January 27, 2020
An analysis of timber used to construct buildings in Europe hundreds of years ago is giving scientists and historians new insights into the region’s history from the 13th to 17th centuries. Using samples of wood taken from old buildings in Europe, Fredrik Charpentier Ljungqvist, a historian and paleoclimatologist at Stockholm University, and Andrea Seim, a dendrochronologist at the University of Freiburg, figured out when the trees used in the buildings were cut down. They then created a huge database of building activity over hundreds of years. The researchers used this information to uncover societal trends. Changes in construction activity often reflect changes in society, making them good indicators of what was happening at a certain time period.
In this episode of Third Pod from the Sun, Ljungqvist and Seim explain how they were able to date construction timbers in buildings in Europe to reconstruct building activity from 1250 to 1699 and used this information to uncover information about society at the time. The researchers explain how they get their samples, the expected and surprising results they uncovered about the Black Death, the Great Famine, the Thirty Years’ War and the Late Medieval Crisis, and how their large collection of tree felling dates can serve as new historic source material for studying European history.
This episode was produced by Nanci Bompey and Liza Lester and mixed by Robyn Murray and Jon Schriner.
Shane: Hi Nanci.
Nanci: Hi Shane.
Shane: Folks don’t know, this is take two because we’re running out of things talk-
Nanci: Shane’s there telling me the exact same story that he told about a year ago. That’s okay, though.
Shane: It’s good, though, because we’ve been doing this that long. That’s exciting.
Nanci: I know. That’s a good thing, right? That means that we’re successful in being a long-running show.
Shane: Yeah. Yeah. I’m going to ask you… We’re talking about time and old things today, specifically old wood, but we’ll get to that. We were talking about like-
Nanci: Old homes, sort of.
Shane: Yeah, and sort of like uncover in home.
Nanci: Yeah, yeah, yeah, yeah, yeah. Yeah, exactly. I once had this house we were living in in college, so it’s like, “How many college students have lived in this house all these times?”
Shane: Yeah. It’s probably garbage.
Nanci: Uncover some weird stuff. But it happens that the bedroom set that I was using, I don’t know where the guy got it. Our landlord, I think he got it from an old motel that closed down because the first day I come there, moved my stuff in, there’s a Bible in the side, one of those Bibles from a motel in the bedside table, so I’m like, “How many people slept in this random bed?”
Shane: Oh, yeah. That’s…
Nanci: Makes you think.
Shane: Welcome to the American Geophysical Union’s podcast about the scientists and the methods behind the science. These are the stories you won’t read in the manuscript or hear in a lecture. I’m Shane Hanlon…
Nanci: I’m Nanci Bompey.
Shane: … and this is Third Pod from the Sun centennial-
Nanci: Wait. It’s not centennial anymore, Shane.
Shane: Well, it’s January. Okay, we’ll get to that. All right, so what… It’s not centennial, so what are we doing?
Nanci: Our centennial is over. It was a lovely year…
Nanci: … 100. Now, we’re 101.
Shane: A lovely year. It was a lovely year.
Nanci: It was a lovely year, centennial, and now it’s centennial plus one.
Shane: Right, but we’re going to keep doing this.
Nanci: Yeah, but we loved our historical stories so much that we were telling during the centennial that we wanted to keep it going.
Nanci: So, these stories… We’ll have our regular episodes that we’re doing, and then we’ll have these stories that kind of have an historical bent, whether we’re talking about a historical story that happened in geoscience or how people are kind of using historical stuff to find things out about geoscience, that kind of stuff.
Shane: So, same idea. We just have centennial to kind of thank for giving us this little oomph, I guess.
Nanci: The legacy continues.
Shane: The legacy continues. All right, so that’s the historical podcast, but today’s episode will… Why were we talking about your creepy dorm furniture?
Nanci: Right, right. Well, so actually, this was, oh, almost a year ago. I was at the European Geosciences Union meeting in Vienna and spoke to some researchers who are doing some cool things. They’re looking at some old homes in Europe because that goes back way longer than us here in the United States, actually, from that wood in the old homes, dating the homes and figuring out what’s actually happening in society and the climate from that old wood, because you have these trees that could be thousands and thousands of years old in these homes.
Nanci: Crazy, huh?
Shane: Yeah. It’s wild, but so… Well, I guess…
Nanci: What are they doing?
