December 24, 2024 • 32 mins
If a being doesn’t have ears, can it hear? And if it doesn’t have a mouth, can it talk? In this episode, we spend a golden afternoon conversing with the flowers, plants, and trees.
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Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Amy Martin (00:02):
I was just sitting in front of my computer trying
to figure out how to start thisepisode, which is all about
plants and pollinators andsound, and I heard this noise
across the room, and it made mewonder, wait, did I leave my
(00:23):
phone on vibrate? And then Iwalk over to track down the
sound, and then I see it's anenormous bee just outside my
window, moving from flower toflower on my snapdragons, which
are in full bloom right now.Nice!
(00:50):
I grabbed my sound gear andwalked out into my yard and
everywhere I looked andlistened, the bees were on a
bender. They were drinkingnectar with so much gusto, they
made me want to try some. Theydisappeared into the blossoms
and lost themselves there, thenstumbled out later with pollen
all over their legs and wingsand flew off into the morning
(01:13):
sun. This is pollination inaction. Plants can't pick
themselves up and move towardpotential mates. They need to
attract helpers to move thesperm from the male plants to
the ovaries of the females. Sothe flowers have essentially
thrown a nectar drinking partybecause they want to have sex.
(01:36):
And it works. Animals like theseinsects pollinate around three
quarters of all floweringplants. Without them, a lot of
plants would die, including manyof the foods we depend on daily.
The amorous intentions of plantsare the hidden force behind a
lot of activity on our planet.Take the sound I heard earlier-
(02:00):
on the surface, this seems likean interaction between two
animals, a human and a buzzingbee, but the flowers are
actually driving all the action.They produced the nectar which
attracted the bee that thenattracted me, all of which is to
say, plants can do things. Theyare doing things, making things
(02:23):
happen around them. Like allliving things, they're using
whatever resources are availableto get their needs met. And one
of the things that's availablein abundance around them is
sound. So what, if anything, arethey doing with all that
acoustic information? Welcome toThreshold, I'm Amy Martin, and
(02:49):
we are living through abotanical paradigm shift. A
growing body of research isdisrupting and reorganizing what
scientists thought they knewabout trees, flowers and all
things vegetal. In our lastepisode, we met Heidi Appel and
Rex Cocroft, the two researcherswho proved that plants can tune
(03:10):
into vibrations made by insectsdoing unfriendly things to them,
like caterpillars biting intotheir leaves. But what about all
of these sounds made by friendlyvisitors? Is it possible the
plants can sort of hear thesepollinators happily buzzing
among the blossoms? While I'mwandering around in my yard
(03:33):
listening to bees, are theflowers listening too?
Dr. Lilach Hadany (03:37):
I wondered about this question.
Amy Martin (03:39):
Dr. Lilach Hadany didn't only wonder about this
question, she decided to try toanswer it, and in this episode,
we're going to follow her downthat primrose path into a whole
new world of plantypossibilities.
(04:18):
Flowers are a time honored partof human courtship rituals. I
mean, just try to imagine awedding with no flowers. And Dr.
Lilach Hadany says this is noaccident. Attracting suitors is
exactly what flowers weredesigned to do. It's just that
plants use them to attractcreatures with six legs.
Dr. Lilach Hadany (04:40):
It is actually well known that the
plant signals to the pollinator.It is large and colorful and
emits smells.
Amy Martin (04:51):
Lilach is an evolutionary theoretician at Tel
Aviv University, and she saysscientists have studied how
plants send pollinators thesekindsof visual and chemical
signals through their flowersfor a long time, but the
assumption has been that soundwasn't really a factor, that
there was no acousticcommunication going on between
(05:11):
the plants and the pollinators.And this seemed odd to her.
Dr. Lilach Hadany (05:15):
Plants are communicating all the time. Why
wouldn't they use sound?
Amy Martin (05:21):
Almost all flowering plants need to attract
pollinators, and a lot of thosepollinators make a fair amount
of noise. Was all of that soundreally just wasted on the
plants?
Dr. Lilach Hadany (05:32):
Pollination seemed to me like one of the
cases where responding to soundswould be immediately beneficial
for the plant. So there was anevolutionary puzzle here.
Amy Martin (05:44):
It was a puzzle she wanted to solve. So she designed
an experiment focused on nectar,the sweet liquid plants make as
a reward for animals that visittheir flowers. Producing nectar
is costly for plants, so it's totheir advantage to time the
production of it reallyprecisely, right when they're
(06:04):
most likely to be visited by thebirds and beesthey most want to
attract. And breezing by isn'tenough. Ideally, the pollinators
will get very interested andhang out a while and then spread
the love around.
Dr. Lilach Hadany (06:20):
If a flower is pollinated by an animal that
makes sounds, then it ispossible to prepare pollination
at exactly the time that thepollinators are likely to be
around. So it is not necessarilyresponding to a single
pollinator, but a singlepollinator is a good indication
(06:40):
that other pollinators may bearound.
Amy Martin (06:42):
So the plant might be kind of, in very metaphorical
terms, the plant might bethinking in quotes, there's the
sound of one pollinator, sothere's probably going to be
others around. So maybe it wouldhelp me to produce more nectar.
Dr. Lilach Hadany (06:57):
So I would put it that, natural selection
could act on the plants toproduce improve the reward in
times where pollinators arelikely to be around.
Amy Martin (07:08):
So this was what Lilach decided to test. When
plants are exposed to soundsmade by pollinators, do they
change something about theirnectar production?
Dr. Lilach Hadany (07:18):
If you hear a pollinator nearby, would the
plant say, me, me, me! Sort of.
Amy Martin (07:24):
Because if they did, that could be a sign that they
were hearing the pollinatorssomehow.
Dr. Lilach Hadany (07:30):
And it might be preparing for fertilization.
Amy Martin (07:36):
Lilach and her team drained the nectar from a bunch
of beach evening primroses,tough little plants with big
yellow blossoms. Then theyplayed the kinds of buzzes that
pollinators, like bees, mightmake.
Did you have like a littleportable speaker? I'm trying to
picture what it looked like.
Dr. Lilach Hadany (07:54):
So the speaker is portable. We were
trying to mimic a bee goingaround the bush rather than
standing in front of the flowerand the buzzing.
Amy Martin (08:06):
I didn't ask Lilach if costumes were involved, but I
really hope so. They also playedother sounds to the plants,
sounds that had nothing to dowith pollination. And sometimes
they played them no sounds atall.
