It’s prime leaf peeping season, and while trees across many parts of the state are showcasing their best yellows, oranges and reds, drought conditions in the northern Vermont and abnormally wet conditions in the southern regions are both at play this fall.
VPR’s Henry Epp spoke with Abby van den Berg, a research associate professor at the University of Vermont's Proctor Maple Research Center, to get a sense of foliage conditions this season. Their interview is below and has been edited and condensed for clarity.
Henry Epp: So, I really should know this, but why do leaves change colors in the fall?
Abby van den Berg: Well, actually, really no one knows.
OK.
Truly, that answer is one that still has a good bit of mystery in it. But some of the very, very basics are that basically, as the daylight begins to get shorter and shorter, the leaves begin to stop making chlorophyll — the green pigment that's responsible for harvesting sunlight, and you know, the tree leaves use that to transform it into fuels — and then, ultimately, toward the fall it begins to break down.
OK well, what are some of the factors that determine how vibrant fall foliage might become in a given year? Of course, some years, it at least feels like the colors are a bit richer than others. What are some of the factors there?
Well, there are a lot of different levels of factors. But the first one, that's sort of at the leaf level, is that we have to first understand that there are two processes that go on.
So first, we see the result of that breakdown and reabsorption of chlorophyll. And so, once that chlorophyll is gone, it sort of reveals these yellows, and sometimes oranges.
But the second part that we see as part of this spectacular phenomenon is when we see the reds and purples. Those are actually new pigments that are being created anew by the leaf that is in the process of dying. We can often see those pigments enhanced with a little bit of stress to the tree.
But then when we take it up to a different level, we have factors like human eye factors and human perception factors. So sometimes a brilliant fall foliage day is about the context that we see those leaves in — the bright blue sky behind it, the dark grey sky behind it sometimes even.
So, there are numerous levels of factors that play into those brilliant colors. Some of them are physiological to the tree, and some of them are in our brains.
That’s really interesting. Well, I want to ask about a few different factors that might be at play this year. First, much of the northern part of the state was in a drought for a good part of the past year. Some areas are still abnormally dry. Does that impact foliage?
It really can. And, you know, this is going to start sounding like a broken record, but in a very complex way that we don't understand totally, fully.
So, in general, we know that a certain level of mild stress may just do things like enhance the production of reds and purple pigments.
That gets a little bit more complicated because it can depend on when that stress occurs, when the drought occurs, for example. So, if we have a tree that has experienced a significant level of drought, so it's not had a great year, let's say, then often that is going to lead to maybe a little bit of an earlier color development, and maybe not so brilliant, because the leaves might be a little dry and crinkly. Versus if it's just a little bit of a mild drought, that might actually enhance some of the colors that we see.
Well, on the flip side, much of southern Vermont saw really heavy rainfall this summer. And I understand that that's led to a fungus that's causing some leaves to drop early. Is that right?
Right. Absolutely. That can happen. And you know, they just kind of turn brown and drop. And it's one of those things when it happens it's very shocking. Fortunately, for most of the trees to which this happens, it's not a huge stress in the long term of the tree. But for the human beings experiencing that, it can be … it's definitely not what we expect to see from our beautiful maple trees, especially those that are you know, out by the roadside.
I mean a lot of these factors we've been talking about — temperature and precipitation — they are changing a lot due to climate change. So, can we say whether climate change is impacting fall foliage in this region? And I mean, is it changing when the leaves turn or the quality of foliage?
I can't say whether it's changing the quality of foliage, or maybe I should say, I can say that it has not changed the quality of the foliage. But certainly, as our autumns get warmer and warmer, it is changing the timing, the phenology, of fall coloration.
Fall coloration is similar in many ways to things like budbreak in the spring. Those are phenological events that respond to temperature, and they are absolutely being affected by our changing climate.
Well, finally, Abby, at least from your perception, how does this season compare to other recent fall foliage seasons so far?
In my perception — which is, you know, I've been doing this for a long time, so I have a very unique perception of this — and it is, it’s spectacular, because it always is.
No matter how the season differs from one to the next — and they are all a little bit different from one another because of all of this variation and complexity that I've talked about — there are always going to be spots where the color is just fantastic.
And if you spend a little time out there looking, you will always find those. So, on that level, and the level that I look at this, it's a fantastic year, just like it always is.
Have questions, comments or tips? Send us a message or get in touch with reporter Henry Epp @TheHenryEpp.
