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tv   France 24  LINKTV  September 27, 2013 2:30pm-3:01pm PDT

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funding for this program is provided by... narrator: ecosystems are a complex web of species interacting each one dependent upon another. stuart davies vestigat the world's most diverse ecosystem -- tropical rainforests. through a worldwide tree census, he hopes to discover how such a wide range of species all comping for the same resources can co-exist. in yellowstone national park robert crabtree and his team of scientists seek to untangle the cascading effects
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in the ecosystem when the top predator -- the wolf -- is removed and years later returned to the park. by looking at the delicate balance between different species, both scientists hope to learn how to manage and preserve these ecosystems and others worldwide. in panama, on barro colorado island an ecological preserve created through the making of the panama canal, stuart davies hopes to uncover some of the mysteries of a complex ecosystem -- the rainforest. man: i'm the director of the center for tropical forest science, which is a group who study the rainforests of the world. and we work together as one very large network to try to understand how rainforests function and how they're gonna change in the
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future. narrator: tropical rainforests are believed to be the oldest terrestrial ecosystems on earth. they are home to over 5 million known species of plants, animals, and insects, with millions more yet to be discovered. and trees play an essential role in the diversity of these intricate ecosystems. dr. davies: one famous ecologist said trees in tropical rainforests are like -- he called them the ecosystem engineers. what he meant by that is that they provide the habitat on which all these other organisms depend. so monkeys that live up in canopies of trees go extinct if you take the trees away. ants and termites -- they're gonna be absent if the trees disappear. trees create the structure in forests and therefore they're central to this whole ecosystem. narrator: although rainforests currently cover only 6% of the planet, they are home to over half of the earth's plant and animal species.
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dr. davies: the key question we're still trying to figure out is why tropical rainforests have this extraordinary diversity and how it continues to be maintained. narrator: to investigate the diversity of the rainforest, the center for tropical forest science of the smithsonian tropical research institute has been conducting a census of rainforest trees. dr. davies: our basic rearch program is to study large pieces of forest. we set up these research plots which are 50 hectares in area, typically -- so that's a kilometer by half a kilometer -- in which we study every single tree species that occurs in those areas. we do it all one by one. we go out, we start at the corner of these big plots and we tag and map and measure every tree bigger th a centimeter in diameter. that's as big as a little sapling in your garden. and we monitor everything. we have, in some of our research plots,
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more species of trees than the whole of north america or the whole of europe. that's a phenomenal number of species -- 1,000 species or 1,200 species in one plot. narrator: at 17 forest-dics plots throughout latin america africa, and asia davies' project, in collaboration with the arnold arboretum of harvard university, maintains an active database of more than 3 million trees of 6,000 species. dr. davies: this is a huge data set, which no one else in the world is doing this kind of research. and the idea of doing it right across the whole world is that then we'll be able to come to some generalizations about what's happening to tropical rainforests. narrator: by statistical analysis of a large number of individuals over long period of time the team can determine the dynamics of forest growth. dr. davies: what we do is we monitor them every five years. we go and remeasure all the trees. the idea is to try to work out
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for hundreds and hundreds of species, their population biology -- that is, the rates with which they grow the ratethey die at -- to try to understand the whole biology of the species. narrator: stephen hubbell of the unirsity of grgia and the smithsonian tropical research institute is one of the pioneers of this study, which began on barro colorado island in 1980. man: when we first set out to plot, it took 12 people two years to tag and measure and identify all of the plants in the plot. and one of the remarkable things we found was that, even though this is a very well-studied island there were species that were unknown to science right here already under our noses -- some of them great big trees that had no scientificame, which was a big surprise to us. narrator: through their exploration, the team has discovered some unusual specimens. so this is one of those puzzling
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traits of trees that we're trying to figure out. it has spines on the trunk that are quite sharp and there's no living reason that we know about for this, though there may have been giant ground sloths in this forest that would have shinnied up this tree, and this would have been a very painful eerience. but this is not a tree you want to cut down today without some caution because its sap is toxic. and if you get it in your eyes it causes the corneas to milk up permanently, so you go blind. this is not something you should do at home. [ laughs ] naator: the many species of trees create varied niches for a diverse array of animals and insects each one adapted to its host. dr. davies: this is a particularly interesting kind of tree because as very tight symbiosiwith ants. ants actually live inside the stems of this tree and they actually defend the tree from herbivores.
