Cover artwork by Ale Silva
Summary
What do you call it when a population of podcasts mysteriously drop episodes on the same topic at the same time? It's Critical Mast!
We're so proud to present this nutty experiment in community podcasting, with its roots going back to the very beginning of our show (and the beginning of our dedication to silly puns).
Thanks to help from our pals at Jumpstart Nature, Golden State Naturalist, Learning from Nature: The Biomimicry Podcast, Nature’s Archive, and Outside/In, it's time for a bumper crop of podcasts about (or inspired by) the perplexing phenomenon known as masting: where plants somehow synchronize their seed production across staggering distances. Give all these pods all a follow, & check out this Spotify playlist (to which episodes will be added as they drop).
Ongoing support for this podcast comes from listeners just like you. To keep this show going, join our community at patreon.com/futureecologies
Our supporters get access to early episode releases, a community discord server, discounted merch, and exclusive bonus content.
Show Notes and Credits
Featuring the voices of Andrew Hacket Pain and Walt Koenig
Production by Mendel Skulski and Adam Huggins, with help from Eden Zinchik
Music by Thumbug, plus our theme by Sunfish Moon Light
This episode includes audio recorded by Mark_Taylor_Echophora_, HYPERBLOODHELL, TRP (2, 3), gfxwiz, pfranzen, princessemilu, hallkev, Bluesy1905, cbenci, iamshort, susychristiansen, and fotoshop accessed through the Freesound Project, as well as from BUTCH HIMSELF under Fair Use
Citations
Bogdziewicz, M., Kelly, D., Tanentzap, A. J., Thomas, P. A., Lageard, J. G. A., & Hacket-Pain, A. (2020). Climate change strengthens selection for mast seeding in European beech. Current Biology, 30(17). https://doi.org/10.1016/j.cub.2020.06.056
Bogdziewicz, M., Kelly, D., Tanentzap, A. J., Thomas, P., Foest, J., Lageard, J., & Hacket‐Pain, A. (2023). Reproductive collapse in European beech results from declining pollination efficiency in large trees. Global Change Biology, 29(16), 4595–4604. https://doi.org/10.1111/gcb.16730
Foest, J. J., Bogdziewicz, M., Pesendorfer, M. B., Ascoli, D., Cutini, A., Nussbaumer, A., Verstraeten, A., Beudert, B., Chianucci, F., Mezzavilla, F., Gratzer, G., Kunstler, G., Meesenburg, H., Wagner, M., Mund, M., Cools, N., Vacek, S., Schmidt, W., Vacek, Z., & Hacket‐Pain, A. (2024). Widespread breakdown in masting in European beech due to rising summer temperatures. Global Change Biology, 30(5). https://doi.org/10.1111/gcb.17307
Hacket‐Pain, A., Foest, J. J., Pearse, I. S., LaMontagne, J. M., Koenig, W. D., Vacchiano, G., Bogdziewicz, M., Caignard, T., Celebias, P., van Dormolen, J., Fernández‐Martínez, M., Moris, J. V., Palaghianu, C., Pesendorfer, M., Satake, A., Schermer, E., Tanentzap, A. J., Thomas, P. A., Vecchio, D., … Ascoli, D. (2022). Mastree+: Time‐series of plant reproductive effort from six continents. Global Change Biology, 28(9), 3066–3082. https://doi.org/10.1111/gcb.16130
Kimmerer, R. W. (2014). Braiding Sweetgrass. Milkweed Editions.
Koenig, W. D. (2021). A brief history of masting research. Philosophical Transactions of the Royal Society B: Biological Sciences, 376(1839). https://doi.org/10.1098/rstb.2020.0423
Koenig, W. D., Knops, J. M., Carmen, W. J., & Pearse, I. S. (2015). What drives masting? the phenological synchrony hypothesis. Ecology, 96(1), 184–192. https://doi.org/10.1890/14-0819.1
Pearse, I. S., LaMontagne, J. M., Lordon, M., Hipp, A. L., & Koenig, W. D. (2020). Biogeography and phylogeny of masting: Do global patterns fit functional hypotheses? New Phytologist, 227(5), 1557–1567. https://doi.org/10.1111/nph.16617
Pesendorfer, M. B., Koenig, W. D., Pearse, I. S., Knops, J. M., & Funk, K. A. (2016). Individual resource limitation combined with population‐wide pollen availability drives masting in the valley oak (Quercus lobata). Journal of Ecology, 104(3), 637–645. https://doi.org/10.1111/1365-2745.12554
Shibata, M., Masaki, T., Yagihashi, T., Shimada, T., & Saitoh, T. (2020). Decadal changes in masting behaviour of oak trees with rising temperature. Journal of Ecology, 108(3), 1088–1100. https://doi.org/10.1111/1365-2745.13337
Starhawk. (2024). The Earth Path: Grounding your Spirit in the Rhythms of Nature. HarperOne.
