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On April 20, 2023, the U.S. Department of the Interior (DOI) and Department of Agriculture (USDA) released a first-of-its-kind inventory of the country’s mature and old-growth forests. The assessment responded directly to a 2022 executive order aimed at fostering healthy forests.
The inventory highlights the importance of forest health in building resilience to future climate-related disturbances like drought or fire, but it omits mention of the service that all forests, but particularly mature and old growth forests, provide in directly mitigating the country’s carbon emissions—a service that Woodwell Climate’s scientists have worked to measure and monitor for over three decades.
The inventory is a critical starting point, from which agencies like the U.S. Forest Service and the Bureau of Land Management will begin to make decisions about how public forests are managed going forward. Not acknowledging the critical carbon storage contribution of mature and old-growth forests runs the risk of de-prioritizing protection for the country’s oldest, most carbon-rich, and hardest to replace ecosystems.
In short: carbon. While all forests sequester carbon as they grow, older and larger trees represent an existing store of carbon in their biomass and soil. Research by Woodwell Climate scientists on carbon stocks in a sample of federally managed U.S. forests found that while larger trees in mature stands constitute a small fraction of all trees, they store between 41 and 84 percent of the total carbon stock of all trees.
An analysis of mature and old growth forests across the country found that approximately 76 percent (20.8 million hectares) of these forests are unprotected from logging. This represents an amount of carbon roughly equivalent to 1 quarter of the US’s annual fossil fuel emissions.
Although younger forests grow faster proportionally, they are not adding as much carbon in a single year as older forests with large trees. Additionally, mature forests continue to pack away carbon year over year in their soils, which is largely protected from effects of disturbance. Cutting down a mature forest creates a “carbon debt” that can take decades—centuries in some cases—to recoup, and in the meantime those mature trees are no longer sequestering carbon each year.
“Forests are like naturally occurring factories, delivering to the planet the unique service of carbon sequestration. Trees of all sizes, but particularly large old trees, are the equivalent of warehouses where the goods produced—tons of carbon—are stored over time,” says Woodwell Climate Carbon Program Director, Dr. Wayne Walker. “Like any warehouse where valuable goods are stored, these natural carbon reserves deserve all the protection we can provide. Their loss could effectively bankrupt our efforts to avoid the worst impacts of climate change.”
Protecting mature forests requires them to be identified and mapped, which was part of the impetus behind the government’s forest inventory. But what actually is a mature forest?
Definitions of “mature” and “old-growth” differ, with no one universally accepted definition. Refining scientific understanding of what constitutes a mature forest has implications for either expanding or reducing the area of forest considered for protection.
In one study of U.S. forest carbon stocks, Woodwell Climate researchers and collaborators outlined a measure of forest maturity based on both the age that the tree canopy in a forest becomes 100 percent closed, called “Culmination of Net Primary Productivity,” and tree diameter size. Across 11 U.S. forests analyzed, the age at which a forest is considered mature ranged from 35 years in Appalachian forests to 75 in Arizona. “Old-growth” represents a smaller subset of mature forests having older and larger trees.
The new inventory from the DOI and USDA uses a slightly narrower definition of maturity, wherein the lower bound occurs when regeneration has begun underneath the canopy. This results in a slightly smaller estimation of the amount of mature and old-growth forests in the US—yet still approximately 63 percent of the total area of federally managed forests.
Other definitions can be based on models that take into account measurements of forest structure like canopy height, canopy cover, and biomass. Another study, co-authored by Woodwell Climate Assistant Scientist, Dr. Brendan Rogers, used these features to determine that federal lands contain the largest concentration of the country’s mature and old growth forests.
Differences in those definitions are important, because forest policy debates surrounding the responsible management of these forests depend on adequately identifying them, particularly mature forests, which are much more loosely defined than old-growth.
“I think the discussion is almost more about what to do with mature forests, as opposed to old-growth,” says Woodwell Climate senior scientist, Dr. Richard Birdsey, who worked in the U.S. Forest Service for four decades. “Mature forests are at a younger stage of growth—trees would be smaller, although they could still be substantial in size and very profitable to harvest. So the question here is whether to let those forests grow into old-growth characteristics, or to start harvesting them for wood products.”
