Every fall, trees put on one of the most familiar seasonal displays of the year. Green leaves shift into shades of yellow, orange, red, purple and brown, sometimes all on the same tree. It can look as though the trees are suddenly creating an entirely new palette, but some of those colors were actually present long before autumn arrived.
Green Has Been Hiding the Other Colors
During spring and summer, leaves contain large amounts of chlorophyll, the pigment responsible for their green color. Chlorophyll plays an important role in photosynthesis, helping plants use sunlight to make energy. Because it is so abundant during the growing season, it masks some of the other pigments already present in the leaf.
Among those hidden pigments are carotenoids, which produce yellow, orange and golden colors. These pigments are present throughout much of the year, but during summer they are usually overshadowed by chlorophyll. As autumn approaches and daylight decreases, trees begin preparing for winter. Chlorophyll production slows, the chlorophyll already in the leaves begins to break down, and the colors underneath become visible.
That means the yellow or gold you see in October may have been there in July. You simply could not see it because the green pigment was dominating the leaf.
Red Leaves Work a Little Differently
Red and purple fall colors have a different story. Many trees actually produce new pigments called anthocyanins during autumn. These pigments are responsible for many of the reds, burgundies and purples we associate with fall.
Sugar remaining inside the leaf helps with this process. Bright sunny days allow leaves to continue producing sugars, while cool nights can slow the movement of those sugars out of the leaf. Under the right conditions, more anthocyanins may develop, which is one reason some autumns seem especially vivid.
Warm, sunny fall days followed by cool nights often create particularly good conditions for red color. A hard freeze, however, can damage leaves and bring the display to an early end.
Why Isn’t Every Fall the Same?
Fall color depends on much more than the calendar. Temperature, rainfall, sunlight and the overall health of the tree can all influence what we see. A summer drought may cause leaves to change color early, turn brown, or fall before they ever develop much color. Long stretches of cloudy or wet weather can also affect how vivid the season becomes.
This is one reason the same hillside can look very different from one year to the next. Even individual leaves on the same tree may change in different ways. One may be yellow with green veins, another may develop orange edges, and another may turn red almost completely.
Nature is apparently not very concerned with consistency. 😂
Even Brown Has a Story
Brown may not receive the same attention as bright red or gold, but it has its own chemistry as well. As other pigments break down, tannins become more visible. These compounds contribute to the brown colors seen in many leaves, especially on oaks.
Tannins also help explain why some dead leaves remain attached to certain trees well into winter. So even the leaves that seem to have lost their color are still showing part of the tree’s seasonal process.
The Tree Is Preparing for Winter
While all of this color is happening above our heads, the tree is also preparing to let the leaf go. A special layer of cells begins forming where the leaf stem meets the branch. This is called the abscission layer.
As that layer develops, the flow of water and nutrients between the tree and the leaf is gradually reduced. Eventually, the connection becomes weak enough that wind or gravity causes the leaf to fall. A protective layer remains behind on the branch, helping shield the tree after the leaf is gone.
At the same time, the tree is conserving resources it will need to survive winter and begin growing again in spring.
Nature, Color and Copper
The more I learn about processes like this, the more interesting the natural world becomes. A leaf is not simply changing from green to yellow. Pigments are being revealed, others are being created, sugars are moving through the leaf, and the tree is preparing itself for another season.
That kind of variation is also part of what I enjoy about making jewelry by hand. Even when I use the same design and process, no two pieces come out exactly alike. Small differences are part of handmade work, and I like that each piece ends up with its own character.
Nature seems to work much the same way. The same tree, the same season and the same basic chemistry can still produce a wide range of color.
That may be one of the things I like most about fall. Once you know what is happening inside the leaves, the color becomes even more interesting. Some of it was there all along, simply waiting for the green to move out of the way.
