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.