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the plants provide a very rich source of lipid food bodies for the ants in return for this defense. we've come down to the side here. you can see the ants are getting agitated by me breaking the leaf. but you can see these holes in the stem. the ants come in and out of the stem. so the whole stem is hollow. the ants will continue to defend this colony from a wide range of herbivores, a wide range of insects, that will eat the leaves of the plant. narrator: the researchers explore hoso many different species all competing for the same resources can coexist. one way the trees have adapted is that they become specialists, surviving in niche condions. specialition is one hypothesis for
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how diversity is maintained. we're standing in the middle of a forest gap. it's the result of this huge tree here which died. it died standing. it dropped all its branches. it cleared a big opening in the understory, killed small trees and left a big opening in the canopy. and in that ening, a rush of trees germinates and establishes. and we call those trees -- they're very fast-growing -- we call them pioneers. they pioneer the new gap. and they're specialists. they don't occur inheerstor theynly cur these gaps. so this promotes diversity because you have species specialized to these gaps. you have species specialized to the dark understory of the forest. and if we look at a big landscape scale the forest is a mosaic of trees and gaps. or: some trees are specialized by the nutrients in the soil. dr. hubbell: this species is rare.
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this is casearia and it only occurs in this local little area that we're in of about 100 feet by 100 feet. and there are a couple hundred individuals here t nowhere se in the pl or very rare in t rest of thelot. and so we're trying to understand why this species likes this particular place in the forest. and one idea is that this particular species likehigh-calcium soils and poor-phosphorus soils. and so thiis one area that has high calcium andow phosphorus. but other species may not be so particular. in particular, this one -- faraa -- grows everywhere and seems to be indifferent to the variation in soil nutrients. so it's much more common. narrator: unke in temperate forests, re speesarmber e commpees. that's not one, but. there you go. over there. this distribution is esstial in promoting diversity. on barro colorado island
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the common species only account for 15% of the total tree population compared with around 80% common species in a typical new england forest. one y to invtite how this diverse composition of the rainfores pertued is by studying the seeds and seedlings. dr. davies: the seedlings on the ground in a forest are the next generation of the forest. and so we have a number of studies where we map very small patches of the forest to monitor these little seedlings. narrator: dividing the 50,000-square-meter plot into 1-meter-by-1-meter sections the researchers gather data for each seedling and note any changes. dr. davies: so we want to know if the seedlings have the same composition or the same species diversity as the canopy. because we want to understand how does the development of a forest occur.
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determina que la planta ha muerto. y aquí se pone el código de que es muerta. narrator: these sties have led to hypotheses on how so many rare species can survive with so few individuals. of the 300 species in this plot 15 to 20 of them are represented by a single individual. dr. davies: how do these individual species, just with one tree how do they survive? how do they reproduce? the two hypotheses about how rare species get maintained -- the pollinators may be very mobile. they may be able to travel large distances to find their mates, to find individuals of the same species to reproduce. the second one is that they may be self-fertile. that means they may just reproduce themselves. and then they don't need any other individuals nearby. rrator: the scientists have also formed theories on why the common species are unable
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to take over. and the reason is that common species when they reproduce seedlings -- they produce more seedlings than rare species, but those common species the common seedlings get affected by pathogens and pests at a very heavy rate. you can imagine a specialist pathogen or predator that likes a particular species will come into a little patch and it'll eat all the seedlings. it'll kill them all. and we call this density-dependent processes. that means if you're at a high-density, you suffer very high mortality. you die more often than if you're rare. and so this balances diversity. narrator: there are still many unanswered questions as to how tropical rainforests maintain diversity. unlocking these mysteries becomes urgent
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as humans impact these ecosystems. due to deforestation rainforests now cover less than half of the area they once occupied. dr. davies: over the last three decades, the loss of tropical rainforest has been significant. and so if we don't understand the biology of these species in their natural habitats, i don't think we have any chance of understanding how they're gonna respond to human modifications of those habitats. narrator: while davies is focused on understanding the diversity of tropical rainforests, another team of scientists investigates an ecosystem centered in yellowstone national park, where human attempts to manage its wildlife have changed the balance of species. [ wolves barking, howling ] robert crabtree is the chief scientist and founder of the yellowstone ecological research center.
