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.”
Millions of acres of rangelands managed by the U. S. Bureau of Land Management are not meeting land health standards, according to a recent report from watchdog organization Public Employees for Environmental Responsibility. Range degradation is also happening on U.S. Forest Service and privately held lands. Healthy rangelands are vital to the economic and public health of the communities that depend on them, which includes ranchers, Indigenous nations, and recreationists. Failing rangelands undermine these groups, lead to loss of habitat, and result in landscape degradation, and they also minimize our ability to mitigate climate change through carbon sequestration. Taking policy action to ensure the longevity of rangelands has the potential to increase climate mitigation potential and improve the health of U.S. ecosystems.
Covering more than 31 percent of the U.S., rangelands are any wilderness or rural open space grazed by domestic or wild herbivores, including grassland, shrubland, and pasture. Rangelands provide a wide array of ecosystem services, including food for livestock, habitat for wild species, and climate regulation through the uptake of carbon dioxide (CO2) by growing plants and the transfer of this sequestered carbon into the soil (as soil organic carbon). Globally, rangelands store 20 percent of the world’s soil organic carbon and U.S. rangelands may have the capacity to offset 2.5 – 3 percent of U.S. CO2 emissions from fossil fuels, but only if the rangelands are considered in “full health”.
The capacity for rangelands to sequester carbon is increasingly threatened by drought and overgrazing and there is an urgent need for improved land use planning to tackle these issues. However, the lack of an integrated monitoring system makes it difficult to know what changes to land management are needed on the individual ranch scale.
An important first step, then, to fostering healthy rangelands is establishing an open-access region-wide range monitoring platform that ranchers can use to verify and track changes in rangeland ecosystem condition and carbon storage across entire land units. Large-scale monitoring for these indicators will make it clearer where land is being effectively managed, and where it is not.
Dr. Jennifer Watts focuses on how climate change and human disturbance are affecting vegetation, soils, and the carbon cycle. She and her colleagues are currently working to develop a monitoring platform to provide stakeholders access to land health information.
“Having free, easy access to long-term information about lands will empower us to become fully aware of how our land use is impacting the health and future of rangeland ecosystems,” Dr. Watts explains. “This gives us the ability to invest in alternative management approaches that provide a more sustainable future for our lands while protecting our communities and ecosystems in the face of climate change.”
Reward systems can then be established across different scales to incentivize land use that improves ecosystem services. Monitoring platforms can be used in conjunction with clear land management directives to ensure rangelands are managed in a way conducive to ecosystem health.
Overgrazing is one of the biggest drivers of rangeland carbon loss and land degradation. It not only undermines the carbon storage potential of rangelands but also compromises other ecosystem services and limits future grazing capacity for livestock and wildlife. Consequently, it is in the best interest of everyone–ranchers, conservationists, Indigenous groups, and recreationists–to ensure that grazing on rangelands is managed in a way that increases vegetation cover, diversity, and rooting depth, while minimizing bare ground. Grazing practices can be addressed through process-oriented approaches.
Practicing management intensive grazing could help limit overgrazing. This adaptive technique involves concentrating grazing animals in one place for a very short period of time and then moving them to a different location. This ensures that the ecosystem has a chance to recover and regrow following a concentrated period of grazing. Ranchers will need technical assistance to develop grazing and management plans. Given that this is a practice under the Environmental Qualities Incentive Program (EQIP) it is likely to receive a boost in funding from the 2022 Inflation Reduction Act. Building more programs, at the federal, state, and county level, that reward ranchers for shifting grazing techniques to those that support the sustainability of ecosystem services and provide equipment needed to support fencing and water distribution could be a way to incentivize more effective land management.
Manipulating grazing fees to more accurately represent the costs associated with maintaining the integrity of rangelands is another option for fostering healthier rangelands given the current low fees and stagnant pricing of grazing fees. Furthermore, revenue generated from increasing grazing fees on public lands could be used to support a monitoring system for all U.S. rangelands.
