Climate Change May Bring Big Trouble to Big Bluestems (and the Cattle That Love Them)
By Susan Cosier
Loretta Johnson tortures plants. She sets them in awkward positions, deprives them of water or gives them too much, then watches how they react. Her victims are tall grasses—big bluestems, specifically, an icon of the midwestern prairie. Johnson isn't tormenting the plants for kicks; she's investigating how they fare under different climatic conditions. And so far, her observations provide clues to how the Great Plains could change within the next century.
Climate models show that warmer temperatures will likely continue to shift north over the next 75 years. Rainfall patterns are also expected to change, with portions of the big bluestem's midwestern range likely becoming drier for at least part of the year.
Big bluestems, which grow throughout nearly all of the U.S., make up 70 percent of the Midwest's tallgrass prairie. How these grasses grow, however, varies quite a bit by region. In drier areas, like eastern Colorado, the plants are short and stumpy. In the wetter eastern Midwest, such as Illinois and parts of Kansas, they reach up to nine feet tall. But no matter where big bluestem grows, cattle love to eat it—and if the grass stops thriving in certain places, ranchers could feel it in their wallets.
Grass seed.Reigh LeBlanc / Flickr
For the past seven years, Johnson, a professor in Kansas State University's division of biology and a codirector of the school's Ecological Genomics Institute, has belonged to a research team whose members hail from a number of states and scientific disciplines, including botany and climatology. To get a handle on what a changing climate might mean for the big bluestem, the scientists collected seeds from pristine prairies (those not degraded by agriculture or mining) in regions with various rainfall patterns. They then planted the seeds in three gardens—a wet locale in Illinois, a wet area in Kansas, and a dry area in Kansas—to test how the grasses might adapt under different conditions.
Interestingly, when these big bluestems grew, they did so exactly the way they would have in their home prairies. No matter how much rain, sunlight or wind (or the types of grasses growing around them), they didn't change. The regional differences between the plants, it appears, are genetic. The grasses may belong to the same species, but they represent what scientists call different ecotypes.
Jersey cattle near Baraboo.Wisconsin Department of Natural Resources
And that could be bad news for cattle ranchers. According to Bruce Anderson, an agronomy professor at the University of Nebraska–Lincoln who has studied cattle and foraging grasses for 35 years, good bluestem land can feed more livestock than other types of land. He said grazing cattle on these plants, which grow well in the summer months, instead of solely on grasses that thrive in the spring, can result in a 20 percent to 25 percent increase in how many animals can feed off the land. If weather conditions change to no longer match the needs of the big bluestems that sustain cattle in an area, those plants would be less productive, which could then affect cattle operations.
We don't know exactly how climate change's impacts on big bluestems might, in turn, influence cattle production, said Melinda Smith, director of the Semi-arid Grassland Research Center at Colorado State University (she is not a member of Johnson's research team). But we do know that changing climate conditions will alter what grasses thrive on the plains.
Take Kansas, for example, where ranchers operate on a third of the land. The state is home to the bluestem pasture region, one of the largest remaining swaths of tallgrass prairie. Smith's research here shows that forbs, which cattle don't like as much, replace grasses during an extreme drought. The bluestems stop growing, but they don't die out (like trees do under similar situations). When and if the rain finally returns, the bluestems come right back, showing resilience.
Researchers are now considering how best to preserve those bluegrass ecotypes that are expected to face soggier or drier seasons. Big bluestems can survive as long as 20 years, but reproducing during that time under suboptimal conditions is not guaranteed. They may release seeds into the wind, but the seeds may not be able to drift far enough to reach an area where conditions are more hospitable. Human intervention may be required.
Big bluestem grass.Matt Lavin / Flickr
Johnson and Sara Baer, a soil and grassland ecologist from Southern Illinois University, are looking into moving big bluestems to different locales but say the idea of doing so raises questions about the species' future genetic diversity and its ability to mix certain ecotypes. Because the grasses' traits are so regionally specific, they flower at different times. "Their timing is off by, like, a month," said Johnson, and that may prevent them from interbreeding. Plus, the plants (or their hybrids) may not grow as well in their new homes, which could change the quality and quantity of plant material available to cattle.
Transporting certain types of big bluestem to new regions also raises questions of where exactly to put them. After all, just 4 percent of the original tallgrass prairie remains. (Less than 1 percent is left of Illinois's historically expansive prairie).