Shane: Yeah, what are they doing? I guess we’ll ask Liza, who’s sitting here patiently.
Nanci: Yes. Liza helped me with this episode. Liza helped me with this episode, and we bring in our science expert, our scientific expert, Liza Lester.
Liza: Oh, no. Expert?
Shane: It’s relative to those in the room, let’s say.
Liza: Okay, well I’ll do my best. This is really neat. We’re talking about old homes today, and they dated the wood using this technique called dendrochronology. Familiar with that?
Shane: Which is wood.
Liza: Which is wood or trees. Yeah. Then, chronology is putting time and sequence, so events and how they happened, timeline.
Nanci: Yeah. I think like a lot of people know about tree rings.
Nanci: It’s kind of like… It is that.
Liza: It is tree rings. Yeah, yeah.
Nanci: [crosstalk 00:04:10]. Yeah, it’s tree rings.
Liza: So, we know that trees, when you cut a cross-section of one of them, you see those beautiful rings, and each ring represents one year because the tree grows at different speeds during the year. This can also tell us a lot about what happened to the tree in that year because maybe it was dry, maybe it was wet, maybe it was cold, maybe there was a lot of sun, and how was the tree doing, right? Then, we can learn a little bit about what was going on in the weather or the climate at the time that the tree was alive.
Nanci: It’s so cool. These homes are really, I guess, unique is the right word, but it’s cool because you can really go back so far because the logs are so old. Where else are you going to find a log that old? You’re not.
Shane: Yeah. Yeah, I guess that’s true.
Nanci: You’re not.
Nanci: What are the other places? No, in structures, they’re preserved in these structures.
Shane: Right, right.
Liza: Right. These structures have been taken care of, and sometimes they even reuse the timbers, which can throw it a wrench in the whole process. How do they do this? If you can accurately date how old something is by these tree rings by counting backwards from the outside, the bark, to the inside, how many years was the tree alive.
Liza: So, if you know when the tree was cut down, you can cut count back to how old that tree was. So, in reverse, they could try to figure out from that tree when the building was built based on… assuming that the tree was cut down and pretty quickly put into a house.
Shane: It’s wild to me to think of not knowing when a building was built. I don’t know.
Nanci: Yeah, because here it’s so-
Nanci: … everything’s so relatively new.
Shane: I have a house from the ’30s. That’s kind of old to me.
Liza: Yeah, but maybe if it was built in 1400-
Liza: … you might be a little-
Nanci: The records may be lost.
Liza: You could look at the type of structure and have an idea, but you don’t know exactly what year, and this can really accurately… by comparing to other trees where, you know-
Liza: … how old it is. Maybe the tree is still alive, for instance. You know you can count back exactly from now to how old that was. They can compare these living trees or known trees as a reference to the logs you see in these buildings and match the rings sort of. I’m sure it’s more complicated than that, but we’ll call it that, and that can give you an idea of when that tree was alive, and then when it was cut down, and when the building was built. Then, this can give you trends of when things were built in the area you’re looking at, which is really interesting for history.
Shane: I think you did a lovely job, Liza.
Liza: Thank you.
Shane: … explaining, so I guess we’ll hear from our interviewees.
Liza: Yeah, let’s do it.
Fredrik: Fredrik Charpentier Ljungqvist. I’m a historian and paleoclimatologist at Stockholm University in Sweden.
Andrea: Yeah, I’m Andrea Seim. I’m from Germany, and I’m a dendrochronologist.
Fredrik: We have made a new reconstruction of European building activity changes from late medieval times all the way to the end of the 17th century. We have reconstructed which year and which decade built, more or less, across mainly Central Europe. We think it’s very interesting to reconstruct past building activity rates because building activity reflects demographic, economic, societal conditions, so if you can reconstruct where and when you build much or very little, you can see time, so prosperity and times of crisis.
Nanci: So, in the buildings, you can actually tell what was going on at the time?
Fredrik: Yes, on a broad scale, especially building activity seems to be a very sensitive indicator of times of crisis. When the building activity decreases, it indicates that some problems in society, we used to quite novel material to start these societal changes to felling dates or preserved construction timber, so dendrochronological dated felling years from pieces of construction timber preserved in different buildings, and we didn’t made all the measurements ourself. We compiled data that had been made available for decades of building heritage work and different archeological labs around Europe. We obtained data from 16 different archeological labs.