Most stakeholders agree that better rangeland monitoring, soil health, and payment for land improvements are important, but a big question is how to actually pay for these services across multiple levels of governance. Exploring how to leverage different options for funding, then, will be the necessary next step in supporting thriving rangeland ecosystems and reaping the potential climate benefits.
At age 12, Woodwell Assistant Scientist, Dr. Jennifer Watts was accustomed to black dirt—the rich, wet, crumbling, fertile stuff she dug through on her family’s hobby farm in Oregon. But after moving with her parents and siblings to a roughly 224-acre dairy farm in Minnesota, all she saw around her was light brown, dry earth.
“A lot of the farms around us were a mix of dairy farms and really intense cropping rotations of corn and soybean,” Dr. Watts says. “And I started to notice, where there was tillage, how depleted the soil looked.”
In the United States, farmland covers more than 895 million acres (an area larger than the size of India), and it has a proportionately massive footprint on the environment. Intensive agriculture pulls nutrients out of the soil and doesn’t always return them, converting natural grasslands into monocultures and releasing large amounts of stored carbon in the process.
But what Dr. Watts saw throughout a childhood spent tending to her family’s farm, was that changing the way agricultural land is managed can sometimes reverse those impacts. In converting their cropland to pasture, to support an organic, grass-based dairy farm, Dr. Watts and her family stumbled upon the principles of regenerative agriculture. A practice that can produce food in a way that works with the ecosystem, rather than against it, and has implications for climate mitigation as well.
“It became, for me, an unintentional transformative experiment that my family conducted on our farm,” Dr. Watts says. “By the time I graduated high school, our lands were so lush and green. It was a healthy, productive, diverse ecosystem again.”
When Dr. Watts talks about her father’s idea to move to central Minnesota and start a dairy farm, she calls him a “rogue.” Originally from Alaska, he intended to work in fisheries, but had to change course after a cannery accident. Searching for something that would allow him to still spend his days outside, he settled on farming.
From the beginning, the Watts’ farming practices were considered unconventional in their rural Minnesota community. Firstly, they planted wild grasses and legumes like clover and alfalfa. Then, they left it alone. No tilling in the springtime alongside their neighbors; they simply let the plants establish themselves and moved the cattle frequently (with the help of a cow dog named Annie) to avoid overgrazing.
“After the first couple of years, I started noticing we had a lot more biological diversity in our fields, relative to our neighbors. We had a lot more bees buzzing, and butterflies, and we were popular with the deer and ducks,” Dr. Watts says. A few more years, and the soil started becoming dark and earthy-smelling again, like the soil she remembered from Oregon.
What was happening on their “rogue” dairy farm, was a gradual, partial reclamation of a lost grassland ecosystem— one that used to stretch across the midwest United States and was tended by native grazing species like bison or elk. Grazing plays a major role in cycling nutrients back into the soil, building up important elements like carbon and nitrogen. The near extinction of bison and the proliferation of monoculture cropping have broken this cycle—but cows have the potential to fill the gap left by ancient grazers, re-starting that process. Simple adjustments to management techniques, like lengthening time between grazing a pasture, can give the land time to recover.
This also has implications for how we combat climate change—a term Dr. Watts wasn’t familiar with until later in high school, when family trips back to Alaska revealed the glaciers she loved to visit were shrinking.
“Seeing the glaciers was our favorite thing to do with my grandma, but they were beginning to disappear. And one year, suddenly, I noticed these informational panels along the walk exiting the National Park talking about this thing called climate change,” says Dr. Watts.
Dr. Watts was also seeing another pattern emerge on the farms in her midwest community. Water was becoming a little scarcer. Many of the farms around her family’s had begun investing in irrigation—something that was previously unnecessary, and remained so for the Watts’ farm. Their rich, black soil held onto the water for longer.
As she grew up and (with the help of a pre-Google web search over dial-up internet) charted a course for her career as an ecologist, Dr. Watts began to study the science underlying these patterns she was noticing, and connected them to climate change.
