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This article is from the In-Depth Report Adapting to the Freshwater Crisis
Science Talk

Tree Ring Science and Tomorrow's Water

Tree ring expert Kevin Anchukaitis, of the tree ring lab at the Lamont-Doherty Earth Observatory, part of Columbia University's Earth Institute, talks about the information available in tree rings. And Colin Chartres, the director general of the International Water Management Institute, talks to Lynne Peeples about water issues. Plus, we test your knowledge of some recent science in the news, specifically the November issue of Scientific American magazine. Web sites related to this episode include http://snipurl.com/sciamwater; http://snipurl.com/sciamnov

Podcast Transcription

Steve: Welcome to the Science Talk, the weekly podcast of Scientific American posted on November 18th, 2009. I am Steve Mirsky. In this episode we'll hear about trees and water with tree ring expert Kevin Anchukaitis and water [maven]Colin Chartres. Plus, we will test your knowledge about some recent science in the news. First up, Kevin Anchukaitis—he is a researcher in the tree ring lab at the Lamont–Doherty Earth Observatory, part of Columbia University's Earth Institute. A group of science writers visited the Observatory just north of New York City on the west side of the Hudson River on October 29th, and we all got a brief primer on tree rings and what they tell us.

Anchukaitis: The raw materials for what we do are of course trees and their rings and [what you're] actually looking at when you see the tree ring is two different types of cells. So in the early part of the growth season, a tree puts on rather large, thin-walled cells and these cells are used for conducting water. So these are the cells that allow water to come from the roots up into the canopy; tree makes use of this for photosynthesis and then photosynthates, the food for the plant as well as hormones come down, back down to the trunk, and dissipate in forming these cells. So the first cells the tree puts on during the year are these thin-walled, somewhat-larger cells and a very large intercellular space, and all the better to pull water up into the canopy.

Voice: Is this the xylem or the phloem?

Anchukaitis: Yep! Exactly, it's the xylem. So phloem is on the outside and that conducts food and hormones down from the canopy, and xylem is the conducting tissue of which the rings are made [up] with.

Voice: Brings stuff up...

Anchukaitis: Brings the water up. As the growing season goes [on], as you get towards the end of the growing season in temperate regions, the days get shorter, the temperature gets cooler. The trees starts to form a different type of cell, so it puts on somewhat smaller but thick-walled cells, and so they have very little intercellular space, very little empty space in the cell. As you can think of these two types of cells as two different types of straws. So early on in the season the thin-walled cells are like a typical drinking straw you get, you know, in a fast-food restaurant something like that. But later cells, the later xylem cells are much more like a cocktail stirring straw, so very little intercellular space. And it's this alternation [between] light color large cells and you could even—you [might] actually be able to see the contrast between the intercellular space and cell wall—and this is why this is connected to water supply in [particularly] semiarid, arid site trees is that the more they can put on more xylem because of more water available. If there is less water available, they have less use for creating these new tissues and they are more likely to put on these smaller thick-walled, small intercellular space to avoid cavitation, to avoid ending up with a cell with no water in it. So this is what actually gives us the [raw material], the rings, which is alternating light and dark, or if you will, thin-walled and thick-walled cells. This is the way it works in coniferous, can even get more complicated in hard woods. So oaks, for instance, the first thing they do is put on a really gigantic circular vessel and then they start to put on smaller vessels and then as the year goes on, they don't put on vessels, and they just have fiber. So different types of cellular structures, but the same motivation. The tree wants—if you don't mind me anthropomorphizing—to get water up from the roots into the canopy to start photosynthesis to start growing for the year. And so it's these alternating types of cells that give us what looks like a ring from some distance. So this is what the tree is doing. What are we doing? Well, we collect two types of samples, and actually we have to get them out of the tree first and that is done using an increment borer like this; and what you see is three parts here. The first part is this borer. It's hollow and it has got several very sharp tips like a drill bit. Now because it's hollow, if you put it up against—and be very careful, it is sharp—put it against the tree and you start to turn it with the handle, do this by hand, in almost [all] cases, you can actually drill into the tree. Because it's hollow though that small little straw, and not even as large as a pencil, piece of wood is going into the borer here. Then when you get inside, hopefully to the center, [you] take the spoon; and the spoon is sort of a half circle and it's got little teeth at the end, but this goes in, and then the sample comes out, sitting on the spoon, and you [store it and] bring it back to the lab. They look, like I said, like [not even the diameter] of a pencil and when we got back to the lab, the sample you have there, we mount the samples in these, sort of, [balsa] wood mounts, [light] wooden mounts, and then we sand them. So we sand them with progressively finer grades of sandpaper. We start with the very coarse sandpaper, move to a finer sandpaper. And so the smooth surface you see on that, there is no stain or anything like that; that's just the result of using progressively finer sandpaper. And the reason we do this is we have to be able to visualize the cells. And you'll see that you can actually see the individual cells, and that's pretty critical because you have to be able to identify the point at which the late wood cells and the new, early-wood cells begin, and that's where you put the boundary of the ring. So once you got—oh and the other type of sample we take occasionally are cross sections; so these are taken usually with a chain saw or a crosscut saw. We don't cut down trees so these are actually—all three of these are from trees that were dead and down. The two large cross sections are from Huon pine in Tasmania, and this is a pretty remarkable species. Brendan Buckley, my colleague, did his dissertation work on this. And what's really remarkable about them is they're really ancient. So one you're holding right there is about 1,000, or was, about 1,700 years old when it died.

