- Hi there.

I'm Frank Graff.

New insights into how and why trees produce spectacular fall colors, why urban areas are heat islands, and building a place for the all important bee.

We're talking tree science in the forest in the city next on "Sci NC."

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I think that I shall never see a poem as lovely as a tree.

Joyce Kilmer wrote that in 1913, while looking out a window of her New Jersey home at a tree covered hill off the distance.

It is one of the most well-known verses celebrating the beauty of trees.

And you could say that trees are most spectacular in the fall, when their leaves explode with color.

Producer Evan Howell shares new science insights into that color change.

- [Evan] Grandfather Mountain, it's mid-October and a bit cloudy, but it's near the peak of what people call fall color.

Right now trees like maples, beech and birch are turning their traditional oranges and reds.

But in a warming world, the question is whether climate change will affect when and how the changing leaves will paint the mountains into a rainbow of colors every fall.

One day later, the sun is opened up at the nearby Blue Ridge Parkway and Linn Cove Viaduct.

- [Hiker] Oh, very cool.

- [Evan] It's here where hikers make their way up the roughage trail to take in some of these postcard-like scenes of Appalachia.

- Yeah, it's steep and there's rocks and they've even cut into the rocks to make sort of little steps 'cause it's otherwise it'd be too difficult to get up.

- Hiking here is not for the faint of heart.

- Well, this trail is, you have to be in good shape for this trail.

- I follow you.

A pleasure to meet you.

- [Evan] Every year these hikers and tourists flock to the area in part because of the words of this man, Howie Neufeld.

Neufeld is known as the fall color guy, and he's a bit of a celebrity among those who love coming up here as much as he does.

- Where are y'all from?

- [Hiker] Knoxville.

- Knoxville!

- [Hiker] We're followers.

- [Howard] Oh well, great.

- [Hiker] I always look every time, what are the leaves doing?

- Yeah, well they're pretty good.

Well, I always get anxiety when people ask me when they should come up here, because I can't predict the weather more than about five or seven days in advance.

And so since the colors are really dependent on the weather, not so much the climate, but the weather, then, if they ask me in May, I really can't get very accurate.

- [Evan] Throughout the year, daily weather brings changes in sunlight, temperature, and precipitation, all things that affect how leaves live.

But the climate is what's happening in the long term.

The big picture.

While Neufeld won't explicitly say whether climate changes affecting the seasonal weather in the mountains, and that includes when peak color arrives, he does say things are getting weird.

- I've been doing this for 17 years now, and so I went back and looked over all my writings, and picked out the week that I said was peak color and then I plotted it.

And from 2008 to 2016, all but one year we're within the 10th to the 20th of October.

So pretty consistent.

But starting in 2017, it was all over the place.

It could be right on time, it could be a week late, it could be up to two weeks late.

2018 was two weeks later than normal.

And the variability in these last eight years is twice as high as it was in those first eight years.

So it's getting harder to predict when it will be.

[water trickling] - [Evan] With so many questions about what's going on at this point, we may want to take a moment to look at the typical life of a leaf.

Plants need three things to stay alive: Sunlight, water and carbon dioxide.

Water comes in through the roots, carbon dioxide through the leaves and other parts of the plant, and sunlight is absorbed through a chemical in the leaves called chlorophyll.

In the spring and summer leaves use light to convert water and carbon dioxide into sugars and generate oxygen.

We call that photosynthesis.

The sunlight reacts with the water and carbon dioxide to produce those sugars, which is essentially plant food.

However, chlorophyll breaks down with the exposure to sunlight.

That's no problem during the summer, leaves just make new chlorophyll.

But when the sunlight fades in the fall, chlorophyll production drops.

- So for trees that turn sort of orange, like that one right there, those pigments are there all summer, but they're hidden by the green chlorophyll.

When the chlorophyll degrades, goes away, these orange and yellows come out.

So they're pretty much constant from year to year.

But it's the red colors like on that bush there and the reds you see on the hillside, those are not present in the summer, but they're made in the fall.

- [Evan] So we'll take red, for example.

- So the the red pigment acts as a sunscreen.

