Deforestation and the Future of the Amazon

Part 1: Consequences of Amazon Deforestation

00:00:07.15 I'm Christopher Neill.
00:00:09.01 I'm a senior scientist at the Woods Hole Research Center
00:00:11.26 in Woods Hole, Massachusetts,
00:00:13.18 and I've been working on the Amazon
00:00:16.03 since the early 1990s.
00:00:18.02 The Amazon is the world's largest tropical rainforest.
00:00:20.20 It covers an enormous area
00:00:23.14 of nearly 8 million square kilometers
00:00:25.12 in northern South America.
00:00:27.13 That's about seven-eighths the size
00:00:29.25 of the entire lower 48 states in the US.
00:00:33.00 It's a globally important ecosystem.
00:00:36.01 It's also one that's changing extremely rapid today,
00:00:38.28 largely because of human activities.
00:00:41.05 In this talk, I'll try to explain
00:00:43.14 why the Amazon is valuable,
00:00:46.10 how it's changing,
00:00:47.25 what's driving those changes,
00:00:49.23 and where those changes will likely drive the Amazon
00:00:53.14 in the future.
00:00:55.19 The Amazon forest occupies nine countries.
00:00:58.18 It's an enormous,
00:01:00.24 but still largely intact, forested area,
00:01:03.27 but it's being changed by human activities,
00:01:07.07 largely driven by deforestation
00:01:10.17 and clearing for agriculture.
00:01:12.23 I want to start by talking about what's at stake in this forest
00:01:16.06 -- what do we lose when forest is converted to other uses?
00:01:19.27 And how might we use what we know about the Amazon
00:01:26.07 to guide management and conservation of Amazon forest
00:01:28.20 into the future.
00:01:30.21 The Amazon contains an enormous storehouse of biodiversity.
00:01:34.14 Just an as example, it has maybe 1300 species of birds,
00:01:38.21 1800 species of fish
00:01:41.02 -- about 40% of those fish probably are not yet described --
00:01:45.16 it has enormous tree diversity,
00:01:48.10 probably 12000 or more species of trees alone,
00:01:51.14 and there are more species in one hectare of Amazon forest
00:01:55.01 than there are in all of Europe.
00:01:57.04 And it has 3000 species of plants.
00:02:01.06 So, there's just a...
00:02:03.09 it's evolved under a very stable, moist climate,
00:02:07.18 warm climate regime for hundreds of thousands of years,
00:02:11.04 which has led to this enormous diversity.
00:02:13.15 It also contains globally important stores of carbon.
00:02:17.28 The atmosphere, today, on Earth,
00:02:20.03 contains about 850 billion metric tons of carbon.
00:02:24.13 Humans, by burning fossil fuels,
00:02:27.09 have contributed about 255 billion metric tonnes.
00:02:30.24 Tropic forests today, on Earth,
00:02:33.29 contain 270 billion tonnes of carbon
00:02:36.00 -- that's more than humans have put into the atmosphere to date.
00:02:39.08 We need to keep that carbon out of the atmosphere
00:02:42.03 to avoid even more dramatic climate changes on Earth,
00:02:45.21 and the Amazon forest, alone,
00:02:48.19 contains about a third of that tropical forest carbon,
00:02:51.10 maybe about 86 billion metric tonnes of carbon.
00:02:55.00 So, thinking about ways of conserving the forest,
00:02:57.23 keeping that carbon in trees and out of the atmosphere,
00:03:00.28 is extremely important.
00:03:03.16 The Amazon is such a large forest that it
00:03:08.03 also regulates the regional South American
00:03:11.17 and even global climate.
00:03:13.10 The Amazon river itself is
00:03:16.20 larger than the next six largest rivers of Earth combined.
00:03:19.18 It contains 20% of the Earth's fresh water.
00:03:22.17 And roughly 50% of the rain
00:03:25.18 that gets delivered onto the Amazon forest
00:03:28.02 is recycled water that has been transpired
00:03:30.27 through the very large cover of trees
00:03:36.05 in the Amazon rainforest.
00:03:38.02 The Amazon is also important because it
00:03:42.04 provides services for people
00:03:43.26 -- people live and use the Amazon.
00:03:45.19 There are at least 220 ethnic groups
00:03:48.17 that live in the Amazon.
00:03:50.16 There are 170 languages that are spoken in the Amazon.
00:03:54.22 And while these 220 groups are probably...
00:03:57.17 are way less than the probably
00:04:00.04 1000 or so groups that existed before European settlement,
00:04:03.15 they're extremely important, diverse,
00:04:06.08 and an absolutely important component of the Amazon forest.
00:04:09.15 And, like this young girl with a Pintado catfish on the screen,
00:04:14.09 these forests are used by people in a lot of ways,
00:04:18.03 for food and sustenance.
00:04:20.11 But today the Amazon is at a crossroads.
