Dr. Christian Hagen discusses his new research on mesquite trees, lesser prairie-chickens and how science can help inform the most effective places to invest restoration dollars.
Dr. Christian Hagen is a researcher and professor at Oregon State University and a science advisor to the Lesser Prairie-Chicken Initiative. Recently, Hagen was the lead author on a new study that analyzed lesser prairie-chicken’s use of habitat in New Mexico where mesquite trees have encroached on the bird’s grassland habitat. The study also analyzed how using a species like the lesser prairie-chicken as a bioindicator species can help land managers and others most effectively target habitat restoration that benefits multiple species of wildlife, including lesser prairie-chickens. We recently caught up with Dr. Hagen to talk about his latest research and what it means for restoration on the southern Great Plains.
Your study shows that lesser prairie-chickens avoid areas with “tall” structures like honey mesquite trees, but the reality is a bit more nuanced. Will you explain the impact trees have on lesser prairie-chickens?
The impacts are akin to a two pronged-fork. At low densities, these trees provide hiding cover or perches for predators that gives them undo advantage over the birds. In time, as the woody cover dominates the prairie, it chokes out the grasses and forbs that serve as the basis for habitat for the birds.
Are trees like the honey mesquite problematic to other species or to the southern Great Plains prairie ecosystem itself?
Yes, tree encroachment is big problem for all prairie obligate species. However, most of the research has focused on birds, and it shows significant effects on prairie birds in particular. Prairie birds, like the lesser prairie-chicken, are an avian community that has sustained some of the larger population declines in North America.
If mesquite trees are such a problem, why not just cut them all down?
It’s a multimillion-acre problem and removal efforts aren’t cheap. Additionally, mesquite is an excellent sprouter, so just cutting a tree at its base does not guarantee it’s gone. You may just make it mad! Finally, there are places where mesquite is meant to occur naturally and removal from those areas would not be ecologically responsible management.
What is a bioindicator species?
A bioindicator species is a critter that lives its life in a particular ecosystem, relying on the ecosystem for all aspects of its life. If the species is abundant in the ecosystem, it shows that the ecosystem is healthy. If the species is missing from the ecosystem, or is there in limited numbers, it suggests the ecosystem is in trouble. In a nutshell, bioindicator species are the “canary in the coalmine” for a particular ecosystem.
Why is the lesser prairie-chicken a good bioindicator species in terms of honey mesquite and prairie restoration?
The lesser prairie-chicken requires prairie vegetation to meet all of its life-history requirements. As this prairie transitions to woodland or savanna, chickens will no longer occupy those areas, thus showing that the health and functionality of the prairie ecosystem itself is declining.
You use the term “conservation triage” in your paper. What do you mean by that? How does your study help managers decide where to “triage”?
Just as a medical doctor in an emergency room has to prioritize how to treat all of the patients, we are applying similar principles to conservation. In short, we treat areas of mesquite with a high likelihood of successful restoration first. Those areas that have surpassed an ecological threshold because they have been infiltrated by high levels of mesquite trees may never be restored. Treating these areas becomes too costly and the time it takes for the prairie to recover is much too slow to make the investment worth it.
Our work helps identify those areas of early infestation that are “bad” for birds but relatively “easy” to restore both methodologically and financially. By focusing on “birdscapes,” it allows managers to concentrate efforts in specific geographic areas until the job is “done.” We have learned elsewhere that it requires watershed-level treatment to yield biologically meaningful outcomes.
How did you get the idea for this study? Have there been comparable studies done for other grouse species? If so, were the results similar to what you found?
Our previous work on greater sage-grouse and western juniper has striking resemblance to the avoidance behavior we observed in chickens with regard to mesquite trees. Earlier work by The Nature Conservancy’s Sharon Baruch-Mordo and other partners found that as little as 4% cover within about 0.75 miles of breeding ground (lek) was enough to lead to those leks being abandoned over time.
We implemented the very same analytical approach as Baruch-Mordo but with prairie-chickens and mesquite and found nearly the same pattern. We had a hunch it would be similar but not almost identical.
There is a growing body of research from different species of grouse, like lesser prairie-chickens and sage grouse that live in treeless landscapes, showing that with somewhere between 2% and 4% canopy of invasive trees, the land becomes uninhabitable by birds. It’s remarkable that both species abandon areas with nearly the same level of invasive trees.
Much of the remaining lesser prairie-chicken habitat is on private lands. How do private land owners put your research into practice? Are there resources they can access that help them prioritize where to remove mesquite or other encroaching woody species from the southern Great Plains?
As you point out, private landowners are critical to helping recover lesser prairie-chickens. This study helps them figure out where to start restoring prairie habitat so their efforts will make the biggest difference for the bird and prairie health generally. The USDA-NRCS has technical and financial assistance available to assist producers in tackling this problem on their land. Various mapping tools are available to NRCS staff to help producers assess costs and treatment types best suited for their operations. Also, Partners for Fish and Wildlife Program through USFWS is geared to assist with these types of treatments as well.
What is the key takeaway you want people to understand from your study?
Mesquite expansion is an ecosystem-wide problem, and it’s going to require significant resources to abate. Our work provides a road map to start tackling the problem, and that road map utilizes what we’ve learned about a charismatic and iconic species of the southern Great Plains – the lesser prairie-chicken.
Meet the Expert
How long have you been studying lesser prairie-chickens?
Nearly 20 years now…
What’s your favorite part of your job?
Making contributions (hopefully) to improving our effectiveness at conserving the last wild working landscapes of the West.
What else do you like to do when you’re not chasing chickens across the southern Great Plains?
Chasing elk with my traditional bow and chasing other upland birds with my two bird dogs.
>>Read the paper in Journal of Arid Environments>>