Zwolak, R., Bogdziewicz, M., Wróbel, A., & Crone, E. E. (2015). Advantages of masting in European Beech: Timing of granivore satiation and benefits of seed caching support the predator dispersal hypothesis. Oecologia, 180(3), 749–758. https://doi.org/10.1007/s00442-015-3511-3
You can subscribe to and download Future Ecologies wherever you find podcasts - please share, rate, and review us. We’re also on Facebook, Instagram, Twitter, and iNaturalist.
If you like what we do, and you want to help keep it ad-free, please consider supporting us on Patreon. Pay-what-you-can (as little as $1/month) to get access to bonus monthly mini-episodes, stickers, patches, a community Discord chat server, and more.
Future Ecologies is recorded and produced on the unceded, shared, and asserted territories of the WSÁNEĆ, Penelakut, Hwlitsum, and Lelum Sar Augh Ta Naogh, and other Hul'qumi'num speaking peoples, otherwise known as Galiano Island, British columbia, as well as the unceded, shared, and asserted territories of the Musqueam (xwməθkwəy̓əm) Squamish (Skwxwú7mesh), and Tsleil-Waututh (Səl̓ílwətaʔ/Selilwitulh) Nations - otherwise known as Vancouver, British Columbia.
Transcription
Introduction Voiceover 00:01
You are listening to Season Six of Future Ecologies.
Megaphone User 00:08
So as traditional with Critical Mass, we usually have some brief announcements before we start. So if anyone has any brief announcements, come up to the microphone, then we'll do a safety talk, and then we'll ride!
Crowd 00:21
[Cheering, honking]
Megaphone User 00:25
I don't see anybody clamoring for the microphone-
Mendel Skulski 00:30
Testing, testing. I'm Mendel
Adam Huggins 00:32
and I'm Adam!
Mendel Skulski 00:34
and this is the sound of Critical Mass here in Vancouver. This tape is from 2009 but it's a tradition that carries on somewhat regularly to this day, here and in cities all over the world.
Adam Huggins 00:51
For the uninitiated, Critical Mass is a periodic occurrence where hundreds or even 1000s of cyclists gather to overwhelm city streets with their presence, all in a joyous protest for safer bicycle infrastructure.
Mendel Skulski 01:10
This flash mob springs up, seemingly out of nowhere
Adam Huggins 01:14
Coming out of the woodwork, as it were
Mendel Skulski 01:16
and just as quickly, ebbs away, vanishing until the next. So that's Critical Mass, but this is Critical Mast... with a T, as in masting. And what is masting? I hear you ask.
Andrew Hacket Pain 01:37
So this is actually quite a difficult question to answer. Masting is quite a tricky topic to define. So I think a relaxed definition of masting is useful, and it helps us to incorporate the real diversity of characteristics or variation that come under this term. So masting kind of boils down to highly variable and synchronized seed production in perennial plants
Adam Huggins 02:03
This is Andrew Hacket Pain.
Andrew Hacket Pain 02:06
I'm a senior lecturer at the University of Liverpool in the United Kingdom. I work on forests generally, but in particular, I work on forest reproduction and on this strange phenomenon that we know as masting.
Adam Huggins 02:17
In the simplest terms, masting is when a population of plants — typically, but not always, trees — all produce a huge crop of seeds at the same time.
Mendel Skulski 02:28
In statistics, I think they call it a crap ton.
Adam Huggins 02:31
Yeah, a crop ton.
Mendel Skulski 02:34
Yeah, in a mast year we've got trees or other plants dropping way more seeds than you would see on average.
Andrew Hacket Pain 02:41
So these are long lived plants, and they're plants that, rather than reproducing regularly each year, so producing an approximately constant seed crop each year, instead, they strongly vary their allocation to reproduction. In a very typical European masting species like Fagus sylvatica, European beech, one of the most common broadleaf species in Europe, or actually, the numbers are very similar for Picea glauca, for white spruce in North America, a big tree in a very good year might produce half a million seeds. And that's not just individual trees deciding that this is the year to go big, but they do that in a synchronized way.
Mendel Skulski 03:22
This isn't just one tree here and one tree there. It's all the trees of a given species in a given area, all masting at once.
Adam Huggins 03:32
How big of an area, how many trees? Why? How
Mendel Skulski 03:37
We're going to get into it. But first, I think we should say a little bit about how this episode came to be. How do you recall the germ of this story, Adam?
Adam Huggins 03:48
Yeah. Critical Mast! This one... this one is a little bit of a blast from the past.
Mendel Skulski 03:53
It was a long time ago!
Adam Huggins 03:55
We were on a road trip together recording sounds for our first season, and we were just spitballing puns on ecology, I think, right,
Mendel Skulski 04:05
yeah, I think this is literally the first time we started from the title of an episode before we had anything else.
Mendel Skulski 04:12
Yeah, the title came first before the story. But do you remember any of the other ones?
Mendel Skulski 04:13
The only one that I can honestly remember is Galls to the Wall, which I think we should still do.