Voice: What actually happens when a tree dies? It just somehow stops doing this process [every year]?

Anchukaitis: Yeah, exactly.

Voice: And there is no—nobody knows why?

Anchukaitis: Well, that's a good question, and there is a whole area of research on why trees get old and why they die, what causes tree mortality. So like any organism they seem to have a [shelf] life and it depends on [the] species and the site. The Huon pine live a very long time, and when they die they tend to, a lot of them, tend to end up in the rivers and the lakes in Tasmania near Frenchman's Cap, and that's where these were retrieved from. So they were dead and down and preserved in sediments. And that's why the chronology, the time series we have (unclear 6:37) rings from Huon pine in Tasmania goes back to 1,700 something B.C., so it's an over 3,000-year-long record of climate from Tasmania.

Voice: These are not fossilized but they are sort of like ...

Anchukaitis: Yeah, we call them subfossil. So they're in the kind of environment that eventually would form a fossil given long enough, but there's still wood, and they haven't been mineralized. It becomes very difficult to work with a tree once it's actually been petrified. There is all sorts of processes that go on in mineralization that make it kind of difficult; but it becomes, yeah if it falls over and becomes mineralized, it tends to get compression and changes due to the mineralization that goes along with petrification.

Voice: Can you tell if the tree was diseased [or if there was a] blight ...?

Anchukaitis: Yeah, absolutely. So there are other things we can do besides climate, and that's so one of the things we can do is we can look for insect outbreaks; defoliators leave a pretty distinct fingerprint on the ring width. So you defoliate a tree, say, with a Pandora Moth, which you find in the Pacific Northwest, you find a very distinct pattern of rings, and what happens is that the rings get narrower and narrower and narrower over a few years, as the defoliation progresses; then you have a series of very narrow years, and then as the tree recovers, they get bigger again. And so it's actually very sort of distinct ramping down and then ramping up that you can see. And what researchers that do dendroentomology, that look for outbreaks like that do is they have a set of host trees, attacked by defoliators, and then non-host trees that aren't, and so you can compare the trees that aren't hosted or don't play host to the defoliators, [and ones that] do. And then you can really see that, look, this tree was growing normally, this nonhost tree was going normally; this host tree has this very distinct ramping down and ramping up. And then you can count the frequency of outbreaks, how long it takes for the tree to recover, those sorts of ecological information. So one of the longest living organisms on the planet is the Bristlecone pine tree and they're found in the White Mountains of California, San Francisco peaks, so around the Great Basin in Nevada, California, Arizona, Colorado as well and they—the oldest living one that has been published on in our field is over 4,500 years old. There was one from Great Basin, that's no longer living that was 4,600-something years old, and there may be older ones out there that the people in the community have not revealed yet.

Voice: These are all living [stock]?

Anchukaitis: Yes.

Voice: But they are not preserved the way [this is because it's a dry climate].

Anchukaitis: Well, it's a very dry [climate] and actually that's why they tend to be preserved. So if you go up to the Bristlecone pine forests, in the White Mountains particularly, it's so dry up there that this wood is laying on the ground and some of it is thousands of years old.

Voice: They can't go back getting these records. How will you be able to do that?

Anchukaitis: Yeah, there is a continuous record back almost 9,000, maybe almost a 11,000 years ago, and then there is a gap, and there's another floating, what we [a] call floating record where it's dated internally amongst themselves; we know roughly—well we know the relative date of a bunch of samples, [but] we only have an vague idea from radiocarbon dating the precise date, so there's actually a gap in the continuous record there. Although every year people go up to the White Mountains, scientists and volunteers and they collect these samples that are literally laying on the ground and you have no idea how old they are until you can date them. So the way that's done is a system of pattern matching. So if you measure these rings and that's what we use, these moving stages for, sorry; so you put the samples on the stage, you sight down the microscope with cross hairs, you put the cross hairs on the boundary of the ring, you press this button and then you move the stage, a very little bit, you can't even see it moving, but there's a linear encoder, and it's recording very small movements of the stage; you get next ring boundary, you put the cross hairs on it, press the button again then you've got the [width] of the intervening ring. You do that tens if, not hundreds of thousands of times and you have got all these data; a computer records it all.