Dr. Lilach Hadany (08:20):
And after three minutes, we test the newly
produced nectar, and wediscovered that indeed, the
flowers that were exposed to thesound of a bee had a higher
concentration of sugar than theones that were not exposed to
these sounds or that wereexposed to irrelevant sounds.
Amy Martin (08:42):
Lilach was shocked. There was a measurable change.
When the plants were exposed tothe sounds of bees, they
appeared to sweeten theirnectar.
Dr. Lilach Hadany (08:52):
It was like, no, this cannot be true. And
then we redid the wholeexperiment.
Amy Martin (08:57):
They actually redid it multiple times, inside and
outside.
Dr. Lilach Hadany (09:01):
Eventually, it was done several times by
different people in differentcontexts. So we were convinced.
Amy Martin (09:10):
Heidi Appel and Rex Cocroft had shown that some
plants respond to an acousticstimulus by sending out a
chemical weapon. Lilach and herteam demonstrated that they can
also respond by making a lovepotion, sweetening themselves
up, maybe so pollinators willlinger longer on their flowers
and come back again later. Andwhile Heidi and Rex were focused
(09:34):
on the vibroscape, acousticwaves moving through the body of
the plant, Lilach's work wasabout airborne sound, bee
buzzes, just like the ones Iheard through my window.
One of the sentences I lovedfrom the paper was this one, "we
found that the flowers vibratedmechanically in response to
these sounds, suggesting aplausible mechanism where the
(09:58):
flower serves as an auditory,sensory organ." So in
non-science speak, it's almostlike you're hinting that flowers
are kind of ears. Is that right?
Dr. Lilach Hadany (10:10):
So I think it is something like the external
ear. It's an amplifier of thesound. And then we can think,
when we think of flowers as theyselected to be visible to the
pollinator or to hear thepollinators better.
Amy Martin (10:27):
Wow, I love that. That's so cool.
Dr. Lilach Hadany (10:32):
It really converted my view of walking in
fields with flowers. Suddenly Ifind myself... little small
ears, and who would be a goodear?
Amy Martin (10:47):
Everyone agrees we need more studies on more
species to figure out what'sreally going on here. But when
this research was published in2019, it catapulted Lilach into
the global spotlight. You mayhave read about it in National
Geographic, or The Atlantic, orany number of other places.
There's just something thrillingabout western science validating
(11:10):
the very ancient idea thatplants are not passive set
pieces. They are maincharacters. They're doing things
and they're highly relational.They're in constant
communication with theirsurroundings and with other
living things, especiallyinsects. And that led Lilach to
ask another daring question, ifplants can detect sound, could
(11:36):
they also be producing it? We'llhave more after this short
break.
Matt Herlihy (11:47):
Hi, my name is Matt Herlihy, and I've been a
Threshold listener and donorsince season one came out in
2017. I was also one of thefirst volunteer board members of
the non profit organization thatmakes Threshold. Over the past
seven plus years, I've had thisunique firsthand look at just
how much work it takes to makethis kind of show. I mean, the
time, the dedication, thedetermination that's required to
(12:08):
tell these, these in depthstories and really make people
think and feel, and give peoplea sense of what it's like to
really go to places where thestories are happening, to talk
to the people who are part ofthem. It creates this rich,
immersive listening experience,and it's like that kind of
reporting, this whole kind ofshow is not easy to make. It's
also not easy to fund. Talkabout slow, in depth, thorough.
(12:29):
These are not often part of theexisting models for making a
podcast, so it's up to peoplelike us to really make sure
Threshold can get made. Ibelieve what Threshold is doing
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Threshold's year end fundraisingcampaign is happening right now
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(12:53):
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thresholdpodcast.org just clickthe donate button and give what
you can. Thank you.
Amy Martin (13:07):
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(14:14):
Welcome back to Threshold, I'mAmy Martin, and I'm going to ask
that question from before thebreak again using terms that
plant scientists woulddefinitely not use. Now that we
know that plants can hear, canthey also talk, or at least make
(14:35):
sounds of some sort? The answeris yes, and this is what it
sounds like. This is the soundof a stressed out tomato plant.
It's making these sounds as it'sdrying out, most likely as
little air bubbles pop insideits planty veins. These noises
(14:55):
were recorded by Lilach Hadanyand her team at Tel Aviv
University.
Dr. Lilach Hadany (15:00):
We used most of the time tomato and tobacco,
but we recorded several otherplants also, and we directed two
sensitive ultrasonic microphonesat the plant.
Amy Martin (15:10):
I'm picturing a plant almost like it's being
interviewed. It has microphonesset up around it.
Dr. Lilach Hadany (15:18):
And then we heard these clicks.
Amy Martin (15:23):
They're happening in ultrasonic range, too high for
us to hear, but they've beenconverted into our audible range
and condensed in time. WhenLilach and her team first heard
them, they were skeptical. Theythought,
Dr. Lilach Hadany (15:37):
Perhaps it's not a plant, perhaps it's an
insect or other sounds.
Amy Martin (15:43):
So they repeated the experiment over and over and
over, including in asoundproofed box in the basement
of a building where no othersounds could intrude.
Dr. Lilach Hadany (15:53):
Then we recorded them also in the
greenhouse and in the botanicalgarden. And then we tried like
wheat and corn and grapevine. Sobasically, we had to be ultra
careful, perhaps more than indifferent areas, and we were
sure that the sounds are emittedby the plants themselves.
Amy Martin (16:16):
Lilach was surprised to find herself in the spotlight
again after this research waspublished in March of 2023. News
outlets around the world coveredthe story.
News Person 1 (16:26):
Researchers have found that plants can make
noise.
News Person 2 (16:30):
There is an actual sound that tomato plants
make when they're thirsty, awhimper or scream, if you will.
News Person 3 (16:37):
But this discovery here is probably one
of the biggest in the last fewyears.
News Person 4 (16:41):
I wonder if our dogs can hear them. Our dogs
often bark at something random,probably like, hey, the plants
are hungry. Feed them.
Amy Martin (16:51):
We've actually known that plants make ultrasonic
clicks and pops since at least1966 when they were documented
by a botanist named JohnMilburn, but those sounds were
detected by sticking wiresinside plants. So it wasn't
clear if the vibrations stayedtrapped inside the stems and
leaves or if they made it outinto the surrounding ecosystem.
