Why are scientists planting tiny forests in big cities?

Healthy forests help combat climate change, provide humans with drinking water and even improve mental and physical health. But it’s hard to imagine an entire forest in the middle of a big city. That’s where micro-forests come into play — public forests on a smaller scale, filled with native plants. They exist around the world, and producer Rachel Carlson went to visit the largest micro-forest in California in this encore episode. She joins host Emily Kwong to chat about what she saw. Interested in more of the science behind urban nature? Email us your question at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Speaker 00

  This message comes from Mint Mobile. Ditch overpriced wireless and get premium wireless for less. Go to mintmobile.com/switch to see which plan works for you.

• 0:12Emily Kwong?

  You're listening to Short Wave from NPR. Hey, Short Wavers. Emily Kwong here. And today, I have a treat for you. We are going to a microforest. If you've never heard of one, they are small, they are lush. And unlike natural forests, microforests are designed entirely by humans for urban environments. And producer Rachel Carlson went to visit one in Los Angeles recently. Hey, Rachel.

• 0:36Speaker 02

  I did. Hey, it was amazing. I had the most fun day ever. I hung out with two scientists who've dedicated themselves to planting these tiny forests to cool down cities and make them more resilient to climate change.

• 0:49Emily Kwong?

  OK, where did you go to see a microforest?

• 0:52Speaker 02

  Ascot Hills Park, which is a park in northeast Los Angeles. It's surrounded by freeways and interstates. It's not too far from the heart of downtown LA. So it's not really an area that I typically associate with lots of green space, but...

• 1:07Speaker 03

  You pull off the freeway and drive this way and you see a green stamp of 10,000 square feet.

• 1:12Speaker 02

  And that's exactly what it looked like, a green stamp. That's Damian Wulet, an associate professor of biology at Loyola Marymount University. He's one of the scientists I met with who's worked on planting and maintaining this microforest for the last two years.

• 1:26Emily Kwong?

  OK, but what makes a microforest a forest?

• 1:28Speaker 02

  In a forest, the canopies of the trees touch one another.

• 1:32Speaker 03

  You plant one tree, that's just a tree. But once you start having the canopy connect, that starts to be what we imagine as a forest. We have this kind of blockage of the sunlight, but also a forest has layers.

• 1:42Speaker 02

  Canopies of trees with layers of plants beneath them. So in that way, a microforest does simulate a natural forest.

• 1:50Emily Kwong?

  OK.

• 1:50Speaker 02

  But what makes a microforest micro?

• 1:54Speaker 03

  It's smaller?

• 1:56Emily Kwong?

  Oh, so this is not like a fairy forest with tiny plants or something. This is just a forest that's got a small footprint.

• 2:03Speaker 02

  Yeah, yeah. A microforest can be anywhere from around 200 square feet to an acre. And the one I visited, about a quarter acre or 10,000 square feet. But it's the largest microforest in California.

• 2:17Emily Kwong?

  So did I in the show, a trip to a small forest with big dreams and real-life contributions to local biodiversity that are making it easier to live with climate change. You're listening to Short Wave, the science podcast from NPR.

• 2:36Speaker 00

  Stay tuned for the following announcements and messages from our sponsors. This message comes from Edward Jones. Where they believe rich is more than caring about the latest and greatest, it's also about taking care of what gives your life meaning. That's why your dedicated financial advisor meets you where you are with personalized financial strategies that help protect what matters, so you can preserve your progress while creating a path forward. The key to being rich is knowing what counts. Let's find your rich together. Edward Jones, member SIPC. This message comes from NetSuite. AI isn't just opening new business opportunities, it's changing the way businesses get work done. That's the

• 3:18Speaker 00

  idea behind NetSuite Next, the next generation of NetSuite with AI woven into the tools your business already relies on. If your revenues are at least in the seven figures, get the free business guide, Aligning for the Agentic Era: How AI is Changing Everyday Work, at netsuite.com/shortwave.

• 3:37Speaker 04

  This weekend, up first, we're in the final days before the midterm elections, and this is one of the wonderful things about politics, one of the wonderful things about humanity. We have all this data, we have all this information, and nobody really knows what's gonna happen. We're gonna follow it day by day, through Election Day and beyond. And you can listen to Up First every morning on the NPR app or wherever you get your podcasts.

• 4:01Emily Kwong?

  Okay, Rachel, so today we are talking about microforests, which are supposed to mimic natural forests, but on a smaller scale and in more urban environments, and people plant them.

• 4:11Speaker 02

  Yeah, ecologists use local plants to help restore biodiversity to the area. So for example, Los Angeles is prone to drought. So there's lots of drought tolerant native plants in the microforest I went to, like Southern California black walnut and blue elderberry. But in other places, ecologists would use different types of plants.

• 4:31Emily Kwong?

  Cool. So do microforests exist in other parts of the world?

• 4:35Speaker 02

  Yeah, there are others in the US. And Damian, our biologist from earlier, told me they're also popular in Europe. The original idea goes back over 50 years to Japan to an ecologist named Dr. Akira Miyawaki.

• 4:48Speaker 03

  And he developed the idea of these kind of tiny forest approach to restoring degraded land.