Nanci: Okay. All right, so how do you… This is wood, I guess, that is in buildings?
Andrea: Yes. Exactly.
Andrea: It’s construction timber used for constructing houses, so on the roof’s construction, they are still preserved, so colleagues going in taking cores, so this increment bore, and they’re measuring then the tree rings and date those tree ring sequences based on reference chronologies, so they’re doing dendrochronological dating.
Nanci: These are, I guess, thousands of buildings that they’re found in?
Fredrik: Oh, yes. We have almost 50,000 dates in our data set and that’s the largest ever compiled data set for this purpose by far. Basically, by compiling all this data from mainly Central Europe, it’s essentially new historical source material when you use it in this way and aggregate it all. We only look at the period from 1250 to 1699, so we have this period from late medieval times to the end of the 17th century, and we have a lot of values per year. Of course, there are more preserved buildings in the recent centuries. It’s a trend because of increasing preservation.
Fredrik: So, we detrend, they take away the trend over long, real long timescales. We also standardize the values, so we get an index value of building activity for each year, an index of building activity for each year from 1250 to 1699, and we, of course, also look at the [inaudible 00:10:02] averages because sometimes we had can have noise in the building activity, of course, in the individual year, and you see some signals of societal crisis or well-being better on longer timescales.
Fredrik: Then, we have looked at the largest compiled data set of plague outbreaks… It’s actually from the 1970s already compiled and recently digitized… and also a compilation of grain prices for Europe because we found, after making many different type of analyses, what might influence building activity change is that it was plague outbreaks, the number of plague outbreaks, and the prices of food, mainly grain.
Fredrik: So, we looked at these two data series and found a very significant correlation. During periods with many plague outbreaks, you have the low building activity, and during periods of no plague outbreaks or very few plague outbreaks, you had typically high building activity, and when the food prices were low, you had plenty of food available, then you had quite high building activity in general. When you had high food prices mirroring a lack of food or shortages of food, you had little building activity.
Fredrik: We also looked at paleoclimate date of hydroclimate precipitation and drought in Europe and temperature, and we found no really consistent significant correlation to climactic conditions. I thought you actually would find some influence because we know that dry and cold condition decreases the harvest, so the grain prices actually contain a climate signal back to felling dates. So, the building history don’t really contain clear climate signals. There’s Too many steps between climate, and food prices, and then the building activity.
Shane: So, they do this by… Essentially, they’re getting… It’s like how you get maple syrup out of a tree. You just plug a hole in it, right? You’re just drilling a hole and plugging a cork.
Shane: But they’re drilling holes in people’s houses?
Liza: Yes. Tiny ones.
Shane: Tiny ones.
Nanci: Very wee.
Liza: Very small. Very small.
Andrea: It’s quite simple. We go over these increment bores. Think about when people sample ice cores, and the architects’ or these artists’ hollow drills. We are using the same, basically, for the timbers or for the beams so that the increment bore is hollow inside. We drill inside, so we have kind of a core of-
Nanci: Small, not that bigger than a [crosstalk 00:12:48].
Andrea: … half a centimeter core.
Nanci: Oh, okay.
Andrea: Of course, we are looking in the building on the construction timber, where there is the outermost part of the tree now, so maybe bark is preserved, or now we see that is close to the bark. This is where we take the sample.
Nanci: Then, what do you do with it back in the lab?
Andrea: Back in the lab? So, we prepare the surface. In Central Europe, it’s mainly oak trees used or conifers. Then, we measure the ring breadth. We’re using an automatic measuring tape and a microscope. Then, basically we transfer the width into values, and then we have kind of a zigzag curve, which we then match. This chronology is reference chronologies. Then, we date this specific timber to a certain period. Now, it can be middle ages, or modern, or whatever. So, where we have the best synchronized position is the reference. Basically, this is how we date the timber.
Nanci: What do people think about when you come to their house or wherever, and you’re like, “We’re going to take a borehole and see how old your house is?”
Andrea: I mean, normally, the people are really excited because, of course, it’s also a curiosity to see, okay, is it built when they believed it was built? Because sometimes you have inscriptions, and sometimes it fits perfectly to the year. Sometimes, it can also happen that the material is reused. So, maybe you have an older materia which is built again. Yeah, I mean, there’s a little hole. I mean, people are happy to live when they know how old the house are… or house is. Sorry.