Adam Huggins 04:23
Yeah, the ones that stick are the ones that we should still do. So Critical Mast stuck.
Mendel Skulski 04:28
And then, you know, some years go by and we have another idea. Some might say... it's nuts.
Adam Huggins 04:38
It's nuts!
Mendel Skulski 04:42
Basically, we thought to ourselves, wouldn't it be funny if a whole population of nature podcasts produced their own stories about masting, or inspired by masting,
Adam Huggins 04:53
and then dropped them all at the same time!
Mendel Skulski 04:55
So from Future Ecologies...
Adam Huggins 04:58
and with supporting episodes from our friends at Outside/In, Nature's Archive, Golden State Naturalist, Jumpstart Nature, and Learning from Nature (the biomimicry podcast)...
Mendel Skulski 05:08
this is Critical Mast
Introduction Voiceover 05:14
Broadcasting from the unceded, shared and asserted territories of the Musqueam, Squamish, and Tsleil-Waututh, this is Future Ecologies – exploring the shape of our world through ecology, design, and sound.
Mendel Skulski 05:57
Okay, just to drive it home, what is masting?
Walt Koenig 06:01
So masting, as you probably already know at this point, is a population level phenomenon. An individual tree does not mast, a population of trees masts. So the problem when I started, and this was back about 40 years ago now, was that nobody had really seemed to pay much attention to defining or figuring out what a population was.
Mendel Skulski 06:28
This is Walt Koenig, research zoologist emeritus at the University of California, Berkeley. And despite being one of the leading researchers into the mystery of masting, Walt is, by his own description, more of a bird person.
Walt Koenig 06:45
What can I say? Masting was just kind of a side thing. I spent most of my career studying acorn woodpeckers. Acorn woodpeckers, surprisingly enough, are highly dependent on acorns. They're famous for storing acorns in what we call granaries. They use trees, they drill hundreds to 1000s of little holes in them and stick acorns in them individually. And so it was clear early on that the birds were highly dependent on the acorn crop. And so we slowly got interested in trying to learn something about that. And now that I'm retired, it's kind of the better project, because I don't have to climb up to nests, and my wife doesn't want me falling out of a tree. So now, starting in another couple of days, I go around every year and count acorns around the state, which can be done on the ground.
Walt Koenig 07:42
And one of the main questions that cropped up early on was how spatially synchronous the acorn crop is. So when it's a good crop here in Upper Carmel Valley, where I live now and where I did most of my research, does that mean it's a good crop up in the Bay Area? Does it mean it's a good crop up in the foothills of the Sierras? Nobody seemed to know the answer.
Andrew Hacket Pain 08:10
So this scale of synchrony is really one of the most remarkable characteristics of masting, I think.
Adam Huggins 08:15
I just want to underline here that this masting behavior shows up in all sorts of different plants and in a diversity of trees, Andrew's research tends to focus on European beech, while Walt is primarily interested in oaks and acorns, and there are a lot of different oaks in California. One of my favorite things about the place
Walt Koenig 08:36
You've got Oregon oak, White oak, Blue oak, Coast live oak, Interior live oak, Black oak. What's that one in Southern California? Yeah, it's a Mexican species. It just makes it up, and we do the Santa Rosa plateau, which has them. And I'll think of it in, as I like to say, in between five minutes and 24 hours.
Adam Huggins 08:55
That one is the Engelman oak, or Pasadena oak, with one of the smallest ranges of any species of oak in California,
Walt Koenig 09:02
and each species has a different pattern.
Mendel Skulski 09:05
Meaning, even just between these different species of oaks, a given year could be a mast year for some, but not for others. And the problem of this spatial synchrony remained central to the mystery.
Walt Koenig 09:18
We spent several years trying to figure out what scale was appropriate. Started out, for example, by starting at the coast and counting acorns every 10 kilometers till we got inland. A ways, we did that for a few years, until it turned out that it was clear that that was too small a scale. And somewhere along the line, in the 1990s I had a postdoc who said we really needed to do this right, and doing it right basically meant spending a week or so driving around California looking at marked trees and doing a survey of the acorn crop at different sites around the state. We go to sites that are over 700 kilometers apart, one end of the Central Valley to the other. And the question is, do they actually produce acorn synchronously or not?
Adam Huggins 10:14
... we were kind of hoping you might answer that?
Walt Koenig 10:17
Well, I'm glad you asked. It turns out that, okay, the way spatial synchrony almost basically always works is that sites that are closer together are unsurprisingly more synchronous than sites that are farther apart. And it turns out they are spatially synchronous over very large distances, hundreds of kilometers, and we're talking millions, if not 10s or hundreds of millions of trees.
Andrew Hacket Pain 10:45
Mast years in Denmark and in Central Europe, in Sweden, seem to happen generally in the same years. The pattern is not periodic. It's not strictly stochastic either. Because while I said there's no periodic pattern, there is one very important pattern, which is that we very, very rarely see consecutive years of high seed production. A year of very high seed production is almost always followed by a failure year. And it was quite common in the old literature for masting to be described as some kind of cyclic pattern. We're still kind of pushing back against this literature and the way that these ideas have seeded in. Oh, sorry, that was an accidental pun.
