Why are scientists planting tiny forests in big cities?

Summary

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Short Wave – "Why are scientists planting tiny forests in big cities?"

Host: Emily Kwong (NPR)
Producer/Guest: Rachel Carlson
Guests: Damian Wollett (Associate Professor of Biology, Loyola Marymount University); Catherine Pokradouni (Horticulturist)
Date: June 2, 2026
Length: ~15 minutes

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Episode Overview

This episode explores the innovative concept of "microforests"—tiny, densely planted forests within urban environments—designed to boost biodiversity, fight climate change, and bring nature into cities. Through a field visit to Ascot Hills Park in Los Angeles, the team investigates what makes a microforest unique, how it’s built, its impact, and the creative scientific methods used to study it.

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Key Discussion Points & Insights

What Is a Microforest?

• Rachel visits the microforest at Ascot Hills Park, surrounded by freeways and far from what you’d expect as natural green space.
• Definition:
  • Microforests are small, human-planted urban forests designed to mimic natural forests through dense planting and multiple layers of vegetation.
  • Damian Wollett: “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.” (01:46)
• ‘Micro’ just means small footprint: Ranges from 200 sq ft to about an acre; Ascot Hills’ microforest is 10,000 sq ft, the largest in California.
• Not a fairy forest: Real trees; just in a contained urban space. (02:08)

Global Roots & History

• Microforests have an international pedigree; the idea traces back 50+ years to Japanese ecologist Dr. Akira Miyawaki, who pioneered tiny forests to restore degraded land. (05:09)

How Microforests Are Designed & Planted

• Ecologists use locally native, drought-tolerant plants (e.g., Southern California black walnut, blue elderberry in LA) to fit the regional ecosystem.
• Emphasis on planting an entire ecosystem at once: trees, shrubs, ground cover, etc. (05:40)
  • Damian Wollett: "You're kind of planting a whole ecosystem at one time. Instead of waiting for nature to...go through succession...it's planting the whole forest at one moment." (05:40)
• Dense, multi-layer growth enables microforests to mature in decades (rather than centuries for natural forests). (05:58)

Microforests as Science Experiments

• Experimental Design: Microforest is paired with a same-sized “control plot” of invasive weeds, allowing researchers to measure impacts side-by-side. (07:20)
• Measured benefits include:
  • Increase in native animal species (about 100 seen in the microforest vs. the same number in the whole park before) (08:04)
  • Higher survivorship of plantings (89%+ after two years) (11:25)
  • Sharp reduction of weeds (80% decrease inside the microforest vs. control plot) (12:04)

Innovative Biodiversity Tracking

• Manual Counts: “Every two weeks, going back and forth between the two...counting how many insects we're finding, what birds are there...” – Damian (07:44)

• High-tech Methods:

  • GPS-mapped every plant
  • Drones measure plant growth and volume
  • Spider webs collect environmental DNA (“nature’s DNA swabs”) for genetic sampling — reveals animals passing through, even nocturnal ones.
    • Damian Wollett: “Spiderwebs are kind of a filter for the air. And as animals move through their environment, they're shedding skin cells…that…stick to the spider web. So then…we collected spider webs and washed the DNA off those spider webs, and then got an idea of what...animals [are] moving through here within…24, 48 hours.” (08:58)

• Cool Findings:

  • Discovery of animals like barn owls and bats that are seldom seen during the day. (09:54)
  • App-based citizen science: Park visitors scan QR codes on plants, estimate their growth, record blooming/seeding, and look for herbivory. (10:14)

Impressive Growth and Community Involvement

• Microforest shows rapid plant growth, with some trees reaching 10 feet in 2 years—much faster than similar trees outside the microforest.
  • Damian Wollett: “Some of the elderberries...are over 10 foot, which is incredibly fast when you think about how long it takes for a plant in Southern California to grow in comparison.” (10:51)
  • Damian—clearly attached to the forest—hugs a tree in delight. (11:11)

Environmental Benefits

• Weed resistance: Dense, healthy growth crowds out weeds, as opposed to the control plot that’s weed-choked. (12:02)

• Carbon sequestration:

  • The microforest currently absorbs about one metric ton of CO₂ annually; projections expect over 50 metric tons a year within 20 years—more than the emissions of ten SUVs. (12:39)

• Other benefits:

  • Cools neighborhoods
  • Provides food and habitat for insects, birds, and small animals
  • Invites the community into nature and inspires curiosity and stewardship

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Memorable Quotes & Moments

• Emily Kwong (joking about scale):
  "Oh, so this is not like a fairy forest with tiny plants or something. This is just a forest forest that's got a small footprint." (02:10)

• Damian Wollett (on planting strategy):
  "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." (05:40)

• Rachel Carlson (on field day):
  "I was on a hike. You can't, can't talk at this point because you're breathing too heavy. That's totally fine. I know my mic's gonna catch me, like, out of breath." (06:53)

• Emily Kwong:
  "He sounds like a proud parent." (11:07)
  "He's like, look how tall my tree grew." (11:09)

• On spider web DNA:
  Rachel Carlson: "Apparently they're like nature's DNA swabs." (08:55)
  Emily Kwong: "I always knew spiders would make good scientists." (09:39)

• On community science:
  "They've had over 150 or so people use their phones to scan QR codes attached to the plants to help measure their growth." (10:14)