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currently, he is investigating the cascading effects on the ecosystem after the top predator -- the wolf -- was removed and years later returned to the park. [ wolves barking, howling ] man: the wolf reintroduction is inadvertently a wonderful experimental setup to try to understand how the wolf can help bring back the yellowstone system into more of a natural and unmanaged state to preserve it for future generations. narrator: yellowstone national park was established in 1872 after explorers discovered its extraordinary hot springs, geysers, and other geothermal features. as america's first and still one of its most popular national parks, much of its original ecosystem has been preserved. dr. crabtree: it really was about drawing a big box around the geothermal resources of the park.
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and of course a wonderful windfall from that was the protection of pre-columbian conditions. all the species and all the wonderful habitats that are not represented in other areas of north america were protected by the original creation of yellowstone national park. go back up and see more of the active fires. narrator: however pristine the park may appear, in fact, human efforts to manage the park have had dramatic effects on the health of its plants and animals. dr. crabtree: in managing and protecting this park many things had to happen. and actually when it was made a park, there was already some big impacts to the park. fur trapping had occurred. elk and deer were being poached. and the park actually formed by bringing in the military to help protect it. and then soon after that they moved into a phase of trying to manipulate it to get it back to a healthy state which included the removal and eradication of predators. they were thought to have been bad at that point.
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narrator: ironically while striving to preserve the animals and landscape, humans implemented changes that affected the health of the ecosystem. in 1926, park rangers exterminated the wolf population, triggering a cascade effect. in the following years the elk population soared, seriously impacting other species. the elk consumed much of the vegetation in the lamar valley an area in the north of the park and many species that depended on this vegetation, such as beavers, grew scarce. to combat this problem different methods were adopted over the years to control the elk population, including trapping and killing them. finally, in a controversial move to restore the park's natural conditions, wolves were brought back into yellowstone
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after a 70-year absence. dr. crabtree: in 1995 and 1996 after 20 years of effort by a lot of organizations, wolves captured as social groups in canada were transported down, acclimated in pens and released. the fundamental question is, is the wolf gonna fit right back into the niche it once had or have things changed substantially enough to where their new niche is actually different than what it was at the turn of the century? narrator: scientists hoped that, as the top predator in the food chain, the wolf would control the population of elk and other herbivores and, therefore, the vegetation that these animals feed on such as willows, would be able to survive. since the return of the wolf the elk population has drastically decreased
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from 20,000 in the 1990s to fewer than 10,000 today. now crabtree and his team hope to discover what effect the wolf has on the plant life. specifically, they're examining riparian systems -- the areas along streams, rivers, and lakes. dr. crabtree: riparian ecosystems often are areas where you see the highest concentration of species or biodiversity. we call them hot spots. and certainly in a semi-arid ecosystem like the yellowstone they really do dominate the landscape. narrator: although these riparian systems only comprise around 1% of the park's land area, they play a vital role providing food or habitat for over 70% of the species in the park. so protecting these systems is essential to maintaining the overall health of the park's ecosystem.
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sarah uhl coordinates the field research in the riparian zones. woman: we're working in a very complex system and we're trying to understand how the introduction of wolves is one factor interacting with a suite of other factors to change willow and other riparian shrub populations. maybe this one that we're looking at is one of these dots. and therefore, we need to go a little bit more... we definitely need to get around. narrator: crabtree has set up around 90 plots throughout yellowstone. every four years a team of field biologists returns to each plot locates each of the trees and shrubs on the plot... what else is around you? ...and updates the master database with the current health of each plant. man: our daily routine usually involves going out and relocating willow plots that were charted, mapped, and studied four years ago in 2002. so we do need to go all the way to the bank there.
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man: then we can set out our measurements for the plot. and we actually take our gps unit, our data sheet and our measuring tools and basically go to each plant individual plant and take all the crucial measurements. an average height of 1.1 meters. swenson: then we're recording the species. we're also recording the various physical dimensions of the plant -- the length of its long axis, the length of its shorter axis its average height, its maximum height, the density -- as in the density of stems on that individual plant. and then we start looking at the browse history along an individual stem that's representative of the whole plant. narrator: browse history refers to how much of the trees and plants were eaten by various herbivores over time. uhl: if we look at this leader, you can see little chomp marks here that are old. and this probably took place during last winter
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when the elk were wintering over ithe park and needed something to eat and came and stopped right here. and after the willow is munched like that the plant can't simply grow from that region of dead tissue. it needs to sprout again from where it was still alive, neath the browsing. and that's what you're seeing right here with this browner, redder stem. that is all new growth. narrator: in order to survive, the willow must grow above the browsing height, where herbivores such as elk can no longer reach it. well, here we have a much larger willow. and its growth pattern over the last few years is pretty different from what we were seeing in the rest of the plot. here we see that the last few years have actually not been browsed. so, for vegetated...