Voice: You are going to match one section of all that, how will you, [you're] overlapping on that, how to use the differences; and I mean, obviously the [trees can't grow] in the same way.

Anchukaitis : Right. So, we are counting on something that can synchronize growth in a bunch of trees over a large area and that thing is usually climate. So all these trees are experiencing the same climate, same broad-scale environment. They may have individual disturbances, they may be growing in a slightly different soils, but they are all experiencing the same climate, and it is that kind of variable that synchronizes growth and that's what allows you to take a sample that you know how old it is, compared to one that you have just picked up off the ground and say, "Right this sequence of rings go up and down together for 50[,000] to 100,000 years. I know what the outer date of this tree is, even though I picked it up off the ground." And so this is decades of work doing this sort of thing. But this was what Brendan and his colleagues did with these. So that's how these records are pushed back into time. Redwoods also very old, Pacific Northwest Douglas fir, very old, and now this sample that I actually passed around is from a species of tree in the Cyprus family; it is from the central highlands of the Vietnam, tropical. And this sample, I don't know how old it is, but this species, we found individuals in excess of a thousands years living in the tropics, in Vietnam; and they contain an excellent climate record of the early season of the monsoon, and so our current research has been to use long-lived trees like this from the tropics to try and do reconstructions of the early monsoon. I did want to talk about the one of the ecological things you can determine from tree rings and that's fire history. So this sample, where you are looking at, these lobes here are actually the results of fire scars, and if you actually get close enough you can see that there's still charcoal, there is still charring on the wood. So what happens in a conifer tree in particular is you get a fire that burns up against the trunk, it can penetrate through the bark, it will destroy the cambium—and the cambium is the living zone of cells around the outside of the tree that's actually producing the xylem on the inside, and the phloem on the outside, the core cambium, so it is basically doing all the work of growing the trunk of the tree. If you kill the cambium, you can't grow the xylem there and so that year you end up with a scar, a fire scar. Now in environments where fire burns frequently—should burn frequently—like the western U.S., ponderosa pine forest, those sorts of mid- and low-elevation pine forest in the west, this happens over and over again. So basically once the bark and tree has been burnt off, has been damaged, you can get cambial cell kills repeatedly. And so what you can see here is that there are actually multiple fires here. And the what the tree has tried to do is to grow back over the damaged cambium. So the year ends, the next year growth begins and the trees starts to try and grow back over the scar. But again in an environment like this where fires burn about every 20 years naturally or did before we start[ed putting them out], it doesn't get, you grow the cambium over completely. You do every once in a while find a tree that succeeds in completely growing over a scar, so you people that study fire like this, that's like a cross section with the chain saw and you can actually uncover hidden scars ones that have actually grown over. So this is another process, so we don't do this so much in this lab, but obviously out west this is a big area of research time, trying to figure out how frequently fires burn.

Steve: Of course, you need water to grow trees and next to the air we breathe, water has always been the world's key natural resource. The Scientific American Web site currently features an In-Depth report on water. One article is by Lynne Peeples. For that piece she interviewed Colin Chartres, the director general of the International Water Management Institute. They met November 5th in the lobby of the Millennium U.N. Plaza Hotel, New York City. It is a noisy environment, but I teased two short clips out of her long interview that I thought were worth hearing despite the background din.

Peeples: Climate change obviously is essential to this, and I recently heard that the current negotiating text for Copenhagen is lacking water at the moment.

Chartres: It does, yeah, yeah.

Peeples: Well, I'm guessing that I know the answer to this, but do you think that needs to change [and why?]

Chartres: Well, in a [very trite way], one of [my] colleagues mentioned previously that climate change mitigation is all about gasses—you might have heard this—[but] climate change adaptation is all about water. Okay, what is it going to do to agriculture? Well, it is going to do a number of things. Temperature rises are going to impact specific crops, so breeding for heat tolerances is going to be important. Less rainfall—well a combination of less rainfall and high temperatures, more evaporation, we will need more drought tolerance. But on the water side there may be more variability, there may be less rainfall in certain areas; [in others] there might be higher rainfall, but more intense storm, so there may be more run off. So [in] those kind of cases, we've got to go to those technologies like, devising ways to capture that excess water and store it, put in place reservoirs, ground water systems where we can utilize that water, and also take [on board all these] efficiency gains. If you look at mountainous regions like the Himalayas and Central Asian region, the estimates are about, in the longer term, about 30 percent decline [in] run off because of snow [melt], because the glaciers and the snowpack [will retreat] higher. So we've got to find ways in which we can do things smarter, more efficiently with water to plug that gap of the 30 percent. It is paradoxical as well because at the same time many of these countries have still got population growth, so they need more fluid production. So the real paradox is growing more with less water. So how people can not even contemplate water in the climate change debate is beyond me; it is the thing which is going to have the biggest [and most severe] impact.