When climate benefits are explicitly considered, the research points strongly to letting these forests grow—protecting and expanding the massive portion of sequestered carbon they represent.
According to Dr. Birdsey, the largest threat facing mature and old-growth forests in the U.S. is logging, which is a threat that humans can reduce instantly, simply by changing policy. A change that would make those forests more resilient to other threats in the long run.
“Others might argue that climate change or wildfire are more significant threats,” says Dr. Birdsey. “Older forests with larger trees are more resistant to those threats—but not more resistant to chainsaws. That’s a human decision.”
A recent paper in Nature Climate Change has laid out a “protect, manage, restore” framework for making decisions about what natural climate solutions to pursue, and the highest priority is always to protect carbon where it is already stored. U.S. policies have made some recent progress in this direction through the enforcement of the roadless rule on Alaska’s Tongass National Forest, prohibiting road-building and industrial logging on the 9 million acre temperate rainforest. But there is still further to go to capitalize on the carbon storage potential of the U.S.’s mature forests.
Federally managed forests contain more high-carbon trees than other lands, so the opportunity for increased carbon storage within them is greatest. Woodwell Climate Distinguished Visiting Scientist, Dr. William Moomaw, helped coin the term “proforestation” to refer to the strategy of letting forests continue to grow as a carbon solution. In order to achieve that, he says, mature forests have to be protected.
“The next steps should be to provide legal protection of as much of these high-carbon forests as possible,” says Dr. Moomaw. “These are public lands that should serve the public good, and reducing climate change is a public good that we should pursue as the highest priority.”
A new study published in the peer-reviewed journal Forests and Global Change presents the nation’s first assessment of carbon stored in larger trees and mature forests on 11 national forests from the West Coast states to the Appalachian Mountains. This study is a companion to prior work to define, inventory and assess the nation’s older forests published in a special feature on “natural forests for a safe climate” in the same journal. Both studies are in response to President Biden’s Executive Order to inventory mature and old-growth forests for conservation purposes and the global concern about the unprecedented decline of older trees.
Scientists have long demonstrated the importance of larger trees and older forests, but when a tree is considered large or a forest mature has not been clearly defined and is relative to many factors. This study develops an approach to resolve this issue by connecting forest stand age and tree size using information in existing databases. This paper also defines maturity by reference to age of peak carbon capture for forest types in different ecosystems. But the approach is readily applicable across forest types and can be used with other definitions of stand maturity.
Key findings include:
Researchers used thousands of forest plots obtained from the U.S. Forest Service “Forest Inventory and Analysis” (FIA) dataset to determine the amount of carbon absorbed from the atmosphere that accumulates and is stored in individual trees as they mature. As trees age, they absorb and store more carbon than smaller trees, making them uniquely important as nature-based climate solutions. Additionally, as the entire forest matures, it collectively accumulates massive amounts of carbon over centuries in vegetation and soils. The study identified the forest age at which carbon accumulation is greatest, and used that as the threshold for defining a “mature” forest. Scientists also determined the median diameter of trees at this threshold age and how much of the forest carbon of the larger trees in mature forests is unprotected from logging. The amount of carbon in unprotected larger trees in mature stands of the 11 forests studied, representing only 6% of federal forest land, is equivalent to one-quarter of annual emissions of carbon dioxide from fossil fuels in the U.S. This is consistent with prior work.
According to lead researcher, Dr. Richard Birdsey of Woodwell Climate Research Center, “our study determined when an individual tree in a forest can be considered mature and when the forest itself is at an optimal rate of carbon capture and storage for conservation purposes. It is directly responsive to the president’s executive order.”
The Biden administration has set bold emissions reduction targets of 50-52% of 2005 levels and recently announced a “roadmap for nature-based solutions” as part of this effort. However, the roadmap neglects to connect the importance of protecting older forests to the climate targets. Federal agencies are proceeding with an inventory of mature and old-growth forests in response to the executive order, but policies regarding their management have not yet been established. By protecting older forests and trees on federal lands from avoidable logging, the Biden administration can help close the gap on its emissions reduction goals. The methodology in this paper provides a readily implementable path for critical policy solutions.