It allows the leaves to stay uninjured when you get highlighting cold, which can be very damaging to a leaf.

And then it can withdraw those nutrients back into the twig and use those nutrients next spring to get the leaves a headstart.

- [Evan] Neufeld says that climate change has been relatively slow to affect peak color of the mountains.

But climate change can result in extreme weather events like flooding and heat.

He says they need more data and says his big question is how hot weather would affect the timing of color in areas down in the central part of the state.

- For the Piedmont, I think you have a bigger chance of getting really extreme temperatures.

You know, an acute heat wave, like a short period where you have say several days in a row at 95 or 100, what that does to the fall color, 'cause it's unprecedented.

- We're definitely seeing the effects of climate change down here in the Piedmont.

This is a black gum tree and- - [Evan] So, three weeks later we went to the Piedmont and met with Nikki Hughes, who's known here as a premier leaf scientist.

Like Neufeld, she stops short of making a direct climate leaf connection, at this point.

- Well, what I would say is climate change is extending the length of the season where we get to see red coloration because some species are still changing early like this.

Tupelo and dogwoods are still changing on time, but others like oaks are waiting longer and longer.

- [Evan] Hughes says to better understand how leaves change in the fall, you need to look at how different species do it.

When chlorophyll leaves a leaf and goes back into the stem, the pigments become the protections.

And there are a lot of pigments: eosinophils, carotenoids, and beta-carotenes, give some of the yellows and oranges, anthocyanins give the reds, mixtures in some leaves of several pigments give a purple.

- Some species synthesize anthocyanins on top of that yellow.

When it's a small amount of anthocyanins, you get an orange leaf.

And when it's larger amounts, you get deeper shades of red, like we see in this Tupelo.

And so some spots you can see the yellows, the anthocyanins and carotinoids, but any oranges are red, you see are coming from anthocyanin.

We don't know as much as you think we know, scientists who study red leaves, 'cause nobody's really researched it.

- [Evan] Hughes says, even with all this science, they simply need more data to make that connection.

- But we're starting to figure out trends with how soon it will be like colder years color change happens sooner, drier years, it happens sooner, but then you have warmer temperatures making it happen later.

So we have a lot of opposing forces at play.

- [Evan] So as mountain leaves might be reacting to a warming climate, one thing is for sure: the leaves will change in the fall.

But we need more data if we're gonna pick the perfect time to schedule our mountain vacation.

- [Howard] I think the trend over the years will be for the peak fall color to come later.

Inevitably, we'll get some warming up here.

- Trees are important for many reasons, absorbing carbon from the atmosphere, habitat for animals, preventing flooding and erosion, forest products, just to name a few.

But researchers are noticing that the presence of trees can also change how severe the urban heat island effect is in cities and urban areas.

Producer Michelle Lotker explains.

- [Michelle] Ah, the urban jungle.

Except it generally has a lot more concrete than an actual jungle.

And that makes it hotter.

- The science behind it is relatively simple.

On a sort of 10,000 foot level, hard surfaces tend to be hotter, dark surfaces tend to be hotter.

Soft surfaces that tend to be cooler, shade tends to be cooler.

Unfortunately, within built environments within these urban areas, we have lots of areas where we have lots and lots of impervious, hard, dark surfaces that hold onto heat and make those areas very, very, very hot.

And we have fewer areas with green space and shade that tend to be cooler.

And because these two can be really close to each other, you can see huge amounts of variations.

Sometimes 15 to even 19 or 20 degree differences between areas within the same city on the same day.

- [Michelle] We call these hotspots urban heat islands.

And with global temperatures on the rise, that heat can turn deadly.

- Heat is our number one weather related killer, and we often don't think about that.

We see the floods, we see the hurricanes, we see the fires on TV, and it's kind of hard to show heat on TV.

But we know that a lot of people die in days with extreme heat.

And also nights that are extremely hot.

We already have hot parts of the city historically and we're adding a few degrees more warming to that and we know they're just going to get more unbearable.

So what we're trying to do is find out where those parts of the city are, so that we can introduce some heat mitigation measures.

