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When it comes to reversing climate change, trees are a big deal. Globally, forests absorb nearly 16 billion metric tonnes of carbon dioxide per year, and currently hold 861 gigatonnes of carbon in their branches, leaves, roots, and soils. This makes them a valuable global carbon sink, and makes preserving and maintaining healthy forests a vital strategy in combating climate change.

But not every forest absorbs and stores carbon in the same way, and the threats facing each are complex. A nuanced understanding of how carbon moves through forest ecosystems helps us build better strategies to protect them. Here’s how the world’s different forests help keep the world cool, and how we can help keep them standing.

Tropical forest carbon

Tropical rainforests are models of forest productivity. Trees use carbon in the process of photosynthesis, integrating it into their trunks, branches, leaves, and roots. When part or all of a tree dies and falls to the ground, it is consumed by microorganisms and carbon is released in the process of decay. In the heat and humidity of the tropics, vegetation grows so rapidly that decaying organic matter is almost immediately re-incorporated into new growth. Nearly all the carbon stored in tropical forests exists within the plants growing aboveground. 

Studies estimate that tropical forests alone are responsible for holding back more than 1 degree C of atmospheric warming. 75% of that is due simply to the amount of carbon they store. The other 25% comes from the cooling effects of shading, pumping water into the atmosphere and creating clouds, and disrupting airflow.  

In many tropical forest regions, there is a tension between forests and agricultural expansion. In the Amazon rainforest, land grabbing for commodity uses like cattle ranching or soy farming has advanced deforestation. Increasing protected forest areas and strengthening the rights of Indigenous communities to manage their own territories has proven effective at reducing deforestation and its associated emissions in Brazil. “Undesignated lands” have the highest levels of land grabbing and deforestation.

Fire has also become a growing threat to the Amazon in recent years, used as a tool to clear land by people illegally deforesting. When rainforests have been fragmented and degraded, their edges become drier and more susceptible to out-of-control burning, which weakens the forest even further. Enforcing and strengthening existing anti-deforestation laws are crucial to reduce carbon losses.

In Africa’s Congo rainforest, clearing is usually for small subsistence farms which, in aggregate, have a large effect on forest loss and degradation. Mobilizing finance to scale up agricultural intensification efforts and rural enterprise within communities, while implementing protection measures, can help decrease the rate of forest destruction. Forests and other intact natural landscapes such as wetlands and peatlands could be the focus of climate finance mechanisms that encourage sustainable landscape management initiatives. 

Temperate forest carbon

Much of the forest carbon in the temperate zone is stored in the trees as well— particularly in areas where high rainfall supports the growth of dense forests that are resilient against disturbances like drought or disease. The temperate rainforests of the Northwestern United States, Chile, Australia, and New Zealand contain some of the largest and oldest trees in the world. 

Two thirds of the total carbon sink in temperate forests can be attributed to the annual increase in “live biomass”, or the yearly growth of living trees within the forest. This makes the protection of mature and old-growth temperate forests paramount, since older forests add more carbon per year than younger ones and have much larger carbon stocks. Timber harvesting represents one of the most significant risks to the carbon stocks in temperate forests, particularly in the United States where 76% of mature and old growth forests go unprotected from logging. Fire and insects are also significant threats to temperate forests particularly in areas of low rainfall or periodic drought.  

Maintaining the temperate forest sink means reducing the area of logging, by both removing the incentive to manage public forests for economic uses and by providing private forest owners with incentives to protect their land. Low-impact harvesting practices and better recycling of wood products can also help bring down carbon losses from temperate forests. In areas threatened by increasingly severe wildfires, reducing fuel loads especially near settlements can help protect lives and property. 

Boreal forest carbon

In boreal forests, the real wealth of carbon is below the ground. In colder climates, the processes of decay that result in emissions tend to lag behind the process of photosynthesis which locks away carbon in organic matter. Over millennia, that imbalance has slowly built up a massive carbon pool in boreal soils. Decay is even further slowed in areas of permafrost, where the ground stays frozen nearly year round. It estimated that 80 to 90% of all carbon in boreal forests is stored belowground. The aboveground forest helps to protect belowground carbon from warming, thaw, decay, and erosion.