(17:15):
Lilach's research showed thatthe noises are indeed audible
outside of the plant, and thatplants make more of them when
they're stressed, like when theyneed water or after they've been
cut. And together, those twofacts point to something
important and pretty exciting.The sounds plants make have the
(17:36):
potential to shape the behaviorof other living things. For
example, picture a field full oftomato plants drying up on a hot
summer afternoon, each of thempopping away. It might make
quite a racket in the ultrasonicrange, and those sounds might be
meaningful to the right kinds oflisteners.
Dr. Lilach Hadany (17:58):
For an organism with the relevant
hearing ability, like a mothflying through the field, maybe
hearing plenty of sounds andalso getting a lot of
Amy Martin (18:07):
Maybe all those little popping sounds cause the
information.
moth to avoid those plants or tofeed more heavily on them, or to
respond in some other way. Andmaybe that affects other
animals, like bats. Lilach'sstudy didn't test all that, she
had to answer the most basicquestions first, but now we know
(18:29):
that the sounds plants produceat least have the potential to
influence all sorts of otherliving things. In short, plants
are talking, so now we can askwho's listening.
I'm curious how you see thefuture of this field of plant
(18:51):
bioacoustics. What are youhoping for?
Dr. Lilach Hadany (18:54):
So I really think we are just seeing the
edge of the iceberg at themoment, and I expect that we
would record plenty of soundsfrom different plants under
different circumstances, and wemight be able to understand the
acoustic interactions of plantswith their environment, which is
the most exciting part for me.I'm hoping that within a few
(19:19):
years, we will be somewherecompletely different, because
now we know that there is thislayer of acoustic information
that we can investigate.
Amy Martin (19:30):
Okay, I'm wandering around in a Swedish forest
looking for people who might beattaching microphones to trees.
I'm in northern Sweden now,walking through a dense and
(19:51):
fairly dark woods. It's kind ofstory bookish, with lots of
lichen hanging off withbranches. But instead of forest
gnomes, there are mysteriouspieces of scientific equipment
tucked among the mossy rocks.
Signs of research projectsaround, but no signs of
researchers.
This is an experimental forestwhere scientists from area
(20:12):
universities come to do researchon one of Sweden's most valuable
and plentiful natural resources: trees. (20:16):
undefined
Hey! Hi!
I've spotted the scientists I'mlooking for: Dr. Jonatan
Klaminder and his three personcrew who are here to set up an
experiment that will runthroughout the summer.
Dr. Jonatan Klaminder (20:32):
My name is Jonatan Klaminder. I'm a
professor at Swedish Universityof Agriculture Sciences in Umea.
I'm totally driven by curiosity,so you can't say a field that
I'm really interested in. I'vebeen interested in so many
things.
Amy Martin (20:48):
One of those things is soil bioacoustics. Jonatan
has done some really interestingstudies on the sounds that ants
and earthworms make underground.But lately he's turned his
attention to trees.
Dr. Jonatan Klaminder (21:01):
Well, trees is a soil organism, if you
think about it. The root systemis underground, and it's
difficult to not think abouttrees if you're in Sweden.
Forestry is an important part ofour economy. And then, of
course, I like being out amongtrees. So trees, there's many
reasons why we should keep trackof the trees. Trees are
(21:24):
important.
Amy Martin (21:25):
The person that I talked to that maybe had the
closest connection to your workwas Lilach Hadany in Tel Aviv.
Is what you're doing acontinuation of her work?
Dr. Jonatan Klaminder (21:36):
Yeah, absolutely. I mean, her work is
really important because theyshow that it worked for tomato
but they don't have bark. Treesin Sweden have bark.
Amy Martin (21:47):
All trees have some kind of bark, actually, or at
least a protective bark, likelayer. Jonatan wanted to know if
these ultrasonic pops were loudenough to make it through that
layer of soundproofing wherethey could be heard in the open
air. And he also wanted to knowif they could be heard in a real
world setting.
Dr. Jonatan Klaminder (22:07):
When you have rain, when you have wind,
when you have cars, that's whatwe're testing. So if we can hear
them,, well, that is the milliondollar question. We're the first
to try this. So we'll see. We'llsee.
Amy Martin (22:20):
I'm joining this team on their very first day in
the field as they figure outwhere to set up their equipment
and how to keep it runningoutdoors all summer long. The
first order of business is toset up a tent. It's big and
green and wedged somewhatawkwardly into a bumpy little
spot, but it's not meant forsleeping in.
Dr. Jonatan Klaminder (22:40):
So this is our lab. We're actually
building our outdoor lab. Wehave some electronics with us
that can't handle rain. Thefield workers, they can handle
rain, right? It's justelectronics.
Amy Martin (22:54):
The field workers, Lena, Matthias, and Sebastian,
look vaguely skeptical, butchoose not to comment, maybe,
because what they're reallywondering is if they're going to
be able to handle the clouds ofblood thirsty mosquitoes
tracking our every move.
Dr. Jonatan Klaminder (23:09):
I mean, the mosquitoes love you the
most, Matthias. Sebastian, youhave been drinking bear blood.
So they won't touch him.
Amy Martin (23:16):
I don't know. I've been seeing a lot of them on
him.
Dr. Jonatan Klaminder (23:19):
Yeah, put on a jacket, maybe.
Amy Martin (23:23):
Jonatan is pursuing this question of whether trees
make sounds that can be heard inthe open air, in part, for a
very simple reason, because wedon't know the answer.
Dr. Jonatan Klaminder (23:34):
So, I mean, we're exploring the
unknown, and I think that's thedriver.
Amy Martin (23:38):
But he's also interested in potentially
applying what he learns. Afterdecades of steady increases,
forests in Sweden have startedgrowing more slowly, possibly
because of drought. That's aproblem for the forestry
industry, but also, for all ofus. Trees are one of nature's
best carbon capture andsequestration systems. Every
(24:01):
ring on a tree represents moreplanet warming gasses sucked out
of the atmosphere and lockedaway, potentially for hundreds
of years. But when trees slowtheir growth, they draw less
carbon out of the air.
Dr. Jonatan Klaminder (24:15):
Our forests have lost productivity,
and we don't really know why.There's different theories, and
one of the theories is that ifyou have a really, really dry
year, the trees suffer fromcavitation, which is bubbles
that forms inside the xylem.
