Deforestation and the Future of the Amazon
Transcript of Part 2: Amazon Ecosystem Dynamics at the Agro-industrial Frontier
00:00:08.07 I'm Christopher Neill, 00:00:09.14 a senior scientist at the Woods Hole Research Center 00:00:11.13 in Woods Hole Massachusetts. 00:00:13.01 In a previous lecture, 00:00:14.23 I talked about how deforestation, 00:00:17.09 fragmentation, 00:00:19.01 fire, 00:00:20.15 the rapid rise of crop agriculture, 00:00:22.00 and changes to regional climate 00:00:24.09 influence the dynamics of the Amazon forest 00:00:26.06 and the potential future dynamics of that forest. 00:00:29.07 In this talk, I want to talk about 00:00:31.28 specific work that we are doing 00:00:34.07 at the Amazon's agroindustrial frontier 00:00:36.26 -- that is, the southern boundary of the evergreen Amazon forest, 00:00:41.12 where crop agriculture is expanding, 00:00:44.27 and where climate and rainfall 00:00:49.07 are just high enough to sustain evergreen forest. 00:00:52.00 So, it's a zone of both 00:00:55.02 rapid human change and potentially rapid ecological change. 00:00:57.14 What I want to do is talk about 00:01:00.24 how all of these factors interact 00:01:03.08 to potentially shape the current dynamics of the forest, 00:01:06.03 the future of agriculture, 00:01:07.28 and the potential future trajectories of the remaining forest. 00:01:11.25 Our work is focused on a very large farm 00:01:14.13 that we call Fazenda, or Ranch, Tanguro. 00:01:17.20 It's an 80000 hectare farm 00:01:20.25 that's situated along the southern boundary of the evergreen forest, 00:01:23.16 in that orange zone on this map, 00:01:25.24 which is the zone of highly deforested land. 00:01:29.23 This farm is an interesting place to do research 00:01:32.18 because it contains about half of its land area 00:01:36.15 in large blocks of remaining forest 00:01:38.23 that both incorporate areas of forest, 00:01:41.18 but entire watersheds. 00:01:43.18 And then half of this farm, 00:01:45.19 the pink area on this right-hand inset map, 00:01:48.22 are croplands. 00:01:50.16 This is what that farm looks like from the air. 00:01:53.25 In the background, you can see these large areas of forest. 00:01:56.22 You also see some protected riparian zones, 00:02:00.06 although they, in this case, 00:02:02.27 in the foreground, they're highly degraded because they don't have much forest left, 00:02:06.13 but these zones are also important parts of this agriculture landscape, 00:02:10.19 which I'll talk about. 00:02:12.15 At Tanguro, 00:02:15.08 we think it's an excellent place to look at 00:02:17.29 the interaction of land cover and land use, 00:02:19.29 how fires interact with forests 00:02:24.06 in this agricultural landscape. 00:02:25.26 We can look at land-atmosphere exchanges, 00:02:27.27 such as how the rise of crop agriculture 00:02:31.21 and the expanding use of fertilizers 00:02:33.11 influences the releases of greenhouse gases 00:02:36.06 to the atmosphere. 00:02:37.17 And we can also look at interactions of soils and waters, 00:02:40.06 and that is, how does rainfall move 00:02:44.16 from forests or upland cropland, 00:02:46.15 through the soil profile, into streams and waters, 00:02:49.21 and what those ultimate effects will be. 00:02:51.27 So, I'm going to cover all of those points, 00:02:54.13 because they're all part of our interacting research 00:02:57.04 at Fazenda Tanguro. 00:02:59.00 And, of course, the big overlay 00:03:01.04 is how all of those interact with climate, 00:03:02.26 and how all of those might play out in the future 00:03:04.29 under a climate that's much more likely to be 00:03:10.13 warmer and with longer dry seasons. 00:03:12.03 I want to start by talking about 00:03:14.29 a unique prescribed burn experiment 00:03:16.14 that our group conducted over 00:03:19.09 more than a decade at Fazenda Tanguro. 