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  • Jacob Bourne

The Inga Tree Model ‘Standing Up to Violent Climate Change’

While reducing fossil fuel burning is the main focus for mitigating climate change, lowering carbon emissions from land-use sources gets significantly less attention. For centuries people in tropical regions have relied on slash-and-burn subsistence farming, otherwise known as shifting cultivation to grow food in acidic rainforest soils. However, with the rise of cash crops, population growth and soils depleted of nutrients, the practice has not held up in the modern era, leading to social and ecological devastation, including elevated carbon emissions.

Inga alley cropping
Mike Hands (left) and Abraham Martinez (right) in an Inga Alley in Los Flores, Honduras. Courtesy of the Inga Foundation

As rainforests serve as a significant carbon sink for the planet, their continued loss is another nail in the coffin for Earth’s habitability. Moreover, the exhausted soils combined with prolonged droughts under climate change have also severely threatened the food security of those who rely on subsistence agriculture, igniting a migration trend out of desperation.

Oxfam recently warned that over-reliance on tree-planting for carbon offsets could increase food prices, especially in the developing world. However, the claim assumes that reforestation and agriculture can’t work in tandem. Evidence of such potential lies in an agroforestry model championed by the Inga Foundation, founded by Mike Hands, who began research on alley cropping in Central America in the mid-1980s.

“We were able to test on the ground in a real environment, six different agroforestry systems and two bare soil systems for the prime production of basic grains — this is the fundamental problem of food security in Central America,” said Hands. “It’s the basic grains, maize and beans, that keep people alive.”

The research funded through the University of Cambridge ended in 2002, yielding the Inga alley cropping approach, which led to the creation of the Inga Foundation in 2007. The foundation’s Land for Life program uses the Inga Tree Model to address the vast deforestation on a range of mountainous areas in northern Honduras, where farmers have been practicing slash-and-burn for many generations. The model relies on the Inga tree’s nitrogen-fixing abilities, using cultivated rows of the tree with crops planted in between to replenish soils, shade out weeds and provide mulch. The system also yields lightweight, clean-burning firewood, which people use for cooking.

The method allows families to settle in one place and achieve food security with grain crops, and income with cash crops like turmeric and peppers. Farmers use a thinner planted version of Inga alley cropping to produce cacao. Meanwhile, the method results in reforested areas that also produce timber for local use.

According to Hands, the system is holding up to the stressors of climate change. For example, soil surface temperatures in degraded rainforest lands have become too hot to grow crops reliably. However, the mulch provided by the Inga alley cropping tends to keep the soils cool and moist.

“This is the only system that's standing up to violent climate change,” Hands said, explaining that during a severe six-month drought in 2019, the Inga system was able to produce maize even without any rainfall.

The Inga Tree Model is also helping restore habitat to degraded lands by attracting biodiversity to the areas around the plantings. Hands said he’s even witnessed springs appearing, providing clean drinking water. However, despite the solid promise of the agroforestry approach, securing funding to expand the program has been a struggle.

Following the Inga Foundation’s inception in 2007, a film was made about the project, which attracted a few wealthy donors enabling the hiring of Director of Operations Abraham Martinez, Chief Agronomist Luis Miranda and the eventual scaling up of the program to about 300 families. However, as more Honduran families have become interested in Inga alley cropping over the years, the foundation has had difficulty keeping up with demand.

Inga Foundation founder and Director of the Land for Life program Mike Hands spoke with The Carbonic about the power of the Inga tree, including its carbon sequestration potential and how it’s transforming the lives of families in Honduras. The following interview has been edited and condensed for clarity.

Q: What are the main barriers to expanding this agroforestry model?

A: Well, there’s funding. And you can only convince people of a revolutionary way of growing food by demonstrating — they have to see it and feel it.

They have to see why the trees are there. They have to see the organic material in the soil, they have to see the crops thriving in the system, and the absence of weeds, because the system controls weeds. So, we have to demonstrate. To that end, we bought a 12-hectare demonstration farm, of which about four hectares are an arboretum for rare and threatened species and seed sources from the future; the rest is for agroforestry systems. We've been training people, including people who have come in from other countries. And the system now, as a result of that, is being replicated in 15 other tropical countries, including three or four in Africa and one or two in Southeast Asia and Hawaii, but mainly in Central and South America. Some are using the Inga tree, but we’ve also identified other genera that will perform as analogs for them as Inga does for us. But Inga is turning out to be quite an unusual genus. It’s a huge genus with 350 species. We have experience with probably about 15 different species.

Some people have called it a magic tree, but I say no, it’s a useful tree. It has properties that we find useful managed in this way. It has a lot of tolerance for acidic soils. I’ve worked with botanists in Africa looking for an alternative there, and there are one or two promising species, but none of them perform there as Inga does for us.

Q: In discussions about climate change, there seems to be a tension between the need for reforestation and the demand for agricultural land. Is the Inga tree model evidence of a middle ground where you can have reforestation and agriculture?

A: Absolutely.

We’re told that the average holding in Honduras is about eight hectares. I’d say it’s somewhat smaller. Some have got a lot while others have considerably less. If you look at that land use, it’s been slashed and burned over many, many episodes. The soil is totally depleted; it supports only invasive grasses though it once supported a rainforest. So for every little plot where the farmer has to pour on expensive nitrogen fertilizer, you might get a crop, or you might not. And they’re struggling just to put food on the plate, and in some cases, they fail.