Amy Martin (24:32):
Sai-lem, or zai-lem, is spelled, X, Y, L, E, M.
Remember that scrabble players.It's the part of the tree
responsible for water transport.Trees take in water through
their roots and pump it upthrough the xylem to their
needles or leaves high above.
Dr. Jonatan Klaminder (24:52):
The basic is that a tree pumps up water
through the xylem and downwardsit pumps sugar through the
phloem.
Amy Martin (25:01):
It's quite remarkable that they can do this
when you think about it, everytree is a carbon eating, gravity
defying water pump, but anessential part of that process
is keeping the pump primed.Water molecules want to hang
together. They kind of pull eachother along in a little train,
if there's enough of thempresent. But if the roots can't
(25:23):
find enough water, and thattrain of molecules is broken.
Dr. Jonatan Klaminder (25:27):
The water transport is going to cease. And
not all trees can just get ridof these bubbles.
Amy Martin (25:35):
Once that link in the water train is broken, it's
really hard for the tree toreconnect it. So these bubbles,
or dry patches in the xylem canstay dry even after the water
returns.
Dr. Jonatan Klaminder (25:47):
You might knock out the water transport
for several years, so thatbubble could be fatal for that
part of the xylem. And if youhave many bubbles, of course,
then you shut off the watertransport. And worst case
scenario is that the trees die.
Amy Martin (26:04):
The process of these bubbles forming in the water
transport shutting down, that'swhat makes these pops and
clicks. That's cavitation.
Dr. Jonatan Klaminder (26:14):
But so far, no one has managed to hear
those cavitations explosions inan outdoor setting through bark.
So it's a challenge.
Amy Martin (26:23):
If Jonatan is able to detect these sounds in the
open air through the bark, thenext logical question would be
the same one Lilach Hadany isasking- who or what might be
listening.
Do you suspect that the treesare producing sound that is
(26:45):
ecologically relevant?
Dr. Jonatan Klaminder (26:47):
So now we're definitely speculating.
Amy Martin (26:51):
Maybe, just as a thought experiment, a bark
beetle might be able to hear thepops of a tree under stress.
That's an insect that kills alot of trees in Sweden, the US
and other countries.
Dr. Jonatan Klaminder (27:04):
So if that information is around, why
should the beetle not use it?That's not far fetched, I think.
I mean, it can be something mindblowing there, but could also be
the dead end. I mean, that'skind of exciting.
Amy Martin (27:20):
Yeah. It is.
Maybe in the future, forestersmight be able to listen to trees
the way doctors listen to ourhearts and lungs to keep tabs on
our health. Maybe the soundstrees make can serve as a kind
of early warning system, lettingus know when they're suffering
from drought before it becomesacute. And maybe we can figure
(27:44):
out which species of trees orvarieties within species can
handle dry conditions better, sowe can grow more climate
resilient forests, not just inSweden, but everywhere.
Dr. Jonatan Klaminder (27:56):
Maybe you can put the drone with a
microphone and fly over theforest and sort of get an
overview how many trees in yourforest that suffers from, from
this. We aim for somethingapplied, but we need to do some
basic research before we canactually do something. Yeah, it
could be a total failure.
Amy Martin (28:15):
That's science, right?
All of the things that Jonatanhopes to learn start with that
embrace of uncertainty, thatwillingness to do bold science.
You seem like you enjoy this.
Dr. Jonatan Klaminder (28:32):
Yes.
I mean, because it's unknown. And I
Amy Martin (28:33):
Why?
mean, when I was younger, I wasa junkie for adrenaline. I can't
do that now, because I should beold and smart and wise. So I do
this is like academic bunjeejumping. I mean, it's high risk.
(28:53):
I like that. It's a high risk,high reward, but it could be
high risk, low reward also, butI mean, our community are
steered towards, the researchcommunity steered towards
getting a number what goes upand what goes down. But the
(29:13):
processes behind them are, Ithink, more interesting than
just getting the numbers. I wantto understand how soils and
forests functions.
A couple of months later, I checked in with Jonatan
to see how things went. Heassured me that the field
workers had not been carried offby mosquitos, and he also sent
this (29:37):
These are the sounds of cavitation happening inside a
birch tree. Jonatan's teamcaptured them in the open air.
As with the plants that LilachHadany recorded, these are
ultrasonic sounds that have beenconverted into our hearing
(29:59):
range. So Jonatan's gamble paidoff. He now has documentation
that when trees dry out, or atleast when some trees dry out,
the sounds they make are loudenough to push through the bark,
and could at least theoreticallybe detected by other organisms,
including humans, if we have theright equipment, and if we
(30:22):
decide we want to listen.
I'm on a hiking trail in westernMontana, looking up at
beautiful, rugged mountainpeaks, and there are wild
flowers all around me, purple,yellow, red, violet, blue. And
(30:45):
there are also tons and tons ofbees right here, moving from
flower to flower to flower.
There's a bee with its entirehead stuck into a like trumpety
(31:05):
flower of a larkspur, just goingfor it. And I wonder if it's
possible that that flower heardthat bee and maybe sweetened its
nectar just a little bit.
(31:26):
I really like plants. I like tolook at them, smell them, eat
them, and just be around them.But even as I appreciate plants,
I've always positioned myself asthe perceiver and them as the
perceived. I've assumed I wasthe subject and they were the
object, but now I realize that'sjust scientifically inaccurate.
(31:51):
Plants are perceivers as well.They are listening, possibly
even tuning into some of thesame sounds I am, and they're
also talking in their way.They're in a sort of
conversation with the lifearound them. There is acoustic
information getting passedbetween pests and pollinators
(32:12):
and plants that has thepotential to affect all the
participants. And if we starttuning in, that conversation
could shape our behavior too,and it's hard to imagine how
that could be anything but goodfor us.
(32:35):
This episode of Threshold waswritten, reported and produced
by me, Amy Martin, with helpfrom Erika Janik and Sam Moore.
Music by Todd Sickafoose. Postproduction by Alan Douches. Fact
checking by Sam Moore. Specialthanks to Lilach Hadany, her
collaborator Yossi Yovel andJonatan Klaminder for sharing
(32:57):
their plant recordings.Threshold is made by Auricle
Productions, a non profitorganization powered by listener
donations. Deneen Weiske is ourexecutive director. You can find
out more about our show atthresholdpodcast.org.