00:03:20.28 This is the basic layout of the main experiment. 00:03:24.05 It contains a control area on the right, 00:03:26.18 and this is a half a square kilometer, 00:03:29.02 a large block -- a kilometer by a half a kilometer. 00:03:32.08 In the middle is a plot that was burned 00:03:36.12 once every 3 years, on a schedule, 00:03:38.16 during the dry season, when fires typically happen. 00:03:40.25 And the plot on the left was burned every year. 00:03:44.09 And we're comparing how those fire regimes 00:03:48.01 affect the structure of the forest 00:03:50.03 and the likely potential that that forest 00:03:54.27 would be flammable enough to burn in a repeated way. 00:03:57.15 So, I'm going to show you a little bit of those results. 00:04:00.26 Like I described before, 00:04:03.15 fires in the Amazon forest, 00:04:05.07 because the forest often doesn't get particularly dry, 00:04:08.21 often occur in the dry season 00:04:12.27 and as fires in the litter layer, in the understory. 00:04:16.07 So, these are fairly low intensity fires to start, 00:04:20.05 but low intensity doesn't necessarily mean 00:04:24.04 that they don't have important ecological effects. 00:04:26.01 So, here's a plot that 00:04:29.02 compares tree mortality and biomass 00:04:31.22 in response to those fire regimes. 00:04:33.28 On the top panel we've got a control forest, 00:04:36.28 which is the line on the bottom of that panel 00:04:40.08 with the open circles, 00:04:41.28 and it shows fairly low, but some, 00:04:48.00 tree mortality over six years of this experiment. 00:04:52.05 But what shows up in those top lines, 00:04:54.08 in the square panels at the top, 00:04:56.24 is that the cumulative tree mortality 00:04:59.20 reaches 50% in the plot that was burned every 3 years. 00:05:04.19 And the same change in live biomass, 00:05:07.11 and the same change in leaf area, 00:05:09.20 which is simply the... 00:05:11.25 sort of the area of leaf surface that occurs in this forest... 00:05:15.23 the leaf area is highest and the live tree biomass 00:05:22.09 is highest in the control, 00:05:24.01 and it takes a real nose-dive 00:05:26.08 in that second 3-year burn. 00:05:27.24 So, what happens is that one fire 00:05:30.13 sets this forest up to burn again, 00:05:32.03 and to burn more severely, 00:05:34.06 because one fire results in some mortality of small trees, 00:05:37.27 increasingly dry conditions during severe dry seasons, 00:05:42.16 that allows that second fire 00:05:45.12 to be much more damaging. 00:05:47.10 And if you burn every year, you're using up fuel. 00:05:49.14 But if you're burning only every few years, 00:05:51.16 in those very dry years 00:05:54.22 that come in the Amazon with El Nino conditions, for example, 00:05:57.25 every several years, 00:06:00.10 you're really setting up that forest to burn 00:06:02.06 and burn in a way that transforms its structure. 00:06:04.07 So, I want to show you how that structure is transformed, 00:06:07.09 just by showing you some pictures 00:06:10.06 from this experiment. 00:06:11.20 On the upper left is an intact forest -- that's the control site. 00:06:15.00 The upper right is the plot 00:06:18.12 that was burned every 3 years after the first burn. 00:06:20.06 And then in the lower left, after the second burn. 00:06:23.27 And then 3 years after that second burn, 00:06:27.29 what you see is that this site has been invaded by grass. 00:06:31.15 That's very important because that grass dries out, 00:06:35.04 becomes fuel during the dry season. 00:06:37.11 So, this change in structure, 00:06:39.28 as it plays out over time, 00:06:41.28 results in a much more flammable ecosystem, 00:06:45.00 and you can see that lower right-hand panel 00:06:48.18 indicates that this forest 00:06:51.23 is well on its way to being transformed 00:06:53.26 into a savannah ecosystem. 