Wildfire— although a natural element in boreal forests— represents one of the greatest threats to boreal forest carbon. With increased temperatures, rising more than twice as fast in boreal forests compared to lower latitudes, and more frequent and long-lasting droughts, boreal forests are now experiencing more frequent and intense wildfires. The hotter and more often a stand of boreal forest catches fire, the deeper into the soil carbon pool the fire will burn, sending centuries-old carbon up in smoke in an instant. Logging of high-carbon primary forests is also a big issue in the boreal.

The number one protection for boreal forest carbon is reducing fossil fuel emissions. Only reversing climate change will bring boreal fires back to the historical levels these forests evolved with. In the meantime, active fire management in boreal forests offers a cost effective strategy to reduce emissions— studies found it could cost less than 13 dollars per ton of carbon dioxide emissions avoided. Strategies for fire management included both putting out fires that threaten large emissions, and controlled and cultural burning outside of the fire season to reduce the flammability of the landscape.

Fund for Climate Solutions awards five new grants

From the Arctic to the Tropics, the 2024 winter cohort of FCS projects fills information gaps to produce actionable insights

Quantifying large greenhouse gas emissions from a retrogressive thaw slump in Alaska

Lead: Jennifer Watts
Collaborators: Kyle Arndt, Patrick Murphy

Retrogressive thaw slumps (RTS) are extreme permafrost thaw landscape features, which occur when a section of ice-rich permafrost becomes warm enough to cause the ground ice to melt and soils to collapse. Once they start, RTS continue to expand and destroy nearby permafrost for months to years. Many RTS have been identified, but because they are often in extremely remote arctic locations, very little is known about the potentially substantial carbon emissions from RTS in the form of carbon dioxide and methane. This study will provide the first continuous measurements of carbon emissions from a RTS, collected over at least a year via an eddy covariance tower. The research is also supported by an equipment loan provided through the U.S. Department of Energy AmeriFlux Rapid Response program, which recognized this project as a valuable opportunity to advance science. The data collected will also serve as a “proof of concept” for a subsequent $1.3M proposal to the National Science Foundation for continued research at the site.

Assessing the impacts of ecosystem disturbance on carbon emissions from Arctic and Amazon ponds

Lead: Elchin Jafarov
Collaborators: Zoë Dietrich, Andrew Mullen, Jackie Hung, Marcia Macedo, Kathleen Savage

Freshwater ecosystems are significant sources of the greenhouse gases that persist in the atmosphere and contribute to warming. However, research is lacking an understanding of how disturbances like wildfire and agriculture can change these emissions. This project will address these information gaps by collecting measurements of carbon emissions from ponds, using autonomous floating chambers developed with funding from a previous FCS grant. With this new high-resolution data, the team will unlock the ability to predict year-round greenhouse gas emissions from ponds in the Arctic and the Amazon. Floating chambers will be deployed in ponds in Alaska affected by wildfires, and in agricultural reservoirs in the Amazon-Cerrado frontier. In both locations, the ability to take more frequent measurements of carbon emissions will help researchers improve models and better assess the ponds’ impacts on regional carbon budgets.

The Polaris Project: Data synthesis from almost two decades of research and student participation

Lead: Nigel Golden
Collaborator: Sue Natali

Established in 2008, the Polaris Project has earned global recognition for its leadership in Arctic research, education, and outreach. Through the commitment to providing students with hands-on experience, Polaris has enabled numerous publications and presentations. Polaris is approaching a critical juncture in the next funding cycle, and this project will complete the first-ever comprehensive synthesis of Polaris Project research to help sustain Woodwell Climate’s sole undergraduate research program. By consolidating past research and educational achievements, the team will create a data synthesis paper to be submitted to a peer-reviewed, open-access scientific research journal, as well as a retrospective analysis of undergraduates’ research experiences with Polaris to be submitted to an education research journal. The team will also launch an online communications piece that documents past Polaris participants’ field experiences and unique journeys with a variety of narrative and artistic communications styles and elements.