Growing plants draw carbon from the atmosphere. When plants die and decay, some of that carbon is released to the air to be drawn back down again by a new season of growth, while some is stored away as organic matter in the soil. Over centuries, this process forms a stable sink of carbon on the land. Regenerative grazing—the way the Watts family did it—stimulates more plant growth to keep this cycle turning, while overgrazing or removing grazers entirely can halt the process, allowing for erosion, less healthy root systems, and the degradation of the carbon sink. In the U.S., rangelands have historically contributed more to the depletion of soil carbon, but Dr. Watts’ research with Woodwell has demonstrated that, with proper management, rangelands and other agricultural lands have the potential to contribute positively to the climate equation again.
For the past two summers, Dr. Watts, alongside the Woodwell Rangelands team and collaborators, has driven across the western U.S. to collect biomass and soil samples and measure carbon flux from working ranches and federal grazing leases in Montana, Colorado, and Utah. These measurements will help calibrate a new satellite remote sensing-informed model that can track how much carbon is being stored on grazing lands. The model will be hosted on the Rangeland Carbon Management Tool(RCMT) platform—a new web application she and researchers at both Woodwell and Colorado State University are developing to give land managers access to carbon and other ecosystem data for their lands.
The idea is that, with a tool like this in hand, ranchers can account for carbon dioxide flowing into and out of the rangeland ecosystem, and track how this changes over time in response to land management adjustments. It will also show changes in correlating ecosystem metrics like plant diversity and productivity, as well as soil moisture—two things that are crucial to maintaining a healthy and economically viable range. With this information, Dr. Watts and colleagues hope to encourage a regional shift in ranch management strategies that protect and rebuild stores of soil carbon, while providing ranchers with essential co-benefits.
Dr. Watts has been working with Jim Howell, owner of sustainable land management company Grasslands LLC, to connect with individual ranchers and discuss how a tool like this could help their operations. Though ranchers can be a tradition-bound group, Dr. Watts says seeing data that confirms their anecdotal experiences of hotter winters, drier summers, longer droughts, and other climate-related changes has opened them up to making changes.
“There are so many times when we just see the ‘aha moment’ in the manager or the land owner’s face, because they’re suddenly able to see these patterns from a very different perspective,” says Dr. Watts. “Most people, we have strong memories, we know that something’s different, but to be able to show that through data and not only memories—it’s so powerful.”
In addition to ecosystem co-benefits, storing carbon on rangelands could have direct economic benefits for ranchers as well. The RCMT will provide baseline data that could be used to verify credits within a voluntary soil carbon market. Rangelands historically haven’t been included in carbon markets because of gaps in monitoring data that the RCMT will help fill. The data could also be useful for local or state governments setting up payments for ecosystem services schemes in their region that would provide money directly to ranchers in exchange for storing carbon on their lands.
Of course, cattle aren’t without their complications, and ranching practices are just one element of a global meat and dairy industry that contributes to 15 percent of global emissions. But Dr. Watts’ roots as a dairy farmer make her enthusiastic about the possibilities this solution holds to both mitigate emissions and keep an important American livelihood resilient as climate conditions change.
“It’s just one aspect in this really complicated global system,” says Dr. Watts. “But if we manage our ecosystems better, building more intact environments where we can, this can sequester more carbon while restoring ecosystem health and productivity. It’s not the solution, but it is a solution that can benefit our planet while supporting rural communities.”
“Talk to Jim. Jim knows everything.”
That’s what everyone told Woodwell Assistant Scientist, Dr. Jennifer Watts, when she started writing up a research plan to study soil carbon on U.S. rangelands. “And indeed, he does,” Dr. Watts says. “He knows everything about the region, about grazing management, species management, anything having to do with land management on these ranches.”
With his felt Stetson, dusty jeans, and perennial tan, ranch manager Jim Howell looks a bit like the kind of cowboy Hollywood might dream up. And in a way he is—despite looking at home on the range, Howell grew up in Southern California. But he spent his summers out in Colorado’s Cimarron mountains, working on his grandfather’s cattle ranch.