00:06:55.28 I want to talk about a little bit of work we're doing 00:07:01.05 in these riparian forest fragments. 00:07:02.24 These areas, as occur in the middle of this picture, 00:07:06.28 are forests that are along streams. 00:07:09.22 Now, Brazilian farmers, by law, 00:07:11.12 are mandated to leave buffer zones 00:07:14.15 along stream channels. 00:07:16.02 These forests, even though they occupy 00:07:18.28 a fairly small total portion of the area, 00:07:21.22 are disproportionately important, I think, 00:07:25.24 because they protect stream water, 00:07:27.26 they provide shade and cover 00:07:30.05 and protect the aquatic ecosystem. 00:07:31.23 We're interested in how the dynamics of these forests 00:07:34.27 play out over time, 00:07:36.23 but they're subject to many of the same dynamics 00:07:39.21 that fragments of upland, 00:07:41.22 or what we call terra firme, forests are subject to, 00:07:44.28 that I talked about last time. 00:07:47.09 One of the things that we see happening, 00:07:49.11 and we've documented, is that these riparian zones are narrow. 00:07:53.00 They also can be invaded by grass, 00:07:56.00 and it looks to some extent like 00:07:59.10 their structure is changing over time, 00:08:01.06 simply because they're fragments, 00:08:03.16 but also because they are subject to disturbance 00:08:07.08 because they dry out and they are invaded by grasses. 00:08:12.04 So, these are an important additional fragment dynamic 00:08:15.23 in this landscape. 00:08:17.26 Now, let's take a step back at the larger scale 00:08:21.03 -- this removal of forest cover 00:08:23.21 caused by deforestation and agriculture, 00:08:26.19 actually, is changing the regional climate. 00:08:28.28 This is a graph, a diagram, 00:08:32.29 of results of a model 00:08:37.18 that come from remote sensing, 00:08:39.19 that show that this large green area 00:08:42.10 in this central part of this image, 00:08:44.15 the land cover on the left... 00:08:46.05 the green area is remaining forest, 00:08:47.25 and on the right you see a graph of temperature. 00:08:51.26 Now, the temperature is low in the big forest area, 00:08:55.24 but it can be 5-7 degrees higher 00:08:58.01 out in that cropland landscape. 00:09:00.04 Well, what does this mean for forest dynamics? 00:09:03.17 It means that higher temperatures are occurring 00:09:05.28 along these edges, 00:09:07.29 just where this change in structure is playing out. 00:09:10.08 So, this flammability is driven by 00:09:12.16 both the changes to forest structure, 00:09:15.11 but these large changes to climate 00:09:17.28 that are driven by the land conversion. 00:09:21.06 Another thing that our group is doing 00:09:25.17 is trying to understand, how do these changes in land cover 00:09:28.12 and cropping influence 00:09:31.16 runoff from streams and the chemistry of streams? 00:09:34.09 We're interested in how water moves from landscapes 00:09:38.24 into streams and rivers, 00:09:40.14 and one way we get at that is 00:09:43.09 we look at the infiltrability of the soils 00:09:45.28 in a landscape that looks like this image behind me. 00:09:49.09 We do this by putting a column of water 00:09:52.26 over the soil 00:09:54.10 and measuring the rate at which soil... 00:09:56.28 the soil can infiltrate that water, 00:10:00.12 and we get information such as the following, 00:10:03.18 and I'll explain why I think this is important. 00:10:06.28 This is simply a graph of the rate at which 00:10:09.11 water infiltrates into surface soils 00:10:12.01 in the forest and in soybean fields. 00:10:14.07 So, there's a clear result that 00:10:16.26 the water infiltrates less rapidly 00:10:19.13 when you have agriculture. 