Determining the climate sensitivity of coastal rivers to guide ecosystem restoration across SE Massachusetts

Lead: Abra Atwood
Collaborators: Marcia Macedo, Chris Neill, Linda Deegan, Scott Zolkos

Coastal rivers, like those that flow into Massachusetts’ Buzzards Bay and Vineyard Sound, are fragile environments that serve critical ecological functions for native fish, downstream estuaries, and coastal wetlands. Different rivers are uniquely sensitive to changes in air temperature based on a variety of characteristics, such as their water source or shade. However, land use changes, including housing development and cranberry bogs, have affected key river characteristics and stream temperatures. This project will investigate MA coastal rivers’ sensitivity to changing air temperature, as well as how that sensitivity is affected by both connection to groundwater and the creation or restoration of cranberry bogs. The temperature sensors and geochemical analyses used in this research may be scalable beyond these rivers and yield insights to inform research approaches relevant to rivers around the world.

A drought early warning system for the DRC: Developing a seasonal forecast based on novel machine learning approaches

Lead: Carlos Dobler-Morales
Collaborators: Christopher Schwalm, Glenn Bush

Seasonal weather forecasts hold immense potential to improve risk management from agricultural failure, water stress, and extreme events. However, significant advances in technical forecasting capabilities remain largely unavailable to communities without the resources to develop or customize them for their region. In 2023, Woodwell Climate Just Access co-produced a national climate risk assessment with the Democratic Republic of Congo’s Ministry of Environment and Sustainable Development. That report identified drought as a major climate threat to the DRC—one which stands to affect almost the entire country. In response, this project will develop a seasonal drought forecasting model tailored to the DRC using cutting-edge machine-learning methods. The forecast will be able to deliver precise rainfall anomaly predictions up to six months in advance for the whole country, and serve as an early warning system to help local people and decision-makers anticipate the impacts of escalating drought risk.

 

Learn more about the Fund for Climate Solutions.

A recent paper, led by Woodwell Climate postdoctoral researcher Dr. José Safanelli, revealed that Brazil’s farms have been steadily moving out of the most suitable regions for agriculture—opening up a significant portion of the world’s agricultural production to vulnerability from the changing climate. 

The study, published in Applied Geography, used an index to assess “Grain-cropping suitability” for two key staple crops—soy and maize.  Suitability was determined by climatic factors (temperature and precipitation), as well as soil quality and terrain. The result was a continuous map detailing the areas of the country with the best biophysical conditions for growing crops.

Overlaying land use change data from the past two decades with this new map revealed a historical trend of agricultural lands expanding towards areas with poorer soil quality and lower suitability for grain-cropping, primarily in the north central and northeastern portion of the country.

Understanding Brazil’s agricultural migration

Farmers in Brazil have been moving north to this “agricultural frontier” since the 1980s— drawn primarily by economic opportunity, as well as the higher quality climate and terrain conditions along the southern edge of the Amazon.

Despite the favorable climate, the soil is inferior. Farmers are seeking cheap land, which often comes in the form of degraded pasture, originally created by clearing forest. Rainforest soils are not naturally nutrient rich and, without any additional inputs, the soil quality becomes depleted after just a few years. Many farmers know this fact, but come anyway. Dr. Safanelli has even seen this trend unfold within his own family.

“I was born in the south of Brazil, a region that has good soil conditions. Recently, two of my uncles who are farmers emigrated to Mato Grosso. There, the climate is wetter and more stable, but the soils are poor—depleted of nutrients.”

Additional research by Woodwell Climate Assistant Scientist Dr. Ludmila Rattis suggests that climatic advantage may be short-lived. Her work indicates that the climate in these areas is changing— becoming drier and hotter as global temperatures rise—and deforestation for agricultural expansion just makes the problem worse. 

“We showed in our paper that these places have good climate and terrain suitability for now,” says Dr. Safanelli. “But they are restricted in soil quality. In Mato Grosso—the largest agricultural production state in Brazil—for example, the climate has been more stable and favorable than in other parts. The problem is that, according to projected climate scenarios, climate change may push these areas out of a good suitability space.”