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all covered. 100% overall. narrator: the research team is finding that the willow population is starting to recover in certain areas of the park. dr. crabtree: in particular, where the wolves have created, you might say, fear in the elk where wolves can go in and effectively kill elk elk might not even be going down into those areas and willow is allowed to grow up and get high enough to where it escapes browse heighth from the elk. and we're seeing this in several areas of the northern part of the park. narrator: since the researchers can only monitor a fraction of the willow from the ground, they must turn to the sky, using remote sensing. radar and advanced-imaging cameras mounted on airplanes and satellites provide data on many factors including tree height, soil and plant chemistry and even the health of the vegetation. dr. crabtree: the major part of remote sensing for ecologists,
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and the greatest utility is that they take detailed images and data sets over large areas. riparian habitats are extended over large areas through the entire ecosystem and we simply don't have the money or the labor force to go out and examine all these. but we can intensively look at representative samples of those riparian habitats and then turn to our remote-sensing data that covers the whole ecosystem and make great inference or extrapolate our results to the whole ecosystem accurately. narrator: one remote-sensing tool used by crabtree's team is nasa's aviris hyperspectral camera. dr. crabtree: you can think of one of these hyperspectral cameras as almost like a biological dna fingerprint of the landscape. as you can see here in this color image, we've got largely a big, green marshy
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riparian area that looks a lot the same. in a hyperspectral image the same area here is much more than just a big, marshy, green area with the river running through it. it's composed of many different kinds of habitat structural differences that's apparent to the hyperspectral camera, that you cannot see in a simple color image of the study area. narrator: the colors in the image represent the amount of light energy at differe wavelengths that's being absorbed and reflected by the plants, something we cannot see with the naked eye. this information can help determine if the willow is stressed or healthy. in this image, within the marked plot the dark green represents healthy willow that have escaped browse height. dr. crabtree: this is what's called released willow. so this is high-stature willow that really erupted in 1997 and 1998
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and it's surrounded by smaller willow that has not released. narrator: using the remote-sensing images in conjunction with the data gathered in the field gives the team a better understanding of the landscape and how it impacts the various tiers in the food web. the researchers have found that willows that escape browsing height create a domino effect within the ecosystem. species like riparian songbirds, insects, and, in particular, rodents, have come back into these preferred habitat types, and other species are starting to respond. for example, fox and coyotes are moving into these areas because there's more prey for them. and there's been an erupting trophic cascade in some of these lush willow riparian habitat sites. narrator: while the willow populations appear to be rebounding,
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scientists are working to determine how much of this regrowth can be attributed to the wolves as compared to other contributing factors. dr. crabtree: we're finding out that it's very complex. and we are seeing some very clear impacts due to the wolf reintroduction but it's not clean or as clear as we'd like it. one of the confounding factors has been in 1995, 1996, and 1997, we had 25-, 50-, and 100-year floods right at the time when wolves were reintroduced. but both, arguably -- and what the evidence is initially showing -- have improved the health of the riparian habitats in the park. and it's the greatest charge sent to us as scientists to try to unravel that and tease apart that complexity and rightfully assign the big signal that is coming from the wolf reintroduction on the entire ecosystem and food web of yellowstone. average height -- 1.25.
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narrator: both crabtree's study of willows in yellowstone and stuart davies' tree census in the rainforest will provide t evidence needed to create improved ecosystem models to better inform policy-makers about future preservation. funding for this program is provided by...
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for information about this and other annenberg media programs...
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funding for this program was provided by... emperor marcus aurelius ruled 50 million people on three continents when he immortalized himself in bronze and gold. now, in the ruins of the roman empire, scholars grapple with an age-old question -- how does any one leader acquire so much power ? from the tribes of highland new guinea and the chiefdoms of the american northwest, to the kingdoms of the ancient maya, archaeologists trace the evolution of human leadership. theirs is a journey through time seeking clues to the emergence of the state.


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