Ask an Expert | Dr. Dirac Twidwell: Saving the Last Grasslands

Nebraska’s Sandhills, one of the largest intact grassland regions on the planet, according to research from Dr. Dirac Twidwell. Photo: Dillon Fogarty

In this Ask an Expert, Dr. Dirac Twidwell, Natural Resources Conservation Service (NRCS) Working Lands for Wildlife (WLFW) Science Advisor and Associate Professor at the University of Nebraska, outlines how to protect and conserve grasslands through conservation.

Dr. Twidwell is responsible for conserving grasslands on the Great Plains through science-backed efforts that span ownership boundaries. His research and publications have identified the largest remaining continuous grasslands in the United States and have outlined a ‘call to action’ to protect and preserve these invaluable biomes. Dr. Twidwell also runs the Large-Scale Rangeland Conservation Lab at the University of Nebraska-Lincoln, which focuses on providing a framework for ecosystem management across multiple states.

You recently co-authored a research paper called “The last continuous grasslands on Earth: Identification and conservation importance. What inspired you to identify the largest intact grasslands on the planet?

When Rheinhardt Scholtz, the paper’s co-author, and I first came up with the idea for this project, we were driving through the heart of the Nebraska Sandhills, discussing the unbroken horizon of prairie, and wondering how many other grassland regions in the world were still as intact as the Sandhills.

In the U.S., we are largely unaware of the large grasslands that persist today. It was rewarding to see the Nebraska Sandhills prairie and Wyoming Basin sagebrush-steppe emerge as two of the most intact and continuous grassland regions remaining on the planet.

Since the paper came out, I’ve heard from so many different people in both Nebraska and Wyoming who have shared their pride in these grasslands of global importance. That’s been pretty cool.

Tell us more about these two regions in the U.S. – what do they have in common and what makes them special?

Grasslands are the most converted, most threatened, and least protected of the world’s major vegetation types. To have two of this size in the U.S. is really special. It’s important to realize that only a few large and intact grassland regions remain anywhere on Earth.

Global grasslands of importance. Figure 2 from Twidwell’s recent paper.


Beyond that, they both host amazing wildlife populations. Wyoming sagebrush-steppe has the largest pronghorn migrations in the world, and the state hosts the U.S.’s largest population of sage grouse. Nebraska’s Sandhills are a critical migratory stopover for sandhill cranes and other birds. It’s awesome that these landscapes still support such large-scale animal migrations.

Finally, the people who live in these regions have played a big role in keeping them intact and productive for wildlife and humans. Grazing is the common thread that has helped keep these regions intact. The people who live in these regions recognize and value the wide-reaching benefits that large and intact grasslands provide, and they have worked together to perpetuate them. Conserving these lands benefits everything that grasslands support, from ranching cultures to some of the largest animal migrations on the planet, and these communities understand the importance of doing so.

What are the biggest threats facing these grasslands?

Land use conversion and woody encroachment are the two primary drivers of native grassland loss in the U.S. Image: NRCS/WLFW

The two biggest threats facing grasslands globally are industrialization, coupled with commercial row-crop agriculture, and afforestation (planting trees in treeless ecosystems, which leads to woody encroachment). These threats are primarily responsible for global grassland losses this past century. These two regions, however, have escaped the major threats responsible for global grassland losses, thanks, largely, to local communities who support grassland culture.

Unfortunately, in the Great Plains, woody encroachment and land use conversion are now occurring at the same rate, so it will be important to prioritize conservation investments in these two regions, prevent land use conversion and woody encroachment, and avoid the collapses that have been observed elsewhere.

In addition to the “Last continuous grasslands on Earth” paper, you also recently co-authored a paper expanding on a rangeland conservation strategy called “Defend the Core.” Explain what “Defend the Core” means?