What this means for agriculture in Brazil

Brazil is currently the world’s top producer of soy, and in the top three for maize. But this expansion into lower-suitability regions has introduced greater vulnerability into the agricultural system. Farmers already must provide greater investment in fertilizing the soil to make it productive, which cuts into their margins for profit. Add to that the fact that poor-quality soils, typically low in organic matter, can make crops less resilient to extreme heat and drought.

“Crop evapotranspiration—a process that directly governs crop growth and yield—depends on soil for absorbing rainfall and storing water. These marginal soils can make farmers more susceptible to climate change’s expected drier and warmer conditions, as they have limited capacity for storing water,” says Dr. Safanelli.

Reducing these vulnerabilities, Dr. Safanelli says, will require an integrated approach— improving land management practices and increasing crop yields on existing land to reduce the pressure to expand. “Reducing the vulnerability of croplands may be possible by adopting management practices that increase the resilience of the farming system, such as fully incorporating the principles of conservation agriculture, integrated production through agroforestry, crop-forest-livestock systems, or irrigation to control dryness. And perhaps allocating some of these marginal lands for land restoration, concentrating our resources in more highly suitable croplands.”

What’s New?

A recent paper offers new insight into the state of global forests. Using remote sensing imagery from MODIS satellites, researchers were able to categorize forest condition in two important biomes—the Amazon and the Siberian Taiga—differentiating between high stability, low stability, and non-forested areas. These “stability classes” provide another metric of assessing the conservation and carbon value of land, as high stability forests tend to be healthier, more resilient, primary forest stands that store large amounts of carbon and contribute to cooling the planet more than lower stability forests.

“Mature forests have higher biodiversity and create their own microclimate,” says paper co-author and Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And then because of that, they tend to be more stable in the face of environmental perturbations over time.”

Understanding forest stability

To estimate forest stability, researchers analyzed satellite data that combined measures of photosynthetic radiation with a canopy water stress index. That new approach was able to identify whether or not a forest has been disturbed by either human land use (ex. logging) or natural processes (wildfire, insects outbreaks, etc.) and map the degradation level.

Co-author Dr. Brendan Mackey from Griffith University in Australia says that stability mapping is a first critical step in making an inventory of the world’s remaining primary forests which store more carbon, support the most biodiversity, and deliver the cleanest water. 

According to Dr. Rogers, the less interruption in the ecological processes of the forest, the more secure the carbon stored in both the trees and soils are. Further human interference in an unstable forest could tip it into decline. 

“I think one of the problems for primary forest conservation globally has been this idea that it’s either a forest or not a forest. So, internationally agreed upon definitions of what constitutes a forest sets a pretty low bar. You can get away with calling a plantation with very young trees a forest, but that could have been converted from a high biomass mature forest, and they’re simply not the same—not in terms of carbon, biodiversity, or ecosystem services,” says Dr. Rogers.

What this means for forest conservation

Using a gradient of forest stability instead of a black and white definition of forest/not-forest allows for more nuanced decision-making where both carbon monitoring and conservation planning are concerned.

“The first priority is to protect stable forests from further human disturbance, as once an area is deforested, it takes decades to centuries—and in some cases millenia—for it to regrow to a primary state. The second priority is to identify forest areas where restoration efforts will be most cost effective,” says Dr. Mackey.

According to the paper’s lead author, Dr. Tatiana Shestakova, this means places where a small investment could have bigger positive results.

“If you pick a forest that was degraded in some way, but it still keeps patches of more or less healthy forests, you can reinstate ecological processes faster and easier,” says Dr. Shestakova.

Dr. Shestakova said she encourages other researchers to apply the methods to their particular regions of expertise and expand estimates of forest stability globally.

“The benefit of this approach is that it was tested in such contrasting ecoregions, and has been proven to be a simple and efficient way to assess this important dimension of forest condition,” says Dr. Shestakova.

