Follow The Foliage!

SciWorks Radio is a production of 88.5 WFDD and SciWorks, the Science Center and Environmental Park of Forsyth County, located in Winston-Salem.

Foliage season has begun! It's time for long, lazy drives through the mountains or kicking casually through fallen foliage. If you're one of my kids, it's the season to dive head first into large, and formerly well-contained, piles of leaves.

The fall is a beautiful time of year here on the East Coast, and in North Carolina, we have a resident expert who has long been the go-to scientist for local leaf-peepers: Dr. Howard Neufeld, professor of biological sciences at Appalachian State University.

The best fall colors are in the United States in the temperate zone. And, here in the Southern Appalachians, we have over 100 species of trees down here. So we get a whole range of color. And we also have the highest mountain peak east of the Mississippi, Mount Mitchell, and we can go all the way down to sea level. So people in the South can start looking at fall colors in September and go all the way almost to Thanksgiving if you keep just moving downhill. The colors move about a thousand feet down every 10 days or so. Here in Boone, it will peak around mid-October, and then at the end of October in Asheville, and then early November in the Foothills after that, and then in the middle of November down in the Charlotte and Raleigh areas.

Even though this beautiful color change is a yearly part of our life experience, scientifically, we know surprisingly little about what causes fall foliage.

We know a lot about what causes leaves to come out in the spring. We know what they do in the summer. But what they do in the fall is less studied. So the more we know about that, the better we can develop models for the people who are looking at how climate change may affect tree productivity and things like this.

One interesting product of climate change may be that species begin to migrate northward,  staying in their comfortable temperature zones. This could vary the coloring patterns over time, as different species take root. But, climate change aside...

I'm still interested in that question of why some trees turn red and some stay yellow. And one of the things we noticed is that, if you look at red trees, the red usually starts at the top of the tree on the outside, particularly on the east side, whereas yellow-turning trees generally just yellow-up all over at once, and then the leaves fall off.

Well, if you think about it, that's where the sun comes up, and the light comes in at that low angle and hits the tree. That's when it's also the coldest in the day. So it makes sense that you'd begin protecting the tree that's exposed to the high level of light at the coldest time of day.

But why do these trees need the red pigment protection from light and cold?

Well, in the fall, that's when trees will take the nutrients that are in their leaves and withdraw them and store them in their twigs so they can use them next year. But the mechanism by which they do can be disrupted by a condition of high light and cold, and that can lead to damage in the leaf, and then they can't withdraw the nutrients out of the leaves. So, if they synthesize this red pigment, it acts like a light shield, so they don't get as much light, and they can withdraw those nutrients.

That seems like a reasonable hypothesis, but how do you scientifically prove that?

So, we're going to plant some seedlings, and we're going to shade them so they don't get the morning light to see if that affects how much of the pigment they make compared to trees that do get morning light. And so, that's one of the things we're kind of setting up to test that hypothesis.

But what about yellow-turning trees?

For yellow trees, how do they survive then if they don't have this red pigment? Are they doing something different inside their leaf? Or maybe they don't care about withdrawing the nutrients, and so they don't need to synthesize the pigment. So, I've got a new master's student, and we're setting up some experiments right now to test this and see if we can answer some of these questions.

I do it just because I'm curious about nature. And this way I can tell people, with a little more confidence, not only when trees are going to turn colors, so they know when to come to the mountains, but why they turn colors.