This is the inaugural edition of a new segment we’ll be doing every other Friday on Morning Edition: “Ask Sam” in which NHPR’s Sam Evans-Brown tracks down answers to questions about the outdoors for our listeners.
Do Drought Conditions Affect Fall foliage?
Oh my gosh, Stephanie, Isn’t it a bit early to already be having fall foliage anxiety‽
We are now, (as reported by the inimitable Annie Ropiek) entering our third droughty summer in a row here In New Hampshire, and drought is a stressor for New England deciduous trees, and so is generally bad for fall foliage. Severe drought can lead to some trees turning color early, moderate drought can lead to some trees turning colors later, and generally speaking a spectacular fall foliage season is one where as many trees as possible change simultaneously. So anything that gets the trees out of sync with each other is likely going to throw off the fireworks display a bit.
And we should note that basically anything that is bad for those trees is bad for fall foliage: a hard frost when the leaves are budding out is bad, a fungal or insect infestation is bad. Though the worst thing for fall foliage can be hard to forecast any more than a few days out: wet and windy weather hitting just as the leaves begin to change.
What makes for good fall foliage? Healthy trees, with sufficient water and nutrients, combined with good weather, but cold nights. A good frost can help to break down chlorophyll — that’s the pigment that makes leaves look green, and fills the chloroplasts, the part of the leaf that does the work of photosynthesis.
This question gives me an opportunity to rant about fall foliage forecasts, which you should view very skeptically, unless they are forecasting only a few days in advance. Since the primary factors influencing fall foliage are basically “what’s the weather going to be?” (cold nights, and not too much wind and rain) it’s very difficult to put out an accurate foliage forecast any farther out than you can forecast the weather.
But wait, there’s more!
This (as you can tell from the work of other journalists I’ve linked to!) is a question that gets answered quite a lot. So let’s use it to jump off and answer another, less common question. Why is New England’s foliage so spectacular to begin with?
The answer according to Paul Schaberg, a researcher with the U.S. Forest Service, is a chemical called anthocyanin, which makes leaves that look red. Chlorophyll gives us green leaves, and during the summer it masks the other pigments that give us yellow and brown — carotenoids and xanthophyll. As the chlorophyll begins to break down and fade from the leaf, these other colors begin to show through, but this is a process that happens in all deciduous trees, and leads to displays like the golden waves of aspen trees in the autumn out west.
However, unlike the rest of the world, here in New England we have an abundance of trees that produce anthocyanin. In the Harvard research forest 70 percent of the foliage is from species that turn can red in the fall. And anthocyanin is different from the other pigments, because it is something that the tree begins to actively create when the autumn arrives.
Which to any biologist prompts a question: why would the tree evolve to put forth the effort to create a new chemical for a leaf that is about to wither and fall off?
“It’s another interesting enigma of this pigment that we all love to see in the fall but science kind of disregarded for a long time,” says Schaberg.
The answer, he says, is that anthocyanin production appears to be an adaptation that allows the tree to wring more nutrients out of a leaf. “Some scientists have referred to anthocyanin as the Swiss Army knife of plant protective compounds,” he says.
The chemical works as sunscreen, bug repellent, and antifreeze. (They are also responsible for the antioxidants in blueberries!) It appears to be stress on the tree that triggers the production of anthocyanin, suggesting that the chemical is a defense that the tree rolls out when it thinks it’s under attack.
What’s more, Schaberg has found that anthocyanin strengthens the junction between a leaf and the branch, so that it takes longer to fall off and the tree has more time to extract nutrients from the leaf.
In other words, our spectacular multi-colored foliage is due to a unique chemical which scientists are beginning to find is broadly beneficial to the trees that produce it. Facts! Huzzah!
**Correction: In the original broadcast of this piece, Sam incorrectly referred to chlorophyll as cellulose. Chlorophylll is the green pigment within a plant cell that is a major part of photosynthesis and cellulose is the fibrous cell wall. Sam is very embarassed about this slip of the tongue and promises to be better.**
Do you want to submit a question for Sam to answer? Call the Ask Sam hotline at 1-844-GO-OTTER or email a voice memo to firstname.lastname@example.org.