I was just sitting in front of my computer trying
to figure out how to start thisepisode, which is all about
plants and pollinators andsound, and I heard this noise
across the room, and it made mewonder, wait, did I leave my
(00:23):
phone on vibrate? And then Iwalk over to track down the
sound, and then I see it's anenormous bee just outside my
window, moving from flower toflower on my snapdragons, which
are in full bloom right now.Nice!
(00:50):
I grabbed my sound gear andwalked out into my yard and
everywhere I looked andlistened, the bees were on a
bender. They were drinkingnectar with so much gusto, they
made me want to try some. Theydisappeared into the blossoms
and lost themselves there, thenstumbled out later with pollen
all over their legs and wingsand flew off into the morning
(01:13):
sun. This is pollination inaction. Plants can't pick
themselves up and move towardpotential mates. They need to
attract helpers to move thesperm from the male plants to
the ovaries of the females. Sothe flowers have essentially
thrown a nectar drinking partybecause they want to have sex.
(01:36):
And it works. Animals like theseinsects pollinate around three
quarters of all floweringplants. Without them, a lot of
plants would die, including manyof the foods we depend on daily.
The amorous intentions of plantsare the hidden force behind a
lot of activity on our planet.Take the sound I heard earlier-
(02:00):
on the surface, this seems likean interaction between two
animals, a human and a buzzingbee, but the flowers are
actually driving all the action.They produced the nectar which
attracted the bee that thenattracted me, all of which is to
say, plants can do things. Theyare doing things, making things
(02:23):
happen around them. Like allliving things, they're using
whatever resources are availableto get their needs met. And one
of the things that's availablein abundance around them is
sound. So what, if anything, arethey doing with all that
acoustic information? Welcome toThreshold, I'm Amy Martin, and
(02:49):
we are living through abotanical paradigm shift. A
growing body of research isdisrupting and reorganizing what
scientists thought they knewabout trees, flowers and all
things vegetal. In our lastepisode, we met Heidi Appel and
Rex Cocroft, the two researcherswho proved that plants can tune
(03:10):
into vibrations made by insectsdoing unfriendly things to them,
like caterpillars biting intotheir leaves. But what about all
of these sounds made by friendlyvisitors? Is it possible the
plants can sort of hear thesepollinators happily buzzing
among the blossoms? While I'mwandering around in my yard
(03:33):
listening to bees, are theflowers listening too?
Dr. Lilach Hadany (03:37):
I wondered about this question.
Amy Martin (03:39):
Dr. Lilach Hadany didn't only wonder about this
question, she decided to try toanswer it, and in this episode,
we're going to follow her downthat primrose path into a whole
new world of plantypossibilities.
(04:18):
Flowers are a time honored partof human courtship rituals. I
mean, just try to imagine awedding with no flowers. And Dr.
Lilach Hadany says this is noaccident. Attracting suitors is
exactly what flowers weredesigned to do. It's just that
plants use them to attractcreatures with six legs.
Dr. Lilach Hadany (04:40):
It is actually well known that the
plant signals to the pollinator.It is large and colorful and
emits smells.
Amy Martin (04:51):
Lilach is an evolutionary theoretician at Tel
Aviv University, and she saysscientists have studied how
plants send pollinators thesekindsof visual and chemical
signals through their flowersfor a long time, but the
assumption has been that soundwasn't really a factor, that
there was no acousticcommunication going on between
(05:11):
the plants and the pollinators.And this seemed odd to her.
Dr. Lilach Hadany (05:15):
Plants are communicating all the time. Why
wouldn't they use sound?
Amy Martin (05:21):
Almost all flowering plants need to attract
pollinators, and a lot of thosepollinators make a fair amount
of noise. Was all of that soundreally just wasted on the
plants?
Dr. Lilach Hadany (05:32):
Pollination seemed to me like one of the
cases where responding to soundswould be immediately beneficial
for the plant. So there was anevolutionary puzzle here.
Amy Martin (05:44):
It was a puzzle she wanted to solve. So she designed
an experiment focused on nectar,the sweet liquid plants make as
a reward for animals that visittheir flowers. Producing nectar
is costly for plants, so it's totheir advantage to time the
production of it reallyprecisely, right when they're
(06:04):
most likely to be visited by thebirds and beesthey most want to
attract. And breezing by isn'tenough. Ideally, the pollinators
will get very interested andhang out a while and then spread
the love around.
Dr. Lilach Hadany (06:20):
If a flower is pollinated by an animal that
makes sounds, then it ispossible to prepare pollination
at exactly the time that thepollinators are likely to be
around. So it is not necessarilyresponding to a single
pollinator, but a singlepollinator is a good indication
(06:40):
that other pollinators may bearound.
Amy Martin (06:42):
So the plant might be kind of, in very metaphorical
terms, the plant might bethinking in quotes, there's the
sound of one pollinator, sothere's probably going to be
others around. So maybe it wouldhelp me to produce more nectar.
Dr. Lilach Hadany (06:57):
So I would put it that, natural selection
could act on the plants toproduce improve the reward in
times where pollinators arelikely to be around.
Amy Martin (07:08):
So this was what Lilach decided to test. When
plants are exposed to soundsmade by pollinators, do they
change something about theirnectar production?
Dr. Lilach Hadany (07:18):
If you hear a pollinator nearby, would the
plant say, me, me, me! Sort of.
Amy Martin (07:24):
Because if they did, that could be a sign that they
were hearing the pollinatorssomehow.
Dr. Lilach Hadany (07:30):
And it might be preparing for fertilization.
Amy Martin (07:36):
Lilach and her team drained the nectar from a bunch
of beach evening primroses,tough little plants with big
yellow blossoms. Then theyplayed the kinds of buzzes that
pollinators, like bees, mightmake.
Did you have like a littleportable speaker? I'm trying to
picture what it looked like.
Dr. Lilach Hadany (07:54):
So the speaker is portable. We were
trying to mimic a bee goingaround the bush rather than
standing in front of the flowerand the buzzing.
Amy Martin (08:06):
I didn't ask Lilach if costumes were involved, but I
really hope so. They also playedother sounds to the plants,
sounds that had nothing to dowith pollination. And sometimes
they played them no sounds atall.
