[MUSIC] Hi, and welcome to the Laboratory for Tree Ring Research. I'm Charlotte Pearson, and it's my pleasure to be able to tell you a little bit about tree rings today. So this is a cross section through a tree. And you'll kind of recognize things like the bark. Maybe the pith. And you'll know that trees form annual rings, and so if we counted each ring in this sample it would tell us how old this tree was when it was cut. But another thing to notice about this tree is that the tree rings aren't all the same width. They vary. And so some areas have very wide rings, and some areas have very narrow rings. And this is another sample. This is a different type of tree. This is a different species of tree. This is oak. And you can see that this oak tree was a really happy tree. This tree had seep soil. It had plenty of water, and it grew very regular, large, even rings that don't really show any variability. So a little change in climate didn't have any impact on this tree. It just carried on growing. This is the same species of tree from the same site. But you can see that there are many more tree rings here, and you can see that within the sequence of tree rings we have again wide bands and narrow bands. That we have wider bands and narrower bands, and that is the signature of climate. Because this tree was a stressed tree, and stressed trees are very good for what we do. Because a little change in climate can make all the difference to a stressed tree. And so recorded in the sequences of tree rings are time capsules of environmental history of what maybe, what the temperature was doing what precipitation was doing over time. But this pattern of climate which is spread across a region, so trees growing in the same region reflect the same climatic pattern. It allows us to do something very interesting and very powerful. Not only can we look at one tree, and the climate in one tree, and the age of one tree, but we can match the growth patterns from one tree to another tree. So if I were to go to an archeological site, well let's start with actually, going back to this sample. If I was to go out, and say I've just gone outside and I've cut this tree down, and I look under the bark, and I know that the tree ring that's forming this year is this year's ring. So I know exactly, where this year is in time. And if I count backwards that means I also know where every other ring in this sample is placed in time. Now if I then went to your house, and I got a timber from your roof and I post it and I measured the tree rings. I don't know when that was cut, but I'd like to find out, so that I can tell you. So what I would do, is I would measure each tree ring in the sample and that would give me a pattern of wide rings and small rings, and wide rings and small rings. And I then take over dendrochronological data that I had from a sample like this one, a living tree, and I would hope that the pattern in your tree and the pattern in the earlier part of this tree would match up. And if it did, then even if the tree in your house died 100 years ago, it was cut 100 years ago, I'd be able to tell you exactly which year in which it was cut. And that's a process called crustating, and it's a process by which patterns from tree rings overlapped, backwards in time, starting in the present, and going right the way back. Now, at this lab we have a huge diversity of work going on, from forest sites, from archaeological sites, all around the world even. And, one of the longest chronologies in the world is the bristlecone pine sequence. It's a privilege to be working in the same building as people that are dealing with these trees, because these trees can live for 5,000 years. And that's been shown by dendrochronological by people in this lab. And one individual tree can live for 5,000 years. We have samples here that were growing before they put the pyramids up in Egypt. Whilst they were constructing the first pyramids, the trees were growing. The trees that we have in our bristlecone pine chronology. And it's absolute annual resolution tree-ring dating. For me that's really exciting, because I am a human and I like to also study archaeology. So I like to study the human past. And tree rings give us a way of measuring human time to within a year. And I like that, because for me a lot happens in a year. There are other dating methods around. Radiocarbon dating for example, which will give you a date, but it has an error margin. And if you have an error margin of 20 years or so, then your connection with the person in the past Is less. But if you have a tree ring date to within one year, then you're a time traveler and you're linking with that person in the past. So that's one of the things that excites me most about working with this stuff. So dendrochronology grew up here at the University of Arizona with a guy called Andrew Ellicott Douglas. And he was an astronomer. And he was studying the effects of sun spot solar activity on tree growth. And working in collaboration with a team of archaeologists, Douglas started visiting Pueblo sites across the southwest. And the idea there was to look at the tree rings from roof timbers in the pueblos, and to see if by looking at the climate pattern in the wood, he could find out whether the different sites were contemporary with one another or not. So did the climate pattern at one site match the climate pattern at another site, showing those two sites were occupied at the same time? When he started by doing that, but then came a day where he found he had sufficient material to overlap all his tree ring chronology patterns backwards in time. And he just had one gap in his sequence and that was the only thing standing in his way of going back to 700 AD