00:04:24.02 That crossroads is caused by the intersection of several forces.
00:04:29.23 The driving, overall force is deforestation,
00:04:32.27 the clearing of forest for agriculture.
00:04:35.22 That leads to fragmentation.
00:04:38.20 The Amazon basin has been wet and green for a very long time,
00:04:44.04 it has not evolved with fire,
00:04:46.11 but the intersection of deforestation and fragmentation
00:04:50.06 and climate
00:04:52.11 leads to increased incidence of fire in the Amazon,
00:04:54.08 and I want to talk about why that's happening
00:04:56.08 and its consequences.
00:04:58.09 And the Amazon has been a site of the expansion of agriculture.
00:05:01.03 It's one of the last remaining areas of the world
00:05:04.15 with adequate rainfall,
00:05:06.09 where agriculture can expand,
00:05:08.22 and agriculture has been expanding
00:05:10.18 and it will continue to expand,
00:05:13.04 and it's important to incorporate
00:05:15.16 our understanding of Amazon ecology
00:05:17.22 into the ways that agriculture might be expanded
00:05:21.22 in tropical regions in the future.
00:05:23.17 And last, the global climate is changing,
00:05:25.27 and that's going to influence the Amazon
00:05:28.20 and it's going to interact with all these other factors.
00:05:30.20 Alright, let's take a look at these.
00:05:32.19 The Amazon has had, historically,
00:05:35.23 from the 1980s through the early 2000s,
00:05:39.16 very high deforestation rates.
00:05:41.23 Now, I live in Massachusetts and I like to show this graph
00:05:45.21 because it shows that through the early 2000s
00:05:48.03 the rate of clearing in the Brazilian portion of the Amazon alone,
00:05:51.28 which is the vast majority of the area and the deforestation,
00:05:56.15 was something on the order of 20000 square kilometers a year.
00:05:59.27 The area of the state of Massachusetts is 22000, roughly, square kilometers.
00:06:04.24 So, we were losing, during this period, every single year,
00:06:07.28 a forest the size of Massachusetts.
00:06:11.14 Most of that clearing during that period was for pasture.
00:06:14.28 Pasturing was a way of people claiming land
00:06:18.21 and using it for agriculture
00:06:21.23 in a not very intensive way,
00:06:25.01 and raising beef over a lot of that area.
00:06:28.24 That was the primary use of forested...
00:06:32.02 cleared forest land through the early 2000s.
00:06:35.15 That's changing and I'll talk about that
00:06:38.11 when I talk about agricultural expansion.
00:06:40.08 Deforestation leads to fragmentation.
00:06:43.07 This picture, here,
00:06:45.25 is an image that shows clearing for agriculture
00:06:51.00 on one side of the screen
00:06:53.00 and a forested reserve on the other.
00:06:55.14 So, it makes two points.
00:06:57.10 One is that when you clear forest,
00:06:59.11 you create lots of edges and lots of patches.
00:07:01.19 those have important ecological consequences.
00:07:04.05 It also shows that when you
00:07:07.26 draw boundaries for protected areas,
00:07:09.29 that that's a very effective mechanism
00:07:12.10 for keeping forests standing.
00:07:14.26 What does fragmentation do?
00:07:16.22 It does a lot things,
00:07:19.01 but one of the most important is
00:07:21.24 it accelerates extinction in fragmented forest.
00:07:26.24 This is just a plot of the proportion of species
00:07:30.11 that go extinct versus the area of fragments.
00:07:34.00 It's from a marvelous study done over decades, now, in Manaus,
00:07:37.23 called the Biological Dynamics of Forest Fragments Projects,
00:07:41.05 and it shows clearly that extinction rates
00:07:45.00 are low in large fragments,
00:07:46.28 over to the right of this graph,
00:07:48.27 and high in small fragments.
00:07:50.22 So, you isolate 1 hectare of forest,
00:07:52.23 you lose a third or more
00:07:57.28 of the total number of species in that fragment
00:08:00.03 over several decades
00:08:04.14 of experimental study shown by this work.
00:08:07.16 So, the other new phenomenon in the Amazon,
00:08:11.28 from my perspective, is fire.
00:08:14.02 Amazon forest is moist for much of the year,
00:08:18.07 it's green for most of the year
00:08:20.19 -- or, all of the year over most of the forest, I should say --
00:08:26.27 and for that reason it's not very flammable.
00:08:28.22 Right?
00:08:30.03 Most of the Amazon forest,
00:08:32.05 aside from some very small edges near that Brazilian cerrado,
00:08:34.06 or savannah,
00:08:36.13 did not evolve with fire as part of its ecological history.
00:08:40.10 So, you have this enormous area of evergreen forest
