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New ways to save endangered habitat

March 24, 2021

Oak savanna has lost over 99% of its historic range—how can we restore this imperiled ecosystem? Graduate researcher Austin Yantes introduces a project that is looking into silvopasture as a potential solution, and explains how partnering with Extension gives this fix a fighting chance.


I stumbled into the world of ecological restoration almost entirely by chance. During my freshman year of college I met a researcher in need of fieldwork help, and before I knew it, I was out working in restored wetlands. I had been looking for a way to get my feet wet in the research world; suddenly there I was, standing in boot-deep water with very wet feet. 

Our mission that summer was to look for rare and threatened species of plants, comparing data between wetlands that had been historically drained and plowed, and those that had not. The results were startling—we never found rare plant species in areas that had been plowed, even if the plowing ceased a century ago. That meant once these plants were gone, they didn’t come back. This troubling pattern of disturbance leading to long-lasting change is found in many other plant communities, including oak savanna.

A rare and imperiled ecosystem

Oak trees amid prairie grasses and flowers on a sunny day
This oak savanna at the Sherburne National Wildlife Refuge has the classic structure of large-canopied, well-spaced oak trees dotted among prairie grasses and wildflowers.

Oak savannas are a unique plant community characterized by a prairie-like ground layer dotted with large, widely-spaced oak trees. Oak savannas are highly biodiverse, often harboring over 300 species of plants, more than are often found in either prairies or forests. 

Savannas also provide habitat for game animals such as wild turkeys, and many bats, birds, reptiles, amphibians, and insects that are currently threatened or in decline. Moreover, certain species like the red-headed woodpecker and Karner blue butterfly are restricted to oak savannas and cannot persist without them. 

In spite of the importance of oak savannas, they have all but disappeared. Throughout history, the existence of oak savannas depended on frequent fires lit by Native Americans or started by lightning, and on grazing by animals like bison and elk. After European settlement, oak savannas were lost due to the removal of fires and large grazers from the landscape, as well as agricultural and urban expansion. As a result, less than 1% of the original 32 million acres remain, making oak savannas one of the most imperiled and rare plant communities in North America.

Is silvopasture the answer?

Cows in a densely vegetated forest
Cows were brought into the research plots at Sherburne National Wildlife Refuge for managed grazing. Researchers are measuring their impacts on vegetation, wildlife, soil and water.

The small number of oak savanna acres that persist today have largely transitioned into woodlands, which are often dense and scrubby. To restore these woodlands back to savanna, the first step is to reintroduce burning. However, fire isn’t always effective as a stand-alone tool, which has pushed restoration practitioners to start experimenting with the reintroduction of large grazers as a secondary approach. Silvopasture, the practice of intentionally combining livestock with the intensive management of trees and forage as one integrated practice, has been successfully used to restore environmental and economic functions of oak savannas around the world. However, its potential has not been assessed in Minnesota. That's where our research project was conceived.

Our team is using Sherburne National Wildlife Refuge as our primary research site to assess the effects of silvopasture as an approach to restore oak savanna ecosystems in Minnesota. At Sherburne, oak savanna restoration via burning has been ongoing for many years, but only recently were cattle brought in, so their impact is largely unknown.

When we started, the vegetation beneath the oaks was dominated by extremely dense shrubs—a far cry from the open, prairie-like structure that savannas should have. Through targeted grazing, we hope to suppress the overgrown shrub layer, and increase the abundance of grasses and flowering species. This shift in the vegetation structure should in turn improve the habitat quality for pollinators and other wildlife. 

A woman checks scientific equipment in a field
Graduate research assistant Austin Yantes checks equipment at one of her research plots at the Sherburne National Wildlife Refuge.

We are tracking our progress through multiple vegetation surveys, which will tell us if shrub density is decreasing and if grass/flower abundance and diversity are increasing. We are also conducting butterfly, bird, reptile, and amphibian surveys to ensure the cattle aren’t having negative impacts on the wildlife community. Lastly, we are taking water and soil samples to assess any changes due to grazing. We do not expect our grazing approach to cause a decline in water quality or soil health; in fact, we hope to see an improvement in soil health. 

Our research project is unique because we care about not only restoring oak savanna vegetation structure, but also maintaining or improving all other aspects of the ecosystem. This holistic approach will give us a deeper understanding of whether or not silvopasture can be an effective oak savanna restoration tool.

Reaching and teaching landowners

While we are conducting our research on federal land, a large portion of former oak savanna in Minnesota exists on private land as unmanaged wooded pasture. Could the introduction of managed grazing in those wooded pastures help with restoration efforts? More importantly, would we be able to achieve adoption of this approach by landowners? Throughout my previous work, both at the Bureau of Land Management and in restored wetlands, I have witnessed over and over that farmers and ecologists were at odds with one another. But by using livestock grazing to achieve oak savanna restoration goals, I believe our approach begins to reconcile a long-standing divide between agricultural and ecological systems.

Another way we strive to bridge this gap is by placing equal emphasis on both research and outreach. In addition to the work we are doing in the field, Extension educators Gary Wyatt and Jeff Jackson, as well as other project partners, are working to scale up the use of silvopasture for oak savanna restoration through the development of the Silvopasture Learning Network, which provides educational programming, facilitates peer learning and promotes volunteerism to expand natural resource conservation.

Hundreds of farmers, natural resources professionals, conservation volunteers and advocates have joined the network in order to learn more about restoring oak savanna through silvopasture, including the research we are doing at Sherburne. I am excited to see how another year of managed grazing impacts the project site as we ramp up for our next field research season. And with help from Extension educators sharing information about our research through the network, I'm hopeful we'll soon see similar impacts of silvopasture on farmsteads across the state.

The Silvopasture Learning Network promotes silvopasture to improve soil health, water quality, and restore oak savanna in Minnesota. This project is a joint effort led by University of Minnesota Extension with the Sustainable Farming Association and Great River Greening, with funding provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).

Austin Yantes, University of Minnesota graduate research assistant, with Emily Dombeck, Extension natural resources program and communications coordinator.

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