Peeples: I've heard people talk about increased conflicts being a potential issue.

Chartres: When you look at it, there haven't been very many conflicts over water yet. Doomsayers say that, you know, there will be conflicts over water, but my view is that there will be [crazy] because there is enough known about what the [re]form agenda has to [be], there's enough known about the science and technology and in terms of improving efficiency, that really we don't have to go down that path. I mean, water is going to have to be shared and there's going to be less of it, and shared between more people, but it doesn't mean it is something that [people] need to fight over—even in the Middle East, there's not been a lot of actual conflict over water, and in fact there has been some quite encouraging [signs] of using water as a conciliatory process about looking at the issues and trying to share it better. I think we have to—internationally in the future, we have to look more increasingly improving our trans-boundary water sharing agreements. We have to look increasingly at getting better [data and] information about how much [water there] is, who is using it, how it is going to change with climate change and other pressures on it, including looking at quality issues. We need to be very cognizant of the fact that [there] has to be an environmental water fraction remaining, because there are a lot of environmental services provided by having freshwater rivers. The first one is, of course, fisheries, which, you know, provide an income, source of work and encounter a large number [of people]; but biodiversity maintenance and just, in general, fresh water is actually made fresh by the environment, by good land use, by natural condition[s], by filtering water gets into the ground water [etcetera] by natural processes. So we need to make sure that we look at that environmental side of water. So [if] we take all those things and put in place good sound management and do business as we should be doing it now, not as we were doing 50 years ago when water was plentiful, [there's some scope for] optimism, I guess.

Steve: Again you can check out the entire In-Depth Report on water called "Confronting a World Freshwater Crisis" at www.ScientificAmerican.com

Now it's time to play TOTALL....... Y BOGUS and all items are related to content in the November issue of Scientific American magazine. We usually interview Editor in Chief Mariette DiChristina about the contents of the new issue of Scientific American every month, but travel and other intrusions meant we didn't get a chance to talk to her about the November issue, so here are four science stories revolving around November issue content, but only three are true. See if you know which story is TOTALL....... Y BOGUS.

Story number 1: About 10 percent of stars belong to clusters, that is swarms of possibly tens of thousands of stars within just a few light years of space.

Story number 2: In 2030 world maximum power consumption using today's fuels will be around 16.9 terawatts, but switching to wind, water, and solar decreases the power demand to only 11.5 terawatts.

Story number 3: Germany leads the world in average broadband connection speed.

And story number 4: The entire world's population uses land equal in area to South Africa to grow food and raise livestock.

Time's up.

Story number 4 is true. South Africa's area represents the total farm land that feeds the world's almost seven billion people, but growing crops in city skyscrapers would save water and fossil fuels, provide fresher food and eliminate agricultural runoff. That's according to the article, "The Rise of Vertical Farms" in the November Scientific American.

Story number 1 is true. 10 percent of starts belong to tightly grouped clusters of lots of other stars. Our sun might have originated in such a cluster but drifted away over time. Check out the article, "The Long-Last Siblings of the Sun" in the November issue.

And Story number 2 is true. World power demand drops to a 11.5 terawatts if sourced by wind, water and solar, because electrification is more efficient. For example, only about 20 percent of gasoline's energy is used to move a vehicle with the rest just producing heat. More than 75 percent of electricity used in an electric vehicle goes toward motion. That info was in the November cover article, "A Path to Sustainable Energy", which outlines a plan to use wind, water, and solar and eliminate fossil fuels entirely and check out the Web version of the article, which has lots of very cool multimedia bells and whistles at www.ScientificAmerican.com.

All of which means that story number 3 about Germany leading the world in average broadband connection speed is TOTALL....... Y BOGUS, because South Korea has the fastest broadband connection speeds averaging a 11.0 megabits per second. They also have enormous penetration with about 90 percent of households getting broadband. Germany's speed is 4.2 megabits per second, same as the U.S. And in both countries about half of homes have broadband. That info was from the article, "The Everything TV", by staff editor Michael Moyer about how the increasing use of the Internet is the source of TV programming is poised to upend the TV viewing experience. Also don't miss Kate Wong's fascinating piece on new discoveries about the fossils of the tiny people of Flores known as the Hobbits, an article on chronic pain and a piece on the future of cars, as well as our usual assortment of news articles and columns including my In-Depth Report on a book called, The Geek Atlas for anyone interested in having a science sightseeing vacation.

Well that's it for this episode of Science Talk; you can follow us on Twitter as SciAm and my personal tweets as Steve Mirsky and check out www.ScientificAmerican.com for the latest science news including coverage of the AMA's decision to try to encourage more research on potential medicinal uses of marijuana. For Science Talk, the podcast of Scientific American, I'm Steve Mirsky. Thanks for clicking on us.

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