- [Michelle] There's a lot of weather data available.

You can easily access a prediction of what your week is gonna be like sometimes down to the hour.

- But the data that we have to measure temperature is from our cell phones, from weather stations.

That data is very sparse and it represents generally large areas.

As we walk through an urban area, we may go under some trees and it's really shady and cooler.

We may walk across that parking lot surface, it's much hotter.

We experience temperature variably throughout an urban area.

The problem is, is that the existing data from weather stations is not fine enough to actually measure those differences.

- Let's go attach this to your car.

- Yeah, let's do it.

- [Michelle] To better understand the true exposure and experience of heat in Raleigh, Durham, and Chapel Hill, the Museum of Life and Science partnered with local organizations and communities to take on the ground measurements of heat in the summer of 2021.

- [Max] So this project is a little bit different from perhaps a traditional scientific study in that so much of the data collection and then a lot of the analysis afterwards is going to be done and publicly owned and available by the people that live there.

- It's really important to know that anybody can be a scientist.

You don't need a PhD to do science.

So what we're trying to do is empower these community members to study their community and hopefully with these data then they can enact some policies or plans to help mitigate their heat stress.

- [Michelle] Routes throughout the cities were developed with community input, and then volunteers carried sensors along those routes three times during the sampling day, morning, midday, and evening.

Data was collected by a car, by a bike, and on foot.

The data collected painted a powerful picture.

- The data did indeed show that there were urban heat islands.

It also found that there are existing heat disparities on that neighborhood by neighborhood or sometimes block by block level.

July 23rd was around 88-89 degrees, which is pretty much the typical summer day that you'd expect here in Central North Carolina.

On that day in the evening, we reached a temperature difference of about 11 degrees, which is a pretty remarkable finding.

It means that within our study area, and indeed here in Durham, some neighborhoods sometimes only miles apart, were 11 degrees warmer than neighborhoods that were close by to them.

A lot of what we have found is that if you live in an urban area, you're not just doomed to live in a warmer area.

There are pockets, individual small level areas that are warmer than other parts of the urban area.

- [Michelle] One of those pockets is the historically significant Hayti neighborhood in Durham, which was heavily altered by urban renewal policies in the late 1960s.

- If you look at any of the photographs or some of the video on what the Hayti community, the district looked like prior to 147, even this venue when it was a church, you know, their trees, there's just a beautiful canopy of greenery.

You know, folks could walk the sidewalks or sit out and just enjoy the environment.

All of that was destroyed.

Data and studies have shown that in general, in other parts of Durham there might be 60% canopy, but in the Hayti communities are only 17% canopy.

That's deplorable.

You've got a lot of residents who can ill afford to be paying higher cooling costs, but that's exactly what they're having to do, because it's so hot in the evenings.

It's not cooling off indoors, because that heat is being held.

And it's just really another indication of how the injustice plagues, plagues communities like Hayti of color, we continue to be impacted by systemic racism and policies and practices that are totally, totally unjust.

- [Michelle] The publicly available data gathered in this study can be used to support changes in policy and infrastructure that will increase heat resiliency.

- We can plant trees.

Parks are great.

I know that when I'm walking around downtown Raleigh, I'm always switching sides of the sidewalk.

If there are more trees on one side versus another.

We can also put things like bus shelters in areas that have shade or build canopies over them.

We can direct people to cooling centers on really hot days.

Maybe you can't afford to turn on the air conditioning in your house, but we can show you a place that will be safe for you and your family to go and cool down.

There are some really tangible things we can do that are almost low hanging fruit.

We're not building a sea wall, but we're just trying to get people out of harm's way.

- [Michelle] UNC Chapel Hill's data-driven Enviro Policy Lab facilitated a hackathon where people dug deeper into the data.

- The idea of a data science hackathon is to open up the data, get mentors, people who are climate scientist or have some knowledge about urban heat or public health, and get people together to try to come up with creative solutions, data analysis, visualization to help better understand the problem of urban heat exposure and what we can do about it.

Globally, 65% of people will live in cities by 2030 and that number will just continue to increase over time.

