Exploring Land Use and Nutrient Availability in Brazil's Dry Tropics

In this episode of Food, Farms & Forests, Dr. Natalie Clay, an associate professor in the entomology and plant pathology department, talks about her research on decomposition in Brazil's dry tropical forests supported by the Fulbright Scholar Program, the world's largest and most diverse international education exchange program.

Clay’s research investigates how changes in land use affect nutrient cycling, soil health, and decomposition rates, revealing unexpected results about sodium levels in farmed and forested lands.

Clay says this research and its results are applicable in other parts of the world because dryland ecosystems make up over a third of Earth's surface.

"It's ultimately tied to carbon cycling at a very big global scale," Clay said. "Especially in these dryland ecosystems, even small changes in the rates of decomposition can have big effects on atmospheric carbon levels. So understanding that from a carbon cycling perspective is important."

Related links:

Arkansas Agricultural Experiment Station

Arkansas Cooperative Extension Service 

U of A System Division of Agriculture

Bumpers College of Agricultural, Food & Life Science

Transcript

[00:00] Intro/Outro

Welcome to the Arkansas Food, Farms and Forests Podcast. The podcast bringing you the latest on food, fiber and forestry research from the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture.

[00:17] Jenifer: 

Welcome to Food, Farms and Forests. I'm Jennifer Fouche. Today, we are learning about the impacts of land use and nutrient availability on decomposition in the Brazilian dry tropics. To talk to us about this research. Is Dr. Natalie Clay, an associate professor in the entomology and plant pathology department and a researcher for the experiment station. Dr. Clay, thank you so much for being here with us.
 
 

[00:41] Natalie: 

Thank you so much for having me.

[00:43] Jenifer: 

And this research was part of the Fulbright Program, the world's largest and most diverse international education exchange program. Congratulations. That's a very prestigious opportunity.

[00:55] Natalie: 

Thank you so much. Yeah, it was very exciting.

[00:57] Jenifer: 

Tell me about that. What was that like? The application process and, you know, the research topic. And then getting accepted and just this whole experience in itself.

[01:08] Natalie: 

The Fulbright program, I, you know, heard about it, but it kind of seemed like this thing that was a little like, oh, this is going to be a long shot, right? It was my first time applying to the program. And when you read about it, it's like, oh, expect to apply many, many times, for this. And I got very lucky. This was my first time applying and I got it. The application process was a little bit different than many of your other just research style grants, because you had to talk about not only what your research would be and making sure it's scientifically sound, but also how you think you're going to succeed living in another country for an extended period of time. So, a lot of the application was not about research, but how are you going to deal with, you know, differences in culture, communication among people when there might be misunderstandings or, you know, challenges living in another country. So, having very different styles of answers and thought processes. Yeah, what will I do in those kinds of situations? So, a very different type of application, but really fun in that way too.

[02:27] Jenifer: 

And what was that like? I know you put it on paper for the application, but then once you got there, what were those four months like in terms of the research and then the cultural experience as well?

[02:38] Natalie: 

So, for the research, as you mentioned, I was looking at how land use change impacts decomposition processes. And so, I was in northeastern Brazil on the coast. So Atlantic Forest area, but the research was more inland in dryland area. And so this part of the country has seasonally dry tropical forest and it houses a significant amount of people, and there is very little of the pristine dry tropical forest left. A lot of it has been converted into agriculture to help sustain a growing population or has been modified, to kind of be multi-use forests for livestock and retaining a little bit of the natural landscape on the habitat. 

So, my research was to examine how when those changes happen, we see changes in nutrients potentially and what may or may not be enough for the organisms that are there versus too little. And then how that impacts decomposition. 

So, decomposition is the breakdown of dead organic matter into molecules and chemicals that organisms need to survive and reproduce, and that ultimately gets recycled back and helps fuel plants grow. And so, the rate at which things break down controls the rate at which nutrients move through that system, and also carbon cycling. 

So, the organisms that are breaking it down are respiring. So fast rates can increase atmospheric carbon and when it's slow it can store it. But it also means then some less nutrient cycling. So, it's a balance of these different processes. 

But my research was just focusing in on how this land use change impacts the rate at which decomposition happens and how it changes with nutrient availability.
 
 

[04:43] Jenifer: 

And what did you find?

[04:46] Natalie: 

So, we actually found results that were not what we were totally expecting. 

So, usually, when you're far away from a coast, nutrients like salts are not widely available. It's one of the reasons we often provide livestock with salt licks. So, usually, when you're away from a coastline organism, start seeking out salt and salt is limited, but in dryland ecosystems, you can get increases in salts because of high rates of evaporation. and definitely with land use change, as we convert more forest ecosystems into agricultural systems, that often comes with things like fertilizer application and irrigation practices that can then lead to increases in salts. 

