Brian Lehrer: Brian Lehrer on WNYC. And for our final minutes today, we note the changing of the calendar. Happy October, everyone. Our listener's favorite month by far, we learned in our recent thoroughly unscientific newsletter survey. One of the biggest reasons is, is that this is the month of fall foliage for most of our region. So listeners, we'll open up the phones for you right now and talk to a guest who definitely knows her fall foliage. What is your favorite leaf peeping spot? Where around the Tristate do you head for the best fall foliage? Got any favorite trees you've been able to identify over the years? Individual trees, certain ones you look out for? Give us a call, 212-433-WNYC, 212-433-9692. You can also text that number. Joining us now to explain some of the science behind leaves changing colors in autumn is Marielle Anzelone, urban botanist and ecologist and founder of New York City Wildflower Week. Hey, Marielle. Welcome back to WNYC.

Marielle Anzelone: Hi, Brian. It's so nice to be back.

Brian Lehrer: So it's definitely what you'd call pre-peak in the immediate New York City area but some leaves are starting to change. What are we seeing right now?

Marielle Anzelone: Yes, it is pre-peak, and some plants respond more quickly to the cues that all plants will be following as they're gearing up towards winter. There are some plants that are early. Poison ivy is actually one of them and there are a number of other plants that have-- and it's actually really interesting. Poison ivy is because the fruits are good for migratory songbirds. They're just loads of fat and help fuel their flight to South America.

Birds see red, and that's the thought behind plants that have those kinds of fruits. They flag to the birds to let them know that the fruits are ripe for the picking. Poison ivy is a big one.

Brian Lehrer: We already have a headline from this segment. Poison ivy is actually a good thing.

Marielle Anzelone: Yes. Mammals are the only ones that react to poison ivy. All other animals, they love it.

Brian Lehrer: How much of the changing of the leaves is a result of more hours of darkness as we get to October?

Marielle Anzelone: Yes, I mean, that's exactly right. A lot of people talk about it as the days shortening in terms of light, but it actually is about the darkness. As the length of nighttime increases, the plants are able to track the time of year via photoperiod, which is the amount of darkness in a 24-hour period. That's what they're measuring in terms of gearing up for winter.

You would respond differently to winter depending on what kind of plant you are. If we're talking about trees, there's the conifers, the evergreens, and then the deciduous but they're all getting ready for winter. The way that they measure that is through the darkness.

Brian Lehrer: And yet the timing of the fall colors varies a bit from year to year. Why is that?

Marielle Anzelone: Oh, my gosh. Well, it's so complicated and I think some people-- you'll read things that say, if you have-- The ideal conditions that most people talk about is that it should be dry and sunny and cool. If you have that consistently and you didn't have a droughty summer, then you'll have really good fall foliage but it's also true that if you were to take a tree in one spot and then dig it up and move it to another spot, it'll change responding to the microclimate. It's also thought to be related to nutrients in soil and in some cases, it might even be related to the gender of the tree. It's really complicated.

Brian Lehrer: Wait, there's another headline from this segment. In addition to poison ivy is actually a good thing, trees have genders?

Marielle Anzelone: Yes. Well, okay, so plants have a really complicated reproductive biology and when we look at the sexual side, there are male and female reproductive parts and typically those are called flowers. They're not always flowers but then in some flowers, they may have both the male and the female. Some flowers might be only female. Some flowers might have only the male parts. Sometimes it changes over time. First they're female, then they're male. It's really complicated.

One really popular example is red maple. Red maples typically, it's thought that trees that have mostly male flowers tend to be redder, while the females have yellow and orange foliage.

Brian Lehrer: Let's take a phone call from somebody calling himself Ukulele Jake in Flatbush, Brooklyn, who has a particular tree to point out, I think. Hello, Ukulele Jake.

Ukelele Jake: Hey, can I get a medium pepperoni pizza? No, just kidding, Brian, you're doing a great job. I wanted to tell you about a special tree in Brooklyn here.

Brian Lehrer: We'll have that pizza to you in 20 minutes, maybe 25. Go ahead.

Ukelele Jake: That's why I listen. I guess it must be a female tree but there's a beautiful yellow tree in between the two southern points in Brooklyn along that big loop. Are you familiar with the loop?

Brian Lehrer: I don't know it personally. Marielle do you?

Marielle Anzelone: Yes, I mean, southern point in Brooklyn, but where? What neighborhood?

Ukelele Jake: You know where that beautiful pavilion is? Where there's lots of birthday parties and stuff like that, like a rectangle.

Marielle Anzelone: Are you talking about Prospect Park particularly?

Ukelele Jake: Say again?

Marielle Anzelone: Are you talking about Brooklyn or Prospect Park?

Ukelele Jake: Prospect park in Brooklyn? Yes, the southern part of the park.

Marielle Anzelone: Okay.

Brian Lehrer: Yes, that was unclear to me, too, whether you're talking about the southern part of Brooklyn in general or the southern part of the park. Tell us about the particular tree there now that we've identified the spot.