So you have eight hectares of wasteland that you can substitute with agroforest, only some of which are intensively managed for food. The only negative is the cost, which I say because the system sounds too good to be true. It resists climate change, it helps recreate springs for clean water, it takes people out of poverty, it reinvigorates the rural economy, it will re-green the landscape. It’s not cheap, it’s not quick, but it can turn around a family’s food security.

So, for us, we’re at year ten of the Land for Life project. It’s working out at roughly $2,000 per family to achieve this, but the costs will go down as soon as the system starts to go viral, neighbor to neighbor. So, this can be replicated — not at no cost but at very little cost. Because it's a groundbreaking, revolutionary system, and we have to convince not only local farmers by demonstration but also decision-makers, we were determined to get the whole system at whatever cost to prove a point. And I don't think that the next 350 families will cost anything like the first 350.

Q: With warming temperatures and changes in precipitation patterns due to climate change, how is this model holding up given negative impacts on forests and agricultural yields?

A: If you had previously asked about the use of Inga, I would have said that I don’t think it will withstand a very long dry season. With that said, what happened in 2019 was the worst drought ever recorded or known in Central America that was part of an El Nino event. We had between six and seven months of pure drought and searing temperatures. People were hoping to prune and plant in June of that year, but there was no way to touch the trees or plant. The Inga defoliated at about four months, but when it started to rain in September, it came back, and that was extraordinary. We hardly lost anything, and by December, the canopy was sufficiently dense that the families could prune and plant and grow crops. The system was working for them.

So that describes resilience to climate extremes. The model is a very powerful avoider of carbon emissions for the obvious reason that people stop slashing and burning and that can release hundreds of tons of CO2 in a single operation. But also the agroforestry system, the model as a whole is sequestering a lot of atmospheric carbon, particularly in the timber.

With eight hectares, assuming a family has a couple of hectares of alley cropping and the rest is a fruit tree, timber tree combination established at one hectare a year — the model assumes 40 families a year. By the end of last year, the avoided or sequestered CO2 was in the region of 300,000 tons of CO2. And that’s just the pilot project.

So it's a powerful weapon in taking away a significant carbon source. Slash-and-burn or land-use change is thought to be contributing between 20 and 25% of all human carbon inputs into the atmosphere, and you hardly hear it mentioned. Everybody talks about flying aircraft, transport, fossil fuel burning, but they don't talk about land-use change much, but it's 20 to 25% globally.

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Q: Is the Inga tree itself central to the success of this method?

A: Rainforest soils typically are very weathered and acidic. By definition, the rain forest has at least 2,000 millimeters of rain a year, no month less than 100 millimeters, and you have a net passage of water down through the soil profile, which is not the case in Sub-Saharan Africa, which is sort of semi-humid and has a rising and falling water level. So this is different; you have a net-constant movement of water, which takes away the nutrients, making the soil more and more acid, up to a point. The limit is somewhere around pH four, and that’s pretty darn acid. But Inga can tolerate that.

I’ve always pushed back at it being called a magic tree because it’s not; it’s a useful tree. Having done a lot of work with botanists in Africa especially, I have reluctantly concluded that there is something about Inga that I don’t fully understand. I think it’s about a symbiotic relationship between organisms and the roots — the fungi and the bacteria that are symbiotic with the Inga.

Q: With heightened concern about sustainability and the push for greener cities and urban agriculture, do you think the Inga tree model could be replicated in urban environments on a small scale?

A: Yes, in the humid tropics. You can put it in a backyard, and it will work. We worked with one NGO that was training in the system. They’re running an orphanage up in the highlands, and they’re essentially doing Inga Alley Cropping in their backyard.

There’s a quasi-government group that has an example of Inga Alley Cropping in the city of La Ceiba in the old Botanical Garden of La Ceiba, which is about two hectares of land with some lovely old trees. So there’s no reason why you shouldn’t do it.

Q: What else is essential to know about the Inga tree model and the Inga Foundation?

A: The model ticks 11 of the 17 United Nations Sustainable Development goals. I think it’s almost unique in doing that. The reason it’s possible to claim that is that we’re working with degraded ecosystems. So what we’re doing is remedial and regenerative; that’s why it’s possible to claim 11 of the SDGs without negatively impacting the remaining six.

Q: What’s the outlook for expanding this?

A: We are struggling. We are inundated with families wanting the system. Mainly as a result of seeing the system in 2016 and 2019 stand up to violent climate change with long ferocious droughts — I think that’s what has tipped it.

There’s nothing more fundamental than how you eat and how you achieve that. So there’s an initial reluctance on the part of farmers, which is entirely understandable. An adventurous handful will go for it in a given community, while others will sit on the fence for a bit. But now that’s changing because we’ve just persisted in what we’re doing, and we have a consistent message. So they trust us now, and it’s gathered momentum as one factor.

There’s one community with 50 families in a deforested basin in the mountains. When we went in in 2014, 18 of the 50 families signed up. There was some reluctance to what we were doing, as project after project had come in and promising things that had failed.

That has now changed. We now have all 50 families on board, and among them are 12 men who had initially decided to go to the States, migrating with the caravans. However, they decided not to go when they saw their neighbors with a successful Inga system and saw that they had a future.

I want the message to get to Joe Biden that funding this will keep people on the ground; I think it'll revive the rural economy. It will mitigate the climate, stop soil erosion. People can get clean water. All of these things — the environmental, social, economic benefits, and people not migrating. People don’t migrate because they want to, but because they feel they have no choice.


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