Fall Colors in the Heights

 In Feature

By Eric Anderson

We in the Washington Heights had the most spectacular fall colors of the past 20 years! I think they were a little later this year; my first photos were dated October 15th. Unlike other years, the colors peaked about the 31st through November 5th, and the vast majority of our maple trees held on to all their beautiful leaves longer. Then suddenly, by the 9th, the trees shed their leaves at about the exact same time! Even the old mighty oak trees in both of my neighbors’ back yards dropped all their leaves in our yard by November 15th! In most years, those trees don’t shed until mid December—after the City of Milwaukee stops collecting leaves. Several years those trees held their leaves until spring, when the new buds start to force them off.

Why do leaves change colors? As summer fades into fall, the days start getting shorter and there is less sunlight. This is a signal for the leaf to prepare for winter and to stop making chlorophyll (the green). Chlorophyll is important because it helps plants make energy from sunlight—a process called photosynthesis. As this slows down, the green color starts to fade and the reds, oranges, and yellows—the natural colors of the trees—become visible! Leaves have color because of chemicals called pigments, and there are four main types of pigments in each leaf: chlorophyll (greens), xanthophylls (yellows), carotenoids (oranges), and anthocyanins (reds). This also explains why one tree may have several colors mixed in.

Why are some years more colorful than others? Warm days and cool low temperatures (above freezing) at night boost the production of the red pigments, producing a more dazzling display, but early frosts weaken the colors.

In the fall, the temperatures get colder and there is also more rain and snow. Changes in these weather conditions can play a role in how early the leaves change and how long they keep their beautiful colors. This year we had record warm temperatures in early November. Remember last year? On October 26th, Hurricane Ulma pummeled our Spooktacular. Then on Halloween, we got 4 inches of snow (6.1” for the month, the second most in history)!

Extreme weather changes can also have an effect on the leaves. For example, a drought or an early frost could make the leaves fall off of the trees before they’ve had time to change colors. So if you want to know how long the colors will last next fall, be sure to keep an eye on the weather!

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