Mendel Skulski 11:25
That's okay, and honestly, totally appropriate for this episode. But myth busted!
Adam Huggins 11:33
Yeah, mast production, as it turns out, is not like the cycles of cicadas or solar storms. We can't just count the years between mast years and call that a reliable pattern. And it's too bad, because we've been trying to figure out masting for a long, long time. Like Karl Marx wrote about mast production, didn't he?
Mendel Skulski 11:58
[Laughing] Oh my god that's so bad.
Andrew Hacket Pain 12:00
Masting has been recognized for a really long time. Really exceptional years of acorn production, particularly in Europe, was, I think, noted by the Romans. But certainly by the medieval period in Europe, there's a lot of interest in masting in relation to acorns as a food source, particularly for pigs.
Walt Koenig 12:20
People have been interested in the acorn crop for many hundreds of years because acorns provided a excellent food resource, particularly for their hogs. Back in the day, people spent a lot of time going out there, hitting trees, trying to knock down the acorns so that they could feed their hogs in various parts of the world.
Andrew Hacket Pain 12:43
That's a process known as pannage. So when pigs are put into oak woodlands in particular to feed on the acorns, that was an important right and important within European legal systems in the medieval period.
Walt Koenig 12:54
And Spain is an interesting case. of course.
Adam Huggins 12:57
In Spain, spacious oak woodlands called dehesas are iconic for their pasture and their acorn fed Iberian ham,
Walt Koenig 13:06
which is highly prized!
Adam Huggins 13:09
Cue happy pigs in a Dehesa. And dear listener, just so you know how dedicated we are to getting you audio straight from the source, I spent a full day pedaling my ass up into the foothills of Spain outside of Sevilla on a janky old bike to get this particular soundscape, only to have the derailleur get sucked into the spokes and break off, leaving me stranded in the middle of nowhere on a Sunday.
Mendel Skulski 13:35
So much for critical mass.
Adam Huggins 13:38
I wish there were like 100 other people biking with me, because do you know what happens in rural areas in Spain on a Sunday, Mendel?
Mendel Skulski 13:47
...What happens in rural areas in Spain on a Sunday, Adam?
Adam Huggins 13:50
A whole lot of nothing. We couldn't even hitchhike out of there. So I recorded this audio while waiting on the side of the road to be rescued by my own mother, who was also on vacation. Thanks, mom.
Mendel Skulski 14:04
That's lucky.
Adam Huggins 14:04
So you're welcome.
Mendel Skulski 14:06
Yeah, whatever the results.
Adam Huggins 14:07
Yeah, I guess it would be better if my sound was better. I'm sorry I did my best.
Mendel Skulski 14:11
It was so high effort, for a very indistinct recording of some pigs
Adam Huggins 14:16
and that, that that's us in a nutshell, Mendel, that's us in a nutshell. High effort...
Mendel Skulski 14:21
indistinct results! Anyway, back to Walt.
Walt Koenig 14:29
Those Dehesas are well tended, and I can't help but think that part of the reason that they do so well is that they've been paying attention to those trees for a long time and probably choosing trees, selecting trees that would produce acorns, produce acorns that are edible. I have a couple of Spanish colleagues who claim that when they get hungry out there, they can just pick off an acorn from one of those trees in Spain and eat the thing, which means not that they don't have tannins, but they do not have the kind of tannins that the Oaks here in California do.
Adam Huggins 15:12
And according to a chapter that Walt contributed to an anthology, the oaks of the Spanish Dehesas may have been selectively cultivated, not only for their palatability, but also to make them mast less! Regularizing the annual acorn crop and making it more reliable for the ham economy.
Walt Koenig 15:32
Oh, well, good for me. I made that up, of course, but my Spanish colleagues did not make me take it out. So I assume that there's at least some possibility it's true.
Mendel Skulski 15:43
In any case, the point stands. People have had plenty of motivation to notice these irregular bumper crops.
Walt Koenig 15:51
So there are data sets that go way back for some of these species.
Andrew Hacket Pain 15:56
German foresters in particular, were describing and making observations of masting in the 17th century.
Walt Koenig 16:03
Well, here in California, the famous use of all those acorns were the Native Americans. There are tribes in California which have been estimated to get half their calories from acorns. Now the amount of effort you would have to go to to collect, protect, and then process enough acorns to get half your calories, half your food out of those things is just mind boggling, but it was a critical resource.
Adam Huggins 16:37
Was and is! Acorns continue to be an important cultural food for the indigenous peoples of California, which we will come back to in a future episode.
Walt Koenig 16:47
Of course, that's why there are these grinding rocks everywhere in the foothills of California, because women spent a vast amount of time hanging out grinding these acorns up. And then they, of course, had to leach them, because here in California, they are completely inedible unless you leach the tannins out of them. But despite that, they've been an important food resource for humans here for a long time.
