Why do leaves change color in autumn?

ROCHESTER, NY (WROC) — Fall is almost here, and with it pumpkin lattes, cooler temperatures and beautiful fall foliage. But have you ever thought about Why Leaves change color especially in autumn? Let’s take a closer look.

So why exactly do leaves change color?

All leaves contain chlorophyll. According to Jason Grabosky, professor and program director for Urban Forestry at Rutgers University, chlorophyll is “a substance that plants use to convert light into sugars that make a leaf appear green.” Therefore, leaves change color when the chlorophyll begins to break down and the plant stops making replacement molecules as the days get shorter.

Other pigments, a class called carotenoids, appear as yellows and contribute to the appearance of orange and brown. Carotenoids are always present in the leaf, but are usually overwhelmed by chlorophyll (green color) during the summer months. When chlorophyll begins to dwindle, we see the color yellow emerge on the leaves. This is usually the first sign that a change is taking place. As Grabosky put it, “The reds come from a ‘more expensive to produce’ pigment, anthocyanin, and develop specifically during the fall months. The reds and yellows together give some tree species the orange fall color.”

Are there factors that could influence the colors we see?

The biggest factors that can affect colors are day length, temperature and weather.

The change in day length triggers various processes to get leaves “ready” for the fall and winter months. Temperatures can trigger or even accelerate these changes. Light can also play a role in this regard. Light is important for leaf color change because light energy is used to make the pigment anthocyanin. So sunnier days provide light energy that can intensify color development. Wind and rain, on the other hand, can cause leaves to detach from the tree before they have reached their full color. Grabosky said, “Because different tree species hold (and thus lose) their leaves in different ways, wind and rain can affect what is present in the ‘color palette’ of the plant community at the landscape level.”

Does the weather play a more positive role?

Yes, that’s right! Sunny days and cooler (but not freezing) nights make all the difference. When both conditions are present, we will see more vibrant colors. Here in western New York State, however, sunny days are less common in the fall months. Rain or heavy cloud cover, as well as warm and long fall months, unfortunately dull the colors even more. But even on cloudy days, fall colors can still shine.

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

According to Grabosky, “Our perception and the way we individually see things and respond to those stimuli can play a role in how we respond to fall colors.” Even though we don’t have the sunniest days here in Western New York, it all depends on how observant we are. It’s also important to take the time to notice the differences in colors. The only other thing that could affect the color of the leaves is lack of water. When this happens, the leaves begin to dry out and are unable to change color properly during the transition, at least not long enough to reach their full potential.

When do fall colors peak here in Western New York State?

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

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