According to Dr. Dominick DellaSala, Chief Scientist at Wild Heritage, “there seems to be a big disconnect between what the White House is wanting and how federal agencies are responding to the president’s forest and climate directives. While the Forest Service recently withdrew a controversial timber sale in older forests on the Willamette National Forest in Oregon (“Flat Country Project”) because it was inconsistent with the president’s directives, dozens of timber sales in older forests remain on the chopping block.”
Dr. Carolyn Ramírez, Staff Scientist with the Forests Project at the Natural Resources Defense Council, pointed to the findings as supporting the push by over 100 conservation groups – the Climate Forests Campaign – for a national rulemaking to protect mature forests and big trees from logging for their superior climate and biodiversity benefits: “This work reinforces how essential mature forests on federal lands are to securing our climate future. It’s now up to the agencies to protect these carbon storing champions from the chainsaw with formal safeguards. Our approach shows that logging protections grounded in a straightforward, age-based cutoff—such as 80 years, as many are calling for—would protect significant amounts of carbon, accommodate forest growth differences, and be readily usable in the field.”
In terms of climate mitigation, forests are like green gold—working overtime to cool the planet, while also supporting a wealth of biodiversity. But we have not been saving them as one would a precious asset. Despite pledges to end deforestation, old growth forests are being cut down at alarming rates. And planting new trees is widely prioritized and incentivized over protecting existing forests. Across the board, standing forests are vastly undervalued. This has to change if we are to stand a chance of limiting warming to internationally agreed targets.
According to a recent study from scientists at Woodwell and the University of Virginia, tropical forests alone are holding back approximately 1 degree Celsius of warming. About 75% of that cooling effect is due to carbon sequestration. Forests grow, trees lock away carbon in their trunks and roots and shunt it into the soil. The other 25% comes from the innate properties of forests that work to cool vast regions of the globe.
Through photosynthesis, plants release water vapor into the air in a process called evapotranspiration. The vapor contributes to cooling near the ground, as well as cloud formation higher in the atmosphere that reduces incoming solar radiation. The shape of the tree canopy also contributes. So-called canopy “roughness” disrupts air flow above the forest. The more uneven the canopy, the more turbulent the air, which disperses heat away from the surface. In the tropics, evapotranspiration and canopy roughness are high, which means that surface temperatures remain relatively low, with the heat dispersed throughout the deep atmosphere.
Forests also naturally produce molecules called biogenic volatile organic compounds (BVOC), which can either contribute to cooling by encouraging the formation of clouds, or to warming by creating ozone and methane. In the tropics, the net effect of these chemicals is cooling.
The cumulative result of these properties is that when forests are removed, the land around them begins to heat up even faster, which can increase the frequency of extreme heat and drought events. Without forests, some regions will become a lot less resilient to sudden shocks. And the release of carbon contributes to global warming which further exacerbates hot, dry conditions.
“Forests act like air conditioners,” says Woodwell Assistant Scientist, Dr. Ludmila Rattis, who studies the impacts of deforestation on agriculture in Brazil. “Deforesting in the face of climate change is like getting rid of your air conditioners before an upcoming heatwave.”
Protecting forests, and maintaining the cooling services they provide, is vital to limiting warming. But, with forests covering 30% of the Earth’s land, prioritizing protection is a massive task. And when it comes to carbon storage, not all forests are equally valuable. Older, healthier forests tend to have a more secure hold on their carbon.
“Mature forests have higher biodiversity and create their own microclimate,” says Woodwell Associate Scientist, Brendan Rogers. “They’re more resistant to drought and other types of disturbance. And because of that, they tend to be more stable in the face of environmental perturbations over time.”
New research from Woodwell and Griffith University has developed a method of identifying high-value forests using satellite imagery. Estimating the metric of “forest stability” through satellite data on the light reflected by vegetation and a water stress index of the tree canopy, researchers were able to determine gradients of stability within forest patches in the Amazon and boreal forests.