Mendel Skulski 17:14
Shout out to another wonderful episode from our friends at Outside/In if you want to know more about how this traditional food is being revived before we eventually get to it, cue up The Acorn — an Ohlone Love Story, from 2021
Adam Huggins 17:30
But before you do that, there are more details of masting to cover. Because it turns out, they've been a hard nut to crack. It's only in recent decades that we've made real scientific progress.
Walt Koenig 17:40
You know, like a lot of things that took a while before they started asking the kinds of evolutionary questions that we are now focused on.
Andrew Hacket Pain 17:49
Yeah, so masting appears across the plant tree of life. It's very common in conifers.
Mendel Skulski 17:55
Which are cone-bearing plants.
Andrew Hacket Pain 17:58
It's very common in angiosperms.
Mendel Skulski 18:00
Which are flowering plants.
Andrew Hacket Pain 18:03
The patterns associated with when masting appears in the tree of life, and when it doesn't appear in the Tree of Life, indicate that it's a strategy that has evolved multiple times over the evolution of plants. So it seems to be a strategy that that emerges and then perhaps when it's not beneficial, it disappears again and then can re emerge.
Adam Huggins 18:16
So masting is a pattern that we see across plant evolution in different lineages arising independently, which means it's got to be a decent survival strategy. But remember that after cashing in all of their energy and resources on a mast year, plants almost always take the next year off.
Mendel Skulski 18:34
Going from tons of seed to... nones of seed.
Andrew Hacket Pain 18:39
In a mast year, as much resource might be allocated to reproduction (so the production of flowers and the fruits and the seeds) as is allocated to tree growth, as much as half of all of the resources allocated above ground might be going into reproduction. And then in a non mast year, they might produce zero. So it's a phenomenal switching of resource allocation. These plants actively miss opportunities for reproduction. So they have a growing season, they have the opportunity to produce flowers and fruits in that year, and yet they pass on that opportunity.
Mendel Skulski 19:14
Which at first seems a little counterintuitive. I mean, like after all, reproduction is kind of the name of the evolutionary game. If masting comes at the cost of taking a year long break, it's got to be worth it.
Adam Huggins 19:29
But why? Spoiler alert, nobody knows for sure, but we have a few solid leads, a crop load of seeds, and we're about to get into the weeds. That's after the break.
Eden Zinchik 20:08
Hi! This is Eden. I'm an assistant producer for Future Ecologies. I think you might be listening to the show because Future Ecologies combines this love for sound arts and storytelling and ecology and people into one big, beautiful narrative. And I just wanted to say that there's a reason we can be as silly and experimental as we want to be. Future Ecologies is completely, 100% listener supported. And if you're glad that this podcast exists, you know, free for everyone and with no ads or sponsors, you can really thank our amazing community, whose names are all on futureecologies.net/join
Eden Zinchik 20:47
The best way to support the show is through our Patreon for as little as $1 each month. Another option is always to share the podcast. Share it with your friends and family, colleagues, strangers on the internet, anyone who will listen, share it on your socials @futureecologies, or you can leave us a comment or review wherever you're listening. And if you want to get our bonus episode feed, merch, access to our community Discord server, book club and more, head to patreon.com/futureecologies and support the show for as little as $1 each month. That's patreon.com/futureecologies. Thank you. Let's get back to the show!
Mendel Skulski 21:31
And we're back. I'm Mendel,
Adam Huggins 21:33
I'm Adam, and today we are taking our own silly pun very seriously.
Mendel Skulski 21:39
You might call it our masterpiece.
Adam Huggins 21:43
Where we left off, we were just about to get into why masting, this strange behavior of synchronous seed superabundance, immediately followed by synchronous seed scarcity, has evolved time and time again, independently all across the plant kingdom.
Andrew Hacket Pain 22:01
Now there are lots of reasons why masting might be beneficial to plants and why it might be selected for but it seems there are two main theories as to why masting is particularly beneficial under some circumstances.
Mendel Skulski 22:13
Once again, we are joined by Andrew Hacket Pain. And the first rationale for masting is that it makes it easier for plants to get pollinated. Here's Walt Koenig.
Walt Koenig 22:24
Oaks, for example, most of these masting species are not self pollinating. They have to be cross pollinated by other trees. So if you're producing flowers, you're dependent on pollen from some neighbor or some other tree down the ways. For true oaks, they're all wind pollinated. There's lots of pollen out there, but it is just floating around in the air in no particular direction, and the odds of any one pollen grain falling on a flower is probably strikingly low, even by astronomical standards.
Andrew Hacket Pain 23:09
It's quite hard to get external pollen into your flowers. If you're for example, in the forest, they could just flower very intensely every year, but that has a pretty major resource cost and would lead to trade offs with, for example, growth.