Nanci: That’s interesting, though. They may have said they think it was built in such and such a year, and you say, “Actually this is older or younger or whatever.” Yeah, yeah.
Andrea: It can happen then also. I mean, as a dendroarcheologist, you look at the construction type, so how was the roof construction built, and how are the joints, and which type is used. So, you normally have a rough estimation, when was the building-
Nanci: Because different types of-
Andrea: … really constructed.
Nanci: They did different types of construction depending on the time.
Andrea: Exactly. Yeah.
Nanci: How do you find them? How do you know what houses to go do to find it? Then, how do you take the sample? I mean, are people still living in these houses or using these buildings?
Andrea: It depends. It’s a wide range, can be anything from monasteries which need a dating. Also, there are private people approaching colleagues saying, “Please, now, can you date the building? When were the trees felled to construct the building?” But it can be also public services. Now, they want to know. Cultural heritage agencies, they want to know how old is the building, and then they approach colleagues. This data set is basically only the timber which has this outermost rings, so below the bark, so this is by its felling date, so we know exactly, in this year, the tree is cut for constructing the house, used as construction.
Nanci: Felling is the date they chopped it down?
Fredrik: Yes, yes.
Nanci: Okay, okay.
Andrea: But of course, there are also timber which they don’t have the last ring preserved below the bark, so they are much more timber, and for this study, [crosstalk 00:16:20]-
Andrea: … can only be used the timber which had basically the bark, the last ring beneath the bark.
Fredrik: That’s a small minority of the actually available material, but we only wanted to use the dates with an exact date in order to also look, for example, on the influence of plague outbreaks. We compare or reconstruct the building history with, for example, historical data, a compilation of documentary data of over 10,000 plague outbreaks in Europe to see how plague influenced, for example, the changes in building activity, and then you need exact dates. Of course, a house might be constructed one or two years after the tree was felled but more or less the same time to see on these influences. We could see, for example, that three to four years after the start, the biggest plague epidemics, the biggest 20 plague epidemics in Europe, you could see a significant decrease, not the first and second year. It started to decrease, but the climax of the decrease is four to five years after the plague outbreak starts, and then already the next year, year six after the plague outbreaks, it’s back to pre-plague building activities.
Andrea: When there was these plague outbreaks, the people are kind of busy or, of course, dying or whatever…
Nanci: [crosstalk 00:17:42].
Andrea: … or just surviving, and of course, they are not thinking about building a house now, and they don’t have the strength to do that either [inaudible 00:17:50]. Yeah.
Shane: I think this is neat.
Nanci: It’s super neat.
Shane: Yeah. I guess why is this important is a silly thing to ask, but what did we find out? What have we found out per se? Cool, something’s how old, but… You said climatic record, but what else? Is there other things in history we can figure out? Or…
Liza: Yeah, well some of it is looking at just demographic change, or what was happening in society could be reflected in the building patterns, as he’s talked about a little bit. So, if you suddenly see a cessation in building, people aren’t making houses. Something’s going on in their lives, and maybe… There were a few cases where they were like, “We didn’t realize this had happened so early.” They knew the plague came, but it seemed like people stopped building before it arrived, so what else was going on?
Nanci: Because the noble people were the people who were writing, the common people, they maybe couldn’t write down the records, so it’s really giving insight into what was actually happening in a larger scale. Or, they found like, “Oh, this actually happened earlier than the common…” The noble people didn’t really feel bad-
Shane: But the noble people.
Nanci: … but the common people, it was bad, so it helps fill in gaps in that kind of record, historical record, right?
Liza: Yeah, we can see these-
Nanci: We can fill in the historical record.
Liza: … these big trends maybe. It kind of applies to broad spots, wider regions of the world, and what’s going on, and does that match with what we think happened from historical records? But they also use this technique for places where you don’t have historical records. This was kind of pioneered in the American Southwest.