It's gonna become an increasingly important issue for citizens and policymakers to be aware of and to do something about.

- [Max] Equitable planning to make sure that we are not only dealing with these urban heat islands, but also dealing with it in a responsible way means making sure that we include residents in the phases of planning, so that whatever happens in these areas is led by their priorities and their preferences.

- While scientists study the effects of urban heat islands, they are also looking at how to ease the problem.

And as Rossie Izlar explains, it's not as easy as just planting any tree anywhere.

[dramatic music] - [Rossie] 2023 was the warmest year on record, and 2024, we'll probably smash that record again.

But in cities, the heat is not equally distributed.

Here's a map of my hometown of Durham, North Carolina.

The red areas can be as much as 10 degrees hotter than the blue areas.

And just looking at satellite images of those two spots reveals obvious differences: pavement and parking lots versus leafy green canopies.

But the obvious solution, plant more trees, is not as easy as you'd think, especially in cities, because trees aren't exactly the predictable pieces of infrastructure that we'd like them to be.

So in a future where every year breaks a new heat record, how do we nurture our best line of defense?

The first rule of an urban forest: right tree, right place.

- So this is an interesting tree.

It's a bald cypress, which you don't see in cities nearly as often as some other species.

But one of the reasons it's planted here is 'cause it can tolerate really wet conditions super well.

And we're right by a stream, which makes perfect sense.

So you plant a species like this in the right place and it does super well.

If you planted a tree that needs to be really dry here, not nearly as good, and it probably wouldn't be nearly as healthy as this one.

- [Rossie] Renata studies urban forests at Duke University, they know the trees in downtown Durham intimately.

And we took a tour to see some happy trees and some not so happy trees.

- So in the last decade, two decades, there's been a lot of emphasis on planting trees 'cause we realize the benefits of them.

And immediately, one of the problems that came up with some of these Million Trees initiatives, for example, is where do you put them?

So in cities like Boston, for example, they have smaller sidewalks in some of these older neighborhoods.

And if you wanna make sure that your sidewalks are accessible to, say, people using wheelchairs, you put a tree in the middle of your sidewalk, a wheelchair can no longer go through.

One of the other things we find is a general idea of right tree right place is really important.

So if you're planting a redwood, which I have seen planted in a very, very small planting space, it's gonna pull up your sidewalk.

It's gonna cause problems, just because it's a big tree, right?

- [Rossie] Also, tree lovers are quick to point out the benefits of native trees.

They're adapted to the region's climate and many species provide food for native wildlife, but natives aren't always the best fit for urban environments.

Trees die younger in cities.

They're surrounded by concrete and there's not much room for their roots to grow.

- And the species that tend to handle urban conditions really well are not always the native species.

So things like ginkgos.

Cool tree, a lot of cities have some of those ginkgos, they're not native to anywhere in the United States.

- [Rossie] Take this lace bark elm, which is a non-native tree in North Carolina.

It can handle the compacted and low quality soil here and it doesn't require much maintenance.

- Notice here we've got construction on one side.

This is all brick and paved over, right?

It is a very stressful place for a tree.

So you need trees that can handle these kinds of conditions.

- [Rossie] The second rule of urban forests, you need the community.

Cities like Durham are leafier than most.

We have a 52% canopy coverage.

Other cities, it's more like 20%, but crucially, more than 90% of that canopy is owned by residents.

So it's up to regular citizens to maintain the trees, and the places that the city can plant trees are limited.

- So in Durham, for example, one of the places that the city can plant trees is in what's called a right of way, or basically an area that is technically public land, but often looks like it's on somebody's property.

And if you're a homeowner minding your business and suddenly a tree pops up in what you think is your property, that can be kind of surprising.

And if you're excited about that, maybe the city talk to you ahead of time, then great, right?

Then you can water the tree, work with the city to take care of the tree and it might do great.

But if you're not expecting it and you may not be excited about it, 'cause you had other plans for that space, then you can have tensions and that tree might not survive as well.

- [Rossie] Getting community buy-in means building relationships with groups that have been marginalized.