Those summers were Howell’s introduction to the idea that the way livestock are managed can change their impact on the land—a thread that would pull him through a college degree in animal production, towards a career “knowing everything” about holistic ranch management. He was first clued into this concept while walking the fence line separating his family’s property from a patch of public land being used to graze sheep.
“I noticed there were lots of very healthy, perennial, bunch grasses on the sheep side, while our side of the fence had degraded to mostly silver sagebrush, Kentucky bluegrass, and dandelions,” says Howell. “And I just didn’t understand why the differences were so stark.”
Howell’s cattle were stocked continuously on the land, low in number but able to graze year round, while the sheep grazing permit required rotation. There might be a great flock of sheep up there one day and nothing but grass for the remainder of the year. That difference, it turned out, dramatically altered the kinds of plants that could flourish on the land.
“I became aware then that the way that we’d been managing our cows in our country up there was leading to its slow, long-term, ecological degradation. And I didn’t know what to do about it,” says Howell.
There have always been animals grazing the American West—before colonizers, even before native peoples. On the Great Plains there were bison; in the mountains and high altitude deserts of Southwestern Colorado, it was bighorn sheep and pronghorn antelope, as well as elk and mule deer. All three are rare sights now, with populations decimated by overhunting and habitat degradation.
Now, if you see any animal grazing on these ranges, it’ll probably be cattle.
Despite displacing native species, cows can still fill a natural niche in the rangeland ecosystem. Antelope, bison, sheep, and cows all belong to a group of animals called ruminants—animals that can digest grass. Many grasslands have co-evolved with ruminant species; their roaming feasts influence plant growth the same way pruning might affect the shape of a tree. Occasional shearing by a hungry cow stimulates new grass growth. It also creates a more competitive environment that supports a diverse array of plant species.
Grazing also plays a part in cycling nutrients and storing carbon in the soil. In a frequently dry climate like this one, digestion breaks down plant matter much faster than it would decay in the environment. Manure fertilizes new plant growth and returns carbon to the soil. Let this process continue unencumbered for a couple hundred thousand years, and you can build up a valuable carbon sink. And as long as the number of cattle isn’t rising, the oft-cited methane emissions from cow burps are minimal and cycled back down into the plants that grow up after grazing.
Since settlers arrived, however, the land has been put through centuries of abuse. Public lands were, for a long time, left open to unregulated grazing. Many rangelands have been over-stocked and grazed too frequently in order to make a profit and meet growing global beef demand. Land has been ecologically degraded, valuable topsoil was lost, and carbon stores declined as a result.
It would be easy to blame cows for this. But really, they’re not behaving much differently than pronghorn or bison would. They eat what’s in front of them. And they eat the tastier plants first. Howell likens it to a salad bar.
“If you go into a salad bar and there’s some lettuce that has been sitting there for three months, and some of it that’s just been replaced that morning, you take the new stuff. So that’s exactly what the cow does,” Howell says. “If she’s not made to move anywhere new, she’s just going to keep coming back and grazing the regrowth of the good stuff as long as it’s there.”
Pretty soon, perennial grass species, important for their deep roots that help prevent erosion and store carbon and water longer, are grazed into nothing. All that’s left are the sagebrush, dandelions, and other less desirable plants that Howell noticed dotting his family ranch.
“So the whole thing is about how the cows are managed, it’s not the cow itself that is a problem,” says Howell.
But if bad management can degrade the land, then good management should be able to restore it. While studying animal science in college, Howell encountered the concepts of “holistic management”, a term that began to decode this relationship between management practices and the health of the land. Controversial at its introduction a half century ago, holistic ranching has been gaining traction, and Howell and his ranch management company, Grasslands LLC, have helped urge its uptake.
The core principle is to make management decisions that restore lands and keep cattle in balance with the rest of the ecosystem—helping them fill the niche of the ancient grazers. This comes with a host of co-benefits, including water retention and higher plant productivity, that actually end up improving economic profitability for ranches in the long run. Simple adjustments, like lengthening the time between grazing a pasture again and wintering cows on native ranges instead of hay, can turn cattle from an ecosystem destroyer to an ecosystem helper.