00:10:21.21 These forests infiltrate a large amount of water; 00:10:24.21 they can absorb a meter or more of water 00:10:27.19 in an hour. 00:10:29.22 It never rains that hard. 00:10:31.07 This dotted line along the lower portion of the graph 00:10:33.17 is the maximum 5-minute rain intensity. 00:10:37.13 So, even when this landscape is soybean fields, 00:10:40.10 it can absorb the maximum... 00:10:45.15 the maximally intense rainfalls. 00:10:47.20 So, what that means is that you 00:10:50.26 almost never get lateral flows 00:10:52.25 -- you don't get a lot of erosion off of this landscape -- 00:10:54.28 and that's an important thing, 00:10:56.25 because if farming can be sustained 00:10:59.16 to maintain soils that maintain this high infiltrability, 00:11:03.26 it means that the risk of erosion and runoff 00:11:07.10 that brings sediment and surface nutrients 00:11:10.19 from land to streams 00:11:13.01 remains fairly low. 00:11:14.17 We also looked at how this land cover 00:11:19.16 changes the discharge of streams. 00:11:21.12 So, this is, again, this map of Fazenda Tanguro, 00:11:23.20 and each of these little gridded areas, 00:11:26.02 the darker areas, 00:11:27.20 are entire watersheds that are either in soybean fields 00:11:30.12 or in forest. 00:11:31.28 And we log water flow out of all these watersheds 00:11:36.23 using level loggers and stream rating curves, 00:11:39.25 and we can come up with a measure of 00:11:43.26 the total amount of water and the timing of that water that left these streams 00:11:46.13 -- a very standard hydrological measure. 00:11:48.24 And when we did this across multiple watersheds 00:11:50.23 at Fazenda Tanguro, 00:11:52.29 we got a very interesting result. 00:11:54.21 And that was that the overall discharge from streams 00:12:00.01 that were 100% -- almost -- in soybean cover 00:12:03.17 was 4-5 times larger, in total, 00:12:06.16 than the runoff from the forest stream. 00:12:09.11 So, this plot... the bars on this plot show rainfall... 00:12:12.21 rainfall is highly seasonal, 00:12:14.11 the maximum rainfall occurs 00:12:17.26 from November through March, 00:12:19.14 and the dotted line at the top is soybean watersheds, 00:12:21.19 and the solid line at the bottom is forest watersheds. 00:12:26.09 And what's, I find, absolutely remarkable is that, 00:12:29.10 despite the intense seasonality of rainfall, 00:12:31.12 streamflows hardly vary over the year at all. 00:12:33.26 And that derives from this very high infiltrability, right? 00:12:38.05 Rainfall falls, it's absorbed into the ground, 00:12:40.10 it goes into the groundwater, 00:12:42.21 and that water just moves out of the groundwater 00:12:44.13 in a very regular fashion. 00:12:47.24 In the soybean fields, there's some indication that 00:12:50.00 there's a little more rapid flower, 00:12:51.24 but the big point is there's much more water 00:12:53.29 coming out in those soybean streams. 00:12:55.23 And why is that? 00:12:57.21 Because you don't have trees that are grabbing water, 00:12:59.23 using deep roots that are down deep in the soil, 00:13:01.29 and pumping that water back into the atmosphere. 00:13:04.04 Without trees, croplands 00:13:07.09 put much less water back into the atmosphere. 00:13:09.01 And that's extremely important, because 00:13:11.11 as that plays out over very large areas, 00:13:13.02 that's going to influence the future of the Amazon climate. 00:13:17.15 So, here's a picture of those very deep 00:13:20.18 but highly permeable soils. 00:13:22.19 These soils are absolutely remarkable. 00:13:24.26 They can be up to 30 meters or more deep, 00:13:28.16 they're very uniform and they're highly permeable. 