It's no coincidence that the hottest areas on this urban heat map are also the same historically Black neighborhoods that were redlined in the 1930s.

These areas were officially designated as risky investments.

And the city planted far fewer trees along sidewalks and roads.

Today, wealthy Durham neighborhoods have 50% more canopy coverage than the redlined neighborhoods.

It's the same story in many southern cities.

But Renata says that solving those past inequities can't happen without community buy-in.

- Is there a plan to take care of these trees for the next 20, 30, 80 years, depending on the age of the tree?

Or are you expecting residents to do that?

Because in some cities it's the resident who has to take care of it.

And if you're already strapped for money, the idea of several hundred or even more dollars they have to spend regularly is not exactly exciting.

Or they had other plans or uses for that space.

If the kids generally play a soccer match on the edge of the road in one person's yard and you put a tree in the middle of it, that may not be exactly what the community wants.

They might want a tree somewhere else, but right there, it may not be exactly what makes sense, 'cause even if you do plant trees, I'm not sure they're gonna do super well if the people aren't excited about them.

- [Rossie] And that leads us to the third rule of urban trees: they require care.

- Water is really important for the first two to five years, or really the first five years of a tree's life post planting.

And it's great if you can come by with a water truck, but it can be more reliable to have something like a gator bag or a... Oh, what is this called?

I think they might call it a tree diaper, to be honest, which is kind of funny.

- [Rossie] Young trees often get damaged by construction or even routine lawn maintenance, like this little red bud that is still against all odds alive.

- [Renata] If you get closer, you'll see the wood path probably happened as it got hit.

Even if you do everything right, especially with young trees, they still don't always make it.

- [Rossie] And sometimes trees grow in places you might not expect or even want.

Though I happen to love this one.

- Trees are still living things, and at the end of the day, they will do what they want.

A tree will not grow always the way you want it to.

It won't always look the way you want it to.

And that's something you have to plan for too.

That we are living with other living beings, not just some slab of concrete.

- Urban areas not only need more trees, they also need bees.

After all, bees pollinate flowers and gardens, and that's where Bee Downtown comes in.

[light music] [light music continues] - Bees are the world's number one pollinator.

Every third bite of food you eat is thanks to a honeybee.

From April, 2015 to April, 2016, the United States lost 44% of its honeybees.

And this is a worldwide issue.

It's not just in the United States.

For millions of years, they've provided the world with the food that it needs to survive.

And now they're struggling and they're trying to tell us that something's wrong.

And so it's time for us to listen.

My name is Leigh-Kathryn Bonner.

I got involved with bees through my family.

I am a fourth generation beekeeper from North Carolina.

The best way I knew how to make a difference was through beekeeping.

And the studies show that bees thrive in urban environments.

So I took that inspiration and brought the bees to the city.

Bee Downtown started as a passion project.

I couldn't keep a beehive at my apartment complex while in college.

And I was interning for American Tobacco, this campus right here.

And I asked the owner of the campus if I could put one bee hive on the roof.

It just snowballed into something so much more, because we saw how much the employees cared about the hives, how much good they were doing in the community and throughout the city.

And so other businesses wanted to sponsor hives and purchase hives from us.

So it's turned into one bee beehive on a rooftop to, this year, we'll have about 100 beehives across the Triangle that we will be maintaining for different businesses.

I mean, the bees are a fantastic analogy for a city and a community.

And our favorite saying is by herself one honeybee makes a 12th of a teaspoon of honey in her life.

But together a hive can generate over 80 pounds of honey in a matter of months.

So if we as communities can work together like beehives, we can collectively create lasting change in the world that we're proud to be a part of and we're proud to tell our children and our children's children that I was a part of that, I was a part of reviving agriculture, of taking care of the environment, of caring deeply about how we leave the world once we're gone.

- And that's it for "Sci NC" for this week.

If you want more "Sci NC," be sure to follow us online.

I'm Frank Graff.

Thanks for watching.

[light music] [light music continues] [light music continues] [light music continues] - [Announcer] Quality public television is made possible through the financial contributions of viewers like you who invite you to join them in supporting PBS NC.