“The trick is to let the cows do all the hard work,” says Howell.
Dr. Watts and Woodwell Senior Scientist Dr. Jonathan Sanderman, along with Dr. Megan Machmuller of Colorado State University, are interested in quantifying those co-benefits. Especially carbon storage.
“In the western US on our rangelands, just like in our croplands, we can change how we manage in a way that potentially could become a natural climate solution,” says Dr. Watts. “One where we’re bringing in more carbon than we’re emitting and we’re creating ecosystems that not only are beneficial for carbon sequestration, but also have more biodiversity, offer more habitat for wildlife, and more water conservation.”
In order to prove that value however, scientists need a baseline understanding of how much carbon is currently stored across both traditionally-and holistically-managed rangelands. It’s hard to get an estimate for such a large area (roughly 30% of the U.S. is covered with rangelands), so they are using a remote sensing model, which they verify with strategic on-the-ground sampling.
Howell’s work also created the perfect conditions for the research team to study the long term carbon benefits of altered ranching practices, which is a tricky thing to test empirically. Ranchers must constantly adjust their management techniques to stay profitable.
“In a classical research setting, you try to control all the variables but one, but in real life that’s not what happens,” says Howell. “Nothing is controlled. Day to day, you have to adapt to constantly changing conditions.”
But the ranches Howell’s company works with make those day-to-day decisions based on the principles of holistic management, so tracking carbon on those ranches over time offers the opportunity to generate baseline data on how they differ from more traditionally managed ones.
Howell also brought the expertise of a life spent on the range. He can identify just about any plant growing in the pasture, tell you which are native, which are invasive, and which used to be the preferred food of prehistoric ground sloths. His eye is trained to see diversity even in martian-esque deserts and read the history of the land in the structure of the soil. In May of 2022, Howell guided Drs. Sanderman, Watts, and Machmuller and their teams on a sample collection trip through Southwest Colorado and Utah. The researchers took soil cores, plant samples, moisture and temperature readings, and analyzed carbon fluxing in and out of the pasture.
The ultimate goal is to create a rangeland carbon management tool that will make the soil carbon data model accessible directly to ranch managers. Dr. Watts hopes having that data in hand will enable more ranchers to make management decisions with climate in mind. Dr. Sanderman also notes that it could be useful in eventually helping ranchers get paid for sustainable practices.
“Rangelands haven’t been included in voluntary carbon credit markets like cropping systems have,” says Dr. Sanderman. “Monitoring is a big problem because there’s so much land—How do you keep track of all that? That’s what our tool will be able to offer.”
There are limits to what grazing can accomplish, though. The lands out west aren’t suitable for large-scale cropping, being too dry or too mountainous, which makes them perfect for cattle. But when the animals take up space on land that would otherwise be used to produce crops—or worse, penned into feedlots—their benefits are compromised. Howell also notes that some grazing lands are already as saturated with carbon as they can be. And there remains the fact that ranching will get more complicated as the climate changes.
At the Valdez ranch in Delta, Colorado, Dr. Sanderman and research assistant Colleen Smith unfold a collapsible table in a field of cracking mud, dotted with the brittle stick skeletons of dead grass. Nearby, Dr. Machmuller is assisting Howell in extracting a long metal cylinder from the ground. It was plunged into the soil by a hydraulic corer attached to a pickup truck that’s idling in the field. Howell and Dr. Machmuller lay it out horizontally on the table and slide out the soil core—a 50 centimeter long history of the land beneath their feet.
Howell breaks open a section of the core with his fingers, revealing clusters of white crystals. This is a pasture that has been abused; over-irrigation by previous owners brought salts to the surface. Now nothing will grow here and wind gusts threaten to blow away loose topsoil. It’s a sacrifice zone. The current owners are considering installing solar panels instead.
Water is a big issue for ranchers and it’s threatening to get bigger. The region is constantly dipping in and out of severe drought, and in a place that depends heavily on winter snows for its groundwater and rivers, a warmer, drier climate is a threat.