00:08:43.20 that is very fire-resistant.
00:08:45.23 Now, why is that?
00:08:47.18 That's because tropical rainforests of the Amazon,
00:08:51.03 over much of the Amazon area,
00:08:53.14 have very deep roots.
00:08:55.02 The soils are very, very deep.
00:08:57.08 They store water over many meters,
00:08:59.24 10 or 20 meters of soil profile.
00:09:02.26 So, it was discovered by Dan Nepstad and his colleagues,
00:09:07.23 in the early 1990s,
00:09:09.24 that these roots penetrated to 3, 5, 8, 10,
00:09:13.21 even 15 meters.
00:09:15.16 They're allowing those trees to access water.
00:09:18.11 So, those trees can sustain
00:09:20.29 a green forest canopy
00:09:23.00 during extremely dry periods of the year,
00:09:26.10 and much of the Amazon is dry for many months
00:09:28.15 -- almost no rain -- but the forest stays green.
00:09:32.04 This graph just shows a plot of forest root profile
00:09:36.03 versus a managed pasture root profile.
00:09:39.03 When you replace the forest with the pasture,
00:09:41.13 you decrease the number of roots going down
00:09:43.25 and the pasture ecosystem turns brown in the dry season.
00:09:48.10 When it turns brown, it becomes flammable.
00:09:50.00 So, one of the things that happens,
00:09:52.21 and I'm going to walk you through
00:09:56.02 this slightly complex graph,
00:09:57.23 is that, in the dry season,
00:10:00.14 when you have pasture,
00:10:03.22 the leaf area and the brownness increases,
00:10:06.07 so the leaf area goes down.
00:10:07.28 So, if you look here and here,
00:10:10.23 this leaf area, actually, in pasture, declines, right?
00:10:13.18 And the forest leaf area actually stays very constant,
00:10:16.25 so the forest stays green and the pasture turns brown.
00:10:20.00 What that does is here...
00:10:22.22 whereas in the forest, here,
00:10:25.00 the window in which the ecosystem is dry enough to burn
00:10:28.29 is minuscule, right?
00:10:30.18 And the chance that there is an ignition source
00:10:33.05 coupled with when it's dry enough
00:10:35.12 almost never happens.
00:10:36.22 But that window is dramatically increased in pasture.
00:10:40.18 So, you've put, now, a very flammable ecosystem
00:10:43.22 right adjacent to a forest ecosystem
00:10:46.09 that never really burned much,
00:10:49.11 and what happens is that fires
00:10:53.04 that start in pastures, either intentionally or accidentally,
00:10:55.25 now sort of move into the forest.
00:10:58.20 They creep into the understory,
00:11:01.00 they don't do a lot of damage the first burn,
00:11:03.04 but they set the forest up for future change.
00:11:06.27 So, there's a lot of this fire, now, this black area.
00:11:09.18 In this paper by Mark Cochrane,
00:11:12.02 he clearly showed that there's a lot of fire
00:11:14.21 sort of creeping in from the edges of pasture,
00:11:16.19 a consequence of fragmentation.
00:11:20.22 Another new phenomenon
00:11:23.02 that dramatically expanded in the 2000s
00:11:26.12 was the dramatic expansion
00:11:33.06 of crop agriculture into the Amazon.
00:11:35.04 So, remember,
00:11:37.18 previous agriculture was largely cattle ranching
00:11:39.18 -- growing of grass,
00:11:42.09 raising of cattle at fairly low densities.
00:11:43.26 Now, today, there's been a
00:11:48.05 dramatic expansion of cropping in the Amazon.
00:11:50.02 Now, 30-40 years ago,
00:11:52.14 the conventional wisdom was,
00:11:55.29 well, you can't grow crops in the Amazon.
00:11:57.18 The soils are too acid,
00:12:00.09 the aluminum is toxic to the plants,
00:12:02.21 the phosphorus fertility is very, very low.
00:12:04.26 Well, those barriers can be overcome
00:12:08.12 with modern farming methods
00:12:10.11 -- fertilization, liming, pesticides to control tropical pests.
00:12:15.05 So, cropland has just expanded very dramatically in the Amazon
00:12:19.10 since the mid-2000s.
00:12:21.08 The principal crop has been soybeans,
00:12:23.09 but, more and more,
00:12:25.11 soybeans have been crown
00:12:29.05 together with a second crop of corn or cotton,
00:12:31.10 and this is moving...
00:12:33.07 has moved very rapidly into the Amazon
00:12:34.29 from the southern end of the Amazon,
00:12:37.03 where there's a seasonal dry season
00:12:39.00 that works to control pests and diseases
00:12:41.16 fairly effectively.
00:12:43.26 This has been a fruit of a green revolution
00:12:46.19 that's developed crop varieties
00:12:49.04 that can grow in hot tropical climates,
00:12:52.06 like the soybean varieties that can adapt to tropical day length
00:12:55.05 and the ability to use large amounts of fertilizer and pesticides.