and creating a new historic timeline for the southwest. In 1929, he got this publication out in the National Geographic magazine. Which told the story of how he collected this wood from all the Pueblo sites and how he put together the sequences, and how he constructed this 700 year sequence. And there's a picture in here of Douglas finding that one piece of wood that filled in the gap. That allowed him to fill in the gap and make the first dendroarchiological sequence for dating tree rings. And so that the discipline of dendrochronology was born. And since then, It's going all around the world. There are tree ring labs all around the world doing all kinds of research using tree rings, because there are so many things that the tree rings can tell us. It's not just about dating archeological sites, although this still, there are people here carrying on Douglas's work. There are people here doing southwestern dendro archeology. I work in the Mediterranean, but there are also people here reconstructing climate, reconstructing drought. Looking at those ringed patterns and finding years where it got really tough for the trees. There are people here who do fire ecology. And this is a tree with a fire scar. So you see that up until this point in time, that this tree was having a very nice life, just growing along. And then suddenly, a fire comes in. The fire would have come from this direction. It's damaged the tree, but it hasn't killed it, cuz this side of the tree was protected. And so what the tree does is, although this part is dead, the rest of it's alive. And it's continues to heal and grow and it heals right at the waveband and seals off that scar. And you can cut down a cross section through a tree and find five or six or seven of these scars buried in a tree. So what that allows you to do is you count your tree rings, and you find the exact date of when that fire event occurred. You count the tree rings, and you find the exact date of the next fire. And in doing so, the researchers here have built up long histories, reconstructions of when fires happened. They've looked at that against climate records, and they're using this to predict data that is so relevent and so useful for our lives today. Other researchers here are looking at drought on it's own. Other researchers are looking at things like stream flow, like flood events. And researchers are on the bristlecone pine record, have shown that the tree line is changing as result of what's happening with the climate today. And that's the other big part of what happens here. There are people who are looking at what the climate's been doing, because the trees don't lie. The trees just stand in a position and they grow. And they just record information, they just record little time capsules. And so if we come along and we extract that information from each time capsule. We can reconstruct what's going on in the history of the life of this tree and the one that links with it, and the one that links with it. And this can allow us to look at the past and use that as a key for the future. For predictions of what climate might do over time in the future. So, just to show you a couple of samples from the sites that I'm involved with the team's researchers in the Mediterranean region. This is a really neat sample. So you can see this is a section that's been squared off because it's been used as a roof timber, so it's from a building. And it's very dark in color because it's charred. And a lot of the time when we're dealing with archaeological sites, material is charred. And actually when it's carbonized like this, it can be preserved for long periods of time because it's resistant to decay. And we're still able to see the tree rings and make measurements. And this has been put into a chronology for this building. What's exciting about this sample, there are many things, but the outermost ring is 141 BC, and this was actually carbonized. We actually know when the sample was carbonized, because right at call plenty the younger was recording a description in 79AD, August 79AD he looked out his window and on the horizon he saw the eruption column for Mount Asivieous rising on the horizon, and he recorded in great detail what happened during that eruption. One of the things that happened that a big pyroclastic flow swept down the flanks of Mt Vesuvius and it buried the building that this timber was used in. And that is why it is now charcoal. So this was carbonized in a pyroclastic flow in 79 AD. This sample doesn't look as impressive. You can see it's kind of a bit yucky and has a bit of sand on it. This is a sample, we have 3,800 samples like this one. They are sections from posts that would have made up the docks in the giant harbor in Istanbul, Turkey, and I can tell you that this sample dates to 535 AD. And, we're putting together a dendrochronology record from this site, which spans the first millennium AD. So we're going to be looking at things like when different docks were put in place, how did that time with economic history of Constantinople. Were there times for example where more grain was coming in from Egypt and so they needed to build more docks. And think about this but although this is you know, it's not the best dendro sample, it's not got very many rings, it's a bit, it's slightly wet, it's not so glamorous, but these are the posts that those boats from Egypt knocked up against 2,000 years ago. It's exciting, it's a privilege to work on material from these amazing diverse sites But as probably as much as we have time for. Thank you very much for giving me the opportunity to tell you a little bit about what we do in this tree ring lab and do come and visit. Because there's lots of exciting things to see.