So, salinization is a current and emerging issue in northeastern Brazil. And so, we were expecting to see, not enough salt in the forest ecosystems there. So, by adding it we would have expected decomposition rates to increase. But in the farms, we would have expected there to be plenty of salt and so little or maybe even decrease decomp when salt becomes toxic, basically, in those environments. 

And we found no difference between the two environments. And sodium in the soils were similar. So, we think a little bit of what might be happening is the forests there were being used not just as pristine forest environments, but also as places for livestock to forage. And livestock can increase salinization through urine and excreta. And so, we think that the land use of the forests with also providing a foraging area for livestock might have led to similar amounts of sodium in both the forests and the fields there.

[06:53] Jenifer: 

So, your results you found really not that much of a difference in the sodium levels. Is that good? Is that bad? As a scientist, you want the land, you want this area to be prime for organisms there. And what do those results mean to you as a scientist and for the forests?

[07:15] Natalie: 

Salt. When it gets too much, it can be a bad thing because it can become toxic to the organisms that break down dead organic matter. It can become too stressful. If there's too much salt, they can't get rid of it fast enough. And so, they're not doing things like out foraging, breaking down dead organic matter, eating. They're just trying to survive. And so that can lead to decreases in ecosystem function. 

We had controls, where we compared decomposition, where we added salts in those …. both the forests and the farm to those controls that didn't receive any salts. And while there was some difference in decomposition between the farms and the forest, there was also no difference between controls and the sodium addition plots. 

And so that means that sodium is probably at an okay level. It might be just getting to the point where it's slightly starting to be stressful, but it also means that the forest there is not functioning like a forest that was pristine in the area would. So, it should have shown signs of increased decomposition. So, sodium limitation and in that case that it's a good thing because it leads to stored carbon in those systems. whereas we didn't see that. And so, you're probably having faster rates of turnover from salt deposition from livestock feeding in those areas.

[08:53] Jenifer: 

What location specifically like city or state were you guys in?

[08:57] Natalie: 

We were in Paraiba state in northeastern Brazil. So, it was over a pretty big area. We had, 13 paired farm and forest sites, so 26 sites total. These were small family-owned farms, and crops were mainly beans, corn, and cactus. And then they owned the forest next to it. So, it was a pretty, pretty large area in the drylands in northeast Brazil.

[09:26] Jenifer: 

So local farmers had paired up with other researchers so that you guys could come in and do this research on their land?

[09:34] Natalie: 

Yes. So, my collaborators were integral in this process. So, they had already been working with these landowners on similar questions or other scientific questions in the area. And we were able to go out and talk to the landowners and ask if they'd be willing to let us use their properties for this project as well. And they were wonderful and or absolutely happy to have us there. And we were happy to share the results with them as we got it, and as we continue to get these results.

[10:12] Jenifer: 

When you share these results with landowners what was their response? What was their feedback? And is there a solution? Was there a recommendation at the end after your findings of what can we do to control these salt levels or minimize them?

[10:32] Natalie: 

So, we are still getting the results. This was just part one of of what we need to look at to really better understand the system. So, we found a lot of variability at each site. So, there was although there were some general patterns, a lot of what was going on was site specific. So, our next goal is to look at landscape variables and other variables associated with each farm, so that we can hopefully get a better idea about what was driving those patterns. And then we might be able to make some recommendations.

[11:11] Jenifer: 

Okay. Yeah. Because four months is really not a lot for all of the research and 26 sites you were looking at.

[11:18] Natalie: 

And we just got back in May. So, I'm still working up these results for sure.

[11:23] Jenifer: 

And with these results, you're looking at land that has been impacted by livestock or agriculture. You traveled to Brazil very different than maybe Arkansas or maybe very similar. How, then, do you take these results you found there and bring it here to the Arkansas region, or even the U.S, or other parts of the world, even. What can we take from what was learned there on those 26 farms specifically to learn about how do we manage forests and agriculture and livestock in other parts of the world?

[11:55] Natalie: 

That's a fantastic question. The first part, dryland ecosystems make up a large portion over a third of Earth's surface. And so, the results are certainly applicable to other dryland ecosystems. 

But more so, I think the results are generalizable because land use is occurring widespread globally in order to support a growing human population. And even in agriculture, our two biggest land uses are forests and agriculture. So, half of the agricultural lands are for livestock and hay production. And so, we see a lot of the same land uses. Then northeastern Brazil, also here in Arkansas. And so, it would be a great next step to see if we see the same kinds of patterns that we saw in northeastern Brazil happening here in Arkansas across a land use gradient as well.

[12:56] Jenifer: 

And what is the big why? What you guys are doing as scientists is very specific, looking at the soil, looking at the sodium composition. But there's a bigger picture that this contributes to. Can you explain a little bit more about the big picture that this research is connected to?