Walt Koenig 23:22
If trees sort of get together and decide, okay, this is going to be a good year. We're going to produce lots of flowers, female flowers, we're going to produce lots of catkins, male flowers, lots of pollen. And that's going to be much more efficient in terms of pollinating everybody, each other, including myself, than if we don't sort of do this synchronously.
Andrew Hacket Pain 23:49
Years of very high seed production have higher pollination efficiency. More of the flowers overall are pollinated. And that's good from a plant's perspective, because producing a flower that doesn't result in a fruit is ultimately a waste of resources.
Adam Huggins 24:01
Another factor here is that once you're a plant in a masting population, there's a pretty severe penalty to you if you don't play along.
Mendel Skulski 24:09
Yeah, if you're the odd one out wasting lots of pollen when everyone else is taking a break or failing to capitalize on the mast hysteria, you're far less likely to pass on your genes into the next generation.
Adam Huggins 24:26
So masting, if you think about it, is kind of a snowball of selection pressure, and it just keeps rolling. The second rationale for masting is called the predator satiation hypothesis.
Walt Koenig 24:38
Almost everybody agrees that predator satiation is probably often a major, if not the primary, factor, evolutionary factor driving masting behavior.
Andrew Hacket Pain 24:50
So plant seeds generally are full of carbon and fats proteins. A side effect of that is that those same nutrients are usually a good source of food for mammals, insects and various other organisms which like to eat seeds.
Walt Koenig 25:06
If trees just produce the same number of acorns every year, the predator populations would presumably end up reaching a point where they would eat most of those seeds every year by varying it a lot, from one year to the next. In a really bad year, they can cut those populations of predators down.
Andrew Hacket Pain 25:28
And then one year or two years or some years later, when that predator population has been suppressed through starvation, the plants go all in. They produce bumper seed crops. And any of those seed predators that are still around? Well, they have a great year, but their population is so small and has been suppressed to be so small by the starvation year that a larger proportion of the seeds escape predation. And that can actually be remarkably effective.
Walt Koenig 25:55
Here in California, we have a fairly intact predator populations. We have lots of band tailed pigeons. We got lots of acorn woodpeckers. We have lots of mice, we have lots of deer. We got lots of everything that loves eating acorns. But in most years, if you go out there, you will not see hardly any acorns on the ground. And if you do, they're usually going to be gone the next morning because some deer is going to come along and scarf it up, whereas in a really good acorn year, every so often, then you'll find acorns lying around on the ground, because there's just not enough animals out there to eat them all as hard as they may try.
Andrew Hacket Pain 26:39
In the 1980s when masting patterns in European beach and UK were really strongly expressed, around 2% of seeds were lost to a specialist seed predator, a very boring little moth that lives in the canopy. I've studied them indirectly for a decade. I've never knowingly seen one, but their larvae feed on beach seeds. They leave a very characteristic drill hole in the seeds.
Mendel Skulski 27:03
Underestimate this specialist seed predator, the beech moth, at your own peril. It's known to be a weapon of mast destruction.
Andrew Hacket Pain 27:16
In the 1980s when masting cycles were really pronounced, overall seed predation losses to this specialist moth were about 2%. In more recent decades, beech masting patterns in the UK have changed. Masting has become quite a lot less pronounced, or remarkably less pronounced. So we don't have such strong failure years anymore. We kind of have low ish years rather than zero years, and we don't have super peak years anymore. We have kind of medium to high years. The whole variability, year to year variability has been dampened, and now losses to this seed predator have exploded. It's more like 40% of seeds, of viable seeds are now destroyed by the seed predator. So it's been a massive shift, and it's a really alarming but effective natural experiment to show just how effective masting can be at suppressing seed predators.
Mendel Skulski 28:05
You might be wondering, given how effective it is at reducing seed predators, why would this particular tree, European beech, not be masting like it used to?
Adam Huggins 28:17
Nothing masts like it used to anymore.
Mendel Skulski 28:19
[Laughing] oh my god... we'll get back to that a little later. But first a wrinkle in the predator satiation theory.
Walt Koenig 28:30
One of the contradictory things about oaks and acorns is that the oaks are producing acorns. The acorns are how they reproduce, and they want to have a lot of them out there. And in order to have a lot of them out there, they have to evade the predators. And this is countered by the fact that their main dispersers are also some of those predators. The obvious examples being the Scrub jays and the Stellar jays out there, because they're the ones that are picking those acorns and then sticking them in the ground in various places, moving them uphill even. There's a famous uphill planters paper written by Joseph Grinnell back in the day. How do oaks disperse uphills? Well, you know, you get those acorns picked by a Scrub jay, and they fly uphill to their territory and stick it in the ground, and there you go.