Using a gradient of forest stability allows for a better prioritization of forest protection strategies based on their carbon value.
“The first priority is to protect stable forests from further human disturbance,” says paper co-author Dr. Brendan Mackey. “The second priority is to identify forest areas where restoration efforts will be most cost effective.”
But if the state of existing forests is any indication, forest protection continues to be deprioritized. Many wildfires are left to burn unless they threaten human settlements. Governments continue to incentivize deforestation for development or agricultural expansion. Indigenous and local communities are not compensated for their work stewarding their territories and keeping forests safe. And the warmer the planet gets, the more susceptible even protected forests become to drought, fire, and disease.
Research has shown that stewarding standing primary forests, and reviving degraded ones, represents the greatest opportunity for near-term carbon storage and removal. A study of global land-based carbon storage potential found that improved management of existing forests alone could store approximately 215 billion metric tons more than they currently do.
Protecting forests is cost effective, too. For example, in the United States, investing in fire fighting in Alaska’s boreal forests would require just $13 per ton of CO2 emissions avoided. That’s easily on par with other mitigation strategies like onshore wind or solar energy generation.
Effective strategies for protecting forests already exist, they’ve just been suffering from a lack of force—and often funding—behind their implementation. For example, forest carbon markets—where landowners and forest stewards are paid to protect standing forests that are otherwise vulnerable to deforestation—have the potential to keep forests safe while offsetting emissions from other sectors. But nascent carbon markets are inefficient, with weak standards for verifying the quality of credits being sold, and lacking the transparency needed to ensure credits are actually reducing overall emissions, rather than greenwashing carbon-intensive business practices.
Credits are also priced incorrectly for their relative climate value—the market currently values reforestation credits more highly, reducing incentive for landowners to conserve standing, old-growth forests when there is a better livelihood to be made in legally deforesting land for other uses. A truly effective carbon markets system would require large investments in science that can verify credit standards.
Forests are like our global carbon savings accounts—when we cut them down, we’re drawing out money and limiting our ability to collect interest and keep growing our funds. Successful mitigation can’t be accomplished without taking the full value of forests into account and strengthening policies to reflect that. If they aren’t, the planet will pay a far greater price for it as temperatures rise.
“We can’t afford to keep cutting forests. We need to reduce emissions now, and protecting forests is one of our best available solutions. Despite the obstacles, it’s worth the investment,” says Dr. Rogers.
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.”
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.
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 Cerrado is a tropical savanna located just southeast of the Amazon rainforest. This biome is a patchwork of forests, savannas, and grasslands, nearly as biodiversity rich as the Amazon yet suffering more due to lax environmental protections. Over 46% of its original land cover has already been cleared for crops or pastures. A recent study assessed the impacts of this conversion on the temperature and water cycling in the region.
The study found that clearing of natural ecosystems resulted in increased land surface temperatures and reduced evapotranspiration — water evaporated to the atmosphere both from soils and as a byproduct of plant growth. Across the biome, land use changes caused a 10% reduction in water being cycled into the atmosphere annually, and almost 1 degree C of warming. Where native savanna vegetation was cleared, temperatures increased by 1.9C and the water recycled to the atmosphere decreased by up to 27%. These changes don’t take into account the additional effects of atmospheric warming from greenhouse gas emissions.
The study also projects forward three potential future scenarios based on different levels of environmental protection. The worst-case scenario assumes an additional 64 million hectares of both legal and illegal deforestation, which would leave just 20% of native vegetation in the Cerrado by 2050. If illegal deforestation is prevented but legal deforestation still advances, an additional 28 million hectares of deforestation would continue to warm and dry out the region. Only in the most optimistic scenario, with enforced zero deforestation policies and restoration of over 5 million hectares of illegally cleared vegetation, would the impacts of past clearing begin to reverse.
