World owes it to Tanzania to keep Eastern Arc forests standing, study shows

  • Tanzania’s Eastern Arc’s evergreen forests provide carbon sequestration that the world benefits, yet it’s local communities alone who shoulder the costs of keeping the forests standing.
  • The authors of a new study recommend that international investments in conservation within the Eastern Arc worth $2 billion need to be made over the next 20 years.
  • Without this, the authors say, the mountains’ forests and their extraordinary levels of biodiversity will be lost or degraded as local communities convert them to agricultural land or harvest timber from them.

Tanzania’s Eastern Arc Mountains, home to nearly 5,000 different plant species and dozens of amphibians unique to each isolated massif, provide the world with ecosystem services worth more than $8 billion, a group of international scientists says. But the challenge lies in translating more of the value of intact forest landscape there into benefits for the more than two million people who live around the mountains, many of them farmers who are expanding their fields into the forests.

“[The massifs] have some of the oldest forests on the planet that have been through many climate cycles, and as forests get isolated on these different ‘sky islands’ they generate an enormous diversity of species,” said study lead author Phil Platts, an environmental scientist and director of U.K.-based carbon ratings agency BeZero Carbon.

Platts and a team comprising more than 70 international and Tanzanian scientists and researchers spent 10 years gathering data in the Eastern Arc, which stretches for 650 kilometers (400 miles) across the east of the country, studying its plants and animals and surveying thousands of farmers, charcoal-producers, pit sawyers, hoteliers, and forest reserve managers.

The team estimated that over a 20-year period the mountain blocks and their forests will provide nature-based benefits to both Tanzanians and the world worth a staggering $8.2 billion, after factoring in conservation costs.

To arrive at this figure, the team first calculated the benefits people could get by conserving the forests and managing them sustainably over time, including things like firewood and timber, or clean water and carbon sequestration. They then calculated the costs incurred from managing the forests, and forgoing income that could be earned if they cleared them for agriculture and harvested the trees unsustainably.

“We constructed two pathways which ran those two scenarios: conservation or complete conversion, through time and across space,” Platts told Mongabay. “You difference the two, basically, and you see which value or cost lands with which stakeholders over time.”

Clouds rise through degraded Usambara's mountain forests.
Clouds rise above forests in the Eastern Arc’s Usambara Mountains. Image by Marije Schaafsma.

The benefits to the international community total $10.1 billion over a 20-year period, according to the study’s projections. This is mostly from the carbon absorbed and emissions avoided by keeping the trees standing within the Eastern Arc’s forest reserves. Tanzanians, on the other hand, incur costs of $1.9 billion for conservation. Some benefits, in the form of ecosystem services like timber and water, do flow to local villagers and other Tanzanians living further from the mountains, but the costs of protecting and managing forest reserves, and incurring damage to croplands from animals, stack up.

The scientists say the international community must play a bigger role in shouldering conservation costs to ensure the region continues to deliver its planetary ecosystem services.

“We’re not paying our way as global beneficiaries,” said study co-author Andrew Balmford, a professor of conservation science at the University of Cambridge. And local communities have to forgo economic benefits that could otherwise be extracted from the forests, which Balmford refers to as forbearance: “Were we to get serious about this for our own benefit in terms of carbon gains, and transfer investments to local communities for their forbearance and for retaining those forests in ways that help their livelihoods, then we could be in a situation like in other parts of the world where local people benefit in dollar terms from conservation.”

The research team said international investors would need to plow $2 billion into conservation efforts, such as promoting sustainable agriculture, in the Eastern Arc to compensate local communities for not clearing the land. Without this kind of investment, they predict there will be continued reduction of the region’s biodiversity and carbon stores.

The researchers conducted surveys of thousands of the Eastern Arc’s farmers, charcoal producers, pit sawyers, hoteliers, and forest reserve managers.

Such wide consultation represents the study’s strength, making it a close examination of the costs and benefits of various ecosystem services through the eyes of different groups who depend on the mountains for economic support, Balmford said.

Understanding that full picture is fundamental to coming up with interventions that are equitable or likely to succeed, he added.

“The world will benefit from retaining as much of its natural habitat as it can in economic terms, but that only gets you so far and, clearly, who wins and who loses is a more complicated picture than that,” he said.

Eastern Arc forest.
Rainfall held and released by the forests of the Eastern Arc is vital for the drinking water supply of millions of people living downstream. Image by Marije Schaafsma.
People living near the Eastern Arc Mountains use poles collected from the forests to build their homes.
People living near the Eastern Arc Mountains use poles collected from the forests to build their homes. Image by Marije Schaafsma.

Land use

Tuyeni Mwampamba, a Tanzanian ecologist who was not part of the valuation study, said the highest-paying crop in the Eastern Arc is cardamom, a spice grown organically and sold internationally.

But cardamom needs semi-shade, and farmers sometimes clear shrubs and smaller trees beneath the large-canopied trees to grow the spice illegally inside forest reserves. After exhausting the soil’s fertility, farmers then fell the remnant trees and switch to other crops like plantains, yams and, finally, maize and beans.

The cardamom farmers who Mwampamba has met in the Eastern Arc do enjoy a higher quality of life: they’ve built themselves brick houses and can afford school fees for their children; some invest profits from the spice in setting up shops in their villages, or buy motorbikes and employ drivers.