The Amazon rainforest is one of the planet’s best natural climate solutions. Roughly 123 billion tons of carbon are estimated to be stored in the trees and soils of the Amazon and, if protected, it has the power to continue sequestering billions of tons of carbon each year.

But that irreplaceable carbon sink is under steady threat from a cycle of deforestation, fire, and drought that is both exacerbated by and contributing to climate change. Preliminary analysis from Woodwell of last year’s data has outlined that the most vulnerable regions of the Amazon are where drought and deforestation overlap.

2021 data shows deforestation drives fire in the Amazon

Unlike temperate or boreal forest ecosystems—or even neighboring biomes in Brazil— fires in the Amazon are almost entirely human caused. Fire is an intrinsic part of the deforestation process, usually set to clear the forest for use as pasture or cropland. Because of this, data on deforestation can provide a good indicator of where ignitions are likely to happen. Drought fans those flames, producing the right conditions for more intense fires that last longer and spread farther. Examining the intersection between drought and deforestation in 2021, Woodwell identified areas of the Amazon most vulnerable to burning.

Areas of deforestation combined with exceptionally dry weather to create high fire risk in northwestern Mato Grosso, eastern Acre, and Rondonia. Although drought conditions shifted across the region throughout the course of the year, deforestation caused fuel to accumulate along the boundaries of protected and agricultural land.

These areas of concentrated fuel showed the most overlap with fires in 2021, indicating that without the ignition source that deforestation provides, fires would be unable to occur, even during times of drought.

In June of 2021, we identified a dangerous and flammable combination of cut, unburned wood and high drought in the municipality of Lábrea, that put it at extreme risk of burning. Data at the end of December of 2021 confirmed this prediction. The observed fire count numbers from NASA showed that last year, Lábrea experienced its worst fire season since 2012.

Fires and climate change form a dangerous feedback loop

As a result of deforestation in 2021, at least 75 million tons of carbon were committed to being released from the Amazon. When that cut forest is also burned, most of the carbon enters the atmosphere in a matter of days or weeks, rather than the longer release that comes from decay.

This fuels warming, which feeds back into the cycle of fire by creating hotter, drier, conditions in a forest accustomed to moisture. Drought conditions weaken unburned forests, especially around the edges of deforestation, which makes them more susceptible to burning and releasing even more carbon to the atmosphere to further fuel warming.

Fire prevention strategies enacted by the current administration over the past 3 years have been insufficient to curb burning in the Amazon, because the underlying cause of deforestation remains unaddressed. Firefighting crews are not sufficiently supported to continue their work in regions like Lábrea that are actively hostile to combating deforestation and fire. If deforestation has occurred, fire will follow. To ensure the safety of both the people and the forests in these high-risk municipalities, the root causes of deforestation must be addressed with stronger and more strategic policies and enforcement.

Woodwell workshop brings Indigenous firefighters to Brasilia

A week-long workshop encourages knowledge sharing between Indigenous Brazilian fire brigades

On March 28, 2022, firefighters from Indigenous communities across Brazil gathered in Brasília, the country’s capitol, for a week-long geography and cartography workshop. The workshop, a collaboration between the Coordination of Indigenous Organizations of the Brazilian Amazon (COIAB) and the Amazon River Basin (COICA), IPAM Amazônia, and Woodwell Climate Research Center, walked participants through the basics of using Global Information Systems technology to monitor and manage their own lands and forests.

Forests and native vegetation on Indigenous lands have been sustainably managed for millenia, and studies have found Indigenous stewardship of forests is an effective measure for preventing deforestation and degradation. Escaped fires can present a threat to forests, and many Indigenous communities have their own brigades that work on detecting and preventing runaway fires. In some places, prescribed burns are used as a tool for shaping and cultivating the land.

Participants attended from Indigenous lands located in a variety of Brazilian landscapes—from the Cerrado to the heart of the Amazon. Despite differences, participants found learning from other Indigenous communities extremely valuable.

“People came with a variety of skill sets,” said Woodwell Water Program Director Dr. Marcia Macedo. “What was most meaningful for participants was seeing other people like them, who do the same work and are also Indigenous people, already dominating material, knowing how to make the maps, and helping others. It gave them confidence that they could also figure it out.”