Walt Koenig 29:27
So they can't do too good a job at, you know, getting rid of all those predators. I always think of them as kind of half assed masters. This gets back to a issue with Acorn woodpeckers, if you don't mind for a minute, which is that they tend to be restricted to areas that have at least two species of oaks, presumably, because when you only have one species, it's going to fail every couple three, four years and. And the populations of the birds are going to be in trouble. Whereas when you have two species, they are not likely to be strongly correlated with each other, and so the odds of both of them failing in the same year is going to be reduced significantly. And the more species you have, the lower the probability that all of them are going to have a bad year in the same time.
Adam Huggins 30:23
So now we come to the big question, how do plants do this? The evolutionary benefits of masting rely on coordination between individuals. So how do all of the trees of a particular species across a vast region, sometimes their entire range, synchronize their seed production.
Mendel Skulski 30:43
Could it be a conspiracy of the fungi? Relaying the signal from root to root across their mycelial fiber optics?
Walt Koenig 30:52
Okay, so trees may very well communicate over short distances. You know, groups of trees that are within the same little meadow or something may communicate in various ways through their roots or whatever, but they are not doing this over distances of 10s or hundreds of kilometers. So that's not likely to be a factor which is really driving the kind of synchrony that we see.
Andrew Hacket Pain 31:20
I think, a good example of how below ground communication can't explain the patterns of masting that we see would be something as simple as to see how strongly masting is synchronized on either side of the English Channel in Europe. So if you are in the south of England, your masting patterns will be almost identical to the populations of beech or oak in northern France. And I don't think anyone is suggesting that there are mycorrhizal networks that extend under the English Channel and connect the United Kingdom with Europe.
Adam Huggins 31:53
I mean, at least not since Brexit. Am I right?
Andrew Hacket Pain 31:56
So, sorry to disappoint you.
Mendel Skulski 31:58
I guess just because it's not mushrooms doesn't mean it's not cool.
Adam Huggins 32:03
I'm proud of you for saying so. So what is the most parsimonious explanation? Drumroll please.
Walt Koenig 32:15
It turns out that if you look at weather, so rainfall, temperature, which are sort of the two main things that there are data on, if nothing else, they are also highly spatially synchronous over distances of hundreds, in some cases, 1000s or more kilometers, basically everywhere in the World. So there is no problem having rainfall or temperature having effects, which is what the trees are all sensitive to, and that is by far the most likely factor which is going to be synchronizing these trees.
Andrew Hacket Pain 32:55
So what's happening here is that plants are responding to variations in their environment, and in relation to masting, there, I think two main sources of of what we might think of as information that they're responding to. So one is weather variability, photo period as well, so day length. That's also something that's important. It helps them to work out when they should be responding to temperature. There may also be some influences with radiation as well.
Andrew Hacket Pain 33:23
The second source of information is their own internal plant reserves and their own internal signaling. They're not going to invest heavily in seed production when their internal reserves are depleted, either because they simply don't have the reserves to fuel a super peak year, or because doing that might deplete their reserves dangerously and lead to trade offs, for example, with mortality. And so it may be that this ecological synchrony in terms of masting, is a kind of emergent property, something that just happens as a consequence of processes that are happening at local scales that are regulated by temperature, and temperature just happens to be spatially synchronized at scales of up to hundreds of kilometers. We just don't really know at the moment, it's one of the open questions as to whether that large scale spatial synchrony has any kind of adaptive benefit for the trees, or if it's just a kind of thing that emerges.
Mendel Skulski 34:16
So there is still lots of mystery. Each masting species appears to be listening for a different set of signals. For some, it's wet, winter weather. For others, it's dry, and plenty more we just don't know!
Walt Koenig 34:30
For the most part, we really have very little idea why weather correlates with the acorn crop of any of these species,
Adam Huggins 34:40
And when your research subject is synonymous with age itself, the venerable oak or the ancient beech tree, it becomes increasingly important that your data look back further than just a single scientific career to tackle that problem, Andrew and his colleague Davide Ascoli took on an immense project, called MASTREE
Andrew Hacket Pain 35:03
Where we focused on European beech and Norway spruce. That was kind of our first step into compiling masting records. We were delving into the literature, contacting foresters and other forest researchers across Europe, diving into some pretty old archives right back from the 17th, 18th, 19th century, and pulling out records, harvest records, seed harvest records, all sorts of observations, and compiling them into one big database for those two species. And then few years ago, we got some funding to ambitiously expand that project into MASTREE+ which, rather than focusing on two species had the ambitious aim of trying to compile everything we could anywhere for any perennial plant species
Mendel Skulski 35:47
Enter MASTREE+, an enormous Open Access database, currently containing over 80,000 geo referenced observations from 974 species of perennial plants in 66 countries organized into nearly 6000 time series dating back as far as the year 1677
Adam Huggins 36:13
Enabling scientists like Andrew and Walt to turn back time and go beyond the question of the year to year weather to get at that of the climate.