00:13:30.14 They don't have the typical layering that we think of... 00:13:33.17 that we temperature zone biologists 00:13:36.26 usually are familiar with. 00:13:38.21 These are what we term oxisols. 00:13:40.20 They're very, very old, highly weathered, 00:13:43.16 but extremely deep. 00:13:45.13 And, despite high clay content, 00:13:47.16 aggregated clays make them very permeable to water, 00:13:50.13 and water can infiltrate quite rapidly. 00:13:53.15 So, one result at a slightly larger scale 00:13:58.00 of these changes to the amount of water 00:14:01.07 that's leaving because we don't have trees under... 00:14:04.17 over cropland, 00:14:06.18 is that we can measure the total amount of water in a large... 00:14:10.06 in a deep soil profile over a fairly large area 00:14:13.10 using a technique of resistivity, 00:14:17.06 which measures water content in soils 00:14:20.10 simply by placing electrodes 00:14:23.07 and measuring electrical resistance. 00:14:24.20 So, what you get when you do that is 00:14:26.25 a two-dimensional picture like this, 00:14:28.24 that actually is soil moisture down to almost 15 meters deep. 00:14:33.24 And we run a transect out from a soybean field, 00:14:38.09 on the left, into the forest, on the right, 00:14:40.12 and what you see absolutely clearly in this image 00:14:42.24 is that the forest is drawing water from deep down, 00:14:45.18 and you get warmer colors, 00:14:47.24 that is, drier conditions, 00:14:50.02 on the right-hand side, under forests, deep down, 00:14:52.08 than you do under soybean fields. 00:14:54.14 There's just a lot of water... 00:14:56.14 wetter soils under soybean fields 00:14:58.08 and that manifests itself in this greater overall runoff. 00:15:02.11 We also are interested in the impacts on aquatic systems, 00:15:05.03 of this intensive agriculture. 00:15:07.17 If you think about what happens in 00:15:11.13 intensively agricultural areas of the Northern Hemisphere, 00:15:14.06 such as the "bread basket" area of the middle of North America, 00:15:17.07 we see very large impacts of runoff of nutrients from farm fields, 00:15:21.15 movement of nitrogen, particularly, 00:15:25.10 into rivers, and when that nitrogen hits the coast, 00:15:27.11 such as in the coast of Louisiana, 00:15:29.08 just as an example shown here, 00:15:31.07 you get this anoxic zones in estuarine regions 00:15:35.16 that are very, very, potentially, 00:15:38.26 damaging for aquatic life. 00:15:40.19 So, we're interested... 00:15:42.22 you know, do you get these changes 00:15:45.29 in this intensive Amazon cropland that you would get in, 00:15:50.14 potentially, the same intensity of agriculture in North America? 00:15:55.14 And so we took our watersheds and we actually added up, 00:15:57.22 by measuring the concentrations of solutes 00:16:01.08 -- these nutrients, nitrogen and phosphorus -- 00:16:03.19 in the water, 00:16:05.28 and comparing between forest and soybean watersheds, 00:16:08.10 we calculated the total export of material 00:16:11.01 -- and we do this as 00:16:13.21 kilograms of nitrogen or kilograms of phosphorus 00:16:16.14 per hectare of land area -- 00:16:18.05 and we can compare export from forest 00:16:21.07 to export from soybeans 00:16:23.08 across multiple watersheds, 00:16:25.09 a very powerful methodology. 00:16:26.28 And here's what we find. 00:16:29.05 For nitrate, we find that the export 00:16:32.24 from soybean watersheds if four times greater 00:16:34.27 than it was for forests, 00:16:37.08 but there was absolutely no increase in the nitrate concentration 00:16:40.28 -- quite a remarkable and surprising result. 00:16:42.21 The difference of four is simply that 00:16:45.10 there's four times more water going out the soybean stream, 00:16:47.07 carrying water with the same concentration of nitrate. 