After a day of introduction to the core concepts of GIS and mapping, participants headed out to Brasília National Park to test their newfound skills. They visited burned areas from both an escaped fire and a prescribed burn, compared the two, marked GPS points, and took pictures. The data gathered on the field trip was used over the next few days to practice making maps. 

“The goal was to not only teach the theory and help them understand the steps for making maps, but also mainly to develop the skills for them to be able to apply to their own lands on their own time,” said Woodwell postdoctoral researcher, Dr. Manoela Machado, who helped organize the event.

The workshop also fostered discussions about the complexity of management when fire can be both a threat and a tool. Because fire manifests differently in different biomes, well-managed fires look different for each community.

“On the final day, we had a discussion of values. Is fire good or bad? For whom—ants, forests, human health?” said Dr. Machado. “You can’t just criminalize fire if it’s a part of traditional knowledge and used as a tool for providing food, for example. So it’s a complex issue.” 

Dr. Machado hopes the conversations will continue. She says the goal would be to host this workshop again to expand its reach, potentially beyond Brazil to include participants in other Amazonian countries.

Despite centuries of successful Indigenous management, the Xingu’s fire regimes are changing

What’s new?

The first designated Indigenous land in Brazil, Território Indígena do Xingu (TIX), has been cited by studies for decades as a successful buffer against the deforestation, degradation, and fires that plague other parts of the Amazon. A recent study, co-authored by Dr. Divino Silvério, Professor at the Universidade Federal Rural da Amazônia, and Dr. Marcia Macedo, Woodwell Water Program Director, shows that fire regimes are changing in the Xingu region, leading to more forest loss and degradation.

The paper shows roughly 7 percent of the TIX has been degraded by drought and fire. Degradation is part of a feedback loop wherein damaged forests become drier and more susceptible to burning in future fires.

“I remember when I started my Ph.D., a 2006 paper showed that Indigenous lands were extremely effective fire breaks—the Xingu just never saw fire. Climate change has completely changed that story,” said Dr. Marcia Macedo.

Understanding: Changing fire regimes

Indigenous communities in the TIX have been managing the rainforest for centuries with finely adapted slash and burn cycles that create space for agriculture and promote the growth of natural species used in construction, medicine, and cooking. These cycles can last three to four decades before an area is burned again. Traditionally, burns were well controlled and the rainforests surrounding burned areas were healthy enough to prevent flames from escaping.

But over the past two decades, the paper observed, escaped fires have occurred more often within the reserve and the likelihood that forest is lost post-fire is rising, particularly in seasonally flooded forests. Indigenous management practices have not changed significantly, the paper explains, so why the increased prevalence of fire and degradation?

Climate change is drying out forests, making them more susceptible to escaped burning from management practices. The other factor driving degradation within the territory is growing population. Indigenous communities are becoming less nomadic, and village populations are rising, increasing the area of forest used for subsistence. Degradation was higher in areas surrounding villages.

“The way Indigenous people manage fire has stayed the same, but we now have a different climate,” said Dr. Divino Silvério. “Indigenous people have been in these regions for many decades or centuries. And all this time they have had their own fire management to produce food that usually doesn’t end in these huge forest fires.”

What this means for Indigenous fire management

Climate change will force Indigenous communities within the reserve to adapt traditional practices to protect the forest against more frequent, intensifying fires—despite these communities not contributing to global emissions.

Previous attempts to manage increasing fires through prescribed burning have clashed with the needs of residents of the TIX. Burning at a different time of year does not cultivate the same species, and residents were concerned it was jeopardizing the growth of plants used for medicine.

Dr. Silvério is working with residents of the Xingu to understand how to integrate changes to fire management practices with traditional strategies in a way that supports community needs. One example, he said, could be shifting the primary construction material from grasses (that grow after fire) to palms.

“Indigenous people will probably need to learn how to live in this new reality, an environment with more drought and more fires. We are trying to work in a participative way to construct solutions with them.”