00:12:58.07 Soybeans is interesting
00:13:01.22 because soybeans is now a global commodity,
00:13:04.02 so, where I work in the Amazon,
00:13:05.25 you see trucks like this lined up on dirt roads
00:13:08.22 more than 1000 miles from the port.
00:13:11.04 They get loaded with soybeans from the Amazon,
00:13:13.22 they travel on dirt roads,
00:13:15.21 and then reach paved roads,
00:13:17.14 and so there's this global transport network
00:13:19.23 that takes soybeans from the central Amazon,
00:13:22.25 you know... agricultural region,
00:13:26.13 all the way to other parts of the world.
00:13:28.12 And what's interesting is that, since roughly 2000,
00:13:32.24 exports to China, here,
00:13:34.28 this blue slab on this graph,
00:13:38.08 have increased dramatically,
00:13:40.23 and China now dominates the Amazon soybean export market.
00:13:45.07 So, we've moved from a world in which
00:13:49.00 soybeans were mostly grown outside the Amazon
00:13:50.28 to a point where Brazil is now
00:13:53.07 the world's largest soybean exporter,
00:13:55.02 and China has been a major destination
00:13:58.00 for Amazon soybeans in very recent years.
00:14:03.09 The other change that's occurring in the Amazon is climate.
00:14:06.21 This map shows, in red,
00:14:09.27 the areas where there are significant numbers of dry months.
00:14:12.20 So, if you look here,
00:14:14.26 in the southern Amazon region...
00:14:17.02 and this just shows the Brazil...
00:14:20.27 the place, here, where I'm pointing is
00:14:25.07 pretty much the area of very dramatic agricultural expansion,
00:14:28.01 there are 4-5 dry months.
00:14:31.10 What's important, now, is those dry months
00:14:33.25 are setting the Amazon up for
00:14:36.07 increased interactions between fire and drought and agriculture,
00:14:40.08 over very large areas.
00:14:42.06 I want to talk about drought,
00:14:44.12 because it's a very hot topic in the Amazon right now,
00:14:47.09 and it's important to understand
00:14:50.03 what the Amazon might look like
00:14:53.00 if droughts increase, and El Niño’s
00:14:55.19 -- strong El Niño’s, especially --
00:14:58.01 bring very dry conditions to the Amazon.
00:14:59.22 This is a picture of an experiment that was done
00:15:02.09 in the central Amazon, near the city of Santarém,
00:15:05.25 and it was called the Dry Forest,
00:15:09.11 or Seca Floresta, Experiment.
00:15:11.08 And this involved placing
00:15:16.08 about 7000 plastic panels in the forest understory
00:15:18.26 to exclude rain,
00:15:21.17 so, in this experiment, rain was excluded.
00:15:23.21 About 60% of the rainfall that fell
00:15:27.25 in the rainy season on this forest was intercepted
00:15:29.21 and moved away,
00:15:31.20 and they studied, over several years,
00:15:33.17 the responses of the trees.
00:15:35.10 And it was very interesting
00:15:37.11 and I'll just highlight one of the results.
00:15:39.10 Drought induced mortality of large trees,
00:15:41.27 and that mortality didn't start in the first year,
00:15:45.05 it wasn't dramatic in the second year,
00:15:48.05 but after three years of induced drought
00:15:51.26 there was a very dramatic increase in tree mortality.
00:15:56.06 And this, really, is an interesting thing,
00:16:01.07 because fire, when it moves through the understory,
00:16:03.06 tends to kill small trees.
00:16:04.24 Drought tends to kill the big trees
00:16:06.14 and it's the big trees that have all the carbon,
00:16:08.17 and it's the big trees
00:16:11.02 that provide the microclimate and other conditions
00:16:13.13 that sort of maintain the forest.
00:16:15.23 So, there's a very big
00:16:20.01 potential impact of increased drought
00:16:22.18 when they come, sort of, year after year after year.
00:16:24.29 The other effect of drought
00:16:27.20 is that it dramatically increases the potential for fire in the forest
00:16:31.28 and fragmented landscape.
00:16:33.18 So, here's a plot of years on the bottom
00:16:36.25 with the years, here,
00:16:39.27 of the water deficits, right?
00:16:43.29 So, you have... these are very dry years in these years, here,
00:16:50.22 where you've got this low water potential.
00:16:52.13 And in the same years where you have dry conditions,
00:16:54.15 this bar graph here is the area of Amazon that was burned.
00:16:58.07 So, when you have dry conditions,
00:17:00.26 like over here in 2010 or 2007,
00:17:03.18 you have a much larger area of Amazon forest that's burned,
00:17:08.25 in the larger Amazon forest region.
00:17:11.19 So, you set up that interaction:
00:17:14.15 drought plus fire means more forest degradation.
00:17:18.20 The worry is that this phenomenon,
00:17:22.11 this interaction,
00:17:24.18 may set up a tipping point where you actually
00:17:27.05 induce Amazon forest to become savannah.
00:17:29.08 You change the vegetation
00:17:31.01 and induce more grass,
00:17:32.19 which begets more fire,
00:17:34.21 and you actually change, over a significant fraction,
00:17:37.09 20-30% of the Amazon...
00:17:39.29 savannah-like conditions in a new global climate,
00:17:43.17 with longer dry seasons
00:17:46.21 and more potential occurrence of multi-year droughts.
00:17:50.03 So, what is the Amazon's future?
00:17:54.25 The good thing is the Amazon is still largely forest.
00:17:58.16 This is a map, again,
00:18:01.05 of the Amazon over nine countries,
00:18:03.27 and what you see in orange, at the bottom,
00:18:07.22 is agriculture expanding;
00:18:10.01 the purple is pasture, which has largely been focused
00:18:12.12 and occurring in the southern and eastern Amazon;
00:18:15.10 but large areas of the basin are still forested.
00:18:18.11 The dark green areas are forest reserves.
00:18:21.16 Those reserve areas have grown
00:18:24.26 and, in fact, Brazil has expanded
00:18:28.13 its protected area network
00:18:30.19 very significantly since the mid-2000s.
00:18:33.20 The other bright spot is that, since 2000,
00:18:38.01 deforestation rates in the Brazilian portion of the basin,
00:18:40.08 which is where the major deforestation was occurring,
00:18:42.27 have dropped dramatically since that period of high deforestation
00:18:47.24 that I talked about, through the early 2000s.
00:18:51.02 In fact, Brazil has gone from having deforestation rates of,
00:18:55.25 say, 20000 square kilometers a year
00:18:58.07 to down in the range of 5000 square kilometers,
00:19:01.08 where it's almost a 75% drop in deforestation.
00:19:05.02 And that occurred for a number of reasons.
00:19:07.08 One is better policing of illegal deforestation.
00:19:12.17 Another is expansion of protected areas.
00:19:16.11 Another region, which is very important
00:19:18.26 now that Brazil is selling soybeans and corn
00:19:22.03 into the international market,
00:19:24.11 is those markets demand
00:19:27.13 that those agricultural products
00:19:30.19 be produced in a more sustainable way.
00:19:34.23 And this was a protest in the central Amazon
00:19:37.04 carried out by Greenpeace,
00:19:39.14 that triggered a series of events
00:19:42.01 that led to a moratorium on the growing and selling of soybeans
00:19:45.14 into international markets,
00:19:47.12 from areas that were cleared after 2006.
00:19:51.20 And what this did is it forced agriculture
00:19:57.08 to occupy lands that were already cleared,
00:20:00.04 rather than the clearing of new land.
00:20:03.16 And I think, if we look forward to the future of the Amazon,
00:20:07.04 an absolutely major, important question
00:20:11.07 is how Brazil and other Amazon countries
00:20:17.17 manage agriculture in ways
00:20:19.29 that allow that agriculture to intensify,
00:20:22.04 to produce more on less land,
00:20:25.19 and act as a reducer of the need to clear new land,
00:20:29.29 to put new land into production.
00:20:32.20 And there's very good evidence that this is already happening.
00:20:35.24 Here's a plot of soy production and beef production,
00:20:40.20 and, remember, the deforestation started dropping in 2006.
00:20:44.24 What it showed is that reducing deforestation
00:20:49.19 doesn't have to lead to a decline in commodity production,
00:20:52.08 either soy or beef.
00:20:54.05 The yields of soy have remained fairly constant.
00:20:56.26 The yields of beef
00:20:59.01 -- that is, the ability to grow cattle, rather than at 1 head/hectare,
00:21:03.29 at 2 or more heads/hectare --
00:21:07.21 have allowed more beef to be produced on less land.
00:21:09.20 So, beef production, even in the face of falling deforestation,
00:21:12.26 has been sustained without...
00:21:16.06 the beef production has been sustained
00:21:20.19 on a smaller total area of pasture.
00:21:24.05 I think this is part of the way
00:21:27.22 we need to think about managing agriculture,
00:21:29.25 which is the driver of most of the deforestation in the Amazon going forward.
00:21:35.15 So, that's an overview of the drivers
00:21:38.22 and the ecological forces
00:21:42.19 interacting and shaping the future of the Amazon
00:21:44.16 -- very, very large questions remain.
00:21:46.07 One of the ones that I'm most interested in,
00:21:48.18 and that I'm actively working on,