00:16:50.13 The same was true for ammonium 00:16:53.14 and the same, basically, was true for phosphate, 00:16:55.26 that there's a small increase in export, 00:16:58.03 but it's driven completely by the fact that 00:17:02.00 there's more water leaving the watershed, 00:17:03.21 and not by any transport or excess amount of nutrients 00:17:07.04 leaving that landscape. 00:17:09.09 So, this is a pretty surprising and interesting result, 00:17:11.17 especially when you compare it to 00:17:15.24 the result of intensive agriculture in the temperate zone. 00:17:18.03 And these are very, very low numbers 00:17:20.16 -- export of less than 1 kilogram/hectare of nitrate, 00:17:23.09 or barely 1 kilogram/hectare of ammonium, 00:17:26.28 or very, very low export, 00:17:30.12 compared with tens of kilograms of nitrogen/hectare potentially 00:17:34.06 going off of cropland that has seen intensive agriculture 00:17:36.29 in other parts of the world. 00:17:39.27 Another factor that's happening in this zone 00:17:42.25 is cropping is further intensifying, right? 00:17:45.26 So, under soybeans, 00:17:48.03 farmers don't use nitrogen fertilizers. 00:17:50.21 Soybean is a legume -- it fixes nitrogen. 00:17:53.22 So, while phosphorus fertilizer and potassium fertilizer are applied, 00:17:58.20 there is very little or no application of nitrogen fertilizer. 00:18:01.24 That game completely changes 00:18:04.08 when cropland intensifies 00:18:06.16 from the single cropping of soybean 00:18:08.25 to the double-cropping of soybean 00:18:11.11 followed by corn or followed by, 00:18:14.03 in fewer cases, cotton, 00:18:15.28 where the second crop does require 00:18:18.16 a substantial amount of nitrogen fertilizer. 00:18:20.12 So, this is a picture of Fazenda Tanguro 00:18:22.28 and what's happening right now at the farm 00:18:25.26 is the spread of a double-cropping regime, 00:18:29.09 and the replacement of single-cropped soybeans, 00:18:31.21 which we see has very little impact 00:18:34.08 on the solute concentration in streams, 00:18:36.08 to the double-cropping of soybeans with corn, 00:18:38.17 with potentially unknown but potentially serious consequences, 00:18:42.08 because there's a large use of nitrogen fertilizer. 00:18:45.26 So, we did another experiment to look at this. 00:18:48.04 This just shows the extent of that 00:18:50.26 across the entire landscape of the state of Mato Grosso, 00:18:53.17 which is a Texas+Oklahoma-sized area 00:18:57.16 where the intensive cropping is occurring. 00:18:59.09 And the left-hand panel, from 2001, 00:19:01.12 shows mostly green cropland, 00:19:03.13 that is, soybean-only cropland, 00:19:05.13 and on the right, the yellow colors shows... 00:19:08.26 this is soybean/corn rotation, 00:19:10.25 in red is soybean/cotton rotation. 00:19:13.10 So, within little more than a decade, 00:19:16.21 almost the entire landscape changed 00:19:19.18 from single-cropping of soybean 00:19:22.09 to double-cropping of soybean with another crop 00:19:25.05 that needs nitrogen fertilizer. 00:19:26.21 So, a very dramatic change occurring in the Amazon 00:19:28.27 over a very short period of time. 00:19:30.21 We conducted a field fertilizer experiment 00:19:32.28 to try to look at the fate of the nitrogen 00:19:35.07 that would be applied in the corn, 00:19:37.02 that second fertilized phase 00:19:39.11 of this intensifying agriculture. 00:19:41.10 We did this by enlisting 00:19:44.18 the farm and the planters 00:19:46.17 -- this is the size of the planters that operate on this farm -- 00:19:48.20 and we created an experiment that compared 00:19:54.04 0, 80, 120, 160, and 200 kilograms of nitrogen. 00:19:57.04 Now, this farm is using itself, on corn, 00:20:00.29 about 80 kilograms of nitrogen/hectare. 