Dr. Lilach Hadany (08:20):
And after three minutes, we test the newly
produced nectar, and wediscovered that indeed, the
flowers that were exposed to thesound of a bee had a higher
concentration of sugar than theones that were not exposed to
these sounds or that wereexposed to irrelevant sounds.
Amy Martin (08:42):
Lilach was shocked. There was a measurable change.
When the plants were exposed tothe sounds of bees, they
appeared to sweeten theirnectar.
Dr. Lilach Hadany (08:52):
It was like, no, this cannot be true. And
then we redid the wholeexperiment.
Amy Martin (08:57):
They actually redid it multiple times, inside and
outside.
Dr. Lilach Hadany (09:01):
Eventually, it was done several times by
different people in differentcontexts. So we were convinced.
Amy Martin (09:10):
Heidi Appel and Rex Cocroft had shown that some
plants respond to an acousticstimulus by sending out a
chemical weapon. Lilach and herteam demonstrated that they can
also respond by making a lovepotion, sweetening themselves
up, maybe so pollinators willlinger longer on their flowers
and come back again later. Andwhile Heidi and Rex were focused
(09:34):
on the vibroscape, acousticwaves moving through the body of
the plant, Lilach's work wasabout airborne sound, bee
buzzes, just like the ones Iheard through my window.
One of the sentences I lovedfrom the paper was this one, "we
found that the flowers vibratedmechanically in response to
these sounds, suggesting aplausible mechanism where the
(09:58):
flower serves as an auditory,sensory organ." So in
non-science speak, it's almostlike you're hinting that flowers
are kind of ears. Is that right?
Dr. Lilach Hadany (10:10):
So I think it is something like the external
ear. It's an amplifier of thesound. And then we can think,
when we think of flowers as theyselected to be visible to the
pollinator or to hear thepollinators better.
Amy Martin (10:27):
Wow, I love that. That's so cool.
Dr. Lilach Hadany (10:32):
It really converted my view of walking in
fields with flowers. Suddenly Ifind myself... little small
ears, and who would be a goodear?
Amy Martin (10:47):
Everyone agrees we need more studies on more
species to figure out what'sreally going on here. But when
this research was published in2019, it catapulted Lilach into
the global spotlight. You mayhave read about it in National
Geographic, or The Atlantic, orany number of other places.
There's just something thrillingabout western science validating
(11:10):
the very ancient idea thatplants are not passive set
pieces. They are maincharacters. They're doing things
and they're highly relational.They're in constant
communication with theirsurroundings and with other
living things, especiallyinsects. And that led Lilach to
ask another daring question, ifplants can detect sound, could
(11:36):
they also be producing it? We'llhave more after this short
break.
Matt Herlihy (11:47):
Hi, my name is Matt Herlihy, and I've been a
Threshold listener and donorsince season one came out in
2017. I was also one of thefirst volunteer board members of
the non profit organization thatmakes Threshold. Over the past
seven plus years, I've had thisunique firsthand look at just
how much work it takes to makethis kind of show. I mean, the
time, the dedication, thedetermination that's required to
(12:08):
tell these, these in depthstories and really make people
think and feel, and give peoplea sense of what it's like to
really go to places where thestories are happening, to talk
to the people who are part ofthem. It creates this rich,
immersive listening experience,and it's like that kind of
reporting, this whole kind ofshow is not easy to make. It's
also not easy to fund. Talkabout slow, in depth, thorough.
(12:29):
These are not often part of theexisting models for making a
podcast, so it's up to peoplelike us to really make sure
Threshold can get made. Ibelieve what Threshold is doing
really matters, and if you dotoo, help them keep doing it.
Threshold's year end fundraisingcampaign is happening right now
through December 31 and eachgift will be doubled through
NewsMatch. So if you give $25they'll receive 50. You can make
(12:53):
your one time or monthlydonation online at
thresholdpodcast.org just clickthe donate button and give what
you can. Thank you.
Amy Martin (13:07):
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(14:14):
Welcome back to Threshold, I'mAmy Martin, and I'm going to ask
that question from before thebreak again using terms that
plant scientists woulddefinitely not use. Now that we
know that plants can hear, canthey also talk, or at least make
(14:35):
sounds of some sort? The answeris yes, and this is what it
sounds like. This is the soundof a stressed out tomato plant.
It's making these sounds as it'sdrying out, most likely as
little air bubbles pop insideits planty veins. These noises
(14:55):
were recorded by Lilach Hadanyand her team at Tel Aviv
University.
Dr. Lilach Hadany (15:00):
We used most of the time tomato and tobacco,
but we recorded several otherplants also, and we directed two
sensitive ultrasonic microphonesat the plant.
Amy Martin (15:10):
I'm picturing a plant almost like it's being
interviewed. It has microphonesset up around it.
Dr. Lilach Hadany (15:18):
And then we heard these clicks.
Amy Martin (15:23):
They're happening in ultrasonic range, too high for
us to hear, but they've beenconverted into our audible range
and condensed in time. WhenLilach and her team first heard
them, they were skeptical. Theythought,
Dr. Lilach Hadany (15:37):
Perhaps it's not a plant, perhaps it's an
insect or other sounds.
Amy Martin (15:43):
So they repeated the experiment over and over and
over, including in asoundproofed box in the basement
of a building where no othersounds could intrude.
Dr. Lilach Hadany (15:53):
Then we recorded them also in the
greenhouse and in the botanicalgarden. And then we tried like
wheat and corn and grapevine. Sobasically, we had to be ultra
careful, perhaps more than indifferent areas, and we were
sure that the sounds are emittedby the plants themselves.
Amy Martin (16:16):
Lilach was surprised to find herself in the spotlight
again after this research waspublished in March of 2023. News
outlets around the world coveredthe story.
News Person 1 (16:26):
Researchers have found that plants can make
noise.
News Person 2 (16:30):
There is an actual sound that tomato plants
make when they're thirsty, awhimper or scream, if you will.
News Person 3 (16:37):
But this discovery here is probably one
of the biggest in the last fewyears.
News Person 4 (16:41):
I wonder if our dogs can hear them. Our dogs
often bark at something random,probably like, hey, the plants
are hungry. Feed them.
Amy Martin (16:51):
We've actually known that plants make ultrasonic
clicks and pops since at least1966 when they were documented
by a botanist named JohnMilburn, but those sounds were
detected by sticking wiresinside plants. So it wasn't
clear if the vibrations stayedtrapped inside the stems and
leaves or if they made it outinto the surrounding ecosystem.