“If we continue down this path of weakening environmental policies, we’re probably heading towards an uncontrolled increase in deforestation,” says Ariane Rodrigues, researcher at the University of Brasilia and lead author on the paper. “As a result, we could reach almost 1 C of temperature increase by 2050 from land use change alone. If we add the estimated temperature increase from global greenhouse gas emissions, we will have a critical situation for food production, biodiversity, water and wildfire risk, affecting areas located way beyond the biome’s limits.”
Incentives for large-scale commercial agriculture in the Cerrado date back to the 1970s. Despite its high biodiversity, only 11% of the Cerrado is protected and technological advancements provided favorable conditions for agriculture to expand rapidly.
The half of the biome that remains unconverted is considered prime agricultural land. The Cerrado alone is responsible for 12% of global soybean production and 10% of global beef exports. Growing demand for these agricultural products is pushing farmers and ranchers to expand into the Matopiba region in the Northeast Cerrado — one of the largest remaining areas of undisturbed native vegetation.
Hotspots of reduced evapotranspiration and increased temperatures can already be seen in areas of Matopiba with intensifying agricultural activity. This means that farms will rely even more heavily on irrigation to combat drought, a strategy made less viable by the warming and drying caused by agriculture itself.
“That is the driest portion of the Cerrado, where there’s the most climate risk already,” says paper co-author and Woodwell Water program director, Dr. Marcia Macedo. “You can see that in the data — it’s getting hotter, and there’s less evapotranspiration, so we are really intensifying conflicts in areas that are already on the edge.”
The results of the paper highlight the urgent need for a paradigm shift that values the additional services the Cerrado provides beyond just crop production. Not only does it house unique ecosystems, but it plays a pivotal role in modulating the climate of the region. In the best-case scenario evaluated by the paper, zero-deforestation and restoration policies could avoid extensive warming and drying and begin compensating for the past transformation of Cerrado landscapes. Continued conversion of natural vegetation will jeopardize both biodiversity and agricultural stability in the Cerrado, as crops struggle to be productive under hotter and drier conditions.
Already, conflicts over water usage and irrigation are occurring in western Bahía state. As the region warms and dries, competition for a scarce resource will become more common and large-scale agriculture will become much less viable.
“We’re making some risky decisions in terms of land use,” says Dr. Macedo, “We’re losing a lot for short term gains in crop production, often in areas that will struggle to sustain large-scale agriculture as climate changes.”
It was supposed to be a quiet season, but only two months into summer and Alaska is already on track for another record-setting wildfire season. With 3 million acres already scorched and over 260 active fires, 2022 is settling in behind 2015 and 2004 so far as one of the state’s worst fire seasons on record. Here’s what to know about Alaska’s summer fires:
Southwestern Alaska, in particular, has been suffering. The season kicked off with an unseasonably early fire near Kwethluk that started in April. Currently, the East Fork Fire, which is burning near the Yup’ik village of St. Mary’s, AK, is among the biggest tundra fires in Alaska’s history. Just above Bristol Bay, the Lime Complex— consisting of 18 individual fires— has burned through nearly 865,000 acres. One of the longest lasting fires in the Lime Complex, the Upper Talarik fire, is burning close to the site of the controversial open-pit Pebble Mine.
For Dr. Brendan Rogers, who was in Fairbanks, AK for a research trip in May, the explosive start of the fire season contrasts strongly to conditions he saw in late spring.
“It was a relatively average spring in interior Alaska, with higher-than-normal snowpack. Walking around the forest was challenging because of remaining snow, slush, and flooded trails,” said Dr. Rogers.
Early predictions showed a 2022 season low in fire due to heavy winter snow. But the weather shifted in the last ten days of May and early June. June temperatures in Anchorage were the second highest ever recorded. High heat and low humidity rapidly dried out vegetation and groundcover, creating a tinderbox of available fuel. This sudden flip from wet to dry unfolded similarly to conditions in 2004, which resulted in the state’s worst fire season on record.
The conditions for this wildfire season were facilitated by climate change, and the emissions that result from them will fuel further warming. The hot temperatures responsible for drying out the Alaskan landscape were brought on by a persistent high pressure system that prevents the formation of clouds— a weather pattern linked to warming-related fluctuations in the jet stream.