00:20:03.03 We wanted to know, what was the limit of intensification, 00:20:07.08 and what could you expect if this large landscape 00:20:10.05 further intensified? 00:20:12.02 To do this, we created a series of plots 00:20:14.23 and we measured two important fates of nitrogen. 00:20:17.05 One was the emission of nitrous oxide, 00:20:19.22 a potent greenhouse gas, 00:20:22.04 to the atmosphere. 00:20:23.25 We expect that to increase following fertilizer application, 00:20:27.17 if what happens here is consistent with what we know from other areas. 00:20:32.00 And, second, we used soil water collectors 00:20:35.13 to measure the concentration of nutrients in the soil 00:20:40.01 that are leeching down and potentially out into streams 00:20:43.05 and into watersheds. 00:20:45.15 Now, I'm just going to summarize these results. 00:20:48.07 This is work in press. 00:20:49.29 Kathy-Jo Jankowski, who was at MBL, 00:20:52.05 is leading this charge. 00:20:53.17 And this table shows 00:20:57.14 the fate of the fertilizer in these different fertilizer treatment levels, 00:21:00.18 right? 00:21:02.09 The 0-200 kilograms/hectare nitrogen. 00:21:05.00 So, what this shows is a lot of the nitrogen 00:21:08.22 that's applied ends up into he biomass. 00:21:10.24 We actually get more nitrogen going into the biomass 00:21:13.04 then we put on in fertilizer, 00:21:15.04 because we're taking advantage of the fixed nitrogen 00:21:19.26 from the soy phase of the cropping, 00:21:22.06 the cropping cycle. 00:21:23.24 But what's remarkable here is that very, very little is leeched, 00:21:26.19 even under high fertilizer. 00:21:29.22 And the N2O release is actually very, very small, 00:21:33.00 it's in fact smaller that releases 00:21:36.21 from a lot of other cropland 00:21:40.11 -- less than one kilogram of nitrogen/hectare. 00:21:41.28 What's surprising is this right-hand column, 00:21:44.07 that there's a lot of nitrogen that's just stuck 00:21:47.07 in these very deep soils, deep down. 00:21:48.29 And this is really an interesting thing that we're finding 00:21:51.28 across these weathered tropical soils, 00:21:54.12 both in Brazil and in places in Africa, 00:21:57.27 where fertilizer use is increasing. 00:22:00.20 And that is, these soils have the capacity 00:22:03.13 to actually absorb nitrate at depth, 00:22:06.02 and we think that this provides 00:22:09.14 a remarkable capacity to buffer watersheds 00:22:12.07 from the increased impacts of higher fertilizer use, 00:22:17.12 when you have this high infiltrability 00:22:19.18 and when you don't generate these erosive surface flows. 00:22:23.06 Now, there's some big questions remaining about this, 00:22:26.06 and we think that this reduces leaching to streams, 00:22:28.10 but we don't really know, 00:22:30.13 what is the ultimate size of this capacity? 00:22:32.27 Or will we, at some point, 00:22:34.29 after decades of fertilizer use, 00:22:36.18 exceed this capacity? 00:22:38.15 Or are there some circumstances, 00:22:40.14 like high flows, 00:22:42.17 that will actually exceed this capacity? 00:22:45.12 So, it looks like there's... 00:22:49.20 done right, this intensification can occur with fertilizer uses 00:22:53.17 up to something like 120 or 160 kilos/hectare. 00:22:58.13 Beyond that, the N2O fluxes appear to increase, 00:23:01.17 but the leaching appears to be buffered, 00:23:03.25 at least for now, 00:23:05.15 but we haven't looked at this 00:23:07.29 over the decades in which this agriculture 00:23:10.11 is likely to remain active 00:23:13.23 in these Amazon croplands. 00:23:15.16 Finally, this is probably important over very large scales. 00:23:19.11 This is an interesting map that we created 00:23:22.28 that shows Fazenda Tanguro, 00:23:25.29 there, circled in black, 00:23:27.24 and the dark green in this case is double-cropping, 00:23:29.28 and the light orange color are these deep oxisols, 00:23:34.03 or latosolos in the Brazilian classification. 