Baer, who has focused on prairie restoration for 20 years, says that small plots of restored prairie exist all over, and that making them more biologically diverse is important. If we plant grasses that can survive the changing conditions, more plant species—and their genetically different ecotypes—just may thrive. Then, she said, we can connect remnant prairies with those that have been restored, creating corridors where the grasses can disperse. That would be ideal.
In the meantime, Baer, Johnson and the rest of the team plan to dig deeper into bluestem's genetic differences and potential climate scenarios. Sorry, bluestems—it's time for a little more torture...
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Clear-cutting a forest is relatively easy—just pick a tree and start chopping. But there are benefits to more sophisticated forest management. One technique—which involves repeatedly harvesting smaller trees every 30 or so years but leaving an upper story of larger trees for longer periods (60, 90, or 120 years)—ensures a steady supply of both firewood and construction timber.
A Pattern in the Rings<p>The <a href="https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/coppice-standards-0" target="_blank">coppice-with-standards</a> management practice produces a two-story forest, said <a href="https://www.researchgate.net/profile/Bernhard_Muigg" target="_blank">Bernhard Muigg</a>, a dendrochronologist at the University of Freiburg in Germany. "You have an upper story of single trees that are allowed to grow for several understory generations."</p><p>That arrangement imprints a characteristic tree ring pattern in a forest's upper story trees (the "standards"): thick rings indicative of heavy growth, which show up at regular intervals as the surrounding smaller trees are cut down. "The trees are growing faster," said Muigg. "You can really see it with your naked eye."</p><p>Muigg and his collaborators characterized that <a href="https://ltrr.arizona.edu/about/treerings" target="_blank">dendrochronological pattern</a> in 161 oak trees growing in central Germany, one of the few remaining sites in Europe with actively managed coppice-with-standards forests. They found up to nine cycles of heavy growth in the trees, the oldest of which was planted in 1761. The researchers then turned to a historical data set — more than 2,000 oak <a href="https://eos.org/articles/podcast-discovering-europes-history-through-its-timbers" target="_blank" rel="noopener noreferrer">timbers from buildings and archaeological sites</a> in Germany and France dating from between 300 and 2015 — to look for a similar pattern.</p>
A Gap of 500 Years<p>The team found wood with the characteristic coppice-with-standards tree ring pattern dating to as early as the 6th century. That was a surprise, Muigg and his colleagues concluded, because the first mention of this forest management practice in historical documents occurred only roughly 500 years later, in the 13th century.</p><p>It's probable that forest management practices were not well documented prior to the High Middle Ages (1000–1250), the researchers suggested. "Forests are mainly mentioned in the context of royal hunting interests or donations," said Muigg. Dendrochronological studies are particularly important because they can reveal information not captured by a sparse historical record, he added.</p><p>These results were <a href="https://www.nature.com/articles/s41598-020-78933-8" target="_blank">published in December in <em>Scientific Reports</em></a>.</p><p>"It's nice to see the longevity and the history of coppice-with-standards," said <a href="https://www.teagasc.ie/contact/staff-directory/s/ian-short/" target="_blank">Ian Short</a>, a forestry researcher at Teagasc, the Agriculture and Food Development Authority in Ireland, not involved in the research. This technique is valuable because it promotes conservation and habitat biodiversity, Short said. "In the next 10 or 20 years, I think we'll see more coppice-with-standards coming back into production."</p><p>In the future, Muigg and his collaborators hope to analyze a larger sample of historic timbers to trace how the coppice-with-standards practice spread throughout Europe. It will be interesting to understand where this technique originated and how it propagated, said Muigg, and there are plenty of old pieces of wood waiting to be analyzed. "There [are] tons of dendrochronological data."</p><p><em><a href="mailto:firstname.lastname@example.org" target="_blank" rel="noopener noreferrer">Katherine Kornei</a> is a freelance science journalist covering Earth and space science. Her bylines frequently appear in Eos, Science, and The New York Times. Katherine holds a Ph.D. in astronomy from the University of California, Los Angeles.</em></p><p><em>This story originally appeared in <a href="https://eos.org/articles/tree-rings-reveal-how-ancient-forests-were-managed" target="_blank">Eos</a></em> <em>and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.</em></p>
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