• 4:55Emily Kwong?

  Interesting. Well, how do you even go about planting a microforest? Like, what is involved?

• 4:59Speaker 02

  Well, a forest isn't just trees. It's a bunch of different species with different roles, from roots in soil to shrubs, to those tall canopy trees that you might think of when you think of a forest. So that's how microforests are planted, too, with dense layers of different kinds of plants.

• 5:17Speaker 03

  So you're kind of planting a whole ecosystem at one time instead of waiting for nature to kind of go through succession, step by step, to get eventually to a forest. It's planting the whole forest at one moment.

• 5:28Emily Kwong?

  Interesting. So why is it strategic to have plants at different heights and different layers of the forest?

• 5:35Speaker 02

  The lowest layers help keep the soil healthy, which ultimately keeps those upper layers growing. And planting a lot of plants all at once contributes to the microforest's growth, and they mature faster than a traditional forest. It might be a couple decades for a microforest instead of something like a century for a bigger forest.

• 5:54Emily Kwong?

  Very cool. Okay, so let's go back to the microforest you visited in LA. Tell me about your field trip.

• 6:00Speaker 02

  I went on a weekday. It was warm, like 75 degrees outside. But I pulled up to the park and met Damian, and he introduced me to someone else.

• 6:08Speaker 03

  There's Catherine right there.

• 6:10Speaker 02

  Oh, great. Hey. Catherine Pacraduni is a horticulturist who helps plant and develop microforests like this one. We walked up a very steep hill to meet her. I was on a hike.

• 6:21Speaker 05

  You can't talk at this point because you're breathing through that. That's totally fine.

• 6:25Speaker 02

  I know my mic's going to catch me, like, out of breath.

• 6:30Emily Kwong?

  Wow, this is like meeting some master gardeners or something, but of the forest.

• 6:34Speaker 02

  It was.

• 6:35Emily Kwong?

  And you said that Damian and Catherine have been working on this particular microforest since 2024, so it's two years old?

• 6:42Speaker 02

  Yeah, they just celebrated its second birthday. And another amazing thing about a microforest compared to a much larger forest is the size allows researchers like Damian and Catherine to use it as a science experiment.

• 6:54Emily Kwong?

  Yeah, you said the microforest is like a quarter of an acre?

• 6:57Speaker 02

  Mm-hmm, 10,000 square feet. And right next to it, there's another plot of land exactly the same size, except it's brown, it's filled with invasive weeds. Catherine and Damian aren't planting anything there, so they can directly compare the plots and see what kinds of insects and birds and other critters show up to each one.

• 7:15Emily Kwong?

  Oh, and study the biodiversity when you create a forest with native plants.

• 7:20Speaker 02

  Yeah.

• 7:21Speaker 03

  Every two weeks, going back and forth between the two of them, counting how many insects we're finding, what birds are there, what lizards are moving through there. We find some cool field mice, some spiders, all sorts of neat things that we find here in the microforest that aren't over there in the control plot.

• 7:41Speaker 02

  All frolicking in the midst of hundreds of trees, shrubs, and other native plants they've cultivated. And Catherine and Damian have seen around 100 different animal species in all, just in the microforest, whereas...

• 7:53Speaker 03

  Which, prior to this microforest being planted, we had an idea of that there were only 100 species being documented in the whole park.

• 8:00Emily Kwong?

  It's the place to be, this microforest. It's bringing the party. How are these scientists tracking the biodiversity, though? Are they, are they walking around and counting everything?

• 8:10Speaker 02

  Partially, yes. They're using a few different methods, though. Damian's lab has mapped out the entire microforest and given each plant a GPS coordinate. And they use drones to measure plant growth, plant volume, and see which species are doing well together and which ones aren't. They also use spider webs to track different animals moving through the microforest.

• 8:30Emily Kwong?

  Wait, why spider webs?

• 8:32Speaker 02

  Apparently, they're like nature's DNA swabs.

• 8:35Speaker 03

  Spider webs are kind of a filter. For the air. And as animals move through their environment, they're shedding skin cells and metabolic waste that floats in the air that sticks to the spider web. So then we came out here, we collected spider webs and washed the DNA off those spider webs and then got an idea of what are all the animals moving through here within the last 24, 48 hours using genetic tools.

• 9:00Emily Kwong?

  That's so useful. Are researchers planting the spiders too? To swap their webs?

• 9:06Speaker 02

  No, it's just the spiders that naturally show up and the researchers don't interfere, aside from studying the webs. Damian says one of his students came up with the idea.

• 9:16Emily Kwong?

  I always knew spiders would make good scientists. Okay.

• 9:18Speaker 02

  I agree.

• 9:19Emily Kwong?

  And what have they found out?

• 9:21Speaker 02

  They've been able to use those webs to figure out what other kinds of animals are hanging out in the micro forest, which is especially helpful for ones that are nocturnal or just harder to spot on their walk-throughs.

• 9:31Speaker 03

  We had a barn owl that I've never seen in there and it's definitely flying through the area at night and we're picking up a signature of that being here.

• 9:40Speaker 02

  That's too.