00:23:36.15 And what this shows is that, 00:23:40.05 not only has double-cropping expanded dramatically 00:23:42.11 on these deep soils, 00:23:44.08 but there's potential for it to expand a lot more, 00:23:47.03 because there's a lot of available soil, 00:23:49.24 a lot of available area on which this could potentially happen. 00:23:54.07 So, those really remain our very large questions. 00:23:56.24 You know, what is the extent that you can intensify production 00:24:01.00 on these deep soils? 00:24:02.14 Brazil has done a very good job over the last decade 00:24:07.02 of reducing deforestation. 00:24:08.25 Here's a graph from work by Marcia N. Macedo at the Woods Hole Research Center 00:24:11.20 -- it simply shows that, since 2006, 00:24:14.24 deforestation has fallen, 00:24:17.03 but cattle production and soybean production 00:24:19.06 has actually continue to increase to some extent. 00:24:22.14 So, what Brazil has done, through a series of policy initiatives 00:24:25.13 and a moratorium on the selling of soybeans 00:24:28.24 from land cleared after 2006, 00:24:32.07 is it's forced cropping and intensification of cropping 00:24:36.09 onto already cleared land. 00:24:39.00 And the questions really remain are... 00:24:42.26 the questions that remain are, 00:24:45.08 how intensive can that cropping be 00:24:47.05 and with what impacts? 00:24:48.23 So, this has been a success. 00:24:50.29 It remains to be seen the extent to which it can remain a success, 00:24:53.18 because as the landscape starts to look like this... right?... 00:24:59.07 soybeans followed by corn, this looks very much like other parts of the world 00:25:01.03 with intensive grain agriculture, 00:25:03.12 we really still have some big unanswered questions 00:25:06.11 about how intensive cropping can be, 00:25:08.27 how much greenhouse gas emission, 00:25:11.09 how much leaching, 00:25:13.10 what are the limits to this intensification 00:25:15.05 before we see environmental damage, 00:25:17.26 especially to waters and to increases in greenhouse gases 00:25:22.07 in the atmosphere? 00:25:23.21 And finally, there's an important question remaining... 00:25:26.25 how much deforestation can this landscape sustain 00:25:29.25 until the evapotranspiration through remaining forest 00:25:35.11 becomes insufficient to sustain the rainfall regimes, 00:25:38.25 which are necessary, both to sustain the remaining forest 00:25:41.09 and to sustain the intensifying cropland 00:25:44.04 that's replacing it? 00:25:45.20 And this is really, I think, 00:25:47.26 the most challenging area of current Amazon climate 00:25:50.29 and forest research. 00:25:52.13 We don't know the answer to that question, 00:25:54.23 but it's absolutely vital for Brazil, 00:25:56.26 and other Amazon countries, 00:25:58.29 to move forward to create a system 00:26:01.13 that allows protection of forest, 00:26:03.08 and agriculture at an intensive level 00:26:05.07 that actually allows forest to remain standing in other places. 00:26:12.03 This work at Fazenda Tanguro 00:26:14.04 was made possible by a very large array 00:26:18.11 of both collaborators and funding sources. 00:26:20.06 I especially want to thank my colleagues at MBL, 00:26:22.09 the Woods Hole Research Center, 00:26:24.05 and the Institute for Amazon Environmental Research, 00:26:26.13 and the University of Sao Paulo, 00:26:28.29 on whose work this talk is based. 00:26:31.03 Our funding comes from NSF, NASA, 00:26:33.08 Gordon & Betty Moore Foundation, 00:26:35.12 the Research Foundation for the State of Sao Paulo, 00:26:37.22 the Brazil national funding agency CNPq, 00:26:40.20 and the US Fulbright program. 00:26:42.22 Thank you.