“With climate change, we tend to get more of these persistent ridges and troughs in the jet stream,” says Dr. Rogers. “This will cause a high pressure system like this one to just sit over an area. There is no rain; it dries everything out, warms everything up.”
The compounding effects of earlier snowmelt and declining precipitation have also made it easier for ground cover to dry out rapidly under a spell of hot weather. More frequent fires also burn through ground cover protecting permafrost, accelerating thaw that releases more carbon. According to the Alaska Center for Climate Assessment and Policy, the frequency of big fire seasons like this one are only increasing— a trend expected to continue apace with further climate change.
Additionally, this summer has been high in lightning strikes, which were linked to the ignition of most of the fires currently burning in Alaska. Higher temperatures result in more energy in the atmosphere, which increases the likelihood of lightning strikes. On just one day in July over 7,180 lightning strikes were reported in Alaska and neighboring portions of Canada.
The destruction from these wildfires has forced rural and city residents alike to evacuate and escape the path of burning. Some residents of St. Mary’s, AK have elected to stay long enough to help combat the fires, clearing brush around structures and cutting trees that could spread fire to town buildings if they alight.
But the impact of the fires is also being felt in towns not in the direct path of the flames. Smoke particulates at levels high enough to cause dangerously unhealthy air quality were carried as far north as Nome, AK on the Seward Peninsula.
“Even though a lot of these fires are remote, that doesn’t preclude direct human harm,” says Woodwell senior science policy advisor Dr. Peter Frumhoff.
Recent research has shown that combatting boreal forest fires, even remote ones, can be a cost effective way to prevent both these immediate health risks, as well as the dangers of ground subsidence, erosion, and loss of traditional ways of life posed by climate change in the region.
Mid-July rains have begun to slow the progression of active fires but, according to Dr. Frumhoff, despite the lull, it is important to keep in mind that the season is not over yet.
“The uncertainty of those early predictions also applies to the remainder of the fire season — we don’t know how much more fire we’ll see in Alaska over the next several weeks.”
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.
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.
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.
The importance of natural climate solutions came to the forefront of climate talks in Glasgow last week as decision makers discussed the “how” of making good on emissions pledges.
One of the most powerful existing solutions we can deploy are land-based mitigation strategies, also known as natural climate solutions. Forest protection and restoration, agroforestry, and other changes to the way we manage land can boost the amount of carbon ecosystems pull from the atmosphere and could help tackle 20-30 percent of the emissions reductions needed to limit warming to 1.5 degrees C. These graphics, based on a recent study in Global Change Biology, break down the potential and feasibility of land-based carbon mitigation.
Although there is great potential in land-based mitigation globally, some actions will be cheaper and easier to implement. Roughly 40 percent of the total carbon mitigation potential of land-based strategies can be considered cost-effective, with estimated price tags up to $100 per ton of carbon sequestered. On a global scale, actions like reducing deforestation or improving carbon sequestration on grasslands are incredibly cost effective. Shifting to healthier, more plant-based diets is another, individual, action that can have big impacts.
On a regional level, the value of different actions varies. In Latin America and the Caribbean, as well as Africa, the greatest mitigation power lies in forests, both protecting existing forests and restoring degraded ones. In Brazil, which holds 60 percent of Amazon forests, the feasible benefits are striking. For developed nations, like the United States, improving sequestration on agricultural lands is a much larger piece of the equation, almost equal to forest-related measures. This is because developed countries like the U.S. have already cut their old-growth forests.
Ecosystems like mangroves or peatlands offer opportunities to make big emissions reductions over relatively small areas. Mangrove forests store vastly more carbon per hectare than most terrestrial forests—primarily due to large soil carbon stores—and only occupy thin strips of coastline across much of the tropics.
Their outsize carbon sequestration and storage potential means that restoring them offers a much greater return on investment than other ecosystems, and failing to protect them could place climate goals in serious jeopardy. Though employing all land-based mitigation strategies at our disposal is crucial, targeting the most carbon-rich forests could be a quicker, easier, more cost-effective first step.