Speaker C: Okay, so the tree there, I swear to gosh, it turns the most crazy, vibrant yellow I've ever seen. Everybody who goes by takes a picture of it so I encourage all the wonderful Brian Lehrer listeners to go out and check out the tree this season.

Brian Lehrer: Ukulele Jake, thank you for chiming in. Why do the leaves on different trees turn different colors? He's talking about that spectacular yellow. Obviously, there are others that turn red, others that turn orange. Why is that?

Marielle Anzelone: Well, because there are different colors within the tree that are produced by different compounds. The one that we know well is chlorophyll, and chlorophyll is obviously green. That's where trees get their green color but there's another pigment hiding behind the chlorophyll and those are called carotenoids, and those produce basically yellows and oranges.

The green is dominant because it's the most. We have mostly chlorophyll in leaves because that's how they create their food but then as the chlorophyll gets pulled back because again, the plants are getting ready for winter and know that the leaves are going to fall and want to take back all of that energy that they expended to save it. It would be very wasteful to drop green leaves on the ground.

They're pulling all of those sugars back into their trunks, and then it reveals this pigment underneath but then, interestingly, there's another kind of pigment that's called anthocyanin, and that is actually produced only in the fall. It's not underneath the leaf the whole time. This is more current research has shown that this is manufactured by the sugars left in the leaf and these colors are also water soluble, unlike the others.

Brian Lehrer: So sweet gum has a huge color range, right? Maybe one of the widest ranges, at least, of local trees. It can turn purple, orange, red, even pink. Why do some trees have such a wide range of colors?

Marielle Anzelone: Yes, that's a good question. I don't really know. I think, again, it's the idea of-- the way in which leaves change color, there's still a lot that we don't know and there's a lot of research happening in this arena because obviously, it's something that scientists want to know, especially because it's also related to fruits as they ripen so it's part of our food industry. I think one of the ways you can see a wide range is to not look at street trees but to look at trees in the wild. Trees in the wild represent a huge genetic diversity.

You can see within one grove of trees, maybe they're all right next to each other. If you're in a swampy area, that's where you'd see the sweet gum and they could be all different colors and it's just really incredible to see. It is a beautiful, beautiful tree.

Brian Lehrer: Karla in West Milford, you're on WNYC. Hi, Karla.

Karla: Good morning. I want to tell you about a little town in the northwest corner of Passaic County where I live, West Milford and I drive home from my job in Westchester as the sun is going down and you pass Monksville Reservoir and the ridges around it are just a spectacular color. Then I continue on my way to Pine Cliff Lake with Beaufort Ridge wrapping around the other side of my lake and it is beautiful. It makes coming home from work a joy every day in the fall when the leaves are in glorious color.

Brian Lehrer: That's great, Karla. Kendall in Queens has another Jersey tree, I think. Kendall, you're on WNYC. Hello.

Kendall: Hi. Hi, Ryan. My spot is River Road just across George Washington Bridge immediately below it. It's beautiful. I've got it down to a science. First week of November. Gorgeous. So many yellows. It's a perfect place to go on a bike ride. It was closed for the-- there was a lot of rain, but I think it'll hopefully reopen soon.

Brian Lehrer: Thank you very much. And that's how long leaf peeping season lasts around here. Yes. I was looking at a map the other day, Marielle, and it said the peak right around here was going to be in the first weekend of November, not even in October. I don't know if that's a difference from the past because of climate change, but that's what they say.

Marielle Anzelone: That's always kind of when I noted peak has been then, but again, it depends where you are because Staten Island is a little bit further along and the Bronx is a little bit further behind. I live in Brooklyn, so it's always-- if I miss something in bloom or if I miss something, fall foliage wise, in Staten Island, you can drive up to the Bronx and check it out there before you miss it altogether.

Brian Lehrer: Counterintuitive because you would think the north changes more quickly or earlier than the south. Another listener writes, my favorite tree is a huge, majestic maple in Central Park that turns into a huge fireball. It stands where the path is from 5th Avenue at 81st and joins the path around the great lawn to the Delacourt Theater. We're almost out of time. Why are there evergreens? Why are there trees that don't change at all?

Marielle Anzelone: They just have a completely different strategy. Evergreens are typically-- the leaves are needles and they hold on to them. They do harden off and they do measure the photoperiod just like all the other plants do but they hold onto their leaves, and it's not totally clear why. The shape of the tree and the reason why the leaves are that shape is because they tend to be in snowier areas. It's the architecture of the tree. It helps to slough off the snow just in the same way you'd have a pointed roof in a snowy area. The reason why they hold on is just to try to photosynthesize through the winter.

Brian Lehrer: Mariel Anzelone, urban botanist and ecologist and the founder of New York City Wildflower Week. Thanks for giving us everything we didn't already know about fall foliage. Oh, and poison ivy. Thanks a lot.

Marielle Anzelone: Thank you, Brian.

Brian Lehrer: And that's the Brian Lehrer Show for today. Stay tuned for Alison.

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