Agriculture will depend more on irrigation as the climate warms and precipitation patterns change. But this empty pasture is proof that it’s not always a viable solution, and will become less so as climate change advances.
It enforces the urgency of the work Howell and team are doing. The faster we can draw carbon out of the atmosphere, the more successful these ranches are likely to be in the long term. The better managed the ranch, the more resilient it will be in the face of tough conditions.
In the end, Dr. Watts says, the outcome rests in the hands of ranch managers—people like Howell.
“Land managers are the ones that ultimately are going to make or break this country.”
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.
It’s a windy morning in May and the Valdez ranch in Delta County, Colorado is alive with the sounds of lowing cattle, chattering sparrows, and the whirrs and clanks of scientific equipment. This particular field is not being grazed at the moment, so Woodwell’s soil carbon team has free rein over the rows of alfalfa and sweetgrass.
In collaboration with Dr. Megan Machmuller at Colorado State University, Assistant scientist Dr. Jennifer Watts and senior scientist Dr. Jon Sanderman have brought their teams here to collect field observations that will help inform a comprehensive model of carbon storage on rangelands across the United States. Grazing lands have the potential to be a valuable carbon sink, provided the livestock on them are being sustainably managed, but the true magnitude of that value is not yet well understood. Developing a regional model of the way carbon moves through rangelands will deepen our understanding of the role they play as a natural climate solution.
Ensuring the model’s accuracy requires the team to collect an array of field data from different ranch types—from irrigated and planted pasture, to the natural vegetation of high mountain and desert grazing lands. Here’s how climate scientists study carbon in the field:
Soil carbon storage begins where plants interact with the air. As they grow, plants draw carbon out of the atmosphere through photosynthesis. When they decay, microbes in the soil digest plant matter and breathe carbon dioxide and methane back out. Measuring the difference between these two processes gives us “net ecosystem flux”—a measure of whether a patch of land is sequestering or emitting carbon overall.
Measuring carbon flux requires a specially made chamber. Dr. Watts and Seasonal Field Technician Jonas Noomah employed a plexiglass contraption that Noomah constructed himself. The chamber is placed over a patch of ground, connected by clear tubes to a machine that can analyze the volume of CO2 within the cube. A handheld fan dangles inside the box to keep the air circulating. The transparent plexiglass allows photosynthesis to continue unhindered. After a few minutes, the box is covered to block out the light and the analysis is run again to capture emissions without the photosynthesis component. The numbers can be compared to assess the rate and overall carbon sink or source status of flux within the ecosystem.
While plants are growing, they lock away carbon as part of their leaves, stems, and roots, so another important metric in the carbon model is plant productivity—more productive plants with established root systems are more likely to store more carbon belowground.
Productivity can be estimated with satellite imagery, but needs to be validated with on-the-ground measurements. Postdoctoral researcher Dr. Yushu Xia and research assistant Haydée Hernández-Yañez walked transects of pasture to collect data on a variety of indicators that could influence aboveground (and belowground) biomass, including height of vegetation, soil moisture, and temperature. Then the scissors come out and all the plants in a plot are cut and put into a labeled paper bag to be weighed and analyzed later in a lab to determine the total mass of plant matter.
Rangelands managed for better carbon storage also come with a host of co-benefits, including higher levels of plant diversity. Different plants cycle carbon and other nutrients at different rates, so Hernández-Yañez sifts through the vegetation before it’s snipped, identifying and recording the species to provide more detail in productivity estimates.
Over time, carbon passes out of the cycle of growth and decay, becoming locked underground as soil organic carbon. Accessing and analyzing soil organic carbon requires coring deep into the earth and pulling out a stratified cylinder of dirt. Dr. Machmuller led the team’s soil coring effort along with Dr. Sanderman and research assistant Colleen Smith.
With a hydraulic soil coring machine attached to the back of a pickup truck, the team rambled through muddy pasture and over sharp bushes to collect 50 centimeter cores. When the terrain was too steep, they pulled out a handheld corer that had to be driven into the soil with a sledgehammer.