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Timestamps for Key Segments

• 00:27 – Introduction to microforests and trip to LA
• 01:21 – What makes a microforest a "forest"?
• 02:08 – Defining the “micro” in microforest
• 04:33 – How microforests are planted (native species, ecosystem approach)
• 05:09 – Origin of the concept: Dr. Akira Miyawaki in Japan
• 05:40 – Planting a whole ecosystem at once
• 07:20 – Microforest as scientific experiment; control plot setup
• 08:04 – Measuring biodiversity: animal counts
• 08:53 – Tracking animals with spider web DNA
• 09:54 – Identifying nocturnal animals (barn owls, bats) via genetic data
• 10:14 – Community involvement through QR code app
• 10:51 – Impressive plant growth in two years
• 11:25 – Plant survivorship and weed suppression
• 12:29 – Carbon sequestration rates and future impact
• 12:52 – Additional benefits (cooling, habitat, people engaging with nature)

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Episode Takeaway

Microforests are a promising urban solution for biodiversity, climate adaptation, and community connection. Through dense, multi-layered plantings tailored to local ecosystems, these tiny forests replicate natural processes, thrive quickly, support wildlife—and inspire both scientists and city dwellers to reimagine the possibilities for greening our cities.

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Transcript

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[Emily Kwong]

You're listening to Shortwave from npr. Hey, shortwavers. 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.

[Rachel Carlson]

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.

[Emily Kwong]

Okay, where did you go to see a microforest?

[Rachel Carlson]

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.

[Damian Wollett]

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

[Rachel Carlson]

that's exactly what it looked like, a green stamp. That's Damian Wollett, 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.

[Emily Kwong]

Okay, but what makes a microforest a forest?

[Rachel Carlson]

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

[Damian Wollett]

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, where you have this kind of blockage of the sunlight. But also, a forest has layers, canopies

[Rachel Carlson]

of trees with layers of plants beneath them. So in that way, a microforest does simulate a natural forest. Okay, but what makes a microforest micro?

[Damian Wollett]

It's smaller.

[Emily Kwong]

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

[Rachel Carlson]

Yeah, yeah. 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.

[Emily Kwong]

So did I end 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.

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[Emily 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.

[Rachel Carlson]

And people plant them? 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.

[Emily Kwong]

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

[Rachel Carlson]

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

[Damian Wollett]

Dr. Akira Miyawaki and he developed the idea of these kind of tiny forest approach to restoring degraded land.

[Emily Kwong]

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

[Rachel Carlson]

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.

[Damian Wollett]

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.

[Emily Kwong]

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

[Rachel Carlson]

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 growth. And they mature faster than a traditional forest. It might be a couple decades for a micro forest instead of something like a century for a bigger forest.

[Emily Kwong]

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

[Rachel Carlson]

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.

[Damian Wollett]

There's Katherine right there.

[Rachel Carlson]

Oh, great. Hey. Catherine Pokradouni 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. You can't, can't talk at this point because you're breathing too heavy. That's totally fine. I know my mic's gonna catch me, like, out of breath.

[Emily Kwong]

Wow. This is like meeting some master gardeners or something. But of the forest.

[Rachel Carlson]

It was.

[Emily Kwong]

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

[Rachel Carlson]

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.

[Emily Kwong]

Yeah. You said the microforest is like a quarter of an acre?

[Rachel Carlson]

Mm, 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.

[Emily Kwong]

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

[Rachel Carlson]

Yeah.

[Damian Wollett]

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,

[Rachel Carlson]

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

[Damian Wollett]

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

[Emily 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?

[Rachel Carlson]

Partially, yes. They're using a few different methods, though. Damien'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.

[Emily Kwong]

Wait, why spider webs?

[Rachel Carlson]

Apparently they're like nature's DNA swabs.

[Damian Wollett]

Spiderwebs 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.

[Emily Kwong]

So useful, our researchers planting the spiders, too, to swab their webs?

[Rachel Carlson]

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.

[Emily Kwong]

I always knew spiders would make good scientists.

[Rachel Carlson]

Okay, agree.

[Emily Kwong]

And what have they found out?

[Rachel Carlson]

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

[Damian Wollett]

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.

[Rachel Carlson]

Bats, too.

[Damian Wollett]

So it just gives us a 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.

[Rachel Carlson]

And they also use human community scientists in addition to their spider scientists. Damien'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.

[Damian Wollett]

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 herbivory. And also, is it alive?

[Rachel Carlson]

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

[Damian Wollett]

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

[Rachel Carlson]

How tall are you?

[Damian Wollett]

So I'm just under 6 foot. So that's a little bit higher.

[Rachel Carlson]

Yeah.

[Damian Wollett]

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

[Rachel Carlson]

to grow 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.

[Emily Kwong]

He sounds like a proud parent.

[Rachel Carlson]

He kind of was.

[Emily Kwong]

He's like, look how tall my tree grew.

[Rachel Carlson]

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

[Emily Kwong]

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

[Rachel Carlson]

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.

[Emily Kwong]

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

[Rachel Carlson]

So the control plot is filled with weeds, but in the microforest, it's a different story. We're crowding out the space with the plants that we do want so that

[Damian Wollett]

the plants we don't want really don't

[Rachel Carlson]

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

[Emily 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.

[Rachel Carlson]

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

[Emily Kwong]

Dang.

[Rachel Carlson]

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

[Damian Wollett]

Okay.

[Emily Kwong]

This micro force is doing its part.

[Damian Wollett]

Plus it's cooling the neighborhood. It's providing food again, the insects, the wildlife that's here.

[Rachel Carlson]

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, what kinds of trees we were looking at and even if they could help.

[Emily Kwong]

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

[Rachel Carlson]

Yeah, thanks, Emily.

[Emily 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 shortwavepr.org 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, Check the facts. Jimmy Keeley was the audio engineer. I'm Emily Kwong. Thank you for listening to Short Wave from npr.

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