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.”
Rangelands occupy more than three quarters of global agricultural land. Many of the world’s native grassland ecosystems have been converted to grazing land for livestock, altering their ecology and changing the flow of carbon on the landscape. However, these lands still have the potential to be a powerful carbon sink if properly managed.
On September 27 and 28, Woodwell Climate Research Center convened a workshop in collaboration with Montana State University (MSU) and Turner Ranches to open discussions on rangeland management in the United States. The workshop took place in Bozeman, Montana, and brought together scientists, ranchers, and conservationists to share their perspectives on rangeland ecology, carbon sequestration, fire management, and herd health, as well as anecdotes from careers spent on the range.
“Montana offers a great location for this conversation because the majority of the state is amazing rangeland including unique grassland and sagebrush steppe environments, in many cases privately held,” said Dr. Stephanie Ewing, an Associate Professor at MSU who co-organized the event. “And because we have a strong academic and extension community at MSU that has been engaged with rangelands and rangeland managers over time.”
Day one began with a series of presentations and panels meant to facilitate discussion about rangeland management. Sessions covered rangeland ecosystem services, rangelands in the American West, management for carbon sequestration, carbon markets, and tools for rangeland monitoring.
For Dr. Jennifer Watts, Woodwell Assistant Scientist, the discussions highlighted the vast untapped potential of rangelands to play a positive part in climate mitigation.
“There’s so much rangeland in the western U.S. and so there is a huge potential for improving ecosystems and improving carbon sequestration and storage,” Dr. Watts said. “But the public doesn’t perceive rangelands with the same reverence that we do with forests or other ecosystems. I think if we start to value them at the national level, and realize the potential for ecosystem services and climate mitigation, that could shape how policy is going to move forward.”
The following day, attendees made site visits to two ranches in the area—Red Bluff Ranch, run by MSU, and Green Ranch, owned by Turner Enterprises—for a hands-on look at the topics they had discussed the day before. They examined soil pits, dug into the grass, and talked about different land management styles.
For Senior Scientist Dr. Jonathan Sanderman, the trip into the field was a catalytic moment in the workshop.
“After just a few hours on the ranches, I felt like a lot of people had lightbulbs go off about how long-term management has affected certain parts of land more than others, and how that feeds back to the soils,” Dr. Sanderman said.
One theme that emerged from the workshop was the need for more and better information on how rangelands could be included in carbon markets. While there was interest from landholders in participating, very few knew enough to get started. Drs. Watts and Sanderman hope future collaborations will allow them to dig deeper into the topic with ranchers.
“A well-functioning carbon market can provide climate benefits and an additional revenue stream, enhancing the economic resilience of ranching communities,” Dr. Sanderman said. “Quantifying and monetizing carbon sequestration from improved grazing management is still in its infancy. This means there is a lot of confusion and few agreed upon standards; but, it is also an opportunity to shape policies and design programs that benefit people and the environment.”
It also became evident that, while many ranchers were interested in carbon storage on their lands, what mattered more to them was the possibility of integrated benefits from holistic range management. Improving carbon storage in the soils can improve water management, nutrient retention, and other ecosystem services.
“Carbon is something that brings it all together,” Dr. Watts said.