their leaves also have structures that allow the pigments to be seen.
In contrast, evergreen conifers like pines and spruces keep their green needle-like leaves year-round. They have lower concentrations of the pigments responsible for autumn colors. Their needles also contain materials like waxes and resins that mask any color transformation.
When the chlorophyll supply gets low in conifer needles, the needles simply fall off while remaining green. The evergreen trees continually grow new green needles to replace those that are shed.
Common Trees with Colorful Fall Foliage
Some of the most striking autumn colors come from these common trees:
- Maples – Reds, oranges, yellows
- Aspens – Golden yellow
- Dogwoods – Purples, reds
- Sourwood – Reds, oranges
- Oaks – Reds, browns
- Hickories – Golden bronze
Trees That Remain Green
These trees retain their green foliage through autumn:
- Pines
- Firs
- Spruces
- Cedars
- Magnolias
- Palms
- Crepe myrtles
- Hollies
Geography and Climate Influences
Where trees grow also impacts if and how they change color in autumn. Climate, latitude, elevation and soil composition all play roles.
Cooler regions with distinct seasonal changes typically have the most vibrant fall displays. The northeastern United States and eastern Canada provide prime leaf-peeping territory thanks to chilly autumn nights and moderate days.
In warmer southern regions, leaves may simply turn brown and fall off trees without much fanfare. However, occasional cold snaps can sometimes trigger colorful autumn displays, even in places like Florida.
Higher elevations typically see earlier fall color changes. In places like the Appalachian Mountains, brilliant colors often develop in late September, while lower areas see peak colors weeks later.
The types of trees dominating a region also impact the intensity of color change. Maples and oaks account for many of the most spectacular autumn displays. Conifers like pines tend to dominate in areas with more muted fall transformations.
U.S. Regions with Vibrant Fall Foliage
| Region | States |
|---|---|
| New England | Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut |
| Mid-Atlantic | New York, Pennsylvania, New Jersey |
| Appalachian Mountains | Virginia, West Virginia, Kentucky, Tennessee, North Carolina |
| Great Lakes | Michigan, Wisconsin, Minnesota |
| Interior West | Colorado, Utah |
Conclusion
The vibrant colors of autumn create beautiful seasonal displays. A mix of leaf pigments, structures and weather conditions interact to produce the transformation from green to shades of red, orange, yellow and purple.
Trees like maples, oaks and aspens that contain high levels of anthocyanins and carotenoids put on the best shows. The emergence of these leaf pigments as chlorophyll fades allows their colors to shine through.
In contrast, evergreens like pines and firs retain most of their green needles through autumn and winter. They lack as much of the pigments responsible for fall colors. Their needle structure and resins also inhibit color change.
Where trees grow influences autumn displays too. Cooler climates with maple and oak trees are best for fabulous fall foliage. Warmer southern regions and areas dominated by conifers see more muted changes.
So as autumn arrives, look for areas with lots of maples, oaks, aspens and other hardwoods that contain generous amounts of anthocyanins and carotenoids. Head to New England, the Appalachians or other northern climes for the best views of nature’s spectacular autumn show.