At its most basic, the Defend the Core strategy shifts rangeland management from reactive, piecemeal efforts to proactive and preventative efforts. For example, instead of focusing our time and limited conservation dollars on treating areas that have already transitioned to a woodland state, we focus on preventing treeless cores from being taken over by trees in the first place. It’s more economical and effective to prevent trees from establishing than it is to remove them once they’re present. New spatial technology allows us to “see” these cores and prioritize them for management in ways we’ve never been able to do before.

Importantly, Defend the Core is a three-part strategy. First, we “Defend the Core,” then we “Grow the Core,” and then we “Mitigate Impacts” in places that have already transitioned. By incorporating all three elements into our work, we can keep intact cores healthy and tree-free, expand the size of those cores, and help communities and wildlife adapt to areas that have been impacted by trees.

The “Defend the core, Grow the core, and Mitigate impacts” strategy focuses on preserving intact cores of native range before they’re lost to woody encroachment or other threats. Once protected, those cores can be expanded. Impacts from already-degraded areas can be managed and mitigated as part of the strategy. Image credit: NRCS/WLFW


How is the “Defend the Core” strategy being applied in the Great Plains?

The Defend the Core strategy is helping refocus the vision for conservation in the Great Plains. For decades, grassland conservation has been reactive and has failed to prevent large-scale collapse. That said, there are still large, intact grassland cores like the Nebraska Sandhills that should be preserved throughout the Great Plains. Doing so requires re-orienting how we defend some of our iconic grassland regions from 21st century global change pressures, and while that re-orientation is happening, it needs to be accelerated. So, right now, I would say the strategy is being applied as “Defend the Core – lite.”

With your leadership, the University of Nebraska partnered with several public universities and other groups to produce a new guide for addressing woody species expansion in the Great Plains called:  “Reducing Woody Encroachment in Grasslands: A Guide to Understanding Risk and Vulnerability”. How would you summarize the approach outlined in the guide?

Twidell played a major role in developing this guide for reducing woody encroachment in grasslands, leveraging the best science, practices, and new spatial technology to craft a 21st century approach to preventing grasslands from converting to woodlands. Click image to read the Guide.

Our past approaches to conserving grasslands in the face of woody expansion have put land managers, producers, and anyone involved in rangeland management in a no-win situation. Because we focused almost exclusively on clearing trees and brush, we never addressed the underlying ecological processes that drive expansion – seeds. Simply clearing trees without also eliminating the seed source just meant that trees regrew in the same places we removed them.

The guide does a few things differently. First, it provides a holistic strategy that focuses on vulnerable grasslands by cutting off the biological mechanism that allows trees to expand – seeds. It focuses on managing the ecology of the problem and not just the problem itself.

Second, it recognizes the scale of this problem and provides solutions to work at that scale. For too long, we’ve focused on a single ranch or landowner, which is unfair and does little to prevent a biome-scale collapse. Woody encroachment isn’t just a local problem, it’s a biome-wide problem that requires a biome-wide approach. The guide was co-produced through partnerships with producers and landowner networks that are working at large scales (100,000 acres and more) and leverages what we’re learning from these efforts – what worked well and what didn’t meet our desired outcomes.

Finally, it shows what we can do to save our grasslands. By combining a strategy to cut off the underlying ecological process of woody expansion with good planning, informed by new spatial technologies, we can prevent a biome-wide collapse of grasslands.

Producing it was a major effort that brought in a lot of different partners – including federal agencies, university extension groups, producers, and landowner groups – all who all wanted it broadly distributed. At their request, we printed and distributed 19,000 copies of the guide to a diverse group of people engaged in grassland management. It is meant to be used, and we’re proud to have it in the hands of so many people.

You serve as a science advisor to the USDA-NRCS Working Lands for Wildlife (WLFW) efforts in the Great Plains. Recently, Kansas and Nebraska have launched the Great Plains Grassland Initiative and South Dakota and Oklahoma will be launching their state-based Great Plains Grassland Initiatives soon. How do these efforts fit into the big picture of WLFW’s vision for conservation solutions that benefit wildlife and landowners?