• 9:41Speaker 03

  So it just gives us more full picture of how is this really behaving like a forest? It's not just when we're conveniently here. It's all hours of the day and night.

• 9:51Speaker 02

  And they also use human community scientists in addition to their spider scientists. Damian's lab developed an app where park visitors can help collect data and they've had over 150 or so people use their phones to scan QR codes attached to the plants to help measure their growth.

• 10:08Speaker 03

  We don't use tape measures. We just say, well, how tall are you? And they kind of estimate the height. We look for signs of flowers or seeds or bivary. And also, is it alive?

• 10:17Speaker 02

  Damian stood next to a Southern California black walnut tree to show me.

• 10:20Speaker 03

  Stand next to a few of them and you can see they're taller than me.

• 10:23Emily Kwong?

  How tall are you?

• 10:24Speaker 03

  So I'm just under six foot, so that's a little bit higher.

• 10:27Emily Kwong?

  Yeah.

• 10:28Speaker 03

  Some of the elderberries down there are over 10 foot, which is incredibly fast when you think about how long it takes for a plant in Southern California to grow.

• 10:36Speaker 02

  In comparison, he told me he has a black walnut tree in his backyard that's nearly a decade old, but it's not as tall as this one.

• 10:44Emily Kwong?

  He sounds like a proud parent.

• 10:45Speaker 02

  He kind of was.

• 10:46Emily Kwong?

  He's like, "Look how tall my tree grew."

• 10:48Speaker 02

  He actually hugged the tree at one point, which was maybe my favorite part of the whole day.

• 10:53Emily Kwong?

  So at the risk of not seeing the forest for the trees, how would you say overall is the health of the totality?

• 11:02Speaker 02

  It's pretty good, and they've measured it in a few different ways. One way is to look at how many plants have survived since they were first planted. And Damian and Catherine say there's an average of over 89% survivorship for the plants now, which is pretty good. And that's one big measure of success. Another is the plant's ability to exclude weeds without humans like Damian and Catherine having to intervene.

• 11:25Emily Kwong?

  Oh, how is the forest keeping weeds at bay on its own?

• 11:29Speaker 02

  So the control plot is filled with weeds. But in the microforest, it's a different story.

• 11:35Speaker 05

  We're crowding out the space with the plants that we do want so that the plants we don't want really don't have much of a foothold. And that's something that we're already observing. Between year one and year two, it's probably been like an 80%, if not more, reduction of weeds inside this space.

• 11:51Speaker 02

  So that microforest density helps keep weeds at bay. And we know that because scientists are comparing it to the control plot.

• 11:58Emily Kwong?

  Got it, got it, got it, got it. Is the microforest also contributing to like carbon sequestration, you know, removing carbon dioxide from the air?

• 12:06Speaker 02

  Yeah, and that leads to improved air quality and soil health. And for this microforest, Damian says it's pulling out one metric ton of carbon per year.

• 12:15Emily Kwong?

  Dang!

• 12:16Speaker 02

  His lab expects that to increase to over 50 metric tons of carbon dioxide per year in the next two decades. And that's more than the emissions of 10 SUVs.

• 12:27Emily Kwong?

  Okay, this microforest is doing its part. Plus...

• 12:30Speaker 03

  It's cooling the neighborhood. It's providing food. Again, the insects, the wildlife that's here.

• 12:38Speaker 02

  It also helps bring people into nature. Even in the short time I was with Catherine and Damian, a few people walked by and asked questions about the microforest. They said they loved seeing the new plants in the park or asked us what kinds of trees we were looking at and even if they could help.

• 12:55Emily Kwong?

  For the love of microforest, Rachel Carlson, thank you for bringing this to the show.

• 13:00Speaker 02

  Yeah, thanks, Emily.

• 13:04Emily Kwong?

  If you liked this episode, follow us on the NPR app or your podcasting platform of choice. And check out our Nature Quest series, which is inspired by listener questions about the environment and how the planet is changing. If you have a question, send it to us. We'll investigate. Email [email protected], your question, and a voice memo, and your name and location. This episode was produced by Hannah Chin and edited by our showrunner Rebecca Ramirez. Tyler Jones checked the facts. Jimmy Keeley was the audio engineer. I'm Emily Kwong. Thank you for listening to Short Wave from NPR.

• 13:48Speaker 00

  Stay tuned for the following announcements and messages from our sponsors.

• 13:53Speaker 06

  This week on the NPR Politics Podcast, the midterm elections are wrapping up, and millions of people have already voted. We're taking one final check of the electoral pulse with a new NPR PBS News Marist Poll. It shows Democrats still poised to make gains, but also with some warning signs for just how many. We'll explain on the NPR Politics Podcast.

• 14:16Speaker 07

  Oh, Kevin, it feels good to be back. It sure does, Casey. And what a time. The world is talking about AI and what's going on in Silicon Valley. And we are here with a new show to tell you all about it. That's right, Kevin. On our new show, Machine Gods, twice a week, we'll be bringing you the biggest news in tech and bring you unmatched access to the real titans of this industry. You can find Machine Gods from NPR on the NPR app or wherever you get your podcasts.