00:21:51.00 is, how can agriculture intensify
00:21:54.09 without increasing environmental impacts to air and water?
00:21:57.01 And what are these impacts?
00:21:58.12 Well, they're greenhouse gas emissions from agricultural fields,
00:22:00.24 they're emissions of methane from cattle production,
00:22:03.11 they're emissions of nitrous oxide from agriculture
00:22:06.00 when you apply large amounts of fertilizers,
00:22:08.18 which is required for growing, especially two crops,
00:22:13.16 in the Amazon.
00:22:14.28 So, those questions are, how can that be managed?
00:22:17.07 How can we precisely use fertilizer
00:22:20.28 and manage agriculture to reduce impacts?
00:22:23.26 Will we end up,
00:22:26.10 if we're using lots of fertilizer,
00:22:28.15 in these now largely agricultural landscapes,
00:22:30.11 will those fertilizers move from land into streams?
00:22:33.26 And result in the degradation of water quality,
00:22:37.05 like we see in many regions,
00:22:40.25 say, the Mississippi Basin or south Florida
00:22:43.20 or the East Coast, Chesapeake Bay, of the United States?
00:22:45.23 That's a really big question,
00:22:47.22 and this intensification is just now beginning,
00:22:50.07 in the long-term time sense.
00:22:52.17 So, we need to understand that and that's a very big question.
00:22:55.21 The other big question that I think is even more and important
00:22:59.06 and, in some ways, harder and more challenging to address,
00:23:02.11 but we can make a lot of progress,
00:23:05.11 is how much forest can be cleared
00:23:07.15 before we reduce rainfall over the remaining forest,
00:23:13.12 and hence sustain this evergreen forest
00:23:16.01 and prevent forest degradation?
00:23:18.22 And sustain the intensive agriculture
00:23:21.22 that we're now depending on to be a bulwark
00:23:24.11 against the need to clear new forest land?
00:23:27.11 If 50% of the rain is coming from evaporated water...
00:23:30.20 you evaporate much less water from cropland than forest,
00:23:34.15 so you absolutely have to maintain
00:23:39.15 a certain amount of that forest to generate the rainfall
00:23:42.25 that you're now counting on to sustain the forest
00:23:45.12 that you're trying to protect,
00:23:47.22 and to produce agriculture and crops
00:23:50.21 in a more intensive way.
00:23:52.12 That's a big unknown,
00:23:55.00 I think that's an absolutely critical area of future research and a big unknown.
00:23:58.02 We think that that number is more than half of the Amazon forest
00:24:04.07 -- we're approaching 25% of the total Amazon forest cleared --
00:24:08.16 so we're reaching a point where we may see
00:24:12.17 these irreversible effects.
00:24:14.18 But I think that it's both the worry and the hope, right?
00:24:17.08 We have to intensify agriculture in the Amazon
00:24:20.01 to be able to have agricultural production,
00:24:23.19 it's... agricultural crops are Brazil's number one export, for example,
00:24:28.16 but we also need that forest to sustain this system
00:24:31.21 that we're counting on as a way of protecting the climate.
00:24:38.18 So, that's an introduction to the Amazon,
00:24:43.08 why it's important,
00:24:45.07 how it's changing,
00:24:47.12 and how it might change in the future.
00:24:49.07 There's progress, a lot of progress has been made on reducing deforestation
00:24:51.25 in the last decade.
00:24:53.20 It's still a challenge to reduce deforestation to zero.
00:24:56.03 Brazil has pledged to reduce deforestation to zero by 2030.
00:25:01.08 That remains a real challenge, but I think now...
00:25:04.19 I wouldn't have said this 15 years ago,
00:25:06.07 but it remains a real possibility.
00:25:10.12 I'd like to acknowledge my collaborators in this work
00:25:13.25 at the Marine Biological Lab
00:25:16.12 at the Woods Hole Research Center.
00:25:18.17 Also, our wonderful NGO collaborators
00:25:20.27 at the Institute for Amazon Environmental Research,
00:25:23.04 based in Brasilia.
00:25:25.05 The University of São Paulo, the University of Potsdam,
00:25:27.19 Max Planck Institute for Biogeochemistry,
00:25:30.04 Brown University,
00:25:32.11 and also to Grupo Amaggi for giving us permission
00:25:35.19 to work on a giant soybean farm in the state of Mato Grosso
00:25:38.17 in Brazil.
00:25:40.05 This work that I've talked about has been made possible
00:25:42.23 by a wide variety of funding sources,
00:25:44.25 including from NSF, NASA,
00:25:47.10 Gordon & Betty Moore Foundation,
00:25:49.16 the Research Foundation for the State of São Paulo,
00:25:51.26 and the Brazilian national science agency, CNPq.