Fredrik: We found a number of different interesting results. The first one was a very significant decrease in building activity occurring around 1300, and that is five decades before the black death hit Europe and two decades also before the Great Famine. Typically, historians have debated over decades, did the late medieval crisis that is called the demographic and societal crisis in Europe in the late medieval times, did it start with the black death? That is the traditional view or more recent research indicate it maybe started with the so-called Great Famine, which was the biggest subsistence crisis in Europe the last millennium, but it occurred 1315 to 1317, so it’s three decades before the black death. But we find that, actually, a decrease in building activity occurred two decades earlier around 1300 already. So, it’s-
Nanci: What do you think was happening?
Fredrik: I mean, historians have for a long time debated this underlying societal crisis where you have a population increase that is much faster than the available increase in resources. You also have more frequent food shortages and more societal conflicts on all levels of society, including not only warfare but all types of societal crisis and also a strain on resources and other epidemics besides plague. There are indications already in the second half of the 1200s that you have some crisis in Europe, but it’s very hard from the written records to grasp because the written records that we at least have in part of Europe in the middle ages, they rarely really go into societal conditions per se, the ordinary peasants or workmen.
Nanci: They were written by the educated.
Fredrik: Yes, mainly clergy, and the nobility, and for certain major trade centers, so we don’t have source material that covers, I mean, the countryside, small towns across Europe to see how the demographic conditions really were. So, this is a new material. I think the most significant finding maybe is that this late medieval crisis started right around 1300, and we can see the black death but not very clear, and that was the big surprise because the crisis, the increase in population, the lack of a need of new buildings have already occurred.
Fredrik: Of course, maybe 25, 30, 35% of the population died in the region, but if you already had the population decrease before, it doesn’t matter if the population decreased 10% or 50%. You still don’t need any new buildings. It’s first when you need new buildings when you’re going to build. Of course, you build all the time and repair buildings but when you have a significant increase in building, and that occurs 1415 according to the felling days, the reconstructed building history, 1415 approximate, but it’s sharp increase there, and it’s about, again, three decades now before what written records indicate is the real economic and demographic recovery in Europe. So, the crisis seems to start earlier and end earlier in the building history than in the written records, so it’s a few decades earlier above, which is a kind of interesting result.
Fredrik: Then, of course, you can capture other trend breaks to increasing building activity in the mid 1500s, which really well corresponds to population boom in Europe. Then, again, the decrease around 1580 that corresponds to the start of a century of different crises in Europe, including famines and wars. What was really interesting to see, the sharpest decrease in building activity occurs 1618, the start of the Thirty Years’ War. It ends, quite exactly a dramatic increase yet again, 1638 at the end of the Thirty Years’ War. It’s not surprising because this war was, in terms of the proportion, the population that died in Central Europe is about 30 to 40% of Central Europe’s population, mainly Germany and present-day Czech Republic that perish, but we have about an equal percentage in the decrease of building activity that exactly fits this interval. It really is a test bed that shows that felling date-based reconstructions or building activities is a sensitive indicator of societal conditions.
Nanci: This stuff is so interesting and so cool. I love all this stuff. It takes us back in time, sort of like how Shane’s mustache is like-
Shane: Oh, God.
Nanci: … a hearkening back to 1970.
Shane: Oh, my gosh.
Nanci: It’s actually more like ’83. I’m going to go with ’83. What do you think, Liza?
Liza: Tom Selleck.
Liza: [crosstalk 00:24:39] look.
Nanci: Yeah. You got the ’80s look going on with that ‘stache.
Shane: I like that you’re going back in time because I wasn’t born in ’83.
Nanci: Oh, now the guns are out. The gloves are off.
Shane: The guns are out. I mean, I was just in Florida, so there were lots of tank tops.
Nanci: Yeah. Ooh.
Shane: Okay. All right. Well, that’s all from Third Pod from the Sun.
Nanci: Thank you so much to Fredrik and Andrea for this story. Thanks to Liza for helping me with this episode.
Liza: Happy to.
Shane: This episode was produced by Liza and Nanci and mixed by [Robin Murray 00:00:25:16] and [John Schreiner 00:25:17].
Nanci: Thanks so much for listening, and please read and review us on Apple Podcasts, and you can always find this podcast wherever you get your podcasts or at thirdpodfromthesun.com.
Shane: Be on the lookout for more let’s just say historical episodes.
Nanci: Yes, and our regular episodes, and welcome to a new year.
Shane: Yeah, happy 2020 everyone. All right. Thanks all, and we’ll see you next time.