In the past few years, I’ve come to consider the many colors of fall foliage as one of the most brilliant reminders—literally—of the far-reaching impact global climate change can have on our lives.
As a teenager, I remember the colors of autumn coming like clockwork. We went back to school, and two to three weeks later, yellows and oranges began to peep through the top of the trees. By Halloween, the trees were bursting with colors, and about two weeks after that, we were in the yard raking. Year after year, this schedule was consistent, and we could always count on seeing the same explosion of colors—red, yellow, orange, gold, purple and copper—as brilliant as the year before. But over the past decade, you’ve probably observed that there seems to be no telling when the leaves will change, how long the foliage season will last, which colors we’ll see or how brilliant they will be. A year or two ago, trees were still lush and green well into the new school year. And in one recent year, it was markedly noticeable to me that the fiery reds weren’t quite as fiery as they were the year before.
A quick science lesson will demonstrate why our recent experience of fall foliage flip-flopping is very much connected to global climate changes—specifically, it is connected to changes in warming trends, drought and rainfall. Leaves will change no matter what, because the change is triggered by the shorter days and longer nights—less sunlight and more darkness—in September. In order to prepare for the onset of winter, trees slow down then cease the photosynthesis that, among other things, keeps leaves green and alive. No longer overshadowed by green pigments, other pigments begin to emerge and form to give us autumn colors. What colors emerge, how brilliant they are and how long they last depend on a “long-cooking recipe” that starts every spring. Let’s look at a few key ingredients:
- Healthy early growing season. The healthiest trees produce the best, long-lasting fall colors. A wet, warm spring gets trees off to a healthy start.
- Healthy mid growing season. Unlike spring, trees thrive on barely adequate rainfall. Too much rain can compromise tree health by flooding pores in the soil and blocking oxygen supply to the roots, creating a breeding ground for fungus to attack and more. Even if “overwatering” doesn’t damage tree health on the surface, it will dull the leaf colors of fall. Conversely, too much drought and/or prolonged high temperatures will cause leaves to die and drop early.
- Low late-summer humidity. A warm but not too hot late August with low humidity helps to produce a consistent display of brilliant colors. High humidity will deliver short “spurts” of fall color.
- Seasonal early–fall temperatures. Starting in September, the ideal foliage formula is cool nights in the 40s-50s and warm, sunny days. However, freezing or frost overnight expedites leaf death, leading to drab, brown leaves and fast dropping.
- Calm autumn. Nor’easters deliver heavy rain and gusty winds. They can cause leaves to drop prematurely and can end foliage-viewing season almost instantly.