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.

Videos in this Talk

Part 1: Consequences of Amazon Deforestation
Audience:
- Student
- Researcher
- Educators
- Educators of H. School / Intro Undergrad
- Educators of Adv. Undergrad / Grad
Part 2: Amazon Ecosystem Dynamics at the Agro-industrial Frontier
Audience:
- Student
- Researcher
- Educators
- Educators of H. School / Intro Undergrad
- Educators of Adv. Undergrad / Grad

Speaker: Christopher Neill

Total Duration: 0:53:13

Recorded: July 2016

Educator Resources for this Talk

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Talk Overview

The Amazon rainforest is the largest tropical forest on earth. It absorbs vast amounts of CO_², and is large enough to impact local and global weather. Dr. Christopher Neill describes the dramatic changes in the Amazon ecosystem that have resulted from deforestation for agriculture. Forest fragmentation has caused more species extinction, more fires and increased concern about drought. Neill ends his talk on a brighter note, pointing out that government intervention and modified agricultural practices have decreased Amazon deforestation by 75% in the past 10 years.

In his second lecture, Neill and his group go to the Tanguro Ranch in the southeastern Amazon of Brazil. The farm is at the interface between agricultural land and forest and provides a perfect area to study how expansion and intensification of cropping practices influence croplands watersheds, and the surrounding forest. Neill’s research explores how to prevent further deforestation by intensifying agriculture on already cleared areas, and how to do this without increasing the environmental impacts to weather, air and water.

Speaker Bio

Christopher Neill

Dr. Christopher Neill is a Senior Scientist at the Woods Hole Research Center (WHRC) in Falmouth, MA. Before joining the WHRC, Neill spent 4 years as Director of the Ecosystems Center at the Marine Biological Laboratory, where he was a scientist from 1996-2016 and retains a position as a Fellow. Neill investigates how changes in… Continue Reading