(17:15):
Lilach's research showed thatthe noises are indeed audible
outside of the plant, and thatplants make more of them when
they're stressed, like when theyneed water or after they've been
cut. And together, those twofacts point to something
important and pretty exciting.The sounds plants make have the
(17:36):
potential to shape the behaviorof other living things. For
example, picture a field full oftomato plants drying up on a hot
summer afternoon, each of thempopping away. It might make
quite a racket in the ultrasonicrange, and those sounds might be
meaningful to the right kinds oflisteners.
Dr. Lilach Hadany (17:58):
For an organism with the relevant
hearing ability, like a mothflying through the field, maybe
hearing plenty of sounds andalso getting a lot of
Amy Martin (18:07):
Maybe all those little popping sounds cause the
information.
moth to avoid those plants or tofeed more heavily on them, or to
respond in some other way. Andmaybe that affects other
animals, like bats. Lilach'sstudy didn't test all that, she
had to answer the most basicquestions first, but now we know
(18:29):
that the sounds plants produceat least have the potential to
influence all sorts of otherliving things. In short, plants
are talking, so now we can askwho's listening.
I'm curious how you see thefuture of this field of plant
(18:51):
bioacoustics. What are youhoping for?
Dr. Lilach Hadany (18:54):
So I really think we are just seeing the
edge of the iceberg at themoment, and I expect that we
would record plenty of soundsfrom different plants under
different circumstances, and wemight be able to understand the
acoustic interactions of plantswith their environment, which is
the most exciting part for me.I'm hoping that within a few
(19:19):
years, we will be somewherecompletely different, because
now we know that there is thislayer of acoustic information
that we can investigate.
Amy Martin (19:30):
Okay, I'm wandering around in a Swedish forest
looking for people who might beattaching microphones to trees.
I'm in northern Sweden now,walking through a dense and
(19:51):
fairly dark woods. It's kind ofstory bookish, with lots of
lichen hanging off withbranches. But instead of forest
gnomes, there are mysteriouspieces of scientific equipment
tucked among the mossy rocks.
Signs of research projectsaround, but no signs of
researchers.
This is an experimental forestwhere scientists from area
(20:12):
universities come to do researchon one of Sweden's most valuable
and plentiful natural resources: trees. (20:16):
undefined
Hey! Hi!
I've spotted the scientists I'mlooking for: Dr. Jonatan
Klaminder and his three personcrew who are here to set up an
experiment that will runthroughout the summer.
Dr. Jonatan Klaminder (20:32):
My name is Jonatan Klaminder. I'm a
professor at Swedish Universityof Agriculture Sciences in Umea.
I'm totally driven by curiosity,so you can't say a field that
I'm really interested in. I'vebeen interested in so many
things.
Amy Martin (20:48):
One of those things is soil bioacoustics. Jonatan
has done some really interestingstudies on the sounds that ants
and earthworms make underground.But lately he's turned his
attention to trees.
Dr. Jonatan Klaminder (21:01):
Well, trees is a soil organism, if you
think about it. The root systemis underground, and it's
difficult to not think abouttrees if you're in Sweden.
Forestry is an important part ofour economy. And then, of
course, I like being out amongtrees. So trees, there's many
reasons why we should keep trackof the trees. Trees are
(21:24):
important.
Amy Martin (21:25):
The person that I talked to that maybe had the
closest connection to your workwas Lilach Hadany in Tel Aviv.
Is what you're doing acontinuation of her work?
Dr. Jonatan Klaminder (21:36):
Yeah, absolutely. I mean, her work is
really important because theyshow that it worked for tomato
but they don't have bark. Treesin Sweden have bark.
Amy Martin (21:47):
All trees have some kind of bark, actually, or at
least a protective bark, likelayer. Jonatan wanted to know if
these ultrasonic pops were loudenough to make it through that
layer of soundproofing wherethey could be heard in the open
air. And he also wanted to knowif they could be heard in a real
world setting.
Dr. Jonatan Klaminder (22:07):
When you have rain, when you have wind,
when you have cars, that's whatwe're testing. So if we can hear
them,, well, that is the milliondollar question. We're the first
to try this. So we'll see. We'llsee.
Amy Martin (22:20):
I'm joining this team on their very first day in
the field as they figure outwhere to set up their equipment
and how to keep it runningoutdoors all summer long. The
first order of business is toset up a tent. It's big and
green and wedged somewhatawkwardly into a bumpy little
spot, but it's not meant forsleeping in.
Dr. Jonatan Klaminder (22:40):
So this is our lab. We're actually
building our outdoor lab. Wehave some electronics with us
that can't handle rain. Thefield workers, they can handle
rain, right? It's justelectronics.
Amy Martin (22:54):
The field workers, Lena, Matthias, and Sebastian,
look vaguely skeptical, butchoose not to comment, maybe,
because what they're reallywondering is if they're going to
be able to handle the clouds ofblood thirsty mosquitoes
tracking our every move.
Dr. Jonatan Klaminder (23:09):
I mean, the mosquitoes love you the
most, Matthias. Sebastian, youhave been drinking bear blood.
So they won't touch him.
Amy Martin (23:16):
I don't know. I've been seeing a lot of them on
him.
Dr. Jonatan Klaminder (23:19):
Yeah, put on a jacket, maybe.
Amy Martin (23:23):
Jonatan is pursuing this question of whether trees
make sounds that can be heard inthe open air, in part, for a
very simple reason, because wedon't know the answer.
Dr. Jonatan Klaminder (23:34):
So, I mean, we're exploring the
unknown, and I think that's thedriver.
Amy Martin (23:38):
But he's also interested in potentially
applying what he learns. Afterdecades of steady increases,
forests in Sweden have startedgrowing more slowly, possibly
because of drought. That's aproblem for the forestry
industry, but also, for all ofus. Trees are one of nature's
best carbon capture andsequestration systems. Every
(24:01):
ring on a tree represents moreplanet warming gasses sucked out
of the atmosphere and lockedaway, potentially for hundreds
of years. But when trees slowtheir growth, they draw less
carbon out of the air.
Dr. Jonatan Klaminder (24:15):
Our forests have lost productivity,
and we don't really know why.There's different theories, and
one of the theories is that ifyou have a really, really dry
year, the trees suffer fromcavitation, which is bubbles
that forms inside the xylem.