Andrew Hacket Pain 36:23
I think the impact of climate change on masting has become one of the priority questions in the field. To see how it's changing over time, you need decades and decades of data. So in beach, mast years typically follow, in fact, very strongly, follow years of high temperature, high summer temperatures. What's happened in the last few decades, as the climate has warmed very rapidly, is that these years of high summer temperatures are happening much, much more regularly. So an imperfect analogy is that the trigger of the gun is now being pulled so regularly that the gun hasn't always had time to be reloaded. The queues are happening so frequently. Sometimes every year, every couple of years, the beech has not been able to replenish the resources. Or some individuals have others haven't. Some have partially. But it seems like some species are more resilient to climate warming than others. This, again, is something that's very much at the frontier of what we know, and that's probably because different species have very slightly different, or in some cases very different ways of regulating year to year variability in seed production. And so some species, like beech might have a particular mechanism which just happens to be really sensitive to climate change. Other species might have mechanisms which are not so sensitive.
Mendel Skulski 37:47
So of course, climate change is starting to affect mast seeding, and in the case of European beech, it's a big problem since its primary seed predator
Adam Huggins 37:59
the voracious beech moth
Mendel Skulski 38:01
has gone from stochastic famine to prefix, you know, three square meals a day and the brood to match.
Adam Huggins 38:09
But as we know, different masting species have wildly varying trigger signals. So just as with climate change, you can imagine, every plant and every place will be its own story.
Mendel Skulski 38:20
A story about more than an individual, more than a population of trees, but of ripples moving outward through an ecosystem
Adam Huggins 38:30
With all of their downstream effects, big and small.
Mendel Skulski 38:33
Rippling into acorn woodpeckers
Adam Huggins 38:36
and ground nesting birds
Mendel Skulski 38:38
Into mice and squirrels.
Adam Huggins 38:40
Deer
Mendel Skulski 38:41
and ticks
Adam Huggins 38:42
and Lyme disease.
Mendel Skulski 38:43
There are like, whole species of bamboo that flower all together all over the world and then immediately die, the ultimate mast.
Adam Huggins 38:54
Yeah, a kind of mast suicide. And then you've got broods of cicadas that sap trees of their energy
Mendel Skulski 39:01
literally
Adam Huggins 39:02
to the point where they might not even have enough to spare to mast when they otherwise would. Masting has all of these cascading ecological implications, many of them unknown or under explored. And so we thought it was appropriate to drop a whole bunch of examples at once here at the end of the episode.
Mendel Skulski 39:23
Especially because if you're hungry for even more stories about masting, our friends at all of these wonderful podcasts have made their own episodes for you to enjoy. Thanks again to Golden State Naturalist, Jumpstart Nature, Learning From Nature, Nature's Archive and Outside/In.
Adam Huggins 39:41
Thank you for joining us on this wildly zany experiment.
Mendel Skulski 39:45
We've got links in the show notes.
Adam Huggins 39:47
And to put the cap on this little acorn, I want to reflect for a moment on where we are right now, not to draw too direct a line from this biological epiphenomenon to our sort of muddled human lives. But in my early 20s, I took a permaculture course delivered by a remarkable woman named Starhawk, and she had just written a book at that time called The Earth Path. And in that book, she was exploring natural patterns, right patterns and processes that we find in nature to learn what they can offer us for our social movements, not just teach us about how to engineer widgets right or how to design our architecture, but about how we organize ourselves, especially for change. And I've been thinking about masting in this respect, because I, like a lot of people right now, am feeling a little depleted.
Mendel Skulski 40:46
No kidding!
Adam Huggins 40:47
And I have this feeling that that there really is a need for, you know, a kind of mast movement, for lack of a better word. And there's something about these plants, right, their ability to coordinate action on a massive continental, intercontinental sometimes, scale, without direct communication, right, without passing information back and forth, but just because they are all responding together to signals that they all recognize. I think there's something to glean there.
Mendel Skulski 41:24
I mean, like, Critical Mass is kind of the perfect example, right, right, right. Like on our own, we're just singular grains of pollen with impossible odds of actually making a change. We're scattered aimlessly on the wind and on any normal day, bikes don't really stand a chance against the car hegemony. But then when enough people tuned in to the right signals, you know, they come together and they're undeniable.
Mendel Skulski 41:55
And they can change the whole landscape.
Mendel Skulski 41:57
So yeah, I guess, as another author, Robin Wall Kimmerer reminds us, in the context of masting, all flourishing is mutual.
Mendel Skulski 42:19
Thanks for listening and thanks for letting us be our silly, nerdy selves. In this episode of Future Ecologies, you heard Walt Koenig and Andrew Hacket Pain. It was produced by me, Mendel Skulski and Adam Huggins, with help from Eden Zinchik. Music by Thumbug and Sunfish Moon Light, cover art by Ale Silva. Once again, check out all the companion episodes from our friends. Links are in the show notes.
Mendel Skulski 42:51
If you want us to keep making this show, the best way to help is at patreon.com/futureecologies. You can support us for as little as $1 each month and get access to early releases, bonus episodes, our community Discord server, merch and more. Let us know what you thought about this one. Leave us a comment or a review wherever you're listening. 'til next time, there's power in numbers.