[13:15] Natalie: 

It's ultimately tied to carbon cycling at a very big global scale. So, especially in these dry land ecosystems, even small changes in the rates of decomposition can have big effects on atmospheric carbon levels. So, understanding that from a carbon cycling perspective is important. 

But in terms of, you know, land use management as well. So, these farm and forest habitats varied in the habitat sizes. They were all small farms, but the forests, some of them were very small remnants left and some of them very big. So, some of the questions we hope to answer with this, and I haven't been able to dive into these data yet - but part of the question we want to answer is, does having a larger forest closer to your farm help kind of buffer some of the effects that you might get with land use change? So, do we see higher amounts of soil, organic carbon in our farms if you've got a forest nearby, for instance. 

And so, we can then if we can answer those questions, we can have a better idea about whether or not we can tell landowners that it might be worth it to keep your forests and not convert all of them into agricultural purposes. 

But I still have to dive into those results. But I would imagine having a forest nearby has a lot of benefits, both in terms of natural predators to those systems as well as nutrients, buffering effects of temperature. So, I anticipate we will find that keeping those forests, nearby is helpful.

[15:12] Jenifer: 

What were the biggest challenges you found down there while conducting this research?

[15:17] Natalie: 

I would say some of the biggest challenges were more to do with timing of working in a seasonally dry tropical forest. So, normally there's very little rain. But we wanted to capitalize on the growing season when decomposition would be active. And so, we set this up at the beginning of the rainy season. And here when it rains, it rains and it rains. And it comes down hard. And the soils - there is poor drainage. And so, you're in what is normally a desert-like habitat. And then all of a sudden, areas that were dry and sandy are now lakes. So, seeing things like cactus sticking out of a body of water where that once was, you know, very desert-like field before is kind of a bizarre sight. But it led to some challenges trying to navigate to our field sites, which were often in very rural places. Where the road was previously, a road was now covered in water and no longer accessible. So, I'd say some of the biggest challenges were just the normal things you get with fieldwork working in each different environment and due to the weather.

[16:35] Jenifer: 

Tell me a little bit about your collaborators. Who were they? And then just that partnership of working with other people overseas on such a big project like this for a long period of time?

[16:47] Natalie: 

Yes. So, my collaborator was Alexandre Vasconcelos at the Federal University of Paraiba in Brazil. And he is a termite and decomposition expert and expert in this region as well. And so, the research would absolutely not have been possible if not for building these working relationships. And the knowledge and, yeah, expertise that he and his lab bring to the field. 

It was incredible to get to work with him and learn from him about these habitats and the organisms that were in there. 

You know, with this whole experience, my personal observations were that everyone was incredibly welcoming and excited to collaborate. So, it was a really easy and natural, working relationship in this process. 

The experience of living in Brazil and working in Brazil was absolutely amazing. We were instantly welcomed. I took the whole family was there for four months. And my husband, Don Shepherd, also independently got a U.S. Fulbright Award. So, he's in biological sciences here at the University of Arkansas. So, he was doing his own research with his own collaborators at the same university. And so, we got to, yeah, live in Brazil, for four months, go into the university there every day. Our daughter, who is three at the time, was in school there learning Portuguese. And it was really just a wonderful and transformative experience, both in terms of our research but also in terms of our family and cultural perspective. 

So, I just think it was absolutely amazing. And the connections and collaborations we formed, I think are growing. Already we'v,  had I've had some continued exchange, cultural exchange. The PhD student who I am now co-advising with my collaborator Alexandre Vasconcelos. The PhD student, Amanda Costa, got her own fellowship to come to the U..S and continue some of her research at University of Arkansas in my lab. 

And so again, this this opportunity has led to a continued exchange of ideas and persons across what's normally very difficult boundaries. This has just been a fantastic experience.

[19:37] Jenifer: 

So, both you and your husband were down in Brazil on the Fulbright program at the same time?
 
 Natalie:
Yes. 

Jenifer:

That's amazing. 

[19:45] Natalie: 

It was absolutely fantastic.

[19:46] Jenifer: 

Wow. Yeah. Very impressive household you guys have here. 

[19:51] Natalie: 

Thank you. We're very lucky. It was it was wonderful.

[19:51] Jenifer: 

Well, Dr. Clay, thank you so much for your time and for sharing your expertise and this experience here with us.

[20:00] Natalie: 

Thank you so much for having me. It was a pleasure talking with you.

[20:03] Jenifer: 

That was Dr. Natalie Clay, an associate professor in the entomology and plant pathology department, talking to us about her recent research: Impacts of land use and nutrient availability on decomposition in the Brazilian dry tropics as part of the Fulbright Program. 
 
 Thanks for listening. I'm Jennifer Fouch. Don't forget to subscribe!

[20:24] Intro/Outro

The Arkansas Food, Farms and Forests podcast is produced by the Arkansas Agricultural Experiment Station, the research arm of the University of Arkansas System Division of Agriculture. Visit aaes.uada.edu for more information.