Amy Martin (24:32):
Sai-lem, or zai-lem, is spelled, X, Y, L, E, M.
Remember that scrabble players.It's the part of the tree
responsible for water transport.Trees take in water through
their roots and pump it upthrough the xylem to their
needles or leaves high above.
Dr. Jonatan Klaminder (24:52):
The basic is that a tree pumps up water
through the xylem and downwardsit pumps sugar through the
phloem.
Amy Martin (25:01):
It's quite remarkable that they can do this
when you think about it, everytree is a carbon eating, gravity
defying water pump, but anessential part of that process
is keeping the pump primed.Water molecules want to hang
together. They kind of pull eachother along in a little train,
if there's enough of thempresent. But if the roots can't
(25:23):
find enough water, and thattrain of molecules is broken.
Dr. Jonatan Klaminder (25:27):
The water transport is going to cease. And
not all trees can just get ridof these bubbles.
Amy Martin (25:35):
Once that link in the water train is broken, it's
really hard for the tree toreconnect it. So these bubbles,
or dry patches in the xylem canstay dry even after the water
returns.
Dr. Jonatan Klaminder (25:47):
You might knock out the water transport
for several years, so thatbubble could be fatal for that
part of the xylem. And if youhave many bubbles, of course,
then you shut off the watertransport. And worst case
scenario is that the trees die.
Amy Martin (26:04):
The process of these bubbles forming in the water
transport shutting down, that'swhat makes these pops and
clicks. That's cavitation.
Dr. Jonatan Klaminder (26:14):
But so far, no one has managed to hear
those cavitations explosions inan outdoor setting through bark.
So it's a challenge.
Amy Martin (26:23):
If Jonatan is able to detect these sounds in the
open air through the bark, thenext logical question would be
the same one Lilach Hadany isasking- who or what might be
listening.
Do you suspect that the treesare producing sound that is
(26:45):
ecologically relevant?
Dr. Jonatan Klaminder (26:47):
So now we're definitely speculating.
Amy Martin (26:51):
Maybe, just as a thought experiment, a bark
beetle might be able to hear thepops of a tree under stress.
That's an insect that kills alot of trees in Sweden, the US
and other countries.
Dr. Jonatan Klaminder (27:04):
So if that information is around, why
should the beetle not use it?That's not far fetched, I think.
I mean, it can be something mindblowing there, but could also be
the dead end. I mean, that'skind of exciting.
Amy Martin (27:20):
Yeah. It is.
Maybe in the future, forestersmight be able to listen to trees
the way doctors listen to ourhearts and lungs to keep tabs on
our health. Maybe the soundstrees make can serve as a kind
of early warning system, lettingus know when they're suffering
from drought before it becomesacute. And maybe we can figure
(27:44):
out which species of trees orvarieties within species can
handle dry conditions better, sowe can grow more climate
resilient forests, not just inSweden, but everywhere.
Dr. Jonatan Klaminder (27:56):
Maybe you can put the drone with a
microphone and fly over theforest and sort of get an
overview how many trees in yourforest that suffers from, from
this. We aim for somethingapplied, but we need to do some
basic research before we canactually do something. Yeah, it
could be a total failure.
Amy Martin (28:15):
That's science, right?
All of the things that Jonatanhopes to learn start with that
embrace of uncertainty, thatwillingness to do bold science.
You seem like you enjoy this.
Dr. Jonatan Klaminder (28:32):
Yes.
I mean, because it's unknown. And I
Amy Martin (28:33):
Why?
mean, when I was younger, I wasa junkie for adrenaline. I can't
do that now, because I should beold and smart and wise. So I do
this is like academic bunjeejumping. I mean, it's high risk.
(28:53):
I like that. It's a high risk,high reward, but it could be
high risk, low reward also, butI mean, our community are
steered towards, the researchcommunity steered towards
getting a number what goes upand what goes down. But the
(29:13):
processes behind them are, Ithink, more interesting than
just getting the numbers. I wantto understand how soils and
forests functions.
A couple of months later, I checked in with Jonatan
to see how things went. Heassured me that the field
workers had not been carried offby mosquitos, and he also sent
this (29:37):
These are the sounds of cavitation happening inside a
birch tree. Jonatan's teamcaptured them in the open air.
As with the plants that LilachHadany recorded, these are
ultrasonic sounds that have beenconverted into our hearing
(29:59):
range. So Jonatan's gamble paidoff. He now has documentation
that when trees dry out, or atleast when some trees dry out,
the sounds they make are loudenough to push through the bark,
and could at least theoreticallybe detected by other organisms,
including humans, if we have theright equipment, and if we
(30:22):
decide we want to listen.
I'm on a hiking trail in westernMontana, looking up at
beautiful, rugged mountainpeaks, and there are wild
flowers all around me, purple,yellow, red, violet, blue. And
(30:45):
there are also tons and tons ofbees right here, moving from
flower to flower to flower.
There's a bee with its entirehead stuck into a like trumpety
(31:05):
flower of a larkspur, just goingfor it. And I wonder if it's
possible that that flower heardthat bee and maybe sweetened its
nectar just a little bit.
(31:26):
I really like plants. I like tolook at them, smell them, eat
them, and just be around them.But even as I appreciate plants,
I've always positioned myself asthe perceiver and them as the
perceived. I've assumed I wasthe subject and they were the
object, but now I realize that'sjust scientifically inaccurate.
(31:51):
Plants are perceivers as well.They are listening, possibly
even tuning into some of thesame sounds I am, and they're
also talking in their way.They're in a sort of
conversation with the lifearound them. There is acoustic
information getting passedbetween pests and pollinators
(32:12):
and plants that has thepotential to affect all the
participants. And if we starttuning in, that conversation
could shape our behavior too,and it's hard to imagine how
that could be anything but goodfor us.
(32:35):
This episode of Threshold waswritten, reported and produced
by me, Amy Martin, with helpfrom Erika Janik and Sam Moore.
Music by Todd Sickafoose. Postproduction by Alan Douches. Fact
checking by Sam Moore. Specialthanks to Lilach Hadany, her
collaborator Yossi Yovel andJonatan Klaminder for sharing
(32:57):
their plant recordings.Threshold is made by Auricle
Productions, a non profitorganization powered by listener
donations. Deneen Weiske is ourexecutive director. You can find
out more about our show atthresholdpodcast.org.
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