Why do leaves change colors during the fall season?

ROCHESTER, N.Y. (WROC) — Fall is almost here and so too are pumpkin spiced lattes, chillier temperatures and the beautiful fall foliage. But have you ever thought about why leaves change colors during the fall season in particular? Let’s break it down.

So, why exactly do leaves change color?

All leaves contain chlorophyll. According to Jason Grabosky , a professor and program director of Urban Forestry at Rutgers University, chlorophyll is “a substance plants use to turn light into sugar that makes a leaf look green.” Therefore, leaves change color when the chlorophyll starts to break down and the plant does not rebuild replacement molecules as the days begin to get shorter.

Other pigments, a class called the carotenoids, show as the color yellow and contribute to the appearance of orange and brown. Carotenoids are always in the leaf but are typically overwhelmed by the chlorophyll (green color) during the summer months. When the chlorophyll starts to fade away, we start to see the color yellow pop on the leaves. This is usually the first indication that change is happening. As Grabosky put it, “the reds are from a more ‘expensive to make’ pigment, anthocyanin, and they develop specifically during the fall months. The reds and yellow together give us the orange fall colors in some tree species.”

Are there factors that could affect the colors we see?

The biggest factors that could affect the colors are the length of day, temperature and the weather.

The change in the length of day begins to trigger several processes to get the leaves “ready” for the fall and winter months. Temperatures can induce or even speed up these changes. Light can also play a role in this respect. Light is important for leaves to change colors because light energy is used to make the pigment anthocyanin. So, sunnier days offer light energy that can help to intensify color development. Wind and rain on the other hand could cause the leaves to detach from the tree before reaching its peak color. Grabosky said, “since different tree species hold their leaves (and thus lose their leaves) in different ways, wind and rain can influence what is present in the plant community ‘color palette’ on a landscape scale.”

Does weather play a more positive role?

Yes, it does! Sunny days and cooler (but not freezing) nights make all the difference. If we get both of these conditions, then we will see more vibrant colors. Here in Western New York though, sunny days are harder to come by during the fall months. Rain or heavy cloud cover, warmish and long autumns, unfortunately dull the colors even more. However, even on cloudy days, the fall colors can still pop.

Is there anything else that could influence the color of leaves?

According to Grabosky, “our perception and how we individually see things and react to those stimuli can play a role in our reaction to the fall colors.” Even if we don’t have the sunniest of days here in WNY, it’s all about how observant we are. It’s also important to take the time to notice the differences in the colors. The only other thing that could influence the color of leaves is the lack of water. When this happens, leaves start to dry out, thus failing to change color properly in the transition, at least long enough to show its full potential.

When will the fall colors peak here in Western New York?

Typically, fail foliage in WNY peaks in late October. However, the exact timing depends on the factors discussed earlier. New York State as a whole has one of the longest and most colorful fall foliage seasons in the country, usually starting in late September and lasting until November.

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