International investments could support farmers to transition from the forest back into the agricultural landscape, while retaining their earning power, she said.

That’s a view shared by Eric Wilburn, an independent expert based in New York who works at the intersection of nature and climate and was not involved in the Eastern Arc study. He told Mongabay it’s critical for industrialized regions of the world to compensate local communities for the conservation of intact ecosystems.

“We live in a world of trade-offs, but we are currently being quite inefficient with how we make those trade-offs of conservation versus development,” he said. “We need to take a landscape approach where development is focused on areas that have lower ecosystem service provisioning, and conserve the areas that have the highest.”

The border between maize fields and standing forest in the Eastern Arc Mountains
The border between maize fields and standing forest in the Eastern Arc Mountains, Tanzania. Image by Marije Schaafsma.

An earlier study by Platts using historical land-cover maps estimates that forest cover across the Eastern Arc has declined by more than 70%, or nearly 3 million hectares (7.4 million acres), since 1908. A more recent study of his estimated that just over 430,000 hectares (1.06 million acres) of forest cover remained.

Agricultural support in the form of investments that boost crop yields on already cleared land and prevent the clearance of more land would likely represent the most equitable way of disbursing conservation investments, Balmford said. He added, however, that such a strategy could also make farming more profitable, and trigger local demand for more land to extend crop production.

“To make it work to its proper extent, there would need to be some conditionality in there, where that support is in exchange for the slowdown in [forest] conversion,” he said.

Strengthening or expanding protection for forests in the Eastern Arc will require local communities to make choices they should be compensated for, said study co-author Marije Schaafsma, an environmental economist at the Institute for Environmental Studies at Vrije University Amsterdam.

“If we think about goals, such as protecting 30% of the planet, such goals come at a high price, and we need to think very carefully about who should pay that,” Schaafsma said, in reference to the Convention on Biological Diversity’s “30 by 30” framework to protect 30% of the planet’s most biodiverse terrestrial, inland water, marine and coastal areas by 2030.

Measuring the value of ecosystem services in biodiversity hotspots like the Eastern Arc is a critical first step toward raising external funding from global beneficiaries to compensate local communities responsible for keeping ecosystems intact, said Wilburn, the nature and climate specialist.

But such valuations aren’t translating into funding on the ground to incentivize protection or empower local inhabitants with land rights and legal support at nearly the rate needed, he noted.

“We need more effort focused on creating the vehicles, whether market-based or regulatory, public or private, that create the mechanisms that can enable these valuations to lead to outcomes,” he told Mongabay.

The voluntary carbon market, which could play a big part in investments into places like the Eastern Arc, is a case in point. Platts, the study’s lead author, said that this year prices for carbon credits from forest conservation have been trading at a global average of $8 per metric ton of carbon dioxide equivalent. In many parts of the Eastern Arc, these prices would generate far less than locals can earn from farming or making charcoal.

“In a well-functioning market with high levels of transparency, there will be better price discovery — so that genuinely good projects fetch higher prices,” Platts said.

Such a scenario isn’t unattainable, Balmford said.

“I think that in the short to medium-term the potential investments that could be made on the scale that’s needed to slow down gross tropical forest loss is through carbon. There are lots of caveats and worries about that,but for now that is the game that is going to potentially be a game changer, and that’s what we need.”

Barbour’s tree frog.
Hundreds of species in the Eastern Arc species are found nowhere else on Earth, including the Barbour’s tree frog. Image by Tim Davenport.
Charcoal produced in the Eastern Arc Mountains gets sold on to major cities.
Charcoal is produced in the forests here for sale in Tanzania’s major cities. Image by Marije Schaafsma.

Mwampamba, the Tanzanian ecologist who was raised in the town of Morogoro near the Eastern Arc Mountains, said local communities can’t be asked to pin their future on carbon alone. Instead, she recommended the “bundling” of the Eastern Arc’s ecosystem services to generate income from multiple sustainable land-use practices.

She said a drawback of the valuation study is its assumption that all forests within the Eastern Arc could be converted to agriculture.

“It suggests people have no decision-making [powers], that they don’t value forests, that all they want is agriculture,” she said, adding that it also assumes there are no systems or a government in place that might take drastic action to ensure the forests aren’t depleted.

“There is a human element — as scarcity comes into play, or as a realization [dawns] that you really are going to lose it — that we need to put into these models and predictions,” she said.

Banner image: Hundreds of Eastern Arc species exist nowhere else on Earth — including the kipunji, a monkey not known to western science until 2003. Image by Tim Davenport.

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Platts, P. J., Schaafsma, M., Turner, R. K., Burgess, N. D., Fisher, B., Mbilinyi, B. P., … Balmford, A. (2023). Inequitable gains and losses from conservation in a global biodiversity hotspot. Environmental and Resource Economics. doi:10.1007/s10640-023-00798-y

Hall, J., Burgess, N. D., Lovett, J., Mbilinyi, B., & Gereau, R. E. (2009). Conservation implications of deforestation across an elevational gradient in the Eastern Arc Mountains, Tanzania. Biological Conservation, 142(11), 2510-2521. doi:10.1016/j.biocon.2009.05.028

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