Simply put, these state efforts are absolutely critical. Working Lands for Wildlife is an approach to conservation that identifies key threats, produces science on how to address those threats, and promotes voluntary conservation solutions that benefit landowners and wildlife, but it doesn’t provide funding directly. Through the Great Plains Grassland Initiative, states are stepping up, adopting WLFW’s approach, and providing funding and resources for landowners to do work on the ground. The state-led Great Plains Grassland Initiatives are incorporating WLFW’s approach, leveraging WLFW’s science, and directly helping landowners and wildlife.

Not only do these initiatives align with the WLFW-produced Framework for Conservation Action in the Great Plains, they also align with the approach outlined in the guide, and with the broader Defend the Core strategy.

Importantly, there are a lot of other partners beyond USDA’s Natural Resources Conservation Service involved in the state-led Great Plains Grassland Initiatives. These state-level initiatives are part of broader efforts to conserve grasslands. For example, these efforts serve as the NRCS’s contribution to the Central Grasslands Roadmap, a broad collaborative effort to conserve grasslands from Mexico to Canada.

How important are working lands in the Great Plains, and by extension, to the state-led efforts to conserve healthy, resilient grasslands throughout this vast region?

Working rangelands in the Great Plains are North America’s contribution to global grassland conservation efforts. More than 90 percent of the Great Plains are privately owned, so working lands epitomize the region. There’s just no way we can conserve North America’s grasslands without working on private land.

If we fail to pull together and conserve the remaining grassland cores here in the U.S., we will likely lose the entire biome. That will cause a cascade of effects: collapsed rangeland production that will impact livestock and wildlife; reduced water supplies for people, industries, and agriculture; increased wildfire risk that will threaten people and property; increased threat of diseases like West Nile Virus and other insect-borne diseases; and reduced funding for social programs like school funding. I hate to be alarmist, but if we lose productive grasslands, we lose a lot of other benefits we’ve come to take for granted.

When grasslands transition to woodlands, a cascade of negative impacts affects plant, wildlife and human communities. Photo: Christine Bielski.


Given the importance of working lands to communities in the Plains and to global grassland conservation, are you seeing the rangeland profession in the U.S. stepping up to meet the challenge of conserving the Great Plains grasslands?

Yes! For the first time in my career, every group with a focus on grasslands is now scaling up the mission relative to what threatens the last big grassland regions. We’re seeing it from industry, wildlife groups, special interest groups, and the people who live and work in these regions. I feel like people are realizing grasslands are cool, which is a big shift from past attitudes. So, there’s a lot of attention focused on grassland conservation, and especially on large, intact grasslands, right now.

But a big question remains: Can we put all the other pieces of the conservation puzzle together and effectively conserve these large, intact grasslands before they transition to woodlands or crop agriculture? The type of attention and planning that is occurring now is just the first step. Collaboratives like the Central Grasslands Roadmap and federal agencies like the USDA’s NRCS are highlighting risks to grasslands and offering strategies for addressing them at scale. That’s huge. I do think that with these broad collaboratives, we’ll be able to conserve at least some of these large grasslands. I didn’t think that a few years ago. We’ve still got a long way to go, but I’m more hopeful now than I’ve ever been.

Loess Canyons, Nebraska

Healthy, resilient, treeless grasslands like these in Nebraska’s Loess Canyons, are possible if we pull together and address threats at landscape scales.

More Resources

Read the full Framework for Conservation Action in the Great Plains Grassland Biome here.

Download “Reducing Woody Encroachment in Grasslands: A Guide to Understanding Risk and Vulnerability” here.

Learn more about the Nebraska Great Plains Grassland Initiative here.

Learn more about the Kansas Great Plains Grassland Initiative here.

Read more about the Defend the Core strategy in the Great Plains.

Read about a broad effort in Nebraska’s Loess Canyons using prescribed fire to halt woodland transition and reclaim healthy native grasslands.

Learn more about the impacts of eastern redcedar on grasslands.