The soil cores are separated into three sections and crumbled up. Smith then uses a handheld scanner that employs the same technology used by astronomers to determine the chemical makeup of distant star systems to read the carbon content of each section. The scanner bounces light off the soil particles and the pattern of reflection gives clues to what molecules are present at different depths. Abundance of carbon is sometimes obvious to the naked eye in the cores, showing up as darker, wet sticky soil.
Drs. Watts and Sanderman and their team are in the process of creating a rangeland carbon management tool that will make the soil carbon data model accessible directly to ranch managers. The website, developed by Dr. Xia, will generate data on carbon and plant productivity, for any geographic area down to the size of a single pasture. The hope is that the tool could be integrated into land managers long-term decision making, and show the results of adapting to more holistic, sustainable management practices over time.
“In the western US on our rangelands, just like in our croplands, we can change how we manage in a way that potentially could become a natural climate solution,” says Dr. Watts. “One where we’re bringing in more carbon than we’re emitting and we’re creating ecosystems that not only are beneficial for carbon sequestration, but also have more biodiversity, offer more habitat for wildlife, and more water conservation.”
Demonstrating the co-benefits of managing rangelands for carbon will also help expand conversations about whether ranching can be done sustainably, from the ground up.
“It allows for transfer of climate solutions into the hands of practitioners who may not otherwise think about climate change. It opens the conversation.” says Dr. Watts.
Ultimately, having that data could be useful for rangeland managers taking part in carbon credit markets, which could help them get paid for sustainable management.
“Rangelands haven’t been included in voluntary carbon credit markets like cropping systems have,” says Dr. Sanderman. “Their monitoring is a big problem because there’s so much land. How do you keep track of all that? That’s what our tool will be able to offer.”
A recent study, published in Proceedings of the National Academy of Sciences (PNAS), has quantified the unrealized potential of land-based carbon storage. A series of maps shows that both plants and soils have the potential to store 287 billion metric tons more across the globe— more than the current annual emissions of the European Union.
“From forests to soils, terrestrial ecosystems store enormous amounts of carbon globally, and are capable of storing even more,” said Dr. Wayne Walker, Carbon Program Director at Woodwell Climate Research Center and study lead author. “But realizing the untapped potential of land to aid in addressing the climate crisis means understanding how much storage space is available, where in the world that space is located, and what actions can be taken in those places to take advantage of the opportunity they offer as rapidly as possible. This study provides the data and conceptual framework for doing that.”
These findings reveal the significant potential for expanding land-based carbon capture globally through protection, restoration, and improved management of forests and other woody systems. Improved management of existing forests alone may offer more than 75% of the untapped potential, with the vast majority (71%) of it concentrated in tropical ecosystems.
“Forest stewardship represents the greatest opportunity for realizing carbon removal and storage in the near term, and the urgency of the climate crisis demands that we prioritize these efforts,” said Peter Ellis, Director of Natural Climate Solutions Science at The Nature Conservancy and study co-author. “Our research shows that after safeguarding lands required for food production and human habitation, improved management of forests and other woody systems — particularly degraded forests across the global tropics — offers tremendous climate mitigation potential.”
The study is timely, coming on the heels of the Intergovernmental Panel on Climate Change (IPCC)’s Working Group III’s latest report, which focuses on the urgent need to reduce carbon emissions in order to limit future warming, and highlights the significant mitigation potential of natural and managed ecosystems given the opportunity they offer to remove additional carbon from the atmosphere. While study results point to the significant opportunity that land offers as a natural climate solution based on what we know now, this work cannot stop there. Future research should build off these findings to support development of policies that take full advantage of the available land-based carbon sink.
“We anticipate these findings will prove valuable for many countries, since natural climate solutions figure heavily in delivering Paris Agreement commitments in most countries. However, these results must be combined with a range of other information to prioritize and effectively implement natural climate solutions.” said Bronson Griscom, Senior Director of Natural Climate Solutions at Conservation International.
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.